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WeirPW User`s Manual
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1. KIKIKIKIK r Cull Radius mm fs T FullScreen Weir PW Mango s141 SwWA3 Raw Data Ny Deg SWA3 Points 4322 Wafers 1 Fields 37 Sites 121 _ Raw Data_ Count 4322 Mean 88 9189 Median 89 3275 SEM 0 0050 Maximum 91 2610 Minimum 87 3940 Range 3 8670 MinMax 91 2610 Variance 0 1065 StDev 0 3263 Mean 3Sigma 89 8977 FDresid um 0 0000 Water Residuals Field Residuals Wafer Field Scale um 89 400 Deg max min 91 261 11 000 Wakall Exp ALL All NA 0 75 PCo 0 00 PCi 0 32 7 Figure 28 Spatial Analysis Screen Wafer contour plot of Side Wall Angle SWA feature variation illustrating variation across the wafer at 121 points per field Focus varied from 0 3 to 0 0 um from wafer top to bottom Process Analysis Page 55 Spatial Analysis Selections frame Located on the right side of the screen summarizes the current analysis selections Selections are made by using choices presented in the four tabs located to the left of the frame Use the Graphic Scope tabs to the right of the graphic region to plot or re plot the data Model re Model Aberrations command button Forces the Weir Analysis to re model the data files Full Screen check box Select this box to expand the graphic region to cover the full window Removal of the selection will return the
2. Display Selection Component Removal Plot Format Selections m Model Components Display Selecti Wafer Models Field Models y No Modeling Wafer Offset C No Modeling Component Re Wafer Ti Row Column Til M C FullWater JE wafer Tity Ful Field Tilty Plot Format I Validate Wafer Bow Validate Curvix zi Whol xY plot Water Residuals P FullScreen gt Microns cD 20 Points 341 Waters 1 Fields 31 Sites 341 Field Model Piston 0 0934 Ti urad 0 1022 Tilt urad 0 0000 Curv um cem2 0 0010 CurvY um em2 0 0000 MSE 0 00000 Residuals __ Count 341 Mean 0 0005 Median 0 0014 SEM 0 0001 Maximum 0 0050 Minimum 0 0023 Range 0 0074 MinMax 0 0050 Variance 0 0000 StDev 0 0010 s 0 0005 Sum 0 1825 RMSS 0 0012 IFDresid um 0 0074 Water Residuals Field Residuals Water Field Scale um 0 002 max min 0 005 0 000 Wafall ExpALL All NA 0 75 PCo 0 32 PCiO 00 7 Figure 50 Viewing scanner slit behavior CD aberrations across the wafer for one row of data using data culling for selection Shown is a vector plot of CD residuals to the average modeled field analysis yields an offset or Piston for the CD 20 threshold at 0 093 um Since there is no data associated with the Y scan direction the TilyY coefficient is zero A moderate amount of average tilt and curvature are shown in the X or lens direct
3. General c Focus Calibration r Data amp reticle Locations Source Directory Follow current directory JD Data FEMed AMAT 3 Import Type AMAT NanoSEM 3D 7 Storage Location JY Store data in source directory el Layout Graphic vector 0 Default Reticle Template Location D vb WeirAnalysis Reticles EY OK Cancel Apply ee Figure 12 Options screen for setting defaults Getting There From the main menu select the Tools Options item General Tab Select the number of files you wish to have posted when you select the main screen File menu item This list retains only workbook data files Storage Locations Tab Source Directory 4 default search directory for raw data This is the directory the software will first look in after startup Follow current directory 5 check box selection will cause the data import current directory to follow the last folder location If unchecked the software always opens the Source Directory Import Type 6 Default raw data format for import Storage Location Store data in source directory If CHECKED then the Weir data spreadsheet will be stored in the same directory as the source data 8 IfUNCHECKED then ALL Weir data spreadsheets will be stored in the directory specified Layout Graphic page 32 Setting Preferences and Defaults 1 10 2005 Weir Main Interface 9 Combo
4. ExpoLat The calculated Exposure dose Latitude as a percentage of the dose r Process Window Data Range Setup Pw Control Model m Process Window Analysis Pw Adjustments Dose Format Graphic C Both Process Window 338 bee ui ese C Rectangle C DoF vs Expolat DoF Ellipse C Dose vs DoF _ExpoLat Joss Rectangle aceon C None Focus vs DoF ExpoLat Ellipse Dose Lat e o aroun Figure 66 PW Control the process window control and interactions tab Figure 65 displays an ellipse or process window commonly associated with a process having random variables You can control display of the process window from the PW Control tab of the interface shown in Figure 66 Notice that the random process Ellipse calculation or the systematic variable process Rectangle figure can be used for the analysis The PW Adjustment frame provides an interactive control for investigating the results of varying the process set points You can optimize Depth of Focus DoF the exposure latitude in percentage points or the set point dose to see it s influence on the process window These adjustments are initially set to the result points of the current analysis Make sure the radio button is set to the proper metric variable the Rectangle or Ellipse metric before adjusting these values Other Views of the Control Curve The Graphic frame of the PW Control tab provides an opportunity
5. Refresh Full Screen Process Window Site Center site 1 18 Dec 02 lsofocal Dose 57 20 DoF 0 940 DoseLat 6 0 Best Focus 0 04 Dose 33 5 PW Dose Focus Figure 65 Process window response for a random element calculation The critical surface contours for the upper lower and target control surfaces are displayed along with the associated data points You can control the curve colors data points and display by using the graph options interface Simply right button click on the graph to enter this screen The process window Ellipse and Rectangle curves can also be found under the Series tab of the interface Use the Background color to define and fill in the curve Data used in the analysis are stored in the ProcessWindowSpace spreadsheet Each row tabulates the results of a process window size calculation for the given dose Variables stored consist of Variable Function Focus Optimum focus for the dose Dose Dose base for the calculation XleftLFocus Left side lower curve Focus value XrightLFocus Right lower curve focus value Ldose Lower Dose XleftUFocus Left side Upper focus XrightUFocus Right side upper focus Ufocus Upper curve best focus Udose Upper curve dose value Page 95 Applications Examples Process Window Analyses Variable Function Area The area under the figure DoF The calculated Depth of Focus ExpoLat The calculated Exposure dose Latitude
6. B ola a gt B Prompt X sheet including the orientation of the wafer wafer flat Data Type Scatter the die size Data Table Slitl 1 5 slot 6 EMS xls TR Inspection BB description of the features Device measured including Level and more DieSizeX DieSizeY NOTES X Dice Field Heading values are in column Y Dice Field Site_x_offset A and start in row 2 bli BestFocus RawFocus 4 2 2 ALL dimensional values are stored in units of millimeters af a yy Figure 5 Information Spreadsheet format gt page 20 Information Sheet Format Data Storage and Formats Row Heading names are critical their sort order is not Row Heading Stored Value Data Type Overlay Registration CD SEM Scatter or Focus Data Table File name example Slitl 1 5 slot 6 EMS xls Inspection Not used Device Device or product name Level Layer or level name DieSizeX X die size in millimeters DieSizeY Y die size in millimeters X_Dice_Field Number of die located in the exposure field Typically 1 Y_Dice_Field 1 Site_x_offset Offset of the field site array in millimeters from field center Site_y_offset Die_x_offset Offset of the wafer array in millimeters from wafer center Die_y_offset Die_x_array Offset of the wafer array in fractional whole die values May be whole or fractional Die_y_array 0 5 Flat Location Flat or Notch location UP DOWN
7. F Process Optimization User s Manual Wavefront engineering software tools for optimization and tuning of the semiconductor manufacturing process Ganas neen Eoocog SSeaceakesy ESPEN Bag fii 3 i stu Howe C Eanan Faga Cw Mables CICE Vaienwe shew GC tse on 85 i TEAS ystems 5 Sdilos 4 Albuns TI al TEL 1 6 62 46 http www TEAsystems com TEA systems 65SchlossburgSt Alburtis PA18011 TEL 01 610 682 4146 http www TEAsystems com Weir Weir PW and Weir PSFM are trademarks of TEASystems Corp Copyright 2004 2005 TEASystemsCorp AllRightsReserved All other product namesandservicesidentified throughout this bookare trademarks or registered trademarks of their respectivecompanies Theyare used throughout this book in editorial fashion only and for the benefit of such companies No such uses or theuseofanytradename is intended to convey endorsement or other affiliationwiththiswork No part of this publication may be reproduced in anyform or stored in a databaseor retrievalsystem or transmitted or distributed in any form by any means electronic mechanical photocopying recordingorotherwise without the prior written permission ofTEASystemsCorporation USA except as permitted by the Copyright Act of 1976 The Weir Software Suite Table of Contents Table Of Contents scssssssssssssssssssosesesssesssssssesssssss L OVErVIEW nrerin The Weir Software Suite 3 Analysi
8. Value feature difference for each site plot Astigmatism View the average astigmatism at each site View the average astigmatism for each Mean field Astigmatism View the maximum astigmatism at each Maximum measured astigmatism for Max site each field Astigmatism View the maximum Y X or Horizontal Maximum measure astigmatic variation H V Max Vertical feature variation at each site for each field XYplot The XYplot scatter plot organizes data as a function of it s position in rows and columns on the wafer and field Using the sections you can view Horizontal and Vertical feature metrology as well as the average Horizontal Vertical 2 values Figure 24 Threshold Two threshold sliders are located in the threshold frame of the screen Figure 22 One slider provides a setting for the maximum allowable value of the display the other sets minimum values When a vector plot or range plot is displayed values exceeding the maximum or lower than the minimum threshold will be displayed in red and their number summarized at the bottom of the display amp Y Plot Options Ordinate Abscissa T Horizontal Rows T Vertical 7 Mean C Columns Figure 24 Metrology XY Plot selections for Visualization of Raw Data Change threshold settings by dragging the sliders with the mouse or by selecting the slider and using the up down arrow keys of the keyboard Raw Data Metrology Page 47 of 11
9. selection for most data sets the default Fast analysis will yield the best results Depending upon the layout of the sites on the field and number of sites the contour may result in incomplete areas If data seems to be omitted from field segments select either Medium or Modeled methods The Modeled method is the most robust because it uses a full field regression model to perform the interpolation however is will be slower and will loose some fine detail in the display Wafer contour plots containing only one point per field will plot the contour based upon the data s position on the wafer Customizing Graphics Page 27 Customizing Graphics Histograms Plot Feature frame selections 2A graphic will display this frame only if more than one feature is available for display This analysis therefore only occurs in focus or overlay file studies In most selections the choice will be Xreg Yreg or Mean implying that you can select to plot the X Y or average values across the surface Xreg and Yreg Feature or variable plots can differ significantly when data originates from a Scanner exposure tool Scanners Xreg direction reflect perturbations across the lens while their Yreg values are averaged or blurred by the scanning action of the slit Histograms Histograms are displayed for one or two variables in Weir Software When two variables are appropri
10. Calibration Tab options 33 focus matrix metrology example 69 72 FocusResponse 94 Format PW analysis 68 Full Field model 9 Full Screen 46 full field 9 27 G GOF 77 Goodness of fit 50 Goodness of Fit 77 graph wafer radius 16 Graph Customization 25 Messages add edit 27 Trend Line Add Edit 27 graphic data format options 46 H Hide Field Text 38 histogram 16 49 for culling 15 use in culling data 80 Histograms and culling 16 general usage 28 I IFD 111 112 Index definition 46 IFDresids 111 Import default data type 32 raw data 35 information sheet format 20 Initial 39 InterColumn 62 74 InterField 61 62 precision 108 interpolation 27 56 Interpolation 27 InterRow 62 Inter Wafer precision 108 IntraColumn precision 108 IntraField 45 46 49 61 62 L Latitude dose 65 layout origin 37 setting exposure value for one field 38 setting focus layout 39 Layout changing display graphic 37 graphic used for 32 specifying layout by each wafer 39 spreadsheet 109 Level 21 License Management 11 12 Limits Show 93 linearity scanner 73 Lot average 59 average definition 87 precision 108 M manual data manipulation 22 Maps Wafer 98 Mask 5 50 90 Max_99 7 111 Mean field removal 87 of X amp Yreg 28 Mean Square Error 74 76 Precision Values Computed 1
11. LEFT or RIGHT Metrologynom Metrology tool Name sn199201 Lot Lot Name Job Metrology tool Recipe Name Date 4 Oct 99 Title ASML Slit Profile size 1 1 5 wafer 200 Comments Any number of lines of text Contents will vary depending upon the data source Typically used to contain notes inserted by the user Exposure Tool Exposure Tool Stepper or Scanner name MeasureTime Time of day the data was measured 17 34 00 Process Step A process step number for the layer Technology The technology used in the device Stepper Job The stepper or scanner recipe name Rework Integer number beginning at 0 Rework cycle of current data set Data Storage and Formats Page 21 of 116 Data Storage and Formats Manual Manipulation of Data Sets Row Heading Stored Value User_name User or operator name from the metrology tool Stepper_ID Exposure tool designator may be exposure tool name Reticle Reticle designator or name FilePath Original Data file full pathname not critical WorkBookPath Original Stored full pathname of the workbook not critical DataFolder Original Data folder name not critical Manual Manipulation of Data Sets Why manually manipulate data There are many reasons for doing so beyond the normal data handling scope of the Weir analysis You may wish to subtract reticle data from metrology measurements subtract the performance results of wafers loaded into two cassettes or compare UltraFlat to Standard flatness subs
12. columns fields Field dear eae SS feia Doffiera Doffe Fields 1 Precision Requires Multiple Fields Field Grid Variation by position on the wafer grid SS oria DOF gria DoF gia fields Requires multiple wafers nee IntraField Variation of measurements within a field excluding the SSrieia SSsite Dofintraricla Sites Precision site measurement variation DofintraField fields Requires Multiple wafers and multiple sites InterField Variation field to field SSwater SSfieia DofinterField fields Egon Requires Multiple fields DofinerFieta H wafers Wafer Requires Multiple wafers SS wafer DOfwafer Dofwafer N Precision Variation within each wafer Diii Inter Wafer Stage stepping errors Requires Multiple wafer SStotat SS wafer Dofiw n Dofiw pts wafer Wafer to wafer variation Lot Precision Overall precision of the lot Equivalent to taking the SStota 0 Dof n standard deviation of the entire data set SWA variation with focus and BARC Page 108 Precision Values Computed Spreadsheets created by Weir PW Spreadsheets created by Weir PW These spreadsheets are created depending upon the data set imported and the analyses performed clsp is nomenclature for Collapsed as in Collapsed Field SE designames the Standard Error or Sigma value of the reported coefficient Spreadsheet Name Analysis Function Index All A
13. is located at the center of the wafer Diey El An integer designating the row location of the die on the wafer Diex location zero 0 is located at the center of the wafer Measured Data Storage A maximum of eight 8 measurement categories can be stored in each datasheet beginning in column F The name of each measurement should be stored in row 1 of the column Weir PW Reports and lot object storage of the data will then use this name The following detail the metrology variables stored and their associated column headers Overlay Focus and Registration Metrology Data is stored as microns of measurement Column F X axis measured data Column G Y Axis measured data Column H Optional X Y 2 average measurement Critical Dimension and other metrology Column F First Feature defined by the user or by the import program Column G 2 feature entered Any number of variables up to the number of columns limited by Excel can be stored in the spreadsheet The first variable must be located in column F Only the first nine 9 columns F to N are loaded into the active Weir program You can cut paste columns of data into these first 9 columns to change their order of appearance or to select different combinations for analysis page 18 Weir Standard Format 1 10 2005 Data Storage and Formats The units of measure for each column are stored in t
14. menu item amp To remove ALL mouse culled data and return the sites to the selected dataset simply click the Select Data command button Data Layout Display or Wafer Frame Displays the Raw or Selected data on a point by point basis using a waver vector plot an example of which is shown in Figure 27 When first displayed the selected and raw data sets will be equal Either data set can be viewed by changing the radio button selection at the top of the display window between Selected and Raw data settings Value Vector Magnitude amp Sign ore o oo o amp Lan Feature Site m Scalefumh 2 002 raaxmin O 1716 0 000 Figure 27 Reading the wafer vector plot The data of Figure 26 was site culled to leave only the field center scan column The vector plot places a circle at each site location and a vector whose the whose length and direction are set by the vector scale shown at the bottom of the plot Process Analysis View plot or cull individual data points in any region of the wafer by using the left mouse button to select and drag a box around the area of interest Data is sorted by it s position on the wafer Data sets with more than one wafer selected for display can contain multiple points at each wafer location i e one for each wafer Cull data points using the same method described above for the field frame Note 22 ae 2 2 2 Righ
15. tab of the window and then check mark the error coefficients you wish to remove No tilt removed X axis tit removed r Figure 68 Effect of removing wafer tilt on Depth of Focus Selecting Multiple Sites Applications Examples Multiple sites that differ because of their load factors or Optical Proximity Correction OPC construction are can be evaluated using the Focus or process window analysis Process window response will also vary across the exposure field because of changes in the lens aberration balance at differing points of the lens Page 97 Single site Field Center BAD prccccecccccocee sssssssssessoso n e adi pe 220 D aa EAE pases noe a Ka n0 T se pART 0021 Dose 120 F 5ce 43 02 01 00 01 02 03 o4 05 Focus Figure 69 Process window variation with multiple field sites The influence of selecting more than one site on the exposure field invariably leads to a reduction in the apparent process window as shown in Figure 69 However the multi site analysis portrays a truer picture of the process This window is sensitive to the aberrations of the individual exposure tool and will thereby vary from tool to tool Similar to matching for overlay tolerances exposure tools can be matched for process window optimization You can interactively select the field sites you wish to analyze using the tools on the right side of the Data Range tab of the Process
16. 0 0004 Page 61 Metrology c0 5 CD 20 CD 50 co 95 co 80 swa tPR LaRC interColumn 0 0008 0 0008 0 0009 0 0012 _0 0011 0 0924 0 0003 0 0002 row 0 0059 _0 0061 0 00671 0 0079 0 0075 0 4020 0 0014 0 0005 InterRow 0 0026 0 0026 0 0026 0 0028 0 0027 0 1505 _ 0 0004 0 0002 Interpreting Precision Values Values are computing by selective sorting of the data into populations representing logical eletro mechanical sub assembly contributions to the tool operation The Average and Range values correspond to the classic definitions of the terms The Lot Precision is equivalent to the user selecting all of the data and calculating the Standard Deviation Precision Estimation of Lot Estimation of the standard error of the variable Wafer Variation from wafer to wafer A measure of the alignment system for registraton A measure of the tools ability to set up for process wafer variations with CD Field Estimation of the precision of placing a field at a given site Essentially stage accuracy in registration data or feature stability in CD variables Site Variation of features across the field Essentually the reticle quality IntraF ield Variation within the field due to magnification focus exposure tilt bow or other changes InterF ield Variation from field to field Stage precision in registration systems Exposure precision with CD variables Column Variation within a single colum
17. E A A OOO Figure 21 FEM Variable Setup interface with right click pop up data entry shown Note The FEM Variable Setup button on the Weir Layout interface is only available when a range of both focus and dose information is contained in the dataset Accessing the FEM Variable Setup Page 43 FEM Variable Setup Interface Using the FEM Variable Interface The FEM variable setup interface provides a standard focus exposure layout as shown in figure 21 Locations on the focus dose surface where a feature has been measured are designated in yellow Use the Max Min and Step fields to specify a range of values for the pop box shown in the figure Setup Command Used initially to assign a Maximum value to each exposure focus dose location Setup values will be populated into a Pop up screen for easy mouse selection Format Field ass Specifies the number of significant digits for the entered data Variable Name Field Variable to which the FEM setup data will be assigned Default is Profile g Save command button Saves or updates the new variable data into the Weir Data workbook Entering Data Hovering over a field with the mouse will provide a tool tip box showing the exposure coordinates of the exposure Use the left mouse button to place a cursor on the field that will allow you to manually type in any numeric value Use the right mouse
18. Field contour analysis methods are described Applications Examples Page 69 Reticle Analysis Reticle Analysis Data File Scatter 110 DPI_ReticleData xls Summary A test reticle has been measured with data obtained from the mask shop CD SEM The data is analyzed and a signature obtained for future analysis of wafer images Background This data set accompanied a test reticle The data was originally in the format of two columns of data CD and feature Pitch There were 121 rows reflecting an 11 x 11 array of features on 2 2 x 2 4 um final size centers Data Format Problem Data as provided is not in the Weir format Only one spreadsheet of 2x121 cells exists Weir requires a minimum of three spreadsheets to describe a dataset The data Sites and an Information header sheets Data was as measured on the reticle that is it was in nanometers and feature sizes were 4x their final size Solution Data was converted in six easy steps ES ES A wafer was exposed using the reticle BBE The user was careful to measure the wafer of features in the same sequence as those on the reticle The data was then imported into Weir A file copy of the wafer measured workbook was made and the first spreadsheet the data sheet was renamed to the reticle file name BB Columns F through the last column AND rows greater than the first 121 were erased EB The reticle data was copied into columns F and G CD and Pitch col
19. Interface From the Main screen select the Exposure Tool tab Page 33 Weir Main Interface Data Import and Layout Tool Frame The tool name is listed at the top of the frame You can re set the tool name by pressing the Set Tool Name command button EA ___substrate Sets the size of the wafer in leciec onnes J Reduction Reduction ratio A 5x stepper has a reduction ratio of 0 2 Used only in field e a calculations EEN Actinic Aeae ane of the tool in nanometers Focal Length Focal length of the main length in millimeters Used only in some tilt Naps E Noten Notch position up down left or a O _ NA Numeric Aperture of the tool Sigma Partial Coherence of the tool Open aperture setting can be entered by inserting a values for Sigma Outer only Ring aperture values should insert both inner and outer values Fi ield This is the overall size of the maximum exposure field Die size information Settings is typically derived from the metrology data Field Size Size of the field in millimeters Center Offset centering of the field in millimeters Sub Fi ield You can define a sub field portion of the field that will be defined and Settings modeled separately The Weir Analysis will form a matrix of all sub fields until the map the entire exposure field Size The size of the sub field in millimeters Offset Offset of the sub field segment relative to the center of
20. Selected Data Manipulation 1 3 2003 7 48PM data wafer Edge data field point 0 12 10 0 50 00 50 100 added Figure 10 Average Field contour plot after edge fields are removed with the mouse cull options 1 10 2005 Weir Main Interface Weir Main Interface Figure 11 Weir Main screen at a glance Screen Navigation Weir Main Figure 11 shows the Weir Main screen and it s major navigation points ses The Main Screen provides central access to all of the setup and analysis screens This screen is used for the initial import of raw data and it s fine tuning for centering and layout User Options and Preferences can be accessed from the Tools Options sub menu Use the Options screen to specify a default raw data import format and data folder location Files are imported as raw text or workbooks from the File menu See the chapter on Setting Preferences and Defaults for more detail Note Use the Escape Esc key to interrupt any analysis The key must be depressed and held Setting Preferences and Defaults Overview This interface allows the user to customize some of the Weir Analysis Settings With it you can set up the size of the recently used items list and customize the default values of the raw data source directory and the metrology format most frequently used Weir Main Interface Page 31 Weir Main Interface Setting Preferences and Defaults Options
21. allows the user to select from four different wafer plot graphics when laying out the settings for Focus Dose NA PCI PCO and Stage Direction This allows the distribution of the data to be viewed or hidden when first orienting an imported data set The Bulls Eye option is default Default Reticle Template Location 10 Directory for storage of reticle metrology data as stored in Weir data spreadsheet XLT format 11 Reticle data can be analyzed or removed from current data sets during an anaysis see Component Removal Tab on page 59 Focus Calibration Tab This tab is used only with Weir PSFM The Focus Calibration tab sets display and calculation preferences for use when converting metrology data to calibrated tool Focus values Focus values can be calculated as either focal plane errors or as focus corrections for the tool Focal plane errors are essentially the measured focus deviation from the tools best focus Focus corrections are the focus values to be added to the exposure tool to minimize focus errors Corrections are essentially opposite in sign to the actual focus error The user can confirm operation by calibrating a focus matrix data set Then using the same data set and it s own calibration template convert the metrology of the exposure tool focus matrix to focus data using the conversion options of the in the Focus Analysis screen If the Report Focal Plane devi
22. also provided to select unique coherence and Numeric Aperture values Double clicking on the check box exposure fields wafer ID focus and dose is an easy way of excluding only one or two values from a large data set Double clicking will toggle the display between the AI selection for the box and the checking of every item in the list This allows you to then un check individual items to exclude them from the data Available Settings Frame Page 52 Process Analysis Calibration Options or Field Frame Provides a graphic of the defined exposure field and the location of data sites A short window above this graphic displays the unique field exposure sets contained in the data Move the mouse over the frame to view site information such as Site Number and it s location on the field in millimeters This information will also be displayed in the frame caption and retained in the status bar display Data sorted by site position can be viewed graphed and culled from the final selection by using the mouse A pop up menu will appear if the left mouse button is depressed and used to drag a rectangle over selected sites of this field Note After selecting the Cull selected data points menu item the display will automatically remove the boxed sites from all points in the selected data To remove data culling from a given area re box the area and select the remove culls from selected
23. and performance of each metrology variable Use the Analyze command button to start the analysis after having selected any of the variables Note Use the Escape Esc key to interrupt any analysis The key must be depressed and held Precision Analysis Process Analysis Precision provides both a calculation of the various contributors to the total variance of the lot and in doing so an automatic estimation of the component sub assemblies to the error budget Precision values are reported as one standard error estimates of the variation due to the component of interest You can see the calculation base for these numbers in the Error Reference source not found appendix Values are stored in the Precision spreadsheet of the workbook c0 5 CD 20 CD 50 co 95 co 80 swa tPR taRc ee ee ee ee ee ee eee Average 1046 0 1018 0 0969 0 0936 __0 0945 91 2810 0 2704 0 0853 Range 0 1838 o 1872 0 1955 0 2043 0 2014 8 8727 0 0441 0 0188 Precision ae Lot 0 0068 0 0070 0 0074 0 0084 0 0080 0 4785 0 0017 0 0005 Field 0 0064 0 0066 _0 0072 _0 0084 _0 0079 0 4261 0 0015 0 0005 site 0 0066 0 0069 0 0074 _0 0083 _0 0079 0 4478 _ 0 0016 0 0004 intraField 0 0015 0 0015 0 0012 0 0017 0 0012 0 1187 0 0005 0 0003 intertield 0 0023 0 0023 0 0020 0 0012 0 0013 0 2221 0 0008 0 0002 Column 0 0064 0 0066 _0 0072 0 0083 0 0079 0 4195 0 0015
24. calibration analysis of the lens aerial image Best Focus and utilities for model building and analysis of focus variations across the lens scan field wafer and lot Weir PW is a semiconductor process analysis tool Weir PSFM can import any format of metrology data It provides tools for modeling simulation setup and characterization of the process exposure and metrology tools Weir Daily Monitor DM provides an easy to use interface for Weir analysis sequences that are repeatedly performed User specified templates encode the analysis sequence graphics and trend charts to monitor the stability of user selected variables over time Weir DM software can be used with any type of metrology data including the specialty calibration and analysis functions of the Phase shift Focus Monitor PSFM Templates provide simple two click analyses of complex custom engineering procedures The analyses can include automated data culling reticle data removal average and modeled field removal focus conversion modeling and the storage of results into trend charts Weir PW Weir PW provides software tools for optimization and tuning of the semiconductor manufacturing process Included are highly automated statistically accurate tools that address the analysis of Critical Dimension CD distributions both statistically and spatially provide predictions of CD limited yield evaluate metrology and exposure tool contributions calc
25. color box plots population color coding and population contour lines Trend lines fitted to any existing data curve of the graph with up to a 4 order polynomial Getting There Right Click on the graphic using the right button of the mouse x Display Titles Axes Chart Options Messages Trend Line r Curve lines and markers Curve J Hide Curve fror_t H_DF_F124_ISO_S_V x Line Marker V Connect i Symbol Filled Circle Me Cc Size 90 0 C a E O L OK Cancel Apply Status 4 16 2004 9 33 AM Figure 6 Graph Options customization screen Functions This interface is available from any graphic Select the tabs to modify the screen background titles or curve symbols Clicking the Apply command button will submit the changes to the current graph without exiting the screen Graphic Options Control Tabs Seven tabs provide control interfaces for the graphic Display tab Customizing Graphics Page 25 Customizing Graphics Overview Adjust background color and the default font used for display Titles Modify the value and fonts for the graph and each of the axes 5 AXes Controls display of each axis Select the axis from the four possible radio buttons on the left side of the screen Add or suppress plot gridlines with the checkbox and 2 Set the scale range tick interfaval and format Series Co
26. compensations Attempts to compensate these swings by assigning only a portion of the coefficient correction or by averaging with past values compensate for over corrections but neglect under correction points Weir uses a proprietary model engine that employs Singular Value Decomposition SVD of the dependant and independent data matrices to assign model coefficient values This engine provides an adaptive modeling technique that applies the SVD analysis techniques to each data set and adjusts its response to avoid coefficient colinearity and to automatically exclude metrology sports from the analysis In addition the model employs user entered culling variables that key on the range and sigma of the population to enhance the tuning capability of the analysis Wafer Model The Weir wafer model implants the format of equation 4 shown above The enables both tilt and bow of the wafer stage to be calculated using orthogonal coefficients This method achieves greater accuracy in the estimates of each coefficient and provides of method of separately determining wafer tilt from that of the reticle platen Wafer models incorporate sixth order models to properly address both the correctable and other higher order errors caused by bowing chucking and film variations The system coordinates are transformed to the center of the wafer and each point in the lot object is assigned an absolute position on the wafer A radial coordinate system is used T
27. easier viewing of the range data plot Un check the box to re view the variable values Constant Serpentine Single Scan Multi Scan Array Format Figure 15 Layout format selections for The array format specifies the form of systematic change automated entry of exposure values experienced by the variable s value The variable s value may be selected to be Constant or to change in a systematic Serpentine Single Scan or MultiScan mode Figure 15 shows four graphic s described by each of these layouts Note that the array origin need not be at a corner of the array Scans are performed relative to the Array Origin selected and the scan direction command button chosen Constant Insert the initial field setting value specified below into all of the fields of the selected wafer s Serpentine Starting at the array origin move to the end of the row or column The variable value for each new field will change with each field position by the amount specified in the Step field Negative values decrease the field value with each step At the end of the row or column step to the next row reverse direction and continue filling in the field variable values Single Scan Similar to serpentine step each field along the row or column changing the field variable value at each step At the end of the row column raster back to the origin AND reset the next field s value to the value stored in the initial field setting Initia
28. full process window study Section Step by Step Tutorial Defining an Focus r Berar bent Sane Sant Cnt Scale wi Scale umf 0 001 caelum _ Piso oas max min 0000 9 999 Figure 60 Typical Focus and Dose layouts for process analysis studies Two screens from the Wier Main layout interface Exposure Layout on page 39 details the layout and method of defining the array such as those shown in Figure 60 FAiveir Process Analysis EXPOWIN XLS Jigi File Edit Data EXPOWIN XLS Help ps sreo ieee Process Window Parameter Setup Variable Target Maximum Minimum Selected IV cD I Height Figure 61 Variables selection Setup tab of the process window interface First you will need to select the variables to include in the analysis and their control limits Enter the Setup tab of the interface shown in Figure 61 This tab lists all of the variables available in the data set Weir initially assumes that the target is the average variable value and the control limits lie at 10 of this mean Selected variables are shown in the right side of the window Setting up for a Process Analysis Page 92 Applications Examples r Process Window Data Range Setup PW Control Model r Data Ranges Center r Focus m ltems to Include in Displ One g Max fioo vi JZ Statistics All c r IV Graphic Row Mn 1 00 zl O V Show Li
29. graphic to normal size Cull Radius command button Used to analyze wafer edge effects and their influence on the selected metrology variable Click on the Cull Radius button to generate an XY plot of the selected variable as a function of it s radius from the wafer center Enter a radius value into the cull radius field immediately to the right of the button This field restricts the data used in the analysis to those sites within the radius The number of data sites removed from the analysis are displayed in blue on the right side of the cull radius field as shown in the figure Press either the re model button or a display tab left side of graphic window to begin the analysis with the new radius restriction Display Selection Tab Selections frame This tab contains the selections for constructing the basics features of the graph It allows selection of the graph and aberrations to include in the modeled data Field Contour and 3D surface plots will have their data saved directly into the workbook into a spreadsheet named Surf _Field_ amp FeatureName These spreadsheets can be directly used with the Excel graphics to generate contour and 3D plots Graph Selections are gss Vector Plot Histogram Contour c Provides 3 selections for data interpolation Fast Medium and Modeled There is no wrong selection for most data sets the default Fast analysis will y
30. model to all points in each field This analysis is best applied to Steppers rather than scanners Also use the model when calculating software corrections such as field tilt to the lens Page 57 Spatial Analysis Validate check box If selected coefficient will be validated before their modeled values are reported If coeffiient values are greater than four times their uncertainty then the coefficient is set to zero and the data is remodeled Coefficients Segment Coefficient Function Wafer Offset Offset of the whole wafer modeled values Model TiltX Tilt of the wafer in the X direction Tilt is reported in um cm or urad TiltY Tilt of the wafer in the Y direction Tilt is reported in um cm or urad Bow Symmetric 2 order variation of the variable about wafer center Field Model Variable Offset of the field model Name TiltX Tilt of the field in the X direction Tilt is reported in um cm or urad TiltY Tilt of the field in the Y direction Tilt is reported in um cm or urad CurvX Curvature 2 order variation of the variable in the X direction CurvY Curvature 2 order variation of the variable in the Y direction Notes Points exhibiting high singularity will be automatically culled from the data set and the remaining population will be remodeled Values entered into the Range and Sigma fields of the Display Selection tab are also used by the model The model compares fitted residuals to test fo
31. range of the mean of the population This had to be done because of the large disparity of values between the two variables We can see a linear relation of BCD with SWA for the entire range the problem arises in the area of the mean or majority of the data points Here the relationship is bimodal There is no clear relationship between high MSE value and bad or good BCD readings Figure 42 further displays the relation by plotting the MSE against the focus range Compare this plot with that of Figure 38 MSE is not a good indicator of the quality of the measurement The metric is MSE as a Measurement Quality Metric Page 76 Applications Examples valid only at the high 0 1 um range of focus and fails to indicate problems above this range and for the range below 0 1 um Valid Metrology Behavior The metrics of the sl10isol8map xls data set illustrate reasonable behavior for a metrology tool and it s evaluators Examination of the covariance table Table 4 shows two potential candidates for quality the Residuals and Goodness of Fit or GOF Table 4 Covariance plot for Scatter data s 10isol8map xls CD 20 CD 80 SWA t_ARC t_PR Pitch Residual GOF CD 20 1 000 0 964 0 891 0 903 0 916 0 553 0 703 0 899 CD 80 0 964 1 000 0 790 0 814 0 835 0 375 0 549 0 809 SWA 0 891 0 790 1 000 0 999 0 994 0 860 0 923 0 999 t_ARC 0 903 0 814 0 999 1 000 0 996 0 838 0 910 1 000 t_PR 0 916 0 835 0 99
32. ridge of feature values extending the whole right side of the exposure As can be seen from this comparison of reticle and isolated feature size distributions a study of the relations between printed wafer images and those on the reticle is traceable Additional work with differing feature sizes and densities will lead to greater understanding of the Mask Enhancement Error Factor MEEF or MEF and it s behavior across the wafer and relationship to previous film uniformities Page 90 Applications Examples TCD and reticle data comparison IT Scatier110 DPI_PetcleD ala_WesOS200 ASML SCATTER 110 DP_AETICLEDAT Microns ta Pacha Field Residuals to CD4x Raw Data Points 121 Wafers 1 Fields 1 a ee a et eee ais Sites 121 f Fa Mo Piston 0100 02195 Tit urad ooo 00000 Lo Curvature um om2 0075 0002 Amba Count 121 121 Mean 01062 02196 ar Median 01063 02139 Wea PW Nano_cypress_ SEM aco 0001 TCD i nm r Maximum 01095 0 2222 odet Al Co as Eee Wafer Modet AI Cools Field Row Modet None Range 0 0064 00047 01 MirMax 01095 0222 Variance 0 0000 0 0000 StDev 0m3 0000 120 SS 1 3848 5835 i f Sum 128498 265744 E E yr aoe E E oa RMSS 01062 02196 120 40 0 30 00 30 60 90 120 IFDresidum 0 0062 00045 Maw Mir 0 11 0 103 Reticle Field plots compare very A closely with a previous m Aa analysis of the reticle data Median pec 7 5 see top graphic Mamm 52112 Range 12 808 Note
33. screen A final touch up of the plot can be added by right button 7 clicking on the first plot and then changing the number of Figure 47 Data flyer histogram bins located in the Category Bars field of the candidate pop ups Axes tab to a higher number so that single entry high categories can be observed We changed the value to 1500 for this plot Automated Data Culling with Range and Sigma Fields From the statistics displayed in Figure 46 we can see that a one sigma variation in the data is about 2 97 nanometers A good place to start culling is with either a 6 nanometer or 2 sigma value Add either of these values to the Range or Sigma data field of the Display Selection tab and view the data again Figure 48 show the improved data distribution and an improvement in the standard deviation to 1 32 nm r Wafer Aberrations T Ful Screen slot3Icorverted as w r 213 energy 10602 Wafer Values CD 5 Raw Data Microns CD 5 Points 3 Wales 1 Fields E Problem lies in these Siet dil Raw Data high amp low readings Count 3751 Mean 97 4276 Median 122 1185 SEM 0 0484 Maximum 219 2912 Minimum 24 9460 Range 194 3452 MinMax 219 2912 Variance 8 7948 StDev 2 9656 SS 35637991 2723 Sum 365450 9477 RMSS 97 4727 IFDresidium 194 3452 S RRBSREKBES 44 4 __ gt 4 A 2 cull sigma entry will cull at 6 nm Figure 46 Histogram of raw data points showing data r
34. subsets of data Spatial g Analyze the selected subset of data as a function of it s location in the lot wafer and field i Data points can be culled using the mouse ii View scan lens or wafer sub areas of data by selecting them with the mouse and then plotting or saving them into new spreadsheets h Model systematic wafer and field changes i View raw modeled and residual errors for any combination of modeled coefficients ii Remove raw modeled or fixed value components from the data prior to visualize variation from a fixed value iii Pre sort analyzed data to view subsets from the whole field calculated average field the absolute maximum value per field or as a function of the IntraField Deviation IFD for each field iv View graphics such as XY plots Vector histogram range contour and field plots of the data Process Analysis Page 49 Screen Navigation Weir Process Analysis v Simulate data performance after systematic errors are removed vi View film thickness and feature profile values as a function of their location in the lens scan on wafer i Calculate Reticle and Mask Error Enhancement Function MEEF or MEF contributions for each variable j Calculate the effects of lens heating of profile and feature size Metrology k Analyze the quality precision and range of the metrological performance of the current data set and the error budget contributions of the tool s sub assembli
35. tabulation of the spreadsheets currently in the active notebook Excluded All Data points removed from the raw data file because of poor readings or being marked by vendor as having failed measurement Layout All Dose Focus Numeric Aperture Partial Coherence Inner amp outer and stage slit scan direction layout information Saved from the first Weir layout screen Reticle All Data Sheet of Reticle measured information imported from the raw data when present Aberrations Spatial Summary of Piston Tilt and curvature modeled values Also reports the row and column model results for every row column of the data set DataSelection Current data set selected in the Data Selection tab of the Process Analysis interface MeanSurface_ XXX Spatial Calculated pivot sheet of Surface data WaferModel_ amp Spatial and Wafer Model Created by the Spatial Analysis command Coefficients of the FeatureName amp Process current features systematic wafer piston tilt and curvature Model is based on FamilyName Window the position of the feature with respect to the center of the wafer Displays the results for each wafer and a summary Ex WaferModel_BCD_Grp223 FullWaferModel Spatial Site by site values of raw fit and residuals for the current wafer model analysis FieldModel_ Spatial and Whole Field Model Created by the Spatial Analysis command Coefficients FeatureName x Process of the current features syste
36. that each time a selection is changed the wafer graphic display shown in Figure 26 will disappear This signifies that the data subset combination has changed be sure to click the Select Data command button to update subset selection Data selection is performed on three levels 1 On a Wafer or Field by Field basis Select exposure options in the Available Settings frame 2 Ona field site basis Use the mouse to manually cull site locations on the field graphic in the Calibration Options frame 3 On an individual data point basis 6 Use the mouse to select and manually cull data points from the wafer graphic in the Data Layout Display frame Process Analysis Page 51 Data Selection Note Two copies of the data are maintained One copy is the full lot object the second copy consists of a sub set of the full lot object and is referred to here as the selected data a Use the Data Selection interface to change the contents of the selected data b Clicking the Select Data command will return the selected data to the subset specified in the Available Settings frame Any points manually culled using the mouse will be returned to the selected data g View the status bar for notifications of the current analysis status The right side of the status bar contains a short summary of the data currently selected g All data points will be selected when the Weir PW interface is first s
37. the initial value of Site i Ci is the value of the center column site on row i of the field Analysis The raw data can be viewed by turning the modeling for the wafer and field off and then selecting the Wafer tab to the left of the display window We also added in 7 nanometers of range cull for noise reduction A contour of the raw feature variation across the wafer is shown in Figure 55 Hot correstedasedi21 Jenengy1 10602 Wafer Values CD S Raw Data Remove Center Cokmn amp Trem Range Cul Microns CD 5 Points 3736 Wafers 1 Fields 31 Sites 3736 Raw Data_ Count 3736 Mean 0 0007 Median 0 0001 SEM 0 0000 Maximum 0 0065 Minimum 0 0064 Range 0 0129 MinMax 0 0065 Variance 0 0000 StDev 0 0013 55 0 0078 Sum 2 4837 RMSS 0 0014 IFDresid ur 0 0000 16 105 anw aS p r e ee amo meen Poetai 2 Dice 10e t a mw v J owes ora aoe TT ES GEE RT WEE Clr Sr Ee Ts 130 150 wa a ao ae 280 Pas ae RO me x vo Hiort amne Porton on Wobet eve Figure 55 Exposure uniformity Contour of raw variable data across the wafer after the center scan column of data was removed from each field A plot of data from two rows in the center field of one die is shown in the XY plot You will first notice that this is the data set containing the repeating reticle error reviewed in the section Reticle Error Detection page 84 Overal
38. the process requires more than knowing a single focus and exposure dose value Proper specification requires the user to understand the variations in exposure caused by the exposure tool and the portion of these components contributed by the metrology and substrate Similar to the aberrations associated with overlay positional distortion an exposure tool exhibits a unique signature of feature dimensions that vary across the lens slit and across the Page 63 Process Window wafer Variations are caused by focus offsets localized image tilt local variation in exposure dose NA sigma and even the mechanical scanning of the reticle Weir PW provides a toolset for examination of all of these factors With Weir PW the engineer can effectively and quickly calculate the true process window That is a determination of imaging performance free from wafer effects the influence of the reticle and metrology The composite process window analysis of multiple features and the measurement of their variation as a function of the optical train associated with individual exposure tools can for the first time is fully evaluated This lends itself to extending the concept beyond the setting of optimum operating points to that of tool matching for critical layers and even tuning to optimize and monitor performance Fiweir Process Analysis FocusCDS2_101599 XLS File Edit Data FocusCDS2_101599 xL5 Help BS PRtepCD gt EEE Data Selection Spa
39. to further explore the relations between process variables such as Depth of Focus and Exposure Latitude and the variations of Dose and Focus with Exposure Latitude See Figure 33 for samples of these graphs and Table for the variables used in their generation Adding Variables and Optimizing the Calculation Other Views of the Control Curve Page 96 Applications Examples 32 0 tf F PRecThk 0 0407 t x 14 0 PRRecThk 0 0366 03 02 01 oo 01 02 0 3 o4 Focus Figure 67 Adding variables to the process window analysis Additional variables can be added to the graphic by selecting each vaiable s check box in the Setup tab Process spaces can become complex as the are added as is shown in Figure 67 In this example there are now two variables CD and Thickness The unusual thickness curve required the Seed dose value of the setup tab to be set to 22 mj The optimum process space for a random or systematic analysis of the window differs greatly under these conditions Removing Systematic Tilt and Bow The calculation of the process window is sensitive to wafer and even field tilt and bow The sensitivity is acute when multiple points across a field are being analyzed for the common process window Figure 68 illustrates how the true system Depth of Focus can be calculated by removing wafer tilt from a calculation To include the removal of wafer and or field modeled errors turn on modeling in the Model
40. to process mis centering and a serendipitous belief that the overall size of the process window is larger than it s true extent The influence on the product yield is two fold first the process will experience a greater number of marginally function devices and a higher level of infant device mortality and second a greater frequency of unexplained yield busts that are the results of poor lithography tool combination choices for critical device levels Applications Weir PW provides a complete set of tools for the analysis of data statistics metrology quality exposure tool characterization and process setup centering Every aspect from setup to characterization can be addressed including Film and Feature o Exposure Tool specific behavior o Edge bead and wafer stress uniformity o Model across wafer and field uniformity Reticle and Mask o Approximate reticle CD variation o Detect reticle repeating errors o Calculate Mask Error Enhancement Factors MEF o Pattern density loading influence on process window o Optical Proximity Correction OPC characterization Exposure Tool o Matching for optimum CD Uniformity yield o Tool specific depth of focus and dose latitude o Best Focus optimum CD and Depth of Focus contour plots across the field from focus matrix data o Exposure tool setup calibration characterization and acceptance o Off axis Illumination characterization and optimization Overview Page 5 Overview An Over
41. values are initially set by the maximum and minimum of the selected variable in the data Cull Frame Enter a cull range in microns or a Sigma value in fractional standard error values For example if a dataset exhibits a 3 nanometer standard error then a sigma entry of 1 5 will exclude all points of the population that exceed 3 1 5 4 5 nanometers from the population mean Data culling occurs prior to analysis of the data The number of points removed from the analysis will be displayed to the right of the respective field Data culling values will also be used by the modeling engine to exclude data points form the fit The number of points excluded appears to the right of the field Page 66 Process Analysis Field Site Graphic The right side of the screen contains a graphic display of the available field sites presented by the data Site numbers are also displayed in the check box listing at the bottom of the area The software defaults to selection of the field site nearest the physical center of the field Selected sites are highlighted on the field graphic display Four radio button options provide basic site selection as gs One t Select the center most site of the field 8 All u Selects all sites gs ROW v Selects the center most lens row of the field Column w Selects the center most scan column of the field Site Checkboxes x Select or deselect individual sites by their displayed site number t
42. variation from the population mean page 14 Data Fundamentals 1 10 2005 Data Storage and Formats exceeds the limit in the case 1 25 times a standard deviation assuming a Normal Binomial population distribution Model Culled Data Weir PW s models employ singular value decomposition SVD methods of regression as opposed to the commonly used least squares regression This approach allow two methods of data removal to be employed user specified Range and Sigma culling and a new adaptive element technique Range and Sigma culling functions similar to the methods previously described however the population now consists of the points measured value as compared to it s model fitted value in other words the residuals All interfaces including the Process Window analysis include fields for user entry of Range and Sigma Adaptive Element modeling occurs automatically during the model sequence The independent variables matrix is de convolved into three separate matrices characterizing among other factors the layout covariance and singular points Singular points are un representative of the true distribution of the data and are automatically removed or lessened in their weighting on the regression A final control over the functionality of the calculated model coefficients is given to the engineer in the form of validity testing Selection of a simple check box entry provides automated coefficient validity checking
43. 04 Figure 38 BCD Variable as a function of focus The average BCD value is 40 nanometers nm and it ranges by 133 nm across the focus matrix Notice that the InterColumn variation is zero an unsurprising value when we consider that the layout has only one column per die as shown in the raw data plot of Figure 39 ECD delta from site Figure 39 Raw data plot of the BCD Variable Another important item note that the fields at the top of the wafer and the bottom contain relatively little CD variation An examination of the covariance matrix of Table 3 displays relatively little BCD variance with Focus but a greater dependency on the MSE or Mean Square Error of the metrology measurement itself Table 3 Metrology Covariance matrix BARC Resist BCD MSE SWA Family Focus Page 74 Applications Examples BARC Resist_ BCD_ MSE__ SWA _ Family Focus To see these relationships we only need to turn to the Weir PW Metrology tab and plot the BCD metrology variables against the focus values as displayed in Figure 38 There is a definite range of metrology for the variable that falls apart at about 0 12 um of defocus This should not be interpreted as a Depth of Focus for the exposure tool rather it is a limitation in the methodology of calculation of the feature size by the metrology tool Scatterometry and ellipsometric tools use one or two basic methods of determining feature characteristics The
44. 15 Precision Values Computed MeanSurface spreadsheet 109 measure setting units 19 measurement units 24 Medium 27 56 MEEF 50 90 MEF 5 50 90 message Adding to graph 27 metrology 4 5 13 16 17 18 19 22 31 33 34 35 37 47 49 50 54 61 63 64 data import 34 sports 8 valid metrics 77 Model implementation 8 Modeled 84 contour 27 56 models focus 6 least square 8 Models derivative description 6 modes field models 9 mouse data culling by 51 plotting data by 29 restoring culled points 53 Mouse selected data 15 29 MSE 50 63 74 quality metric 76 Multi Scan 38 N NA 13 33 34 37 38 41 64 Navigation Process Window 50 Weir Main Screen 31 Notch 21 34 o Offset 21 34 58 60 111 Options 31 Graphs amp Charts 26 menu 32 origin 37 orthogonal coefficients 8 Overlay spreadsheet format 18 SWA variation with focus and BARC Overview 3 11 31 49 69 Process analysis 49 raw data metrology 45 Weir Focus Models 6 P Partial Coherence layout example 40 Photoresist contour plotting 100 piston 9 Piston 8 83 111 pitch 9 82 Pitch 70 71 72 77 Plot Options 60 Plot Feature frq e 28 Plot Format 46 polynomial Trend Line adding 27 population 8 pop up menu 53 Precision 6 50 61 62 110 calculation 107 Preferences 10 31 37 process centering 79 process window
45. 2 will be created and can be used as a backup Return to the Sites worksheet Select the Test number to be removed by highlighting all entries in the row Press the Delete key o This will erase and leave a blank row of data o DO NOT use the Edit Delete menu selection from the top of the row This selection may delete the entire row moving all subsequent rows up and out of their proper location Sites can later be re installed into the data by either copying data from the Sites 2 spreadsheet or by deleting the current sheet and renaming the copy to Sites Range and Sigma Culling Culling examines the data and organizes it around a logical population center Depending upon the current type of data and analysis screen the population grouping changes as needed For example Feature data populations can organize around the data associated with a specific site on the field Data culling during a model operation will examine the residuals remaining after a coefficient fit and remove outlier points that exceed the specified allowable range or sigma variation There are two variables for culling data Range and Sigma Range culling will examine each population and remove data based upon a user specified range from the mean of the population Sigma culling allows the user to input a standard deviation value such as 1 25 sigma The culling software then removes all data members whose
46. 4 0 996 1 000 0 821 0 900 0 996 Pitch 0 593 0 375 0 860 0 838 0 821 1 000 0 947 0 844 Residual 0 703 0 549 0 923 0 910 0 900 0 947 1 000 0 909 GOF 0 899 0 809 0 999 1 000 0 996 0 844 0 909 1 000 98 0 97 0 96 0 95 0 94 0 93 0 EVVA 92 0 91 0 30 0 0 930 GOF Figure 43 SWA profile variable response and the GOF It s quite interesting to note the dependencies of SWA on the ARC thickness and the relationship between the CD 20 threshold and the thickness of the photoresist In this data there is a very low correlation between pitch and any of the CD metrology Pitch does seem to follow both the SWA and Residuals to the fit statistic The GOF statistic tracks all of the variables well especially and suspiciously the t_ARC or ARC thickness Applications Examples Page 77 Metrology Characterization and Tool Algorithm Verification SLIOISO1SMAP SLIOISOISMAP Water Values SWA Raw Data Water Values CD 80 Raw Data Scale umt 94 000 921 Scalelumk 53 500 max min 9A 91 1 90 682 max min 1 06 702 36 971 Figure 44 SWA and CD contour maps of the test wafer The behavior of SWA and GOF is reviewed in Figure 43 We see a linearity of response and a a large segment of data with the GOF residing up at 97 5 this segment must be very close to the optimum design point of the algorithm Examining the contour profiles of the data for SWA and CD in Figure 44 we see that there a
47. 7 FEM Variable Setup Interface Selections Frame The displayed values currently selected are summarized in this frame Selections Frame Page 48 Process Analysis Analysis Overview Weir standard data format workbooks can be directly opened into this screen Note Weir imports the first eight data columns of the datasheet The variables are stored under the name designated in row I of the column a Columns F through M are data columns b You can include any number of data columns in a spreadsheet To view columns beyond the M copy and paste the entire column s into the data range F to M c Column headers of data with the keywords SWA Angle Ang Slope or SLP are treated as side wall angle or feature profile slope variables They will not be scaled during analyses Any type of data can be analyzed in this interface but most often the data is of the types Critical Dimension CD Side Wall Angle SWA Slope or film thickness The software has four sections that allow the user to select subsets of the data and optimize the analysis to discriminate between lens metrology and process variations The four interfaces are zData Selection d Provides selection of data sub sets selected by wafer or any of the field exposure values or value ranges e Cull data by individual points or by site f Use the mouse to display or plot selected
48. 96 Tat wad 0 0000 0 0000 Curvature um em2 0 0075 00012 Raw Data Count 121 121 Mean 0 1062 0 2196 Medan 0 1063 0 2198 SEM 0 0001 0 Masamum 0 1095 0 2222 Mirsmum 0 1031 02176 Range 0 0064 0 0047 MiniMax 0 1095 0 2222 Vanance 0 0000 0 0000 StDev 0 0013 0 0010 s 1 3648 5835 Sum 128498 265744 k AMSS 0 1062 0 2196 Max Min 0109 0103 IFDresidjum 0 0062 0 0045 Figure 34 Reticle Statistics final size and a contour plot of the field The statistics for the reticle data are shown in Figure 34 for both the wafer final size CD and pitch measurements Figure 35 displays a contour map of Ao oz the pitch measurements Lv TIUUM_AETRALELAlA Codepesd Feit Pichdc Row Dats 021 120 30 60 30 Gb 30 60 W 120 Mao 0 2224 216 Figure 35 Reticle Pitch raw data contour 4x Pitch x Cdum _ CD Pitchum Pitch Family CD x 1 000 0 685 1 000 1 000 0 685 0 685 0 000 Pitch4x 0 685 1 000 0 685 0 685 1 000 1 000 _0 000 Coum 1 000 0 685 1 000 1 000 0 685 0 685 0 000 cD 1 000 0 685 1 000 1 000 0 685 0 685 0 000 Applications Examples Page 71 Metrology Characterization and Tool Algorithm Verification CD4x Pitch x Cdum _CD Pitchum Pitch Family Pitchum 0 685 1 000 0 685 0 685 1 000 1 000 0 000 Pitch 0 685 1 000 0 685 0 685 1 000 1 000 0 000 Family 0 000 0 000 0 000 0 000 0 000 0 000 _1 000 Table 1 Reticle feature covariance matrix CD and pitch values track on a 1 1 basis as shown
49. C Perra T2 thickness decreases Count 4322 io en e Plot in lower left generated by Masini 340 0100 boxing in center die and displaying Minmi 310 1800 Renge 23 8300 data Use Excel for plot MinMax 340 0100 Vatiance 125179 StDev 3 5381 Means3Sigms 937 2385 IFDresid um 0 0000 WePwrap_ ata SWAB 17 Data um max mine94Q 010 11 000 Variance 0 1065 StDev 0 3263 Meane3Sigma 89 8977 FOresidtum 0 0000 EBARCand BWA Scale um 63 400 Deg max min S1 251 11 000 Figure 78 BARC and Side Wall Angle uniformity across a focus matrix Example Wafer Maps A wafer was exposed in a focus matrix varying from 0 3 um at the top row to 0 0 um defocus at the bottom most The scatterometer then measured 121 points 11x11 per field and the raw data analyzed for BARC and SWA is shown in the figure The BARC contour response is a negative image of the SWA variation This is shown by the XY graphic of the lower left Use the mouse to box in several dice in one row in the center of the wafer and then use the pop up menu to display the selected data in an Excel spreadsheet Excel plotting functions are then used to create the BARC vs SWA graphic The change in SWA can be explained by the top to bottom focus variation of the wafer BARC thickness should be uniform across the developed resist wafer therefore the relationship of BARC and SWA variation is unexpected BARC ranges by 30 Angstroms
50. CD Site 1 Focus 0 4 CD Site 1 Focus 0 5 CD Site 1 Focus 0 6 CD Site 1 Focus 0 7 CD Site 1 Focus 0 8 CD Site 1 Focus 0 9 CD Site 1 Focus 1 0 CD Site 1 CD_Min Dose Residuals Target Dose Dose Target 0 007431 0 018 44 851 0 001786 0 02 43 741 33 598 76 8 0 010097 0 005 40 045 5 943 14 8 0 007053 0 007 37 689 8 507 22 6 0 005568 0 011 37176 10 776 23 0 0 006247 0 005 34 772 9 604 27 6 0 005569 0 007 34 084 10 775 31 6 0 001877 0 006 34 017 31 974 94 0 CD 02 0 006253 0 008 32777 9 595 23 3 CD Od 0 004127 0 008 32683 14 538 44 5 oy QUE an 1 1 1 1 1 1 1 Peak cD UTEE 0 007884 0 008 30 756 7 61 24 7 1 1 1 1 1 1 1 1 1 1 ED 0 8 CD AO CD O6 CD 0 5 cD 04 CD 03 CD 0 1 0 008382 0 009 31 822 7 158 22 5 cD 0 2 0 008182 0 008 33 004 7 333 22 2 cD 0 3 0 008921 0 008 33 574 6 725 20 0 cD 0 4 0 00692 0 003 34 948 8 67 24 8 CD 0 5 0 005312 0 01 36 222 11 295 31 2 0 6 0 008072 0 009 38 274 7 433 19 4 CD 0 7 0 011251 0 014 39 535 5 333 13 5 CD 0 8 0 001277 0 013 43 052 46 997 109 2 cD 0 9 0 008971 0 022 45 261 6 688 14 8 cD 1 0 012223 0 028 47 834 4 909 10 3 Wafall ExpALL All NAAI PCo 0 60 PCi 0 00 4 Applications Examples Calculating the Process Window The process window analysis is setup the same way as when analyzing focus and dose responses When the PW tab is selected you will get a curve similar to that displayed in Figure 65 m Process Relations
51. CD1202 Accent_Scatteromett D ata_ File Edit View Calibration Analyses Tools Accent_Scatterometry_Data_ Vertical XLS Help saulas eeng ai Layout Metrology Exposure Tool Display m Data Set p Data Selection Display Selection Component Removal Plot Format Wafer Display Selections Vector Histogram C Contour C 3D Surface XYplot Scale Data Type Items to Include in Display Screen W Statistics Graphic 0 bot_cd1 X X 3 m Water Aberrations T FullScreen p Cull F Range Sigma P T 2 Microns bot_cd1 Accent_Scatterometty_Data_Vertical Count 39 Water Whole Field Waters 1 Threshold bot_edi AllFeatures Fields 33 Min lt dx lt Max Maximum 0 202 Minimum 0 181 Range 0 021 Mean 3Sigma 0 204 Display Selection Histogram Component Removal 12 6 2002 6 36 PM Figure 22 Raw data metrology screen View the data by Wafer and Field layout basis Restrict the data under analysis based upon wafer number or the Scan Direction settings specified on the Layout tab View multiple graphic displays including Vector Histogram Contour and XY plot formats with summary statistics 2 Remove selected components such as the Mean Average field or a fixed value Set data display thresholds to view data points that exceed upper and lower limits View the data as organized under several format
52. If validity checking is selected coefficients judged invalid by their estimation uncertainty are replaced with zero values and the model is re calculated to provide the most accurate control surface correction for the process or equipment Employment of validity checking in during process or tool setup results in greater accuracy of equipment tuning and minimizes the ringing that so often results from repeated over and under correction in automated process control sequences Mouse selected culling Many of the interfaces allow you to box in a selection of the data and then display plot or cull it from the analysis Data culled in this manner can also be re inserted using the same method see section Mouse Selected Data Manipulation on page 29 Culling by selected variable range The data selection and process window interfaces in Weir PW provide culling by range for any variable Each selection has a command button a variable selection combo field and High Low range limits fields Pressing the range command button with plot a histogram of the variable selected in the combo box Use the quartile designators for QO and Q4 to specify the low and high range values Data points will then be removed when the data selection command button is selected The number of points culled will appear in the status panel and on the range command button Weir PSFM provides data culling in the analysis screen by comparing the X and Y focus values La
53. Lat bb Illustrate the relationship between the DoF and Dose Latitude Dose vs DoF amp Expo Lat cc Explore the dose setting and how it influences the process window Focus vs Dof amp ExpoLat dd Explore optimum focus and the process window Model Provides controls to turn on the modeling of systematic wafer and field errors By default all of the coefficients are selected for removal however it is customary to only select wafer tilt and or bow PW Control Page 68 Applications Examples Applications Examples Overview Many of the applications reviewed in the Weir Manual are related The user can also access the Weir Data files for each of these applications and reproduce the results This appendix provides a quick and easy summary of the relationship of the reports and the data files used for each Application Title Data File Summary Reticle Analysis Scatter 110 A test reticle has been measured with data obtained from DPI_ReticleData xls the mask shop CD SEM The data is analyzed and a signature obtained for future analysis of wafer images Metrology Scatter 110 Scatterometry data of focus matrix illustrating a study of Characterization and DPI_ReticleData xls metrology tool algorithm validation Two examples are shown One in which the effective focus range of product metrology is limited by a poorly designed algorithm setup on the metrology tool The second example looks at the effectiveness of a metr
54. Window interface Sites can be selected in two ways simply click on the check box next to the site number or double click on the field site itself to turn it ON or OFF When the site is selected the field graphic will highlight the box located at the site position Example Wafer Maps Direct Comparison SWA and CD Direct Comparison SWA and CD Page 98 Applications Examples Full Wafer plots of data variation can be applied to help us understand the process variations induced by exposures wafer topography and the mechanical induced variations of reticle scanning Bow errors can also be induced when a reticle is chucked onto the platen resulting in saddle point behavior of the focus plane and the resulting feature size variations Wafer Values SWA Raw Data Wafer Values CD 80 Raw Data 92 75 Scale um 34 000 92 1 Scale um 53 500 max min 9A 911 90 682 915 max min 1 00 702 36 971 Figure 70 Contour of feature values and corresponding Side Wall Angle distributions Data contained 121 sites per field measurement of SWA and CD Engineers in lithography have been using profile cross sections for years to verify feature integrity of and side wall angles SWA during exposure tool acceptances With the advent of the new faster metrology tools side wall angles and the corresponding feature maps can be printed side by side as in Figure 70 with a fraction of the effort of past studies R
55. a Seed value dose into the field of the same name on the Data Range tab If Weir returns an announcement that there are an insufficient number of data points to calculate the process window control surface you may be able to continue the analysis by adding in a Seed dosage value Calculating Focus Response Applications Examples After setting up the process variables as described in the previous section you may desire to further limit the dose interactions or number of lines on the graph Double clicking the Al check box in the field will alternate checked entries between the All entry and the marking of every possible dose entry If you wish to exclude only one or two dose entries then double click the All entry and follow up by un selecting the dose values for exclusion Begin the analysis by selecting the Focus tab located to the right of the display window Weir PW will plot out a table summarizing the fit for every dose curve and a graphic of the plot as shown in Figure 63 Individual point and curve values can be investigated by hovering the mouse over a section of the graph A yellow text box will appear similar to the one shown for the 60 mj dose curve of Figure 63 The Depth of Focus for any dose can be found by plotting its left and right focus values for the crossings of the UCL maximum and LCL minimum target markers Notice that the title of the graph details the field sites in
56. across the wafer with 95 of the data residing within a span of 14 Angstroms out of 926 This 1 variation may in fact be a physical phenomenon only shown by the new metrology techniques or it may be an artifact of the metrology tools Rigorous Coupled Wave Analysis RCWA algorithm SWA variation with focus and BARC Page 106 Precision Values Computed Appendices Appendices Precision and Error Budget Calculation Precision values allow the user to examine behavior of the metrology and exposure tools without data modeling The operate using the currently selected data subset and increase in accuracy as the number of data points increase in number Values shown in the software reflect the one sigma standard error of the calculate variance Sigma is defined as the square root of variance of the data The Variance is the sum of squares of the data population s variation from the mean of the population divided by the degrees of freedom dof of the data Note that the precision values shown below will not appear forall data sets For example the wafer precision will not be calculated if the dataset has only one lot worth of data in it Precision Values Computed SS Sum of Squares of difference of each measurement from the mean of the group Note that the SS measurement is influenced by the grouping of the data Constants n Total measurements m Total die dof Degrees of Freedom Precision Requir
57. ader Cell Function Location X_DIE_SIZE Bl Not currently used but data must be present in the data Y_DIE_SIZE Cl Not currently used but data must be present in the data Data Storage and Formats Page 19 of 116 Data Storage and Formats Information Sheet Format Header Cell Function Location TEST Correlates with the TEST column of the data sheet previously discussed Data Begins on row 2 with a value of 1 Subsequent rows must include a value of row 1 for each test number NOTE Rows may be left blank without data but keep the tule test number row number 1 Any data row that does not have a corresponding site row on the Sites spreadsheet and location information will be excluded from the loaded lot object xX LOC El X Location of the measured site on the exposure field Values stored in millimeters Note X Y 0 0 is located at the field center Y LOC Fl Y Location of the measured site on the exposure field Values stored in millimeters Note X Y 0 0 is located at the field center FAMILY Gl Used only for non overlay non registration data May contain the values of IsoLine DensePack Via F3 Microsoft Excel Slit1 1 5 slot 6Foc uis 65 x Information Sheet Format File Edit View Insert Format Tools Data window Help 18 x Stores header information for the data D gH
58. afer spatial characteristics as these must be considered additive in nature On this basis the measured feature response can be described by the following equation FR x y RET x y IF x y Wo x y DD x y r 3 The spatial distribution of feature response is described by x and y variables representing Cartesian coordinates on the wafer The terms in eq 3 are RET x y Reticle variations contributing to a static field signature IF x y IntraField periodic signature composed from a reticle component added by any plate tilt or bowing from loading and a systematic within wafer periodic component describing the scanner field slit and scan signatures 2 W x y feature response variability caused by disturbances with slow and continuous function of wafer position Wafer periodic This component is primarily a result of the whole wafer at a time process steps characteristic to resist and track DD x y is the Die to Die variability of the feature response This component exhibits mainly discrete distribution sets rather than a continuous variation within the wafer DD distributions occur from exposure field to field and result from variations in discrete scanning disturbances such as effective dose the incidental focus or scan direction yr the residual component or the random error remaining after subtracting feature response to all non random components The residual component has a zero mean valu
59. ain removed wafer and field aberrations The center site of each field was also removed from all of the data prior to field modeling This is accomplished by selecting the Center Site option button on the Component Removal tab In this example the mean field was not plotted rather all of the fields were collapsed and their residual values to the wafer and field systematic errors were plotted The advantage here is that the actual spread of data across the wafer is not visible To view all data overlaid in this fashion select the Whole Field option button on the Plot Format tab and then use the Field tab to the left of the display window to model and display the data In Figure 58 we can see excellent tracking from reticle to wafer feature across most of the reticle One site located at 6 mm to the left of field center is not behaving well We would need to analyze additional rows to see if it s a function of the metrology or exposures The right side of the slit is exaggerating feature sizes a full analysis of the other rows of the reticle would help to determine the source of the problem If the average field with systematic errors and field to field offsets are removed we can plot the contours shown on the right side of Figure 59 Comparing this contour with the reticle plot on it s left we see the high points in the upper left and lower left of the field The shallow valley in the center and exaggerated
60. al to the range scale displayed at the bottom of the plot This display provides a view of the variation in raw data across the field grid location The value of the variable focus dose etc selected will be displayed in a text box superimposed upon the field location You can change the display graphic by modifying it s value in the options directory See the section entitled Setting Preferences and Defaults By default a collapsed composite of all wafers in the lot are displayed Individual wafers values can be addressed by selecting the wafer number from the Wafer drop down field located to the left of the graphic area Array Origin The array origin is the field surrounded by a dark box The array origin can be changed to any field by double clicking the desired die Page 37 Weir Main Interface Specifying Field Exposure Layouts Modifying Variable Values for One Specific Field A single mouse click of the left button on a field text box will allow direct entry or modification of the value for the field If the Wafer drop down field is set to All all fields located at this position will be modified When scan direction is the selected variable clicking on a field will cycle the value from up to down left and then right Exposure Entry Automation Controls o EEE Hide Field Text check box Selecting this box will hide the variable text displayed on the wafer field This allows
61. ange and flyers Automated Data Culling with Range and Sigma Fields Page 80 Applications Examples Mictore cesy Ports WF Waters 1 Field EL Sies 3732 Ran Dala Count Man Meda SEM Miani Miram Range MrMax Vamance SDev S AMSS Qvesiium Figure 48 After flyer removal Manual Data Culling to Enhance an Analysis Applications Examples The method of data removal described in this section can be used to remove poor data metrology by the exclusion of data points on a point by point basis The technique can also be applied as shown in this section to enhance an analysis Exposure Tool Scanners provide a relatively stable lens signature By it s very nature this signature is a narrow slit approximately 10 x 32 mm or so in size Most scanners today have a horizontal lens slit and this slit is then scanned vertically or Up and Down in the layout interface nomenclature of Weir The illumination across the slit may be uniform or Gaussian in profile in which case the effective slit width can be reduced to as low as 2 mm The effect of this scanning is that aberrations in the horizontal or X direction follow those of the lens aberrations in cross section Aberrations of the lens in the vertical Y direction are averaged by the scan thereby smearing the aberrations and reducing feature contrast in this direction Page 81 Data Culling Methods The scanner
62. as the origin Weir Main Interface Select the relative location and travel direction of the array you will be filling In this case click the origin button located as shown For this location fields to the left and then upward of the origin die step 5 will be filled in Page 39 Weir Main Interface Step by Step Tutorial Defining an Exposure Layout Click on Update to fill in the array values Then click Save to save the data to the Layout spreadsheet Figure 17 Specifying Focus variation layout Adding a Constant Partial Coherence Value to the Array Now that we have set up the focus we desire to specify a constant Sigma or Partial Coherence PC for all die in the data set Note that if PC varies from wafer to wafer you need to first select the appropriate wafer ID from the dropdown list Refer to Figure 18 for this exercise Select the PC_outer variable Note PC inner is used to define ring and other apertures Change the format to Constant Change PC initial sigma to 0 63 page 40 Step by Step Tutorial Defining an Exposure Layout 1 10 2005 Weir Main Interface Step will automatically change to 0 because of the Constant setting With Constant settings it is not necessary to set an origin die Weir Wavelroet Engineering O Data KL Array pstne 2 Spoink 0823 85 aloj xf Fie Et wem Calbration Anstyses Tools p
63. ata culling in the Data Selection tab of the Weir PW Analysis screen can be used to select a single column or row of the field for analysis This provides not only a reduced data set but also a simplified view of just what is happening during the scan procedure Additional information can be gained if the Scan direction selection check box is used with the layout entries to selection only those fields whose scan occurs in the same direction i e up or down Manual Data Culling to Enhance an Analysis Page 82 Applications Examples For this analysis we will cull data points across the field leaving only the center row of data for analysis The Data Selection screen partially shown in Figure 49 exhibits the data set where sites have been removed in the lower right side of the field The user next boxed in the site located in the upper half and is about to select these sites for data culling Moving to the Spatial interface shown in Figure 50 we next selected to display a vector plot of the data Wafer modeling has been turned off and from the statistics displayed on the right the full field A Weir Process Analysis slot3iconyverted File Edit Data slot3iconverted as wfr 213 energy110602 xls Help amp amp amp co 20 E Data Selection Spatial Metrology Process Window m Focal Plane Aberrations 1
64. ate such as Scan X and Slit Y Feature then the data plot actually contains two graphics sharing a common base as shown in Figure 7 The common baseline provides an easy comparison of the two distributions The scale factor is used as a multiplier for the values reported on the abscissa For example the 0 1 um factor shown in the figure tells us that the abscissa values should be multiplied by 0 1 The abscissa of the figure therefore extends from 0 196 to 0 192 microns You can display the display of the histogram just like any graphic Right click on the graph and the Options screen shown on the right side of the figure will appear The number of bins or category bars determines the ordinate scaling The abscissa tick formatting is set by the selection of the Format field You can also manually type in format options 14 Options ee xl 12 Display Tites Ave Series Number of Axes items in X C Khia F Plot GidLine category en ee Fort Color yZbsis pao Mamm pere Cis o20 Minimum o Category Bars 00 Resolution Number of emo E Fame items in Y a i category 84 104 4 12 4 OK Cancel Soply X axis 14 d scale y pjt 4 1501 2 1 02 078 034 030 D 0 16 038 060 082 1 04 1 26 1 48 1 70 1 92 factor Figure 7 Two variable Weir Histogram and Options screen page 28 Histograms 1 10 2005 Customizing Graphics Mouse Selected Data Manipulation Waferl_Slotl RAWFOCUS Tool Focus Corrections Wafer Focus fro
65. ations option is set to Errors then focus data for a field exposed at 0 5 um exposure tool offset will display negative vectors of about 0 5 um in error However if the option is set to Corrections then the 0 5 um field will display focus vectors of 0 5 um the correction needed for tool focus error minimization Editing Exposure Tool Settings The Exposure Tool defaults set up the default values used by the stepper and or scanner These setting will influence the displays some of the modeled calculations and the headers of the various statistics tables The most readily noted function of the Exposure Tool selection is the setting of the wafer size and notch or wafer flat location for wafer graphics Die Size and centering on the wafer and field are typically set up in the Information spreadsheet using the Display tab of the main screen Exposure settings including Focus NA Sigma Coherence and scan stage direction are part of the data file and can be modified in the Layout tab Exposure tool library setting provide the ability to switch wafer and notch variables Future analyses of Weir may include references to the data variables stored in the library but they are not currently used A library of exposure tools is stored in a worksheet located in the Reticles sub folder of the Weir analysis folder The library is named the ExposureToolLibrary xls Getting There Weir Main
66. button to display a pop up selection list The click on the list entry to place it into the field Variable Entry Concept Variable values are entered into each exposure field using the keyboard and mouse You can specify any variable name and range that you wish For example enter a quality scale form 0 to 10 or enter the number of lines standing in a nine feature group The example shown in figure 21 is an example where the total number of lines in a metrology site was seven 7 The observed features on the sites ranged from 1 to 7 This data was then applied to the process window analysis shown in figure 19 using the setup criteria shown in the bottom interface of figure 20 Data Storage and Viewing The data is saved as a new column of measurements within the Weir data workbook Data can then be reloaded and modified again in the future The Data menu of the interface provides the ability to view the focus dose matrix on a worksheet or as a data file This worksheet can in turn be save as a separate workbook or as another sheet in the Weir data workbook Using the FEM Variable Interface Page 44 Raw Data Metrology Overview Raw Data Metrology Raw Data Metrology Raw data imported from an Vendor s file or a Weir Worksheet can be viewed using the Metrology tab of the Weir Main Screen see Figure 22 This screen will allow you to Weir Wavefront Engineering ver 1 95 D Data TIdata_
67. cluded in the analysis Page 93 Process Window Analyses The statistics chart at the bottom of the graph is duplicated on the workbook s FocusResponse spreadsheet This spreadsheet is a convenient resource for performing additional custom calculation within the Excel environment You can also plot variables such as the Best Focus verses Dose curves The Best Focus point is the inflection point that is the maximum or minimum point of the dose curve Calculating Dose Response To calculate the response of the feature size to Dose follow the same procedure as when calculating the Focus Response discussed in the previous section The analysis occurs simply by selecting the Dose tab located on the left side of the plot window and concludes by presenting the graph and statistics of Figure 64 Statistics optionally presented at the bottom of the chart are also saved into the Weir Workbook in the DoseResponse spreadsheet Filweir Process Analysis EXPOWIN XLS File Edit Data EXPOWIN XLS Help HS teal gt SEE Data Selection Spatial Metrology l Process E r Process Window m Process Relations Refresh v Full Screen Pw Dose Focus 1 8 ilar 415 CD 1 42 cae ea CD_Target E 44 00 1 368 ae CD_Max Feature Focus Site Slope Sigma Dose Latitude Latitude cD 1 1 9 8 074 18 0 Feature Variation with Dose Focus 0 2 CD Site 1 Site Center site 1 Focus 0 3
68. d 86 Selections frame 56 Setup 86 Model re Model Aberrations command button 56 Analysis 87 Full Screen check box 56 Wafer Feature Comparison to Reticle Data 88 Cull Radius command button 56 Background 88 Display Selection Tab 56 Process Window Analyses 91 Model Components Tab 57 Setting up for a Process Analysis 91 Component Removal Tab 59 Calculating Focus Response 93 Plot Format Tab 60 Calculating Dose Response 94 XY Plot Options 60 Calculating the Process Window 95 Metrology 61 Other Views of the Control Curve 96 Precision Analysis 61 Adding Variables and Optimizing the Calculation 96 Covariance Metrology 62 Removing Systematic Tiltand Bow 97 Process Window 63 Selecting Multiple Sites 97 Overview 63 Example Wafer Maps 98 Associated Worksheets 65 Direct Comparison SWA and CD98 Data Range 66 Reticle Data or Mean Field Removal for Photoresist Setup 67 Analysis 99 PW Control68 Variations Across Field and Wafer 100 Model 68 Film Deposition Uniformity across the Wafer 101 Photoresist variation by 6 order modeling 102 Applications Examples csssssssssccsessssseees OD ARC thickness O order waler mapping 103 Overview 69 Critical Feature Uniformity with 6 order wafer Reticle Analysis 70 models 104 Background 70 Modeled Side Wall Angle 6 order uniformity 104 Analysis of the Reticle 71 SWA variation with focus and BARC 105 Metrology Characterization and Tool Algorithm Werfication 72 Ap
69. d from the analysis and residuals were plotted We then created an XY graph plot of the average field and overlaid a mouse boxed center column XY graph of the reticle s center data column the results are shown in Figure 57 To view the mean field data select the Field Mean option button on the Plot Format tab of the interface prior to modeling The scan direction signature is apparent in the reticle field please note the scale of the plot ranging only a total of 2 nm There appears to be more noise in the lower half of the field possibly due to scan instability or scan speed variations The upper half of the field tracks quite nicely Applications Examples Page 89 Wafer Feature Comparison to Reticle Data Background Problem spots Center Field Slit a Rn fn Solera ETET TNTET T A Diefx y mm 26 00 28 00 50 100 so asessasssasnosssassosssasedih soose J cscnecctscuceMlcceuss Mesnedcanec dccuccadponcses gpccccooscsont Scaefum 0 00 xe 50 do 150 Hormone afl cute Pooran on F midir Figure 58 Slit lens signature analysis Left Field plot displaying the center row of data Right Plot of all field data for center row blue overlaid with reticle data points red In similar fashion the slit signature can also be examined In the plot of Figure 58 only the center slit row of data remains after culling field sites above and below it The analysis ag
70. d so the process has reduced feature size from the reticle s 106 nm toa median 80 6 nm with an increased range of 56 nm due largely to the underexposed field at the bottom of the wafer The wafer graphic scale however demonstrates the 20 nm range of contours for the plot Similarities between the reticle contour and that of the wafer fields are there Mean field wafer aberrations removed Plot Mean field Center Column back image g 0015 Mberene dow G v UN T t 6200 10 0008 6 1000 oom 5290 10 tt 16 tee a 4 si x Scale jun 0 001 150 a0 50 90 59 120 150 Dieix y mmt 26 00 28 00 Vete Aora Poster on F ektra Seems abe off ite Reticle Center Column filled diamonds Over laid in blue background with Water average field open diamonds Figure 57 Wafer average Field center scan column feature size compared with the reticle Wafer and field systematic aberrations including feature mean were removed Left Wafer data average field of center column data Right plot of reticle feature signature overlaid on wafer field We want to see just how close the signatures compare between reticle and wafer The techniques of section Manual Data Culling to Enhance an Analysis were applied to the data set to allow only the center scan column of the figure to be studies Similar to the previous paragraph the wafer bow tilt and field tilt were remove
71. dataset Living with reticle errors There are three avenues of correction for a data set with reticle errors Use the data culling range and sigma fields to attempt to exclude the points Return to the Data Selection tab and cull the data site from the display by using the mouse to box the site in the field window on the left side of the screen and then selecting the Cull selected data points item of the pop up menu This will remove the data from the current data set but not from the source spreadsheet Remove the data from the appropriate row of the Sites spreadsheet This will prevent any data from the site from being loaded the next time the spreadsheet is opened ee To do this simply note the site number column D in the popup display of figure as being site 51 of the reticle Then switch to the Excel Spreadsheet workbook containing the data and select the Sites tab Use the mouse to select all of the columns and delete the entries of the 51 st row Note This will be the row containing the TEST number 51 Do NOT delete the entire row just the data contained in it ff Finally reload the spreadsheet site 51 data will not be loaded Field to Field Exposure Stability Data File Slot31converted xls Summary A wafer has been measured using scatterometry The data is modeled for systematic wafer aberrations and then field tilt The residuals to Applicati
72. des with the wafer center by inserting x y 7 5 10 mm into the mm fields OR by inserting x y 0 5 0 5 dice in the dice fields Make sure the Grid command button displays Grid data to view the results Field Section Control centering of the measured sites upon the center of the exposure field Offsets are entered in millimeters Click on the Grid command button to display the field and the measured sites located on it The positioning of these sites corresponds to the data stored in the Sites spreadsheet Display the results by selecting the Grid command button page 36 Data Import and Layout 1 10 2005 Weir Main Interface Note that when the Field is displayed the label of this control toggels to Field Sub Field Settings These settings are used to specify a portion of the field to perform a model analysis upon Similar to breaking down a wafer into individual fields the sub Field setup breaks down a field into analysis cells Use the x y Size fields to specify the sub Field window size and the x y offset values to offset the window relative to the center of the whole exposure field Display the field data to view the defined sub Field s layout on the exposure field Specifying Field Exposure Layouts The Layout screen shown in Figure 17 allows the user to specify exposure conditions for the individual fields of each wafer in the lot Exposure variables include F
73. distribution ster O asda OOOO O y y Standard Error Standard Error Calculated using the formula for standard deviation but the user must recognize that the population is not normally random distributed Sigma Statistics Shortened name for Standard Deviation or Standard Error Optics Partial Coherence of the illumination NA Numeric Aperture of the optical System Average Focus X focus Y focus 2 X focus Vertical feature or lens slit focus Y focus Horizontal feature or slit scanning focus variation Piston The focus offset or constant term of a systematic error model a eee Precision Values Computed 113 Precision Values Computed 3 3D 54 56 57 109 3D Surface 27 controls 27 A aberrations 65 sources of 6 Aberrations spreadsheet 109 spreadsheet 9 adaptive 57 modeling 8 Adaptive Modeling Culling of Data 15 algorithm metrology 72 metrology fine tuning 79 metrology poor design example 69 72 Angle 49 APC 75 Applications 5 ARC 77 101 Astig Y Xmax definition 46 Astigmatism definition 46 Axes XY plot modify 26 B BARC 73 Uniformity 106 BCD 73 BoxPlot definition 26 BoxPlots add to graph 26 C Capabilities 5 Cartesian 8 categories in histograms 80 SWA variation with focus and BARC Index CD and SWA 98 wafer contour 78 coeffecient modeled 101 coefficient validation 8 colinearity 8 collapsed
74. dual data are always available through their storage in the worksheets of the data workbook 2 Any graph or table s data can be viewed and separately saved in a separate worksheet generated by selecting the Data View Data menu item of the interface 3 Any subset of data in a vector or contour plot can be viewed or plotted or saved in a separate worksheet generated by boxing in the area of the graph while depressing the left mouse button Storage of data Weir PW requires the prior installation of Microsoft Excel Raw metrology data is converted into the Weir Standard Format and stored an Excel Workbook of the same name as the raw data file Workbooks contain a minimum of three spreadsheets a measurement data sheet of the same name as the file a Sites sheet containing the location and format of each unique data site and an Information data sheet with header information on the die size offsets metrology tool name etc See the section Weir Standard Format for detailed descriptions of the Weir Standard format Weir Spreadsheet Data Formats Data is typically imported from a metrology tool s binary or ASCII format data file The data formats are then converted into the Weir Standard Format and stored into Spreadsheets After a data set has been imported into a spreadsheet the spreadsheet should then be opened and re used for future work since there is no need to re import the raw data Minimum W
75. e and no spatial systematic characteristics Next step in formalization is to model the feature response as function of wafer coordinates Each component of feature response to process disturbances as presented in eq 3 is modeled by high order polynomial fitting functions which could be described either in terms of wafer radial coordinate radius and angular position or in wafer rectangular x y coordinates Both cases are shown in equation 4 and 5 below i AATE D AN T ar gt ri 2 cos 79 y sin j8 ra ai A t O fa g 4 16 776 FR x kA gt aryl sAd 120 920 5 Equation 4 describes feature response to disturbances dependent on the radial and angular distance of the measured location from the center of the wafer while equation 5 describes identical response but in wafer rectangular coordinates For both equations the rightmost term describes the link between feature responses to process disturbances through each sensitivity parameter Page 7 Overview An Overview of Weir Feature Modeling Model Implementation Weir implements both forms of equation 4 and 5 during an analysis in the Spatial tab interface see section Model Components Tab page 57 You can control the level of interaction with the terms and turn modeling on or off from this tab The actual number of terms implemented during an analysis can be restricted by the Terms drop down The modeled anal
76. ecifies the format of the graph and the items to be viewed This section will allow you to view data using graphic tools such as the Vector Plot Histogram Contour and XY graph scatter plots Control the display of Statistics and or graphics on the viewer by using the Display Screen check boxes The Scale control is used to specify the vector plotting scale in microns of the display Component Removal An analysis of the sources of variation in the data is enhanced by the ability to remove constant values such as a fixed offset or mean field The Mean Field is the average of all values for each site Plot Format The data format selections shown in Figure 23 allows you to specify the format of the data analyzed Field Wafer Statistics Display Page 46 Raw Data Metrology Field Wafer Whole Field View all points on a Collapsed field View all data points as measured on the basis substrate Field Mean View data points averaged at each field View the mean value for each field one site measured value per field location on the wafer Field View the maximum deviation from the View the maximum deviation from the Min Max mean for each site on the field mean for each field One value per field location IFD View the IFD variation at each site View the maximum spread of values for each field location Astigmatism View the Y X or Horizontal Vertical View the value for each field on a range
77. ed Data values can be easily manipulated if you are familiar with the basic Microsoft Excel commands There are three key items to watch for to insure a valid comparison Make sure that your field locations and test numbers are the same on both data set s You may not want to subtract the metrology of a field in the wafer center from one on the wafer s edge Site values are also critical because they define where the metrology is located on the wafers edge Insure that each data set has the same number of rows Remove if necessary rows that do not match page 22 Manual Manipulation of Data Sets 1 10 2005 Data Storage and Formats if you use Excel functions to calculate a data value remember that Excel saves the function into the cell even though the data value is displayed If you then copy the cell value to a new location Excel will copy the formula not the value An example of an Excel functin J232 F232 G232 2 You copy cell values rather than formula by using the menu command Edit Paste Special and then selecting the Values radio button Example Subtracting two data sets Load both workbooks into Excel It s a good idea to save the workbooks to new names Examine the Summary Data section of the Information spreadsheet to determine the total number of data points If they are equal you can probably simply paste from one workbook to the other If they a
78. ees can be seen to occur at 4 9 and 11 o clock positions on the wafer edge This may be due to chucking or the uniformity of previous film layers Again these are the same 300 mm wafers we have examined in the previous sections The right hand figure illustrates the SWA variation obtained after the wafer systematic errors and the average field are removed We can now see how Swa is varying from field to field most like due to focus or dose variations during exposure A side study of this data set and exposure tool using the Critical Feature Uniformity with 6th order wafer models Page 104 Applications Examples sl Omap fullwaferfullfield floatP barcW en Wafer Values SWA Wafer all Coefs map tullwatertullheld toatP barcW es Seale um 0 300 Scale um 0 400 max min 0 750 0 137 max min 1 383 6 334 Figure 77 Side Wall Angle SWA or feature profile uniformity Benchmark PSFM focus reticle and Weir PSFM software can tell if the variations are from focus or scan nonlinearity SWA variation with focus and BARC Figure 78 presents both expected and surprising response from data obtained from a scatterometer s measurement of the base anti reflective coating BARC and measured side wall angle SWA across a wafer BARC and SWA Weir PW Nanp_cyptess_1 7 T2 14 ha W7 w Data Points a2 Comparing these two images we can Waters 1 Fe Z see that the SWA increases as BAR
79. eferences and Defaults 3I Overview 31 Getting There 32 General Tab 32 Storage Locations Tab 32 Focus Calibration Tab 33 Editing Exposure Tool Settings 33 Getting There 33 Tool Frame34 Data Import and Layout 34 Importing Raw Data 35 Centering data on the Wafer and Field 35 Specifying Field Exposure Layouts 37 Getting There 37 Graphic Display37 Modifying Variable Values for One Specific Field 38 Exposure Entry Automation Controls 38 Step by Step Tutorial Defining an Exposure Layout 39 Setting up a Serpentine Focus Variation 39 Adding a Constant Partial Coherence Value to the Array 40 FEM Variable Setup Interface 41 Adding an Exposure Dependant Variable 41 Accessing the FEM Variable Setup 43 Using the FEM Variable Interface 44 Variable Entry Concept 44 Raw Data Metrology ssssssesssssocscccesssssosoccceees 45 Overview 45 Statistics Display 46 Definitions 46 Display Selection 46 Component Removal 46 Plot Format46 XYplot 47 Threshold 47 Selections Frame 48 Process AnalysiS s ssssssssssssossesssossssssscsnsssosssssesss 4I Overview 49 Screen Navigation Weir Process Analysis 50 Data Selection 51 Available Settings Frame 52 Calibration Options or Field Frame 53 The Weir Software Suite Table of Contents The Weir Software Suite Data Layout Display or Wafer Frame 53 Living with reticle errors 85 Spatial Analysis 54 Field to Field Exposure Stability 85 Associated Worksheets 54 Backgroun
80. efm t3pomt 0023 25 Hele 36 6 neg oa Layo Metclogy Expose Toci Display Mevolog Layout Pimtinoe ea SSC s C Vex 155 aaia Dose NA Pirmi Poder 5 eom i 15 065 0 O63 Any Fama Constar bed Ts Hide Field Test Inte Fi Stings FC foes sep Dvecion fil ai J0 P E gt upane s Peet f Cad Figure 18 Specifying constant Partial Coherence in the layout Click on Update to fill in the array values Then click Save to save the data to the Layout spreadsheet Check that the Dose NA etc values are correct You can reset these values in the same manner as this by changing the Variable field This field will add additional rows as additional unique values are added to the array FEM Variable Setup Interface Adding an Exposure Dependant Variable Weir Main Interface There are times when a qualitative approach to metrology must be added when Automated metrology can measure the width period side wall angle and other attributes of a feature but this does not characterize the entire profile as observed in the field of view An excellent example occurs when observing dense packed features in a focus dose array FEM Variable Setup Interface As focus and dose vary across and beyond the normal process window feature sizes are changing along with profile quality Under some exposures the individual feature widths may become so thin that the struc
81. elected in the combo display at the top of the screen in other words the average of the variable you are currently plotting This capability allows the user to obtain a more accurate assessment of the perturbation contribution of the stage and scan slit dynamic components to the overall aberrations of the exposure tool A Remove average or fixed values Display Selection Model Comaanent Component Removal Pict Fermat Nore Field C Ceme Row Center Site F LotAvsage Comer Cohme C Wae foo Saxe Row Column Value Row Column a Row Offset a 6 C fo 0 00 C Field T Pr oT foo foo uad F LotAverage Cuvawe FO F ea om Figure 29 Systematic Component Removal Use the Display Toggle command button to select between average or model based values Removal Basis Select the basis of component removal as either the Lot Average or individual field If Lot Average is checked then the values are first averaged across the entire lot of data and then removed from each individual point If unchecked then the average component for the field is removed Selecting the Row Column radio button results in calculation of the value for each individual row and column it is located in The Field radio button averages all rows and column calculated values across the entire field The actual value removed depends upon the component selected by the user Removal Selection Choices Process Analysi
82. ement amp Explanation Variance dof Calculated Pure Error Represents the static or dynamic measurement precision of SS dof Dof a single data point Requires Multiple measurements of a pomt pe pe single site measurements of single point 1 Site Precision The variance of values for each unique site on the SSsite SS pe DOfsp dofsp n sites exposure field Requires Multiple die with same site location Row The variation of values within a single exposure row SS iow Dofrow Dof y n Rows Precision On a scanner this represents the variation in features across the lens slit Loss of precision will result from lens aberrations and variation in exposure Requires Multiple sites in a single row on a die multiple die IntraRow Variation seen from row to row or in the case of a SSriela SSrow DoFintraRow rows scanner from slit to slit DoFhntrarow fields Column Column precision is the variation of data across the SScolumn Dofcol Dof o n Precision columns of the field For a scanner these variation are Columns caused by errors in the reticle and or stage scanning mechanics Requires Multiple sites in a single column Precision Values Computed 107 Precision Values Computed Precision Requirement amp Explanation Variance dof Calculated on a die Variation seen across the column IntraColumn Variation seen from column to column SSiai DoFntracolumn SS cotumn DOF hntracotumn
83. er tilt and bow turn on wafer modeling by using the Full Wafer radio button on the Model Components tab see the section Model Components Tab on page 57 Select the coefficients you wish to view using the check boxes next to each coefficient and then press the Wafer tab to the left of the plot screen to begin modeling and view the results The resulting plot will show a graphic of the wafer based aberrations and the statistics to it s right displays the modeled coeffecient values as well as the statistics describing the contribution of the selected components to the variable s range budget Figure 73 displays the graphic portions of the modeled wafer variations of the Anti Reflective coating T_ARC photoresist T_PR and the side wall angle SWA for a single wafer This is scatterometry Applications Examples Page 101 Example Wafer Maps data of one wafer with 121 sites per field Wafers display modeled Tilt and Bow so the offset film values are not shown and variations range about zero rather than a constant film thickness Scale um 0 001 max min 0 001 0 000 Water Values SWAN Ala Tit Wafet Bow Scale um 0 001 max min 0 001 0 000 Scale um 0 259 max min 0 259 0 008 Figure 73 Wafer modeled film thickness perturbation signatures Photoresist variation by 6 order modeling Photoresist measured by a scatterometer tool is shown modeled for across wafer variatio
84. erface for modeling Data Culling Methods Weir PW employs multiple devices for removing poor or unwanted data Separate techniques allow the selection of sub sets of data based on exposure condition during model regression and by direct selection of site and point level data using the interactive mouse These methods can be employed by the user singularly or in multiples Wafer Selection Graphic check boxes are provided in the data selection screen to allow subset selection of data based on the wafer ID or number Single or any combination of multiple wafers can be selected Exposure Condition After data is first imported into the Weir PW standard format the user can view and modify the basic exposure criteria specified for the dataset Exposure criteria are specified on a field by field basis using the graphic layout interface of the main screen There are six criteria available for customization they are 1 Focus 2 Exposure Dose 3 Numeric Aperture NA 4 Partial Coherence Inner Ring PCi 5 Partial Coherence Outer Ring PCo 6 Stage and Scan Direction Data Storage and Formats Page 13 of 116 Data Storage and Formats Data Fundamentals The Stage or Scan Direction criterion allows four settings Up Down Left or Right Graphic check boxes are provided in the data selection screen to allow subset selection of data based on the value ranges of any of these six criteria Because t
85. errors after the average field is removed A series of horizontal striations are evident across the wafer ranging about 5 nm in value sil Omaptulwatestulield tloatP barcw er sh Omapfulwafeitullield tloatP barcw en Water Values CO IS Quad amp Hex only Water Residuals to C D 95 Water coals Remove Field Remove Field I 001 Ke Se NS Scalefun 0 001 max min 0002 0 004 006 0 005 Figure 76 Critical Feature 95 threshold metrology 6 order wafer maps The wafer map on the right side again displays only the higher order 4 and 6 order across wafer variations of feature size Modeled Side Wall Angle 6t order uniformity The classic method of field imaging evaluation has always been to measure feature profile stability across the exposure Past techniques required tedious hours cleaving wafers at selected profile sites and then cross section SEM photo sessions Results were always difficult to evaluate because of the judgmental viewing of cross sections composed of sites from many different dice across the wafer Today scatterometers can measure film thickness and feature side wall angles to evaluate quantitatively the profile slopes and how they vary not only across a single exposure but across the entire 300mm wafer In Figure 77 we have a plot of the variation of SWA as it varies systematically across the wafer using the Weir PW 6 order wafer models Higher slope errors 0 3 degr
86. es 1 Precision i Calculate the precision components of the data to display a table of one sigma variations of the data populations ii The precision tab can be used to investigate the contributors to the error budget of the system and it s electro optical subassemblies m Covariance Matrix i Use graphics and statistics to investigate the relationships between up to eight variables ii Determine ellipsometry and scatterometric metrology algorithm performance and profile range Process Window n Perform the classic process window calculation of best focus and exposure dose for process features o Remove wafer and field systematic errors of tilt and bow to determine the true process window p Calculate Depth of Focus and Exposure Latitude i Easily remove wafer and field tilt and bow prior to the analysis q Calculate best focus feature uniformity and Depth of Focus uniformity when all field sites are analyzed for focus response r Select up to eight features to test at any number of sites on the field i Set target upper and lower control thresholds for each feature ii Each feature represents a family or type of metrology s Display control surfaces for each type of analysis t Display other statistics such as isoFocal Dose Note Include variable data columns for Goodness of fit Residual Precision MSE etc to evaluate the metrology model and it s ability to handle
87. ess Analysis Page 67 Process Window g R command z Restores the variable Taget to it s population mean value PW Control The PW Control of Figure 32 is used after a Process Window analysis It provides the ability to view four graphics associated with the analysis control the method and explore effects of the various focus dose set points Process Window Data Range Setup FW Control Model r Process Window Analysis Pw Adjustments s Dose Format Graphic Both Process Window 22 197 ae J Reset C Rectangle C DoF vs ExpoLat DoF C Ellipse C Dose vs DoF _ExpoLat 0 49 a Rectangle A tal ToC tat C None C Focus vs DoF ExpoLat Ellipse Figure 32 PW Control tab for exploring the process window Format Frame Allow selection of the method of determination of the process window A Rectangle window assumes systematic errors to be present in the data This format is the most demanding of the process and is the most realistic When selected a rectangle will be placed on the graph highlighting the currently selected Dose Latitude and Depth of Focus DoF The Ellipse window analysis assumes random variations to be present in the data This is the most forgiving analysis for the prcess Graphic Frame Four graphics shown in Figure 33 are available for examination of the window Process Window aa Presents a graph of the Dose Focus control contour DOF vs Expo
88. eticle Data or Mean Field Removal for Photoresist Analysis Applications Examples Figure 70 as a comparison plot shows the variation of the CD for each field it s range modeled variations and relationship to the SWA are clearly shown However the influence of the reticle is obviously there also Reticle data is not always available but Weir PW can also remove the average field leaving only those variations resulting from the underlying substrate or films Figure 71 is a good example of this technique In this display of scatterometer data the thickness of the photoresist is plotted after removal of the average field In a scale range of 5 nanometers local variations and striations of the resist and spinning are evident in the hurricane like waves of the contours resulting from spin deposition Signature is typical of the develop footprint of a develop process or a multiple dispense single revolution puddle develop This technique provides an excellent tool for track and bake setup Page 99 Example Wafer Maps 0 0 002 Figure 71 Photoresist variations across wafer after mean field removal Variations Across Field and Wafer Film thickness and feature size contours for a single wafer are presented in Figure 72 Here we can see critical feature sizes upper left data plot compared against their corresponding side wall angle SWA It has long been known that critical feature sizes are frequently depe
89. exposure is a function of the velocity of the slit slower scan implies greater dose The X direction actinic wavefront will have a best focus signature that is essentially one dimensional in nature reflecting the aberrations of the lens If the scanning stage of the reticle is not planar then the image focus wavefront in the scan direction will reflect the overall roll pitch and yaw of the reticle stage The final image of course sees the convolution of these two aberrations m Site 12 11 149 9 816 Data Layout Display Doe A Se Pcie PCpiter SelectedData Raw Data 17 0 75 0 032 Selected Data Display selected data Plot selected data Remove culls from selected Cull selected data points Select Data Scalefum 0 219 max min 0 219 0 025 Figure 49 Culling site locations with the mouse The lower right portion of the field has already been removed from the data set this is reflected in the selected data plot on the right side of the screen The sites located in the top half of the field have next been selected and the data culling selection of the pop up menu selected Whipping back and forth in it s scan direction the reticle plate experiences accelerations on the order or ten 10 gravities or more as directions reverse Any residual acceleration component during the exposure phase of the scan will result in dose variations and therefore aberration averaging D
90. f the figure Closer inspection of the wafer map reveals that the error repeats on every exposed field of the wafer Reticle error N 0101 03 327 T i hk as ae T 0 093 100 4 120 90 60 30 00 30 60 90 120 Max Mm 0 104 0 093 97 47 94 54 91 61 Scalefum 103 327 max min 103 327 91 619 Figure 51 Repeating error on the reticle A contour map of raw reticle data illustrates the small spot located in the upper right of each field of the wafer left side of figure Selected fields shown in dark blue were underexposed as part of another experiment The contour of the average field is shown on the right side Background Page 84 Reticle error NET atoll Sek Sor eer ee bs Ga Soe Osmala tba ore E fe 1 EL b 100 oor oe EEL oA 2 rong 2 9 7239913940429 41 Raw Data Wafer Field Site absolute Yabsolute CD 5 CD20 zi 30 4849 99 72693 95 56094 30 454 99 61824 95 75552 8 8 8 8 8 8 8 AIPM Weirbata Shest Z sheets J Ready EREE Figure 52 Pop up display of selected data from around the reticle error We then used the mouse to examine the data error using the left mouse button to draw a box around the area immediately surrounding one of the points on any die Select the Display selected data menu that appears in the pop up and a spreadsheet display of the data points Figure 52 will appear These points clearly show the error on the
91. field 90 column common data removal 86 model 9 tilt 9 Column 18 19 49 59 60 61 62 67 precision 107 Combining field amp wafer models 9 Component Removal 46 Confirmation ID 11 contour 16 27 35 49 54 56 57 68 109 lines on plots 30 pitch measurements 71 wafer and one point per field 27 57 Contour 27 56 Controls 27 display options 27 56 graph data profile 26 controls for Contour amp 3D Surface 27 coordinates 8 covariance 72 74 Covariance 50 62 110 Critical Dimension process window 49 spreadsheet format 18 cross sections 30 cull process window 49 Cull Analysis button 15 frame 66 Radius button 15 selected data 53 culling 69 79 by mouse 15 Culling by Exposure Condition 13 by Sites Spreadsheet 14 by wafer radius 15 during modeling 15 Page 114 Model Culled Data 15 Range 14 Sigma 14 Curv See Curvature Curvature 58 60 111 D data combining data sets 22 default storage location 32 Formats 16 header information 20 import and layout 10 34 storage 16 Data culling methods example 79 Flow 13 manual conversion example 70 manual manipulation 22 maouse selected 15 29 Overview 13 selection 51 specifying exposure layout 37 units setup 24 Viewing 16 Weir storage format 18 Data Culling Methods 13 Data Selection tab 51 data culling 53 Delta 63 demonstration period
92. focus at each site Field can then be contour plotted and modeled DoseResponse Process Statistics and curve fitting results from the Dose Latitude analysis Window FieldPWModel_ Process Field by Field summary of modeled field systematic coefficients and their FeatureName Window _ standard errors for removal prior to a process window analysis FamilyName WaferPWModel_ amp Process Wafer by Wafer summary of modeled Wafer systematic coefficients and their FeatureName amp Window _ standard errors for removal prior to a process window analysis FamilyName ProcessWindowSpace Process Worksheet for Process Window analysis Calculations of depth of focus Window dose latitude and their relation to Focus and Dose SWA variation with focus and BARC Page 110 Precision Values Computed Modeled Statistics Definitions Modeled Statistics Definitions Top Section Count Number of points in data Wafers Number of substrates Sites Total number of sites per die Dice Total number of dice measured IFD Intra Field Deviation Maximum deviation of measured values of the raw data IFDxy_max Maximum H to V measured deviation across the raw data Raw Astig Raw Data H V maximum on a per point basis Astig Yxmax Raw Data H V maximum across all points Modeled Data Results Center Section Piston or Offset Fitted Piston from the model Tilt am cm Tilt of rows columns measured in microns per centimeter Tilt urad Tilt i
93. format and direction selected Direction Specifies the location of the array relative to the Array Origin Selecting any of the eight command buttons will reset the array orientation relative to the origin Save Saves all layout values to the Spreadsheet located on the Layout tab Creates the tab if one does not already exist Update Updates the layout and variables settings into the array and re draws the array Draw Re draw the array without updating the graphic with new array and variable values Step by Step Tutorial Defining an Exposure Layout Setting up a Serpentine Focus Variation In this section we will go through a step by step account illustrating how the exposure values of a focus dose matrix array can be specified using the automated layout controls of the Weir Main screen We want to specify a serpentine variation in focus across the wafer starting at 0 6 microns defocus in the lower left and stepping from right to left in 0 1 um incrments Follow the text boxes illustrated in Figure 17 Note Values will be added to ALL wafers of the data set unless you first manually select an individual wafer from the Wafer drop down control Select the Layout tab Press Draw to display the previously centered array Change the format to Serpentine Change fo initial focus to 0 6 and and Step to 0 1 Double click on the outer die selecting it
94. he Sites worksheet They can be interactively changed from the Weir program by accessing the Data Units Setup menu Sites Format E23 Microsoft Excel Slit1 1 5 slot 6Foc xis Eile Edit View Insert Format Tools Data Window Help laj x CEKEL TEREI COO EEECE DensePack ri zZ G X_DIE_SIZE Y_DIE_SIZE TEST X_LOC Y_LOC FAMILY 2 Site12013s1 26 8 1 11 82 0 DensePac 3 Site12013s1 26 8 2 9 45 0 DensePac Site12013s1 26 8 3 7 09 0 DensePac Site12013s1 26 a 4 4 73 0 DensePac 6 Site12013s1 26 5 2 36 0 DensePac in 4 O E E ai aa 3 Draw eC autoshepes 3 OOM amp A 2 a es es a a Figure 4 Sites worksheet with feature locations on field Stores information on the X and Y Field location of individual test sites Also stores die size information but this is not currently used For diesize information please see the Information datasheet NOTES Heading values are in row 1 starting in column B Any data may be placed in column A Overlay and Registration data formats require only columns B through F Column G the FAMILY is used for linewidth and other metrology to describe the feature type as DensePacked or Isolated Sites Data Storage Convention Metrology data is stored in columns Data starts in column 2 the B column Headers should be located in row 1 He
95. he criteria are specific field based the entire field is removed from the analysis Culling Data by Field Site Location The data selection interfaces allow individual field sites to be selected for inclusion or removal from the analysis This is usually accomplished using the mouse or by check boxes for selection Data for a single or selected data sites can also be easily removed from an analysis Using the following method data can be easily restored at a later date if desired The Sites spreadsheet contains one row for each site location with site 1 beginning on row 2 of the spreadsheet because of the Header row If a row is empty without data or X and Y location entries then the Weir assumes the data is not present or wanted Any data entries whose Test number corresponds to the empty row will not be loaded for an analysis even if they are present on the data sheet Note however that Test number data sheet Test number Sites sheet Row number 1 of the Sites sheet so that test 10 information must always be on row 11 of the sites sheet To remove selected data sites from the data Right click on the Sites tab of the workbook and select the Move or Copy pop up menu item Check the Create a copy box on the Move or Copy window and optionally highlight the Sites entry in the Before Sheet window to place the copy in after the current worksheet A new worksheet called Sites
96. he current data set Analysis Flow Follow the illustration of Figure 28 to see the overall frames and control tabs for the analysis Note Use the four analysis selection tabs at the top of the graph window to set up the analysis You can force a re modeling of the data by selecting the re Model Data command button at any time Use the for tabs Wafer Wafer Residuals Field and Field Residuals to begin an analysis and display the data graph Data will be remodeled only if modeling features are changed that will influence the overall model configuration gZ You can use the mouse left button at on any vector or contour graph to cull additional data points and view or plot sub sets of the graph Use the Escape Esc key to interrupt any analysis The key must be depressed and held Associated Worksheets Associated Worksheets WaferModel_ amp Wafer Model Created by the Spatial Analysis command Coefficients FeatureName amp of the current features systematic wafer piston tilt and curvature FamilyName Model is based on the position of the feature with respect to the center of the wafer Displays the results for each wafer and a summary Ex WaferModel_BCD_Grp223 FieldModel_ amp Whole Field Model Created by the Spatial Analysis command FeatureName amp Coefficients of the current features systematic field piston tilt and FamilyName curvature Model is based on the positi
97. he model is applied separately to each wafer of the lot and summarized on the user interface Individual wafer model results can be examined in the Wafer Aberrations spreadsheet see the Appendices for a detailed listing of these spreadsheets The primary correction coefficients of the wafer model are Piston Tilt X and Y and Bow The residuals of the wafer model plus the Piston values are submitted to the field model for the analysis of field aberrations Field Model Field models are Cartesian in nature and use a simple format described in equation 5 above Three methods of implementation are provided for analysis allowing them to be employed for both stepper and scanner exposure tool formats page 8 An Overview of Weir Feature Modeling 1 10 2005 Overview The Full Field format is used for steppers exhibiting symmetric field aberrations The model can be employed to analyze data across the entire field at once The full field analysis is best employed when determining corrections for an exposure During this analysis the data for the entire field is collected and modeled to determine an optimum set of coefficients describing the field aberrations The modeled results of each field are logged in the WholeFieldAberrations spreadsheet and summarized on the user s screen Scanners incorporate aberration contributions from both the slit lens and reticle scan stage Implementing a Row model w
98. he scan direction of a slit Y focus direction Focus response of the edges of a horizontal line Vertical Line or feature whose edges parallel the Y axis of a Cartesian coordinate system Horizontal Line or feature whose edges parallel the X axis of a Cartesian coordinate system Manhattan Geometry Geometries in which feature edges parallel only the X or Y axis of a Cartesian coordinate system Bospherphedonic Travel or a path that follow a zig zag or serpentine path That is a path that goes left to right then up then right to left then up and so on Name is derived from the ancient shipping lanes along the Bospherous and Dardanelle seaways from the Mediterranean into the Black Sea Ships had to zig zag up or down the channels IFDxy_max Range or IFD variation of the max absolute X or slit value to the max absolute Y or scan value Raw Astig Greatest magnitude or Astigmatism Y X value of the data displayed and described in the statistics at the bottom of the statistics table Astig YXmax Greatest Y greatest X value Astigmatism max max focus Y focus X abs min focus Yx focus X sign of j or k H Vmeans Xfocus Yfocus 2 Systematic Values that change in a fashion described by a mathematical expansion or relation SWA variation with focus and BARC Page 112 Precision Values Computed Abbreviations and Definitions Term Definition ee a y y y O who exhibit a Binomial Normal
99. hic to display r Provides interactive controls for the Focus Dose operating point Model s Select the spatial systematic errors to remove from the data prior to performing an analysis Notes Analysis in this interface requires a dataset with a focus and or dose matrix Use the four tabs located at the top of the window to set the analysis up prior to analysis The type of analysis is selected and started by clicking on the Focus Dose or PW tabs to the left of the graphic display window Setup threshold values are estimated at 10 of nominal by Weir when a data set is opened Use the Escape Esc key to interrupt any analysis The key must be depressed and held z Right click on the graphs to edit display properties and ranges Associated Worksheets Spreadsheet Name Analysis Function FocusResponse Process Statistics and curve fitting results from the Process Analysis Page 65 Process Window Spreadsheet Name Analysis Function Window Depth of Focus analysis DoseResponse Process Statistics and curve fitting results from the Window Dose Latitude analysis FieldPWModel_ Process Field by Field summary of modeled field FeatureName amp Faia Window systematic coefficients and their standard errors for removal prior to a process window analysis WaferPWModel_ amp Process Wafer by Wafer summary of modeled Wafer FeatureName amp FamilyName Window sys
100. ic process window 49 T Template Reticle storage default 33 Test and site loction 22 TEST 20 85 Test Number Culling by 14 The Exposure Tool editing settings 33 Threshold Raw Data Metrology 47 tilt corrections 9 Tilt 58 109 111 Tool control 9 tuning 8 U uncertainty of coefficients 9 units of measure setting 19 Units specifying 23 Units Setup 19 Index V Validate 58 validation 8 variable culling by 15 Variable frame process window 93 variables additional in PW 97 units of measurement 24 Variance in precision calculation 107 Vector 45 46 49 56 plots with feature data 79 View data selected by mouse 29 Ww wafer ID 52 size setting 34 Wafer centering the array 35 layout specification for individual 38 precision 108 Selection 13 selection layout 39 Weir models used 6 whole field data formation display 46 Whole Field 47 60 90 workbook creation 34 workbooks opening in 50 X Xreg 28 XY plot cross sections of 30 from mouse selected data 29 XY plots 49 XYplot 47 57 raw data 47 Y yaw 82 Yreg 28 Precision Values Computed 117
101. iduals to the coefficients of the wafer model This is handled automatically Tool or process control applications should always include a wafer model Removal of the systematic errors associated with the wafer films results in greater accuracy of the estimation of the field correction coefficients The combination of field and wafer models is the only method of successfully deconvolving the tilt corrections associated with the reticle platen wafer stage and optical column alignments Getting Started Overview When the software is first started the user should move to the Tools License Maintenance menu to obtain the Installation ID s needed to obtain a demonstration or permanent license This license is Page 9 Overview System Requirements keyed to the hardware upon which it is installed and if your basic system is changed a new license must be obtained See the section on License Management for more details After installing a license select the Tools Options menu and customize your installation by specifying the data import conversion filter that fits your metrology tool and the most common path to raw data from the tool The Setting Preferences and Defaults section of this manual provides information on customizing your interface To import Raw Metrology data into a Weir Spreadsheet you must be in the Weir Main interface Weir spreadsheets can be opened from the Main Menu the Weir PSFM Focus Analys
102. ield the best results Depending upon the layout of the sites on the field and number of sites the contour may result in incomplete areas If data seems to be omitted from field segments select either Medium or Modeled methods d The Modeled method is the most robust because it uses a full field model to perform the interpolation however is will be slower and will loose some fine detail in the display Page 56 Process Analysis e Wafer contour plots containing only one point per field will plot the contour based upon the data s position on the wafer 23D Surface f Functional only for Field and Field Residual plots XY plot g An additional tab the Xyplot options will appear when selected to set up additional graph options Statistics and Graphics Check Box Select each to include in the plot Scale field Sets the scale in microns of the plot If set to 0 the plot will auto scale for best display of the data Scale can also be set by right clicking on the graphic and modifying the graph Y axis options Range and Sigma Fields Enter a cull range in microns or a Sigma value in fractional standard error values For example if a dataset exhibits a 3 nanometer standard error then a sigma entry of 1 5 will exclude all points of the population that exceed 3 1 5 4 5 nanometers from the population mean Data culling occurs prior to modeling of the data The number of points removed from the analysis w
103. ill apply the model to each individual row of every field Row field wafer and lot coefficients summarized on the FieldRowModel_feature name or FieldColumnModel_feature name spreadsheets A column analysis when selected analyzes each column of the exposure separately to model scan behavior across the field wafer and lot The summary of the analysis is reported on the user interface Individual row and column aberrations for every field in the lot are logged on the Aberrations spreadsheet Field models are applied to each individual exposure and summarized in the display You can see the field specific results on the spreadsheet The models operate in two modes as selected by the controls of the interface The modes are called Full Field and Row Column In almost every instance the final coefficient values calculated by each method are the same within the uncertainty of the calculation Again the coefficients and their uncertainty levels of the Row Column model are visible in the associated spreadsheet The benefits and information gained from the differing analysis technique of each model will differ significantly The Full Field mode available in the uniformity analysis interface replicates the method of model application used today in the industry This mode optimizes the speed of the analysis by applying the model to the entire field Individual fields are summarized to obtain the exposure t
104. ill be displayed to the right of the respective field Model Components Tab Process Analysis Weir PW uses adaptive element models As the data is being prepared the software examines the points for singularity or non consistency with respect to the range and distribution of the data Select the model segments you want to include in the analysis Both full wafer and field based models are supported Refer to Figure 28 to see the items of this tab 6 No Modelin Turns off modeling for the segment Row Model Applies the model to each row of each individual field Row model values are detailed in the FieldRowModel and the model is summarized in the FieldModel_ spreadsheet The row model provides information on the slit uniformity of the lens A plot of the piston offset values corresponds to the Y travel path of the scan Examine the residuals to see aberrations of the lens higher than 2 order curvature Column Model Similar to the Row Model the Column Model selection applies the model separately to each column of every field in the data selection The piston offset values of the column models plotted as a function of their X location on the field will yield a profile of the aberrations of the lens Examination of the residuals illustrates the higher than 2 order curvature errors such as bearing bump associated with the scan Full Field Model Applies the
105. in the feature covariance values of Table 1 However the pitch and CD values have a higher than expected covariance value of 0 685 This relationship can be seen in the XY plot of data shown in Figure 36 The cause of this variation in pitch is unknown It may be an artifact of the metrology algorithm of the CD SEM used to acquire the data or it may be actual variation on the reticle that occurred during manufacture Having this data in hand we can begin to characterize the images that are then transferred to the wafer ASHL Scatter 110 DP_ReticleData Wesl200Q ASML SCATTER 110 DAI_RETICLEDATI PCr WD Waf Al Expalt AINA O65 PCo0 60 3721 2002 0110 ttt ttt ANG fecencnccccccsccccccccccccccecccccccccceccccncecsescccccsccscscccces 2 2 E eee eee B 0109 e RIOD bo et a Laie a Bix TRE a m 68 sad PS ee Po coe 0 ete M os gest n i KA ee E et 8 amp 0106 s gt P z a 0 105 z TO eee 2 fy 0105 ge oe poe e s a 1i E ener eee eens cece cece ne ce re ceceeecesascecsnsesnscsrecerscscecesssesess on a 0 103 Qiaccsccesccnccscnssesscesanese n 0102 T T T 02170 02180 anw 02200 02210 0222 0 0 Figure 36 CD vs Pitch data Metrology Characterization and Tool Algorithm Verification Analysis of the Reticle Data File Scatter 110 DPI_ReticleData xls SL10isol 8map xls Summary Scatterometry data of focus matrix illustrating a st
106. ing the Display tab shown in Figure 14 Wer Wavelrant trigaweenng Oc Date EL Array paler pent SPS Fe Dit Yew Collection Ancyses Toots osfnelipontORams tip SI 4 l LA Boba Layout Metvotogy Sarp zs 3 DeSee 1 Select Display tab 2 Select Display command button to iang Aree pe display vector plot p a fo fon i J3 Set values to properly center the Y f o y direction shel I le ee eee Econ bs Se r zs Ser 2 aie ei i s A Site M p as e EEE oh aoe a Sorter We Ae feie aw ie a i y be i dj 4 Press to re display i centering e nameri MEARI 27 2002 S10 AM Figure 14 Data import and conversion The Grid command button will toggle between Grid amp Field The overall die size can be adjusted by simply entering new values into the Die Size fields at the top of the screen Press the Display button to view the change and record it into the Information spreadsheet Grid Section This section controls centering of the fields on the wafer The center of the wafer is indicated by the dashed cross lines The array can be centered to move a die edge or center to the wafer center position The grid has two methods of centering specify the offset in millimeters mm or in fractional values of the total die size dice For example a die that is 15 mm x 20 mm can be moved so that the center of the die coinci
107. ion Values are displayed for the average field The workbook now conatins two additional tabs FieldModel_CD 20 AllFeatures which contains the modeled values for every field in the data Applications Examples Page 83 Reticle Error Detection and Modeled_CD 20 a listing for of the raw fit and residual values for every data point Notice that only the CD 20 or piston check box has been selected If we had selected the Wafer or Field tab for display we would have seen the modeled piston values for every field Selecting the Wafer Residuals tab resulted in a display of the residuals to the model plus the fitted tilt and curvature for each field on the wafer Reticle Error Detection Data File Summary A wafer has been measured using scatterometry The data is modeled for systematic wafer aberrations and then field tilt The residuals to these aberrations are then plotted and compared to the reticle Background A test wafer was exposed containing six die with offsets in the exposure After measuring the critical features on a scatterometer the data was analyzed with Weir PW Analysis Weir PW s spatial tab provided a contour plot of the raw data Figure 51 The first item noticed was a single anomalous point that appeared to rise as a metrology data error sometimes called a sport or flyer The error point is located near the center of the field shown on the right side o
108. is and Weir PW Analyses File menu structures Be sure to review the section on Data Import and Layout the first time that you import data for guidance on importing the data and information on the various spreadsheets created during import and the subsequent analyses System Requirements page 10 The larger the data set the greater the needs of the system Weir analyses can be very complex when modeling simulation and the removal and sorting of fields sites and data points are involved As a minimum we recommend lt Windows Windows 2000 or XP Pentium II or greater processor Clock speeds gt 1 Gigahertz recommended 2 Gigabyte of Hard Disk Space 2256 Megabytes of RAM Monitor 1024x780 or greater Microsoft Excel software System Requirements 1 10 2005 License Management License Management Installing the software and Confirmation ID Overview lolx The Weir Wavefront Engineering Software Suite uses a license management system that does not require hardware add ons At first use of the software you will be presented with a screen that shows an installation date and two numbers The date and numbers are keys for computing a Confirmation Identification code that will turn on the software for a demonstration period or for permanent use Figure 2 If you do not enter a Confirmation ID the software will continue to run with full functionality for a total of ten 10 restarts before shut
109. ize the contribution of the metrology tool to the noise of analysis and to characterize the sub assembly contributions to the error budget and their respective precision in terms of the image integrity Raw analyzed and modeled data are maintained in a Microsoft Excel workbook that is easily accessed by the user reir PSFM Weir PW Common Tools Process Daily far i Analysis N PSEM Reticle Fixed Fecus d One click DM Template calibration Data conversion lesa Analysis setup Selection Spatial Anal i Automation Best Focus g rs Trend Chart calcalation Full Wafer and Metrology Any dataset Workbook Lews Aerial Field Analysis creation Image Amalysis Models T Models Calibration caii Trend Charts Template Error Budget Error Budget Generation Peia Process Window Overview Figure 1 Weir Wavefront Analysis Software Suite Page 3 Overview Weir PW Analysis Modules The Weir Analysis combines three modules to provide an easy to use graphic analysis and data model for raw data stage lens and scan slit Focal type Aberrations and stage lens and scan slit process window characterization and matching These modules shown in Figure 1 are provided in two systems Weir PSFM and Weir PW Weir PSFM functions with the Benchmark Technologies Phase Shift Focus Monitor PSFM as a calibration and analysis engine for exposure tool focal plane aberrations Weir PSFM provides
110. l Field Settings fo fo Step ft Every row or column is repeated across the array Multi Scan Direction This format is similar to single scan however at the next E y field value continues to change with each The field is E E never reset back to the initial field setting Variable Field l l Allows selection of the layout variable to be displayed Variables are Focus Dose NA Numeric Aperture PC inner Partial Coherence inner ring PC outer Partial Coh outer ri d Scan Direction oherence outer ring and Scan Direction Figure 16 Controls for Wafer setting up the initial field value and the direction that data entry will take page 38 Specifying Field Exposure Layouts 1 10 2005 Weir Main Interface Allows All or individual wafers to be selected for modification and display Array formats and variable values can be individually modified by focusing this field on the wafer number Selecting All will modify all wafers in the display simultaneously Initial Field Settings Settings in this frame shown in Figure 16 control the variable values entered into the layout of the array specify the incremental step value for the next field and specify the relative origin of the field array to be filled x lnitial Field The value that will be placed into the field designated as the Array Origin we Step Field stepping value that will be added to subsequent fields of the array in the
111. l exposure uniformity is shown as base color changes from Applications Examples Page 87 Wafer Feature Comparison to Reticle Data field to field Turn on the field modeling if you wish to view the base exposure or feature piston variance for each field Piston can be viewed as the offset coefficient of the model and each field s values are stored on the FieldModel_ amp FeatureName amp FamilyName spreadsheet created during the analysis Individual field data and plot are viewed by boxing in a section of any die or range of dice and selecting the plot option from the ensuing pop up menu A careful examination of the XY plot shows the relative error of the reticle error site still resident in this data set at the 28 mm X distance from wafer center The shape of the field s contours now exhibit constant signatures across the wafer Color changes from field to field are indicative of base changes in the offset feature size caused by a change in exposure Adjacent field differences may be a function of scan direction The engineer at this point could return to the data selection interface and select only those die with equal scan directions to determine if the scan direction is a cause of the focus offset or some other phenomenon Selecting all die of the same scan direction can be accomplished by selecting either the up or down direction check boxes in the data selection interface Figure 26 Wafer Feature Comparison
112. license 11 depth of focus 5 6 54 63 65 Depth of Focus 93 interactive analysis of 96 Depth of Focus 75 Device 21 die size 20 directory default data storage 32 Display graphic format options 46 selected data 85 DoF as Depth of Focus 68 dose curve 94 response 94 Precision Values Computed Dose Latitude 68 DoseResponse 94 Double clicking 52 66 E edge exclusion of 30 wafer 30 ellipse 96 ellipsometric algorithm method 75 error repeating 84 Error factor 90 Escape stopping an analysis 31 46 54 61 65 estimation of coefficients 8 Excluded 109 excluding data points sites fields and by range 79 exposure scanner 82 Exposure layout specification 37 manual specification of 38 F Fast contour method 27 56 feature profile process window 49 FEM variable entry 43 variable setup 43 field average model values 83 setting exposure value for one field 38 Field Centering 34 centering sites on the field 36 collapsed 47 exclusion by mouse 30 Mean 47 model 8 Model data 88 precision 108 site culling 14 Size 34 FieldModel 83 File Most Recently Used 32 film uniformity 90 fine structure of scanner exposure 9 Flat 21 flight path of scan 9 flyer 84 focal plane errors displaying 33 Focal Plane errors vs corrections 33 focus and feature variation 106 Focus Best curve of 94
113. lues ARCA Water Coefs Wafer Residuals to ARCAN Water Coefs Water Residuals to ARG Resids to al Water Coefs Remove Field ao Scaelum 0 000 Scaelum 0 001 0 Sooner tr 082 man eana 0101 1 0 004 maane 0010 000 Wafer Model Residuals to all Wafer Residuals to Wafer Model Coefs Mean Field Removed Figure 75 ARC uniformity with 6th order wafer mapping some 6 order wafer model results for scatter measured ARC across a 300 mm wafer The left wafer map again shows only the variation due to wafer modeling The effective uniformity across each die site is then shown in the center wafer map of the figure Applications Examples Page 103 Example Wafer Maps Finally we can see the effect of removing the average field and replotting to display the residuals to wafer systematic sixth order errors and the average thickness variation across the field Critical Feature Uniformity with 6t order wafer models H Onap fullwalertulbekt flootP ebar wer Wates Values CDGS5 W ater a components R Feli max mn 0l0027 ar ES 0 002 Scalu 00 Scalelumy 0001 0 00 ira ae gt Feature uniformity for the same 300 mm wafers as shown in the previous two sections Metrology measured critical feature dimensions the results for the 95 threshold values are shown in Figure 76 Again the left wafer map shows only the wafer systematic errors The center wafer map shows the residuals to the wafer systematic
114. m Raw Data Vertical Features AGNAARaS EEEE EE PEELE EET EDLY ee ee ee eee HELLE etc Display selected data Remove cils from selected xY Graphic by Rows Cull selected data points xYGraphic by Columns 0 250 Scale um 0 100 max min 01609 0 721 0 325 0 400 Figure 8 Full wafer contour of Y focus variation with mouse selection of data subset You can always view the data associated with a graphic by selecting the view data menu item however vector and contour plots support additional mouse selected data manipulation Using the left button of the mouse box and zoom in on any subset of data to View the data on a Weir spreadsheet window This is anew workbook so you can also save it and use all of the Microsoft Excel functions and macros to manipulate it Cull the selected data se including culling by wafer number if there is more than one wafer in the dataset Restore points culled in the boxed in region to the analysis Plot the data as a histogram or XY plot BoxPlot etc ze If you select XY plotting of the data you can then select to plot it by row Y or scan axis or by column the X or slit axis Trend lines and population contours can be fitted to any data curve using the right mouse button see section Trend Line Customizing Graphics Page 29 Customizing Graphics on page 27 Mouse Selected Data Manipulation This analysis i
115. matic field piston tilt and curvature Model is FamilyName Window based on the position of the feature with respect to the center of the current field Displays the results for each field and a summary Ex FieldModel_TCD_Grp233 FieldColModel_ amp Spatial and Row or Column based Field model is fitted to each row or column of Feature Process each field This sheet summarizes the modeled rusults on a row by OR Window row or column by column basis FieldRowModel_ amp Ex FieldRowModel_BCD Row Model or FieldColModel_ TCD Feature column model Surf Field amp Spatial and Calculated display surface Surface data used in the field contour or 3D plot FeatureName Process generation Columns contain the X Location and rows the Y Location of the Window data Precision Values Computed 109 Precision Values Computed Spreadsheet Name Analysis Function Ex Surf_FieldResids_SWA for field residuals Precision Metrology Metrology Precision calculation statistics Covariance Metrology Metrology covariance statistics FocusResponse Process Statistics and curve fitting results from the Depth of Focus analysis Window Best Focus Process Generated when a focus response analysis is perform for All sites on the Window field Spreadsheet is a Weir Data sheet that can be loaded and analyzed separately Contains a field with the Best Focus calculated PLUS the feature size and depth of
116. mits Column C v m Cull m Variable AE fo Height X Sigma o i 0 0 Max 0 84815 Min 0 4900 l Figure 62 Process Analysis setup for Data Selection The range of the analysis should be checked and updated if needed by using the fields of the Data Range tab shown in Figure 62 Note that the Variable frame in the lower left allows you to specify any of the metrology variables of the data set as a range limiting key The Max and Min values default to the variables maximum and minimum values in the current data The Seed variable is used as a manual aid for the starting point during aProcess Window analysis The field shape and sites measured on it will be displayed on the right side of the tab The analysis defaults to selecting one field site and attempts to select that site nearest the center of the exposure field Finally select how you wish the graphic to appear using the check boxes in the Items to include frame The Show Limits check is meaningful only if a Graphic is being display It will display the target Upper Control Limit UCL and Lower Control Limit LCL as bounded lines on the graph Data culling during the modeling cycles is controlled with the Range and Sigma controls Notes Weir searches for an optimum process window by optimizing the depth of focus If the resulting selection is obviously out of the proper dose range then you can override the automated analysis by adding
117. n condenser optical column and lens elements Weir PW provides separate model analyses and methods to address all of these perturbations and aberrations Weir Feature Models Uniformity of process conditions within the wafer are subject to process disturbances which on their turn exhibit characteristic spatial dependencies In terms of statistical values disturbances are related page6 An Overview of Weir Feature Modeling 1 10 2005 Overview Overview to a feature response through a linear function where a constant coefficient describes feature disturbance sensitivity 2 FR A D as where FR is the response of feature a to a process disturbance m and A is the sensitivity coefficient A typical example is the CD response to small variations in thickness of the bottom antireflective layer Tbarc In this case the feature response is the CD value the disturbance is the barc thickness variation and sensitivity is the linear coefficient of CD f Tbarc function as follows CD f Tra Ming PU ning SRO Bs are Depending on the time characteristics of wafer process a typical lithography process presents two types of spatial distributions Consequently the response of a lithography feature to a disturbance should also present two types of spatial distributions In real situations when both type of disturbances are present the feature has a combined response to disturbances with both continuous and discrete w
118. n metrology validation focus left and scan direction right layout A focus matrix has been measured on a scatter metrology tool The original objective was to evaluate exposure tool scan linearity and uniformity It is not possible to accomplish the linearity study with this data however the data illustrates the influence of the metrology tool measurement algorithm and the range of it s effectiveness The data layout as shown in Figure 37 is defined to contain information on both the field focus and the reticle stage scan direction Examine the error budget precision matrix for the feature measurement BCD or bottom CD as shown in Table 2 Table 2 Focus matrix metrology precision matrix Applications Examples BARC Resist BCD MSE SwA Average 395 951 1614 843 0 040 24 691 88 478 Range 83 263 3999 345 0 113 434 889 14 398 _Precision EL o Lot 14 909 450 193 0 039 89 777 34173 Field 7 632 329 237 0 008 47 449 1 130 Site 14 974 452 482 0 039 90 486 __a 199 IntraField 13 568 335 998 0 040 81 230 3 128 InterField 13 649 338 496 0 040 81 338 3431 Column 7 632 329 237 0 008 47 449 1 130 InterColumn 0 000 0 000 0 000 0 000 0 000 Row 6 283 294 841 0 0071 46 928 1 042 InterRow 5 179 197 709 0 005 22 203 0 641 Page 73 Metrology Characterization and Tool Algorithm Verification Background ooo ecar_1 1_5_tht_10_FM WatAl Exp ALL AINA 0 65 PCo 0 60 PCi 0 00 0127 0115 01
119. n micro radians ppm Curv um cm2 Mean Curvature measured in microns per centimeter squared IFDresids um The maximum IFD of the residuals to the model in microns Raw Modeled or Residual Data section Mean Average value Median Maximum Minimum 2 SEM Standard error of the means Std Err Standard Error or Sigma of the population Maximum Maximum positive value Minimum Minimum or negative most value Mean 3Sigma Mean plus 3 standard errors sigma Max_99 7 Maximum point deviation of the 99 7 of the data May be positive or negative sign abs Maximum 99 7 data Precision Values Computed 111 Precision Values Computed Abbreviations and Definitions Term Definition Count Number of measured values or points in currently selected data set Wafers Number of wafers Sites Total number of unique field site positions in the data Dice Number of unique exposure fields in the dataset Best Focus Mean focus of the data selected for display Statistics for the display are located below any Modeled coefficient displays May represent Raw Fitted or Residual average focus IFD IntraField Deviation Range of measurements within any one field Can be any variable of X Y Mean Slit Scan or H Vmean Range of measurements within any one metrology variable Slit Variation along the scanner slit X focus direction Focus response of the edges of a vertical line Scan Variation along t
120. n or vertical scan of the lens A measure of the noise due to the reticle scan stage InterColumn Variation between columns A measure of the lens contribution of variation Row Variation within a single row or within the lens slit Similar to InterColumn but without the averaging effects of the entire column of data InterR ow Variation from row to row Essentially the contribution of the scan averaging When considering the Error Budget InterRow values can be considered to be from the scan while column values a measure of the reticle consistency etc Covariance Metrology The covariance analysis provides both a graphic and statistical approach to the examination of variable linear interdependencies The statistics yield a standard covariance matrix showing the behavior of each variable compared with the remaining seven other variables plus the exposure setups of Focus Dose etc when present Data is saved in the Covariance spreadsheet Covariance Metrology Page 62 Process Analysis The diagonal of the table is always equal to one 1 Variance is normalized to vary from 1 a perfect 1 1 dependency to 1 or exactly opposite behavior For example the covariance table can be used to examine the effectiveness of MSE or Residual variables from ellipsometer scatter metrology in modeling consistent data or the variation of SWA profile with focus or feature top measurements Metrology model robust
121. ndant upon the uniformity and thickness of previous films but now the user can plot out these variations as shown in the Photoresist thickness Tpr and anti reflective coating T_ARC plots on the right side of the figure Variations Across Field and Wafer Page 100 Applications Examples These figures are raw data without model removal of wafer variations If the object of the analysis is to view across field variation and it s stability across the wafer and or as a function of exposure then remove wafer aberrations and view the residuals CD 5 a TERED wo M aTe Hie S jz SER fe Cr par oto Sedeium 00 0 002 er ee p aoi maxz mm 0 0547 0 0065 d pe oca om I SWA p CEON TLARC c E HED N S OT DOA EEEE eng BEEEE d 0 ian d I o 0 00 Scalefum 000 2500 mase eran 11295 9 128 1000 Q Figure 72 Field modeled signatures Scatterometry Data 121 Sites per field Film Deposition Uniformity across the Wafer In the previous paragraph we discussed viewing the true across field variations of features and films Across wafer uniformity of films can be analyzed by observing the wafer aberrations The photoresist plot of Figure 71 is one method of observing feature variation fine structure by removing the mean field component form the raw data This method only provides basic statistics on the variable To quantify the systematic variations of feature size waf
122. ness can be estimated by examination of the variables and their variance in a focus or focus dose matrix The display allows the user to select one variable for the abscissa using a drop down listing Multiple variables can then be selected by checking the ordinate box associated with each variable in the listing Many variables will have quite different data ranges but can have very high linear dependencies These variables can be plotted on the graph by selecting one of the three plot options Full Value Plots the full value of all variables selected for the graph Delta Plots the variation from the average or mean value of each variable Illustrates only perturbations from the mean Standardize Standardize the range of each variable to correspond to a 1 to 1 range then plots each variable Process Window Overview Process Analysis The Process Window PW analysis has long been a staple of setting the operating focus and exposure point for a process The objective is to set operation at a point that optimizes the balance of depth of focus with exposure latitude by selecting a nominal dose and focus for operations The balance point depends upon the mix of a fabs tool set the design tolerances of the product in manufacture the imaging media and process recipe Typical wisdom sets the desired exposure latitude at about 12 of the operating dose This then leaves the process engineer the task of optimizing the nominal focus of
123. nfirmation ID fields Page 11 of 116 License Management Installing the software and Confirmation ID Obtaining a License To obtain a license send the Installation date and two Confirmation ID s shown on the screen to either TEA Systems Corporation 65 Schlossburg St Aburtis Pa 18011 USA Phone 01 610 682 4146 WeirENGR TEAsystems com A Confirmation ID for the appropriate product will be returned to you via mail or electronic mail When you receive your Confirmation ID enter it into the appropriate ID field Also insure that the Installation Date field corresponds to the original date that you submitted with numbers or to the new date given to you with the license You can change the illustrated date by using the Set Date command button Selection of the Enter Confirmation command button will then validate the license entries and turn on the software When a valid Confirmation License is entered this screen will no longer appear at software startup You can access this screen at any time using the Tools License Management menu If you obtain a demonstration license the software will notify you at startup during the last ten days of your demonstration period At the end of this period the software will no longer function Enter a full license confirmation ID to continue to use the software Retain a copy of this screen and your Confirmation ID for your records If you reinstall the soft
124. ns in Figure 74 The left wafer map shows the variations from all six wafer terms The center variation exhibits only the higher order contributions to aberrations Photoresist variation by 6th order modeling Page 102 Applications Examples The most interesting values come when the wafer is modeled and the average resulting field is removed The residuals are then plotted in the wafer map shown in the right side of the figure Notice the near normal distribution of residuals in the histogram displayed sll Onap ftulwatectullielttloetP barcw er 11 Omap fullwatertulfield floatP barcWer 1 Omap tubwatertubfield foatP barcwer Wafer Values LPR Wafer Bow bit quad amp Hex Wafer Values t_ PR Quad amp Hesfal only Water Residuals to LPR Water Bow tit etc R e Field Re ove Field Remove Field 00010 0 000051 0 00000 7 z Scalelum 0 000 Sarama V 000 t pion max mn O015 0 015 All terms 4th amp 6t only Residuals to allterms Scalefum 0 001 max min 001 70 000 Figure 74 6th order wafer model of Photoresist thickness Residuals right image plot feature variation after all wafer terms and the mean field values have been removed ARC thickness 6t order wafer mapping ARC deposition and etch resistance uniformity is critical for feature uniformity Figure 75 presents M1 Omaptulwatertbeldtloat ebarcwer si Omap lulwateruliekt floatP baic wer ef Omap fullwater ulield floatP baicw ei Wafer Va
125. ntrols the display of each data series on the plot including the markers used line type line size and colors Individual series can be hidden using the hide curve checkbox Chart Options This tab provides an interface for adding and modifying boxplots A BoxPlot is a way of summarizing a set of data measured on an interval scale The median for each dataset is indicated by the black center line and the first and third quartiles are the edges of the red area which is known as the inter quartile range IQR The extreme values within 1 5 times the inter quartile range from the upper or lower quartile are the ends of the lines extending from the IQR Points at a greater distance from the median than 1 5 times the IQR are plotted individually in black These points represent potential data outliers One BoxPlot is generated for each unique data location on the abscissa of the graphic Select the BoxPlot checkbox and press the Apply command button to add new BoxPlots to the graphic 2 BoxPlot outline colors are adjusted with the Foreground selection Fill colors are adjusted using the Background selection The Box Size field adjusts width of the box structure which defaults to 1 5 character widths Individual box structure colors and linewidths can be modified by then selecting the curve in the Series tab Data Profile Contours BoxPlots represent population distributions by their quartile posi
126. o include them in the analysis When selected the site will be highlighted on the field graphics to it s right NOTE Sites can also be individually selected or de selected by hovering the mouse over the site and then clicking el eed boo n Data Selection Spatial Metrology Process Window Process Window Data Range Setup PW Control Model r Parameter Setup Target 10 0 Target Maximum Minimum Selected Reset BOTTOM_TH_DF_F124_1SO0_ H MC ToP THF Fi24isosv foraor faraar_ foros BOTTOM_TH_DF_F120_1S0_ H BO MSLOPE_TH DF Fi24iso s o1007 forios 0 0906 H BM B0TTOM_TH_DF_F124_150_5_V 0 100 0110 fo oso H E MSLOPE_TH OF Fi2z0iso s o 0877 oo965 0 0789 f H BO TOP_TH_DF_F120_Iso_s_v Joiors forte Joos H MM BOTTOM_TH_DF_Fi20Iso_s_v 0090 0 099 0 081 x Refresh Full Screen mn fa u Process Relations Figure 31 Setup tab for Process Window Analysis Variable names are listed by row in this screen shown in Figure 31 The names are defined in the data Set the target maximum and minimum control limits prior to performing the analysis Select variables to include by checking the box to the left of the variable The list can be scrolled by using the bar to the right of the frame Currently selected variables are summarized in the region to the right of the frame gss H command y Plots a histogram with BoxPlot of the selected data Proc
127. ocus Exposure Dose Numeric Aperture NA Sigma or Partial Coherence PC and the wafer stage or slit scan direction PC is normally specified as the PCo or outer Ring value Ring apertures can specify values for PC outer and inner Exposure values are used in calibrations and the calculation of control parameters such as best focus proper exposure dose and the depth of focus They can also be used for data exclusion or limiting functions Weir provides multiple controls to limit or exclude points based on their exposure Metrology data variation is a function of the setup variables of the exposure tool Data values can systematically vary as a function of the exposure conditions of the die For example is the stage moving to the right or left during the exposure or is the slit scanning up or down for the specific field site Layout values may or may not be contained in the original data file The presence of layout data is a function of the metrology source Layout can always be entered and modified from this screen Getting There Main screen Layout button This is the default screen for the Weir Analysis Graphic Display Weir Main Interface The default graphic is a square range plot of the wafer Measured fields are marked with a square tan colored range target Measurements on each die are displayed as small circles placed out from the center of the square The distance from the center is proportion
128. ology validation Tool Algoritm Verification SL10iso18map xls Data Culling Methods General application Examples on culling data using the Range and Sigma auto culling Additional uses for culling using the mouse to remove single point and field sites Reticle Error A wafer has been measured using scatterometry Detection i z The data is modeled for systematic wafer aberrations and then field tilt The residuals to these aberrations are then plotted and compared to the reticle Field to Field Slot3 1converted xls A wafer has been measured using scatterometry Exposure Stability The data is modeled for systematic wafer aberrations and then field tilt The residuals to these aberrations are then plotted and compared to the reticle Wafer Feature Scatter 110 A test reticle and it s measured features were previously Comparison to DPI_ReticleData xls analyzed in the Reticle Analysis section Reticle Data Sl10map_fullwaferP barc xls Wafers were exposed with this reticle and features analyzed to see how well they track against the original data on the reticle Process Window Expowin xls Expowin xls provides a classic Focus Exposure Matrix Analyses FocusCDS 2 xls FEM of CD SEM measured feature sizes The method of layout is presented and the data analyzed for optimum focus and depth of focus Analysis methods for multiple features and sites on the field are presented Example Wafer Maps Wafer and
129. on of the feature with respect to the center of the current field Displays the results for each field and a summary Ex FieldModel_TCD_Grp233 FieldColModel_ amp Row or Column based Field model is fitted to each row or Feature column of each field This sheet summarizes the modeled rusults on a row by row or column by column basis OR acs P Ex FieldRowModel_BCD Row Model or FieldColModel_ TCD oe amp column model Surf_Field_ amp Calculated display surface Surface data used in the field contour or FeatureName 3D plot generation Columns contain the X Location and rows the Y Page 54 Process Analysis Location of the data Ex Surf_FieldResids_SWA for field residuals Field Removal Raw or Modeled data values can optionally be removed from the input data stream When this occurs the average field calculation is stored on the FieldRemoval tab Fiweir Process Analysis File Edit Data Nano_cypress_1 1 XL5 Help BS melan Data Selection Spatial Metrology Process Window m Focal Plane Aberrations Display Selection Component Removal Plot Format Selections te Model Data m Model Components Display Selection m Wafer Models Field Models Contour No Modeling No Modeling Component Removal C Row None C Full Wafer Tix Column Plot Format Validate TitY Full Field Whole Field Bow IV Validate xY plot Quadrafoil4 x
130. ons Examples Page 85 Field to Field Exposure Stability these aberrations are then plotted and compared to the reticle Field Aberrations T Full Screen slot31 convertedaswtr21 3energy1 10502 SLOT 31CONVERTED AS WFR 213 ENER Microns CD 5 G Collapsed Field CD 5 Raw Data Points 121 3 Fornat Field Mean Waters 1 j i Fields 1 H if Sites 121 Ream aN ts wl 7 ls axi i J He See Sl hel gt ba A ye j y gt y e i A F ft f z ie EE l K s MEE alt FDresid um ado Fy A ai E 3 j i z OJ j 1 i fgg s 120 30 60 30 00 30 60 30 120 Max Min 0 170 095 MO na wmo es 60 48 2a ob 3 so ce so wo ne wo Harada Peren on feiden Figure 53 Average field with XY plots of center scan column left side and center row slit bottom data Background The objective is to observe lens slit anomalies as the exposure tool scans across multiple die on the wafer To see these clearly Weir removed the average center column of site data from every point in the data field Data has been imported and the Spatial Analysis button of the Weir PW Process Analysis interface selected Figure 53 displays the average Raw Data field of data The plot was obtained by entering the Weir PW spatial tab turning off both the wafer and field models selecting Contour from the Display Selection tab and selecting the Field tab We can see a profile of the
131. ool control parameters The mode allows you to see how the whole field reacts to the exposure settings applied by the stepper or scanner For a stepper whose exposure is captured in the single flash of the entire field this is sufficient However the model loses the fine detail of the exposure slit s accelerations pitch roll and yaw as it scans across the reticle during the exposure sequence of a scanner The fine structure of exposure imposed by a scanner is best viewed by the Row Column model This model applies itself to every individual row and column of every field in the dataset The application of the model is therefore slower than that of the Full Field since every row and column must be applied and summarized for every field The benefits gained allow you to examine the model response to Feature piston offset tilt and curvature as they change during the scan exposure sequence For example an analysis of the coefficients associated with the rows of a field essentially shows the flight path of the scanning slit You can see the tilt coefficient change as the roll of the slit changes from a positive slope at field bottom to a negative slope at the top Height changes in the path of the scan trace the planarity of the scan bearing etc Some examples of the application of these two models can be seen in the tutorials contained on the Weir installation disk Combining Field and Wafer Models Field models operate on the res
132. operations at a point that maximizes the resulting depth of focus the focus range that will maintain the critical device feature within process control limits Soon realization came about that the process exhibits different behavior when other feature types are examined For example setting the optimum process point for a gate does not automatically set the ideal point for exposure of vias or feature profiles Even more crucial critical feature operating windows may not even overlap for some selections of focus and dose As a result the ability to examine process variations for multiple types of features was soon supported in PW analysis products The past decade has seen a evolution of philosophy in the lithography area The concept of relying on the next generation of exposure tool and photoresist to meet the process margins required for new device designs has largely gone by the wayside This can be observed by the attention in the literature to operations of the process in the low k1 essentially low process contrast regimes Depth of focus is now recognized to be not only a function of the feature examined but is subject to the location of the feature in the lens it s orientation the setup of the illumination source the manufacturing perturbations of the individual lens the uniformity of the photoresist and previous films on the wafer wafer flatness and tilt of the wafer and individual field during the exposure Analysis and control of
133. optimum 93 Process Window graphics 68 profile 6 50 63 79 81 86 99 swa 99 Pure Error 107 Q quartile BoxPlot and culling 15 R radial coordinates 8 radio 27 range culling 8 variable culling 15 Range 14 15 57 58 61 62 65 66 69 73 79 80 93 98 culling example 80 raw data threshold view 47 Raw data Page 116 visualization amp statistics 45 RCWA Algorithm validation 106 Rectangle 68 reflective anti 100 Registration spreadsheet format 18 removal wafer tilt and bow 89 Removal 59 remove culls 14 46 50 53 60 65 systematic errors 65 Remove 45 49 50 Residual 50 residuals 14 15 58 59 61 69 80 84 85 89 101 109 111 from models 8 viewing 8 Residuals 54 58 as metrology metric 77 Resist 73 response dose 94 reticle contribution to error budget 6 errors 54 errors living with 85 plate stresses 82 scan 99 subtraction from data 22 to wafer tracking 90 Reticle data analysis example data analysis example data analysis example error detection 84 87 spreadsheet 109 storage directory 33 roll 82 slit 9 Row 21 59 60 62 67 precision 107 row column model 9 TOWS deleting 22 S scale 57 factor for histograms 28 scan single multi serpentine etc 38 single scan layouts 38 scanner best model 9 Precision Values Computed Scanner viewing scan blur 28 Scanner
134. orkbook Format There s a minimum of three worksheets stored in each workbook lt DataSheet page 16 Minimum Workbook Format 1 10 2005 Data Storage and Formats 1 The primary imported data as measured The sheet name is the same as the data set name g Sites 2 A sheet of field locations and feature family information Information 3 Header information containing die size flat location etc Formats and conventions for these are discussed below Weir Standard Format The as measured metrology is stored in this sheet shown in Figure 3 The name of the sheet should default to the name of the raw data file Rules for construction lt The name of the sheet should default to the name of the raw data file That is a raw data file named SlitData5_1_NA45PC35 tlg should store data in a sheet named SlitDataS_1_NA45PC35 The workbook will also by default be the same name as the raw data file Sheet names are limited to a maximum of 31 characters Naming restrictions follow standard Microsoft Excel Cell A1 must contain a comment note with the text DATASHEET NOTES Any number of datasheets can be stored in a workbook Each datasheet is designated with a spreadsheet comment DATASHEET stored in cell Al being the same name as the workbook system file designates the primary data Position information columns B through E mus
135. pendices seeseeseesescessesoeseeseesessesoeseeseeseeseeseee 107 Background 73 MSE as a Measurement Quality Metric 76 Valid Metrology Behavior 77 Data Culling Methods 19 Spreadsheets created by Weir PW 109 Background 79 rat eo Automated Data Culling with Range and Sigma Fields Modeled Statistics Definitions 111 Precision and Error Budget Calculation 107 Precision Values Computed 107 80 Sogi ima Mattea eeo oi aA Bi Abbreviations and Definitions 112 Reticle Error Detection 84 Ind XK sscsrsisiscsssserisossiosisorininrcnnn nann L LA Background 84 Analysis 84 page2 The Weir Software Suite 1 10 2005 Overview Overview The Weir Software Suite A Weir is a restriction or an aberration of a wavefront that results in a change in the behavior of the wave The Weir Wavefront Analysis Suite or Weir Suite is a group of programs designed to help the Lithographic Process engineer Measure the focal plane uniformity of an exposure tool Characterize the wavefront s variation with Numeric Aperture Partial Coherence and Dose Measure the tool specific feature and process behavior for each exposure tool In addition to these capabilities there are a number of features within the Weir Analysis that extend the analysis capabilities to the aberrations unique to scanning slit exposure tools often referred to as Scanners Utilities are also provided to character
136. profile changes of the features Screen Navigation Weir Process Analysis Figure 25 shows the Weir PW interface and it s major navigation points New Weir data workbooks can be opened from the File Open menu Selections Frame Page 50 Process Analysis The current features available for analysis are listed in the two drop down lists located at the top of the form Feature names will track the data column headers of the workbook currently open The Data Selection tab will be the first screen opened In this screen you can choose a subset of the data before proceeding to any of the next three analysis tabs At any point in later analysis you may return to this screen and re select another data subset Note that when data points or field sites are culled using the mouse they are not removed from the original data set and can be recovered by re selection View or save Analysis as a function data currenily of location on wafer Current Workbook spreadsheet navigation Depth of Focus Exposure Latitude amp ss Window aT Process Window tab Mal Select data Precision and subset range Fekk Currenily and manual AE RA analyzed culling tab feature and family Figure 25 Navigation on the Weir PW Interface Data Selection The Data Selection interface has three sections The Available Data Data Layout Display and the Calibration Options frames Notice
137. r data point exclusion If points are excluded the remaining population is again re modeled Selecting a check box next to the coefficient name will include the results of it s coefficient into the plot and fitted data statistics when Wafer and Field plot tabs are selected h Coefficients not selected will result in their point values being added to the Wafer Residuals and Field Residuals display as well as the residuals statistics report 2 Double click on the coefficients frame to select or de select all coefficients SAI coefficients are included in the actual modeling of the data as long as the No Modeling radio button is not selected However only the coefficients selected will be reported when the Wafer or Field graphic is selected Raw data can be viewed by i Select No Modeling for both the wafer and field or Model Components Tab Page 58 Process Analysis j Select Full Wafer and Field modeling but de select all coefficients To view field response with wafer systematic errors removed k Turn on all modeling l1 Select all wafer coefficients m De select all field coefficients and n Select the wafer residuals or field residuals tab i Results in the reporting of all field systematic and all residual values Component Removal Tab Removes selected values or modeled coefficient contributions prior to modeling the data The variable removed will be the variable s
138. range of CD 4x column Wafer TCD is biased at 80 nm CD size see piston while reticle measured at 106 nm MinMax Wee PW N Scale um 7 591 nm max min7 691 11 000 Figure 59 Reticle and Field contour Left Top Reticle contour analysis Right and bottom Field variations are plotted for 121 points per field after the wafer modeled aberrations are removed A blow up of wafer center shows the similarity of die fingerprint to the reticle and a mean wafer field plot bottom center heightens the similarity Process Window Analyses Setting up for a Process Analysis Data File Summary Applications Examples Expowin xls FocusCDS2 xls Expowin xls provides a classic Focus Exposure Matrix FEM of CD SEM measured feature sizes The method of layout is presented and the data analyzed for optimum focus and depth of focus Analysis methods for multiple features and sites on the field are presented Page 91 Process Window Analyses Background Expowin xls is a classic Focus Exposure Matrix It s very simplicity provides an excellent example for illustrating navigation and analysis principals for the analysis of the parameters leading up to a full process window evaluation Process data typically contains both focus and dose variations from field to field as in figure Weir does not require both to be present for a Focus or Dose response but they must of course be there for a
139. re not equal use the Window Arrange menu command to display and compare the rows that differ Delete any rows prior to copy Highlight the data columns you wish to copy Paste the highlighted columns into columns T through K of the target data worksheet Tn cell L2 insert the formula E2 I2 Copy the contents of cell L2 into columns L M and N and into all rows that contain data 2 You now have the original data columns F H the second data set columns I K and a difference data set columns L N If loaded now Weir PSFM will work only with columns F H Highlight all rows in columns F H Select the Insert Columns menu item Three new and blank data columns will be inserted F G and H Highlight columns L M and N rows to N then N is the total number of rows Select the Copy menu or copy button to copy the contents into memory Click on cell F1 Select Edit Paste Special from the menu select the Values radio button and press OK The new data values will be copied Optionally delete the columns beyond column H Load the workbook into Weir and analyze Note If you renamed the workbook to a new file name then the first time you load data into Weir it will ask you if you wish to use the data spreadsheet containing the old name Simply answer Yes and proceed Units of measurement specification Unit
140. re two fields with poor exposures the field located directly at the bottom of the array and one located at 9 o clock the left side of the array If we look at the plot of SWA and GOF for these CD s in Figure 45 we can see the relationship that CD and SWA play with the data Valid Metrology Behavior Page 78 Applications Examples B di 0 E ALL AA 0 65 PCo 0 60 PCL 0 00 ottom e Demo Wat Al Exp ALL All NA re t 93 101 128 164 Weiraisenon biei 107 site 114 297 107 617 100 937 94 287 87 577 80 897 74217 67 537 60 857 54177 47 497 40 817 T T T T T T T T T T T J 89932 90682 91 432 92182 92502 93682 94432 95182 95932 W 97422 98182BRottom die SWA _ lt site To coezo 80 0 d 0 CD 80 70 0 O 0 0 000 40 0 0930 0935 OS40 ags O950 05 0960 0965 090 0975 0 980 Figure 45 GOF and SWA response to two CD thresholds gy profiles approaching 90 degrees the majority of the profile exhibits a profile that would be undercut if the numbers are correct Also we can see from the GOF plot that this same rogue die is receiving the greatest GOF statistic This suggests either a problem in centering of the process or reticle size if cross sectional profiles of the features confirm the results shown or an algorithm tuning opportunity for the scatterometry tool vendor Data Culling Methods Data File General application Summary E
141. rge differences in X and Y metrology values are assumed to be metrology failures The Cull Analysis command button will display a graphic and the number of points removed with the current selection Culling by Wafer Radius The Raw Data metrology Spatial Analysis and Focus Analysis interfaces provide a Cull Radius command button and radius field Metrology sites located outside of the radius value specified in the radius field are excluded from the analysis Data Storage and Formats Page 15 of 116 Data Storage and Formats Storage of data The Cull Radius button when pressed will display an plot of the variable value verses it s distance from the wafer center A 3 order polynomial is fit to the data and displayed as a message on the graph Graphic assistance Histograms are the best tools for observing population spreads Selecting a histogram or the data culling button provides the user with the ability to visualize the population shape prior to entering the data Use either the histogram graphic selection or box in a portion of the data on a vector or contour plot to plot the histogram A BoxPlot appears over the histogram to show the systematic range of data distribution The quartile values for the box plot are summarized below the right hand section of the graph s abscissa Viewing Data There are three basic methods of viewing or accessing the current data set 1 Raw modeled and resi
142. s Each main analysis screen contains a menu item corresponding to the name of the current data file Selecting this menu will result in a submenu drop down where each item corresponds to a spreadsheet tab of the current workbook Selecting any of these spreadsheet names Raw Data File Selection 2x Lookin 3K O O a eG P A 1 40PSFM_W23 08 24 02 20 00 14 dat E 140PSFM_W23 08 24 02 20 00 14 2ip saaton 24_02_20_00_14 x15 KLAarcher_140 SFM_23_0802 txt Desktop My Documents My Computer ce E My Netwak P Fenne gt B Files of type KLA Soo CD SEM z Data Import selections Figure 13 Data import and conversion Importing Raw Data Metrology data from either the classic metrology tools or from exposure tool self metrology functions can be easily imported Data can only be imported from the Weir Main screen File Open or file open button Imported data is automatically converted into the Weir Standard Format and stored into a Workbook as shown Figure 13 The workbook will be the same name as the raw data file and in the same directory Workbooks can then be renamed and moved to other locations if desired Centering data on the Wafer and Field Weir Main Interface Page 35 Weir Main Interface Data Import and Layout Data fields are typically properly centered on the wafer however their size and location can be easily fine tuned us
143. s Page 59 Spatial Analysis Values can be chosen from either the Average of the measurement sub set or modeled components The Display Toggle command button shown in Figure 29 toggles the selections displayed You cannot select both average and modeled values for removal Removal of Average or Fixed Values Field will remove the field values for each site in the field Center Row Column removal corresponds to removal of values based on the point row column position in the field Center Site removes the value corresponding to the site closest to the center of the exposure field Removal of Modeled Values Select from the Field Offset Tilt or Curvature coefficient check boxes to remove the contributions of each coefficient from the data If both Row and Column boxes are selected then the average value will be removed Selecting a Value check box is exclusive of the removal of modeled components You must manually enter a row and or column coefficient value into the data fields to see the effects of it s removal Plot Format Tab Provides four options for viewing graphics and statistics Field Plots Wafer Grid Plots Whole Field Plot all data on a collapsed field Plots all data as modeled or measured Field Mean Plot the mean of each site using Calculates the mean for each field the collapsed field as a data plotting one data point per field source Field Plots the vector of greatest Plo
144. s slit analysis example 81 scanning 3 37 60 64 81 82 99 107 scatterometer algorithm evaluation 106 scatterometry 4 69 79 84 85 101 Scatterometry algorithm method 75 scope 66 Seed 66 93 97 selection of data 51 SEM 21 111 profile entry 42 Series graph curves 26 serpentine layout example 39 Serpentine 38 39 side wall angle 5 49 101 sigma 14 40 50 57 64 111 culling 8 Sigma 14 15 33 34 37 40 57 58 66 69 79 80 93 109 111 culling example 80 in precision 107 signature 63 69 70 81 82 88 89 90 Simulate process window 50 Single Scan 38 Singular value decomposition 8 singularitie 79 site culling methods 85 information 53 location 53 Site Culling 14 precision 107 Sites Format 19 Selecting for PW 97 worksheet units of measurement 24 slider 65 Slope 49 Source default data directory 32 Spatial 49 54 80 109 tab model implementation 8 spin deposition profile 99 sport 84 sports 8 Standard data format 17 Standard Error 109 111 Standardize 63 Statistics Definitions 111 status bar 52 53 Std Err See Standard Error or Sigma Step 21 38 39 41 92 stepper best model 9 Sub Field 34 settings 37 Substrate 34 subtract data set 22 surface control 8 SVD 8 SWA 49 73 76 and CD 98 BARC and SWA relation 105 contour 78 symbols modify in graph 25 systemat
145. s Modules 4 Weir PW Unique Capabilities of the Software Applications An Overview of Weir Feature Modeling Weir Feature Models 6 Model Implementation 8 Wafer Model 8 Field Model 8 Combining Field and Wafer Models 9 Getting Started 9 System Requirements 10 Nan License Management ssscscsosssssssssessssscsseel 1 Installing the software and Confirmation ID 11 Overview 11 Obtaining a License 12 Data Storage and Formats ccccsssssessee 13 Data Fundamentals 13 Data Flow 13 Data Culling Methods 13 Viewing Data 16 Storage of data 16 Weir Spreadsheet Data Formats 16 Minimum Workbook Format 16 Weir Standard Format 17 Data Storage Convention 18 Measured Data Storage 18 Overlay Focus and Registration Metrology18 Critical Dimension and other metrology 18 Sites Format 19 Sites Data Storage Convention 19 Information Sheet Format 20 Manual Manipulation of Data Sets 22 Example Subtracting two data sets 23 Units of measurement specification 23 Available units for variables 24 Storage and Designation 24 Customizing Graphics scccccccsssssssssssereeee 20 Overview 25 Getting There 25 Functions 25 Contour and 3D Surface Plot Controls 27 Interpolation Methods 27 Plot Feature frame selections 28 Histograms 28 Mouse Selected Data Manipulation 29 Wafer base analysis 30 Field based analysis 30 Weir Main Interface ssccccsssssssrrsssserrro I L Screen Navigation Weir Main 31 Setting Pr
146. s a convenient method of investigating repeating errors slit response scan response at different parts of the wafer or the variation of variables as they near the edge of the wafer Wafer base analysis Figure is a contour plot across a 300 mm wafer of the raw Y Feature data Examination of the figure 74 shows the stage travel fine structure of the reticle scan stage as small pop s or high points on the left side of each field image In this figure you can also see the selection box to the upper left of the left most pop up menu We ve selected to plot the data across this one die looking at the vertical feature as a function of X axis position The resulting plot is shown in Figure 9 We could just as easily plotted a histogram or from Raw Data oax 33 3 0 1445 Wafers 1 Area Selected Y 38 0 32 0 to 14 0 30 0 Microns 30 0 25 0 20 0 15 0 Horizontal Columns Position on Weater mm the first menu row viewed the Field based analysis page 30 The analysis of Figure has strong edge and scan direction effects effects can be minimized by selecting areas of the wafer around the edges and culling the We can then plot the average shown in Figure 10 From this we could also have taken cross sections of this field for additional in depth study Note The contour lines are by right clicking on the plot and turning on the Z axis Plot Gridline option Mouse
147. s including average Maximum Min Max IntraField Deviation IFD and Astigmatic Y value Xvalue formats using a simple radio button interface as shown in Figure 23 Plot XY graph scatter plots based upon field and substrate position Page 45 of 117 FEM Variable Setup Interface Notes Use the Full Screen check box in the upper right of the viewing area to expand th e display graphics to their maximum size The Wafer and Field tabs are used to select between view formats and to begin a data plot Use the Escape Esc key to interrupt any analysis The key must be depressed and held Data Format Options Whole Field Field Mean C Field Min Max C IFD Astigmatism S C Value C Mean C Mas C HA Max Figure 23 Metrology data format selections for Visualization of Raw Data Statistics Display The statistics shown to the right of a graphic reflect the data selected and restricted by the Data Selection frame Use the Statistics check box to turn statistics display on or off Definitions IFD is the IntraField Deviation or maximum range of measurements in the exhibited dataset Astigmatism the Y X or Horizontal Vertical feature measurement difference Astig Y Xmax the maximum absolute Horizontal value the maximum absolute Vertical feature value This represents the maximum split observed between horizontal and vertical features Display Selection Sp
148. s of measurement by default are assumed to be microns Data Storage and Formats Page 23 of 116 Data Storage and Formats Units of measurement specification Units can be changed by either the raw data import program or by manually editing them using the Weir main menu path Data Units Setup Available units for variables Weir software accepts the following units of measurement Microns g Angstroms lt Nanometers Millimeters Centimeters Meters gs Degrees Radians Seconds Hours Minutes MilliSeconds Centigrade Farenheit eDegPerSecond Thermal Flow KdegMinutes Energy Flow Storage and Designation Metrology units can be specified uniquely for each individual variable imported They are stored on the Sites worksheet starting in column H The software stores one variables designation in each column the unit value being located in row two of the column G H l J Family TOP_UNITS BOTTOM_UNITS SLOPE UNITS Edges_1_2 um um Radians page 24 Units of measurement specification 1 10 2005 Customizing Graphics Customizing Graphics Overview Graph colors line weight display range scale format titles and fonts can be interactively modified by clicking on the graphic using the right mouse button Trend and XY plots can access all of the above plus the user can also add and modify on plot messages plot symbols line and axes weight
149. scan by using the mouse to box in the center column of data points and plotting the resulting data as a function of row position Data Selection Spatial Metrology Process Window r Focal Plane Aberrations Display Selection Model Components Component Removal Plot Format r2 Systematic Component Removal Modeled Values one Mean Basis None Row C Field Column G Field C Center Row Center Site Center Column C Value 0 00 Lot Average Figure 54 Setup for Reticle Error Detection Lot Average has not been selected and the raw Center column of data for each field will be removed Background Page 86 Applications Examples The objective is to examine uniformity of the exposure across the wafer Weir PW provides the option of removing slit or scan values from the data set The setup tab for data or modeled error removal is shown in Figure 54 Since the objective is to see variations across each field the Lot Average check box has not been selected The Center Column radio button has been selected from the Remove Mean frame This combination of selections will result in the center column values of each field being subtracted from the all the values in the field on a row by row basis In other words for any given field on any wafer Vi Si Ci Where Vi is the final value of site i that is then presented for modeling Si is
150. se methods either employ a look up table library of known scatter signatures for process variations or they perform a real time analysis of the signal The fault here can be caused by either technique the success rate reduces to a measure of the robustness of the implementation algorithm for the vendor 1 28 1 12 0 96 0 8 O64 048 032 016 SWA Figure 40 Standardized plot of MSE and BCD as a function of SWA This algorithm would be marginal in a normal process application on product wafers since autofocus variation of 50 nm is not uncommon Any APC application employing this vendor s tools will have difficulty controlling the process stream without ringing and a large rework level Applications Examples Page 75 Metrology Characterization and Tool Algorithm Verification MSE as a Measurement Quality Metric Table 3 suggests a strong linear correlation between the Side Wall Angle SWA measurement and the Mean Square Error MSE of the fit The Weir Metrology segment easily plots this relationship in Figure 41 T T T T T T T 76 0 73 0 80 0 82 0 84 0 86 0 88 0 30 0 92 0 SWA Figure 42 MSE behavior over the Focus range Compare this plot with the BCD versus Focus plot of Figure 38 MSE could be used as a threshold parameter for SWA however we should look at it s performance in relation to the BCD and SWA parameter combination Figure 40 Here the variables have been standardized relative to their 3 sigma
151. t be filled in for each row of measured data For data that is not overlay or registration columns can be left blank that is without any data and individual row entries may be left blank Additional data can be used to store information such as measured reticle information and data derived by Weir during an analysis Diary heski Bemmi SWA BARC MSE 5 TH 069 OIE Ge See 401008 Oe 5 i Eee 01035 8814017 H25 H 5 272 a oira Ba H15 Ai a Oe ie ba Ba Fa Ba hE nhm 7 ErP heute rece Fach SS SSS SSS SS SS See Figure 3 Data spreadsheet for the Weir Standard Format Data Storage and Formats Page 17 of 116 Data Storage and Formats Weir Standard Format Data Storage Convention Metrology data is stored in columns Data starts in column 2 the B column Headers should be located in row 1 The first four columns are standard to any data set They define the location of the measurement Header Cell Function Location Wafer B1 Designator for each substrate May be any alphanumeric Test Cl Key for each unique site location on the field providing a pointer to the row location in the Sites spreadsheet Defines a unique field position and feature type Stored as an integer number designating the row number of the detailed information stored on the Sites spreadsheet Diex D1 An integer designating the column location of the die on the wafer Diex location zero 0
152. t click on the graphic to change the graphic properties including scale background color titles and fonts Data sets with more than one wafer of data will have additional rows appear in the pop up data menu representing one row for each wafer to allow all or single wafer exclusion of the data After selecting the Cull selected data points menu item the display will automatically remove the boxed sites from all points in the selected data To remove data culling from a given area box the area and select the remove culls from selected menu item To remove ALL mouse culled data and return the sites to the selected dataset simply click the Select Data command button Page 53 Spatial Analysis Spatial Analysis Critical metrology values are subject to the variations in the process exposure electromechanical sub assemblies and local perturbations caused by reticle errors or wafer back side dirt An analysis of each feature s variation as a function of the physical space it occupies is needed to discover the variations attributable to these sources of error The Spatial Analysis tab provides the tools to examine model and simulate these variations Modeled variations will also help during a process analysis Often depth of focus and exposure latitude are masked by wafer and field tilt during exposure of the wafer These errors can be removed from the data if we have a clear understanding of the tools available and t
153. tarted or when a new Weir workbook is loaded I weir Process Analysis Nano_cypress_1 1 XLS Data variable and pro duct family Pie Edt Data Nano cypress 1 1 5 ne 3 currenily under analysis BS 4 mi MA z Data Selection patia maa powinien ReCaloviale ome Cull by variable range Numeric e Naw os 2 les PCouter ie es Jf fise Select the variable and insert the maximum range All other variables ii Min WET will be culled when the 20 sites selected variable r Calibration Option Daa Layou Digis exceeds these limits Doe NA Penne Poodle SelectedDats C RawDate 15 075 o Selected Data 11 5 Histogram Click on the command button to see a histogram of the variable Controls for setting data range restrictions Field data distribution The mouse can be used to select and cull individual sites Full wafer data distribution or full areas The mouse can be used to select and cull individual points dice or areas Scale unt 270004 mas min 2 24 000 0 70 000 Over Thweshokii20 20 4329 1A Dore Wala ExpALL Al NAO7S PCo0 00 POS 4 Figure 26 Data Sub Set Selection Screen Available Settings Frame Displays all of the field exposure values contained in the dataset Provides controls to limit the range of focus dose and the scan direction selected and the wafer ID s to analyze Controls are
154. ted as an Mreg statistic and a pThk measurement as a pThk statistic This is a critical feature for ellipsometric and scatter data where the engineer is allowed to define the metrology variables page4 Weir PW 1 10 2005 Overview With these tools the full spectrum of contributors to the process error budget can be evaluated and process parameters adjusted to optimize functional product yield and manufacturing flow Unique Capabilities of the Software Engineers in the semiconductor industry often simplify the factors involved in understanding the process window of critical focus and exposure dose ranges They often neglect the influence of exposure and metrology tool and even wafer induced aberrations on the setting and extent of the available process window During a typical process window evaluation one or at the most two or three critical features are evaluated Features typically include a vertical and horizontal feature of the critical format and perhaps the photoresist side wall angle as a measure of quality The tacit assumptions of this approach are that all of the metrology is good for the entire focus and range of the data the process will respond uniformly across the field of the exposure tool and from tool to tool the influence of the reticle can be ignored and the wafer itself has little or no influence on the calculation Following the simplified course of these assumptions will lead
155. tematic coefficients and their standard errors for removal prior to a process window analysis ProcessWindowSpace Process Worksheet for Process Window analysis Window Calculations of depth of focus dose latitude and their relation to Focus and Dose Data Range Data Range This tab shown in Figure 30 is used to set the scope of the analysis and the display formats Focus Frame The outer boundaries of Focus can be easily set by using the drop down fields for maximum and minimum focus The controls default to the full range of focus Individual focus values can be excluded from the analysis by using the focus check box listing Double clicking on the Al selection will alternate checked values Dose Frame A check box control appears for each dose value in the data set Individual dose values can be excluded from the analysis by using the dose check box listing Double clicking on the AI selection will alternate checked values The Seed field provides a method of biasing the process window search This function is used only with the process window study and will bias the start of the search for the optimum window size Setting the value to zero 0 0 will force automated searching by the software Variable Frame The process window search area can be limited in scope by selecting any of the variables from the drop down list Variable names are those defined by the data set Maximum and minimum
156. the exposure field Data Import and Layout Weir stores saves and maintains all data in Microsoft Excel Workbooks Workbooks can be opened from the Weir Main screen the Weir PSFM Analysis interface and the Weir PW process window interface All metrology formats are stored under the identical Weir Standard spreadsheet layout described earlier so any Weir product can open any type of data To open a workbook simply select the Open Worksheet from either the file menu or by using the Open Workbook button on the command toolbar A windows standard file open form appears for your selection Note 4 Each workbook contains an Index spreadsheet The index is a dynamic directory of every spreadsheet in the data workbook Each entry contains the name of the spreadsheet it s creation date and comments on the contents page 34 Data Import and Layout 1 10 2005 Weir Main Interface g As each analysis model or surface contour map is generated a corresponding spreadsheet in the workbook is created and updated to contain the current data analysis At each update the spreadsheet will be brought to an active positon allowing you to directly view the data and perform any Excel based analysis or graphics on the data subset lt The user can modify add or delete any worksheet in the workbook without corrupting or changing the raw data The only exceptions here refer to the original data Site and Information spreadsheet
157. tial Metrology Process Window r Process Window Data Range Setup Pw Control Model r Data Ranges 5 Focus m Dose Items to Include in Displ One O Max oa I Statistics All Cc M Graphic Row Min I7 Show Limits Column C m Cull Variable Rangefo N one x Sigmalp Max fo Min fo r Process Relations Refresh Full Screen Feature Variation with Focus Sites 2 5 Pw Dose Focus PRT rapCD 0 3324 1Fit 22 0 PRTrapCD Site 5 Point 0 11 0 323 m 1 Dose 22 0 PRTrapCD Site 5 o 1 Dose 22 0 PRTrapCD Site 5 m PATrapCD_Target m PATrapCD_Max m PRTrapCD_Min PRTrapCD 0 3021 Variable 0 2 0 2 0 1 i 0 2 0 3 Residuals Target Feature Dose Site BestFocus BestFocus Offset Slope Quadratic Sigma cD UCL LCL PRTrapCD 2 2 0 108 0 3205 0 321 0 054 0 244 0 002 0 3021 0 3324 0 2719 PRTrapCD 2 5 0 12 0 3001 0 3 0 163 0 783 0 008 0 3021 0 3324 0 2719 WafAll ExpALL All NA 0 65 PCo 0 60 PCi 0 00 4 Figure 30 Process Window interface Depth of Focus analysis for two sites in the field Graph is mouse sensitive and displays the location on the graph as well as any data or curve information such as shown in the yellow box on the graph Overview Page 64 Process Analysis The analysis provided b
158. ting down or for a maximum of six months whichever comes first The license maintenance screen will first appear at each restart until either a demonstration or permanent license is entered Welcome to the Weir Wavefront Engineering Software Suite Installation is keyed to your computer To validate the license you will need to provide the customer service agent with the installation date and the two instalation ID s This installation will work up to ten 10 times without a Confirmation ID Contact TEA Systems email WeirEngr TEAsystems com Phone USA 01 610682 4146 OR Benchmark Technologies email info BenchmarkTech com Phone USA 01 781 246 3303 1 You will need to provide the customer service agent with the following information Installation Date W ednesday August 13 2003 v Installation ID Af 38D690BD AE a 2 Enter the Confirmation ID provided by the customer service agent Weir PSFM Weir PW There are Confirmation ID lp B8D5B8415 38D 4A33BF ey 7 3 re confirmation Exit Activate Later Enter Confirmation Confirmation k ET remaining License Management Figure 2 The Weir license management screen The License Management screen will continue to appear at each software startup The screen can also be accessed from the Weir Main window s menu item Tools License Management Weir PSFM and Weir PW each require separate licenses entered in the Co
159. tion The selections in this section provide additional information on distributions Color Profiles Each data point is color coded according to it s location in the population Contour Profiles Adds in a contour line linking the population gradients of each BoxPlot For example checking the 50 profile will link the median of each BoxPlot to track the population median variation across the median of all data Each profile is color coded by their contour location in the population Line weight and color can then be modified by selecting the curve in the Series tab 2 Messages Messages and labels can be added modified in this tab page 26 Overview 1 10 2005 Customizing Graphics To modify a message select it from the combo list control The text is directly modified in this field by clicking on the appropriate section of the field The location of each message on the graph is set using the units of each data axis to specify the lower left corner of the text Use the ordinate axis units to set the Y location on the graph Conversely the abscissa data values set the X location Messages can be located above or below the plotted graph area by specifying a Y value above or below the plotted range Adding a new message Press the Add command button Modify the text in the Messages field Adjust the X Y location of the message on the graph Trend Line A polynomial of an
160. to Reticle Data Data File Scatter 110 DPI_ReticleData xls Sl10map_fullwaferP barc xls Summary A test reticle and it s measured features were previously analyzed in the Reticle Analysis section Wafers were exposed with this reticle and features analyzed to see how well they track against the original data on the reticle Macsons Codex Ports 3630 W ster 1 Freid 30 Stet 3457 Daa Court 3457 Mean 64 8639 Madan 80 6778 SEM M mamam Meum Range Me om Vanance StDev SS 147563537707 i red Sum 224234 5692 Reticle Measured n ape CD s Figure 56 Contour plot of isolated features Plot is of feature distribution after systematic wafer and field errors are removed Inset is a plot of the reticle field contour feature distribution Background Previously we found the reticle mean 4X feature mean to be 106 nanometers nm with a 6 4 nm range The contour plot and distinctive signature of this reticle is shown in Figure 34 Background Page 88 Applications Examples Figure 56 is a plot of the full wafer measured features after removal of the wafer tilt and bow coefficients and also field tilt for the individual fields To perform this removal simply model both wafer and field coefficients Check the wafer tilt wafer bow and field tilt coefficients for removal Click on the Wafer Residuals tab to the right of the display window The feature bases were measure
161. trates by subtracting the metrology from each and looking only at the difference metrology You can manually manipulate or combine data sets after a data file has been imported into a Weir Spreadsheet The primary data file is always the first spreadsheet of the workbook the spreadsheet will be the same name as the file itself Weir uses the first five 5 columns of the spreadsheet for positional information that is columns A through E Two or if present three data columns are imported for each row F X_reg G Y_reg and H Zmean The titles of these columns are located in row of the spreadsheet Their text labels are not important and can be any valid column name Weir will follow the given data label in reports NOTE You can add additional columns of data to the worksheet without effect on the Weir PSFM analysis These columns are loaded as data but are not used in the Weir PSFM portion of the analysis Saving the original 3 columns of data into locations above column H is a good method for retaining your original dataset You can delete or add data rows at any time When you delete a row you can either remove the contents of the cells or remove the entire row Remember that position on the field is keyed by the Test number in column C Test numbers in the data do not have to be sequential but they must have a corresponding entry on the Sites worksheet or data will not be load
162. ts one data point for each field as a Min Max absolute variation from the grid point Data point is the greatest mean with it s sign for each absolute variation of the field with it s site sign IFD Intra Plots the range of measurements Plots the maximum range of Field of the collapsed field for each measurements for the field as a single Deviation site grid point XY Plot Options Plot Format Tab This tab appears and is functional only for X Y graph plots Abscissa Select whether Row or Frame Column position values will be displayed on the X axis of the plot Rows Plots selected data as a For a vertical scanning system function of their Y axis horizontal slit this will allow height on the field viewing of aberration variation resulting from the scanning stage Columns Plot aberration as a For a vertical scanning system this function of their X axis or allow viewing of aberrations across Page 60 Process Analysis Metrology columnar position on the the slit due to the lens field Ordinate Frame Plot raw data Select a fit order greater than zero to see the best fit systematic eal the data Plots fitted data Plots fitted datapoints Residual Plots the residuals to the fit This section does not use the Feature and Feature Family drop down selections at the top of the screen The function of the section is to provide the ability to compare the behavior
163. tures are unstable and can be damaged during subsequent bake and development A field exposure occurring near the edge of this window may display within a single dense packed structure both feature profiles that are erect and easily measured by the metrology tool as well as structures that have collapsed during processing Most often the metrology tool will simply capture the first structure having the optimum feature profile within this nest ignoring the poorly Procers Window Lot Wer _Process_2 cD System errors 10 EL 0 41 Random errors 10 EL 0 66 Process Reetgnons Refer f FullScreen Line collapse and CD OPW System errors 10 EL 0 42 Random errors 10 EL 0 58 Figure 19 Top Process window calculated from SEM metrology data Bottom True window as constrained by fields without collapsed profile structures defined or collapsed structures next to it Figure 19 illustrates the overall effect of this restricting behavior The process window calculated for a 10 exposure latitude using metrology that ignores line collapse will be larger than the true lithographic process window One method of overcoming this problem is to gather information of the profile side wall angle SWA along with feature width data However SEM SWA data can often be misleading and is poorly measured for retrograde angles Adding an Exposure Dependant Variable Page 42 FEM Variable Setup Interface The Weir sof
164. tware package adds another method of inputting qualitative data values for such focus dose exposures by using the FEM Variable Setup interface Weir Layout Interface ose NA a is Penne PCoute Lot Wes Process 1 cus Waters 0 44 able Focus Waters All 6 i oN aa EEE E Ye EE p Interface ooos o Fie Edt Dota Help Weir Process_1 5 46 Fel fa lt a Data Selection Spatial Metala Process Window r Process Window DateRange Setup PW Cortol Mode Ansiysis Options Parameter Setup Taga 100 I Remeber Seting C FEM Variable Sup D Variable 754833 83023 673355 HJ MT cades oo foo 5000 Figure 20 Accessing the FEM Variable Setup Interface from the Main Layout interface top or the process window setup interface bottom Accessing the FEM Variable Setup FEM variable setup can be accessed either from the Weir Main layout button bar or from the command button located on the Setup tab of the process window analysis interface as shown in figure 20 Z FEM Variable Setup o x File Edit Data B S alel r Variable setup by Focus Expo Matrix FEM fro Variable Name Setup ies zp Collapse Save Eis jo Format Step 20 0 z Dose 205 21 Focus vaj ef 2 a E E E O O O orp E E E E E E E E E oE EE A AF A A A A E TS S A E S A A A A a a E a a a ca a A E A oop E E S E E E E os a A E
165. udy of metrology tool algorithm validation Two examples are shown One in which the effective focus range of product metrology is limited by a poorly designed algorithm setup on the metrology tool The second example looks at the effectiveness of a metrology validation statistics the Goodness of Fit and evaluates it s effectiveness and in doing so raises some questions regarding the process centering or fine tuning of the metrology algorithm Page 72 Applications Examples Background p e dr e ch ee a yeni ee 0 06 0 05 faoz anatona on 0 fom oz ost 0 yo 0540 06 oe s na S a dad ad DA iesgs e ia pi up Dowry Up Dont Up SDove Up i fupi sssdisssejiasss sssadrssashasssissasdtsssat CE ie ai ale aata aa eh Bere arenas at ah ah a foi ed a Soa Dovei Up Donn Up Downe Up D oner Up Doverti Up Dowrg Up tn 4 a aS E A g terse em i neko nae 37 0 ok esata ta St eb Pap Pepe ei spol nee aca gs ee ee ee E ates et de aE Sets 0 O74 0 084 0 05 0 1 Mansailaanattinnad a for no 1260 1334 0 14 0 N50 16 0 17 0105 0 19 eo ate ate 0 96 8 47 8 47 6 eh ee a H tome Up Doan Up jDowrt Up Downi Up Douari Up tDowrit Up pennn Mana s terer onan Henn atanwecthnwwn beoentonne mn t rea Fae fe ee ee ee peas re ae Serer yrree se rere ees DowrgDonnt Up 0 Figure 37 Sca
166. ulate the true process window and determine the statistical contributions of each element to the process error budget The method of analysis employs metrology data gathered from many classic data sources such as overlay tools and CD SEMs Critical Dimension Scanning Electron microscopes to the new sources of ellipsometry scatterometry and electrical linewidth metrology ELM The data can then be modeled statistically evaluated and visualized using easy to select and mathematically rigorous procedures and graphics Data are stored in open format Microsoft Excel workbooks that are easily accessible to the user The user will find that as analyses are conducted using Weir additional worksheets are added to workbook for each analysis In this manner the user has full access to the raw data modeled results calculated process surfaces and statistical summary tables In this manner the data is open to addition of excel calculations macros and visual basic application procedures customized by the user In the spirit of user friendliness extended by the new generation of scatterometry Weir allows the user to specify multiple data variables and the name for each data variable Models statistics and raw data labels follow the user customized naming Any source of metrology data can be imported into Weir PW Weir PW allows the analysis to function with the variables names selected by the user Therefore an Mreg variable is always repor
167. umns BE BS We then used the Excel utilities to create additional columns that reduce the reticle data to final size that is we divided by 4x This created the CD4x and Pitch4x data sets The site locations and header information were already correct having been imported along with the wafer metrology The final data table looked like this Wafer _ Site Diex Diey CD4x Pitch4x Cdum Pitchum CD _ Piten J al al ol ol 0 105 0220 0 420 0 879 _420 _879 M al al ol of o106 _0 219 0 424 0 876 424 _876 Jo al al ol ol o4107 _o 220 0427 0 879 427 879 i 4 0 _0 0 106 0 218 0 424 0 873 424 _873 J al 5 o_o 0 405 0 220 0 420 0 880 420 880 _ i dl 0 __0 0 108 0 220 0 433 _0 878 433 _ 878 J al ol o omo 0220 0 423 0 881 423 881 M af al ol o _0 107 _0 221 _0 429 __o 882 _429 _ a82 Jo al o ol ol o107 _o218 0 426 0 874 426 _874 do al io 0 o _0 105 _0 222 _0 420 __o 889 _420 _ 889 Background Page 70 Applications Examples Water Site Diex Diey CD4x Pitchax Cdum Pitchum CD _ _Pitch_ J ab nl ol ol o107 _o218 0 426 0 872 426 872 Jo al 12 ol of 0107 0 220 0 427 0 880 427 880 Where the last two columns show the original data from the mask shop Analysis of the Reticle SCATTER 1 10 DPI_RETICLEDATA Microns CD4x Pitch4 Collapsed Fiekd CD4x Raw Data Ponts 121 Waters 1 Fields 1 Sites 121 fed __Model_ Piston 0 1060 0 21
168. view of Weir Feature Modeling o Stage and sub assembly precision o Wafer stage and reticle platen tilt and bow corrections o Scan and Slit contribution to the error budget o Scan non linearity measurement o Wafer edge effects o Reticle loading effects o Feature sensitivity Process and Photoresist Process supported depth of focus and dose latitude o Process Window characterization o Best Focus across the exposure field o With Feature uniformity and Depth of Focus DoF o Film uniformity scatter tools o Line edge roughness uniformity o Across lot wafer and field feature profile uniformity Metrology o Measurement algorithm verification o Precision o Feature specific accuracy Automated Error Budget calculation An Overview of Weir Feature Modeling This section details the various models used for critical feature analysis and the methods of their application There are four basic sources that must be considered when analyzing feature response Variation from the reticle Process perturbations caused by bake cycles film thickness and reflectivity Perturbations caused by the substrate o it s transport mechanisms and electro mechanical interfaces such as the autofocus system o Wafer edge and edge bead Induced variations of the reticle scan stage o Exemplified by a pitch roll and yaw of the slit as it scans the exposure of the field Aberrations of the aerial image o Generated by the illuminatio
169. ware onto the same computer you will need to re enter the Installation Date and Confirmation ID Your confirmation ID keys upon The Installation Date The base hardware of your computer and The disk upon which the Weir Software is installed If any of the above three items are changed you will have to request a new Confirmation ID page 12 Installing the software and Confirmation ID 1 10 2005 Data Storage and Formats Data Storage and Formats Data Fundamentals Data Flow Raw metrology data direct from the tool must be imported and converted into the Weir PW data format The conversion is automatic and only requires the user to select the data file and the data source The conversion sequence will re format the data into the Weir PW Standard format specified later in this manual and save it into a Microsoft Excel workbook of the same name as the data set After the initial import the raw data file can be ignored or discarded All further Weir PW analyses use the workbook Workbooks of course can be re opened directly into Weir PW and handled like any other Excel workbook Raw data can only be imported using the Weir PW main screen Weir PW workbooks can be opened from the Weir PW main or the analysis screens Additional data sets are frequently generated by modeling These may include focus uniformity optimum feature uniformity or combined analysis sets These data sets can also be loaded into the Weir int
170. xamples on culling data using the Range and Sigma auto culling Additional uses for culling using the mouse to remove single point and field sites Background Applications Examples Often a small number of data points will be poorly measured because of metrology alignment or poor processing at the site These sites are not representative of the exposure tool nor the process and should be removed from consideration Poor metrology sites are easily identified during spatial plotting of the data Vector plots will contain points with very large or odd angled vectors will appear Contour plots will exhibit singularities similar to Figure 47 totally out of context with the remainder of the surface Weir PW offers several methods of analyzing and culling excluding poor metrology data points First the data range can be observed by creating a histogram of the data as shown in Figure 46 This Page 79 Data Culling Methods plot can be generated from either the Raw Data Metrology tab of the Main screen or from within the Spatial tab of the Weir PW analysis To generate the histogram you must examine either the raw data or the residuals to a modeled fit Modeled data will not display these data points While in the Spatial analysis interface select the Histogram for plotting Next click on the Model Components tab and turn off both the wafer and field models Finally click on the Wafer tab to the left of the display
171. y Weir PW provides tools to easily select the range of exposure conditions for the study setup the variables to examine and their control limits and define the modeled components to remove from the data to exclude the spatial influence of the wafer and individual field aberrations The type of analysis depth of focus dose latitude or process window is easily selected using the tabs located to the left of the graphic window Also the inclusion of one or any combination of points in the exposure field is easily selected using check boxes or direct selection of the field site by the mouse The process window analysis contains a number of graphic aids including the ability to select any nominal dose or depth of focus setting using slider controls and the easy display of multiple graphs Three analyses can be easily performed with Weir PW by selecting the three tabs to the left of the graphic window z Depth of Focus Exposure Dose Latitude and Process Window control surface calculation The interface shown in Figure 30 contains four setup tabs for the analysis Data Range Define the range of data and exposure conditions for the analysis as well as control of items to display data culling and field sites to include in the analysis Setup o Select the variable to include and specify their target values and control limits PW Control p Used for only the analysis of the formal Process Window q Select the format and grap
172. y order up to the 4 power can be added to any data curve Format Ordinate A B X C X D X E X The polynomial equation can be optionally displayed on the chart Polynomial equations are added as Messages and will then appear in the Messages tab for modification if desired The independent ordinate variable of the data is used as the label for the fitted equation polynomial The trend line is created when the Add command button is pressed and subsequently added to the Series listing of the graphic Select the trend line in the Series tab to modify the format color and weight of the curve Contour and 3D Surface Plot Controls Contour and 3D Surface plots are available in most interfaces When a contour or 3D Surface graphic is selected a new frame will appear The frames provide controls for optimizing the surface display the Interpolation frame and in some applications a selection of data variables for display the Plot Feature frame Both frames present options in the form or radio buttons that allow only one selection Sites plotted in these graphs must interpolate between measured sites to display the full surface Interpolation methods will vary depending upon the layout of measured sites on the surface that is some methods work better than others Interpolation Methods Provides three 3 selections for data interpolation Fast Medium and Modeled There is no wrong
173. ysis or residuals are viewed by using the tabs to the left of the graphics screen Statistics displayed at the bottom of the table reflect the type of data displayed Raw Fitted or Residual The models can be run with or without coefficient validation by selecting the Validation checkbox on the model section of the user interface When validation is selected coefficients that are less than 3 sigma times the value of the error in their estimation are considered to be undistinguishable from zero and are therefore returned to zero The model is automatically re run until all of the coefficients return significant or zero values This method of application results in improved prediction and setup for equipment control and minimizes the ringing over under shoot often seen in control algorithms The Weir applications do not use common least squares regression modeling found in most applications of the industry Least squares models force a value to every coefficient in a blind effort to minimize the residuals of the fit This method of application looks good when residuals are used as a metric of quality However it results in gross over or underestimation of the individual terms in doing so The application of the resulting coefficients to a control surface for the process or exposure tool then generates uncontrolled performance swings or ringing as the corrections of the current analysis attempt to compensate for those imposed by the previous
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