CA1198797A

CA1198797A - X-y addressable workpiece positioner having an improved x-y address indicia sensor

Info

Publication number: CA1198797A
Application number: CA000348761A
Authority: CA
Inventors: Karl-Heinz Johannsmeier; Edward H. Phillips
Original assignee: Optimetrix Corp
Current assignee: Optimetrix Corp
Priority date: 1980-03-27
Filing date: 1980-03-27
Publication date: 1985-12-31
Also published as: CA1217257A

Abstract

ABSTRACT
In an X-Y addressable workpiece positioner, the workpiece to be positioned, such as a semiconductive wafer to be sequentially exposed at different regions thereof in accordance with a pattern of a mask, is disposed for movement with a work stage along coordinate X and Y axes. The work stage has a two-dimensional array of X and Y coordinate addressing indicia enclosed within a border and affixed to the work stage for movement therewith.
A portion of an enlarged image of the array of addressing indicia is projected onto a sensor stage to derive an output indicative of the X and Y coordinates of the array of addressing indicia relative to the position of the sensor stage. The X and Y coor-dinates of the array of addressing indicia are sensed through addressing indicia recognition windows of the sensor stage and are differentially compared to remove unwanted background effects.
Concomitantly, the border is sensed through border sensing windows of the sensor stage to provide a frame of reference for the sensed X and Y coordinates of the array of addressing indicia. The sensed X and Y coordinates of the array of addressing indicia are compared with the X and Y coordinates of a selected addressed position of the work stage to derive an error output. In response to this error output the work stage is moved to the selected addressed position so as to position a region of the workpiece for exposure in accordance with the pattern of the mask. The work stage is sequentially moved to succeeding addressed positions in the same manner to position each of the remaining regions of the workpiece for exposure in accordance with the pattern of the mask.

Description

7~7 X-Y ADDRESSABLE WORKPIECE POSITIONER
HAVING AN IMPRUVED X-Y ADDRESS
IN~.ICIA S~N~nR

BACKGROUND OF THE INVENTION
The present invention relates in general to X-Y addressable workpiece positioners and, morP particularly, to an improved p~sitioner particularly useful in an alignment and exposure machine c~f the type employed for s~quentially ali~ning images of different regions of a semiconductive wa:Eer s7ith a ma~k and :for exposing eaeh ~uch region of the semiconductive wafer in accordance with a pattern of th e mask .
DESCRIPTION OF TEIE PRIOR ART
Heretofore, X-Y addres~ble workpi~ce positioniers hava been proposed in which a mask is sequentially stepped to different ~ and Y
coordinates :~or sequentially exposing different portions of the ;~0 mask in accordance with a patte~rn of a rsticle. One such prior art stepper is manufactured by Jade Manuacturing Co~ In that 3tepper the ma~k is disposed on a work stage that i~ addressably movable to different X and Y coordirlates along coordinate X and Y axes and that is ~equentially addressed to position difiEerent r~gion~ of the mas}s for~xpc~sure în accordanc~ with the pattern o t~he reticl2. Two $eparate on~-dimensional array~ of re~pective X and Y parallel scribe lines are affixed to the wor~ age for use in moving it to the X and Y coordinates of an addre#sed posi-tion selected by an opsrator. Sensors are set up t~ se~se the X
and Y c~ordinates ~f an adclr~ssed p~ition of the work stage by respectively ~equentially sensing the X and Y scribe lines of these arrays. X and Y servu motors respc~nsive to the sensed X
and Y co~rdinates move the work stage ~o the addressed position ~elected by the operator. Howeve-, the work stage does not move simultan20usly along both the X and Y axes ts the addre~sed posi-~ion. Rather, the Y coordinate of the addressed position is first ensed and the work stage moved along the Y axi ~ to that Y cvor-dinate. Then the X coordinate of the addressed position is sensed and th~ work stage mv~ed along the X axis to that X coordinate.
This ~t~pper has the disadvantage that the work stage cannot move along the shortest path from a first addressed position to a second addres~ed p~sition, ~ut, on the contrary, must move from the first addressed position to a reference position from which the X or the Y scribe lines may be ~equentially sensed for moving the work stage to any new X or Y coordinate, respectively, of the second ~ddressed position. If the second aadre~sed po~ition has both new X and Y coordinates, the work stage is initially moved to a reference position from which the Y scribe lines are sequentially sensed and the work stage moved to another reference position having the new Y coordinate. From the latter raference position the X scribe lines are ~equ~n ially sensed and the work stage moved to the ~econd addressed position having both the new X and Y coordinates. In addition, thi~ stepper depends for its accuracy upon the orthogonality of Y axis bearing support of the work ~tage with respect~to the X axi~ of motion of the work stage.
Whi$e this orthogonality ~an be accurately controlled, it requires ~xpensive c~mponents to do 50.
It is also Xnown, from the prior art in such addr~ssabl~
workpiece positiQners, tcl ~.mploy a mirror afixed to the work 30 ~tage for l.,o~ _nt therewith and thus or movement with the wor.kpiece.

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A laser beam is directed along an optical path onto the mirr~r in such a manner as to produce X and Y interference fringes of the : laser beam, ~uch fringes being counted for precisely p~sitioning the work stage and, henc~, the workpiece at the X and Y c~ord~nates of an addressed p~sition.
The problem with this scheme is that the standard for deter-mining both the X and Y coordinates of an addressed position of the workpiece is the wavelength of the laser beam. The wavelength of the laser ~eam, however, is a function of ~he temperature, pressure and humidity of the optical path used to produce the interference fringes. As a consequence, the work stage must be contained within an environmental chamber for ~ontrolling the temperature, pressure and humidity to a very high degree. Such a chamber is relatively expensive and complicates the addressable workpiece positioner and the use thereof.
Therefore, a less expensive and less complicated X-Y addres-sable workpiece positioner is desired which is cap~ble of moving a work stage for a workpiece to a sequence of repeatably addressed positions with an accuracy of better ~han on~ tenth of a micron~ It is also desired that the work stage move in a more direct path from a first addressed position to a ~ubsequent addressed position ~o as to reduce the time required for moving between the sequentially addressed positions.
SUM~RY OF THE PRESENT I~VENTION

An obiect of an as~ect of the present invention is the provi-~i~n of an ~mprov~d X-Y addressable workpiece positioner and an improv~d alignment and exposure machine using s~me.
According to an aspect of the present invention, the workpiece to be positioned is affixed to a work stage movable alon~ X and Y coordinates with a common two-dimensional array ,~ _ of X and Y coordinate p~sitioning indicia affixed to the movable work stage. A sensor stage senses an enlarged image of at least a portion of the X and Y coordinate positioning indicia. Drive means are responsive to the sensed X and Y
coordinate positioning indicia for driving the work stage from a first address to a subsequent address.
According to an aspect of the present invention, an image of the two-dimensional array of X and Y coordînate positioning indicia affixed to and movable with the work stage is projected onto the sensor stage, which includes two pairs of pattern recognition windows for independently recognizing and sensing the X and Y coordinate positioning indicia.
According to an aspect of the present invention, the recognition pattern of one window of each pair of pattern recognition windows includes an array of parallel transparent elongated regions, the axis of elongation being orthogonal to the respective X or Y coordinate positioning indicia being sensed.
According to an aspect of the present invention, the sensor stage includes means for moving the sensor stage relative to the projected image of the X and Y coordinate positioning indicia for interpolating the sensed X and/or Y coordinates of the position of the work stage and for causing the work stageto be moved to the interpolated position to address a portion of the~ workpiece.
According to an aspect of the present inventioll, the image of an addressed portion of a workpiece, such as a semiconductive wafer, and the image of a stationary pattern to be aligned with respect to one another are superimposed, and the sensor stage is moved ~or interpolating at least one of the sensed X and Y

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coordina~es of the posi~i.on o~ the work stage to precisel~
align those two images.
Variows aspects of this i.nvention are as follows:
An addressable positioner comprising: stage means, movable along a pair of coordinate axes, for holding an object to be positioned; a two-dimensional array of coordinate addressing indicia, a~fi~ed ~o the stage'means, for movement with the stage means; sensor means for sensing the coordina~e adress-ing indicia to provl.de outpu~ inormation determinative o the coordinate position of the stage'means; and control means, responsive to the output information ~rom the sensor means and to input control information, for moving the stage means'to coordinate positions. determined by the input control information.
An addressable positionging method comprlsing the steps of: p~acing an object to be positioned on a stage that is movable along coordinate ages in a plane containing or parallel to those a~es and that has a two~dimensional arra~ o~
coordinate addressing indicia a~i~ed thereto ~or movement there-;
with; projecting an image of at least a portion of the array of coordinate addressing indicia onto a.sensor; sensing thecoordinate addressIng indicia o~ ~he''image to derive output in~ormation determinative o the coordinate posltion of the stage; comparing t'he coordinate position o the stage with a designated coordinate position to derive an error outpu~; and mo~ing the sta~e to the designa~ed coordinate position in response to the error outputi An adaptive..servo contxol s~stem comprising: irst and second stage means respectively'movable along orthogonal a~es for positioning a workp.i'ece relative to a work apparatus; iirst and s.econd drive means respec~ively responsive to fi~st and second .. .1 '7~

drive signals and operative to drive said first and second stage means along said axes; position de~ector means for monitoring the position o~ said first and second stage means relative to the work apparatus and including a reference substra~e carried by one of said stage means and having orthogonal dimension position related indicia disposed thereupon, and means for sensing said indicia and developing first and second ac~ual position signals oorresponding to the positioning of said substrate along said axes; input means for generating first and second desired position signals corresponding to positions along said axes to which said first and second stage means are to be driven; and first and second position control means for respectively comparing said first and second desired position signals to said first and second actual position signals and for developing said first and second drive signals for appli.-cation to said first and second drive means,respectivelyJtv cause said workpiece to be driven to a desired position.
A servo control system comprising: stage means movable along orthogonal axes for positioning a workpiece relative to a work apparatus; Eirs~ and second drive means respectively responsive to first and second drive signals and operative to drive said stage means along said axes; position de~ector means for monitoring the position of said stag~ means relative to the work apparatus and including a referenee substrate carried by said stage means an~dhaving orthogonal dimension position related indicia disposed thereupon, and means for sensing said indicia and developing first and second aotual position signals corresponding to ~he positioning of said substrate along said axes; input means for generating first and second desired position 30 signals corresponding to positions along said axes to which said --7~
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stage means is to be driven; and first and second position control means for respectively comparing said first and second desired position signals to said first and second actual position signals and for developing said first and second drive signals for application to said first and second drive means, ~ spectively,to cause said workpiece to be driven to a desired position.
An X-Y addressable workpiece positioning method comprising the steps of: coupling a workpiece to a work stage movable in X and Y directions within a common plane of movement defined by the X and Y directions and within which the workpiece is to be positioned, the work stage having a two-dimensional array of X and Y coordinate positioning indicia affixed thereto for effecting positioning of the work stage with the workpiece;
- projecting an enlarged image of at least a portion of ~he array of X and Y coordinate positioning indicia onto a relatively stationary sensor stage; sensing the enlarged image projected onto the sensor stage to determine ~he X and Y coordinates of the position of the work stage; comparing the X and Y coordinates of the position of the work stage with the X and Y coordinates of a different position of the work stage to derive an error output; and moving .the work stage with the workpiece and thP
array of ~ and Y coordinate positioning indicia to the different position in response to the error output to address a portion of the workpiece.
An X-~ addressable workpiece positioning apparatus comprising:
work sta~e means movable in ~oth X and Y directions within a common plane of movement defined by the X and Y direc~ions and within which a workpiece is to be positioned; said work stage means including holding means for holding the workpiece for ~J

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~ ava movement with the work stage means; indicia means comprising a two-dimensional array of X and Y coordinate positioning indicia affixed to the work stage means and movable therewith for effecting positioning of the work stage means; relatively stationary sensor stage means for deter~;n;ng the Y and Y
coordinates of the work stage means; projector means for projecting an enlarged image of at least a portion of the array of X and Y coordinate positioning indicia onto the sensor stage means; said sensor s~age means sensing the enlarged image 19 projected thereon to derive an output determinative of the X and Y coordinates of the position of the work stage; comparative means for comparing the X and Y coordinates of the position of the work stage means with the X and Y coordinates of a different position of the work stage means to derive an error output; and drive means for moving the work stage means and the array of X and Y coordinate positioning indicia to the different position in response to the error output ~o address a portion of the workpiece.
BRIEF DE~C~IPTION OF THE DRAWINGS
Figure 1 is a perspective view of a step-and-repeat alignment and exposure machine employing fea~ures of the present invention.
Figure 2 is a schematic perspective view, partly in block diagram for~, of a portion (including an X-Y addressable workpiece positioner employing features of ~he present inven~ion) of ~he ~chine of Figure 1.
Figure 3 is an ~nlarg~d detailed view of a portion of an array of X and Y coordinate addressing indicia employed as part of a work stage of the pos:itioner of Figure 2 as delineated by line 3-3.
Figur 4 is a plot of triangular output current waveforms derived _g _ 3'7~

from an X coordinate addressing indicia sensing portion of a sensing diode plate employe~ in ~he p~sitioner of Figure 2 as a func-tion of movement of the work stage in the X direction.
Figure 5 is a plot of ~guare wave output waveform~ deriv~d from the triangular output current waveforms of Figure 4.
Figure 6 is a plo~ of a portion of one ~riangular ~utput current wav~form of Figure 4 employed in locking the work stage to the X coordinate of an addressed position.
Figure 7 is a plot o signal intensity of another output waveform derived rom a border sensing portion of the sensing diode plate of ~igure 2 as a function of distance away from ~ border enclosing the array of X and Y coordinate addressing indicia.
Figure 8 is a schematic circuit diagram of a horder sensing circuit employed for sensing the border enclosing the array of X and Y coordinate addrecsing indicia.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referrin~ now to Figure 1, there is shown a step-and-repeat pro~ection alignment and exposure machine 20 incorporating features of the present inventionO ~his machine 20 includes a ba~e unit 22, a precision work ~tage 24 supported on the base unit f or holding a workpiece, such as a semiconductive wafer 30, and for Rrecisely positioning the workpiece along coordinate X and Y axes in a hori-zontal plane. An ~ptical unit 26 i~ supported from the base unit 22 fvr u~e in aligning and exposing the wafer 30. An automatic workpiece han~ling unit ~8 is also supported on th~ base unit ~2 for transporting wafers 30 to and fr~m the work stage ~4. The base unit 22 ~d~a s~ rygr ~ tebaa~kh~nganupper reerance ~urface which is flat to within one micron across khe ~urface thereof and having a cylindriral bvre extendlng vertically there-~hrough for a Ben~Or ~tage 46 ( ~e ~igure 2) .

i Referring now to both Figures 1 and 2, in operating the align-ment and expo~ur~ ~r~i ne 2~, the operator intxoduc~s a wafer 30 into the automatic workpiece handling unit 28 which th~n precisely positions the wafer on the wor~ ~tage 24. The operator moves a ~icro~cope 105 of the optical unit 26 into position for use with a projection lens 104 in viewing a pattern bearing ~urface of a photographic mask 98 and an image of an addressed region of the upper ~ur~ace of the wafer 30 to be precisely optically aligned.
Following this alig~ment, the addressed region of the upper sur-face of the wafer 3û is exposed in accordance with the pattern ofthe mask 98.
The operator selects the addr~ssed region of the wafer 30 to be exposed in accordan~e with ~he pattern of the masX 9B. X and Y
servo motors 76 and 77 are coupled to the work stage 24 for moving the work stage and a two-dimensional array 45 of X and Y coordinate address-ing or positioning indicia affixed thereto over the sensor stage 46 to po~ition the addressed region of the wafer 30 for exposure. The operator then views ~he addre~d region of the wafer 30 illuminated by light projected through the optical unit 26 onto th~ addressed region of the wafer. An image of the illuminated addressed region of the wafer 30 is pro~ected onto he back side of the mask 98 and thereby ~uperimposed on the pattern ~f the masX for viewing by the operator through the microscope 105 while controls are manipulated to adjuRt the po~ition of the sensor stage 46. This manipulati~n causes a 31ight corr~ti~n to b~ made in the position of the work st~ge 24 (then locked t~ move with the sen~or stage 46~ ~or precisely aligning the viewed image of the illuminated addressed region of ~he wafer 30 with the pattern of ~e ma~k 98. ~he op~ratGr then ~oves the micro-~c~pe 105 out of ~he w~y and move~ a projection light sourc~ 29 into position for expo~in~ the a~dresse~ region o ~h0 wafer 30 ? n accor-dance with the pattern of the ~k 98 through the projection len~ 104. ~ wing ~his exposure, the programmer 73 .

'7~71 causes the work stage 24 to advance to the next addressed position at which anoth~r region of the wa~er 30 i~ exposed. The wafer is sequentially ~xposed b~ this step-and-repeat process until the wafer is totally exp~sed, at which point the operator or programmer initiates operation of the automatic workpiece hanclling unit 28 to remove the exposed wafer from tne work stage 24 and advance a new wafer into position on the work stage.
Referr~ng now specifically to Figure 2, there is shown an X-Y
addressable workpiece positioner forminq part of the alignment 10 and exposure machine 20 of Figure 1 and incorporating features of the present invention. In this workpiece positioner, the wafer 30 is positioned on and held by the work stage 24 above the array 45 of X and Y coordinate addressing indicia affixed to and moveable with the wor~ stage. The sensor stage 46 is disposed below the work stage 24 and the array 45 of addressing indicia. A lamp 47 provides illumination that is projecte~ by a l~ns 48 into a beam directed onto a beam splitting mirror 49, which in turn directs the illumination through a magnifying lens 51 onto a relatively ~mall region of the array 45 of X and Y coordinate addressing indicia or illuminating same.
An image of the illuminated region of the array 45 of X and Y coor-dinate addressing indicia is proje~ted via the magnifying lens 51 through the beam splitting mirror 49 and focused onto an opaque sensing window plate 52 ~ ng part ofthe sensor tage ~6and havingaplur~ity of~iR~nn~ w~GwS 53foDm~d ~E~n and dispo~ along ~hecoDn~na~e X and ~ axes f~r ~ensing the X and Y coordinate addressing indicia. In a typical ax~mple, ~he magnification M of the magnifying lens 51 is 13X
such that the aforementioned image, as project~d onto ~he sensing window plate 52, i~ thirteen times a~tu~l size. The windows 53 permit the ligh~ incident thexeon to pass ~h0rethrough ~o resp~ctive -~2 7~

stick lenses 54 ~rranged in registration with the respective windows. Thus, the sti~k lenses 54 receive the light passing through the respective windows 53 and focus that light onto res-p~ctive PIN diodes 55 disposed o~ a sensing diode plate 56 of the sensor stage 46.
Two pairs 57 of the diodes 55 are arran~ed and connected for recognizing and sensing the X coordinates of the array 45 of addressing indicia, whereas two additional pairs 58 of the dio~e~
55 are arranged and connected for s~nsing the Y coordinates of the array 45 of addressing indicia. The diodes of each pair 57 and S8 are connected in bucking r~lation so as to provide a zero output when the illumination of each respectivP diode of the pair is equal.
Referring now to Figure 3, there is shown a portion of the array 45 of X and Y coordinate addressing indicia. The indicia 59 comprise, for example, quare dots of chromium plating on a fus~d ~ilica plate 61. A b~rder 62 of chromium plating surrounds the array 45 o addressing indicia 59, ~hich are arranged in rows and columns along the X and Y axes, respectively. The X co~rdinates ~0 of the array 45 of addressing indicia 59 compri~e the c~lumns, and the Y
coordinates comprise the rows. Thus, each addressable po3ition of the work stage 24 of Figure 2 is defined by a given indicium 59 having a column number corresponding to the number ~f the X
coordinate columns from the lef-t~hand side of the border 6~ twhich is aligned with the Y axis) to that indicium and a row number c~rresponding to the number of Y coordinate rows from the front ~ide of the bordar ~which is ali~ned with ~he X axis) ~o that indicium. In a typical ~xample, he indicia 59 hre 10 micrOn~
~quare located on 20 micron centers along both the X and Y axes.
Referring now to bot~ Figur~s 2 and 3, the sensing window plate 52 includ2s ~olumn and row recognition windows 53 which are of generally two kinds. A first kind of these windows i~ a trans-parent re~tangle having a width of 1300 microns and a length of 1560 microns or viewing a magnified image of a rectangular area of lO0 micr~ns by 120 microns o the array 45 of addressing indicia 59 (this area corresponds to the space occupied ly a 5x6 Bub-array of addressing indicia 59~. Eac~ window oi- this first kind is paired with a window of the second kind comprising an array of eight parallel, elongated transparent slots having a center-to center spacing of 260 microns corresponding to a magni-fied image of the 20 micron center-to-center spacinc3 of ~he addres-sing indicia 59. Six of these slots have a width of 130 microns and a length of 2080 microns for viewing a magnifi~d image of a rectangular area of lO microns by 160 microns of the array 45 of addressing indicia 59, and the remaining two s~ots have a width of 130 microns and a length of 1560 miCrGnS for viewing a magnified image of a rectangular area of lO microns by ~20 microns of the array of ~ddressing indicia. This permits an image of eight or six addressing indicia 59 to be observed through each o these respective types of ~lots of each window o~ the second kin~. Thus, each window of the se~ond kind permits a magnified i.mage of sixty addressing indicia 59 to be o~served, whereas each window of the f.irst kind permits a magnified image cf thir~y addressing indicia to be o~served (i.e., permits illumination from thirty indicia to pass therethrough). ~o~ver, both types of windows ar0 of equal transparent ar~a. Thus, the output fr~m ea~h of the p~irs 57 or 58 of diodes 55 c~nnected in bucking relat.ion will be ~ero or a null when ~he ~ensed magnified images of ~he addressing indicia 5g di~posed in a column ~r row aligned parallel to the ~lo~s ~f one of ~he wind~w~ of the second -14.

kind are half covered by ~he opaque spacing between those slots (i.e., when a marginal edge of ea~h ~f those slots falls along the center p~ints vf ~he ~ensed magnified images of the addressing indicia of each such column or row). It should be noted that the slots of the windows of the second kind are elongated in a direction normal t~ the direction being sensed (i.e., the slots of a column recognition window of the second kind are oriented along the Y axis and the slots of a row recognition window of the ~econd kind are oriented al~ng the X axis).
Each X or Y coordinate sensing diode Pair 57 or 58 produces a tri-angular output current waveform 50 or 60 of the type shown in Figure 4 as the work stage 24 is moved. Each cycle of each triangular output current waveform 50 or 60 corresp~nds to the counting ~f a given X coordinate column or Y coordinate row of the array 45 of addres-sing indicia 59 depending upon whether the waveform is produced by an X or a Y coordinate sensing diode pair 57 or 5S, respectively.
The tw~ window pairs of the sensing window plate 52 which correspond to the two X coordinate sen3ing di~de pairs 57 of the s~nsing diode plate 56 are offset relative to one ano~her along the X axis by an amount equal to one fourth ~f the magnified image of the 20 micron center-to-center spacing of the addressing indicia 59 as projected onto the sensing window plate li-e., 65 microns).
This offset results in a 90 spa~ial offset in t'he tri~n~ll~r ou~ut current waveforms 50 and 60 produced by the two X coor~te sensing diode pairs 57 when ~he~X COQrdinate of the array 45 of addressing ~ndicia 59 is ~eing $ensed. A~ sh~wn in Figure 4, when the work stage 24 is ~eing advan~d in the positive X direction along the X axi~ the triangular output ~urrent waveform 50 produ~ed by a first X coordinate ~ensiny diode pair 57 will lead ~he other tri angular output current waveorm 60 produced by the sec~nd X

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co~rdinate sensing diode pair 57, whereas wh~n the work stage is bQins advanced in the negative X direction al~ng the X axis, the triangular output current waveorm 60 will lead the triangular output current waveform 50.
Similarly, the two window pairs of the sensing window plate 52 whic~ ~orrespond to the two Y coordinate s~nsing diode pairs 58 of the se~sing di~de plate 56 are offset along the Y axis ~y an amoun~ equal to ~ne f~urth ~f the magnified image of the 20 micron center-to-center spacing of the addressing indicia 59 as projected onto the sensing window plate ~i. e., 65 microns1 . This provides a 90 spacial offset similar to that shown in Figure 4 in the triangular output current waveforms 50 and 60 produced by the two Y c~ordinate sensing dio~e pairs58~henthework stag~ 24 is being advanced along the Y axis to sense the Y coordinate of the array 4'; of addressing indicia. The triangular output current waveform 50~produced by a first Y coordinate sensing diode pair 58 will either lead or lag the triangular output c~r~we~ef~rm60pno~edby the second Y coordinate ~ensing diode pair ~8 depending on whether the work stage 24 is being advanced in the positive or the negative direction, respec-tively, along the Y axis.
Referring now specifically to Figure 2, the triangular output current waveforms 50 and 60 from ~he two X co~rdinate s~nsing diode pairs 57 are applied to respectiv~ amplifiers and wave shapers 65 coupled to an X ~ounter 68~ Similarly, the triangular output current waveform~ 50 and 60 from the tw~ Y coordinate ~ensing diode pairs 58 are applied to respectiv~ amplifiers and wave shapers 66 coupled to a Y counter 69. The ampli~iers and wave ~hap~rs 65 produce ~quare wave ~ignals 50' and 60' of the type shown in Pigure 5 from the respectiv~ triangular output current waveforms 50 and 60 applied thereto, and the amplifiers t t7 and wav~ shapers 66 al~o produce such square wave signals 50~ and 60 ' from the resp~ctiv~e tria~gular ~utput current waveforms 50 and 6(:) applied ~hereto. Thus, ~here is one square wav~ pulse per X coordinate column or Y co~rdinate row of addre-~sing indicia ~en~ed by the sensing window plate 5~ and sensing diode plate 56.
~en t~he s~are wave ~i~als 50' and 60' fro~ the amplifiPrs ~nd wave shapers 65 or 66 are derived fran a le~fl;n~ trT~ r output current waveform 50 (produced by the first X or Y coordinate sensing diode pair 57 or 58) and a lagging triangular output current wa~eform 60 10 Iproduced by the second X or Y coordinate sensing diode pair 57 or S8), as when the work stage 24 is being advanced in the p~si-tive X or Y direction along the X or Y axis (i.e., when the square wave signal 50' leads the square wave signal 60' as shown in Figure 5), the r~spective X or Y counter 68 or 69 is latched for counting X coordinate columns or ~ coordinate rows of addressing indicia in a positive direction pro~ucing a p~sitive count. Simi-larly, when the square wave sign~ls 50' and 60' are derive~ rom a lagging triangular output current waveform 50 and a leading triangular output current waveform 60,as when the work stage 24 is being advanced in the negative direction along the X or Y axis ( i . e ., when the square wave signal 50 ' lags the square wave signal 60' ), the re~pective X or Y counter 68 or 69 is latched or counting X coordinate columns or Y courdinate rows of addressing indicia in a nega~ive direction producing a negativ,e rount~ The outputs of the X and Y ~ounters 68 and 69 are applied t~ respective error detectors 71 and 72 for co~nparison with X and Y coordinate reference address inputs derived from the programme:r 73, which i~ progra~med by the operator to select predetermine~d address positions of the work ~tage 24 (and, herlce, of the wafer 30 held 30 thereby). Error output~ deriv~d :Erc~m ~e respeetive error 7~

detectors 71 and ~2 are hppll~d t~ the inputs of respçctive servo amplifiers 74 and 75, the ~tputs o~ which are applied to the respec-tive X and Y servo motors 76 and 77 for driving the work stage 24 in such a direction as to cause ~he error outputs from the error detectors to go toward zero, The programmer-73 keeps track of the counted number of X
c~ordinate columns and Y coordinates rows of addressing indic~a and of the remaining number of X coordinate columns and Y coordinate rows to reach the X and Y coordinates of the desired reference 10 address (i.e., the addressed position of the work stage 24~ and controls the rate at which the X and Y servo motors 76 and 77 move the worX stage so that certain predetermined acceleration and deceleration limits are not exceeded. For example, the pro-grammer 73 controls the acceleration and deceleration to one tenth of a G (the force of gravity). When the error output from the error detector 71 is within one X coordinate col~m of the X
coordinate of the addressed posïtion of the work stage 24, the programmer~73 ets a switch Sx for applying the output of the first X coordinate sensi~g diode pair 57 to an analog servo amplifier 81~ Similarly, when the error output from the error detector 72 is within one Y coordinate row of the Y coordinate ~f the addressed position, the programmer 73 sets another switch Sy for applying the output of the first Y coordinate sensing diode pair 58 to another analog servo amplifier 82. The outputs of the analog servo amplifi rs 81 and ~2 are applied to the inputs of the respec-tive ~ervo amplifierQ 74 and 75 for caus ng the respec~ive X and Y ~ervo motors 76 and 77 to lock ~he work stage 24 in place (rela-tive to the sensor stage 46) at respective X and Y coordinates corresporlding to the respactive crossovers 83 o t~he respective 30 portions of the respec~ive triangular output waveform5 50 applied ~f'~~`

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to the respective analog servo amplifiers 81 and 82 as shown in ~igure 6. Each such cros~over 83 corresponds to the center of a : 10 micron wide region of t~ workpiece in the X or the Y direction an~ is precisely determined and repeatable with an error of less than ~ne tenth of a micron. Thus, the work stage 24 (and, hence, ~ wafer 30 held thereby) can be programmed to move to any selected one of a number of addressable positions spaced at 20 micron intervals along both the X and Y axes. In addition, the~e addres-sable positions can be repeatably addres~ed to within one tenth of a micron.
In addition, each addressed position of the work stage 24 can be interpolated (i.e., changed relativP to a fixed position on the granite ~lock~ plus or minus 20 microns along both the X and Y
axes by producing a relatively slight displacement of the sensor stage 46 ~which otherwise remains stationary) and, hence, of the worX stage (once the work stage is locked in place relative to the se~sor stage so as to move therewith) relative to the granite block. More particularly, he sen~or stage 46 (including the sensing window plate 52) is displaceable along both the X and Y
~0 axes by means of X and Y ~ervo motors 84 and 85.
These servo motors are controlled by error signals from respective X and Y error detectors 86 and B7. The output of an X displace-ment linear variable differen-tial transformer 88 and the output of a Y displacement linear variable differ~ntial transformer 89 (both of which tr~nsfor~ers ar~ fixedly referenced to ~he granite blocX for detection o~ X and Y displacements of the ~ensor stage 46) are appli~d to the respective X and Y error det~ctor~ ~6 and 87 for comparison with respPctive reference signal derived from respectivs X and Y reference potenti~meters 91 and 92 under the control o the oper~tor. The err~r ~ignals f rom error detectors .

3t~7 86 and B7 are amplified by r~sp~ctive s~rvo amplifier~ 93 and 94 and applied to the respective ~ and Y ~er~o motors ~ and 85~ Thus, the X and Y referenc~ potentiometers 91 and g2 permit interpolation of the X and Y coordin~tes of the addressed position of the work stage 24 to better than one tenth of a micron along both the X
an~ Y axes.
In a totally automated system the interpolation sektings of the X and Y reference potentiometers 91 and 92 and, henc~,the r~r~ce signals derived from those potenti~meters for comparison with the outputs of the X and Y displacement linear variable differ-ential transformers 88 and 89 in interpolating the X an~ Y
coordinates of the addressed poSitiGn, could be selected by the programmer 73. Hcwever, in a preferred embodiment of a step-and-rep~at alignment and exposure machine 20, such as that shown in Figures 1 and 2, for aligning the pattern bearing surface of the mask 98 and an image of a selected addressed region 99 of the upper surface of the wafer 30, it is particularly advantageous for the operator to have control over the interpolation settings of the X and Y reference potentiometers 91 and 92 as will become apparent below.
The addressed region 99 of the upper surface of the wafer 30 is illuminated by light directed from a lamp 101 to an illumina-tion projection lens 102 and thence to a beam splitting mirror 103 ~rom which it is re~lected through the projection lens 104 onto the addressed region o~ the upper surface of the wafex. An image of ~he illuminated addressed region 9g of the upper surface of th~ wafer 30 i~ projected back through the project~on lens 104 onto the back Yide of the mask 98 for viewin~ with the patte n of the maRk through the microscope 105. Thus, the operator is 30 ~ble to observe through the microRcope 105 a portion 106 of the ~. !

r7~r~

pattern of the masX 98 (i.e., that portion falling within the field o~ the micro~4~ n~ a corre~ponding portion of the image of the illuminated r~gion 99 of khe upper surface of the wafer 30.
In cases ~here the ~)af~r 30 has been through one or more s~eps in its processing, an image of a circuit pattern formed on the illuminated address~d region 99 of the upper surface of the wafer is observable with the pattern of the mask 98 through the microscope 105. The pattern of the mask 9B and the image o the circuit pattern of the wafer can be brought into precise alignment by observing them through the microscope 105 while adjusting the interpolating settings of the X and ~ reference p~tentiometers 91 and 92 to align them to within better than one tenth of a micr~n.
This precision is obtainable because the mask 98 is stationary rela-tive to the granite block while the wafer 30 and, h~nce, the image of the illuminated addressed region 99 of the wafer are moved rela-tive to the mask and the grani$e block with the worX stage 24, which is locked by the X and Y servo mQtors 76 and 72 as described abovP,for movement with the eenSor stage 46.
The interpolated addressed region 99 of the wafer 30 is then ~xposed in accordance with the pattern of the mask 98 by employing the projection light source 29 of Figure 1 to illuminate the pa~-tern of the mask and ~y projecting an image of the illuminated pattern o~ the masX through the projection lens 104 onto ~he region 99 of the wafer. Following this exposure opera~ion, the interpolated (or zeroed). addressed p~si~ion of the work st~g2 24 is used as a referenc~ position from which the programmer 73 automatically causes the wor~ stage to be ~equentially ~oved to other pred*termined addre~ed positions so as to sequentially p~sition o~her regions of the wafer 30 for exp~sure in accordance with the pattern o ~he ma~k 98 (those regions being spaced froM

~rJ

each other by predetermined distances related to the ~ize of the image of the pattern o~ ~h~ ~sk as projected onto the wafer).
The step-and-repeat alignment and exposure machine 20 o~ Figures 1 and 2 thu~ permi~s adjustments to be made in the addressed position of the work stage 24 in order to compensate for slight errors in the po~it~oning of the wafer 30 on the work stage by the automatic workpiece handling unit 28 during the wafer loading operation.
As previously described with reference to Figures 2 and 3, an image of an illuminated region ~f the array 45 cf addressing indicia 59 i5 projected onto the sensing window plate 52 of the sensor stage 46. This is done in such a manner that the front sid2 of the border 62 (~hich is aligned with the X axis and employed as a reference ~or the Y coordinate rows of addressing indicia 59 and which is di posed cl~sest to the reader in the orienta~ion of Figure 2) is projacted onto the sensing window plate 5?
along the far side thereof from the reader. Similarly, the left-hand side of the bordsr 62 (which i5 aligned with the ~ axis and em~loyed as a reference for the X coDrdinate c~lumns of addres-~0 sing indicia 59) is projected onto the ~ensing window plate 52along the right-hand side thereof. Border senqing windows 114 ~nd 115 of the ~ensing window plate 52 and corresponding dio~e~
116 and 117 of the sensing diode plate 56 are arranged for sensing the re~pective Y and X reference sides of the border 62. The 3ignals produced by the~respective diodes 116 and 117 ~as shown in Figure 7 ~or one of the diodes) are each applied ( as ~hawn in Figure 8 for the diode 116) ~o a respective amplifier 118 for amplification and thence to one input of ~ respective threshold detector 119 for compari~on with a reference signal d~rived from a r~spective refer~nce pot~nti~m~ter 120 and applied to another 7~

input ~f the thre~hold detector. m e output of each threshold dete~tor 119 is applie~ to the programmer 73 (such as a ~exas Instrument 16 bit Model ~99Q0 microprocessor) to indicate the crossing o~ the respective Y or X reference sides of the b~rd~r 62.
More particularly, the signal level I produced by each di~de 116 or 117 is shown:in Figure 7 as a function of the po~ition of ~he respective border sensing window 114 or 115 relative to the image of the illuminated region of the array 45 ~f addressing indicia 59 projected thereon. When ~he border sensing window 114 or 115 is disposed entirely within a portion of that image con-taining only the addressing indicia 59, which provide a reflectivlty coefficient of approximately 25 percent9 the signal level I pro-duced by the corresponding di~d~ 116 or ~17 is at 25 percent of full scale. Mowever, as a portion of that image containing a portion of the ~order 62, which has a reflPctivity c~efficient of 100 percent, moves across the border sensing window 114 or 115, the signal le~el I produced by the c~rresponding diode 116 or 117 begins to increase as ~he image of that p~rti.on of the border beginR to cover the border sensing window. When the image of that pcrtion of the border 62 completely covers the border sensing window 114 or 115, the signal level I produced by ~he corresp~nding diode 116 or 117 is at 100 percent of full scale. Each threshold detector 119 i8 set so that a signal 10vel corresp~ndlng ~o five eighths of full scale (5~8 Iloo% as shown in Figure 7) triggers ~he threshold detector ~o provide an output indicating ~he sensing oE the border 62~
W~en the step and-repeat alignment and exposure machine 20 of Figures 1-3 is turned on, the progr~mmer ~3 c~u~es the work 3tage 24 to be moved 50 ~hat the sensor ~tage 46 senses the X and Y referen~e sides o ~he border 62 enclosing ~he array 45 of X

~ ~Q ~ ~7 coordinate ~olumns and Y coordinate rows of addressing indicia 59 and so that the X and Y count~rs 68 and 6g are set to ref~rence the X coordinate column and Y coordinate row counts to the respec-tive X and Y reference sides of the bord~r. More particularly, the X reference ide of the border 62 is sens~d by the proyrammer 73 causing th~ work st~ge 24 tv be moved in the negative direction along the X axis, while maintaining an initial Y coordinate address, until such time a~ an image of the X reference side o the border is detected by border sensing window 115, the corresponding diode 117, and the corre~pondinq threshold detector 119 (see Figure 8) as described a~ove. The output of ~he corresp~nding ~hreshold detector 119 is applied to the programmer 73 for referencing the X co~rdinate column count of the X counter 68 to the respective X re~erence side of the border 62. ~he programmer 73 then causes the work stage 24 to be moved in the positive direction along the X axis, while maintaining the initial Y coordinate address, until such time as the X counter 68 has counted to the center X co~r-dinate column of the array 45 of addres~ing indicla 59. The pro-y- r then causes the wor~ stage 24 to be moved in the negative 20 direction along the Y axis, while maintaining the center X coor--dinate address, until such time as an image of the Y reference side of the border 62 is detected by the border ~en~ing window 114, the corresponding diode 116, and the corr~sponding thre~hold detector 119. The output of the corresponding threshold det~ector 119 is applied to ~he programmer 73 for referencing the Y c~ordinate row count of the Y counter 69 to the respective Y reference ~ide vf the border 62.
It should be noted that the fir~t senqing diode pair 57, whic~h is empl~yed wi~ the l3witch Sx and the anal~g ~ervo amplifier ~0 131 in locking the work stage 24 in pïace ( relative to the sensor '7~7 ~, stage 46) at the X co~rdinate of the addressed p~sition, as pre-viously described with re~erence to Figures 2-4 and 6, comprises the sensing diode pair 57 furthest from the diode 116 employed for sensing the Y reference sid~ of the border 62. m is permits the ~ensor stage 46 to be e~ficiently employed both in ~ensing the Y reference ~ide of:the border 62 and in stopping the mo~ement of the wor~ ~tage 24 and locking it in place at the X coordinate of the addressed position. For similar reasons, the sensing diode pair 58, which is amployed with the switch Sy and the analog servo amplifier 82 in locking th~ work stage 24 in pla~e at the Y coor-dinate of the addressed p~sition, similarly comprises the sensing diode pair 58 furthest from the diode 117 employed for .~ensing the X reference side of the bvrder 62.
The above-described X-Y addressable workpiece positioner and step-and-repeat alignment and exposure machine 20 using ~ame have the advantage of permitting the work stage 24 and, h~once, a w~rk-pi~ce held thereby to be stepped sequentially to addressable pasi-tions precisely determinable to better than one ten th of a micron .
The stepping of the work stage 24 and, hence, the workpiece held 20 thereby from one addressable position to the next is accomplished by movement of the work stage and the workpiece along a path which is the shortest distance between those two addressed positions and which is precisely defined by a c~ on two-dimensional array 45 of X and Y ~oordinate addressing indicia. This shor~ens the ~t~pping time and increases the t~x~hput of the machine. More-over, the accuracy of ~he addres~ed positions is precisely deter-mined by ~he precise po~itioning of the X and Y coordinate addressing indicia rather than being dependent upon the pr~cision o the orthogonality of costly bearing a~emblies or upon laser inter-Xerometers requiriny envi~ ntally oontroll~d chambers.

` C~

'7~ 7 , ..~

As used herein, a "two-di~nensional array" of addressing indicia shall be defined to include irldicia arrayed ( i . e ., serialized) in two directions. 'rhlls, a series of parallel lines i9 a one-dimensional array, whereas a series c~f dlots æeriali~d in two dir~ctions, as in Figure 3, comprises a ~wo-dimensi~nal array.

~J

Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows;

1. An addressable positioner comprising:
stage means, movable along a pair of coordinate axes, for holding an object to be positioned;
a two-dimentional array of coordinate addressing indicia, affixed to the stage means, for movement with the stage means;
sensor means for sensing the coordinate addressing indicia to provide output information determinative of the coordinate position of the stage means; and control means, responsive to the output information from the sensor means and to input control information, for moving the stage means to coordinate positions deter-mined by the input control information.

2. An addressable positioner as in claim 1 wherein said control means includes first control means, responsive to the output information from the sensor means and to input control information determinative of a desired coordinate position of the stage means, for moving the stage means to the desired coordinate position.

3. An addressable positioner as in claim 2 wherein:
said sensor means is also movable along a pair of coordinate axes; and said control means further includes second control means for moving the sensor means to effect movement of the stage means to an interpolation of the desired coordinate position.

4. An addressable positioner as in claim 3 wherein:
said positioner includes detector means for providing output information determinative of the coordinate position of the sensor means; and said second control means is responsive to the output information from the detector means and to input control information determinative of a different interpolating coordinate position for moving the sensor means to said interpolating coordinate position to effect movement of the stage means to said interpolation of the desired coordinate position.

5. An addressable positioner as in claim 4 wherein said sensor means is movable along the same pair of coordinate axes as the stage means.

6. An addressable positioner as in claim 3 wherein said stage means may be coupled for movement with respect to movement of the sensor means.

7. An addressable positioner as in claim 6 wherein said first control means includes switchable means for coupling the stage means to move with respect to movement of the sensor means.

8. An addressable positioner as in claim 7 wherein:
said switchable means is operable, once the stage means is moved to within a preselected tolerance of the desired coordinate position, for effecting movement of the stage means to the desired coordinate position and for thereupon coupling the stage means to move with respect to movement of the sensor means; and said second control means may then be employed for moving the sensor means to effect movement of the stage means to said interpolation of the desired coordinate position.

9. An addressable positioner as in claim 3 wherein said first and second control means may be concurrently employed for moving the stage means and the sensor means to effect movement of the stage means to said interpolation of the desired coordinate position

10. An addressable positioner as in claim 9 wherein said first control means includes switchable means, operable once the stage means is moved to within a pre-selected tolerance of the desired coordinate position, for effecting movement of the stage means to said interpolation of the desired coordinate position.

11. An addressable positioner as in claim 10 wherein said switchable means is operable for Coupling the stage means to move with respect to movement of the sensor means once the stage means is moved to said interpolation of the desired coordinate position.

12. An addressable positioner as in claim 6 wherein:
said positioner includes imaging means for imaging a region of the object adjacent to a pattern with which the imaged region of the object is to be aligned;
said positioner further includes optical means for viewing the pattern and the imaged region of the object, and said second control means is operable for moving the sensor means and the stage means, when coupled for movement with respect to movement of the sensor means, to bring the pattern and imaged region of the object viewed by the optical means into alignment.

13. An addressable positioner as in claim 12 wherein:
said first control means is operable for sequentially moving the stage means to different desired coordinate positions to sequentially address different regions of the object;
said imaging means is operable for sequentially imaging each addressed region of the object adjacent to the pattern;
said optical means is operable for sequentially viewing the pattern with each imaged addressed region of the object; and said second control means is operable for selectively moving the sensor means and the stage means, when coupled for movement with respect to movement of the sensor means, to bring the pattern and the imaged addressed region of the object viewed by the optical means at selected ones of the different desired coordinate positions into alignment.

14. An addressable positioner as in claim 8 wherein:
said pattern comprises the pattern of a mask; and each of said addressed regions of the object is to be exposed in accordance with the pattern of the mask.

15. An addressable positioner as in claim 4 wherein.

said second control means includes variable input means for providing the input control information deter-minative of said interpolating coordinate position of the sensor means;
comparative means, responsive to the output informa-tion from the detector means and to the input control information from the variable input means for deriving an error signal; and servo drive means, coupled to the sensor means and responsive to the error signal from the comparative means~
for moving the sensor means to said interpolating coordinate position to effect movement of the stage means to said interpolation of the desir~d coordinate position.

16. An addressable positioner a^ in claim 15 wherein:
said detector means comprises a pair of linear variable differential transformers, each operable for providing output information determinative of a corresponding different coordinate of the actual coordinate posi~ion of the sensor means;
said variable input means comprises a pair of potentio meters, each operable for providing input control information determinative of a corresponding different coordinate of said interpolating coordinate posi~ion of the sensor means;
said comparative means comprises a pair of comparator means) each responsive to the output information from a corresponding different one of the linear varia~le differen-tial transformers and the input control information from a corresponding different one of the potentiometers, for ~ 31 -deriving an error signal; and said servo drive means includes a pair of servo motors, each coupled to the sensor means and each responsive to the error signal from a corresponding different one of the comparator means, for moving the sensor means along a corresponding different coordinate axis to a corresponding different coordinate of said interpolating coordinate position of the sensor means.

17. An addressable positioner as in claim 2 wherein said first control means includes switchable means, operable once the stage means is moved to within a preselected tolerance of the desired coordinate position, for effecting movement of the stage means to the desired coordinate position.

18. An addressable positioner as in claim 17 wherein said switchable means is also operable for coupling the stage means to move with respect to move-ment of the sensor means once the stage means is moved to the desired coordinate position.

19. An addressable positioner as in claim 17vwherein said first control means includes:
control input means for providing the input control information determinative of the desired coordinate position of the stage means;
comparative means, responsive to the output information from the sensor means and to the input control information from the control input means, for deriving an error signal;
and servo drive means, coupled to the stage means and responsive to the error signal from the last-mentioned comparative means, for moving the stage means to within a preselected tolerance of the desired coordinate position.

20. An addressable positioner as in claim 19 wherein said first control means further includes:
first amplifying means for receiving and amplifying the output information from the sensor means; and counting means, responsive to the amplified output information from the first amplifying means, for providing the last-mentioned comparative means with input position information indicative of the position of the stage means.

21. An addressable positioner as in claim 20 wherein:
said switchable means includes second amplifying means for receiving and amplifying a portion of the output information from the sensor means;
said switchable means further includes switching means, operable once the stage means is moved to within the preselected tolerance of the desired coordinate position, for switching said portion of the output information from the first amplifying means to the second amplifying means;
and said last-mentioned servo drive means is responsive to the amplified portion of the output information from the second amplifying means for moving the stage means to the desired coordinate position.

22. An addressable positioner as in claim 21 wherein:

said control input means comprises a pair of control inputs, each operable for providing input control informa-tion determinative of a corresponding different coordinate of the desired coordinate position of the stage means;
said first amplifying means comprises two pairs of amplifiers, each pair being operable for receiving and amplifying output information determinative of a correspond-ing different coordinate of the coordinate position of the stage means;
said counting means comprises a Fair of counters, each responsive to the output information from a corresponding different pair of said two pairs of amplifiers, for providing input position information indicative of a corresponding different coordinate of the coordinate position of the stage means;
said last-mentioned comparative means comprises a pair of comparator means, each responsive to the input position information from a corresponding different one of the counters and to the input control information from a corresponding different one of the pair of control inputs, for deriving an error signal;
said last-mentioned servo drive means includes a pair of servo motors, each coupled to the stage means and each responsive to the error signal from a corresponding different one of the last-mentioned comparator means, for moving the stage means along a corresponding different coordinate axis to within the preselected tolerance of a corresponding different coordinate of the desired coordinate position;
said second amplifying means comprises another pair of amplifiers, each operable for receiving and amplifying a portion of the output information determinative of a corresponding different coordinate of the coordinate position of the stage means;
said switching means comprises a pair of switches, each operable once the stage means is moved to within the preselected tolerance of a corresponding different coordinate of the desired coordinate position, for switching a portion of the output information determinative of a corresponding different coordinate of the coordinate position of the stage means from one of the amplifiers of a corresponding different pair of said two pairs of amplifiers to a corresponding different one of the amplifiers of said other pair of amplifiers; and each of said last-mentioned servo motors is responsive to the amplified portion of the output information from a corresponding different one of the amplifiers of said other pair of amplifiers for moving the stage means to said corresponding different coordinate of the desired coordinate position.

23. An addressable positioner as in claim 22 wherein:
said sensor means is operable for supplying each of said two pairs of amplifiers with a corresponding pair of output signals comprising output information determinative of a corresponding different coordinate of the coordinate position of the stage means;
each of said switches is operable, once the stage means is moved to within the preselected tolerance of the corresponding coordinate of the desired coordinate position, for switching the amplified output signal from said one of the amplifiers of the corresponding pair of said two pairs of amplifiers to the corresponding one of the amplifiers of said other pair of amplifiers; and each of said last-mentioned servo motors is caused to lock the stage means to the corresponding different coordinate of the desired coordinate position when the amplified output signal switched to the corresponding one of the amplifiers of said other pair of amplifiers attains a preselected value.

24. An addressable positioner as in claim 2, 3 or 17 wherein:
said sensor means provides a plurality of output signals comprising the output information determinative of the coordinate position of the stage means; and said stage means is located at the desired coordinate when each of selected ones of the output signals from the sensor means attains a preselected value.

25. An addressable positioner as in claim 24 wherein the preselected value is zero.

26. An addressable positioner as in claim 1 wherein said coordinate addressing indicia are uniformly arrayed in rows parallel to one of the first-mentioned coordinate axes and in columns parallel to the other of the first-mentioned coordinate axes.

27. An addressable positioner as in claim 26 wherein said coordinate addressing indicia are of uniform size.

28. An addressable positioner as in claim 26 or 27 wherein said coordinate addressing indicia are rectangular in shape.

29. An addressable positioner as in claim 26 wherein said coordinate addressing indicia are square.

30. An addressable positioner as in claim 26, 27 or 29 wherein said coordinate addressing indicia comprise reflective regions formed on a transparent plate disposed between the sensor means and the position of the workpiece.

31. An addressable positioner as in claim 2 wherein said coordinate addressing indicia are uniformly arrayed in rows parallel to one of the first-mentioned coordinate axes and in columns parallel to the other of the first-mentioned coordinate axes.

32. An addressable positioner as in claim 31 wherein said coordinate addressing indicia are of uniform size.

33. An addressable positioner as in claim 31 or 32 wherein said coordinate addressing indicia comprise reflective regions formed on a transparent plate disposed between the sensor means and the position of the workpiece.

34. An addressable positioner as in claim 3, 17 or 18 wherein said coordinate addressing indicia are uniformly arrayed in rows parallel to one of the first-mentioned coordinate axes and in columns parallel to the other of the first-mentioned coordinate axes.

35. An addressable positioner as in claim 26 wherein said sensor means comprises a plurality of sensing means disposed for sensing the coordinate addressing indicia to provide the output information determinative of the coordinate position of the stage means.

36. An addressable positioner as in claim 35 wherein said plurality of sensing means includes:
at least a first pair of sensing means disposed for sensing the coordinate addressing indicia arrayed in rows parallel to said one of the first-mentioned coordinate axes to provide output information determinative of one coordinate of the coordinate position of the stage means; and at least a second pair of sensing means disposed for sensing the coordinate addressing indicia arrayed in columns parallel to said other of the first-mentioned coordinate axes to provide output information determinative of another coordinate of the coordinate position of the stage means.

37. An addressable positioner as in claim 36 wherein:
said sensing means of the first pair of sensing means are offset from one another along said other of the first-mentioned coordinate axes to provide output information determinative of the coordinate position and the direction of movement of the stage means along said other of the first-mentioned coordinate axes; and said sensing means of the second pair of sensing means are offset from one another along said one of the first-mentioned coordinate axes to provide output information determinative of the coordinate position and the direction of movement of the stage means along said one of first-mentioned coordinate axes.

38. An addressable positioner as in claim 35 wherein each of said sensing means comprises a transparent window communicating with a corresponding photodetector.

39. An addressable positioner as in claim 38 wherein each of said windows comprises a group of parallel, transparent, elongated, rectangular regions formed in an opaque plate with each region having an axis of elongation parallel to the rows or columns of addressing indicia to be sensed thereby, having a width equal to that of each respective row or column of addressing indicia to be sensed thereby, having a length equal to that of an integer multiple of the center-to center spacing of the respective rows or columns of addressing indicia to be sensed thereby, and having a center-to-center spacing equal to that of an integer multiple of the center-to-center spacing of the addressing indicia.

40. An addressable positioner as in claim 37 wherein waid sensing means of each pair of sensing means are offset from one another along the respective first-mentioned coordinate axis by substantially an odd integer multiple of ninety degrees.

41. An addressable positioner as in claim 31 wherein said sensor means comprises a plurality of sensing means disposed for sensing the coordinate addressing indicia to provide the output information determinative of the coordinate position of the stage means.

42. An addressable positioner as in claim 41 wherein said plurality of sensing means includes:

at least a first pair of sensing means disposed for sensing the coordinate addressing indicia arrayed in rows parallel to said one of the first-mentioned coordinate axes to provide output information determinative of one coordinate of the coordinate position of the stage means; and at least a second pair of sensing means disposed for sensing the coordinate addressing indicia arrayed in columns parallel to said other of the first-mentioned coordinate axes to provide output information determinative of another coordinate of the coordinate position of the stage means.

43. An addressable positioner as in claim 42 wherein:
said sensing means of the first pair of sensing means are offset from one another along said other of the first-mentioned coordinate axes to provide output information determinative of the coordinate position and the direction of movement of the stage means along said other of the first-mentioned coordinate axis; and said sensing means of the second pair of sensing means are offset from one another along said one of the first-mentioned coordinate axes to provide output information determinative of the coordinate position and the direction of movement of the stage means along said one of first-mentioned coordinate axes.

44. An addressable positioner as in claim 41 wherein each of said sensing means comprises a transparent window communicating with a corresponding photodetector.

45. An addressable positioner as in claim 44 wherein each of said windows comprises a group of parallel, transparent, elongated, rectangular regions formed in an opaque plate with each region having an axis of elongation parallel to the rows or columns of addressing indicia to be sensed thereby, having a width equal to that of each respective row or column of addressing indicia to be sensed thereby, having a length equal to that of an integer multiple of the center-to-center spacing of the respective rows or columns of addressing indicia to be sensed thereby, and having a center-to-center spacing equal to that of an integer multiple of the center-to-center spacing of the addressing indicia.

46. An addressable positioner as in claim 38 wherein:
said windows are transparent regions formed in an opaque plate; and said photodetectors are disposed on another plate.

47. An addressable positioner as in claim 38 including optical means for projecting an image of a portion of the array of coordinate addressing indicia onto the sensor means.

48. An addressable positioner as in claim 47 including a plurality of lenses each disposed between a corresponding different one of the windows and a corresponding different one of the photodetectors for imaging light from the last-mentioned optical means through the corresponding window onto the corresponding photodetector at an intensity determined by the portions of coordinate addressing indicia detected by the correspond-ing window.

49. An addressable positioner as in claim 1 wherein:
said positioner includes optical means for projecting an image of a portion of the array of coordinate addressing indicia onto the sensor means; and said sensor means is operable for sensing the coordinate addressing indicia in that image to provide the output information determinative of the coordinate position of the stage means.

50. An addressable positioner as in claim 49 wherein said last-mentioned optical means includes a magnifying lens for enlarging the image of said portion of the array of coordinate addressing indicia projected onto the sensor means.

51. An addressable positioner as in claim 49 or 50 wherein said last-mentioned optical means includes means for illuminating said portion of the array of coordinate addressing indicia.

52. An addressable positioner as in claim 1 wherein said input control information for the stage means is provided by a microprocessor.

53. An addressable positioner as in claim 52 wherein said input control information for the sensor means is also provided by the microprocessor.

54. An addressable positioner as in claim 1, 2 or 3 wherein:
said first-mentioned coordinate axes are orthogonal X and Y axes; and said stage means is movable in a plane parallel to or containing those X and Y axes.

55. An addressable positioner as in claim 1, 2 or 3 wherein said object is a semiconductive wafer.

56. An addressable positioner as in claim 4 or 5 wherein said stage means may be coupled for movement with respect to movement of the sensor means.

57. An addressable positioner as in claim 1, 2 or 3 wherein said sensor means comprises a plurality of sensing means disposed for sensing the coordinate addressing indicia to provide the output information determinative of the coordinate position of the stage means.

58. An addressable positioner as in claim 57 wherein each of said sensing means comprises a transparent window communicating with a corresponding photodetector.

59. An addressable positioner as in claim 58 wherein each of said windows comprises a group of parallel, transparent, elongated, rectangular regions formed in an opaque plate with each region having an axis of elongation parallel to the rows or columns of addressing indicia to be sensed thereby;

having a width equal to that of each respective row or column of addressing indicia to be sensed thereby, having a length equal to that of an integer multiple of the center-to-center spacing of the respective rows or columns of addressing indicia to be sensed thereby, and having a center-to-center spacing equal to that of an integer multiple of the center-to-center spacing of the addressing indicia.

60. An addressable positioner as in claim 58 wherein:
said windows are transparent regions formed in an opaque plate; and said photodetectors are disposed on another plate.

61. An addressable positioner as in claim 60 including a plurality of lenses each disposed between a corresponding different one of the windows and a corresponding different one of the photodetectors for imaging light through the corresponding window onto the corresponding photodetector at an intensity determined by the portions of coordinate addressing indicia detected by the corresponding window.

62. An addressable positioning method comprising the steps of:
placing an object to be positioned on a stage that is movable along coordinate axes in a plane containing or parallel to those axes and that has a two-dimensional array of coordinate addressing indicia affixed thereto for movement therewith;

projecting an image of at least a portion of the array of coordinate addressing indicia onto a sensor;
sensing the coordinate addressing indicia of the image to derive output information determinative of the coordinate position of the stage;
comparing the coordinate position of the stage with a designated coordinate position to derive an error output;
and moving the stage to the designated coordinate position in response to the error output.

63. An addressable positioning method as in claim 62 including the step of moving the sensor to effect movement of the stage to an interpolation of the designated coordinate position.

64. An addressable positioning method as in claim 62 including the steps of:
imaging a region of the object adjacent to a stationary pattern with which the imaged region of the object is to be aligned; and moving the sensor to effect movement of the stage to an interpolation of the designated coordinate position and bring the imaged region of the object into precise alignment with the stationary pattern.

65. An addressable positioning method as in claim 64 including the steps of:
sequentially changing the designated coordinate position of the stage to address different regions of the object;
sequentially moving the stage to each designated coordinate position;

sequentially imaging each addressed region of the object adjacent to the stationary pattern with which each imaged addressed region of the object is to be aligned; and selectively moving the sensor to effect movement of the stage to an interpolation of selected ones of the designated coordinate positions and bring the addressed region of the object at each selected designated coordinate position into alignment with the stationary pattern.

66. An addressable positioning method as in claim 62 wherein the sensing step comprises sensing the coordinate addressing indicia through at least two pairs of pattern recognition windows included in the sensor with each pair disposed for independently recognizing and sensing coordinate addressing indicia aligned parallel to a different one of the coordinate axes to derive output information determinative of a different coordinate of the designated coordinate position and to derive a sensed output through each window of each pair.

67. An addressable positioning method as in claim 66 wherein the object comprises a semicon-ductive wafer.

68. An addressable positioning method as in claim 66 or 67 wherein each of the pattern recognition windows includes an array of parallel transparent elongated regions with the axis of elong-ation of those regions being parallel to one of the coordinate axes to derive output information deter-minative of a coordinate of the designated coordinate position along the other of the coordinate axes.

69. An addressable positioning method as in claim 63 wherein the sensing step comprises sensing the coordinate addressing indicia through at least two pairs of pattern recognition windows included in the sensor with each pair disposed for independently recognizing and sensing coordinate addressing indicia aligned parallel to a different one of the coordinate axes to derive output information determinative of a different coordinate of the designated coordinate position and to derive a sensed output through each window of each pair.

70. An addressable positioning method as in claim 69 wherein the object comprises a semi-conductive wafer.

71. An addressable positioning method as in claim 69 or 70 wherein each of the pattern recognition windows includes an array of parallel transparent elongated regions with the axis of elongation of those regions being parallel to one of the coordinate axes to derive output information determinative of a coordinate of the designated coordinate position along the other of the coordinate axes.

72. An addressable positioning method as in claim 62, 63 or 64 wherein the coordinate addressing indicia are uniformly arrayed dots.

73. An addressable positioning method as in claim 64 or 65 wherein:
the object comprises a semiconductive wafer; and the stationary pattern to be aligned therewith comprises the pattern of a masking element in accordance with which the semiconductive wafer is to be exposed.

74. An adaptive servo control system comprising:
first and second stage means respectively movable along orthogonal axes for positioning a workpiece relative to a work apparatus;
first and second drive means respectively responsive to first and second drive signals and operative to drive said first and second stage means along said axes;
position detector means for monitoring the position of said first and second stage means relative to the work apparatus and including a reference substrate carried by one of said stage means and having orthogonal dimension position related indicia disposed thereupon, and means for sensing said indicia and developing first and second actual position signals corres-ponding to the positioning of said substrate along said axes;
input means for generating first and second desired position signals corresponding to positions along said axes to which said first and second stage means are to be driven; and first and second position control means for respec-tively comparing said first and second desired position signals to said first and second actual position signals and for developing said first and second drive signals for application to said first and second drive means, respectively to cause said workpiece to be driven to a desired position.

75. An adaptive servo control system as in claim 74 wherein said indicia are embodied in a plurality of uniformly configured reflective surface areas of said substrate and uniformly arrayed in rows and columns.

76. An adaptive servo control system as in claim 74 or 75 wherein each element of said indicia is rectangular in configuration.

77. An adaptive servo control system as in claim 74 wherein said substrate is translucent and said indicia are opaque.

78. An adaptive servo control system as in claim 74, 75 or 77 wherein said means for sensing said indicia includes light source means and photodetector means.

79. An adaptive servo control system as in claim 74 wherein:
said position detector means includes an optical system for casting an image of at least a portion of said reference substrate onto an apertured reticle, and photodetection means disposed behind the apertures of said reticle and operative to generate electrical outputs from which said first and second actual position signals are developed; and said control system further comprises third drive means responsive to a third drive signal and operative to move said reticle in a first direction relative to said optical system, fourth drive means responsive to a fourth drive signal and operative to move said reticle in a second direction relative to said optical system, first reticle follower means for developing a first reticle position signal, second reticle follower means for developing a second reticle position signal, first reticle position control means including a first servo system responsive to a first input adjust signal and said first reticle position signal and operative to generate said third drive signal, and second reticle position control means including a second servo system responsive to a second input adjust signal and said second reticle position signal and operative to generate said fourth drive signal.

80. An adaptive servo control system as in claim 74 wherein said position detector means includes:
an optical system for casting an image of at least a portion of said reference substrate onto an apertured reticle; and photodetection means disposed to receive said image and operative to generate electrical signals from which said first and second actual position signals are developed.

81. An adaptive servo control system as in claim 80 wherein the indicia contained on said reference substrate include a plurality of like, rectangularly-shaped reflective surface areas arrayed in orderly rows and columns.

82. An adaptive servo control system as in claim 80 wherein the indicia contained on said reference substrate include a plurality of like, rectangularly-shaped opaque surface areas arrayed in orderly rows and columns.

83. An adaptive servo control system as in claim 74 wherein said position detector means includes:
means for illuminating said indicia; and photosensitive means for detecting movement of said indicia relative to said photosensitive means.

84. A servo control system comprising:
stage means movable along orthogonal axes for positioning a workpiece relative to a work apparatus;
first and second drive means respectively responsive to first and second drive signals and operative to drive said stage means along said axes;
position detector means for monitoring the position of said stage means relative to the work apparatus and including a reference substrate carried by said stage means and having orthogonal dimension position related indicia disposed thereupon, and means for sensing said indicia and developing first and second actual position signals corres-ponding to the positioning of said substrate along said axes;
input means for generating first and second desired position signals corresponding to positions along said axes to which said stage means is to be driven; and first and second position control means for respec-tively comparing said first and second desired position signals to said first and second actual position signals and for developing said first and second drive signals for application to said first and second drive means, respectively, to cause said workpiece to be driven to a desired position.

85. A servo control system as in claim 84 wherein said indicia are embodied in a plurality of uniformly configured reflective surface areas of said substrate uniformly arrayed in rows and columns.

86. A servo control system as in claim 84 or 85 wherein each element of said indicia is rectangular in configuration.

87. A servo control system as in claim 84 wherein said substrate is translucent and said indicia are opaque.

88. A servo control system as in claim 84, 85 or 87 wherein said means for sensing said indicia includes light source means and photodetector means.

89. A servo control system as in claim 84 wherein:
said position detector means includes an optical system for casting an image of at least a portion of said reference substrate onto an apertured reticle, and photodetection means disposed behind the apertures of said reticle and operative to generate electrical outputs from which said first and second actual position signals are developed; and said control system further comprises third drive means responsive to a third drive signal and operative to move said reticle in a first direction relative to said optical system, fourth drive means responsive to a fourth drive signal and operative to move said reticle in a second direction relative to said optical system, first reticle follower means for developing a first reticle position signal, second reticle follower means for developing a second reticle position signal, first reticle position control means including a first servo system responsive to a first input adjust signal and said first reticle position signal and operative to generate said third drive signal, and second reticle position control means including a second servo system responsive to a second input adjust signal and said second reticle position signal and operative to generate said fourth drive signal.

90. A servo control system as in claim 84 wherein said position detector means includes:
an optical system for casting an image of at least a portion of said reference substrate onto an apertured reticle; and photodetection means disposed to receive said image and operative to generate electrical signals from which said first and second actual position signals are developed.

91. A servo control system as in claim 90 wherein the indicia contained on said reference substrate include a plurality of like, rectangularly-shaped reflective surface areas arrayed in orderly rows and columns.

92. A servo control system as in claim 90 wherein the indicia contained on said reference substrate include a plurality of like, rectangularly-shaped opaque surface areas arrayed in orderly rows and columns.

93. A servo control system as in claim 84 wherein said position detector means includes;

means for illuminating said indicia; and photosensitive means for detecting movement of said indicia relative to said photosensitive means.

94. An X-Y addressable workpiece positioning method comprising the steps of:
coupling a workpiece to a work stage movable in X
and Y directions within a common plane of movement defined by the X and Y directions and within which the workpiece is to be positioned, the work stage having a two-dimensional array of X and Y coordinate positioning indicia affixed thereto for effecting positioning of the work stage with the workpiece;
projecting an enlarged image of at least a portion of the array of X and Y coordinate positioning indicia onto a relatively stationary sensor stage;
sensing the enlarged image projected onto the sensor stage to determine the X and Y coordinates of the position of the work stage;
comparing the X and Y coordinates of the position of the work stage with the X and Y coordinates of a different position of the work stage to derive an error output; and moving the work stage with the workpiece and the array of X and Y coordinate positioning indicia to the different position in response to the error output to address a portion of the workpiece.

95. A method as in claim 94 including the step of moving the relatively stationary sensor stage relative to the enlarged image projected thereon in at least one of the X and Y directions for interpolating the position of the work stage and thereby causing the work stage, which is being moved in response to the error output, to be moved to the interpolated position.

96. A method as in claim 94 or 95 wherein the array of X and Y coordinate positioning indicia comprises a two-dimensional array of dots.

97. A method as in claim 94 including the steps of:
imaging the addressed portion of the workpiece;
imaging a stationary pattern to be aligned with respect to the imaged addressed portion of the workpiece;
superimposing the images of the addressed portion of the workpiece and of the stationary pattern; and moving the relatively stationary sensor stage relative to the stationary pattern in at least one of the X and Y directions to cause the position of the work stage to be interpolated for precisely aligning the images of the addressed portion of the workpiece and of the stationary pattern with respect to one another.

98. A method as in claim 97 wherein:
said workpiece is a semiconductive wafer; and said stationary pattern is a mask pattern in accordance with which the addressed portion of the semi-conductive wafer is to be exposed.

99. A method as in claim 98 including the step of sequentially changing the position of the work stage to sequentially address different portions of the semi-conductive wafer and allow those portions of the semi-conductive wafer to be sequentially exposed in accordance with the mask pattern.

100. An X-Y addressable workpiece positioning apparatus comprising:
work stage means movable in both X and Y directions within a common plane of movement defined by the X and Y directions and within which a workpiece is to be positioned;
said work stage means including holding means for holding the workpiece for movement with the work stage means;
indicia means comprising a two-dimensional array of X and Y coordinate positioning indicia affixed to the work stage means and movable therewith for effecting positioning of the work stage means;
relatively stationary sensor stage means for deter-mining the X and Y coordinates of the work stage means;
projector means fox projecting an enlarged image of at least a portion of the array of X and Y coordinate positioning indicia onto the sensor stage means;
said sensor stage means sensing the enlarged image projected thereon to derive an output determinative of the X and Y coordinates of the position of the work stage;
comparative means for comparing the X and Y coordinates of the position of the work stage means with the X and Y
coordinates of a different position of the work stage means to derive an error output; and drive means for moving the work stage means and the array of X and Y coordinate positioning indicia to the different position in response to the error output to address a portion of the workpiece.

101. An apparatus as in claim 100 including means for moving the sensor stage in at least one of the X and Y directions for interpolating the position of the work stage means and thereby causing the work stage means, which is being moved in response to the error output, to be moved to the interpolated position.

102. An apparatus as in claim 100 or 101 wherein said two-dimensional array of X and Y coordinate position-ing indicia comprises a two-dimensional array of dots extending in both the X and Y directions.

103. An apparatus as in claim 100 including:
imaging means for imaging the addressed portion of the workpiece;
imaging means for imaging a stationary pattern to be aligned with respect to the imaged addressed portion of the workpiece;
superimposing means for superimposing the images of the addressed portion of the workpiece and of the stationary pattern; and means for moving the relatively stationary sensor stage relative to the stationary pattern in at least one of the X and Y directions to cause the position of the work stage means to be interpolated for precisely aligning the images of the addressed portion of the workpiece and of the stationary pattern with respect to one another.

104. An apparatus as in claim 103 wherein:
said workpiece is a semiconductive wafer; and said stationary pattern is a mask pattern in accordance with which the addressed portion of the semiconductive wafer is to be exposed.

105. An apparatus as in claim 104 including means for sequentially changing the position of the work stage means to sequentially address different portions of the semiconductive wafer and allow those portions of the semi-conductive wafer to be sequentially exposed in accordance with the mask pattern.