CA1253021A - Alignment and focusing system for a scanning mask aligner - Google Patents
Alignment and focusing system for a scanning mask alignerInfo
- Publication number
- CA1253021A CA1253021A CA000437145A CA437145A CA1253021A CA 1253021 A CA1253021 A CA 1253021A CA 000437145 A CA000437145 A CA 000437145A CA 437145 A CA437145 A CA 437145A CA 1253021 A CA1253021 A CA 1253021A
- Authority
- CA
- Canada
- Prior art keywords
- mask
- wafer
- pattern
- grid
- patterns
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
- G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
- G03F9/7003—Alignment type or strategy, e.g. leveling, global alignment
- G03F9/7023—Aligning or positioning in direction perpendicular to substrate surface
- G03F9/7026—Focusing
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
- G03F7/70—Microphotolithographic exposure; Apparatus therefor
- G03F7/70216—Mask projection systems
- G03F7/70358—Scanning exposure, i.e. relative movement of patterned beam and workpiece during imaging
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
- G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
- G03F9/7049—Technique, e.g. interferometric
-
- G—PHYSICS
- G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
- G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
- G03F9/00—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically
- G03F9/70—Registration or positioning of originals, masks, frames, photographic sheets or textured or patterned surfaces, e.g. automatically for microlithography
- G03F9/7073—Alignment marks and their environment
- G03F9/7076—Mark details, e.g. phase grating mark, temporary mark
Abstract
Abstract of Disclosure The present invention is directed to an improvement in an alignment system for a scanning mask aligner employing a pattern on the mask or the wafer or both in the scribe lines that run in the direction of scanning, the improvement comprising a viewing system having optical grids, a system for moving the patterns across the optical grids in the viewing system, the grids corresponding to the directions and spacings of the patterns so that light transmitted through the grid is strongly modulated, and circuitry for comparing the phase modulation from the mask and wafer alignment targets to obtain alignment error signals; further according to the invention, the same system used to measure alignment can also be used to measure how well the mask is focused on the wafer. In this case two images of the mask pattern are arranged so that one is slightly inside of focus and the other is slightly outside of focus, and by comparing the amount of modulation on the two channels it is possible to deduce which of the two is closer to focus and therefore how to shift the focus so that they are equal.
Description
Ml-2955 ~ ;3~2~
ALIGI~MENT AND FOCUSING SYSTEM FOR
A SCANNING MASK ALIGNFR
Field of Invention This invention relates to the field of microlithography and, more particularly, to alignment and/or focusing systems for scanning mask aligners.
The svstem according to the present invention is particularly adapteA, among other possihle uses, for use with a step and scan microlithography projection system.
_ackground of the_Inventlon In the making of micro-circuits the general process followeA is that of generating an oxide film on the sem;conductor su~strate; coating tlle oxide film with a photoresist and then ill~lminating the photoresist through a mask to expose selected portions of the resist. After exposure, the photoresist is Aeveloped, etcheA and further processed. Once this is done the same steps are repeateA a numher of times.
The exposure pattern on the photoresist is determined
ALIGI~MENT AND FOCUSING SYSTEM FOR
A SCANNING MASK ALIGNFR
Field of Invention This invention relates to the field of microlithography and, more particularly, to alignment and/or focusing systems for scanning mask aligners.
The svstem according to the present invention is particularly adapteA, among other possihle uses, for use with a step and scan microlithography projection system.
_ackground of the_Inventlon In the making of micro-circuits the general process followeA is that of generating an oxide film on the sem;conductor su~strate; coating tlle oxide film with a photoresist and then ill~lminating the photoresist through a mask to expose selected portions of the resist. After exposure, the photoresist is Aeveloped, etcheA and further processed. Once this is done the same steps are repeateA a numher of times.
The exposure pattern on the photoresist is determined
2~
_ 2 ~ .
by masks which are prepared for the purpose. Separate masks are used for each of the successive steps. If everything is to appear in the proper place on the micro-circuit a high degree of alignment is necessary between steps. Typical alignment systems employed heretofore are described in U.S. Patents 3,975,364;
4,011,011; 4,006,645; and 4,353,087, for example.
Almost all the current automatic alignment systems require that the mask and wafer be essentially fixed with respect to the alignment system during the alignment process. This is no problem in a step-and-repeat type system, but it is far from ideal in a scanning projection printer since misregistration can occur when the mask and wafer move with respect to the projection system. Furthermore, better alignment is achieved if the alignment is done continuously during scanning and exposure, rather than at a single place over the scan field. Not only does this eliminate the time lost during static alignments thereby increasing throughput, but it will do a better job, especially on large subfields. Further, the system provides a high signal-to-noise ratio even with a moderately high alignment system bandwidth.
Most focusing systems are indirect and bring the wafer to a fixed location. Thermal changes in the projection system which cause the best focus location to move are not accommodated by indirect systems. The system according to the present invention is direct, is ideally suited for a scanning system, and does not ~ 3~21 MI-2955 requ;re any vibrating or oscillatory motions that c~uld degrade system performance. A ~irect working system is very important if a glass cover is used to protect the mask since such covers could be expected to have a considerable variation in thickness requiring a different focus setting for each mask.
~ hile a number of different types of alignment an~,tor focusing system~q have been employe~
heretofore with moderate success, my contribution to 1~ the art is a new system, which is an improvement over such prior art systems, as will become apparent as the description proceeds.
_m ary of the Invention In orAer to accomplish the desired results, the invention provides, in one form thereof, a new and improved alignment system for a scanning mask aligner employing a continuous pattern on both the mask and wafer in the scribe lines that run in the direction of scan, the combination comprising a viewing system having optical grid means, means for moving the patterns across the optical grid means in the view;ng system, the grid means corresponding to the directions and spacings of the patterns so that light transmitted through the grid means is strongly modulated. The system further comprises means for comparing the ~hase modulatinn from the mask and wafer alignment targets to obtain alignment error signals. According to one aspect of the invention the mask anA wafer patterns may, for example, be a diamon~-shaped pattern. The system may be used with many different forms of illumination such as bright field, dark field or ~ 3~2~ MI-2955 ....
i~omars~e phase contrast, for example. Aecording to an aspect of the invention the optical grid means inelude.s a pair of ortl1ogonally disposed optieal gri-3s, one beinq deposed plu~s about 45 and the other minus a~out 45 with respect to the seanning direetion.
~ ccording to a further aspect of the invention the means For eomparing the phase modu1ation ineludes different detectors on whieh the mask and wafer patterns are imaged. In fact a deteetor array eomprising a plurality of independent detectors ean be used so that a numt)er of alternate positions for the ma~sk and wafer patterns is available in eaeh scribe line.
Many of the components of the alignment system are also compatible with a continuous foeusing system.
In this case two images of the mask pattern are arranged so that one is slightly inside of focus and the other is slightly outside of focus, and by comparing the amount of modulation on the two ehannels it is possible to decluee whieh of tl1e two is eloser to foeus and therefore how to shift the foeus so that they are equal.
There has thus been outlined rather broadly the more i~portant features of the invention in or-1~r that the detailecl deseription thereoE that follows may be better unc1erstood, and in order that the pre~sent contribution to the art may be better appreciated.
There are, of eourse, ac1ditional features of the invention that will be c1eseribed hereinafter whieh will - ` MI-2955 ~j3~2~
form the subject of the claims appended thereto. Those skilled in the art will appreciate that the conception upon which the disclosure is based may he readily utilized as a basis for the de~signing of other ~systems 5 for carrying out the several purposes of the invention.
It is important, therefore, that the claims be regarded as including SUCIl equivalent systems as do not depart from the spirit and scope of the invention.
Specific embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of this specification.
Brief Description of the Drawings -Fig. 1 is a view of several mask, wafer, grid and signal patterns according to the invention;
FigO 2 is a plan view of a detector array on which the mask and wafer patterns are irnaged;
Fig. 3 is a view showing successive relative positions of the grid and alignment pattern ~showing how light frorn the edges of the wafer pattern i~s modu]ated by a grating of s;milar orientation;
Fig. 4 is a schematic (liagram showing a projection ~system and an alignment systern according to the invention; and Fig. ~ is a schematic diagraln showing a focus sencing svstem accordin~ to the inv~n~i~n.
~ 2955 ~i;3~2~
Detailed Description of the Invention In the embo~iments of the invention illustrated, the alignment targets are continuous diamolld patterns contained in the mask and wa~er scribe alleys or lines, whicll rur parallel to the scanning direction. Fig. 1 shows a low fre~uency and a high frequellcy E,attern either of which can be put on t~e m.~sk or in the wafer scribe alley ~or alignment. The wafer pattern can, for example, be either raised or recessed diamonds as indicated at ln, which when dark field illuminated will have edges appearing as bright lines on a dark background.
If dark field illumination is also used on the mask, as indicated at 12, then the mask pattern can he either opaque or clear with only the edges being visihle in the viewing system in either case. In general, the mask signal is substantially weaker than the wafer signal hecause the pattern edges are thinner and Steeper than their wafer counterparts and therefore scatter less light into the viewing system. The mask pattern signal can l~e substantially increased by employing bright field illumination as indicated at 14, and a pattern consisting of narrow slots in an opaque background. The slots are positioned to correspond to the edge positions in the dark field mask pattern. ~n important feature of both the mask and wafer patterns is that they remain centere-3 whetller or not they are over or under etched.
~ 2955 ~2~ 2~
The Si7.P of the alignment patterns referred to the waFer can he varied to suit the Applicat;nn, but might typically be five or ten m;crons across so that there is room for about ten patterns or tracks in a scribe line, as the scribe lines are typically 4 or 5 mils wide. ~ne pnssibility is to switch the track containill~ tlle mask and wafer alignment pattern with each masking step. This involves switching between the different 3etectors monitoring each track as indicated at 16 at Fig. 2. The width of each detector might correspond to about l0 microns on the wafer and the leogth could be as long as the width o~ the zone of yood cnrrectinn in the projection system. In fact, there are two detector arrays which view identical ~ortions of the mask and wafer via a beam splitter, as will be discus~ed more fully hereinafter. Optically superimposed on each detector array is an optical grid consisting of regularly spaced clear and opaque lines corresponding to the spacing of the alignment target e(3ges. One grid has lines slanting to the right as indicated at 18, Fig. l, and the otller to the left as indicated at 2~, Fig. l. The scanning operation moves the alignment patterns across the grids producing a strongly modlllate~ signal on the correspnnding detectors. Fig. 3 shows the relative positions of the grid and alignment pattern illustrating how light from the edges of the wafer pattern is modulated by a grating of similar orientation. The resulting signals, as indicated at 22 in Fig. 1, have a periodicity e(~ual to the mask and wafer alignment patterns. The maximum acquis;tinn ranqe is there~ore e~lual to plus or minus one-half the alignment nattern period. A nine micron ~2~3~12~
period alignment pattern thus provides a + 4.5 micron maximum acquisition range. The low frequency pattern shown in Fig.l illustrates how the periodicity can be modified without increasing the width of the pattern.
In general, acquisition range can be traded for signal-to-noise ratio and alignment accuracy~ Since the alignment pattern can be viewed over the width of the projection system's slit, possibly 1.5 to 2.0 mm, and this encompasses a lot of edges, it may be possible to have a large signal-to-noise ratio as well as a large acquisition range.
A schematic representation of the alignment system is shown in Fig. 4, wherein dark field mask illumination, indicated as 24, is focused on a mask 26.
The mask pattern is imaged on a wafer 28, by a projection system indicated generally at 30, which includes lens means. The wafer acts as a mirror of the mask image so that the mask is reimaged and the wafer is imaged into the focal plane of a relay lens means, 32, via a beam splitter 34 in the projection system. A
second beam splitter 36 behind the relay lens splits the relayed image into two components so that two grids can be used, one oriented at +45 and the other at -45. Thus, one component includes a +45 grid 38, a lens system 40 and a detector array 42. The appropriate detector to sense the mask and wafer signals is selected by a multiplexor, i.e., a mask signal MUX 44 or a wafer signal MUX 46. From there the modulated signals are fed into a +45 phase comparator 48. The other component from the beam splitter 36 is reflected to a -45 Moire grid 50, a lens system 52, and a detector array 54. The appropriate detector to sense the mask and wafer signals is selected by a multiplexor, i.e., a mask signal MUX 56 or a wafer ~ 2955 ;3~2~
g signal ~1~!X 58. From there the modulate-l signal is fec3 into a -45 pllase comparator 60. The outputs from the two phase comparators, 48, 60 correspond to A~ ignment errors in the directions normal to the corresponding optical grid + 4S. These ~signals are readily convert~d into X an(3 Y ~r 0 and ~0 align1nent signals in a coordinate transformation system 62, which OUtpl3ts mask and wafer stage correction signals 64. Scanning the mask an~3 wafer relative to the projection and viewing ~systems generates an alternating signal 22, Fig. 1, in each detector array. The relative phase between mask and wafer signals is a measure of their alignment in a direction orthogonal to the pattern lines. Since there are grid patterns which are mutually orthogonal the alignment signal~s can be algebraically combined to correspond to any desire-l coordinate systems such as X & Y, etc.
The size of tl)e ali~nment pattern on the wafer is limited hy the spacing between chips and the number of different alignment patterns made necessary either l-~ecause earlier patterns are degraded by subsequent wafer processing or because a particular critical alignment re~uires that one layer be alignecl directly rather than hoth layers to a third layer. There is no need to print the mask pattern, and in fact, it w0l31d be very desirable to avoi(l it. Where printing the mask pattern is unavoidable, this .sllould he done on a reasonably clean portion of tl-e wafer. If attempts are made to superimpose the mask and wafer patterns ~so that their edges are coincident, then alignment errors might occur hecau~se of the light lost after heing diffracte(l out of the projection system aperture ty the sloping edges of tl~e wafer topography. For tlle same reason it 2~
is probably not a good idea to superimpose successive mask patterns either if the masks pattern is printed.
As a result, 2(n-1) possible mask and wafer target positions are required between lines where n is the number of layers and (n-l) the number of alignments. I~
the signal processing electronics and mask layout rules are arranged so that the mask signal is always 180 out of phase with the wafer signal, then the mask target can be superimposed on previously used wafer targets and the number of target positions reduced to n-l provided a new wafer target is laid down each step. If the electronics and mask layout rules are modified so that the phase between the mask and wafer signals may be either 0~ or 180, then the number of target positions can be as small as (n + m)/2 where m is the number of wafer target positions. This option opens the way for an operator induced error if the relative phase is inputted incorrectly, but it reduces the number of tracts to 8 taking a worst case where n = 12, m = 4 situation. This permits each alignment pattern to be 8 or 9 microns wide.
In the event that printing the mask target can be avoided by removing the utlraviolet component from the scribe line illumination, then only a few tracks are required such as, for example, one for the mask and a few for the wafer, depending on how well the wafer pattern stands up under the various process steps.
MI-2~55 ~ ~5~2~
The simplest way to ~se this alignment system i~s to try to keep the alignment track as close to the center of the projection field as possible. This minimizes the effects of skew and magnification and presents no problem as long as the width of the projection system field, 20 or 25 mm., is at least twice as ~ide as the chip size so that at least two rows of chips can be included on the mask.
Magnification in the slit direction can be inferred indirectly hy ~easuring the magnification along the scan direction. Adjusting the magnification in the scan directinn should also correct it in the other direction a~ssuming isotropic changes ;n the wafer.
Skew is caused by lateral misalignment in the project;on system and can prohably be controlled by periodic checking w;th special masks or wafers.
There is also the possibility of putting two alignment tracks on each mask; one at the top and one at the hottom. With this arrangement a total of four alignment s;~nals are derived which can be used to control X and Y alignment, magnification along the slit, and skew. Skew can he adjl]sted either hy a ]ateral mot;on of one of the project;on system elements or by rotating the mask with resl)ect to the wafer.
rlagnification along the slit adjustm~nt can prohahly be obtained by axial motion of one of the projection system refractive components. Instead of correcting ~skew and magnification along the slit the effects can be minimize~ by balancing the runout at the top and bottom o the field.
~ 21 MI-2955 By m.~king a few ~small cllanges, the same system used to me~sure alignment can al.so be used to measure how we~.l the mask is focused on the wafer.
~he re~uired cllanges are shown in Fig. 5. The +45 pattern grid has been shifted slight].y inside the normal ft~cus and the -45 pattern grid sli~htly outside of focus. The focus of the mask on the wafer i.s determir)ed by measuring the relative modulat;on amplitude of either the mask or wafer targets on the i.nsi~e focus and outsi.de focus detectors. Since the viewing relay can be situated physically close to the mask image plane, the relayed focus conjugates shol~].d accurately repre.sent the mask position. Ilowever, it is possible to ~separate projection system focus errors from relay system errors by deriving both mask and wafer target focus errors. The tar~et error is proportional to the projection system error plus the viewing relay error whereas the mask target error is proportional to twice the projection system focus error pl~s the viewing relay focus errors. Still referring to Fig. 5, a mask pattern modulation detector, 66, is disposed behind the mask signal MUX
44 and a secon~ mask pattern modulation detector 6~, is disposed behind the mask signal r~ux 56.
Sllbtracting the inside and olltside focus modulations yields a signal indicating the sign and magnitude of the amount of defocus for small focus errors. The operation performed by the modulation detectors is to provide a signal por~ortional to the mo(lnlation. TE
the maximum and minimum signal levels are Vmax and vmin, then:
Modulation = Vmax - Vmin Vmax + Vmin MI_2955 2~
The two modulation signals are subtracted by an operational amplifier 70 to output a defocus signal 72. If the mask is correctly focused on the wafer, then the modulation amplitude .should be the same on both ma~sk pattern modulation detectors and the difference should be zero.
If the mask is out of focus, then the modulation levels will be different and a defocus signal will be generated.
1~ It will thus be seen that the present invention does indeed provide an improved alignment and/or focusing system which effectively meets the objects specified hereinbefore. Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various ~odifications may be made without departing from the spirit and scope of the invention which is to be limited solely by the appended claims.
_ 2 ~ .
by masks which are prepared for the purpose. Separate masks are used for each of the successive steps. If everything is to appear in the proper place on the micro-circuit a high degree of alignment is necessary between steps. Typical alignment systems employed heretofore are described in U.S. Patents 3,975,364;
4,011,011; 4,006,645; and 4,353,087, for example.
Almost all the current automatic alignment systems require that the mask and wafer be essentially fixed with respect to the alignment system during the alignment process. This is no problem in a step-and-repeat type system, but it is far from ideal in a scanning projection printer since misregistration can occur when the mask and wafer move with respect to the projection system. Furthermore, better alignment is achieved if the alignment is done continuously during scanning and exposure, rather than at a single place over the scan field. Not only does this eliminate the time lost during static alignments thereby increasing throughput, but it will do a better job, especially on large subfields. Further, the system provides a high signal-to-noise ratio even with a moderately high alignment system bandwidth.
Most focusing systems are indirect and bring the wafer to a fixed location. Thermal changes in the projection system which cause the best focus location to move are not accommodated by indirect systems. The system according to the present invention is direct, is ideally suited for a scanning system, and does not ~ 3~21 MI-2955 requ;re any vibrating or oscillatory motions that c~uld degrade system performance. A ~irect working system is very important if a glass cover is used to protect the mask since such covers could be expected to have a considerable variation in thickness requiring a different focus setting for each mask.
~ hile a number of different types of alignment an~,tor focusing system~q have been employe~
heretofore with moderate success, my contribution to 1~ the art is a new system, which is an improvement over such prior art systems, as will become apparent as the description proceeds.
_m ary of the Invention In orAer to accomplish the desired results, the invention provides, in one form thereof, a new and improved alignment system for a scanning mask aligner employing a continuous pattern on both the mask and wafer in the scribe lines that run in the direction of scan, the combination comprising a viewing system having optical grid means, means for moving the patterns across the optical grid means in the view;ng system, the grid means corresponding to the directions and spacings of the patterns so that light transmitted through the grid means is strongly modulated. The system further comprises means for comparing the ~hase modulatinn from the mask and wafer alignment targets to obtain alignment error signals. According to one aspect of the invention the mask anA wafer patterns may, for example, be a diamon~-shaped pattern. The system may be used with many different forms of illumination such as bright field, dark field or ~ 3~2~ MI-2955 ....
i~omars~e phase contrast, for example. Aecording to an aspect of the invention the optical grid means inelude.s a pair of ortl1ogonally disposed optieal gri-3s, one beinq deposed plu~s about 45 and the other minus a~out 45 with respect to the seanning direetion.
~ ccording to a further aspect of the invention the means For eomparing the phase modu1ation ineludes different detectors on whieh the mask and wafer patterns are imaged. In fact a deteetor array eomprising a plurality of independent detectors ean be used so that a numt)er of alternate positions for the ma~sk and wafer patterns is available in eaeh scribe line.
Many of the components of the alignment system are also compatible with a continuous foeusing system.
In this case two images of the mask pattern are arranged so that one is slightly inside of focus and the other is slightly outside of focus, and by comparing the amount of modulation on the two ehannels it is possible to decluee whieh of tl1e two is eloser to foeus and therefore how to shift the foeus so that they are equal.
There has thus been outlined rather broadly the more i~portant features of the invention in or-1~r that the detailecl deseription thereoE that follows may be better unc1erstood, and in order that the pre~sent contribution to the art may be better appreciated.
There are, of eourse, ac1ditional features of the invention that will be c1eseribed hereinafter whieh will - ` MI-2955 ~j3~2~
form the subject of the claims appended thereto. Those skilled in the art will appreciate that the conception upon which the disclosure is based may he readily utilized as a basis for the de~signing of other ~systems 5 for carrying out the several purposes of the invention.
It is important, therefore, that the claims be regarded as including SUCIl equivalent systems as do not depart from the spirit and scope of the invention.
Specific embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings, forming a part of this specification.
Brief Description of the Drawings -Fig. 1 is a view of several mask, wafer, grid and signal patterns according to the invention;
FigO 2 is a plan view of a detector array on which the mask and wafer patterns are irnaged;
Fig. 3 is a view showing successive relative positions of the grid and alignment pattern ~showing how light frorn the edges of the wafer pattern i~s modu]ated by a grating of s;milar orientation;
Fig. 4 is a schematic (liagram showing a projection ~system and an alignment systern according to the invention; and Fig. ~ is a schematic diagraln showing a focus sencing svstem accordin~ to the inv~n~i~n.
~ 2955 ~i;3~2~
Detailed Description of the Invention In the embo~iments of the invention illustrated, the alignment targets are continuous diamolld patterns contained in the mask and wa~er scribe alleys or lines, whicll rur parallel to the scanning direction. Fig. 1 shows a low fre~uency and a high frequellcy E,attern either of which can be put on t~e m.~sk or in the wafer scribe alley ~or alignment. The wafer pattern can, for example, be either raised or recessed diamonds as indicated at ln, which when dark field illuminated will have edges appearing as bright lines on a dark background.
If dark field illumination is also used on the mask, as indicated at 12, then the mask pattern can he either opaque or clear with only the edges being visihle in the viewing system in either case. In general, the mask signal is substantially weaker than the wafer signal hecause the pattern edges are thinner and Steeper than their wafer counterparts and therefore scatter less light into the viewing system. The mask pattern signal can l~e substantially increased by employing bright field illumination as indicated at 14, and a pattern consisting of narrow slots in an opaque background. The slots are positioned to correspond to the edge positions in the dark field mask pattern. ~n important feature of both the mask and wafer patterns is that they remain centere-3 whetller or not they are over or under etched.
~ 2955 ~2~ 2~
The Si7.P of the alignment patterns referred to the waFer can he varied to suit the Applicat;nn, but might typically be five or ten m;crons across so that there is room for about ten patterns or tracks in a scribe line, as the scribe lines are typically 4 or 5 mils wide. ~ne pnssibility is to switch the track containill~ tlle mask and wafer alignment pattern with each masking step. This involves switching between the different 3etectors monitoring each track as indicated at 16 at Fig. 2. The width of each detector might correspond to about l0 microns on the wafer and the leogth could be as long as the width o~ the zone of yood cnrrectinn in the projection system. In fact, there are two detector arrays which view identical ~ortions of the mask and wafer via a beam splitter, as will be discus~ed more fully hereinafter. Optically superimposed on each detector array is an optical grid consisting of regularly spaced clear and opaque lines corresponding to the spacing of the alignment target e(3ges. One grid has lines slanting to the right as indicated at 18, Fig. l, and the otller to the left as indicated at 2~, Fig. l. The scanning operation moves the alignment patterns across the grids producing a strongly modlllate~ signal on the correspnnding detectors. Fig. 3 shows the relative positions of the grid and alignment pattern illustrating how light from the edges of the wafer pattern is modulated by a grating of similar orientation. The resulting signals, as indicated at 22 in Fig. 1, have a periodicity e(~ual to the mask and wafer alignment patterns. The maximum acquis;tinn ranqe is there~ore e~lual to plus or minus one-half the alignment nattern period. A nine micron ~2~3~12~
period alignment pattern thus provides a + 4.5 micron maximum acquisition range. The low frequency pattern shown in Fig.l illustrates how the periodicity can be modified without increasing the width of the pattern.
In general, acquisition range can be traded for signal-to-noise ratio and alignment accuracy~ Since the alignment pattern can be viewed over the width of the projection system's slit, possibly 1.5 to 2.0 mm, and this encompasses a lot of edges, it may be possible to have a large signal-to-noise ratio as well as a large acquisition range.
A schematic representation of the alignment system is shown in Fig. 4, wherein dark field mask illumination, indicated as 24, is focused on a mask 26.
The mask pattern is imaged on a wafer 28, by a projection system indicated generally at 30, which includes lens means. The wafer acts as a mirror of the mask image so that the mask is reimaged and the wafer is imaged into the focal plane of a relay lens means, 32, via a beam splitter 34 in the projection system. A
second beam splitter 36 behind the relay lens splits the relayed image into two components so that two grids can be used, one oriented at +45 and the other at -45. Thus, one component includes a +45 grid 38, a lens system 40 and a detector array 42. The appropriate detector to sense the mask and wafer signals is selected by a multiplexor, i.e., a mask signal MUX 44 or a wafer signal MUX 46. From there the modulated signals are fed into a +45 phase comparator 48. The other component from the beam splitter 36 is reflected to a -45 Moire grid 50, a lens system 52, and a detector array 54. The appropriate detector to sense the mask and wafer signals is selected by a multiplexor, i.e., a mask signal MUX 56 or a wafer ~ 2955 ;3~2~
g signal ~1~!X 58. From there the modulate-l signal is fec3 into a -45 pllase comparator 60. The outputs from the two phase comparators, 48, 60 correspond to A~ ignment errors in the directions normal to the corresponding optical grid + 4S. These ~signals are readily convert~d into X an(3 Y ~r 0 and ~0 align1nent signals in a coordinate transformation system 62, which OUtpl3ts mask and wafer stage correction signals 64. Scanning the mask an~3 wafer relative to the projection and viewing ~systems generates an alternating signal 22, Fig. 1, in each detector array. The relative phase between mask and wafer signals is a measure of their alignment in a direction orthogonal to the pattern lines. Since there are grid patterns which are mutually orthogonal the alignment signal~s can be algebraically combined to correspond to any desire-l coordinate systems such as X & Y, etc.
The size of tl)e ali~nment pattern on the wafer is limited hy the spacing between chips and the number of different alignment patterns made necessary either l-~ecause earlier patterns are degraded by subsequent wafer processing or because a particular critical alignment re~uires that one layer be alignecl directly rather than hoth layers to a third layer. There is no need to print the mask pattern, and in fact, it w0l31d be very desirable to avoi(l it. Where printing the mask pattern is unavoidable, this .sllould he done on a reasonably clean portion of tl-e wafer. If attempts are made to superimpose the mask and wafer patterns ~so that their edges are coincident, then alignment errors might occur hecau~se of the light lost after heing diffracte(l out of the projection system aperture ty the sloping edges of tl~e wafer topography. For tlle same reason it 2~
is probably not a good idea to superimpose successive mask patterns either if the masks pattern is printed.
As a result, 2(n-1) possible mask and wafer target positions are required between lines where n is the number of layers and (n-l) the number of alignments. I~
the signal processing electronics and mask layout rules are arranged so that the mask signal is always 180 out of phase with the wafer signal, then the mask target can be superimposed on previously used wafer targets and the number of target positions reduced to n-l provided a new wafer target is laid down each step. If the electronics and mask layout rules are modified so that the phase between the mask and wafer signals may be either 0~ or 180, then the number of target positions can be as small as (n + m)/2 where m is the number of wafer target positions. This option opens the way for an operator induced error if the relative phase is inputted incorrectly, but it reduces the number of tracts to 8 taking a worst case where n = 12, m = 4 situation. This permits each alignment pattern to be 8 or 9 microns wide.
In the event that printing the mask target can be avoided by removing the utlraviolet component from the scribe line illumination, then only a few tracks are required such as, for example, one for the mask and a few for the wafer, depending on how well the wafer pattern stands up under the various process steps.
MI-2~55 ~ ~5~2~
The simplest way to ~se this alignment system i~s to try to keep the alignment track as close to the center of the projection field as possible. This minimizes the effects of skew and magnification and presents no problem as long as the width of the projection system field, 20 or 25 mm., is at least twice as ~ide as the chip size so that at least two rows of chips can be included on the mask.
Magnification in the slit direction can be inferred indirectly hy ~easuring the magnification along the scan direction. Adjusting the magnification in the scan directinn should also correct it in the other direction a~ssuming isotropic changes ;n the wafer.
Skew is caused by lateral misalignment in the project;on system and can prohably be controlled by periodic checking w;th special masks or wafers.
There is also the possibility of putting two alignment tracks on each mask; one at the top and one at the hottom. With this arrangement a total of four alignment s;~nals are derived which can be used to control X and Y alignment, magnification along the slit, and skew. Skew can he adjl]sted either hy a ]ateral mot;on of one of the project;on system elements or by rotating the mask with resl)ect to the wafer.
rlagnification along the slit adjustm~nt can prohahly be obtained by axial motion of one of the projection system refractive components. Instead of correcting ~skew and magnification along the slit the effects can be minimize~ by balancing the runout at the top and bottom o the field.
~ 21 MI-2955 By m.~king a few ~small cllanges, the same system used to me~sure alignment can al.so be used to measure how we~.l the mask is focused on the wafer.
~he re~uired cllanges are shown in Fig. 5. The +45 pattern grid has been shifted slight].y inside the normal ft~cus and the -45 pattern grid sli~htly outside of focus. The focus of the mask on the wafer i.s determir)ed by measuring the relative modulat;on amplitude of either the mask or wafer targets on the i.nsi~e focus and outsi.de focus detectors. Since the viewing relay can be situated physically close to the mask image plane, the relayed focus conjugates shol~].d accurately repre.sent the mask position. Ilowever, it is possible to ~separate projection system focus errors from relay system errors by deriving both mask and wafer target focus errors. The tar~et error is proportional to the projection system error plus the viewing relay error whereas the mask target error is proportional to twice the projection system focus error pl~s the viewing relay focus errors. Still referring to Fig. 5, a mask pattern modulation detector, 66, is disposed behind the mask signal MUX
44 and a secon~ mask pattern modulation detector 6~, is disposed behind the mask signal r~ux 56.
Sllbtracting the inside and olltside focus modulations yields a signal indicating the sign and magnitude of the amount of defocus for small focus errors. The operation performed by the modulation detectors is to provide a signal por~ortional to the mo(lnlation. TE
the maximum and minimum signal levels are Vmax and vmin, then:
Modulation = Vmax - Vmin Vmax + Vmin MI_2955 2~
The two modulation signals are subtracted by an operational amplifier 70 to output a defocus signal 72. If the mask is correctly focused on the wafer, then the modulation amplitude .should be the same on both ma~sk pattern modulation detectors and the difference should be zero.
If the mask is out of focus, then the modulation levels will be different and a defocus signal will be generated.
1~ It will thus be seen that the present invention does indeed provide an improved alignment and/or focusing system which effectively meets the objects specified hereinbefore. Although specific embodiments have been illustrated and described, it will be obvious to those skilled in the art that various ~odifications may be made without departing from the spirit and scope of the invention which is to be limited solely by the appended claims.
Claims (18)
1. In an alignment-system for a scanning mask aligner employing a pattern on both the mask and wafer in the scribe lines that run in the direction of scan, the combination comprising:
a viewing system having optical grid means;
means for moving the patterns across said optical grid means in the viewing system, the grid means corresponding to the directions and spacings of the patterns so that light transmitted through the grid means is strongly modulated; and means for comparing the phase modulating from the mask and wafer alignment targets to obtain alignment error signals.
a viewing system having optical grid means;
means for moving the patterns across said optical grid means in the viewing system, the grid means corresponding to the directions and spacings of the patterns so that light transmitted through the grid means is strongly modulated; and means for comparing the phase modulating from the mask and wafer alignment targets to obtain alignment error signals.
2. The system according to Claim 1 wherein said pattern is a diamond-shaped pattern.
3. The system of Claim 1 wherein said patterns are illuminated with dark field illumination.
4. The system of Claim 1 wherein said patterns are illuminated with bright field illumination.
5. The system according to Claim 1 wherein said means for moving the patterns is the scanning operation means.
6. The system of Claim I wherein said optical grid means includes a pair of orthogonally disposed optical grids.
7. The system according to Claim 1 wherein said optical grid means includes a first grid having about a plus 45° pattern and a second grid having about a minus 45° pattern with respect to the scanning direction.
8. The system according to Claim 1 wherein said means for obtaining the phase modulation includes multiple detectors on which the mask and wafer patterns are imaged, separately.
9. In an alignment system for a scanning mask aligner employing a continuous pattern on both the mask and wafer in the scribe lines that run in the direction of scan, the combination comprising means for mounting said mask in spaced relationship with respect to said wafer, a projection system interposed between said mask and wafer including a first beam splitter so that the mask pattern is imaged on the wafer by said projection system and the wafer acts as a mirror of the mask image so that the mask is reimaged and the wafer is imaged into the focal plane of viewing relay means via said beam splitter, a second beam splitter behind said relay means for splitting the relayed images into two components, a detector array, grid means, multiplexor, and phase comparator for each component, the detectors sensing the mask and wafer signals selected by the multiplexor which feeds the modulated signal into the phase comparator, coordinate transformation means for receiving the outputs from the phase comparators and outputting mask and wafer stage correction signals.
10. The system according to Claim 9 wherein one of said grid means has of the order about a plus 45°
grid pattern and the other of said grid means has of the order about a minus 45° Moire pattern.
grid pattern and the other of said grid means has of the order about a minus 45° Moire pattern.
11. In a focusing system for a scanning mask aligner employing a pattern on both the mask and wafer in the scribe lines that run in the direction of scan, the combination comprising a viewing system having optical grid means, means for moving the patterns across said optical grid means in the viewing system, the grid means corresponding to the direction and spacing of the patterns so that light transmitted is strongly modulated, means for arranging one image of the mask pattern so that it is slightly inside of focus, means for arranging a second image of the mask pattern so that it is slightly out-side of focus, means for comparing the amount of modulation of said images to output a defocus signal.
12. In a focusing system for a scanning mask aligner employing a pattern on both the mask and wafer in the scribe lines that run in the direction of scan, the combination comprising a viewing system having a pair of optical grids, means for moving the patterns across said optical grids in the viewing system, the grids corresponding to the direction and spacing of the patterns so that light transmitted is strongly modulated, one of said grids having a pattern orthogonally disposed with respect to the other of said grids, one of said grids being mounted so the pattern moving thereacross is inside nominal focus, a modulation detector for each grid and means for comparing the output of said modulation detectors to output a defocus signal.
13. The system according to Claim 12 wherein said pattern is a diamond-shaped pattern.
14. The system of Claim 12 wherein said wafer pattern is dark field illuminated.
15. The system of Claim 12 wherein said mask pattern is dark field illuminated.
16. The system of Claim 12 wherein said mask pattern is bright field illuminated.
17. The system according to Claim 12 wherein said optical grid means includes a first grid having lines and spaces oriented at about plus 45° to this scan direction and a second grid having lines and spaces oriented at about a minus 45° to the scan direction.
18. In a focusing system for a scanning mask aligner employing a continuous pattern on both the mask and wafer in the scribe lines that run in the direction of scanning, the combination comprising:
means for mounting said mask in spaced relationship with respect to said wafer, a projection system interposed between said mask and wafer including a first beam splitter so that the mask pattern is imaged on the wafer by said projection system and the wafer acts as a mirror of the mask image so that the mask is reimaged and the wafer is imaged into the focal plane of a viewing relay lens means via a first beam splitter, a second beam splitter behind said relay lens means for splitting the relay image into two components, a grid means, multiplexor, and modulating detector for each component, one of said grid means being mounted so the pattern moving thereacross is inside nominal focus and the other of said grids means being mounted so the pattern moving thereacross is outside nominal focus, and means for comparing the output of said modulation detectors to output a defocus signal.
means for mounting said mask in spaced relationship with respect to said wafer, a projection system interposed between said mask and wafer including a first beam splitter so that the mask pattern is imaged on the wafer by said projection system and the wafer acts as a mirror of the mask image so that the mask is reimaged and the wafer is imaged into the focal plane of a viewing relay lens means via a first beam splitter, a second beam splitter behind said relay lens means for splitting the relay image into two components, a grid means, multiplexor, and modulating detector for each component, one of said grid means being mounted so the pattern moving thereacross is inside nominal focus and the other of said grids means being mounted so the pattern moving thereacross is outside nominal focus, and means for comparing the output of said modulation detectors to output a defocus signal.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US451,900 | 1982-12-21 | ||
| US06/451,900 US4549084A (en) | 1982-12-21 | 1982-12-21 | Alignment and focusing system for a scanning mask aligner |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1253021A true CA1253021A (en) | 1989-04-25 |
Family
ID=23794161
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000437145A Expired CA1253021A (en) | 1982-12-21 | 1983-09-20 | Alignment and focusing system for a scanning mask aligner |
Country Status (5)
| Country | Link |
|---|---|
| US (1) | US4549084A (en) |
| EP (1) | EP0111648B1 (en) |
| JP (1) | JPS59132621A (en) |
| CA (1) | CA1253021A (en) |
| DE (1) | DE3377815D1 (en) |
Families Citing this family (25)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4634876A (en) * | 1983-05-13 | 1987-01-06 | Canon Kabushiki Kaisha | Object position detecting apparatus using accumulation type sensor |
| EP0135597B1 (en) * | 1983-09-23 | 1987-07-22 | Ibm Deutschland Gmbh | Process and device for mutually aligning objects |
| US4645338A (en) * | 1985-04-26 | 1987-02-24 | International Business Machines Corporation | Optical system for focus correction for a lithographic tool |
| GB2186359B (en) * | 1986-01-18 | 1990-05-30 | Automatix International U K Li | Automatically and accurately positioning a workpiece |
| WO1988000362A1 (en) * | 1986-06-24 | 1988-01-14 | Stephen Hugh Salter | Improved registration method in photolithography and equipment for carrying out this method |
| US4965842A (en) * | 1986-07-22 | 1990-10-23 | Schlumberger Technologies, Inc. | Method and apparatus for measuring feature dimensions using controlled dark-field illumination |
| US5109430A (en) * | 1986-07-22 | 1992-04-28 | Schlumberger Technologies, Inc. | Mask alignment and measurement of critical dimensions in integrated circuits |
| JPS63128713A (en) * | 1986-11-19 | 1988-06-01 | Matsushita Electric Ind Co Ltd | Correction of distortion in scanning aligner |
| US4908656A (en) * | 1988-01-21 | 1990-03-13 | Nikon Corporation | Method of dimension measurement for a pattern formed by exposure apparatus, and method for setting exposure conditions and for inspecting exposure precision |
| US5047631A (en) * | 1989-12-22 | 1991-09-10 | Synergy Computer Graphics Corporation | Self-referencing start of plot system and method |
| US5289262A (en) * | 1992-03-09 | 1994-02-22 | Calcomp Inc. | Photodiode transmissive media sensor for aligning media |
| US5477057A (en) * | 1994-08-17 | 1995-12-19 | Svg Lithography Systems, Inc. | Off axis alignment system for scanning photolithography |
| US5991004A (en) * | 1996-04-03 | 1999-11-23 | Mrs Technology, Inc. | Lens focus shift sensor |
| GB9705105D0 (en) | 1997-03-12 | 1997-04-30 | Brown & Sharpe Limited | Optical surface measurement apparatus and methods |
| US5767523A (en) * | 1997-04-09 | 1998-06-16 | Svg Lithography Systems, Inc. | Multiple detector alignment system for photolithography |
| US7095904B2 (en) * | 2000-04-12 | 2006-08-22 | Ultratech, Inc. | Method and apparatus for determining best focus using dark-field imaging |
| US6628406B1 (en) | 2000-04-20 | 2003-09-30 | Justin L. Kreuzer | Self referencing mark independent alignment sensor |
| US6956659B2 (en) * | 2001-05-22 | 2005-10-18 | Nikon Precision Inc. | Measurement of critical dimensions of etched features |
| US6535280B1 (en) * | 2001-08-31 | 2003-03-18 | Advanced Micro Devices, Inc. | Phase-shift-moiré focus monitor |
| US6974653B2 (en) * | 2002-04-19 | 2005-12-13 | Nikon Precision Inc. | Methods for critical dimension and focus mapping using critical dimension test marks |
| US7130020B2 (en) * | 2003-04-30 | 2006-10-31 | Whitney Theodore R | Roll printer with decomposed raster scan and X-Y distortion correction |
| KR100712289B1 (en) * | 2005-04-07 | 2007-04-27 | 삼성에스디아이 주식회사 | Flat Panel Display and Fabrication Method of the Same |
| US7511826B2 (en) * | 2006-02-27 | 2009-03-31 | Asml Holding N.V. | Symmetrical illumination forming system and method |
| JP4274214B2 (en) * | 2006-09-08 | 2009-06-03 | セイコーエプソン株式会社 | Liquid jet head alignment apparatus and alignment method thereof |
| CN112305708B (en) * | 2019-07-29 | 2023-04-18 | 英属开曼群岛商音飞光电科技股份有限公司 | Thin film optical lens device |
Family Cites Families (10)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3957364A (en) * | 1974-09-26 | 1976-05-18 | The Perkin-Elmer Corporation | Coarse viewing system for an annular field projection system |
| US4037969A (en) * | 1976-04-02 | 1977-07-26 | Bell Telephone Laboratories, Incorporated | Zone plate alignment marks |
| JPS53135654A (en) * | 1977-05-01 | 1978-11-27 | Canon Inc | Photoelectric detecting device |
| CH629000A5 (en) * | 1978-05-22 | 1982-03-31 | Bbc Brown Boveri & Cie | METHOD FOR OPTICALLY ADJUSTING COMPONENTS. |
| JPS5534490A (en) * | 1978-09-01 | 1980-03-11 | Canon Inc | Alignment device |
| FR2450468A1 (en) * | 1979-02-27 | 1980-09-26 | Thomson Csf | OPTICAL SYSTEM FOR ALIGNING TWO PATTERNS AND PHOTOREPECTOR USING SUCH A SYSTEM |
| US4353087A (en) * | 1979-03-12 | 1982-10-05 | The Perkin-Elmer Corporation | Automatic mask alignment |
| JPS56122128A (en) * | 1980-02-29 | 1981-09-25 | Telmec Co Ltd | Positioning system for printing device of semiconductor or the like |
| JPS56130707A (en) * | 1980-03-18 | 1981-10-13 | Canon Inc | Photo-printing device |
| US4326805A (en) * | 1980-04-11 | 1982-04-27 | Bell Telephone Laboratories, Incorporated | Method and apparatus for aligning mask and wafer members |
-
1982
- 1982-12-21 US US06/451,900 patent/US4549084A/en not_active Expired - Fee Related
-
1983
- 1983-09-20 CA CA000437145A patent/CA1253021A/en not_active Expired
- 1983-09-22 EP EP83109458A patent/EP0111648B1/en not_active Expired
- 1983-09-22 DE DE8383109458T patent/DE3377815D1/en not_active Expired
- 1983-12-20 JP JP58238996A patent/JPS59132621A/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| US4549084A (en) | 1985-10-22 |
| JPH0442815B2 (en) | 1992-07-14 |
| EP0111648A1 (en) | 1984-06-27 |
| DE3377815D1 (en) | 1988-09-29 |
| JPS59132621A (en) | 1984-07-30 |
| EP0111648B1 (en) | 1988-08-24 |
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