.mwams totn mtmfw PdPom ePmPbe m
Contents
1. by making the assumption that any flat on the wafer will adhere to sizes set down by industrial standards and that the chamfer can preclude the need to test part complete devices on the periphery of the wafer This problem is overcome by calculating whether it is possible to fit one and a half devices into the space remaining on the wafer in an analogous manner to the previously listed algorithms Use of this method elmi nates the need for multiple edge sensors and avoids the missing of complete chips which may occur in prior art apparatus if the wafer has an awkward aspect ratio The tips of a probe card are generally arranged to lie in a common plane Three main reasons have been found for failure of probe cards i Lack of planarity between wafer surface and prob ing fixture caused solely by mechanical misalignment of the workpiece holder relative to the chuck surface ii The probing system attempting to probe incom plete devices resulting in unequal stress across the probe In most cases this has been caused by excess travel in use of the normal edge sensing technique iii When using a simple dead lift operation of the chuck That is to say a chuck lifting mechanism which is solenoid operated This gives rise to excessive instan taneous force being applied to both wafer and probing fixture Also the resultant switch bounce of the probe tips gives unpredictable contact characteristics which dramatically eff2. positive save it set up x linits chuck centre dest left branch H quadrant save left offset chuck centre dest right branch quadrant dest left x dest_left rad x rad dest left x dest left branch error s test dest_y x dest_y 3 branch out of linit 3 do it j ok flag j set flags ar 3 dest right chuck centre save offset 3 dest right x dest right 3 rad x rad dest right x dest right branch error limit dest_y x dest_y 5 branch out of linit j else pass ok 3 two s complement j save dest right j dest right x dest right 3 rad x rad dest right x dest right j branch error test dest y x dest y branch out of limit s dest left x dest left rad x rad dest left x dest_left s branch error j test dest y x dest_y branch out of limit loop passed 4 694 776 17 These algorithms determine whether a single point on the wafer is located under the probing fixture As the die or device to be tested is always two dimensional the software needs to perform a die sized fit into the theoretical wafer area The edges of wafers are usually slightly non circular for two reasons i A flat is used for orientation and tooling purposes ii Chamfering of the edge of the wafer Apparatus in accordance with this invention may overcome any difficulties caused by non circular wafers
3. 7 6x10 2 cm in diameter A further problem is caused by dragging the probing fix ture tips through the ink dot which may be 0 008 0 009 2 0x10 2 2 3x10 2 cm in height above the wafer surface causing the probe tipes to be coated with marking ink This may cause partial or total electrical isolation between the testing system and the device under test i In order to overcome this problem the system is pro vided with the ability to remember during its next index to an adjacent device whether or not the device has been marked inked If the current device has been inked the chuck is caused to lower by a pre pro grammed amount in order to clear the offending mountain of ink If the device has passed the testing stage the chuck will only lower the required amount to ensure that the probe tips are clear of the wafer surface Another situation that can cause premature termina tion of the useful life of a probing fixture is fouling of the edge sensor To overcome this problem physical points in the chuck lift cycle are established at which the edge sensor should have been expected to have opened and closed Failure for the edge sensor to perform in the expected manner causes the chuck system to cease movement and the operator is advised of the problem This prevents any further damage to the probing fixture and of course to the wafer under test The step and repeat apparatus system software has an internal non user acces
4. T APPARATUS BACKGROUND AND SUMMARY This invention relates to step and repeat apparatus of the kind used for performance of operations upon an approximately planar component Such a component may be one of a large number each having features located in a not necessarily regular array on the planar surface The apparatus may be used for performing operations repeatedly on successive components Ex amples of step and repeat apparatus include micro processor wafer probes printed circuit manufacturing apparatus laser trimmers and other apparatus for manu facture of hybrid circuits Wafer probe apparatus is required to move and accu rately position a wafer in relation to a probe head Once in position the wafer is raised into contact with the probe Conventional apparatus comprises a first bed accurately movable in a first dimension a second bed mounted upon the first and accurately movable in a second perpendicular dimension and a support located upon the second bed The support is raised by a lifting mechanism when the wafer is brought into contact with the probe The lifting mechanism is relatively sophisticated since it must raise the whole wafer a precise amount for performance of an operation upon the wafer The posi tion of the wafer is observed by use of a microscope Difficulties in design arise in arranging for the micro scope beds and lifting mechanism to fit in the distance between a seated user s knees and eyes According t
5. United States Patent 9 Sandbach et al 54 STEP AND REPEAT APPARATUS 75 Inventors Rex H Sandbach Stockport Alan Poole Macclesfield both of United Kingdom 73 Assignee Co Ordinate Technology Ltd Lancaster England 21 Appl No 747 662 22 Filed Jun 21 1985 30 Foreign Application Priority Data Jun 21 1984 GB United Kingdom 8415912 May 20 1985 GB United Kingdom 2 8512679 151 Int Chti BOSC 13 02 52 U S CI 118 500 269 56 58 Field of Search 1 118 500 269 56 58 269 60 250 491 1 1 Patent Number 45 Date of Patent 4 694 776 Sep 22 1987 56 References Cited U S PATENT DOCUMENTS 3 143 791 8 1964 Lanahan et al ou eee 269 56 4 485 387 11 1984 Drumheller 2 118 697 X Primary Examiner John P McIntosh Attorney Agent or Firm Harry M Weiss amp Associates 57 ABSTRACT Step and repeat apparatus used for performance opera tions upon a generally planar component such as a mi croprocessor wafer comprises a support for a work piece the support being attached by means of an arm to a mechanism adapted to move the support in two di mensions the arm being pivotally secured to said mech anism at a location remote from the support and lifting means arranged to move the support about the pivot in a plane perpendicular to said two dimensions 2 Claims 1 Drawing Figure U S Patent Sep 22 1987 4 694 776 N N i 4 694 776 1 STEP AND REPEA
6. c method for determining where to go next involves the questions a is the stage left or right of centre b which direction is it moving i c from a and b above does the length of the row increase or decrease In most instances the system will already know the current direction of travel and only a and c would need to be calculated The following are examples of the two algorithms stage must move forward on index and increase the row 10 from the right co ord left g check left co ordinates if error move to next for right required i gt A ia call calc next left 3 move to next left emp use x 0 3 null index jz left fail a 3 branch yes call set up x prepare x sub ax factor x 4 make destination je left fail a branch out of limit call which x 3 which sector je ok_left_a j branch positive mov dest_x ax 3 save destination offset call prepare y pos 3 set up y limits call centre down j chuck centre dest down je pos pos quad 3 branch quadrant mov dest down ax save down offset call centre up chuck centre dest up jc pos neg quad 5 branch quadrant mov dest_up ax j save it call up squared 3 dest up x dest up call rad up radius x radius dest up x dest up je left fail 1 branch out of radius call test est x j test dest x x dest x je left fail 1 3 branch out of limit ok left a call index left j index left ok left mov al 0ffh ok flag left test end om al 0
7. centre 3 o clock to 6 o clock on a clock face If the stage is in quadrant relative to the probing fixture position and if the direction of travel is to the left then there is no further calculation required until quad rant B is reached If the direction of travel is to the right then when the edge is predicted for the next index right the stage must move forward one index and shorten the row from the left If the stage is in quadrant B relative to the probing fixture position and if the direction of travel is to the right then there is no further calculation required until quadrant A is reached If the direction of travel is to the left then when the edge is predicted for the next index left the stage must move forward one index and shorten the row from the right If the stage is in quadrant C relative to the probing fixture position and if the direction of travel is to the left then no further calculation is required until quadrant D 4 694 776 5 is reached If the direction of travel is to the right then when the edge is predicted for the next index right the stage must move forward one index and increase the row from the left If the stage is in quadrant D to the probing fixture position and if the direction of travel is to the right then there is no further calculation required until quadrant C is reached If the direction of travel is to the left then when the edge is predicted for the next index left the 6 The basi
8. e next x branch yes 3 ok to go down j branch no and try again j do index flag change direction exit gt 3 do it 3 waste return 3 exit auto correct skip it branch yes calculate next down do it we we We me left fail 2a call calc next left l cap use x 0 jz left fail 32 call set up x sub ax factor_x je left fail 3 call centre dest x call do fail ir je left fail 3 call test dest x je left fail 3 jmp short left fail 2a left fail 3 call calc next right left fail 32 cell index left left fail skip 2 nov al 0 jmp left test end co ord right we MS mm we check right co ordinates if error move to next for left call calc next righ emp use X 0 Hi jz right feil call set up x add ax factor x call which x jnc ok right not ax inc ax mov dest x 8x call prepare y pos tall centre down je pos pos quad right mov dest down ax ell centre up je pos neg quad right mov dest Up ax call up squared call rad up 23 je right fail 1 call test dest x Je right fail I me we m 6 sag 190 4 694 776 10 j calculate next left index null index l 3 branch yes 3 prepare x make destination j branch out of limit 3 chuck centre dest x calc a bit branch error j test dest x x dest_x s branch out of limit 3 loop for more correct set change direction loop back calculate next right null index branch yes prepa
9. e main slow anti clockwise 1011 Single step main anti clockwise 1100 Traverse aux till aborted anti clockwise 1101 Single step aux anti clockwise 1110 Drive to limit n main axis 1111 Drive to limit n aux axis The above description is included to illustrate the operation of the preferred embodiment and is not in tended to limit the scope of the invention The scope of the invention is to be limited only by the following claims From the above description many variations will be apparent to one skilled in the art that would yet be encompassed by the spirit and scope of the present invention What is claimed is 1 Step and repeat apparatus comprising a support for a workpiece and an arm said support being attached by 15 20 25 30 35 40 45 30 55 60 65 20 means of said arm to a movement control mechanism adapted to move said support in two dimensions said arm having a pivot end and a movement end opposite said pivot end said pivot end of said arm being secured to allow said arm to rotate about a horizontal pivotal axis at said pivot end with said movement end of said arm secured to said movement control mechanism at a location remote from said support said apparatus fur ther comprising lifting means arranged to move the support about the pivot in a plane perpendicular to said two dimensions said lifting means positioned substan tially at said movement end of said arm G 2 Apparat
10. ect the results obtained in parametric testing The present apparatus may overcome these problems as follows The provision of the edge sensing capability de scribed above eliminates the risk of probing incomplete devices By confining the use of the edge sensing circuit purely as a height detector to establish the moment of wafer touchdown as opposed to wafer presence the chuck will only lift the amount required and will not bounce the probing fixture Mechanical accuracy of the chuck lifting mechanism is achieved by the unique platter lift pusher assembly It now follows that the incremental lift of the chuck needs to be of such a small magnitude as to correct for any small taper in the wafer caused by the sawing or slicing process The chuck lift on the system described above may have a single step up or down resolution of approxi mately 0 00025 of an imperial inch 6 3x 10 4 cm By using such a fine resolution in chuck lift reliable and accuraie probing force can be maintained The apparatus may be provided with the ability to store the last height location at which the wafer was detected By operating a search window of 0 0005 and 0 0005 1 27x 10 cm to allow for taper of the wafer the possibility of damage to the probing fixture caused by a malfunctioning edge sensor can be precluded 10 15 20 25 30 35 18 Failed devices are marked with a dot of ink which may be up to 0 030
11. endicular grid of a wafer mounted on the support 1 Maintenance of the x y mechanism does not involve interference with the support 1 in contrast to prior art devices in which the support surmounts the x y mecha nism The lightweight construction of the x y mechanism allows the use of lightweight recirculating ball screws 4 694 776 3 for the drives Prior art devices employ more expensive ball or lead screws The apparatus finds application in wafer probes laser trimmers and other apparatus for manufacture of hybrid circuits and other electronic components In addition to the mechanical arrangement described above the apparatus also incorporates a microprocessor control system edge sensors to detect the edges of a wafer under test and markers for applying ink marks to defective chips The apparatus is coupled in use to a host computer system adapted to test a chip connected to the contacts of the probe The control system serves to give a user manual and automatic control of the location of microscope stage and of the height and attitude of the chuck The control system includes three sub systems a main subsystem and two motor control sub systems The main sub sys tem serves to actuate the user system interface i e a keyboard and VDU display Operation of the motor control sub systems which actuate the motors is con trolled by the main sub system The main sub system also communicates with the host computer controls the in
12. ffh set flags ret left fail ar jmp left fail 2 x pos neg quad call do cal up 3 start calc je left fail 1 branch error call test dest x 4 694 776 7 test dest x x dest_x i Je left fail 1 3 branch out of linit call down squared call rad dom je left fail 2 call test dest x Je left fail 2 jep short ok left a pos pos quad call do cal down jc left fail 2 call test dest x je left fail 2 jmp short ok left a left fail 1 call calc next right cap skip it Offh jnz left fail skip 4 call down fit jnz left fail 12 left fail skip 1 nov 31 0 jmp left test end left fail fa cell calc next right emp use X 0 jz end of slice left call centre next x je end of slice left call doun fit jnz left fail 43 call index right mov 31 0 jmp left test end end of slice left Jr pall index right pop ax jmp go load left fail 2 call cal cnex t Tight left fail 2 x emp skip it Offh jnz left fail skip 2 call calc next down call index down 3 dest down x dest down rad x rad dest down x dest down branch error j test dest x x dest_x j branch out of limit 3 loop passed Start calc s branch error 3 test dest_x x dest x branch out of limit 3 loop passed correct 3 skip this 3 branch no ok to go down branch no flag change direction j exit calc next right index null index branch error Chuck centr
13. hange direction loop back 3 two s complement 3 save Gest up dest up x dest up 3 radius x radius dest up x dest up one s complement two s complement save it 3 dest down x dest_down 3 rad x rad dest down x dest_down 3 save it gt 3 set up y co ordinates 3 dest down chuck centre gsaveit j prepare down limit create new limit public down_fit up fit down fit call calc next down cmp use y 0 jz down fail a Ty calculate next down index null index branch yes 15 call set up y sub ax factor_y je down fail call which y je ok down 2 mov Gest_y ax call prepare x pos call centre left je pos pos quad down mov dest left ax call centre right je pos neg quad down call left squared call rad left je down fail call test dest y je down fail ok down call index down ok down mov al Offh down test end emp al 0ffh ret down fail a jep down fail y pos pos quad dom call right centre mov dest right ax call right squared call rad right jo dom fail call test dest y je down fail jmp short ok down pos neg quad down not ax inc ax mov dest right ax call right squared call rad right je down fail call test dest y je down fail call left squared call rad left je dam fail call test dest y je don fail jmp short ok dom a 4 694 776 16 prepare y make destination branch out of limit s which sector branch
14. o the present invention step and repeat apparatus comprises a support for a workpiece and an arm the support being attached by means of the arm to a mechanism adapted to move the support in two di mensions the arm being pivotally secured to said mech anism at a location remote from the support the appara tus further comprising lifting means arranged to move the support about the pivot in a plane perpendicular to said two dimensions The lifting means may be remote from the said mech anism Furthermore the mechanism is preferably not located beneath the microscope reducing the knee to eye distance of the apparatus Avoidance of the need for stacking the said mecha nism confers great advantage The lifting mechanism may have a simple lightweight design The mechanism does not need to include relatively massive beds which are rigid to support the lifting mechanism The mecha nism may be concealed beneath a dust cover whereas beds movable with the workpiece are difficult to cover In addition concealment of the mechanism reduces noise Furthermore access to the workpiece is facili tated for example for wafer handling apparatus laser marking devices probes line width measurement de vices etc Manufacture of the apparatus is much easier with consequent savings in costs The invention is further described by means of exam ple and not in any limitative sense BRIEF DESCRIPTION OF THE DRAWINGS The attached drawing is a diagramma
15. or modify index size Z lift parameters etc The host system communicates with each motor con trol sub system along a twenty six way bus The bus local bus comprises the following Data Out 4 lines of binary coded decimal data Data In 4 lines of binary coded decimal data Status In 4 lines of co processor status Status Out 4 lines of main processor status Drive Select Out 8 lines permitting a maximum of 8 co processors to share the bus at any one time Reference Supplies 2 lines tying up to logic 0 v to 5 v supplies The data sent and received along the Local Bus con sists of two main types of numeric values vem 5 20 25 35 40 45 50 55 60 65 4 i Absolute position data for both axes ii Stop when position data for both axes The host computer communication system provides a capability of exercising control and the ability to set up or modify wafer parameters remote from the system itself i e on line The message interchange via either of the two com munication systems available fall into two categories namely i Passive commands these are commands that result in no change in position of the stage after com mand execution The ATE tester interface readily permits the user to link the probing system and test system A system ancillary port permits the monitoring of the edge sensing system and activation of the three linker drive circuits A password pro
16. re x make destination which sector branch negative tuo s complement san s e WO we DO mu ar wa save it set up y limits chuck centre dest down branch H quadrant save down offset chuck centre dest up 3 branch quadrant j save it 3 dest up x dest up rad x rad dest up x dest up 4 4 3 branch error 3 test est x x dest x 3 branch out of limit 11 ok right a call index right ok right mov al Offh right test end emp al Offh ret ge right fail a jmp right fail 2 x pos neg quad right call do cal up Je right fail 1 call test dest x je right fail 1 call down squared call rad down je right fail 2 call test dest x Je right fail 2 jmp short ok right a pos pos quad right call do cal down je right fail 2 call test dest x je right fail 2 jep short ok right 2 tight fail 1 call calc next left call down fit jnz right fail fa mov 21 0 jap right test end right f sil fa call calc next left op use X 0 jz end of slice right call centre next x nc end of slice right call down fit jnz right fail 1a call index left mov 31 0 jmp right test end j ok flag set flags start calculation 4 branch error j test dest_x x dest_x branch out of limit dest down x dest down 4 rad x rad dest down x dest_down 4 branch error j test dest x x dest_x branch out of limit loop pa
17. sed local bus The local bus is physically configured as previously described The local bus supports one controller inter face and two motor control co processors The local bus interface has the facility to read and write information to and from the selected CO processor 45 50 55 60 65 at any mutually convenient time This time is ascer tained by the main processor polling the ready busy status line The main processor has the capability of initialising the current position of one or all the available co processors or the bus with a value of 0 16 500 inclu sive The main processor has the capability also of being able to interrogate read the position of the stage at any point of travel The main processor can command the coprocessor to 80 to a location on their respective axes simply by send ing the desired location 0 16 500 as a destruction com mand j The main processor has the facility of sending single four bit commands to the co processor with the inter pretations as listed below 0000 Traverse main fast clockwise 0001 Traverse main medium clockwise 0010 Traverse main slow clockwise 0011 Single step main clockwise 0100 Traverse aux until aborted clockwise 0101 Single step aux clockwise 0110 Next data is absolute position 0111 Next data is absolute destination 1000 Traverse main fast anti clockwise 1001 Traverse main medium anti clockwise 4 694 776 19 1010 Travers
18. ssed Start calc branch error i i test dest_x x dest x branch out of limit i loop passed j Correct 3 ok tolgo down branch no i flag change direction j exit 3 calculate next left index 3 null index branch error 3 Chuck centre next x 3 branch yes ok to go down 3 branch no and try again 3 do it j flag change direction exit 13 end of slice right pop ax jmp 90 load right fail 2 call calc next left right fail 2 x call calc next dom call index down right fail 2a call calc next right omp use x 0 jz right fail 3a call set up x add ax facter x mov dest_x ax call dest x centre call do fail l r je right fail 3 call test dest x je right fail 3 imp short right fail 22 right fail 3 call calc next left tight fail 33 call index Yight mov 21 0 jmp right test end do cal up not ax inc ax mov dest up 3x call up squared jep rad up do cal down not ax inc ax mov dest down ax call down squared jep rad down do fail dr mov dest_x ax call prepare y pos call down centre mov dest_down ax call dom squared jmp rad down 4 694 776 14 s waste return 3 exit auto 3 correct cale next index down s do it j calculate next right 3 null index branch yes j prepare x 4 make destination save it do it j calc a bit 4 branch error test dest x x dest x branch out of limit loop for more correct sj Go it set c
19. tection system prevents accidental or unathorised access to the data contained within the apparatus The apparatus incorporates means for detecting the edge of a wafer and for minimising the time spent locat ing the chips on the wafer The traditional approach to this has been the use of a two crossed probe assembly known as an edge sensor such as a break on contact switch The switch opens as it contacts the wafer Opening of the contact pair indi cates that the probing fixture is positioned above the wafer If the contact pair remains closed this indicates that the probing fixture has stepped over the edge of the wafer This action of stepping over the edge of the slice should then cause the stage to drive forward one index size in the Y axis Preferred apparatus in accordance with this invention is provided with the ability to determine the location of a complete device for test relative to the location of the preceding device In order to ascertain whether the system needs to increase or decrease to the left or right the length of a row of complete devices to be probed the system first determines which of four quadrants of the wafer the probing fixture is in The four quadrants may be defined as A Upper left of centre 9 o clock to 12 o clock on a clock face B Upper right of centre 12 o clock to 3 o clock on a clock face C Lower left of centre 6 o clock to 9 o clock on a clock face D Lower right of
20. terface with the host computer and controls the edge sensing equipment and chip marker The motor control sub systems are adapted to com municate with the host computer and to generate sig nals for actuation of the respective motors Accelera tion and deceleration of motors and protective func tions are also controlled by these sub systems The keyboard of the user system interface may have the following keys i DISP this key allows the existence and termination of system functions ii HOME this key returns the stage to the HOME or load positions iii PAUSE this key permits the operator to PAUSE or suspend function operation iv VAC this key permits the operator to activate or deactivate the vacuum hold down circuit v LCL this key permits the operator to interrupt the host computer in the event that the operation of the machine is impaired or malfunctioning vi MARK this key has several functions dependent on a sub function activated at the time in question vii CONT this key permits the operator to CON TINUE the function operation after previously being PAUSED viii DEL this key permits the operator to DE LETE a previously entered data digit ix ENTER this key permits the operator to EN TER a selected function or sub function or to termi nate data string entry x numeric these keys enable the operator to enter numeric data in order to select
21. tic view of a wafer probe apparatus in accordance with this inven tion 20 25 30 40 60 65 2 DETAILED DESCRIPTION The apparatus illustrated in the drawing which is not to scale comprises a support for a workpiece 1 located at the end of an arm 2 which is pivotally mounted by means of a hinge 3 remote from the support 1 but lo cated in the horizontal plane of the latter when engag ing the probe to ensure vertical movement of the wafer as it contacts the probe The workpiece may be secured to the support by application of a vacuum from a suc tion device A counterbaiance 4 is arranged so that tne arm 2 and support 1 pivot about their centre of gravity This al lows the arm to have a relatively simple and inexpensive sheet metal construction The counterbalance of alter native embodiments of the invention may be replaced by a spring in order to reduce the inertia of the appara tus A motor 5 drives a concealed chain loop not shown connected to the chuck or platter 6 of the sup port 1 The chuck 6 is rotatable about a vertical z axis the motor 5 providing means for adjusting the angular disposition 0 of a workpiece secured to the chuck The hinge 3 is attached to mechanism which enables the arm and hence the support to be moved in two perpendicular dimensions x and y A block 7 from which the hinge 3 depends is ar ranged to slide in the x direction upon an accurately machined bar 8 A ball screw 9 dri
22. us as claimed in claim 1 the workpiece comprising a carrier for carrying a succession of de vices
23. ven by a motor 10 engages a ballnut contained in the block 7 to drive the block along the bar 8 End supports 11 12 of the bar 8 are arranged to slide in the y direction upon respective accurately machined bars 13 14 The bars 13 14 are aligned perpendicular to the bar 8 A ball screw 15 actuated by a motor 17 and chain drive 16 drives the end support 11 The x y mechanism is located upon four accurately machined supports 18 Movement of the chuck 6 about the pivot in the z direction is controlled by a lift mechanism 19 such as a threaded member driven by a drive belt 20 and motor 21 The chuck 6 is not attached to the lifting mechanism but merely rests upon it The advantages of the invention are apparent from consideration of the steps involved in assembly of the apparatus In the first step four coplanar location sites 18 are machined on the base plate not shown Prior art appa ratus comprising x and y beds require entirely machined baseplates to support their weight The parallel shafts 13 14 are located in inexpensive recirculating ball bushings attached to the location sites 18 The shafts 13 14 may be simply aligned with a gauge The cross bar 8 is mounted on the end support slides 11 12 between the bars 13 14 In prior art devices a cross table is suspended between beds movable on an orthog onal axis The arm 2 is mounted upon the bar 8 Perpendicular ity of the bar 8 may be easily checked against the accu rately perp
Download Pdf Manuals
Related Search