Version 4.0 User Manual
Contents
1. 00000assssaaaaaana nanasa 41 9 Installation and Calibration Procedure Checklist 43 9 1 Parts E C eE E S IAN ENG 43 9 2 Installation Procedure INANI NANANA NANANA nG 43 9 3 Training Procedure Checklist 1 44 10 INOW a AA APA AA PAPA ANA HAN 45 10 1 Version 4 0July 1 2002 mamamana nina aan 45 10 2 Version 3 2 June 30 2001 ccccesecceesesseeecesseeeceessneeceeesseececsnsessaneneeseeees 45 10 3 Version 3 1 March 45 2004 isccisisiiccss civicicsined ANAN ABANGAN a ka 45 07 17 02 AVI Photomask Metrology System User Manual 4 Version 4 0 1 Introduction 1 1 Overview The AVI Photomask Metrology System measures photomask defects and linewidths using images from a reticle inspection system or other microscope video source It provides highly accurate and repeatable measurements that are generally used to decide if a given defect or linewidth is large enough to require repair or disposal The system also maintains a database of measurements and allows an image of any measurement to be printed along with a report on the defect In addition to defects and linewidths the AVI system measures CD and edge uniformity corner radius butting error OPC sizes and maximum dimensions of large defects It also allows manual point to point measurements 1 2 How lt Works The AVI Photomask Metrology System uses the patented Flux Area Measurement technique to me2. e Lambda NA and Sigma unitless for the Stepper These are defined in the Custom Specs menu Ctrl U Multiple setups can be defined by entering different mask types then entering the values for each mask type in the Custom Specs menu These values can be modified manually they are reset when the program is restarted e Exposure arbitrary units This is set automatically to produce the CD defined in the Design CD parameter It can be adjusted manually The automatic value is restored when the Design CD is changed e Focus microns This defaults to best focus This can be adjusted manually The CD measurements and exposure are recomputed for each de focus value e Design CD clear and dark microns These values are computed from the mask image and can be modified manually The exposure is computed to produce 07 17 02 AVI Photomask Metrology System User Manual 22 Version 4 0 this CD in the simulator image The design values can be restored by clearing a manual value Measured CD clear and dark percent error These values are computed from the image at the defect position at the exposure which gives the design CD in the normal area Measured Contrast clear and dark percent error These values are computed from the image at the defect position These values are independent of the exposure and design CD KI value unitless This is computed on lines only It is the ratio of the defect size to the stepper opti
3. e To restore a saved calibration and setup select File Restore Calibration Select A to restore from the floppy or select another directory 07 17 02 AVI Photomask Metrology System User Manual 21 Version 4 0 4 AVI Stepper Simulator The AVI Stepper Simulator capability is an option Please contact your AVI sales representative for more information The stepper simulator function is normally activated automatically when a defect is measured Its display can be toggled manually by clicking the Simulator button The display can be zoomed in the same fashion as the main image Measurements CD and contrast are performed simultaneously for dark and clear lines so that the defect is dispositioned on the smaller more sensitive feature The parameter display box can be dragged so that it does not obscure the key part of the image The pixel intensity under the cursor is displayed in red when the cursor is on the simulator image It can be toggled between percent and absolute values by pressing the e0 key Simulator Source Steppe Lambda 0 48 0 248 NA 0 63 0 6 Sigma Exposure 37 4 gt Focus 0p a 23996 494 210 4 1 Simulator Parameters e Lambda microns and NA unitless for the Source image These are defined in the System Setup menu These values can be modified manually although changes made from the main screen are not saved to disk they are reset when the program is restarted
4. transformer using a short cable Either connection on the ground transformer can be input or output 8 2 Computer Setup Make sure there is a Photo32 icon on the desktop Copy the Photo32 icon to the Start Programs Startup folder 07 17 02 AVI Photomask Metrology System User Manual 37 Version 4 0 Set the computer s display properties to 800x600 or 1024x768 and 24 32 or 16 bits pixel in that preference order Using higher resolution makes the text and images too small for most users 8 3 Digitizer Setup ET Digitizer Setup Video Sot Comp C Vid M RS170 8 3 1 8 3 2 8 3 3 8 3 4 8 3 5 8 3 6 ince Contrast 34 mp Auto Ok 0 sro Brightness 34 4 gt Contr Cancel Rotate Lasertec i E m 313 PAL ExtPixCIkT TRT 30 SWinterlace Restore Stop Live Gray range 54 to 137 mean 117 3 St Dev 10 1 Too noisy Select File Digitizer Setup or Ctrl D Display a mask edge near the center of the image with large clear and chrome areas On KLA systems be sure the system is in review mode because alignment mode uses different video levels Click on AutoContrast and wait for the contrast and brightness controls to stop changing The Gray range should end up around 16 240 Click OK to save this setting You will need to enter the system password camera after you click on OK The password will remain active for the next 30 minutes or until you quit o
5. Best Measurements e Defects near geometry within about 0 5 micron need a reference image which is an image of a correct feature without the defect That image may be a new one from a different region typically an adjacent die or it could be the same image using a similar but non defective feature e When measuring several defects with the same reference as when measuring VeriMasks or doing a repeatability study on a singe defect use the VeriMask Mode To do this mark the relevant spot in the reference image ignore the measurement and then turn this mode on Now each time you mark a feature to measure it will use that specified reference image Note this checkmark is enabled by the Show Verimask Chk item in the system setup menu e With isolated holes or spots with no geometry nearby there can be an issue of determining the actual system contrast For example an image with a totally isolated spot has the intensity of full white but not full black In this case the AVI will use the most recently measured full black value e Be sure that you have measured an image with significant chrome area recently on the current mask If not you should move to a region with a chrome edge and measure it ignoring the result This will allow the AVI to measure the current intensity range The intensity range is displayed in the bottom left of the screen so you can see if there was any change 6 2 How the AVI
6. Metrology System is a commercial product and is protected by patents and strict copyright laws Any unauthorized distribution is illegal This manual and the software described in it are copyrighted with all rights reserved 07 17 02 AVI Photomask Metrology System User Manual 2 Version 4 0 X sintrod ction nsa ARI PA PANA mtn set lente ste wav ene a 5 1 1 ONEENVIEW 223225 eza bigaan A P use E NA EEE E E EE EE 5 1 2 aCA AAA LoT h C E E E E ATT EAEE 5 1 3 Specifications and Limitations 0x0000000000 a saasasasususususuaan 5 1 4 Environment paman NANA ABA area aree AAO E ANAN NAA ian inai 7 1 5 How the AVI is Used in Production 1 1 7 7 22222 ussasssususususssuusuwas 8 1 6 Typical Application Processes cccccceccceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeseeeeeeeeeeees 8 2 Measurement Fea UO S aaa 9 2 1 AVI Measurement Displays 9 2 2 Using the Measurement Statistics FUNCtIONS cccccceeseeeeeeeeeeeeeeeeeeeeeees 10 2 3 Other Items on the Main Screen ussnnsssnssnrnnnrnnnrnnnnrnnnnnnnrnnnnnnnrnnnnnnnnnnennne 11 T NGA 0 po AA AA AA E AA E PA 14 3 1 Calibration Description ssssssssssnnsnnnrnnnrnnnrnnnrnnnrnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnnn nnne 14 3 2 Monitoring Calibra non AA AA AA ANIAAAS 18 3 3 Calibration T60 Namana snaoisein Eaa a aeaaea aaea auaa Suia Sau EaP UaK anaE 18 3 4 Calibration Backup Save and Restore ssssssssnnnnr
7. Patent 5966677 File Yiew Mode Calibration Database Direction Reference 8 12 39 PM Review Images Automatic Zoom Simulator Measurement Summary 8000X Transmission O gf SEM Te 0 907 1 0 Ca een es Eva lang Measurement history Average of 1 901 std 0000 mo 000 g f Difference image 7 m Defect Image Um pai Intensity profile AT Measurement Region Display Grid f 50 microns Pixel range 175 0 44 to 219 89 9 6min Blur 0 48 PB 0 98 x 0 94 pm 16x15 pix at 237 210 Intensity 1 to 95 mean 34 0 sd 30 9 range 95 4 Pixel intensity statistics inside box Pixel intensity Pixel intensity Measurement range minutes since under cursor box size and last measurement position 2 1 AVI Measurement Displays e Input parameters Mask Type often renamed to Customer Reticle or Mask Name Operator The top value Mask type or Customer is a drop down list You can add new values by selecting the blank value and typing in the new value You can then enter custom specs and stepper setups in the File Custom Specs screen The other two values are recorded in the defect database for use in reports e Measurement Type Displays the measurement type Depends on the feature marked for measurement as described in Chapter 6 Two ambiguous cases linewidth vs butting error and contacts vs hole are specified by 07 17 02
8. as File Print You can setup the printer with File Printer Setup e Review Images This button brings up a screen for reviewing the database including a button for searching for specific measurements and saving them to a spreadsheet file See Database sections under Procedures 07 17 02 AVI Photomask Metrology System User Manual 13 Version 4 0 Contrast This button performs a contrast enhancement that makes small spots and holes more visible It has almost no effect on edge defects This can be used on live or saved images Zoom Clicking this button or right clicking on any spot in the image expands the image to make it easier to see and mark small defects Note that right clicking on the image centers the image on the spot you clicked VeriMask Mode Used for taking a series of measurements all using the same reference image Mark the relevant spot in the reference image ignore the measurement and then click this mode on Now each time you mark a feature to measure it will use that specified reference image Note this checkmark is enabled by the Show Verimask Chk item in the system setup menu 3 Calibration 3 1 Calibration Description This is critical information for getting good results from the AVI system Please read it carefully For best calibration results be sure that the digitizer gain is set correctly and that field correction is enabled if needed not needed on KLA and Lasertec systems The AVI has thr
9. less accurate measurements even SEM then the effective accuracy of the AVI will only be as good as the specification measurements Production Mask nspection parameters Defect image Specs Edge amp Isolated defects amp Min Contact Effective Size of Defect Defect CD OPC Report Over Under or Corner email or Spec Report paper 1 6 Typical Application Processes 1 6 1 Determine the maximum defect size specification Optimally a test mask is printed with the lithography process and the largest acceptable edge and isolated defects are determined along with a guard band based on the measured variability of the wafer and the mask measurements The mask defects are measured on the AVI so that the specifications are calibrated to the flux area size Frequently the specifications are already given and no testing is performed 07 17 02 AVI Photomask Metrology System User Manual 8 Version 4 0 1 6 2 Measure and disposition defects After inspection determine if defects are larger than spec requiring repair 1 6 3 Measure repairs Repairs often affect the quartz transmission in a fashion that inspection tools have difficulty detecting The AVI is very accurate for measuring CDs of repaired features 1 6 4 Monitor mask writers Measure corner radius and edge roughness to detect mask writer problems before they cause failures 2 Measurement Features avi Photomask Metrology System Version 4 00 0 U S
10. measurement is retaken with a new image Press Esc key to stop it before it s done To retake the measurement continuously in the same spot hold down the Shift key when you click on Rpt and press Esc to stop Automatic statistical analysis of the previous n measurements Mean standard deviation and range of those measurements are displayed below the n most recent measurements Display the values of all measurements used in the statistics useful when you re doing statistics on more than 5 values Right click on any of the individual measurement values Clearing Statistics Clear an individual bad measurement from the statistics by clicking on it The value is removed and the statistics recomputed Clear all measurements click on any of the 3 statistical displays average standard deviation or range or press the O key Saving Statistics to Other Programs Copy measurement history to clipboard File Copy Measurements Ctri C Save measurements to a spreadsheet file CSV format File Save Measurements Ctrl V 2 3 Other Items on the Main Screen 07 17 02 AVI Photomask Metrology System User Manual 11 Version 4 0 e Display of Previous values Average and Standard Deviation of recent measurements These are found above the measurement image on the main screen You can change the number of measurements that are averaged by clicking on the Average of box Up to five most recent values are di
11. po Marked Image Measurement Image Mark around a line end with OPC Serifs Three measurements are taken 1 The bulge area the area contained in the serifs is displayed as an effective diameter 2 The separation distance between the line end and the nearest line or line end This is a flux area measurement similar to linewidth so it takes into account any kind of excess chrome or dirt 3 Asymmetry the net shift of the line end up or down in this image due to excess or missing chrome on one side It is the distance the line end is shifted relative to the rest of the line in microns 07 17 02 AVI Photomask Metrology System User Manual 32 Version 4 0 To measure an OPC Serif on a simple corner measure the corner and use the corner radius measurement That corresponds to the effective serif area 6 12 Point to Point aaa Eee Pt Pt line 1 81 microns Marked Image Sample Measurement Display Point to point measurement is an assist for manual measurement Right click and drag between the points to measure The distance will appear in the box above the large image The distance is corrected with the XY Ratio calibration 7 Data Export Reports Database and Image Files 7 1 Data Export Copy Measurements to Clipboard Ctrl C Select File Copy Measurements The measurement history is copied to the clipboard This is the easiest method to get measurements into a spreadsheet Only the displayed measurements are
12. reproduce Low resolution inspection tool Easy to reproduce and closest to the stepper output d Stepper output or AIMS or Simulator A logical choice but different steppers will require different calibration offsets and only AVI systems have software to perform defect measurements to this calibration Non Linear Calibrations Conventional linewidth calibrations such as NIST and others based on NIST e g KMS and LWM are not based on optical transmission They generally report opaque lines 0 1 um wider and clear lines 0 1 um narrower than AVI For example a 2 micron pitch grid with SEM 1 micron lines and 1 micron spaces will transmit about 45 of the incident light instead of the expected 50 The SEM Correction allows you to derive SEM measurements from the AVI flux area measurements 07 17 02 AVI Photomask Metrology System User Manual 20 Version 4 0 3 4 Calibration Backup Save and Restore We strongly recommend that you make two copies of the backup on floppies keep one with the AVI tool and one at your desk These can be usedin case of a catastrophic failure of the AVI computer or to restore a new system to the old calibration Be sure to update these backups whenever you change the calibration rarely maybe once or twice a year e To save the current calibration and setup to a floppy or other file click on File Backup Calibration Select A to save to the floppy or select another directory
13. set to 5 larger values 8 are used with very low magnification around 7 pixels micron XY Ratio Ratio of scale factors in X and Y directions Normally set close to 1 0 The XY ratio will vary from 1 0 if the source video signal timing is not exactly the NTSC or PAL standard Most easily set in the Linear Calibrate menu Values of 1 02 to 1 05 are common on KLA installations Blur Microns Amount of blurring in image Usually 0 5 or 0 36 microns according to illumination wavelength Primarily affects red box size Second parameter specifically adjusts the red box height Always set to 0 5 unless image quality is very poor Third parameter is used to optimize dense line measurement Blur Pixels Used in opacity correction and XY measurement This is set with the Calibrate Opacity command after measuring a 0 3 0 5 micron chrome defect The defect size should be within 0 2 microns of the illumination wavelength This is approximately equal to Blur microns times Pixels per Micron Frames to Average Average images to reduce noise from vibration and noisy images Usually set to 10 The averaging occurs at 30 frames second so averaging 15 takes 0 5 second You may want to increase this when measuring very small defects or suffering from severe vibration Guard Band Amount added to defect measurements Used to assure that no overspec defect is passed due to mis measurement Spec Min Iso Dist Used with Show Specs belo
14. that you are giving a reference position not a defect to measure 07 17 02 AVI Photomask Metrology System User Manual 28 Version 4 0 6 4 Large Defects or Dirt Marked Image Measurement Image Mark the defect as usual by clicking and dragging diagonally across it The perimeter of large defects greater than 1 micron are traced and the maximum distance across the perimeter is measured and displayed This is used for measuring large dirt particles mostly on glass and pellicles This measurement is not used for defects lt 1 micron 6 5 Contact Holes Marked Image Measurement Image Mark the defect as usual by clicking and dragging diagonally across it The defect size will be displayed above the measurement image look at the Sq value below the Dia Square Root of Area This gives the effective size of square features such as contact holes VeriMask defects or other defects designed to be compared to their edge to edge size 07 17 02 AVI Photomask Metrology System User Manual 29 Version 4 0 6 6 Linewidth Critical Dimension and Line Uniformity Marked Image Measurement Image Linewidths also called Critical Dimensions or CD s are measured by marking across the line The average width in the marked area is calculated Note that if one line is too close to another then the reported measurement will be somewhat less accurate The linewidth uniformity is measured along the marked box It is d
15. 0 113 159 10 272 0351 079 10 272 0351 L075 5 59 10 272 0 113 159 0 353 0 512 158 10 353 Jo 194 i5a 10 353 o 433 oso p0353 0433 oso o0353 o512 158 10 353 Jo 194 p158 JEU E Seperate XY Seperate Clear _ ox _ Cancel SE a Linewidth Cals x Dark Corner Cals e Define a non linear calibration Calibration data can come from the following sources Verimask or SEM defect sizes PSL spot sizes AVI sizes from a different inspection tool design size from a test mask 1 Open the Non Linear calibration screen Ctrl N or Calibration Non Linear 2 Type in the name for the new calibration at the top 3 Type in the AVI measurements and the Desired measurements You can also use cut and paste Ctrl C and Ctrl V to copy values from Excel or a text file 4 Click OK The calibration button will then be visible on the main screen Click on that button to enable the calibration The button is pink when it is enabled and gray when the calibration is disabled e Create a SEM size calibration A Theoretical enter the correct wavelength and NA in the system setup menu and then click the SEM Defaults button The offsets will be calculated and displayed Then click OK B Experimental 1 Measure several clear and dark lines on a SEM and with the AVI 2 Determine the average difference between the AVI and SEM typically 0 125 u 3 Type Ctrl N or Calibration Non Linear to see the Non Linear Cal
16. AVI Photomask Metrology System User Manual 9 Version 4 0 selecting the type in the drop down box above the main image e Calibration SEM in the figure When enabled click on it all measurements are corrected as defined in the non linear menu e Dia Sq label for the Diameter and Square Root of Area below e Dia This is the effective defect area converted to a diameter It is the diameter of an opaque circular defect that would absorb or pass the same amount of light as the measured feature This is the most accurate and repeatable measurement and is the best predictor of defect printability e Sq Square root of the area This is a useful measurement for square objects such as contact holes e Opac Opacity This is the measured opacity or transmission of the defect 1 00 means perfectly opaque for a spot or chrome extension or perfectly clear for a hole or clear intrusion It is accurate to 5 for defects larger than 0 5 micron or 0 36 micron on UV images e CorDia Corrected Diameter This is the Diameter corrected for measured opacity A non opaque or non transparent defect absorbs light like a smaller opaque or transparent defect The corrected diameter is the diameter you might measure on a SEM or other measurement system The Diameter will correlate better to what prints on the wafer This value is not displayed if the Opacity is close to 1 0 e MaxDim Max Dimension The perimeter of large defects greater t
17. Determines What You Want To Measure When you mark a region the AVI uses the shape of the geometry in that region to determine the test to do Isolated defect or contact Edge or edge defect A square box requests a defect measurement Linewidth or butting error depending on selection at top Corner radius Geometry crosses two adjacent edges 07 17 02 AVI Photomask Metrology System User Manual 27 Version 4 0 mia OPC Geometry crosses one edge only 6 3 Spots Holes and Edge Defects 6 3 1 Measuring Defects Fr Marked Image Measurement Image e Mark the Defect by clicking and dragging diagonally across it Start and end in the middle of the defect s edges Do this carefully to reduce the frequency of retries e The defect will appear with a box drawn around it in the measurement image in the lower left corner of the screen e The defect size is displayed in the boxes above the measurement image if it measured successfully A record of the five most recent measurements is displayed below the Current size display 6 3 2 Using a Reference Image e Use a reference image for defects near corners or defects where the red box has a corner or angle in it e Mark the defect as usual by clicking and dragging diagonally across it but ignore the measurement e Find a similar pattern and CLICK do not drag on the spot corresponding to the defect location in this reference pattern The click tells the AVI
18. KLA system above then this step will be a verification that you selected the correct values Measure the pitch by drawing the measurement box across as many lines as possible If possible skip the first and last lines in a line set Those lines are slightly asymmetrical because they have a dense pattern on one side and none on 07 17 02 AVI Photomask Metrology System User Manual 15 Version 4 0 the other Cover as much of the length of the lines as possible to average out non uniformity in the lines View the Linear Calibration screen in the Calibration menu or Ctrl L and enter the design pitch Verify that the change is reasonable and press Use new scale Current Scale 5 25 New Scale 5 198 Change 0 99 Use New Scale Current XY Ratio 1 0000 Modify KY Ratio Linear Calibration should be performed on both vertical and horizontal lines for best results Measure one direction and set the pixels per microns then measure the other direction and set the XY Ratio The XY Ratio varies by about 2 on laser scan inspection tools because the scan rate for review mode is not controlled as carefully as for inspection On tools with regular cameras such as Aris I and microscopes the XY Ratio is usually exactly 1 0 The result of this calibration is the Pixels per micron parameter that can be seen at the top of the System Setup screen This calibration does not change from year to year unless t
19. N GARIN AG NA KANTA AGA 29 07 17 02 AVI Photomask Metrology System User Manual 3 Version 4 0 6 6 Linewidth Critical Dimension and Line Uniformity 2 2 30 6 7 Edge Roughness Edge Statistics 2 0 0 ccccccccssseeseneeeeeeeeeeeeeeeseeeeeeeeeeeeneenees 30 6 8 Butting Error and Line Position Uniformity 31 6 9 Pitch Measuremenb AN ENTNNIN ANAN NAN GATING NANANG 31 6 10 Corner RAIUS sei ccscsccccsscccsscvesieeessccecesecvecavatesconsected sevedavecs NAAAGNAS 32 6 11 OPC Optical Proximity Correction Measurement eeeeeeeeeeeeeees 32 6 12 Point to Poihti an KARA eia 33 7 Data Export Reports Database and Image Files 33 7 1 Data Export aha 33 7 2 Defect Repon ANAN ANAN E NG 35 7 3 Database Save Search and Output Data 111 1 222000202masananaaaaaaaaaas 35 7 4 Saving and Recalling Images 1111 2 707077 aaassaa 36 8 Setup and Troubleshooting eeeeeeeeeeeeeeneaaaanananananasann 36 8 1 Hardware Connections sciicciisicitcccessceesssscussscstcsessessssseceseccevecceasscarsssneesvesterss 36 8 2 COMPUTER Setup aaa AKA ousehisddacuudestsdecsisusvescetintsts 37 8 3 Digitizer Set p ua EBA AN 38 8 4 Field Correction Procedure seeeseeeseeeseeeseeesseeeseeeseeeeeeeseeeeeeeeees 39 8 5 Other Setup Parameters nl a amma aaa maan 39 8 6 Trouble Shooting and Diagnostics
20. The contact offset and area loss is displayed along with the contact size above the measurement image When the variation of reference contact sizes is above 3 a yellow warning message is displayed 10 2 4 Vibration Tracking Vibration in the live image is tracked and reduced This also operates during image averaging before taking a measurement This can be disabled by setting the Align Pixels value in the extended setup menu to zero 10 3 Version 3 1 March 15 2001 10 3 1 View menu This provides options for viewing pixel statistics in the selected region viewing the image with contrast normalized in the region or in false color Also provides a command to turn off the yellow warnings that intentionally obscure the measurement image Each of these commands has a key for easy access s for statistics n for normalize f for false color y for turn off yellow message 10 3 2 Reference Menu Allows you to mirror or rotate the image especially for aligning a corner for use as a reference The Restore command is used for restoring the original image especially after field correction of saved images 10 3 3 Non linear calibration menu Allows you to set up a SEM correction or other more complicated correction A button is visible above the 07 17 02 AVI Photomask Metrology System User Manual 45 Version 4 0 measurements when there is a correction set up Clicking that button will toggle the correction on all the visible v
21. Version 4 0 AVI PHOTOMASK METROLOGY SYSTEM USER MANUAL D Know for Sure E Automated Visual Inspection 952 S Springer Rd Los Altos CA USA Phone 1 650 941 6871 Fax 1 650 941 4821 Website www aviphotomask com Email info aviphotomask com 2002 Automated Visual Inspection all rights reserved 07 17 02 AVI Photomask Metrology System User Manual Version 4 0 Credits The AVI Photomask Metrology System is copyright 1995 2002 Automated Visual Inspection AVI It is also protected under U S and foreign Patents This manual is copyright 2002 Automated Visual Inspection All rights reserved The AVI Photomask Metrology System is a trademark of Automated Visual Inspection The magnifying glass logo and Know For Sure are trademarks of Automated Visual Inspection All other brands and product names are registered trademarks of their respective holders Automated Visual Inspection 952 South Springer Road Los Altos CA 94024 USA www aviphotomask com email info aviphotomask com Phone 1 650 941 6871 Fax 1 650 941 6871 Disclaimer Great effort has been made to ensure that this product operates according to its specifications However Automated Visual Inspection makes no warranty of any kind with regard to this software and shall not be liable for any consequential incidental or indirect damages incurred through the use of this software and hardware Copyright and Distribution Notice The AVI Photomask
22. alues Use Calibration Non Linear Calibration to set up the correction See the help in the screen 10 3 4 Contact Position and Statistics Selectable from the drop down measurement type menu When selected a larger region is analyzed allowing a contact s size and position to be compared to the ones around it The relative area and offset compared to the contacts around it or a reference image are displayed in the box above the main image The statistics of the surrounding contacts Area range and standard deviation is displayed in the box below the main image 10 3 5 Isolated Defect Distance from edge When an isolated defect is within 1 micron of an edge the distance from the center of the defect to the edge is displayed in the box below the main image Note edge to edge distance is not used because the edge of a small defect compared to the wavelength of the illumination is not really measurable 07 17 02 AVI Photomask Metrology System User Manual 46
23. aseline outside the bump should have at least a little bit of flat area on both sides No flat area in the baseline is caused by features near the measurement area corners or angles Nearby straight lines won t cause confusion If the blue and red boxes are ok but the profile is poor a reference image should be used If you re measuring with a reference image then the difference image at the top of the measurement image should show just the defect If other details show up with nearly as much contrast as the defect then the measurement is probably not accurate The other details are contaminating the measurement 5 4 Retaking an Invalid Measurement Retake the measurement being more careful in marking the defect region Try using the Zoom feature If the red box is lined up wrong not parallel to the adjacent line click on the Direction menu and select the box direction that should be used If there is too much clutter use a reference feature find a suitable reference and then click on a spot that corresponds to the center of the defect that you re measuring 07 17 02 AVI Photomask Metrology System User Manual 25 Version 4 0 5 5 After the Measurement e Average multiple measurements to reduce noise click on the Rpt button after a good measurement has been taken The measurement will be taken the selected number of times with new images and the mean standard deviation and range of the measuremen
24. asure the amount of light absorbed by a dark feature or transmitted by a clear feature It takes an image from an existing microscope and generates a reference image of the region around the defect as if the defect was not present It then computes the difference in total light between the real image and the reference image This is the light flux that was absorbed or transmitted by the defect The flux is proportional to the effective area of the defect That area is converted to a diameter and displayed Conventional systems measure the edge to edge size of a feature This does not directly correlate to effective area and does not accommodate partially opaque regions 1 3 Specifications and Limitations 1 3 1 Accuracy The AVI system accuracy has been tested in several studies by comparing AVI measurements of design defects on test masks to wafer prints measured with SEM Average deviation between the AVI measurements and wafer CD errors is 3 nm on the wafer which is the repeatability of the wafer SEM measurements By comparison SEM measurements of the test masks show about twice as much deviation from the wafer measurements compared to AVI flux area size 07 17 02 AVI Photomask Metrology System User Manual 5 1 3 2 1 3 3 1 3 4 1 3 5 1 3 6 Version 4 0 Repeatability A typical system using images from a KLA353uv will provide rms repeatability of 5 nm for defects larger than 0 2 microns and 6 8 nm for defects smalle
25. cal resolution Low K1 features are the most difficult to print correctly When clear and dark lines are measured the K1 of the smaller of the two is computed 4 2 Linewidth Error Measurements The image is rotated as needed and the dark and clear linewidths are measured at the defect and nearby for a reference value If a line is very wide it is not measured and its width is not displayed The peak intensities dark and clear are measured adjacent to the defect and at the location of the reference value If you click on a separate reference location the new location is used as the reference This will give spurious CD errors if the wrong reference feature is selected 4 3 Contact Error Measurements Simulator Exposure 39 4 Jel Focus1 0p 4 gt Design Measured J CD width Contrast Dark 42 3 Contacts in the region that was marked are located and measured By default the closest six contacts are used as references for CD and contrast If you click on a contact that single contact is used as the reference Click away from a contact or on the image edge to restore the automatic reference average of nearby contacts Very faint contacts are not measurable because they are too small to print or detect 07 17 02 AVI Photomask Metrology System User Manual 23 Version 4 0 5 Standard Measurement Operation Summary Put the defect to measure near the center of the image Make sure that t
26. e and source 07 17 02 AVI Photomask Metrology System User Manual 34 Version 4 0 7 2 Defect Report The Defect Report contains both large and measurement images the inspection summary and the detailed measurements e Printing the Report Click the Print button on the Main screen or select File Print For printer setup select File Printer Setup e Sending the Report via E mail Select File Send Defect Report and a screen capture will be put in your mailer ready for you to type in the address and a comment This requires that the AVI system be connected on your network and that your company s mail program is installed on the AVI system 7 3 Database Save Search and Output Data The AVI system includes a defect database which allows you to save defect images and their measurements for later review and statistical analysis e Save a measurement to the database press F2 or Database Database Save to bring up the database save screen Enter your comments and press Save to Database Note that this box will come up automatically after each measurement when the Database Database Auto Save is checked e Move through database Press the Review Images button to see the Review screen Press the f key to move forward quickly and press the r key to move in reverse quickly You can also press b to move to the beginning of the database and e to move to the end Mask ID C photo32 a8
27. e images for 12 seconds and then save and display the correction image 3 Test the correction Press F7 to capture a new image and correct it View it in false color it should be totally uniform If not capture a new image Ctrl F7 and try again 8 5 Other Setup Parameters Tool Name Tool name Displayed on main screen if there are multiple calibrations and saved in database and defect report Instructions Reminder information Typically 4x2700 Transmission for KLA3xx at 4x Displays above the main image Target Dia microns List of diameters of circular targets in microns using Pixels per Micron value below For concentric circles separate values by commas for example 4 10 15 Some installations on Nikon inspection tools use target circles to help the operator position a defect in the same position each time To enable them enter a value such as 2 in this entry and then check the display target check box on the main screen below the measurement image Then click on Live 07 17 02 AVI Photomask Metrology System User Manual 39 Version 4 0 Smoothing Smooth image set to 4 for KLA 4x Electronic Magpnification Set to 1 for other tools without electronic magnification On Lasertec systems set to 2 to reduce the affect of the edge enhancement used in those systems Pixels per Micron Scale factor Used to convert computed pixel sizes into microns The second parameter height is normally
28. ee levels of calibration 1 Linear Calibration required o Performed using pitch measurement only or using specified resolution from KLA inspection tool o Matches the AVI parameters to the optical system it is being used with o Set at installation remains set until the optical system is modified o Typically takes 5 to 15 minutes 2 Nonlinear Calibration optional o Multipoint correction for spots holes edges dark lines clear lines and contacts o Matches the flux area measurements to an existing standard such as SEM Verimask measurements PSL sizes KMS measurements etc o Set at installation remains set until the optical system is modified or the reference system changes o Typically takes 1 hour if the reference values are available o SEM correction values can be calculated automatically 3 Intensity Calibration required o Determines the observed intensity levels for dark and clear regions on current mask and current illumination 07 17 02 AVI Photomask Metrology System User Manual 14 3 1 1 3 1 2 Version 4 0 o Performed by measuring an edge between clear and dark areas larger than 1 X 1 micron o Must be performed at the start of each new mask Typically takes 30 seconds to 2 minutes Automatically performed any time a measurement is made near large dark and or clear areas Initial System Parameter Setup The AVI has preset calibrations for many optical systems in the extended system se
29. ement 6 9 Pitch Measurement Marked Image Measurement Image Mark across several lines The pitch center to center spacing between the lines will be measured and displayed In addition the width of the dark and clear parts are calculated based on the total average transmission and displayed The pitch measurement is independent of mask processing parameters except scale so it is frequently used to check system calibration 07 17 02 AVI Photomask Metrology System User Manual 31 Version 4 0 6 10 Corner Radius eit Marked Image Measurement Image Mark a corner and its radius and missing area are displayed The actual light getting past the corner is compared to the amount expected from a perfect corner extrapolated from the edges The top image in the measurement image is the difference between a perfect corner and the measured image after being blurred by the imaging system s optics Usually it appears as a simple blur because the radius of curvature is smaller than the blurring of the optics The difference is displayed as a radius or square root of the missing area It is also displayed as the effective radius of the corner If you then click ona reference corner then the difference is simply displayed as an edge defect The absolute radius of a referenced corner can t be calculated because the radius of the reference image is not known 6 11 OPC Optical Proximity Correction Measurement md
30. er than 2 micron 9 3 Training Procedure Checklist D DO oO DODO U o oO O Each of these items is explained in the manual Digitizer setup Field Correction Only for Aris and camera imaged systems Linear Calibration using known pitch Perform Measurements Spot Hole and Edge Defects Spot Hole and Edge Defects using a Reference Large Defect or Dirt Contact Hole Linewidth CD CD Uniformity Edge Roughness Pitch Measurement Corner Radius Butting Error and Line Position Uniformity Point to Point Non linear Calibration Save and Restore Calibration backup to floppy Measurement Statistics Use the defect database save review search output to Excel file U O O DO DD DO 0 0 0 0 07 17 02 AVI Photomask Metrology System User Manual 44 Version 4 0 10 New Features 10 1 Version 4 0 July 1 2002 10 1 1 Stepper Simulator 10 1 2 Improved non linear calibrations added corner and separate X and Y linewidth calibrations 10 2 Version 3 2 June 30 2001 10 2 1 Save Measurements to Spreadsheet You can quickly save data to a spreadsheet after a measurement you can save the history of measurements 3 or 5 or whatever you have it set to to a CSV comma separated values spreadsheet file using the File Save Measurements Ctrl M command 10 2 2 Pixel Value Display The intensity under the cursor is displayed in a box below the left corner of the main image 10 2 3 Improved Contact Statistics
31. f the video filter box Four of the five outputs are connected to the monitor 3 RGB plus Sync The signal to AVI is T ed from the one remaining output On ETEC Aris l tools take the video out from the video monitor If an older KLA has a video output connector on the back panel use that If not e Connect a BNC T to the video input going through the bulkhead to the Sun There are 2 BNC s going through that panel The thin one is the video They re both labeled This cable is often accessible at the back of the main chassis On some units the cable is accessible inside the lower center panel at the back e Route the video cable If the AVI will be on the right side of the KLA then open the right side door too and thread the cable across the floor of the KLA e Use 3 5 cable ties inside the KLA to attach the cable neatly to the chassis e In most cases you will run the cable out the door where it will get slightly pinched Sometimes you can find a hole to run it through Ground Transformer In many cases a Ground Isolation Transformer is required if there is too much noise on that input due to a long ground loop between the AVI and the inspection tool This can be seen in the Digitizer Setup screen When the stdev value is above 1 5 with a uniform image and a small 1 2 active area then you should consider using a ground transformer Ground transformer connection The signal is passed through the ground
32. g into account the optical effects of edge slope This correction is available in the Nonlinear Calibration screen Another consequence is that SEM measurements of isolated defects spots and holes are significantly inaccurate compared to the effect seen in a 0 13 micron process wafer The error is typically 0 2 microns This was measured by comparing the wafer linewidth variation caused by isolated defects near an edge See Improved Method for Measuring and Assessing Reticle Pinhole Defects for the 100nm Lithography Node by Darren Taylor Anthony Vacca et al presented at SPIE Photomask Japan April 2002 A third consequence of this is that all optical feature measurements will vary depending on the optical resolution For example there is typically a 30 nm difference between an edge defect s measured size from a KLA blue light 25 micron pixel inspection system and a KLA high resolution 15 micron pixel system This means that a mask shop with various inspection tools or with customers using a range of inspection tools must use a uniform calibration corrected to a single mask or inspection tool The difference between optical and SEM line widths is accommodated in the lithography process by adjusting process line widths and exposures However defect sizing is not treated as carefully in lithography process definitions If it were then the spec for maximum pinhole size would be about 0 5 micron larger than the spec for maximum
33. h defect type The defect will appear with a box drawn around it in the measurement image in the lower left corner of the screen The defect size is displayed in the boxes above the measurement image if it measured successfully A record of the five most recent measurements is displayed below the Current size display Use a reference image if needed corner defects or defects where the red box has a corner or angle in it e Mark the defect as usual but disregard the measurement 07 17 02 AVI Photomask Metrology System User Manual 24 Version 4 0 e Find a similar pattern and CLICK do not drag on the spot corresponding to the defect location in that reference pattern The click tells the AVI that you re giving a reference position not a defect to measure Click on the Rpt repeat button to average several measurements to reduce noise 5 3 Determining if a Measurement is Valid After making a measurement check these things Make sure that the blue box surrounds the defect you re measuring Make sure that the red box lines up parallel to adjacent lines if any Make sure that the difference Image at the top of the measurement image looks like the defect you re measuring usually just a dark or bright spot Make sure that the profile displayed on the image looks like a bump ona flat line the bump may go up or down where the bump s width corresponds to the defect or linewidth The b
34. han 1 micron are traced and the maximum distance across the perimeter is measured and displayed This is used for measuring large dirt particles mostly on glass and pellicles Sometimes a medium size defect will display an overly large value here because it is affected by surrounding detail The measurement image will display the perimeter in green and the location of the maximum dimension in red 2 2 Using the Measurement Statistics Functions There are several functions available to help you get better measurements using Statistics 2 2 1 Measurement History and Statistics e By default diameter measurement history and statistics are displayed in the statistics section To display history and statistics for another measurement such as Opacity click on the desired measurement This 07 17 02 AVI Photomask Metrology System User Manual 10 2 2 2 2 2 3 Version 4 0 applies to all measurement types such as corner radius and OPC Setting the number of measurements to analyze click on the Average of n box History displaying of the last n measurements The last 5 measurements are displayed Additional measurements can be seen by right clicking on any of the individual values Retake a measurement in the same location Right click on the Rpt button or press the Enter or R key Automatic collection of n measurements press Rpt button All previous measurements are cleared and the most recent
35. he inspection tool type in the machine name verify the Instructions and customize the displays Customize button See Other Setup Parameters for details Validate calibration using lines of known pitch Set up non linear calibration as needed Perform Opacity Calibration Measure a 0 4 0 6 micron defect then select Calibrate Opacity Calibration Perform repeatability test 20 measurements of a 0 3 0 4 micron defect One sigma deviation should be 002 micron 2 nm or less 1 2 nm is expected Try increasing of images to average in the system setup menu if deviation is too high To change the of measurements included in the 07 17 02 AVI Photomask Metrology System User Manual 43 o Version 4 0 measurement statistics click on the Average of __ label and enter a new number Complete Windows setup Set a password for Windows and or the screen saver if desired Start Settings Control Panel Passwords Windows Password Sometimes it gives you the option to make it the same as screen saver password highly recommended Set the time and time zone double click on the clock at the bottom right of the desktop Remove NetBeui network driver clean up the desktop remove icons for network services Backup calibration keep one copy make another copy for the customer Acceptance testing measure all the edges spots holes in a VeriMask Compare to design size Demonstrate repeatability on defects bigg
36. he optical system geometry is modified Non Linear Calibration Procedure Please read the following section on calibration theory You can define any number of calibrations corresponding to measurements from other tools depending on your customers needs Each non linear calibration defines separate size mappings from AVI to the reference sizes for spots holes extensions intrusions dark lines clear lines and contact area ratios Each measurement type can have 0 16 separate points defined for each measurement type Each point is an AVI size and the corresponding desired size Multi point calibrations allow you to duplicate measurements from non linear metrology techniques most frequently this is used to duplicate Verimask and PSL sizes Click on the Help button in the Non Linear Calibration menu for instructions for entering the correction points AVI Corrected size pairs 07 17 02 AVI Photomask Metrology System User Manual 16 Version 4 0 ij Non Linear Calibration ioj x n Standard Calibration Name SEM x SEM Defaults ae eal x pit x Help b SEM m Calibration Tables z KLA uvhr 15p z Hole Spot Intrusion Extension KLA uv 186p Dark Line Cont AVI DesiredDiff AVI DesiredDiff AVI DesiredDiff AVI DesiredDiff KLA Blue 25p ff AVL Desired Diff AVL Des 0 000 0 000 pooo pooo o 000 O00 foo pooo pooo fonao 0 000 poog stepper 13 nm Prong fooga fo ooo pooo 0 000 foo 0 272 10 431 159 10 272 1
37. he reticle inspection tool is set to the proper magnification and default contrast and brightness Enhance the image using the Zoom and Contrast buttons if the defect is difficult to see Measure the defect usually by clicking and dragging the mouse diagonally across it see The Different Defect Measurements section for details on measuring each defect type Check the measurement image for proper measurement Retake measurement if needed by marking the defect more carefully Or mark a reference image point if needed when the profile doesn t have flat baseline regions near both ends Read the measurement off the screen 5 1 Capturing and Enhancing the Image Click on the Live Image button Click on the Zoom button if necessary Right clicking on the defect produces the same effect and centers the image where you clicked Click on the Contrast button to enhance an isolated defect This is useful only on isolated defects it has no effect on edge defects 5 2 Measuring Defects Be sure that the Reticle Inspection System is set to the correct magnification and the default contrast and brightness Be sure the desired calibration is selected Mark the Defect usually by clicking and dragging diagonally across it Try to start and end in the middle of the defect s edges Doing this carefully will reduce the frequency of retries see The Different Defect Measurements section for details on measuring eac
38. ibration screen 4 Click on SEM Defaults and enter the difference offset for your system 5 Click OK e Create a size calibration to other optical system A Theoretical Click the drop down box labeled Standard Calibrations Select an existing calibration or Other to enter the wavelength and NA of the target system The theoretical values will be entered B Experimental 1 Measure two instances of each feature type on the target system the smallest and largest considered significant and record this Desired size 2 Measure those same features on the current system and record the AVI 07 17 02 AVI Photomask Metrology System User Manual 17 Version 4 0 sizes 3 Enter those sizes in the given columns Keep zeros on the top row to insure that very small features never come up as negative size e Separate XY Linewidth Calibrations Enable this only if you are duplicating linewidth measurements from a KMS or Leica metrology system these systems give different measurements in the X and Y directions e Separate Clear Dark Corner Calibrations Enable this only if you are calibrating corner defects to Verimask corner sizes 3 1 4 Intensity Calibration Procedure e Accurate flux area measurement require accurate measurement of the illumination intensity In laser scan images such as KLA or Lasertec inspection tools the illumination is very stable and only needs to be measured at the start of meas
39. iew However the printability of a feature larger than about 2 wavelengths corresponds to its shape more than its area so conventional edge to edge measurements are usually used for precise sizing of large features larger than about 0 8 micron The AVI will accurately measure the defect s area but in some cases point to point measurements may be more useful The AVI measures the Maximum Diameter of large defects such as glass and pellicle side particles It also allows two click point to point measurements on the live image Allowable Backgrounds Isolated and edge defects can be measured with one click when a corner is not in the immediate area The immediate area is defined as twice the blur distance which is 0 4 microns on visible light systems and 0 3 microns on UV systems This is the size of the red box in the measurement image If there is a corner too close to the defect indicated by the profile in the measurement image not having any flat baseline a reference image 07 17 02 AVI Photomask Metrology System User Manual 6 Version 4 0 should be provided see the procedures section This is because the AVI system figures out what the image would look like if the defect was not there When the background consists of straight lines this is easy However corners can not be interpolated because their intended radius of curvature is unknown so a reference image defines correct Note that using a reference image wil
40. ipg Operator fe and Type Intrusion Date Time 12714701 3 59 00 AM Test Tool Tool 1 Delete Img T Dia sarA Opac CorDia Ht axDi 11 543 1 367 1 00 1 54 0 00 Comments Compact Database n All Records Al Records Database egesna n E e Search Database On the Review screen press the Database Search button Enter any search parameters you want in the left side and press Search Select the data types to display in the Search Display selection box Basic Data All Data Calibration Data or Custom Data You can modify any display by dragging the line between columns in the title row and pressing the Reset Columns resets the display to its default You can save your modification for reuse by pressing Save Display 07 17 02 AVI Photomask Metrology System User Manual 35 Version 4 0 Database Search Mask ID Search Cang Operator em Comment Search Display Basic Data x Reset Columns Save Display Deed Save to Spreadsheet Search Results 1 records found Delete Rows CalibSize Pa Waa o Bas bk 15428 Intrusion 12 14 01 59 00 AM Caohato lii e Save selected database data to Excel file CSV format readable by any spreadsheet program Display selected data in the Search screen see above You can now save the display to a spreadsheet file by pressing Save to Spreadsheet You will be prompted for the file name and location When reading this fi
41. isplayed as a standard deviation and a range The linewidth profile is displayed on the measurement image in green This helps you judge if a CD measurement is meaningful For example if the deviation in the area of the measurement is 30 nm then the meaning of the least significant digits is questionable 6 7 Edge Roughness Edge Statistics en Marked Image Measurement Image Mark a long segment of an edge The roughness is measured and displayed as a standard deviation and a range and the edge profile is displayed on the measurement image in green The line must be exactly horizontal or vertical To measure an edge defect make the box square Although edge roughness offers another way to measure edge defects the edge defect measurement s effective diameter will correlate best to what prints on the wafer 07 17 02 AVI Photomask Metrology System User Manual 30 Version 4 0 6 8 Butting Error and Line Position Uniformity Marked Image Measurement Image Select Butting Error from the drop down selector above the main image and mark the area around the butting error When you select Butting Error the two linewidth measurement boxes are offset by one blur distance usually 0 5 or 036 microns and the distance between their centroids is measured and displayed The line must be exactly horizontal or vertical Butting error is the only measurement that requires selection to distinguish it from linewidth measur
42. k the Show Specs box and press OK To set the specs for each mask type click on any of the spec displays above the main image The Customer Specs screen will appear Set the Spec Min Iso Dist minimum isolated distance This is measured from the defect center to the edge Defects closer than one blur distance 0 5 micron for optical systems and 0 36 microns for uv will always be considered edge defects because the distance to the edge cannot be accurately measured e View Menu This provides options for viewing pixel statistics in the selected region viewing the image with contrast normalized in the region or in false 07 17 02 AVI Photomask Metrology System User Manual 12 Version 4 0 color Also provides a command to turn off the yellow warnings that intentionally obscure the measurement image Each of these commands has a key for easy access s for statistics n for normalize f for false color y for turn off yellow message e Specifying a direction to measure Top menu line This lets you override the automatic measurement direction logic Use it if the red box in the measurement image isn t parallel to adjacent lines Retake the measurement after setting this This is reset after each measurement unless you set the Direction Don t Reset item The direction menu also allows you to turn off image rotation if the image is being rotated when it shouldn t e Reference menu Allows you to mirror o
43. l increase the noise in your measurements because you are adding the video noise and edge roughness from the two images 1 4 Environment The AVI Photomask Metrology System operates from a standard video signal provided from a KLA Terastar Lightning KLA 3xx KLA 2xx DRS I DRS 2 Lasertec or other similar machine called the Test Tool The AVI machine consists of a PC computer running Windows 98 equipped with a high quality video digitizer system and the software The system comes with a built in 10 100 Ethernet adapter The software can also be run under WinXP or Win2000 07 17 02 AVI Photomask Metrology System User Manual 7 Version 4 0 1 5 How the AVI is Used in Production The AVI Mask Metrology System is primarily used to improve defect disposition to improve the decision of what to do when defects are found during mask inspections To get maximum value from the AVI metrology system s excellent accuracy and repeatability it should be used to help define the defect acceptance specifications as well as for measuring defects in production Ideally a test mask with designed defects such as a VeriMask is printed on a wafer The smallest design defects will not print on the wafer The largest defect that does not cause a misprint on the wafer is considered to be the largest acceptable defect on masks for this process Typically there are separate specs for edge and isolated defects If the specifications were defined based on
44. le into a program such as Excel you may need to specify the file type as CSV Usually you can just select all files and Excel will recognize the CSV format e Printing database image and information In the Review screen click the Print button 7 4 Saving and Recalling Images e Saving Images to Disk Select File Save Image File or type Ctrl S You will select the image type JPG is the most compressed format thus easiest to copy to floppy The compression will not detectably affect images from Reticle Inspection Systems Then give the image a filename e Recalling Images from Disk Select File Open Image File or type Ctrl O This allows you to read in an image that wasn t saved to the database Note that if the image is from another system the calibration may be incorrect 8 Setup and Troubleshooting 8 1 Hardware Connections 8 1 1 Standard computer connections e Monitor keyboard mouse and power These are the same as with any PC Be sure that the voltage switch on the back of the computer and sometimes the monitor is set properly to 120V or 220V If there is any doubt start at 220V 07 17 02 AVI Photomask Metrology System User Manual 36 8 1 2 Version 4 0 Video Input Standard NTSC or RS 170 video is received from the inspection tool via a BNC coax cable The cable connects directly into the BNC connector on the AVI PC On KLA Terastar and Lightning tools take the signal of
45. ng towards the chrome thickness This means that sometimes the chrome is not cleared out of the bottom of features and it means that if a chrome edge is not vertical its slope will cause a significant reduction in light flux through a clear feature For this reason since 1999 there has been increasing debate about measuring the top middle or bottom of chrome edges in SEM measurements 07 17 02 AVI Photomask Metrology System User Manual 18 Version 4 0 3 The optical size of a feature is different than its physical size Imagine a grid of 1 micron lines and spaces pitch of 2 microns with 100 opaque chrome and vertical edges You would expect to measure exactly 50 total light transmission through the grid In fact the transmission is less because light that passes close to the chrome edges is diffracted away from the microscope lens making the chrome lines appear wider and clear lines narrower This effect is called edge diffraction The optical size of a chrome line is approximated by OLWdark PLW Ores 2 where OL Wdark is the Optical linewidth of a dark line PLW is the physical linewidth e g measured with a SEM and Ores is the optical resolution Ores 0 61 wavelength NA known as the Rayleigh limit The size of a clear line is the complement OLWclear PLW Ores 2 One consequence of this is that we can estimate the SEM size of a line accurately from its optical absorption takin
46. nnectors e Run the test program C Flashbus FBG FBG32 exe If you see an image here but not in Photo32 then check the Digitizer Setup e f the video connections are good and even FBG32 exe doesn t show an image then try swapping the video capture board Contact AVI Can t see dim holes even when using contrast command e Increase the brightness of the AVI monitor Measurements are erratic e Make sure you are marking the defects correctly e Make sure that the Reticle Inspection System contrast and brightness are set to their defaults e Make sure that the RIS is operating at the proper magnification and that the Pixels per Micron is correct in the System Setup 07 17 02 AVI Photomask Metrology System User Manual 41 Version 4 0 Measurements have started coming up wrong e Check that magnification is correct e fa maintenance operation was performed on the inspection tool then AVI may need recalibration e Make sure that the contrast and brightness on the inspection tool are being set to normal for all measurements Error message comes up on the AVI screen or the computer hangs doesn t respond e Ignore it press OK e Reboot the computer Win98 should be rebooted at least weekly e lf it returns consistently then reboot the computer If it still comes up consistently contact your local PC maintenance team e f your PC expert says the PC is ok then contact AVI 07 17 02 AVI Phot
47. nnnrnnnrnnnnnnnnnnnrnnnnnnnennne 21 4 AVI Stepper Simulator 000 000maaaananananananasasaaaannaaanaaanaaasaaaananann 22 4 1 Simulator Parameters mai aaae aaa eaa a aD aa aeae apea aaa apanata aia raia 22 4 2 Linewidth Error Measurements eesseesseeseeeeeeeeeeeeeeeeeeeeeeeeeeeeeees 23 4 3 Contact Error Measurements s usssrsssrnnnrnnnrnnnrnnnrnnnrnnnnnnnnnnnnnnnnnnnnnnn nenne 23 5 Standard Measurement Operation Summary 24 5 1 Capturing and Enhancing the Image cccccccceeseeeeeeeeeeeeeeeeeeeeeeeeeneneeeeeees 24 5 2 Measuring Defects minana AANGAT ANAN 24 5 3 Determining if a Measurement is Valid 25 5 4 Retaking an Invalid Measurement 25 5 5 After the Measurement uu LL aaa naaa awww ww ww anan K KKK KKGKKKKKKK ABAKA SAKN SAKA SKN nannamamma 26 5 6 Testing with VeriMask and VeriThoro Masks eseeeeeeeeeeeeeeeeeeeeeeeeees 26 6 Measurement Procedures eeeeeeeeeeeeeenenenanasnnananasasansnonn 27 6 1 Getting the Best Measurements cseseeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeneeeeeneeeeeeees 27 6 2 How the AVI Determines What You Want To Measure 2 2 27 6 3 Spots Holes and Edge Defects 11 11 0 0 00mumuuuuuuuunaaaaanananunanunanunaaaanaaana 28 6 4 Large Defects r Dikbamanaaiaaai NA AA 29 6 5 Contact Holes LANANG N NINKINA
48. omask Metrology System User Manual 42 Version 4 0 9 Installation and Calibration Procedure Checklist 9 1 Parts List o Oocooocvo oo oO DO 00 AVI PMS Computer with software security key Monitor or monitor switch box and cables if multiplexing existing monitor Keyboard mouse power cord for appropriate country Printer if purchased CCD Camera KLA 219 DRS Nikon AM6 plain video User Manual plus training page on cleanroom paper Video isolation transformer Video cables 75 ohm 1 3 10 15 BNC barrel connectors 2 BNC T connector S Video to BNC cable if 2 camera inputs KLA 219 DRS plain video Backup floppy disks AVI Tool Kit Small monitor for adjusting focus amp rotation KLA 219 DRS plain video 9 2 Installation Procedure o o Install computer monitor keyboard mouse make sure it starts Install camera KLA 219 DRS Nikon AM6 plain video gain offset range should be 16 240 10 Nikon AM6 adjust focus Typical adjustment is to screw on just one thread with out the 5mm C mount extender rotation Load a VeriMask plate into the KLA or other system get it to review mode Connect the video cable and Video isolation transformer as described in the section on hardware setup Adjust digitizer gain with image of an edge in review mode Take Bright field image For Aris and microscope based systems only In the System Setup screen click on the setup for t
49. pindot size in the same process Because process definitions still define a single isolated defect spec and a single edge defect spec the defect measurement system calibration must adjust for the edge diffraction effect in the stepper 3 3 2 Conclusions 1 The optical size of mask features are different from their physical ideal SEM size 07 17 02 AVI Photomask Metrology System User Manual 19 3 3 3 Version 4 0 The optical size of mask features must be corrected for edge diffraction to allow comparison between machines with different optical resolution The difference between the optical sizes at various resolutions including SEM infinite resolution is a constant offset for all feature sizes The offset does vary with shape edge defects have approximately 75 the offset for lines and isolated defects The AVI system will calculate the theoretical size correction to SEM infinite optical resolution other inspection systems or to the stepper resolution Because the flux area measurement is very linear a correction can also be made by measuring a particular defect of each type on all systems whose measurements are to be matched and using the Non linear calibration to match them There is a trade off in deciding what so use for a calibration standard a SEM Intuitive and fairly easy to reproduce but farthest from the stepper output b High resolution inspection tool Intuitively good easy to
50. r rotate the image especially for aligning a corner for use as a reference The Restore command is used for restoring the original image especially after field correction of saved images e Display Grid on measurement image Below the measurement image You can display a grid adjust its spacing in microns by typing in a new value and drag the grid to align with your defect e Display Target on live image This is used to help an operator position a feature to the same spot every time or give a visual reference for a certain size e g 2 microns especially for measuring on chrome defects Note the check mark is hidden if no target diameters are given in the system setup screen Seldom enabled e Intensity range display This is a diagnostic for identifying illumination problems The first pair of numbers is the visible intensity range in a scale of 0 255 The second pair is the confidence level for the first pair If the confidence is low below 8 then the intensity from the most recent good image is used The visible intensity range shouldn t change by more than 10 when images with good bright and dark areas are measured The last number is the time in minutes since the AVI software was last able to measure both bright and dark intensity e Print Image This button prints the Defect Report large and measurement images the inspection summary and the detailed measurements to any attached or network printer Same
51. r than 0 2 microns or larger than 0 5 microns Long term repeatability is typically twice the short term and tool to tool repeatability is typically better than 10 nm dependent on calibration Soft non opaque Defects The AVI measures the effective size of a defect regardless of its opacity The effective size is the size of an equivalent opaque defect that would absorb or transmit the same amount of light and therefore cause the same effect on the printed wafer Conventional systems try to measure the physical size of the soft defect if it is visible which provides only a rough guess of how that defect will print Minimum Feature Size The AVI will accurately measure any defect that can be seen The smallest defects on VeriMask 890 masks 0 08 microns are measured with the same accuracy deviation from the design size of the defect as are larger defects As defects get smaller the repeatability gets worse because there is so little light coming from the defect More measurements need to be averaged to get the same repeatability as larger defects The smallest defect that can be seen is typically 1 10 the size of the optical wavelength 0 05 microns for visible light 0 03 microns for l line Note however that the edge roughness of typical masks is about 0 05 microns so measurement of features smaller than that can be meaningless Maximum Feature Size The largest measurable defect is limited only by the provided image s field of v
52. saved Use Save Measurements to File to save all the measurement parameters If you do not have a spreadsheet program available then paste the values into a text file using Notepad or WordPad Press 0 to clear the history before each set of measurements Click the Average of label to change the maximum number of measurements in the history Save Measurements to File Ctrl V Select File Save Measurements You are prompted for a file name and then a data description The measurement history is written to a CSV file for use by any spreadsheet program This includes complete information for each measurement including type size and intensity range Pixel Value Report v Select View Pixel Values The current measurement intensity range and pixel values inside the measurement box are saved to the clipboard If you have a copy of AVI s DATALOG EXE program in the C Photo32 or the C Windows directory then Datalog will be displayed and you can save the 07 17 02 AVI Photomask Metrology System User Manual 33 Version 4 0 data to a text or CSV file Datalog exe is provided with its simple Visual Basic VB source code so that you can quickly customize it to your needs Customization typically takes 15 60 minutes for a someone who has used VB before The executable and source are available from the AVI website http www aviphotomask com datalog zip This file is 10 KB including executabl
53. splayed where it says History even if you average more Click on the to get a list all the things you can do and change NOTE This feature does not know if you have moved to another defect unless you use the Rpt button so you should clear old values by clicking on the average value or pressing O before starting a new set of measurements e Specifying customer mask and operator information Click on the text area and type the information This information is printed in defect printouts and saved in the database e Setting defect specifications You can set up maximum defect size specifications for edge and isolated defects In addition the minimum distance of an isolated defect from an edge can be specified The spec settings are displayed just above the main image You can have different specs for each layer or customer The specs will update when you select a new layer or customer from the top box in the Info box To enter new specs click on any of the specs above the main image and the Customer Specifications screen will appear Click on any values to change them Click on the Help button or on any of the grid headers to get an explanation of each column Customer Specs CUSTOMER SPECIFICATIONS Catone pe Spec Layer apoc Band lambda PES NA Sigwa Default 0 248 S5fSSES 552 2 Layer 2 T 3 T 248 To enable specifications in the System Setup screen File System Setup or Ctrl Y chec
54. ts will be displayed e Save measurement and image to database Press F2 or select Database Database Save to display the Save Measurement screen and click on Save to Database e Print a defect report click the Print Image button e Send defect report via email select File Send Defect Report e Review images in the database click on Review 5 6 Testing with VeriMask and VeriThoro Masks VeriThoro Masks VeriMask x90 690 890 1090 1590 have a wide range of defects beyond the usual spots holes edge defects and linewidth defects Here is how to measure them e When measuring VeriMasks remember that most of the defects are square e A D Edge Defects measure as described above e E H Corner Defects measure a reference use the VeriMaskMode then measure the defects e L Missing Chrome same as corner defects e M N Contact Size errors measure around the contact Use the Sqrt Area display in the Defect Details screen e O P Contact Position errors measure the linewidth between adjacent contacts e Q R Linewidth Measure as described above e S T Isolated defects Measure as defined above Note that 690 and sometimes 890 masks require you to take reference images first Be sure to save the reference images so you can re measure the images in the database 07 17 02 AVI Photomask Metrology System User Manual 26 Version 4 0 6 Measurement Procedures 6 1 Getting the
55. tup menu Ctrl Y Ctrl Y In the right side of the menu you will see a list of common tools Click on the tool that you are using as an image source for the AVI System Setup Tool Name Instructions 4x3300Transmission O XYNormalize Target Dia microns 0 Smoothing 4 Pixels per Micron 26 66 a XY Ratio 11 025 Blur Microns 0 26 0 5 0 25 Blur Pixels 179 0 fo Frames to Average 15 Image src lambda NA 0 365 0 78 u pixel x 7 Active Tool 1 M 1 Zoom Setup for 10 p micron Test DJ Show Specs MinPeak 500 KLA SL hr 8000x 25p 2 Ae a ng KLA3x1 2000x 25p 4X KLA3x1 8X G Ehem Hango Mtaa KLA3xx uv 2700x 186p 4X KLA uv 8X 4X 8X bai j KLA3xx uvhr 3300x 15p 4X KLA hr 1X j Setup for Lasertec SMD83_ MD2000 Setup for Nikon ARIS i OK fone KM5 100X KM5 50X For image sources that are not predefined you must enter the image source wavelength lambda and numerical aperture NA These values are used in calculating the SEM correction and in the Stepper Simulator You can measure the PixelsPerMicron parameter below or compute it Pixels Micron Electronic Mag PixelSize For example 4x magnification with 15 um pixels gives 26 67 um pixel Linear Calibration Procedure This must be performed on a set of lines with known pitch Performing linear calibration on line widths contacts or anything else will produce inaccurate and non reproducible results If you selected a setup for a
56. urements on each plate e To set the intensity range find an edge between large dark and clear areas or any region with dark and clear areas larger than 1 5 microns square In that region mark anything such as an edge to measure During that measurement the AVI will detect and record the intensity range between clear and dark areas The measurement result can be ignored but the intensity range will be measured 3 2 Monitoring Calibration e Many shops check the calibration of the AVI weekly although customers report that no recalibration is required except after major hardware adjustments on the image source Two years between recalibrations is typical e Calibration monitoring consists of measuring the same set of defects on a reference mask typically a VeriMask at the given interval We recommend taking 5 measurements of each defect using the Rpt button and recording the mean and standard deviation of at least three different edge defects in the critical size range 0 3 0 7 microns 3 3 Calibration Theory This section discusses application of the AVI s non linear calibration capability 3 3 1 Calibration To SEM Standards The ideal mask metrology calibration standard has been SEM measurements until recently There are two problems with SEM measurements both due to the fact that photomasks are used optically but SEMs measure mechanical electrical qualities 2 Interpretation of height and slope Feature sizes are shrinki
57. ut of the Photomask program Note that the image will display light blue where the digitizer is overflowing If you see blue or yellow areas in an image during operation you should return to the Digitizer Setup screen and click on AutoContrast to adjust the contrast Restore allows you to recall the hardware standard or previous contrast and brightness values Video Source is normally set to Comp src 0 Rotate 90 rotates the live image 90 degrees This is used for Lasertec and Nikon systems 07 17 02 AVI Photomask Metrology System User Manual 38 Version 4 0 PAL and Lasertec 9MD83 are normally off PAL is enabled for Lasertec systems and Lasertec 9MD83 is a software interlace designed for old Lasertec systems 8 4 Field Correction Procedure 1 Decide if field correction is required Laser scan systems KLA and Lasertec don t require field correction Camera based systems such as the ARIS I and CD microscope systems usually require field correction Find a clear field of view on a mask Press Shift F for high resolution false color Normally the image will be a uniform color If you can easily see regions where the color shifts typically brightest in the center of the image then field correction will be required Perform the following steps 2 Take a bright field image Use the clear field you found in step 1 and select Calibrate Field Correction Take Bright Field Image or Ctrl F7 The software will averag
58. w Determines when a defect is considered isolated instead of edge Defects farther than this from an edge are considered isolated for Show Specs assessment Size is in microns Show Specs Display pass fail sizes on the main screen Both edge and isolated defects sizes may be set Show Height Display computed height and width on the main screen Show Opacity Display computed opacity and corrected height on the main screen Full Menus Display Review shortcut menus plus non linear calibration items Field Correction Display field correction options in Setup menu Right Half Only Only display the right half of a live image For KLA3xx with database image on the right side only 07 17 02 AVI Photomask Metrology System User Manual 40 Version 4 0 Show VeriMask Chk Show VeriMask Mode checkbox on main screen Customize Displays Custom Parameters screen Enter company information for printed defect report and titles for each line in the Inspection Summary box and in the defect report Setup Customize Displays Custom Parameters Inspection Summary Titles Line 1 Product IV Use List Line 2 Reticle M Use List Printed Report Heading Co Name AMD Fab25 Co Address1 Co Address 2 OK Cancel 8 6 Trouble Shooting and Diagnostics No image from the inspection tool KLA or other e Check all video connections try swapping cables 90 of video problems are caused by bad co
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