CA1078240A - Modulation alignment of mask pattern relative to semiconductor substrate - Google Patents
Modulation alignment of mask pattern relative to semiconductor substrateInfo
- Publication number
- CA1078240A CA1078240A CA265,868A CA265868A CA1078240A CA 1078240 A CA1078240 A CA 1078240A CA 265868 A CA265868 A CA 265868A CA 1078240 A CA1078240 A CA 1078240A
- Authority
- CA
- Canada
- Prior art keywords
- mask
- grating
- substrate
- gratings
- radiation
- 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
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- 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
-
- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B27/00—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00
- G02B27/18—Optical systems or apparatus not provided for by any of the groups G02B1/00 - G02B26/00, G02B30/00 for optical projection, e.g. combination of mirror and condenser and objective
-
- 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
Abstract
ABSTRACT:
A method and arrangement are described for aligning a mask comprising a mask-pattern relative to a substrate when the mask-pattern is repeatedly and directly imaged on the substrate, gratings in the mask and on the substrate being employed as alignment references. The gratings in the mask are located outside the mask pattern and the phase gratings are located on the substrate outside the area where the mask-pattern is imaged. The substrate gratings are imaged on one of the masks In the substrate with a projection system which is also used for projecting the mask-pattern on the substrate. The image of the gratings on the grating in the mask is modulated, Thus, a very accurate alignment can be achieved.
A method and arrangement are described for aligning a mask comprising a mask-pattern relative to a substrate when the mask-pattern is repeatedly and directly imaged on the substrate, gratings in the mask and on the substrate being employed as alignment references. The gratings in the mask are located outside the mask pattern and the phase gratings are located on the substrate outside the area where the mask-pattern is imaged. The substrate gratings are imaged on one of the masks In the substrate with a projection system which is also used for projecting the mask-pattern on the substrate. The image of the gratings on the grating in the mask is modulated, Thus, a very accurate alignment can be achieved.
Description
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1~782~0 "Method and arrangement for aligning a mask pattern ; relative to a semiconductor substrate".
,, _______ , The invention relates to a method of aligning a mask pattern formed in a mask relative to a substrate when the mask pattern is repeatedly imaged directly on the substrate, gratings on the substrate and in the mask being used as alignment references. The invention also relates to an arrangement for carrying out this method.
~owadays use is made of diffusion techniques J
:. and associated masking techniques for the fabrication ~, of integrated circuits (I.C.'s). A multiplicity of masks with different configurations are then consecutively images at the same location of the substrate. Between the ~,, ! ` .
successive imagings at the same location bhe substrate is subjected to the desired physical and chemical changes.
Thus, a passive and/or active element is obtained which is known by the name of integrated circuit, abbreviated ~`
as I.C.
Diffusion and masking techniques are also '~ employed in the fabrication of so-called magnetic domain memories (bubble memories) for the formation of trans-port pa-tterns and detection patterns on a magnetizable :;
layer which is provided on a substrate. Also in this case :.
the accurate alignment of the mask patterns to be used in the consecutive process steps presents a problem.
This problem is so serious that attempts are made , ;`'`
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1~7l3240 PHN. 8429.
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(compare I.E.E.E. Transactions on Magnetics, Vol. ~ag. 9, No. 3, Sept. 1973, pages 474-480) to use only one pattern on the layer of magnetizable material, which pattern serves both for the transport and for the detection of ; 5 the magnetic domains. However, as the requirements imposed on a transport pattern differ from those imposed ~! on a detection pattern, a compromise is to be made with ` respect to the thickness of the pattern on the magnetizable i~ material and the properties of the material of the pattern.
The accuracy with which integrated circuits are manufactured has to satisfy increasingly exacting require-ments. 'rhis requires that the location at which successive ,., ~; masks are to be imaged on the substrate should be defined with ever increasing accuracy. Deviations greater than for example 1 micron may be prohibitive.
In the U.S. Patent 3,811,779 - May 21, 1974 ,~ (PHN~ 5368) an arrangement is described for aligning a cGmposite mask which comprises a m~ltitude of identical I.C. Patterns, with respect to a semioonductor substrate.
'rhis composite mask can be manufactured as follows:
First of all the relevant I.C. pattern is drawn to an enlarged scale with the aid of a machine which is for example computer-controlled. Subsequently, the I.C.
Pattern is optically reduced. Ihe pattern thus obtained is then further optically reduced with a so-called repea~r camera and repeatedly imaged at different :,. .
~ locations on a photographic plate, so that a com~osite '.`':
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mask with I~Co patterns of the desired size are obtained.
mis ccmposite mask can be projected at once on a semi-conductor substrate.
The present invention relates to an arrangement for the formation of a plurality of patterns on a sub, strate, the substrate itself being repeatedly exposed to an image, which m~y be reduced, of one pattern. For ; the fabrication of, for example integrated circuits a composite mask is then no longer required and the use of a photorepeater camera is no longer necessary.
~hereas in the arrangement in accordance with the U.S.
Patent (supra) a so_called contact copy of the composite mask is formed on the substrate, the arrangement developed by the Applicant projects an image of the I.C. pattern onto the substrate. In the last mentioned arrangement the I.C. pattern can be imaged onto the substrate in reduced form (for example 5X), so that a reducing step may be dispensed with when making the mask.
However, it is also possible that a 1 to 1 image of the ; 20 I.C. pattern is formed on the substrate.
A general advantage of projection is that dur-ing projection no wear of the mask occurs. As a result, the mask has to be checked only once, instead of several times. E~rtherm~re, accurate alignment of the mask i 25 during projection can be effected more quickly. m is is beca~se when a contact copy is made the mask and the , .
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substrate must still be mDved towæds one another after the mask and the substrate have been aligned with respect to each other. This may then lead to the substrate being shifted relative to the mlsk in a direction p æallel to the plane of the mask or of the substrate. In that case either reaLign-ment is necessary or a less accurate alignment must be accepted.
As the mask to be used in the ærangement according to the present invention comprises only one I.C. pattern, inspection of the mask is simple.
~r. This inspection is even further simplified if the I.C. pattern is to be imaged in reduced form, so that the details of the I.C. pattern in the mask are i 15 correspondingly large.
The present invention relates to the method , in which and the means with which the mask pattern is ; aligned relative to the substrate. The method accord-ing to the invention is characterized in that tWD
phase gratings, which are located outside the area on ; the substrate where a pluralit~ of images of the mask pattern is to be formed, are imaged on a first of tWD
gratings which are located in the mask outside the ~ mask pattern, with the aid of a prDjection system j- 25 which is used for imaging the mask pattern on the sub-strate, and that the position of the observed image ; of a grating, which is being aligned relative to the first grating in the mask, is m~dulated.
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The method of alignment described in the U.S. Patent supra differs fram the method in acoord- -~
ance with the invention inter alia in that the first mentioned method the individual gratings of the subr '~ 5 strate and the mask æe aligned relative to a refer-ence grating which is disposed on a separate support.
Mbreover, the position of an image of grating is not mDdulated in the arrangement in accordance with the U.S. Patent supra.
It is to be noted that, when projecting - I.C. patterns onto a semiconductor substrate, it is known Fer se from United States Patent Specification 3,695,758 Tanaka - Octoker 2, 1972 to pass the align-ment beam of radiation and the radiation beam with which the I.C. Fattern is imaged on the substrate through the same projection system. However, the said Patent Specification does not describe the alignment procedure. It is not clear whether gratings are used for the alignment and there is absolutely no , ., indication where the phase gratings, if any, would have to be located on the substrate. Furthe D re, it - is not known from the Uhited States Patent Specifica-tion 3,695,758 to modulate the position of an image of a grating. Finally, the alignment beam and the projection beam in the knGwn arrangement traverse a semi-transparent mirror on their way to the sub-strate, so that the radiation :-... ..
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``i ~078240 : intensity of said beams is halved, which is a drawback, i in particular for the projection of the I.C. pattern ,. .
onto the substrate.
. A preferred embodiment of a method in . 5 accordance with the invention is characterized in that f first of all, by rotation about an axis perpendicular ,~
to the plane of the mask, the lines of an image of the i.......... second.grating in the mask, which lines extend in a ~; :
,., first direction, are aligned relative to the corres-~;. 10 ponding lines of the first grating in the mask, that subsequently the grating lines of ~ first:of the two : substrate gratings, which lines extend in two mutually perpendicular directions, are aligned relative to the corresponding grating lines of the first great:ing in the mask, that afterthis the substrate is moved in . the direction of the line which connectes the centres of the first and the second mutually aligned gratings in the mask over a distance equal to the distance between the two substrate gratings, and that finally, by rotation about an axis which extends substantially ~¦ through the centre of the first substrate grating, .. l the grating lines of the second substrate grating are :: i .~ aligned relative to the corresponding grating lines ;',.- !
of the first grating in the mask.
.~ 25 An arrangement for carrying out the method ~,; in accordance with Claim 1, which arrangement comprises . a radiation source which supplies an alignment beam, :, :
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a lens system for each time imaging one of the substrate `` gratings on a first grating in the mask, and a radiation-sensitive detector which is disposed in the path of the alignment beam behind the mask, is characterized in that `:
said lens system is constituted by the projection system utilized for imaging the mask pattern on the substrate, and that in the path of the alignment beam between the system of projection lenses and the detector optical elements are included which are controlled by periodic signals for periodically moving the image of a grating observed by the detector and formed in the plane of the mask, the displacement of the observed image being of the order of magnitude of the period of the first ~;~ grating in the mask.
A preferred embodiment of an apparatus in accordance with the invention is furthermore characterized in that in the path of the alignment beam between the -l projection system and the mask a diaphragm is included ~:¦ which only transmits the first-order subbeams of the alignment beam diffracted by the substrate gratings to the mask. The alignment accuracy for a specific period of a substrate grating in the case that only the first-order beams are employed, is two times higher than ~:"
in the case that the zero-order beam were also used.
, 25 In order to prevent magnification errors in imaging the substrate gratings on the first grating ~ of the mask, owing to flatness errors of the substrate :.`., ,~
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.~ or the mask, or owing to the plane of the substrate or ! .~, .~ the mask not being perpendicular to the optical axis ~ of the system of projection lenses, an arrangement : in accordance with the invention is further characterized , ..
s in that the projection system is a telecentric system i; and comprises three lens systems, of which the system which is nearest the substrate is movable along the optical axis, whilst the two other lens systems along the optical axis are immovable.
~. 10 In order to enable the angular position of Y the mask itself to be adjusted before the substrate is aligned relative to the mask, an arrangement in accordance with the invention is characterized in that in addition to a first radiation path for each time imaging one of the lS substrate gratings on the first grating in the maslc, . which radiation path extends from the radiation source v1a a radiation-reflecting element, which may optionally be included in the path of the radiation emitted by the source, via the projection system, a reflection at one of the substrate gratings, a second passage through the projection system, and the diaphragm, to a beam splitter s which is disposed underneath the first grating in the mask, 1` a second radiation path is provided for imaging the .~, :`: second grating in the mask onto the first grating in ;' :;:, ; 25 the mask at full true size, the position of the image -~ of the second grating in the mask only depending on the ,:., .; direction of the line which connects the centres of the . . ,.~, '.'i .:~
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first and the second grating in the mask relative to . the direction of movement of a carriage with which the substrate is moved, which second radiation path extends from the radiation source via reflecting S elements above the mask, through the second grating in ` the mask, and via further reflecting elements under-neath the mask, and a lens system to the said beam ~.
~ splitter, which beam splitter combines the two radiation i` paths to a common radiation path through the mask to ...... ..
~j 10 the radiatior. sensitive detector.
.~ A preferred embodiment of an arrangement in.~accordance with the invention, in ~hich the radiation source emits a linearly polarized beam of radiation, : ;, - is furthermore characterized in that the optical elements ~, 15 for periodically moving the image of each time one of the substrate grat:ings and the second grating in the mask !. ,' ¦
... ~ respectively, are constituted by a polarization-sensitive element which is disposed in the common radiation path ~; before the mask, which element splits the alignment `'''`'''! 20 beam into two subbeams with mutually perpendicular directions of polarization, which subbeams form images of the second grating in the mask and one of the :`~:, substrate graings respectively at the location of .s~ the first graing in the mask, which images are mutually `I" ' :.l 25 shifted by one half period of the first grat:ing in the ,:: .~, . mask, by a polarization switch which is disposed in the ; common radiation path before the detector and which .',"; , ~, _ 10 -..... .
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1~78Z~0 PHN. 8429.
'.'' ' '~i is controlled by a squarewave voltage, which switchswitches the ~;rections of polarization of the subbeams through 90, and by an analyser between the polarization switch and the detector, the contr~l w ltage for the polarization switch also being applied to an electronic circuit in which the detector signal is processed to a control signal for correcting the grating position.
Furthermore, it is to be noted that in an embodiment described in the U.SO Patent 3,811,779 tWD
subbeams which are polarized at right angles to each other are employed for the alignnent. However, the , ...
object of this is merely to enable dynamic detection.
i~ These subbeams do not form tw~ shifted images of one substrate grating.
In order to ascertain whether during the alignment of the substrate gratings relative to the first grating in the mask the image of a substrate grating has not shifted a whole nu~ber of grating ::
periods relative to the first grating in the mask, an - arrangement in accordance with the invention is fur-thermore characterized in that the co~mDn radiation path behind the mask includes a second beam splitter which produces tw~ beams, one of which is aimed at the detector and the second at a camera tube which is .;, coupled with a TV mDnitor on which the gratings are - monitored.
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1078~240 he invention will now be described by way of example with reference to the projection of an I.C. pattern on a semiconductor substrate. For this reference is made to the drawing in which:
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~ 5 Figs. 1 and 2 show an embodiment of an 1',.'.
arrangement for carrying out the method in accordance with the invention.
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Figs. 3a, 3b, 4a and 4b illustrate the . ......................................................................... -, .
operation of some components of this arrangement, Figs. 5, 6 and 9 show examples of gratings to be used in this arrangement;
Fig. 7 shows a composite radiation- -sensitive detector for use in the arrangement in ~- accordance with the invention, ~ ,, Fig. 8 shows a different embodiment of I a part of the arrangement, and . '~.~ .
Fig. 10 schematically shows a set-up for . ..
measuring the displacements of the X and Y-carriage.
~` In Fig. 1 the reference numeral 5 denotes a ....
; 20 mask, which comprises two alignment references Ml and M2 in the form of gratings. Between these alignment -references an I.C. pattern 17 is disposed, which '~ is schematically represented by dashes. This pattern ~ is to be imaged a number of times on the semiconductor ,.~ 25 substrate 8 which also comprises two alignment gratings rj Pl and P2. The gratings Pl and P2 are disposed outside ; the area in which a number of images of the I.C. pattern :;
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are to be formed. m e gratings ~ and M2 tak2 the form of amplitude gratings and the gratings Pl and P2 f ; phase gratings. Compared with other alignment references such as for example squares in the mask and on the sub-strate, the periodic gratings have the advantage that i' when positional errors are mea Æ ed these are averaged over the grating. Thus accurate alignment is possible, even if one or mDre grating lines are mlssing or when the grating lines are serrated lines instead of straight lines. Es~pecially in the fabrication of integrated cir-cuits gratings have the advantage that during the consecutive diffusion processes they cannot grcw asymme-trically or become closed, as would be possible when other alignment references such as for example squares were used. In comparison with amplitude gratings phase gratings on the substrate have the advantage that they are etched into the semiconductor material for example silicon, so that no extraneous material need be deposited on the substrate. Mbreover, the p~ase grat-ings can satisfactorily withstand the mNltitude of s diffusion processes to which the substrate is to be subjected during the fabrication of integrated circuits.
; When ~he I.C. pattern is imaged on the sub-strate the projection beam 18 which is supplied by a radiation source, not shown, only illuminates the I.C.
., pattern. The gratings ~ and ~ are not imaged, :
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so that the I.C. designer need not make allowance for these gratings and no space has to be reserved for these gratings on each portion of the substrate .:. , .
on which one I.C. pattern is projected.
`~ 5 Figure 1 merely shows the optical elements which are used in detecting deviations between the desired and the actual positions of the gratings relative to each other. Of the mechanical elements which ,:?, serve for correctly positioning the mask and the, 10 substrate relative to each other only the turntable 55, on which the mask is disposed, and the turntable 56, on which the substrate is disposed are shown : .
schematically. All optical elements, except for the , laser 1, are accommodated in a vertical projection `'; 15 column, not shown, which is movable in the Y-direction i~ vla a carriage drive. The turntable 56 is connected to a carriage 60 via a column 90, which carriage is ;,l movable in the X-direction. The manner in which and the ;, menas with which the carriages are driven are no object , . . .
of the present invention and will not be discussed.
The displacements of the carriages in the X and Y
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!'~'" directions can be measured accurately with the aid of ::,, :;:
~; an interferometer arrangement which will be described .~ briefly with reference to Fig. 10.
The table for the mask is provided with stops, not shown, between which the mask is arranged, .',, !
~ so that the mask is coarsely positioned-subsequently~ the . ~
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` 1~78Z40 ~ . .. -angular position of the mask relative to the directions in which the carriage 60 is movable is to - be adjusted. For this purpose an image of the grating .;'5 .' Ml is formed on the grating M2. The mask is rotated ~ 5 until the image of the grating Ml is in alignment '.:;
. with the grating M2. The optical elements which form the image have been selected so that if alignment is obtained, the line which connectes the centres of the gratings M
and M2 is parallel to the direction X in which the carriage 60 is movable.
Subsequently, the substrate grating P2 is aligned relative to the grating M2 by displacement ;` in the X and the Y-direction. The substrate is then moved in the X-direction over the known distance between ;~ 15 the centres of Pl ar,d P2. The substrate table 56 is :
then rotated about an axis, not shown, through the centre of the grating P2 until the grating lines of the grating Pl which extend in the y-direction (see Fig.9) are in alignment with the corresponding grating lines :., in the grating M2. If necessary, the steps described ' for the alignment of the substrate relative to the mask may be repeated. However, in most cases it suffices to - carry out said steps only once.
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. After this alignment the radiation beam 18 can form a first image of the I.C. pattern 17 on the ';~ substrate with the aid of the system of projection ;j l ` lenses Ll, L2, L3. In between the consecutive projections : .
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., - 1078Z~) .' ' the substrate can be moved over very accurately ; defined distances, for example within 0.05 ~ m, in the X and the Y direction, alignment being no longer ,: .
necessary.
In the arrangement of Fig. 1 the radiation : beam b which is emitted by a radiation source 1, for example a laser, is reflected to a prism 4 via the prisms 2 and 3. The prism 4 is movable. If the prism 4 is disposed in the path of the beam b, the beam is reflected to the substrate 8 by this prism and the prism 7. The lenses L2 and Ll focus the beam to a small radiation spot, for example with a diameter of 1 mm, on the grating P2. This grating is a two-dimensionsl diffraction grating with rulings in the ~ and , 15 ~-directions. (see Fig.6). The grating P2 reflects the incident beam so that a number of subbeams of different diffraction orders are obtained, inter alia the subbeams b(+l, 0) and b(-l, 0) in the ~ direction and the subbeams b(0, +1) and b(0, -1) in the ~ -direction.
,; 20 The lenses Ll and L2 focus these subbeams at different ,...................................................................... . ..
~ positions in the back-focal plane of the lens system :~ Ll, L2. In the back focal plane a diaphragm 9 is arranged.
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, This diaphragm has four apertures and only transmits the first-order subbeams. The subbearns traverse the dividi~g ~:
. 25 prisms 6 and first-order images of the phase grating P2 ~,r~l are formed on the grating M2. Since only the first-orders ¢~ are utilized, the period of the grating image is half . .~;, r;`
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10~8Z40 that of the phase grating itself, when neglecting ; the magnification by the lens system I2, Ll, L3.
As a result, the accuracy with which the gratings are aligned for a specific period of the grating P2 ;
is twice as high as in the case that the zero-order subbeams are also used.
Fig. 2 shows the part of the arrangement above the line aa' of Fig. l in more detail. The subbeam b(+l, 0), b(-l, 0), b(0, +1) and b(0, -1) are represented by a single beam bl for the sake of simplicity. After the passage through the dividing prism 6 and the grating M2 the beam bl is reflected to a radiation-sensitive detector 12 via the prisms 20 and 22.
. .
In accordanee with the invention -the 15 position of the image of the phase grating P2 in the plane of the grating M2 is modulated. Thus, the alignment can be observed dynamically which substantially improves the accuracy. Moreover, the influence of drift in the electronic circuit which processes the detection signal is then negligible. For this purpose the dividing ~, prism 6 in the embodiment of Figs. l and 2 takes the . ,~
: form of a polarization-sensitive dividing prism, which ~; only transmits radiation with a specific direction of polarization. The laser 1 produces linearly polarized radiation. The dividing prism 6 is followed by a ~/2 ; plate 25 and a Savart-plate 26. As is shown in the right-hand part of Fig. 2 the Savart-plate comprises ':
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i, two plane-parallel quartz plates 30 and 31 of equal , . .
thickness, whose optic axes 32 and 33 make an angle of with the plane-parallel surfaces and cross each ~,~ other. The ~ 2 plate 25 ensures that the direction of polarization of the beam bl makes an angle of 45 ::~
.~ with the optic axes of the Savart plate. The beam b ` which incident at the plane-parallel faces of - The savart plate is divided into an ordinary beam ,~, and an extraordinary beam in the first quartz plate 31, which are converted into an extraordinary and an ~i;;'' .
ordinary beam respectively at the plane of separation .
of the first and the second quartz plate respectively.
~' This is because the optic axes of the two plates are perpendicular to each other. Two subbeams which are 'i"l/'' i '"' polarized at right angles to each other emerge from the Savart plate 26 which beams are shifted relative to each other. For the sake of clarity the subbeams are not shown separately in Fig. 2.
A polarization modulator 10 and an analyser 11 are arranged before the radiation-sensitive detector 12.
The modulator is controlled by a squareware voltage Vb which is supplied by a generator G. As a result of this, the direction of polarization of the radiation beam which traverses the modulator is alternated through 90 . The direction of transmission of the analyser is parallel to one of the directions of polarization of the ordinary and extraordinary beams .,'(~
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~ 1078240 emerging from the Savart-plate. Thus, at any instant either the ordinary or the extraordinary beam will be transmitted to the detector. At a specific instant this detector "views" either an ordinary image of the grating P2 formed by the ordinary beam or an extra-ordinary image of this grating formed by the extra-ordinary beam, the ordinary and the extraordinary image being superimposed with the grating M2. The indexes of refraction of the Savart plate and the thicknesses of the constituent plane-parallelplates have been ~^ , selected so that the ordinary and the extraordinary image are shifted relative to each other by half a period of the grating. If the grating M2 is disposed exactly between the ordinary and the extraordinary ~, lS image of the grating P2 (or Pl), the intensity of "!,,,,, the radiation received by the detector 12 will be ;, consta*t as a function of time.
~; Fig. 3a shows this situation for one direction of the grating lines. The lines of the grating M2, of the ordinary image P2 O and of the extraordinaryimage P2 e of the grating P2 are normal to the plane of drawing.
During a time interval (tl) the detector receives the radiation intensity transmitted by P2 O and M2 (see ~ig.3b) and during a subsequent time interval (t2) the radiation intensities are equal, so that the detector signal Sd :: , remains constant as a function of time.
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In the grating M2 is not disposed exactly between P2 0 and P2 e' see Fig. 4a, the detector signal will not be constant as a function of time, as is shown : -'r' in Fig. 4b. The differences in the signal Sd can be ri', ~h 5 detected very accurately. As a result, it is possible ,.,;~
~ to align the grating lines of the grating P2 (or P1) . ~
very accurately, for example within l/200 of theperiod of this grating, relative to those of the grating M2 ` lO In the situation of Fig. 4b, in which the grating M2 is shifted to the right relative to the desired position, the detecotr signal in the time interval tl is greater than the detector signal in the time interval t2. If the grating M2 were shifted to the .~'il left relative to the desired position, the detector ~! signal is the time interval tl will be smaller than in the time interval t2. The signal from the generator G
is also applie dto an electronic circuit 57, in which the detector signal is processed. By comparing in which of the time intervals tl and t2 the detector signal is greater, the direction of a positional error of the ~ grating P2 relative to the grating M2 can be detected.
,~ The gratings M2 and P2 are two-dimensional gratings, i.e. they consist of component gratins whose grating lines extend in the y and the ~ direction.
. In Figs. 5 and 6 examples of these gratins are shown, ` whilst Fig. 7 shows an example of a detector 12.
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The detector has a square shape and its sides are effectively parallel to the ~ and ~ directions of .~ the grating lines, i.e. when the gratings are correctly aligned the detector sides are effectively parallel to the ~ and the ~ direction and when the gratings are not yet correctly aligned the detector sides make a small angle with the ~ and ~ directions. The detector consists of two detectors Dl and D2, one of them each i time being associated with the component gratings of 10 the gratings M and P . By means of the detector section Dl it is possible to ~etect whether the mask and the substrate are correctly aligned in the ~ direction of ,c: the gratings, and thus in the Y-direction of the . projection machine; with the detector section D2 :; 15 it is possible to ascertain whether the alignment is . correct in the y direction of the gratings and thus, in :
~ . the X-direction of the projection machine. The detector may consist of four sections Dl', Dl", D2' and D2", the sections Dl' and Dl" as well as the sections D2' ::
l 20 and D2" being interconnected.
J After the grating P2 has been aligned, ~:~
, ;;:~) ~j the carriage 60 is moved in the X-direction over an .:
., .: .
. accurately distance until the grating Pl is disposed underneath the grating M2. Subsequently, the grating P
J. 25 is aligned realtive to M2 in a similar way as described 1 for the grating P2. In that case only the position ., in the Y-direction of the grating Pl need be adjusted by rotation of the substrate table 56. For the grating P
it therefore suffices that it has grating lines which ., . ~ . , ;'.~ . .
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~, extend in the y direction. However, there is no ; objection against making the grating Pl identical J' to the grating P2 and using only the grating lines ,~ of the gratingPl which extend in the ~ direction.
In a realized embodiment of an arrangement in accordance with the invention, in which the substrate was repeatedly exposed to a reduced image of the same I.C. pattern, the period of the grating M2 was 4~ m and that of the gratings P2 and Pl approximately l9.S~ m.
The magnification of the system of projection lenses ,, i was approximately 5x. The distance between the chief .,~
rays of the ordinary and extraordinary beams emerging from the Savart plate was approximately 25 ~ m both in the X-direction and in the Y-direction. Thus a ~' 15 correctly reproducible alignment accuracy of approximately 0.1 m could be achieved. It is to be noted that the grating M2 in ~ig. 5 is shown 20x enlarged and the grating P2 in Fig. 6 lOOx.
The output signals from the sub-detectors ~ 20 are applied to an electronic circuit 57 in which, in a `~,' manner known per se, control signals are derived for correcting the positions of the grating P2 or Pl in !,~ the X-direction and the Y-direction, as is schematically ~ represented in Fig. 1 by the connection 58.
-; 25 The method and arrangement described so far ,,, j only allows detection of whether the strips of the gratings M2 and P2 (or Pl) are correctly aligned.
, However, it might occur that the gratings M2 and P2 (or Pl) are shifted relative to each other by exactly ..,.'i ~ 1 ,.1 ., :~
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, one grating period. In order to ascertain this, in accordance with the invention, a part of the radiation which passes through the grating M2 is utilized to display the centres of the gratings M2 and P2 for the operator, so that the operator can ascertain whether the centres coincide. If the centres do not coincide the operator may for example depress a button so that the servo-system caused by substrate s~ to be moved in the desired direction over exactly one grating period.
As can be seen in Fig.2, the arrangement in accordance with the invention includes a semi-:' transparent prism 23 which divides the beam which traverses the mask into two beams b' and b". The beam b' is reflected to the detector by prism 22. The beam B"
'i;,~' is passed to a TV monitor 16 which is provided with ' a camera tube, by the prism 24 and 22 of Fig. 2 and the further prisms 13, 14 and 15 of Fig. 1. On the monitor images are displayed of the centres of the gratings M2 .;,, 20 and P2 (or Pl).
Instead of a Savart plate 26 it is alter-natively possible to employ a Wollaston prism 26'.
~, As can be seen in the right-hand part of Fig. 2, such a prism consists of two congruent component prisms ', 25 34 and 35 of unaxial double refracting crystals which are assembled to a plane-parallel plate. The optic axis 36 is parallel to the plane of drawing and the optic axis 37 is normal to the plane of drawing. The radiation beam .. ..
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which is incident on one of the plane-parallel major faces of the prism 26' is split into two sub-beams by the prism, which subbeams are polarized at right angles to each other and make a small angle with each other. By a suitable choice of the parameters of the prism 26' it is possible to ensure that the images of ;.~ the grating P2 formed at the location of the grating M2 by the subbeams are shifted by half a grating period.
,~ Instead of with a polarization-sensitive ~, 10 beam splitter and a polarization switch alignment errors can also be detected dynamically if an image of the ~; grating P2 (or Pl) is continuously moved over the ~ grating M2. For this purpose a linearly movable optical !~ wedge or a rotatable plane-parallel plate may be included ~ 15 in the radiation path instead of the elements 25 and 26 '~i`'l , in Fig.2. In Fig. 8 the last-mentioned plate is designated ~ 38. In this Figure only a part of the radiation path ,'~ of Fig. 2 is shown. The polarization switch and the ` analyser of Fig. 2 are no longer present in the arrangement ~' 20 of Fig.8. The plane-parallel glass plate 38 of Fig.8 ~; can oscillate about its axis 39, which for alignment in '; the X- and Y-directions is disposed at 45 with these ~" .
directions. Thus, the image of the grating P2 is moved to and fro over the grating M2. The oscillation is obtained with the aid of a generator 40 and drive means, ~, not shown. If the generator produces a signal c sin wt, ,.. ..
~ the signals Sd of the detector 12 is: d sin (2 wt + 0).
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The phase of the detector signal is compared with the phase of the generator 40 in the electronic circuit 41.
If e has a specified value eO, the correct adjustment of the grating P2 (or P]) relative to the grating M2 5 is obtained. The output signal Su of the circuit 41 is again applied to the drive means for the X and Y
carriages.
The use of a polarization switch in ; comparison with a mechanically moved transparent element, has the advantage that the zero point of the measurement cannot change owing to for example mechanical wear.
Furthermore, if a polarization switch is used, the ; rate with which the position of an image of a grating is switched can be greater than the speed with which said image can be moved with mechanical means.
' In order to enable the mask and the sub-strate to be aligned with the desired accuracy using .
the method and the arrangement described above, no ' magnification errors should occur during imaging of the substrate gratings. The projection system which ; serves to image the I.C. pattern on the substrate, ~ should have a comparatively large image field, for : .
; example with a diameter of approximately 12 mm. The align-, ment gratings are located at the periphery of the image :
' 25 field of this lens system, so that the image of the substrate gratings on the grating M2 is very susceptible to magnification errors. In order to avoid magnification ., " , . .
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.`, .:j iO78Z40 errors, the distance between the substrate and the lens system and the distance between the mask and the lens system would have to be maintained highly constant . and the substrate would have to be very flat.
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However, in practice the flatness error of the substrate is already approximately 5 ~ m, so that without further steps magnification errors might occur.
In accordance with-the invention magnification - errors are substantially avoided if the lens system is telecentric. As is shown in Fig. 1, the system of pro-. jection lenses comprises three lenses Ll, L2, L3~.
The lens Ll is vertically movable, said lens floating ` for example on an air cushion formed between the lens ; ~ and the substrate. Thus, the distance between the substrate and the lens Ll can be maintained constant, ,, also if the plane of the substrate is not perpendicular ...... .
~] to the optical axis of the system of projection lenses or if flatness errors occur in the substrateO Each radiation beam coming from an arbitrary point on the ~''' 20 substrate grating traverses the path between lenses Ll and L2 as a parallel beam. The lens L2 is rigidly ..~., t'i'''"' connected to the projection column. The lens L3 makes ;. the system of projectionlenses telecentric at the side ~ of the mask, i.e. this lens ensures that the chief ray ,. . .
of any radiation beam which traverses the lens L2 is normally incident on the plane of the mas~. A vertical movement of the mask can then no longer give rise to a magnification error. As a result of this, the vertical ... .
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~078240 : tolerance at the side of the mask increased to ~or ;; example 25 ~ m. Without the lens L3 the axial position of the mask would have to be accurate within for example 5 ~ m.
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Above the alignment of the substrate , relative to the mask has been described. However, before this is possible the mask itself must be aligned. For this purpose, the prism 4 in the . .
,-~ arrangement of Figs. 1 and 2 is moved out of the path of the beam supplied by the source. The radiation " beam b2 is reflected by the prisms 45 and 46 so as to illuminate the grating Ml. ;The beam b2 is subsequently ,~ reflected to the grating M2 by the prism 47, 48 and 51 and ~ the dividing prism 6. The radiation path of the beam b2 ,~ 15 furthermore includes two lenses 49 and 50. These lenses, in conjunction with the prisms 47, 48, 51 and 6, ensure that the grating Ml is imaged at full size on the ~' grating M2. The l-to-l imaging system is adapted so :i!
~' that the position of the image of Ml only depends on the direction of the line which connects the centres of A~ the gratings Ml and M2, relative to the X-direction.
y rotating the table 55 it is possible to align the gratings Ml and M2. The llne whlch connects the centres of the gratings Ml and M2 is then parallel to the direction of movement of the carriage 60.
,., The mask Ml for example has the shape ,1 shown in Fig. 9, the grating period being equal to that .~,,,, ~
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of the grating M2. After passage through the grating M2 the beam b2 traverses the same elements as the beam bl.
By ensuring that the centres of the gratings ,: M2 and Ml remain visible on the TV monitor the operator can adjust the mask in the X and Y direction with an , accuracy up to for example 100~ m. The periodic signals -; suppled by the detector 12 when the beam b2 traverses the alignment system, and which consequently can only provide an indication of a possible deviation between the desired and the actual direction of the line which connects the centres of the grating Ml and M2, are again applied to an electronic processing circuit 57 ~, whose output is connected to means, not shown, for rotating the table 55, schematically represented by the , 15 connection 59.
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; Fig. 10 schematically shows the arrangement ~ by means of which the movements of the X-carriage, ,~ on which the substrate is disposed, and of the Y-carriage, which is rigidly connected to the vertical projection S' 20 column, can be measured. This arrangement is based on the principle of the laser interferometer which is ' described in "Philips Technical Review" 30, No.6/7, ......
" pages 160-165. The known arrangement has been adapted so that both the displacement of the X-carriage and ,;
that of the Y-carriage can be measured with the aid of one laser. A beam splitter 62 splits the laser beam 1 into a subbeam 11 for measuring the displacement of the ,~
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Y-carriage and a subbeam 12 for measuring the displacement of the X-carriage. The beam 11 is reflected to a polarization-sensitive beam splitter 65 by the prisms 63 and 64. This beam splitter is secured to a plate 83 which is rigidly connected to the Y-carriage 82 and rigidly connected to a frame on which the beam splitter - 62 and the prism 63 are mounted. A movement of the Y-carriage then means a variation in the distance between the beam splitter 65 and the side of the X~carriage. In the top-right corner of Fig. 10 the beam splitter 65 and the elements arranged around it are shown slightly enlarged. These elements are a ~ /4 , plate 66, a reference mirro 67, a ~/4 plate 68, and ; an analyser 70. For further details of the measuring method reference is made to the article in the , : .
~;~ "Philips Technical Review" 30, No. 6/7.
The beam 12 which emerges from the beam splitter 62 is reflected to a polarization-sensitive ~':. , beam splitter 75 by a prism 74. The elements 76, 77 and 78 which are arranged around said beam splitter have the same functions as the elements 68, 67 and 70.
i The beam splitter 75 is arranged on aplate 85 which is . .
rigidly connected to the X-carriage. A movement of the - X-carriage means a variation in the distance between . , .
~; 25 the beam splitter 74 and the reflecting side of the Y-carriage. The subbeams reflected by the Y-carriage and the reference mirror 77 are intercepted by a ..
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detector 73. The detectors 73 and 72 are connected ..
to electronic circuits 86 and 87.
In the circuits 86 and 87 the number o~
pulses counted, which is a measure of the displacement, can be compared with a reference number for moving the carriages over a specific distance. The outputs of the electronic circuits 86 and 87 are connected to drive means 87 and 88 for the X and Y carriages, so that ~ these carriages are stopped when a specific number of ! :; 10 pulses has been counted.
; :~
The invention has been described with ,~ reference to the projection of an IC pattern on a semi-conductor substrate. It is obvious that the arrangement ~:, ;~' described hereinbefore may also be used for other litho-.~' ' ' graphic techniques where a plurality of masks must be '~ consecutively projected on a substrate and very accurately positioned relative to the substrate. In this respect the fabrication of transport patterns and detection '; I
.~' patterns for magnetic domain stores may be mentioned.
In the above description "IC pattern" should then read:
~' "transport pattern" or "detection pattern" and "I.C. substrate" should read "layer of magnetizable ,~ material".
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1~782~0 "Method and arrangement for aligning a mask pattern ; relative to a semiconductor substrate".
,, _______ , The invention relates to a method of aligning a mask pattern formed in a mask relative to a substrate when the mask pattern is repeatedly imaged directly on the substrate, gratings on the substrate and in the mask being used as alignment references. The invention also relates to an arrangement for carrying out this method.
~owadays use is made of diffusion techniques J
:. and associated masking techniques for the fabrication ~, of integrated circuits (I.C.'s). A multiplicity of masks with different configurations are then consecutively images at the same location of the substrate. Between the ~,, ! ` .
successive imagings at the same location bhe substrate is subjected to the desired physical and chemical changes.
Thus, a passive and/or active element is obtained which is known by the name of integrated circuit, abbreviated ~`
as I.C.
Diffusion and masking techniques are also '~ employed in the fabrication of so-called magnetic domain memories (bubble memories) for the formation of trans-port pa-tterns and detection patterns on a magnetizable :;
layer which is provided on a substrate. Also in this case :.
the accurate alignment of the mask patterns to be used in the consecutive process steps presents a problem.
This problem is so serious that attempts are made , ;`'`
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1~7l3240 PHN. 8429.
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(compare I.E.E.E. Transactions on Magnetics, Vol. ~ag. 9, No. 3, Sept. 1973, pages 474-480) to use only one pattern on the layer of magnetizable material, which pattern serves both for the transport and for the detection of ; 5 the magnetic domains. However, as the requirements imposed on a transport pattern differ from those imposed ~! on a detection pattern, a compromise is to be made with ` respect to the thickness of the pattern on the magnetizable i~ material and the properties of the material of the pattern.
The accuracy with which integrated circuits are manufactured has to satisfy increasingly exacting require-ments. 'rhis requires that the location at which successive ,., ~; masks are to be imaged on the substrate should be defined with ever increasing accuracy. Deviations greater than for example 1 micron may be prohibitive.
In the U.S. Patent 3,811,779 - May 21, 1974 ,~ (PHN~ 5368) an arrangement is described for aligning a cGmposite mask which comprises a m~ltitude of identical I.C. Patterns, with respect to a semioonductor substrate.
'rhis composite mask can be manufactured as follows:
First of all the relevant I.C. pattern is drawn to an enlarged scale with the aid of a machine which is for example computer-controlled. Subsequently, the I.C.
Pattern is optically reduced. Ihe pattern thus obtained is then further optically reduced with a so-called repea~r camera and repeatedly imaged at different :,. .
~ locations on a photographic plate, so that a com~osite '.`':
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--` ~078~40 PHN. 8429.
mask with I~Co patterns of the desired size are obtained.
mis ccmposite mask can be projected at once on a semi-conductor substrate.
The present invention relates to an arrangement for the formation of a plurality of patterns on a sub, strate, the substrate itself being repeatedly exposed to an image, which m~y be reduced, of one pattern. For ; the fabrication of, for example integrated circuits a composite mask is then no longer required and the use of a photorepeater camera is no longer necessary.
~hereas in the arrangement in accordance with the U.S.
Patent (supra) a so_called contact copy of the composite mask is formed on the substrate, the arrangement developed by the Applicant projects an image of the I.C. pattern onto the substrate. In the last mentioned arrangement the I.C. pattern can be imaged onto the substrate in reduced form (for example 5X), so that a reducing step may be dispensed with when making the mask.
However, it is also possible that a 1 to 1 image of the ; 20 I.C. pattern is formed on the substrate.
A general advantage of projection is that dur-ing projection no wear of the mask occurs. As a result, the mask has to be checked only once, instead of several times. E~rtherm~re, accurate alignment of the mask i 25 during projection can be effected more quickly. m is is beca~se when a contact copy is made the mask and the , .
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substrate must still be mDved towæds one another after the mask and the substrate have been aligned with respect to each other. This may then lead to the substrate being shifted relative to the mlsk in a direction p æallel to the plane of the mask or of the substrate. In that case either reaLign-ment is necessary or a less accurate alignment must be accepted.
As the mask to be used in the ærangement according to the present invention comprises only one I.C. pattern, inspection of the mask is simple.
~r. This inspection is even further simplified if the I.C. pattern is to be imaged in reduced form, so that the details of the I.C. pattern in the mask are i 15 correspondingly large.
The present invention relates to the method , in which and the means with which the mask pattern is ; aligned relative to the substrate. The method accord-ing to the invention is characterized in that tWD
phase gratings, which are located outside the area on ; the substrate where a pluralit~ of images of the mask pattern is to be formed, are imaged on a first of tWD
gratings which are located in the mask outside the ~ mask pattern, with the aid of a prDjection system j- 25 which is used for imaging the mask pattern on the sub-strate, and that the position of the observed image ; of a grating, which is being aligned relative to the first grating in the mask, is m~dulated.
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The method of alignment described in the U.S. Patent supra differs fram the method in acoord- -~
ance with the invention inter alia in that the first mentioned method the individual gratings of the subr '~ 5 strate and the mask æe aligned relative to a refer-ence grating which is disposed on a separate support.
Mbreover, the position of an image of grating is not mDdulated in the arrangement in accordance with the U.S. Patent supra.
It is to be noted that, when projecting - I.C. patterns onto a semiconductor substrate, it is known Fer se from United States Patent Specification 3,695,758 Tanaka - Octoker 2, 1972 to pass the align-ment beam of radiation and the radiation beam with which the I.C. Fattern is imaged on the substrate through the same projection system. However, the said Patent Specification does not describe the alignment procedure. It is not clear whether gratings are used for the alignment and there is absolutely no , ., indication where the phase gratings, if any, would have to be located on the substrate. Furthe D re, it - is not known from the Uhited States Patent Specifica-tion 3,695,758 to modulate the position of an image of a grating. Finally, the alignment beam and the projection beam in the knGwn arrangement traverse a semi-transparent mirror on their way to the sub-strate, so that the radiation :-... ..
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``i ~078240 : intensity of said beams is halved, which is a drawback, i in particular for the projection of the I.C. pattern ,. .
onto the substrate.
. A preferred embodiment of a method in . 5 accordance with the invention is characterized in that f first of all, by rotation about an axis perpendicular ,~
to the plane of the mask, the lines of an image of the i.......... second.grating in the mask, which lines extend in a ~; :
,., first direction, are aligned relative to the corres-~;. 10 ponding lines of the first grating in the mask, that subsequently the grating lines of ~ first:of the two : substrate gratings, which lines extend in two mutually perpendicular directions, are aligned relative to the corresponding grating lines of the first great:ing in the mask, that afterthis the substrate is moved in . the direction of the line which connectes the centres of the first and the second mutually aligned gratings in the mask over a distance equal to the distance between the two substrate gratings, and that finally, by rotation about an axis which extends substantially ~¦ through the centre of the first substrate grating, .. l the grating lines of the second substrate grating are :: i .~ aligned relative to the corresponding grating lines ;',.- !
of the first grating in the mask.
.~ 25 An arrangement for carrying out the method ~,; in accordance with Claim 1, which arrangement comprises . a radiation source which supplies an alignment beam, :, :
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a lens system for each time imaging one of the substrate `` gratings on a first grating in the mask, and a radiation-sensitive detector which is disposed in the path of the alignment beam behind the mask, is characterized in that `:
said lens system is constituted by the projection system utilized for imaging the mask pattern on the substrate, and that in the path of the alignment beam between the system of projection lenses and the detector optical elements are included which are controlled by periodic signals for periodically moving the image of a grating observed by the detector and formed in the plane of the mask, the displacement of the observed image being of the order of magnitude of the period of the first ~;~ grating in the mask.
A preferred embodiment of an apparatus in accordance with the invention is furthermore characterized in that in the path of the alignment beam between the -l projection system and the mask a diaphragm is included ~:¦ which only transmits the first-order subbeams of the alignment beam diffracted by the substrate gratings to the mask. The alignment accuracy for a specific period of a substrate grating in the case that only the first-order beams are employed, is two times higher than ~:"
in the case that the zero-order beam were also used.
, 25 In order to prevent magnification errors in imaging the substrate gratings on the first grating ~ of the mask, owing to flatness errors of the substrate :.`., ,~
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.~ or the mask, or owing to the plane of the substrate or ! .~, .~ the mask not being perpendicular to the optical axis ~ of the system of projection lenses, an arrangement : in accordance with the invention is further characterized , ..
s in that the projection system is a telecentric system i; and comprises three lens systems, of which the system which is nearest the substrate is movable along the optical axis, whilst the two other lens systems along the optical axis are immovable.
~. 10 In order to enable the angular position of Y the mask itself to be adjusted before the substrate is aligned relative to the mask, an arrangement in accordance with the invention is characterized in that in addition to a first radiation path for each time imaging one of the lS substrate gratings on the first grating in the maslc, . which radiation path extends from the radiation source v1a a radiation-reflecting element, which may optionally be included in the path of the radiation emitted by the source, via the projection system, a reflection at one of the substrate gratings, a second passage through the projection system, and the diaphragm, to a beam splitter s which is disposed underneath the first grating in the mask, 1` a second radiation path is provided for imaging the .~, :`: second grating in the mask onto the first grating in ;' :;:, ; 25 the mask at full true size, the position of the image -~ of the second grating in the mask only depending on the ,:., .; direction of the line which connects the centres of the . . ,.~, '.'i .:~
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first and the second grating in the mask relative to . the direction of movement of a carriage with which the substrate is moved, which second radiation path extends from the radiation source via reflecting S elements above the mask, through the second grating in ` the mask, and via further reflecting elements under-neath the mask, and a lens system to the said beam ~.
~ splitter, which beam splitter combines the two radiation i` paths to a common radiation path through the mask to ...... ..
~j 10 the radiatior. sensitive detector.
.~ A preferred embodiment of an arrangement in.~accordance with the invention, in ~hich the radiation source emits a linearly polarized beam of radiation, : ;, - is furthermore characterized in that the optical elements ~, 15 for periodically moving the image of each time one of the substrate grat:ings and the second grating in the mask !. ,' ¦
... ~ respectively, are constituted by a polarization-sensitive element which is disposed in the common radiation path ~; before the mask, which element splits the alignment `'''`'''! 20 beam into two subbeams with mutually perpendicular directions of polarization, which subbeams form images of the second grating in the mask and one of the :`~:, substrate graings respectively at the location of .s~ the first graing in the mask, which images are mutually `I" ' :.l 25 shifted by one half period of the first grat:ing in the ,:: .~, . mask, by a polarization switch which is disposed in the ; common radiation path before the detector and which .',"; , ~, _ 10 -..... .
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1~78Z~0 PHN. 8429.
'.'' ' '~i is controlled by a squarewave voltage, which switchswitches the ~;rections of polarization of the subbeams through 90, and by an analyser between the polarization switch and the detector, the contr~l w ltage for the polarization switch also being applied to an electronic circuit in which the detector signal is processed to a control signal for correcting the grating position.
Furthermore, it is to be noted that in an embodiment described in the U.SO Patent 3,811,779 tWD
subbeams which are polarized at right angles to each other are employed for the alignnent. However, the , ...
object of this is merely to enable dynamic detection.
i~ These subbeams do not form tw~ shifted images of one substrate grating.
In order to ascertain whether during the alignment of the substrate gratings relative to the first grating in the mask the image of a substrate grating has not shifted a whole nu~ber of grating ::
periods relative to the first grating in the mask, an - arrangement in accordance with the invention is fur-thermore characterized in that the co~mDn radiation path behind the mask includes a second beam splitter which produces tw~ beams, one of which is aimed at the detector and the second at a camera tube which is .;, coupled with a TV mDnitor on which the gratings are - monitored.
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1078~240 he invention will now be described by way of example with reference to the projection of an I.C. pattern on a semiconductor substrate. For this reference is made to the drawing in which:
.
~ 5 Figs. 1 and 2 show an embodiment of an 1',.'.
arrangement for carrying out the method in accordance with the invention.
. .
Figs. 3a, 3b, 4a and 4b illustrate the . ......................................................................... -, .
operation of some components of this arrangement, Figs. 5, 6 and 9 show examples of gratings to be used in this arrangement;
Fig. 7 shows a composite radiation- -sensitive detector for use in the arrangement in ~- accordance with the invention, ~ ,, Fig. 8 shows a different embodiment of I a part of the arrangement, and . '~.~ .
Fig. 10 schematically shows a set-up for . ..
measuring the displacements of the X and Y-carriage.
~` In Fig. 1 the reference numeral 5 denotes a ....
; 20 mask, which comprises two alignment references Ml and M2 in the form of gratings. Between these alignment -references an I.C. pattern 17 is disposed, which '~ is schematically represented by dashes. This pattern ~ is to be imaged a number of times on the semiconductor ,.~ 25 substrate 8 which also comprises two alignment gratings rj Pl and P2. The gratings Pl and P2 are disposed outside ; the area in which a number of images of the I.C. pattern :;
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are to be formed. m e gratings ~ and M2 tak2 the form of amplitude gratings and the gratings Pl and P2 f ; phase gratings. Compared with other alignment references such as for example squares in the mask and on the sub-strate, the periodic gratings have the advantage that i' when positional errors are mea Æ ed these are averaged over the grating. Thus accurate alignment is possible, even if one or mDre grating lines are mlssing or when the grating lines are serrated lines instead of straight lines. Es~pecially in the fabrication of integrated cir-cuits gratings have the advantage that during the consecutive diffusion processes they cannot grcw asymme-trically or become closed, as would be possible when other alignment references such as for example squares were used. In comparison with amplitude gratings phase gratings on the substrate have the advantage that they are etched into the semiconductor material for example silicon, so that no extraneous material need be deposited on the substrate. Mbreover, the p~ase grat-ings can satisfactorily withstand the mNltitude of s diffusion processes to which the substrate is to be subjected during the fabrication of integrated circuits.
; When ~he I.C. pattern is imaged on the sub-strate the projection beam 18 which is supplied by a radiation source, not shown, only illuminates the I.C.
., pattern. The gratings ~ and ~ are not imaged, :
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so that the I.C. designer need not make allowance for these gratings and no space has to be reserved for these gratings on each portion of the substrate .:. , .
on which one I.C. pattern is projected.
`~ 5 Figure 1 merely shows the optical elements which are used in detecting deviations between the desired and the actual positions of the gratings relative to each other. Of the mechanical elements which ,:?, serve for correctly positioning the mask and the, 10 substrate relative to each other only the turntable 55, on which the mask is disposed, and the turntable 56, on which the substrate is disposed are shown : .
schematically. All optical elements, except for the , laser 1, are accommodated in a vertical projection `'; 15 column, not shown, which is movable in the Y-direction i~ vla a carriage drive. The turntable 56 is connected to a carriage 60 via a column 90, which carriage is ;,l movable in the X-direction. The manner in which and the ;, menas with which the carriages are driven are no object , . . .
of the present invention and will not be discussed.
The displacements of the carriages in the X and Y
.~....................................................................... .
!'~'" directions can be measured accurately with the aid of ::,, :;:
~; an interferometer arrangement which will be described .~ briefly with reference to Fig. 10.
The table for the mask is provided with stops, not shown, between which the mask is arranged, .',, !
~ so that the mask is coarsely positioned-subsequently~ the . ~
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` 1~78Z40 ~ . .. -angular position of the mask relative to the directions in which the carriage 60 is movable is to - be adjusted. For this purpose an image of the grating .;'5 .' Ml is formed on the grating M2. The mask is rotated ~ 5 until the image of the grating Ml is in alignment '.:;
. with the grating M2. The optical elements which form the image have been selected so that if alignment is obtained, the line which connectes the centres of the gratings M
and M2 is parallel to the direction X in which the carriage 60 is movable.
Subsequently, the substrate grating P2 is aligned relative to the grating M2 by displacement ;` in the X and the Y-direction. The substrate is then moved in the X-direction over the known distance between ;~ 15 the centres of Pl ar,d P2. The substrate table 56 is :
then rotated about an axis, not shown, through the centre of the grating P2 until the grating lines of the grating Pl which extend in the y-direction (see Fig.9) are in alignment with the corresponding grating lines :., in the grating M2. If necessary, the steps described ' for the alignment of the substrate relative to the mask may be repeated. However, in most cases it suffices to - carry out said steps only once.
,~;
. After this alignment the radiation beam 18 can form a first image of the I.C. pattern 17 on the ';~ substrate with the aid of the system of projection ;j l ` lenses Ll, L2, L3. In between the consecutive projections : .
...
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:.
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., - 1078Z~) .' ' the substrate can be moved over very accurately ; defined distances, for example within 0.05 ~ m, in the X and the Y direction, alignment being no longer ,: .
necessary.
In the arrangement of Fig. 1 the radiation : beam b which is emitted by a radiation source 1, for example a laser, is reflected to a prism 4 via the prisms 2 and 3. The prism 4 is movable. If the prism 4 is disposed in the path of the beam b, the beam is reflected to the substrate 8 by this prism and the prism 7. The lenses L2 and Ll focus the beam to a small radiation spot, for example with a diameter of 1 mm, on the grating P2. This grating is a two-dimensionsl diffraction grating with rulings in the ~ and , 15 ~-directions. (see Fig.6). The grating P2 reflects the incident beam so that a number of subbeams of different diffraction orders are obtained, inter alia the subbeams b(+l, 0) and b(-l, 0) in the ~ direction and the subbeams b(0, +1) and b(0, -1) in the ~ -direction.
,; 20 The lenses Ll and L2 focus these subbeams at different ,...................................................................... . ..
~ positions in the back-focal plane of the lens system :~ Ll, L2. In the back focal plane a diaphragm 9 is arranged.
. !..
, This diaphragm has four apertures and only transmits the first-order subbeams. The subbearns traverse the dividi~g ~:
. 25 prisms 6 and first-order images of the phase grating P2 ~,r~l are formed on the grating M2. Since only the first-orders ¢~ are utilized, the period of the grating image is half . .~;, r;`
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i~j .
.
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:
10~8Z40 that of the phase grating itself, when neglecting ; the magnification by the lens system I2, Ll, L3.
As a result, the accuracy with which the gratings are aligned for a specific period of the grating P2 ;
is twice as high as in the case that the zero-order subbeams are also used.
Fig. 2 shows the part of the arrangement above the line aa' of Fig. l in more detail. The subbeam b(+l, 0), b(-l, 0), b(0, +1) and b(0, -1) are represented by a single beam bl for the sake of simplicity. After the passage through the dividing prism 6 and the grating M2 the beam bl is reflected to a radiation-sensitive detector 12 via the prisms 20 and 22.
. .
In accordanee with the invention -the 15 position of the image of the phase grating P2 in the plane of the grating M2 is modulated. Thus, the alignment can be observed dynamically which substantially improves the accuracy. Moreover, the influence of drift in the electronic circuit which processes the detection signal is then negligible. For this purpose the dividing ~, prism 6 in the embodiment of Figs. l and 2 takes the . ,~
: form of a polarization-sensitive dividing prism, which ~; only transmits radiation with a specific direction of polarization. The laser 1 produces linearly polarized radiation. The dividing prism 6 is followed by a ~/2 ; plate 25 and a Savart-plate 26. As is shown in the right-hand part of Fig. 2 the Savart-plate comprises ':
... ,: , . . ' . . ' : ' ' . ., . . . ~ . .
i, two plane-parallel quartz plates 30 and 31 of equal , . .
thickness, whose optic axes 32 and 33 make an angle of with the plane-parallel surfaces and cross each ~,~ other. The ~ 2 plate 25 ensures that the direction of polarization of the beam bl makes an angle of 45 ::~
.~ with the optic axes of the Savart plate. The beam b ` which incident at the plane-parallel faces of - The savart plate is divided into an ordinary beam ,~, and an extraordinary beam in the first quartz plate 31, which are converted into an extraordinary and an ~i;;'' .
ordinary beam respectively at the plane of separation .
of the first and the second quartz plate respectively.
~' This is because the optic axes of the two plates are perpendicular to each other. Two subbeams which are 'i"l/'' i '"' polarized at right angles to each other emerge from the Savart plate 26 which beams are shifted relative to each other. For the sake of clarity the subbeams are not shown separately in Fig. 2.
A polarization modulator 10 and an analyser 11 are arranged before the radiation-sensitive detector 12.
The modulator is controlled by a squareware voltage Vb which is supplied by a generator G. As a result of this, the direction of polarization of the radiation beam which traverses the modulator is alternated through 90 . The direction of transmission of the analyser is parallel to one of the directions of polarization of the ordinary and extraordinary beams .,'(~
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~ 1078240 emerging from the Savart-plate. Thus, at any instant either the ordinary or the extraordinary beam will be transmitted to the detector. At a specific instant this detector "views" either an ordinary image of the grating P2 formed by the ordinary beam or an extra-ordinary image of this grating formed by the extra-ordinary beam, the ordinary and the extraordinary image being superimposed with the grating M2. The indexes of refraction of the Savart plate and the thicknesses of the constituent plane-parallelplates have been ~^ , selected so that the ordinary and the extraordinary image are shifted relative to each other by half a period of the grating. If the grating M2 is disposed exactly between the ordinary and the extraordinary ~, lS image of the grating P2 (or Pl), the intensity of "!,,,,, the radiation received by the detector 12 will be ;, consta*t as a function of time.
~; Fig. 3a shows this situation for one direction of the grating lines. The lines of the grating M2, of the ordinary image P2 O and of the extraordinaryimage P2 e of the grating P2 are normal to the plane of drawing.
During a time interval (tl) the detector receives the radiation intensity transmitted by P2 O and M2 (see ~ig.3b) and during a subsequent time interval (t2) the radiation intensities are equal, so that the detector signal Sd :: , remains constant as a function of time.
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In the grating M2 is not disposed exactly between P2 0 and P2 e' see Fig. 4a, the detector signal will not be constant as a function of time, as is shown : -'r' in Fig. 4b. The differences in the signal Sd can be ri', ~h 5 detected very accurately. As a result, it is possible ,.,;~
~ to align the grating lines of the grating P2 (or P1) . ~
very accurately, for example within l/200 of theperiod of this grating, relative to those of the grating M2 ` lO In the situation of Fig. 4b, in which the grating M2 is shifted to the right relative to the desired position, the detecotr signal in the time interval tl is greater than the detector signal in the time interval t2. If the grating M2 were shifted to the .~'il left relative to the desired position, the detector ~! signal is the time interval tl will be smaller than in the time interval t2. The signal from the generator G
is also applie dto an electronic circuit 57, in which the detector signal is processed. By comparing in which of the time intervals tl and t2 the detector signal is greater, the direction of a positional error of the ~ grating P2 relative to the grating M2 can be detected.
,~ The gratings M2 and P2 are two-dimensional gratings, i.e. they consist of component gratins whose grating lines extend in the y and the ~ direction.
. In Figs. 5 and 6 examples of these gratins are shown, ` whilst Fig. 7 shows an example of a detector 12.
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. .
The detector has a square shape and its sides are effectively parallel to the ~ and ~ directions of .~ the grating lines, i.e. when the gratings are correctly aligned the detector sides are effectively parallel to the ~ and the ~ direction and when the gratings are not yet correctly aligned the detector sides make a small angle with the ~ and ~ directions. The detector consists of two detectors Dl and D2, one of them each i time being associated with the component gratings of 10 the gratings M and P . By means of the detector section Dl it is possible to ~etect whether the mask and the substrate are correctly aligned in the ~ direction of ,c: the gratings, and thus in the Y-direction of the . projection machine; with the detector section D2 :; 15 it is possible to ascertain whether the alignment is . correct in the y direction of the gratings and thus, in :
~ . the X-direction of the projection machine. The detector may consist of four sections Dl', Dl", D2' and D2", the sections Dl' and Dl" as well as the sections D2' ::
l 20 and D2" being interconnected.
J After the grating P2 has been aligned, ~:~
, ;;:~) ~j the carriage 60 is moved in the X-direction over an .:
., .: .
. accurately distance until the grating Pl is disposed underneath the grating M2. Subsequently, the grating P
J. 25 is aligned realtive to M2 in a similar way as described 1 for the grating P2. In that case only the position ., in the Y-direction of the grating Pl need be adjusted by rotation of the substrate table 56. For the grating P
it therefore suffices that it has grating lines which ., . ~ . , ;'.~ . .
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.
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-` 1078Z~0 '::
~, extend in the y direction. However, there is no ; objection against making the grating Pl identical J' to the grating P2 and using only the grating lines ,~ of the gratingPl which extend in the ~ direction.
In a realized embodiment of an arrangement in accordance with the invention, in which the substrate was repeatedly exposed to a reduced image of the same I.C. pattern, the period of the grating M2 was 4~ m and that of the gratings P2 and Pl approximately l9.S~ m.
The magnification of the system of projection lenses ,, i was approximately 5x. The distance between the chief .,~
rays of the ordinary and extraordinary beams emerging from the Savart plate was approximately 25 ~ m both in the X-direction and in the Y-direction. Thus a ~' 15 correctly reproducible alignment accuracy of approximately 0.1 m could be achieved. It is to be noted that the grating M2 in ~ig. 5 is shown 20x enlarged and the grating P2 in Fig. 6 lOOx.
The output signals from the sub-detectors ~ 20 are applied to an electronic circuit 57 in which, in a `~,' manner known per se, control signals are derived for correcting the positions of the grating P2 or Pl in !,~ the X-direction and the Y-direction, as is schematically ~ represented in Fig. 1 by the connection 58.
-; 25 The method and arrangement described so far ,,, j only allows detection of whether the strips of the gratings M2 and P2 (or Pl) are correctly aligned.
, However, it might occur that the gratings M2 and P2 (or Pl) are shifted relative to each other by exactly ..,.'i ~ 1 ,.1 ., :~
,~
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, one grating period. In order to ascertain this, in accordance with the invention, a part of the radiation which passes through the grating M2 is utilized to display the centres of the gratings M2 and P2 for the operator, so that the operator can ascertain whether the centres coincide. If the centres do not coincide the operator may for example depress a button so that the servo-system caused by substrate s~ to be moved in the desired direction over exactly one grating period.
As can be seen in Fig.2, the arrangement in accordance with the invention includes a semi-:' transparent prism 23 which divides the beam which traverses the mask into two beams b' and b". The beam b' is reflected to the detector by prism 22. The beam B"
'i;,~' is passed to a TV monitor 16 which is provided with ' a camera tube, by the prism 24 and 22 of Fig. 2 and the further prisms 13, 14 and 15 of Fig. 1. On the monitor images are displayed of the centres of the gratings M2 .;,, 20 and P2 (or Pl).
Instead of a Savart plate 26 it is alter-natively possible to employ a Wollaston prism 26'.
~, As can be seen in the right-hand part of Fig. 2, such a prism consists of two congruent component prisms ', 25 34 and 35 of unaxial double refracting crystals which are assembled to a plane-parallel plate. The optic axis 36 is parallel to the plane of drawing and the optic axis 37 is normal to the plane of drawing. The radiation beam .. ..
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' ... . .
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, , .
which is incident on one of the plane-parallel major faces of the prism 26' is split into two sub-beams by the prism, which subbeams are polarized at right angles to each other and make a small angle with each other. By a suitable choice of the parameters of the prism 26' it is possible to ensure that the images of ;.~ the grating P2 formed at the location of the grating M2 by the subbeams are shifted by half a grating period.
,~ Instead of with a polarization-sensitive ~, 10 beam splitter and a polarization switch alignment errors can also be detected dynamically if an image of the ~; grating P2 (or Pl) is continuously moved over the ~ grating M2. For this purpose a linearly movable optical !~ wedge or a rotatable plane-parallel plate may be included ~ 15 in the radiation path instead of the elements 25 and 26 '~i`'l , in Fig.2. In Fig. 8 the last-mentioned plate is designated ~ 38. In this Figure only a part of the radiation path ,'~ of Fig. 2 is shown. The polarization switch and the ` analyser of Fig. 2 are no longer present in the arrangement ~' 20 of Fig.8. The plane-parallel glass plate 38 of Fig.8 ~; can oscillate about its axis 39, which for alignment in '; the X- and Y-directions is disposed at 45 with these ~" .
directions. Thus, the image of the grating P2 is moved to and fro over the grating M2. The oscillation is obtained with the aid of a generator 40 and drive means, ~, not shown. If the generator produces a signal c sin wt, ,.. ..
~ the signals Sd of the detector 12 is: d sin (2 wt + 0).
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~' -24-~' :, ,':
. .
The phase of the detector signal is compared with the phase of the generator 40 in the electronic circuit 41.
If e has a specified value eO, the correct adjustment of the grating P2 (or P]) relative to the grating M2 5 is obtained. The output signal Su of the circuit 41 is again applied to the drive means for the X and Y
carriages.
The use of a polarization switch in ; comparison with a mechanically moved transparent element, has the advantage that the zero point of the measurement cannot change owing to for example mechanical wear.
Furthermore, if a polarization switch is used, the ; rate with which the position of an image of a grating is switched can be greater than the speed with which said image can be moved with mechanical means.
' In order to enable the mask and the sub-strate to be aligned with the desired accuracy using .
the method and the arrangement described above, no ' magnification errors should occur during imaging of the substrate gratings. The projection system which ; serves to image the I.C. pattern on the substrate, ~ should have a comparatively large image field, for : .
; example with a diameter of approximately 12 mm. The align-, ment gratings are located at the periphery of the image :
' 25 field of this lens system, so that the image of the substrate gratings on the grating M2 is very susceptible to magnification errors. In order to avoid magnification ., " , . .
, ''' i~
., .
. .
, , .
.`, .:j iO78Z40 errors, the distance between the substrate and the lens system and the distance between the mask and the lens system would have to be maintained highly constant . and the substrate would have to be very flat.
:.
However, in practice the flatness error of the substrate is already approximately 5 ~ m, so that without further steps magnification errors might occur.
In accordance with-the invention magnification - errors are substantially avoided if the lens system is telecentric. As is shown in Fig. 1, the system of pro-. jection lenses comprises three lenses Ll, L2, L3~.
The lens Ll is vertically movable, said lens floating ` for example on an air cushion formed between the lens ; ~ and the substrate. Thus, the distance between the substrate and the lens Ll can be maintained constant, ,, also if the plane of the substrate is not perpendicular ...... .
~] to the optical axis of the system of projection lenses or if flatness errors occur in the substrateO Each radiation beam coming from an arbitrary point on the ~''' 20 substrate grating traverses the path between lenses Ll and L2 as a parallel beam. The lens L2 is rigidly ..~., t'i'''"' connected to the projection column. The lens L3 makes ;. the system of projectionlenses telecentric at the side ~ of the mask, i.e. this lens ensures that the chief ray ,. . .
of any radiation beam which traverses the lens L2 is normally incident on the plane of the mas~. A vertical movement of the mask can then no longer give rise to a magnification error. As a result of this, the vertical ... .
~.. i ~.-f ,'.' "'-. .
. .
~078240 : tolerance at the side of the mask increased to ~or ;; example 25 ~ m. Without the lens L3 the axial position of the mask would have to be accurate within for example 5 ~ m.
.~
Above the alignment of the substrate , relative to the mask has been described. However, before this is possible the mask itself must be aligned. For this purpose, the prism 4 in the . .
,-~ arrangement of Figs. 1 and 2 is moved out of the path of the beam supplied by the source. The radiation " beam b2 is reflected by the prisms 45 and 46 so as to illuminate the grating Ml. ;The beam b2 is subsequently ,~ reflected to the grating M2 by the prism 47, 48 and 51 and ~ the dividing prism 6. The radiation path of the beam b2 ,~ 15 furthermore includes two lenses 49 and 50. These lenses, in conjunction with the prisms 47, 48, 51 and 6, ensure that the grating Ml is imaged at full size on the ~' grating M2. The l-to-l imaging system is adapted so :i!
~' that the position of the image of Ml only depends on the direction of the line which connects the centres of A~ the gratings Ml and M2, relative to the X-direction.
y rotating the table 55 it is possible to align the gratings Ml and M2. The llne whlch connects the centres of the gratings Ml and M2 is then parallel to the direction of movement of the carriage 60.
,., The mask Ml for example has the shape ,1 shown in Fig. 9, the grating period being equal to that .~,,,, ~
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of the grating M2. After passage through the grating M2 the beam b2 traverses the same elements as the beam bl.
By ensuring that the centres of the gratings ,: M2 and Ml remain visible on the TV monitor the operator can adjust the mask in the X and Y direction with an , accuracy up to for example 100~ m. The periodic signals -; suppled by the detector 12 when the beam b2 traverses the alignment system, and which consequently can only provide an indication of a possible deviation between the desired and the actual direction of the line which connects the centres of the grating Ml and M2, are again applied to an electronic processing circuit 57 ~, whose output is connected to means, not shown, for rotating the table 55, schematically represented by the , 15 connection 59.
';'`.
; Fig. 10 schematically shows the arrangement ~ by means of which the movements of the X-carriage, ,~ on which the substrate is disposed, and of the Y-carriage, which is rigidly connected to the vertical projection S' 20 column, can be measured. This arrangement is based on the principle of the laser interferometer which is ' described in "Philips Technical Review" 30, No.6/7, ......
" pages 160-165. The known arrangement has been adapted so that both the displacement of the X-carriage and ,;
that of the Y-carriage can be measured with the aid of one laser. A beam splitter 62 splits the laser beam 1 into a subbeam 11 for measuring the displacement of the ,~
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Y-carriage and a subbeam 12 for measuring the displacement of the X-carriage. The beam 11 is reflected to a polarization-sensitive beam splitter 65 by the prisms 63 and 64. This beam splitter is secured to a plate 83 which is rigidly connected to the Y-carriage 82 and rigidly connected to a frame on which the beam splitter - 62 and the prism 63 are mounted. A movement of the Y-carriage then means a variation in the distance between the beam splitter 65 and the side of the X~carriage. In the top-right corner of Fig. 10 the beam splitter 65 and the elements arranged around it are shown slightly enlarged. These elements are a ~ /4 , plate 66, a reference mirro 67, a ~/4 plate 68, and ; an analyser 70. For further details of the measuring method reference is made to the article in the , : .
~;~ "Philips Technical Review" 30, No. 6/7.
The beam 12 which emerges from the beam splitter 62 is reflected to a polarization-sensitive ~':. , beam splitter 75 by a prism 74. The elements 76, 77 and 78 which are arranged around said beam splitter have the same functions as the elements 68, 67 and 70.
i The beam splitter 75 is arranged on aplate 85 which is . .
rigidly connected to the X-carriage. A movement of the - X-carriage means a variation in the distance between . , .
~; 25 the beam splitter 74 and the reflecting side of the Y-carriage. The subbeams reflected by the Y-carriage and the reference mirror 77 are intercepted by a ..
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detector 73. The detectors 73 and 72 are connected ..
to electronic circuits 86 and 87.
In the circuits 86 and 87 the number o~
pulses counted, which is a measure of the displacement, can be compared with a reference number for moving the carriages over a specific distance. The outputs of the electronic circuits 86 and 87 are connected to drive means 87 and 88 for the X and Y carriages, so that ~ these carriages are stopped when a specific number of ! :; 10 pulses has been counted.
; :~
The invention has been described with ,~ reference to the projection of an IC pattern on a semi-conductor substrate. It is obvious that the arrangement ~:, ;~' described hereinbefore may also be used for other litho-.~' ' ' graphic techniques where a plurality of masks must be '~ consecutively projected on a substrate and very accurately positioned relative to the substrate. In this respect the fabrication of transport patterns and detection '; I
.~' patterns for magnetic domain stores may be mentioned.
In the above description "IC pattern" should then read:
~' "transport pattern" or "detection pattern" and "I.C. substrate" should read "layer of magnetizable ,~ material".
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Claims (10)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of aligning a mask pattern formed in a mask relative to a substrate, the mask pattern is repeatedly imaged directly on the substrate, gratings on the substrate and in the mask being used as alignment references, characterized in that the gratings on the substrate are two phase gratings, which are located outside the area on the substrate where a plurality of images of the mask pattern is to be formed, are imaged on a first of two gratings which are located in the mask outside the mask pattern, with the aid of a projection system which is used for imaging the mask pattern on the substrate, and that the position of the observed image of a grating, which is being aligned relative to the first grating in the mask, is modulated.
2. A method as claimed in Claim 1, characterized in that first of all, by rotation about an axis perpen-dicular to the plane of the mask, the lines of an image of the second grating in the mask, which lines extend in a first direction, are aligned relative to the corres-ponding lines of the first grating in the mask, that subsequently the grating lines of a first of the two sub-strate gratings, which lines extend in two mutually per-pendicular directions, are aligned relative to the corresponding grating lines of the first grating in the mask, that after this the substrate is moved in the direction of the line which connects the centre of the first and the second mutually aligned gratings in the mask over a distance equal to the distance between the two substrate gratings, and that finally, by rotation about an axis which extends substantially through the centre of the first substrate grating, the grating lines of the second substrate grating are aligned relative to the corresponding grating lines of the first grating in the mask.
3. An arrangement for carrying out the method in accordance with Claim 1, which arrangement com-prises a radiation source which supplies an alignment beam, a lens system for each time imaging one of the substrate gratings on a first grating in the mask, and a radiation-sensitive detector which is disposed in the path of the alignment beam behind the mask, characterized in that said lens system is constituted by the projection system utilized for imaging the mask pattern on the substrate, and that in the path of the alignment beam between the projection system and the radiation-sensitive detector are included optical elements which are controlled by periodic signals, for periodically moving the image of a grat-ing observed by the detector and formed in the plane of the mask, the displacement of the observed image being of the order of magnitude of the period of the first grating in the mask.
4. An arrangement as claimed in Claim 3, char-acterized in that in the path of the alignment beam between the projection system and the mask a diaphragm is included which only transmits the first-order sub-beams of the alignment beam diffracted by the substrate gratings to the mask.
5. An arrangement as claimed in Claim 3 or 4, characterized in that the projection system is a tele-centric system and comprises three lens systems, of which the system which is nearest the substrate is movable along the optical axis, whilst the two other lens systems along the optical axis are immovable.
6. An arrangement as claimed in Claim 3 or 4, characterized in that in addition to a first radiation path for each time imaging one of the substrate grat-ings on the first grating in the mask, which radiation path extends from the radiation source via a radiation-reflecting element, which may optionally be included in the path of the radiation emitted by the source, via the projection system, a reflection at one of the substrate gratings, a second passage through the pro-jection system, and the diaphragm transmitting only the first-order subbeams of the alignment beam to a beam splitter which is disposed underneath the first grating in the mask, a second radiation path is pro-vided for imaging the second grating in the mask on the first grating in the mask at full true size, the posi-tion of the image of the second grating in the mask only depending on the direction of the line which con-nects the centres of the first and the second grating in the mask relative to the direction of movement of a carriage with which the substrate is moved, which second radiation path extends from the radiation source via reflecting elements above the mask, through the second grating in the mask 1 and via further reflect-ing elements underneath the mask, and a lens system to the said bean splitter, which beam splitter combines the two radiation paths to a common radiation path through the mask to the radiation-sensitive detector.
7. An arrangement as claimed in Claim 3 in which the radiation source emits a linearly polarized beam of radiation, characterized in that the optical elements for periodically moving the image of each time one of the substrate gratings and the second grating in the mask respectively, are constituted by a polarization-sensitive element which is disposed in the common radiation path before the mask, which element splits the alignment beam into two subbeams with mutually perpendicular directions of polarization, which sub-beams form the images of the second grating in the mask and one of the substrate gratings respectively at the location of the first grating in the mask, which images are mutually shifted by one half period of the first grating in the mask, by a polarization switch which is disposed in the common radiation path before the detector and which is controlled by a squarewave voltage, which switch switches the direc-tions of polarization of the subbeams through 90°, and by an analyser between the polarization switch and the detector, the control voltage for the polari-zation switch also being applied to an electronic circuit in which the detector signal is processed to a control signal for correcting the grating position.
8. An arrangement as claimed in Claim 3, charac-terized in that the common radiation path between the beam splitter and the mask includes a movable transpa-rent element which moves the image of the second grating in the mask or one of the substrate grating respectively to and fro over the first mask, and that the output of the detector is connected to an electro-nic circuit in which an output signal of the detector is processed to a control signal for correcting the grating position, to which circuit also a signal is applied which is proportional to the driving signal for the movable element.
9. An arrangement as claimed in Claim 3, charac-terized in that in the radiation path between the mask and the radiation sensitive detector a beam splitter is included which produces two beams, one of which is aimed at the detector and the second at a camera tube which is coupled with a TV monitor on which the gratings are monitored.
10. An arrangement as claimed in Claim 3, charac-terized in that the detector has the shape of a square and comprises at least two sub-detectors whose separat-ing lines extend diagonally in the square, the straight sides of the square being effectively parallel to the two directions of the grating lines of the first grating in the mask.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7606548A NL7606548A (en) | 1976-06-17 | 1976-06-17 | METHOD AND DEVICE FOR ALIGNING AN IC CARTRIDGE WITH REGARD TO A SEMI-CONDUCTIVE SUBSTRATE. |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1078240A true CA1078240A (en) | 1980-05-27 |
Family
ID=19826386
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA265,868A Expired CA1078240A (en) | 1976-06-17 | 1976-11-17 | Modulation alignment of mask pattern relative to semiconductor substrate |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4251160A (en) |
| JP (1) | JPS52154369A (en) |
| CA (1) | CA1078240A (en) |
| DE (1) | DE2651430C3 (en) |
| FR (1) | FR2379097A1 (en) |
| GB (1) | GB1571907A (en) |
| NL (1) | NL7606548A (en) |
Families Citing this family (90)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4172664A (en) * | 1977-12-30 | 1979-10-30 | International Business Machines Corporation | High precision pattern registration and overlay measurement system and process |
| FR2436967A1 (en) * | 1978-09-19 | 1980-04-18 | Thomson Csf | METHOD FOR OPTICAL ALIGNMENT OF PATTERNS IN TWO CLOSE PLANS AND ALIGNMENT DEVICE IMPLEMENTING SUCH A METHOD |
| DE2845603C2 (en) * | 1978-10-19 | 1982-12-09 | Censor Patent- und Versuchs-Anstalt, 9490 Vaduz | Method and device for projection copying |
| US4422763A (en) * | 1978-12-08 | 1983-12-27 | Rca Corporation | Automatic photomask alignment system for projection printing |
| DE2905636C2 (en) * | 1979-02-14 | 1985-06-20 | Censor Patent- Und Versuchs-Anstalt, Vaduz | Method for copying masks onto a workpiece |
| FR2450468A1 (en) * | 1979-02-27 | 1980-09-26 | Thomson Csf | OPTICAL SYSTEM FOR ALIGNING TWO PATTERNS AND PHOTOREPECTOR USING SUCH A SYSTEM |
| JPS5612728A (en) * | 1979-07-12 | 1981-02-07 | Nippon Kogaku Kk <Nikon> | Alignmening device for ic projection exposure equipment |
| JPS5612729A (en) * | 1979-07-12 | 1981-02-07 | Nippon Kogaku Kk <Nikon> | ?alignmening device for ic projection exposure equipment |
| DE2939044A1 (en) * | 1979-09-27 | 1981-04-09 | Ibm Deutschland Gmbh, 7000 Stuttgart | DEVICE FOR ELECTRON BEAM LITHOGRAPHY |
| FR2472208A1 (en) * | 1979-12-18 | 1981-06-26 | Thomson Csf | OPTICAL SYSTEM FOR ALIGNMENT OF TWO REASONS AND PHOTOREPERATOR USING SUCH A SYSTEM |
| US4309813A (en) * | 1979-12-26 | 1982-01-12 | Harris Corporation | Mask alignment scheme for laterally and totally dielectrically isolated integrated circuits |
| JPS56110234A (en) * | 1980-02-06 | 1981-09-01 | Canon Inc | Projection printing device |
| DD151231A1 (en) * | 1980-06-02 | 1981-10-08 | Dietmar Klingenfeld | OPTICAL ARRANGEMENT FOR PROJECTION SLITHOGRAPHIC EQUIPMENT |
| JPS58193547A (en) * | 1982-05-07 | 1983-11-11 | Hitachi Ltd | Reduced projection exposing device |
| US4388386A (en) * | 1982-06-07 | 1983-06-14 | International Business Machines Corporation | Mask set mismatch |
| JPS5936220A (en) * | 1982-08-25 | 1984-02-28 | Toshiba Corp | Fixed slit type photoelectric microscope |
| JPS5998525A (en) * | 1982-11-26 | 1984-06-06 | Canon Inc | Deviding printer |
| JPS59101828A (en) * | 1982-12-01 | 1984-06-12 | Canon Inc | Alignment device |
| JPH0619280B2 (en) * | 1983-09-24 | 1994-03-16 | 名古屋大学長 | Optical automatic positioning device |
| US4568189A (en) * | 1983-09-26 | 1986-02-04 | The United States Of America As Represented By The Secretary Of The Navy | Apparatus and method for aligning a mask and wafer in the fabrication of integrated circuits |
| DE3336901A1 (en) * | 1983-10-11 | 1985-04-18 | Deutsche Itt Industries Gmbh, 7800 Freiburg | Mask marking and substrate marking for a method of aligning a photomask having a mask marking on a substrate marking |
| US4631416A (en) * | 1983-12-19 | 1986-12-23 | Hewlett-Packard Company | Wafer/mask alignment system using diffraction gratings |
| US4596467A (en) * | 1984-03-16 | 1986-06-24 | Hughes Aircraft Company | Dissimilar superimposed grating precision alignment and gap measurement systems |
| US4765714A (en) * | 1984-04-03 | 1988-08-23 | Horner Joseph L | Binary phase-only optical correlation system |
| DE3573864D1 (en) * | 1984-11-13 | 1989-11-23 | Hitachi Ltd | Alignment method for reduction projection type aligner |
| JPS61215905A (en) * | 1985-03-22 | 1986-09-25 | Nippon Kogaku Kk <Nikon> | Position detecting device |
| DE3512615A1 (en) * | 1985-04-06 | 1986-10-16 | Ernst Leitz Wetzlar Gmbh, 6330 Wetzlar | ARRANGEMENT FOR ALIGNING, TESTING AND / OR MEASURING TWO-DIMENSIONAL OBJECTS |
| DE3517070A1 (en) * | 1985-05-11 | 1986-11-13 | Ernst Leitz Wetzlar Gmbh, 6330 Wetzlar | METHOD AND ARRANGEMENT FOR ALIGNING, TESTING AND / OR MEASURING TWO-DIMENSIONAL OBJECTS |
| JPS61287229A (en) * | 1985-06-14 | 1986-12-17 | Nippon Kogaku Kk <Nikon> | Exposure device |
| US4771180A (en) * | 1985-10-11 | 1988-09-13 | Matsushita Electric Industrial Co. Ltd. | Exposure apparatus including an optical system for aligning a reticle and a wafer |
| NL8600638A (en) * | 1986-03-12 | 1987-10-01 | Philips Nv | DEVICE FOR ALIGNING A MASK AND A SUBSTRATE WITH REGARD TO EACH OTHER |
| NL8600639A (en) * | 1986-03-12 | 1987-10-01 | Asm Lithography Bv | METHOD FOR ALIGNING A MASK AND A SUBSTRATE AND DEVICE FOR CARRYING OUT THE METHOD |
| JPS62229942A (en) * | 1986-03-31 | 1987-10-08 | Univ Nagoya | Optical positioning device |
| EP0243520B1 (en) * | 1986-04-29 | 1991-11-27 | Ibm Deutschland Gmbh | Interferometric mask-wafer alignment |
| NL8601278A (en) * | 1986-05-21 | 1987-12-16 | Philips Nv | DEVICE FOR DETECTING AN ENLARGEMENT ERROR IN AN OPTICAL IMAGE SYSTEM. |
| JP2569544B2 (en) * | 1987-04-08 | 1997-01-08 | 株式会社ニコン | Positioning device |
| JP2658051B2 (en) * | 1987-05-15 | 1997-09-30 | 株式会社ニコン | Positioning apparatus, projection exposure apparatus and projection exposure method using the apparatus |
| JPS63153821A (en) * | 1987-10-27 | 1988-06-27 | Nikon Corp | Alignment device |
| US5734478A (en) * | 1988-10-12 | 1998-03-31 | Nikon Corporation | Projection exposure apparatus |
| US5189494A (en) * | 1988-11-07 | 1993-02-23 | Masato Muraki | Position detecting method and apparatus |
| JPH02192114A (en) * | 1989-01-20 | 1990-07-27 | Canon Inc | Aligner |
| JP2650396B2 (en) * | 1989-02-07 | 1997-09-03 | キヤノン株式会社 | Position detecting device and position detecting method |
| USRE36799E (en) * | 1990-06-13 | 2000-08-01 | Nikon Corporation | Projection optical apparatus using plural wavelengths of light |
| JP3033135B2 (en) * | 1990-06-13 | 2000-04-17 | 株式会社ニコン | Projection exposure apparatus and method |
| NL9001611A (en) * | 1990-07-16 | 1992-02-17 | Asm Lithography Bv | DEVICE FOR IMAGING A MASK PATTERN ON A SUBSTRATE. |
| JPH0488624U (en) * | 1990-12-14 | 1992-07-31 | ||
| NL9100410A (en) | 1991-03-07 | 1992-10-01 | Asm Lithography Bv | IMAGE DEVICE EQUIPPED WITH A FOCUS ERROR AND / OR TILT DETECTION DEVICE. |
| EP0737330B1 (en) * | 1994-06-02 | 1999-03-10 | Koninklijke Philips Electronics N.V. | Method of repetitively imaging a mask pattern on a substrate, and apparatus for performing the method |
| DE69531854T2 (en) * | 1994-08-02 | 2004-08-19 | Koninklijke Philips Electronics N.V. | METHOD FOR REPEATING IMAGE OF A MASK PATTERN ON A SUBSTRATE |
| JP2870461B2 (en) * | 1995-12-18 | 1999-03-17 | 日本電気株式会社 | Photomask alignment mark and semiconductor device |
| JPH11504770A (en) * | 1996-03-04 | 1999-04-27 | アーエスエム リソグラフィ ベスローテン フェンノートシャップ | Lithographic apparatus for step and scan imaging of a mask pattern |
| DE69704998T2 (en) * | 1996-03-15 | 2001-09-27 | Asm Lithography Bv | ALIGNMENT DEVICE AND LITHOGRAPHIC APPARATUS WITH SUCH A DEVICE |
| KR19980042190A (en) | 1996-11-07 | 1998-08-17 | 요시다쇼이치로 | Mark for position detection, mark detection method and apparatus therefor, and exposure apparatus |
| US5837169A (en) * | 1996-11-19 | 1998-11-17 | Northern Telecom Limited | Creation of bragg reflactive gratings in waveguides |
| JP3570728B2 (en) | 1997-03-07 | 2004-09-29 | アーエスエム リソグラフィ ベスローテン フェンノートシャップ | Lithographic projector with off-axis alignment unit |
| TW367407B (en) * | 1997-12-22 | 1999-08-21 | Asml Netherlands Bv | Interferometer system with two wavelengths, and lithographic apparatus provided with such a system |
| US6160622A (en) * | 1997-12-29 | 2000-12-12 | Asm Lithography, B.V. | Alignment device and lithographic apparatus comprising such a device |
| US6417922B1 (en) | 1997-12-29 | 2002-07-09 | Asml Netherlands B.V. | Alignment device and lithographic apparatus comprising such a device |
| JP2002528895A (en) * | 1998-10-20 | 2002-09-03 | コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ | Method of manufacturing a semiconductor device on a silicon substrate having on its surface a lattice and at least partially a recessed oxide pattern |
| US6368763B2 (en) | 1998-11-23 | 2002-04-09 | U.S. Philips Corporation | Method of detecting aberrations of an optical imaging system |
| US6248486B1 (en) | 1998-11-23 | 2001-06-19 | U.S. Philips Corporation | Method of detecting aberrations of an optical imaging system |
| US6544694B2 (en) | 2000-03-03 | 2003-04-08 | Koninklijke Philips Electronics N.V. | Method of manufacturing a device by means of a mask phase-shifting mask for use in said method |
| US7541201B2 (en) | 2000-08-30 | 2009-06-02 | Kla-Tencor Technologies Corporation | Apparatus and methods for determining overlay of structures having rotational or mirror symmetry |
| US7068833B1 (en) * | 2000-08-30 | 2006-06-27 | Kla-Tencor Corporation | Overlay marks, methods of overlay mark design and methods of overlay measurements |
| TW526573B (en) * | 2000-12-27 | 2003-04-01 | Koninkl Philips Electronics Nv | Method of measuring overlay |
| TW556296B (en) * | 2000-12-27 | 2003-10-01 | Koninkl Philips Electronics Nv | Method of measuring alignment of a substrate with respect to a reference alignment mark |
| US7037626B2 (en) * | 2001-05-18 | 2006-05-02 | Koninklijke Philips Electronics N.V. | Lithographic method of manufacturing a device |
| US7804994B2 (en) * | 2002-02-15 | 2010-09-28 | Kla-Tencor Technologies Corporation | Overlay metrology and control method |
| JP3872782B2 (en) * | 2002-08-29 | 2007-01-24 | Ｔｈｋ株式会社 | Method and apparatus for correcting position and orientation of holding object |
| TWI227814B (en) | 2002-09-20 | 2005-02-11 | Asml Netherlands Bv | Alignment system and methods for lithographic systems using at least two wavelengths |
| US6807503B2 (en) * | 2002-11-04 | 2004-10-19 | Brion Technologies, Inc. | Method and apparatus for monitoring integrated circuit fabrication |
| US6891598B2 (en) * | 2003-02-14 | 2005-05-10 | Asml Netherlands B.V. | Lithographic device and method for wafer alignment with reduced tilt sensitivity |
| US7053355B2 (en) | 2003-03-18 | 2006-05-30 | Brion Technologies, Inc. | System and method for lithography process monitoring and control |
| US7075639B2 (en) * | 2003-04-25 | 2006-07-11 | Kla-Tencor Technologies Corporation | Method and mark for metrology of phase errors on phase shift masks |
| US7608468B1 (en) | 2003-07-02 | 2009-10-27 | Kla-Tencor Technologies, Corp. | Apparatus and methods for determining overlay and uses of same |
| US7346878B1 (en) | 2003-07-02 | 2008-03-18 | Kla-Tencor Technologies Corporation | Apparatus and methods for providing in-chip microtargets for metrology or inspection |
| US7288779B2 (en) * | 2003-12-17 | 2007-10-30 | Asml Netherlands B.V. | Method for position determination, method for overlay optimization, and lithographic projection apparatus |
| US7557921B1 (en) | 2005-01-14 | 2009-07-07 | Kla-Tencor Technologies Corporation | Apparatus and methods for optically monitoring the fidelity of patterns produced by photolitographic tools |
| US7837907B2 (en) * | 2007-07-20 | 2010-11-23 | Molecular Imprints, Inc. | Alignment system and method for a substrate in a nano-imprint process |
| TWI401529B (en) * | 2008-06-27 | 2013-07-11 | Au Optronics Corp | Alignment mark on the mask and method for identifying the position of shielding elements via alignment mark |
| WO2010085632A2 (en) * | 2009-01-23 | 2010-07-29 | University Of Washington | Virtual core flow cytometry |
| US9927718B2 (en) | 2010-08-03 | 2018-03-27 | Kla-Tencor Corporation | Multi-layer overlay metrology target and complimentary overlay metrology measurement systems |
| KR20140027298A (en) | 2011-04-22 | 2014-03-06 | 마퍼 리쏘그라피 아이피 비.브이. | Lithography system for processing a target, such as a wafer, and a method for operating a lithography system for processing a target, such as a wafer |
| WO2012144904A2 (en) | 2011-04-22 | 2012-10-26 | Mapper Lithography Ip B.V. | Position determination in a lithography system using a substrate having a partially reflective position mark |
| JP5932023B2 (en) | 2011-05-13 | 2016-06-08 | マッパー・リソグラフィー・アイピー・ビー．ブイ． | Lithographic system for processing at least part of a target |
| US10890436B2 (en) | 2011-07-19 | 2021-01-12 | Kla Corporation | Overlay targets with orthogonal underlayer dummyfill |
| US9030661B1 (en) | 2013-03-15 | 2015-05-12 | Kla-Tencor Corporation | Alignment measurement system |
| US9230050B1 (en) | 2014-09-11 | 2016-01-05 | The United States Of America, As Represented By The Secretary Of The Air Force | System and method for identifying electrical properties of integrate circuits |
| US10451412B2 (en) | 2016-04-22 | 2019-10-22 | Kla-Tencor Corporation | Apparatus and methods for detecting overlay errors using scatterometry |
| US10270947B2 (en) | 2016-09-15 | 2019-04-23 | Microsoft Technology Licensing, Llc | Flat digital image sensor |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3695758A (en) * | 1969-06-30 | 1972-10-03 | Nippon Kogaku Kk | Illumination device for projector type ic printer |
| NL7100212A (en) * | 1971-01-08 | 1972-07-11 | ||
| JPS5117297B1 (en) * | 1971-03-11 | 1976-06-01 | ||
| US3739247A (en) * | 1971-05-17 | 1973-06-12 | Canon Kk | Positioning device using photoelectric scanning |
| GB1391270A (en) * | 1971-12-08 | 1975-04-16 | Rank Organisation Ltd | Photolithography |
-
1976
- 1976-06-17 NL NL7606548A patent/NL7606548A/en not_active Application Discontinuation
- 1976-10-14 FR FR7630898A patent/FR2379097A1/en active Granted
- 1976-11-11 GB GB46979/76A patent/GB1571907A/en not_active Expired
- 1976-11-11 DE DE2651430A patent/DE2651430C3/en not_active Expired
- 1976-11-17 CA CA265,868A patent/CA1078240A/en not_active Expired
-
1977
- 1977-01-24 JP JP669177A patent/JPS52154369A/en active Granted
-
1978
- 1978-07-13 US US05/924,351 patent/US4251160A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| FR2379097A1 (en) | 1978-08-25 |
| JPS52154369A (en) | 1977-12-22 |
| JPS619733B2 (en) | 1986-03-25 |
| NL7606548A (en) | 1977-12-20 |
| DE2651430A1 (en) | 1977-12-29 |
| FR2379097B1 (en) | 1983-06-17 |
| GB1571907A (en) | 1980-07-23 |
| DE2651430B2 (en) | 1980-03-13 |
| US4251160A (en) | 1981-02-17 |
| DE2651430C3 (en) | 1980-11-20 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |