Projection optical apparatus using plural wavelengths of light

Abstract

A projection optical apparatus comprising a projection optical system for projectively focusing a pattern image of a mask under illumination by light of first wavelength onto a sensitive substrate, a stage holding the sensitive substrate, a fiducial plate disposed on the stage, a first mark detector for illuminating light of second wavelength different from the first wavelength, through a first mark area formed on the mask and the projection optical system, onto the sensitive substrate or a second mark area formed on the fiducial plate, then detecting optical information produced from the second mark area, a fourth mark area formed on the sensitive substrate or the fiducial plate and arranged in a predetermined positional relationship relative to the second mark area, a third mark area formed on the mask and arranged in a predetermined positional relationship relative to the first mark area, a second mark detector for illuminating the light of first wavelength onto the fourth mark area through the third mark area and the projection optical system, and then detecting optical information produced from the fourth mark area, under a condition that the first mark detector is detecting the optical information produced from the second mark area, and an error detector for detecting detection errors due to a distortion at respective positions in the view field of the projection optical system where the first mark area and the second mark area are present, based on the detected results by the first mark detector and the second mark detector.

Description

plane IP (i.e., the plane conjugate to the fiducial plate FP or the wafer W). Accordingly, at the fiducial grating plate 21, the 1st order diffracted lights D₁1, D₁2 cross each other to produce an interference fringe in the crossed area. The resulting interference fringe of course flows or drifts one-dimensionally at the beat frequency Δf (30 KHz). As shown in FIG. 7A, therefore, a transmission type diffraction grating 21A is provided on the fiducial grating plate 21 covered with a chromium layer, and an interference light BTr between two diffracted lights is coaxially produced from the grating 21A. This behavior will now be described by referring to FIG. 8. Because of meeting an image conjugate relation, the fiducial grating plate 21 is conjugate to the plane IP and the wafer mark WMu (or the surface of the fiducial plate FP) so that the interference light BT also impinges upon the fiducial grating plate 21 in addition to the 1st order diffracted lights D₁1, D₁2. However, since the wafer mark WMu and the reticle marks Aua, Aub are arranged in the X-Y plane to be shifted laterally, the interference light BT returns to a portion (light shielding portion) 21B on the fiducial grating plate 21, which portion is adjacent to the grating 21A where the two 1st order diffracted lights D₁1, D₁2 cross each other, as shown in FIG. 7A.

Accordingly, by just setting the position and size of the grating 21A on the fiducial grating plate 21 in match with the size of the mark Aua or Aub, the interference light BT from the wafer mark WMu can be shielded.

Respective 0th order lights BTo of the 1st order diffracted lights D₁1, D₁2 illuminating the grating 21A on the fiducial grating plate 21 propagate so as to deviate from a photoelectric element 23, and only the interference light BTr between two 1st order diffracted lights vertically produced from the grating 21A is received by the photoelectric element 23. This technique is the same as the case of taking out the interference light BT from the wafer mark WMu as shown in FIG. 4. In either case, the grating pitch of the wafer mark WMu or the grating 21A is set exactly two times the pitch of the interference fringe produced thereon.

The intensity of the interference light BTr thus received by the photoelectric element 23 is changed sinusoidally at the beat frequency Δf (30 KHz). Therefore, an output signal Sm of the photoelectric element 23 becomes an AC signal which is linearly changed in a phase difference relative to the reference signal SR depending on the amount of displacement of the reticle marks Aua, Aub in the pitch direction on the basis of the reference grating 16.

On the other hand, the interference light BT and the 1st order diffracted lights D₁1, D₁2, all reflected by the beam splitter 20 shown in FIG. 2, reaches the field iris 22. The iris 22 is formed with an opening 22A which allows only the interference light BT to pass therethrough, as shown in FIG. 7B, while the two 1st order diffracted lights D₁1, D₁2 are shielded by a light shielding portion 22B.

The interference light BT having passed through the iris 22 reaches a photoelectric element 26 through a mirror 24 and a condenser lens 25. The photoelectric element 26 produces an output signal Sw depending on change in the intensity of the interference light BT. This output signal Sw also becomes an AC signal of which level is changed sinusoidally at the beat frequency Δf, the phase of the AC signal relative to the reference signal SR being changed in proportion to the amount of deviation of the mark WMu on the wafer W or the fiducial mark Fu on the fiducial plate FP from the reference grating 16.

The reference signal SR and the output signals Sm, Sw are inputted to a phase difference measurement unit 27 which determines a phase difference φm of the output signal Sm relative to the reference signal SR, determines a phase difference φw of the output signal Sw relative to the reference signal SR, and further a difference therebetween Δφ=φm-φw. In the case of this embodiment, since the diffraction grating pitch on the fiducial plate FP (or the wafer W) is two times the pitch of the interference fringe produced thereon, one period (±180°) of the phase difference Δφ corresponds to 1/2 (±1/4 pitch) of the diffraction grating pitch. Based on the phase difference Δφ, the measurement unit 27 calculates position correction amounts (or position shift amounts) ΔX, ΔY of the water stage ST or the reticle stage RS, values of those amounts being delivered to the main controller 5.

In the foregoing, the system from the driver 10 to the measurement unit 27, including the object lens OBJu, corresponds to first mark detecting means in the present invention.

Meanwhile, in FIG. 2, the mark RMr on the reticle R is detected by a TTR alignment system for exposure (corresponding to AO₁ in FIG. 1) which comprises a mirror M₂, an object lens OBr, a beam splitter 30, a lens system 31, an illumination field iris 32, a condenser lens 33, a fiber 34, a focusing lens 35, a beam splitter 36, and CCD image sensors 37A, 37B. The fiber 34 emits an illumination light at the exposure wavelength to uniformly irradiate the iris 32 through the condenser lens 33. The illumination light having passed through an opening of the iris 32 enters the object lens OBr through the lens system 31 and the beam splitter 30, following which it is bent by the mirror M₂ at a right angle to vertically illuminate a local area of the reticle R including the mark RMr downwards. The iris 32 is conjugate to the reticle R so that an opening image or the iris 32 is focused on the reticle R. The beam splitter 30 is located near a front focus plane or the tele-centric object lens OBr, i.e., a plane conjugate to the pupil EP of the projection lens FL, thereby reflecting a part of the light returned from the object lens OBr toward the focusing lens 35. The CCD image sensors 37A, 37B have their light receiving surfaces which are conjugate to the reticle R through the object lens OBr and the focusing lens 35, and also conjugate to the wafer W or the fiducial plate FP through the projection lens PL. Incidentally, an exit end of the fiber 34 is located to be conjugate to the pupil EP of the projection lens PL for achievement of the Keller's illumination. In the case of this embodiment, the optical path between the object lens OBr and the beam splitter 30 exhibits an afocal system and, therefore, a deviation in the position of the mark RMr can be compensated for by arranging the object lens OBr and the mirror M₂ integrally with each other in such a manner as able to move together horizontally in FIG. 2. But, in consideration of stability of the system, the mirror M₂ is here fixedly located at a position outside the pattern area PA having the maximum dimension possibly expected on the reticle R.

CCD image sensors 37A, 37B are arranged to have an angular spacing of 90° therebetween so that their horizontal scan lines coincide with the X and Y directions, respectively, for making position measurements of the crossshaped mark RMr in the X and Y directions separately. The reason is to avoid a difference in resolution as developed when using a single CCD image sensor to detect shifts of the mark image in both the horizontal and vertical directions, because a usual CCD image sensor have has different degrees of pixel resolution in the horizontal and vertical directions. An image processing unit 38 receives respective image signals (video signals) from the CCD image sensors 37A, 37B, detects a position shift amount of the mark RMr on the reticle R from the fiducial mark FMr on the fiducial plate FP, and then deliver delivers information of the position shift amount to the main controller 5.

In addition to the above configuration, there are also provided a global mark detection system 40 of off-axis type for detecting a global aligment mark on the wafer W, a latent image in a resist layer or the respective fiducial marks on the fiducial plate FP, and a processing unit 42 for processing a signal from the system 40. Furthermore, adjustment units 50A, 50B for adjusting or correcting various focusing characteristics of the projection lens PL are provided and supervised under control of the main controller 5. The adjustment unit 50A has a function of changing magnification, focus position, distortion, etc. of the projection lens PL by, for example, controlling pressure of a predetermined air chamber in the projection lens PL. The adjustment unit 50B has a function of finely moving in the axial direction or tilting a lens element as one component of the projection lens PL (for example, a field lens on the reticle side).

The different wavelength TTR alignment system and the exposure light TTR alignment system are preferably arranged as schematically shown in FIG. 9. As will be seen from FIG. 9, reticle grating mark areas Au, Al, Ar, Ad, each being arranged as shown in FIG. 5, are formed in the respective sides of the light shielding band ESB around the pattern area PA on the reticle R. The mark areas Au, Ad are used for alignment in the X direction plotted in FIG. 9, whereas the mark areas Ar, Al are used for alignment in the Y direction.

Outside the light shielding band ESB, there is also provided a reticle mark RMl similar to the reticle mark RMr at a symmetrical position.

Therefore, object lenses OBr, OBl, of two exposure light TTR alignment systems are arranged to respectively detect the marks RMr, RMl below the dichroic mirror DM, and object lenses OBJu, OBJd, OBJr, OBJl of four different wavelength TTR alignment systems are arranged to respectively detect the mark areas Au, Ad, Ar, Al through the dichroic mirror DM.

When the reticle R and the wafer W are actually aligned with each other on a die-by-die basis by using the different wavelength TTR alignment systems, the four eyes are not always required to be used simultaneously, but three or two eyes may be used instead. This is relied on the fact that even in the case where any of corresponding marks (WMu, WMd, WMr, WMl) in one shot area on the wafer is defective, if one eye in the X direction and one eye in the Y direction at minimum properly output photoelectric signals, an alignment error (interruption of the sequence) can be avoided to the utmost by executing the alignment for the shot area of interest.

The mark arrangement on the reticle R as shown in FIG. 9 and the mark arrangement on the fiducial plate FP suitable for this embodiment will be next described with reference to FIGS. 10 and 11.

FIG. 10 shows one preferred example of a pattern layout on the reticle R, in which the pattern area PA having the maximum dimension projectable by the projection lens PL is supposed. The cross-shaped reticle marks RMr, RM RMl are provided on a line passing the center Rcc of the pattern area PA on the reticle R and extending parallel to the X axis. These marks RMr, RMl are set substantially at the respective centers of the view fields of the object lenses OBr, OBl. In the reticle R shown in FIG. 10, the four mark areas Au, Ad, Ar, Al are each located at a position farthest from the reticle center Rcc. Stated otherwise, rectangular areas Su, Sd, Sr, Sl indicated by broken lines in FIG. 10 respectively stand for one are examples of ranges where the optical axes (detection centers) of the object lenses OBJu, OBJd, OBJr, OBJl of the four different wavelength TTR alignment systems are movable. Then, in the case of FIG. 10, the mark areas Au, Ad, Ar, Al are each provided at the outermost position of the movable range of the corresponding object lens.

FIG. 10 is illustrated by way of example and, depending on cases, the movable ranges Sr, Sl of the object lenses OBJr, OBJl may protrude into a region between the movable ranges Su, Sd of the object lenses OBJu, OBJd from the right and left.

FIG. 11 shows the mark arrangement on the fiducial plate FP with double cross-shaped fiducial marks FMr, FMl provided on the left and right sides of the center in the X direction. The center-to-center distance between the two fiducial marks FMr and FMl is set equal to a value resulted from multiplying the center-to-center distance between the two marks RMr and RMl on the reticle by the projection magnification (l/M). Accordingly, when the center Fcc of the fiducial plate FP is made coincident with the reticle center Rcc, the fiducial mark FMr and the reticle mark RMr are simultaneously observed by the object lens OBr of one exposure light TTR alignment system under a condition that the reticle mark RMr is positioned between the double lines of the fiducial mark FMr, and the fiducial mark FM FMl and the reticle mark RMl are simultaneously observed by the object lens OBl of the other exposure light TTR alignment system under a condition that the reticle mark RMl is positioned between the double lines of the fiducial mark FMl.

On the fiducial plate FP, there are also provided fiducial mark areas Fu, Fd, Fr, Fl in which diffraction gratings are engraved in positions and sizes respectively corresponding to the movable ranges Su, Sd, Sr, Sl on the reticle R when the center Fcc of the fiducial plate FP is made coincident with the reticle center Rcc. In the fiducial mark area Fu, for example, a group of grating lines engraved in the X direction with the constant pitch are formed similarly to the mark WMu on the wafer W and used for detecting a relative position shift in the X direction from the mark area Au on the reticle R. This equally applies to the other fiducial mark areas Fd, Fr, Fl. Accordingly, even if the size of the pattern area PA (or the light shielding band ESB) is changed upon replacement of the reticle R with another one, it is possible to simultaneously detect an X-directional shift of the mark area Au from the fiducial mark Fu, an X-directional shift of the mark area Ad from the fiducial mark Fd, a Y-directional shift of the mark area Ar from the fiducial mark Fr, and a Y-directional shift of the mark area Al from the fiducial mark Fl by the four eyes (OBJu, OBJd, OBJr, OBJl) so long as the mark areas Au. Ad, Ar, Al on the reticle are present within the movable ranges Su, Sd, Sr, Sl, respectively.

In FIG. 11, the two groups of plural grating lines making up the fiducial marks Fr and Fl on the left and right sides correspond to each other in one-to-one relation with respect to the Y direction, whereas the two groups of plural grating lines making up the fiducial marks Fu and Fd on the upper and lower sides correspond to each other in one-to-one relation with respect to the X direction. Further, the center-to-center spacing in the X direction between the mark area Au and Ad shown in FIG. 10 is accurately equal to integer times as much as the grating pitch of the fiducial marks Fu, Fd, whereas the center-to-center spacing in the Y direction between the mark area Ar and Al is accurately equal to integer times as much as the grating pitch of the fiducial marks Fr, Fl.

Operation of this embodiment, that is, base line measurement of the exposure light TTR alignment system and the different wavelength TTR alignment system in consideration of a distortion, will be described below. At first, an arbitrary reticle (such as shown in FIG. 10, for example) is set on the reticle stage RS and the reticle alignment is performed by picking up images of the reticle marks RMr. RMl and the marks FMr, FMl on the fiducial plate FP by the CCD sensor elements 37A, 37B of the exposure light TTR alignment systems.

Then, the object lenses OBJu, OBJd, OBJr, OBJl (i.e., the holders 11) of the four different wavelength alignment systems are set at positions respectively corresponding to the mark areas Au, Ad, Ar, Al, followed by checking shifts in illumination position of the two beams L_m1, L_m2 in the X and Y directions and a tele-centric error of the two beams L_m1, L_m2 by the use of the fiducial marks Fu, Fd, Fr, Fl on the fiducial plate FP. After completion of the checking, the four different wavelength alignment systems each determines amounts of relative position shifts between the reticle R and the fiducial plate FP at that position. In other words, the shift amounts in the X direction between the fiducial mark Fu (and Fd) and the reticle mark Au (and Ad), as well as the shift amounts in the Y direction between the fiducial mark Fr (and Fl) and the reticle mark Ar (and Al) are detected through the respective measurement units 27.

Based on the detected shift amounts, the main controller 5 controls the driver 1 and the stage driver 4 for servo-driving the reticle stage RS or the wafer stage ST. Since the different wavelength alignment systems of this embodiment are each of the heterodyne type allowing successive measurement of the relative position shift amount even in a condition that the reticle mark and the fiducial mark remain at rest. The, the measurement units 27 continue successively outputting the information on the relative position shifts (such as in the X, Y and rotating directions). Therefore, the alignment between the reticle R and the fiducial plate FP is continued so that all the phase differences Δφ measured by the measurement units 27 of the four different wavelength alignment systems become zero (or a fixed value). During the above step of the different wavelength alignment, the image processing units 38 of the exposure light TTR alignment systems continue successively (at certain intervals of time) outputting the position shift amounts (ΔXr, ΔYr) in the X, Y directions between the reticle mark RMr and the fiducial mark FMr, as well as the position shift amounts (ΔXl, ΔYl) in the X, Y directions between the reticle mark RMl and the fiducial mark FMl. It is to be noted that in the case of a large distortion, the corresponding shift amount is added as an offset amount to a design value beforehand. Thus, the shift amounts (ΔXr, ΔYr), (ΔXl, ΔYl) determined by the exposure light TTR alignment systems correspond to averages of distortion differences at the alignment positions (i.e., the marks Au, Ad, Ar, Al) between the wavelength of the exposure light and the different wavelength therefrom. To put it in more detail, when the results of detecting two pairs of the reticle mark Au (the fiducial mark Fu) and the reticle mark Ad (the fiducial mark Fd) show that the phase differences Δφ therebetween are both zero, the shift amounts (ΔXr, ΔYr), (ΔXl, ΔYl) detected by the image processing units 38 are stored plural times, following which the stored results area averaged to determine overall alignment errors (in X, Y and θ directions) caused by a distortion difference between the reticle R and the fiducial plate FP. In the case of this embodiment, the reticle R and the fiducial plate FP are simultaneously aligned with each other by using four eyes of the different wavelength TTR alignment systems, the. The reticle R and the fiducial plate FP exhibit, as a consequence of the alignment, slight errors in the X, Y and θ directions depending on distortion characteristics of the projection lens PL at the different wavelength. These errors can be assumed as fixed offsets so long as the reticle marks Au, Ad, Ar, Al are not changed in their positions. Therefore, by detecting the shift amounts between the marks RMr, RMl and the fiducial marks FMr, FMl using the exposure light TTR alignment systems, the resulting shift amounts give offset amounts in the X, Y and θ directions which include the distortion amounts of the projection lens at the positions of the marks RMr, RMl under the exposure light.

Accordingly, when actually carrying out alignment of the shot area on the wafer W by the different wavelength TTR alignment systems thereafter, it is only required to control the reticle stage RS or the wafer stage ST so that the aligned position is shifted by the above offset amounts to reach the true alignment position. The offset amounts caused by the distortion difference in the X, Y and θ (rotating) directions are calculated in the main controller 5 based on information of the shift amounts from the image processing unit 38, and stored until the reticle R will be realigned or replaced with another one.

As the distortion difference in the projection lens PL between the wavelength of the exposure light and the different wavelength therefrom may be changed upon the adjustment unit 50B being actuated, it is desirable that immediately after actuating the adjustment unit 50B to a large extent, the offset amounts are measured again by using the fiducial plate FP.

With this embodiment as stated above, since the mark areas Au, Ad, Ar, Al for the different wavelength TTR alignment are respectively provided on the four sides of the reticle R and the corresponding fiducial marks Fu, Fd, Fr, Fl on the fiducial plate FP are simultaneously detected, it is possible to precisely determine the overall alignment errors through TTR which are caused by an influence of distortions at the different wavelength. Further, with this embodiment, since the different wavelength TTR alignment systems and the exposure light TTR alignment systems are simultaneously operated through the projection lens PL and the values measured by the interferometer 3 on the wafer stage ST are not used at all, errors due to fluctuating air in the atmosphere, which would raise a problem associated with the interferometer 3, will not be involved so that the offset amounts can be measured with very high precision.

In addition, since this embodiment employs the different wavelength TTR alignment systems of heterodyne type having extremely high resolution, the highly accurate measurement is achieved. For example, assuming that the pitch of the diffraction gratings on the fiducial plate FP is on the order of 4 μm, the phase difference detectable range (±180°) is given ±1 μm. Also, assuming that the practical phase measurement resolution is ±2° in consideration of noises and so on, the position shift detecting resolution becomes as high as about ±0.01 μm.

Consequently, with such an arrangement that the reticle R and the fiducial plate FP are subjected to alignment servo control by using the different wavelength TTR alignment systems of heterodyne type, the highly stable positioning can be achieved.

While the projection lens PL of this embodiment has been explained as being tele-centric on both sides thereof, it may of course be tele-centric on either side only. In the case of a projection lens being tele-centric on both sides, the optical axis of the object lens of the exposure light TTR alignment system is vertical to the reticle surface and also coincident with the principal ray passing the pupil center of the projection lens PL. Therefore, if the mark patterns on the reticle are formed of reflective chromium layers, the light regularly reflected by the patterns are so strongly detected by the CCD image sensors that both the reticle mark RMr, RMl and the fiducial mark FMr, FMl may appear bright. In the case where the fiducial plate FP made of quartz glass or the like is entirely covered with a chromium layer and the fiducial marks FMr, FMl are formed by removing the chromium layer by etching or the like into desired patterns, it may happen that the fiducial marks FMr, FMl look black, but the whole of the surroundings become bright, thereby greatly lowering the contrast of the reticle marks RMr, RMl. In this case, an aperture iris (spatial filter) having a ring-shaped opening may be disposed in the illumination optical path of each exposure light TTR alignment system, e.g., in the pupil conjugate plane between the beam splitter 30 and the lens system 31 in FIG. 2, for illuminating the reticle R in the dark field. With this arrangement, dark field images are focused on the CCD image sensors such that only respective edges of the reticle marks RMr, RMl and the fiducial marks FMr, FMl glint brightly. Moreover, the spatial filter disposed in the pupil conjugate plane may be formed of a liquid crystal, electrochromic (EC) or the like in which multiple ring-like openings arc patterned in concentric relation, allowing the illumination to be switched between the dark field and the light field. It is also possible to change the number of aperture for the illumination light.

A manner of improving superposition accuracy when using the apparatus as shown in FIG. 2, in particular, a manner of improving the matching between different units of the apparatus, will be described below.

FIG. 12A exaggeratedly represents distortion characteristics (broken lines) of the projection lens PL under the exposure wavelength and distortion characteristics (one-dot-chain lines) thereof under the different wavelength (i.e., the wavelength of the alignment light) on the basis of an ideal lattice (solid lines).

A distortion map like that can be drawn by, for example, making a trial print using a test reticle. Note that the distortion map under the different wavelength cannot be obtained by the trial printing, but can be obtained by using the method similar to the above stated embodiment in a combined manner.

At first, a test reticle having vernier marks for superposition measurement at respective ideal lattice points in the pattern area is prepared and aligned by the exposure light TTR alignment system. Then, a reticle blind in the exposure illumination system is fully opened and the test reticle is exposed onto a dummy wafer (such as a photosensitive resist layer, photo-chromic layer or bare silicon wafer coated with an opto-magnetic medium).

Next, the reticle blind is narrowed so as to illuminate only the vernier mark provided at the center of the test reticle. Following that, while stepping the wafer stage ST at the pitch of the ideal lattice points, an exposure is made in superposed relation to each latent image of the vernier mark on the test reticle having been exposed in advance on a step-by-step basis.

In this case, on assumptions that the stepping of the wafer stage ST is coincident with the division pitch of the ideal lattice, the distortion characteristics under the exposure wavelength on the basis of the ideal lattice can be determined by measuring the superposition accuracy between the latent image of each vernier mark exposed at the first time and the latent image of the same vernier mark printed at the second time in superposing relation. In the above measurement, the latent images of the vernier marks on the dummy wafer may be detected by the global mark detection system 40 of off-axis type shown in FIG. 2, or by the exposure light TTR alignment system after properly modifying a shape of the vernier mark. Where the dummy wafer is formed of a usual photoresist layer, the measurement may be performed by the different wavelength TTR alignment system, etc. after once developing the dummy wafer to build resist images of the vernier marks.

Then, amounts of superposition errors are determined at each of the ideal lattice points in that way, and the resulting error amounts are statistically processed by the method of least squares for determining the respective offsets in the X, Y and θ directions. Based on those offsets, the shift amounts (ΔOF_x1, ΔOF_y1), (ΔOF_x2, ΔOF_y2) of the images RMr', RMl' of the reticle marks RMr, RMl under the exposure wavelength, indicated by broken lines in FIGS. 12B and 12C, from the ideal positions (solid lines) can be presumed as system offsets.

Consequently, when aligning the reticle marks RMr, RMl by the exposure light TTR alignment systems, it is possible to always make an exposure on the distortion map with the least errors from the ideal lattice, by taking into account the system offsets.

Further, since the difference in distortion between the exposure wavelength and the different wavelength can be determined following the above first embodiment, the reticle pattern can be exposed in superposed relation to each shot area on the wafer under a condition closest to the ideal lattice, by further taking into account (or compensating for) the distortion difference, even in the case of die-by-die alignment using the different wavelength TTR alignment systems. This implies that the matching between different units of plural steppers jointly constituting a single semiconductor manufacture line can be achieved on the order of the ideal lattice, and hence that the matching accuracy in the manufacture line can be improved.

Since the above embodiment is premised on using the stepper shown in FIG. 2, the detection center of the exposure light TTR alignment system is fixedly positioned in the view field of the projection lens. Therefore, after determining and compensating for the system offsets (ΔOF_x1, ΔOF_y1), (ΔOF_x2, ΔOF_y2) during the reticle alignment beforehand so that the distortion map under the exposure wavelength becomes closest to the ideal lattice, as explained in connection with FIGS. 12B and 12C, distortion errors under the different wavelength may be determined at each alignment position using the different wavelength TTR alignment system.

According to the present invention, as described above, since a different wavelength TTR alignment system and an exposure light TTR alignment system are arranged to be separated from each other and to simultaneously detect a group of fiducial marks located on the image plane of a projection optical system, the distortion difference as developed in when using the different wavelength can be precisely measured. In other words, since the alignment light at the exposure wavelength and the alignment light at the different wavelength are detected by the respective TTR alignment systems exactly at the same timing through the projection optical system, the detected results commonly include measurement errors due to minute fluctuations in air flows, temperature distribution, etc. within the optical paths, thereby allowing those measurement errors to be canceled out. Another advantage is in that since the present invention does not rely on the method using a laser interferometer while running a wafer stage or the like, the results will not be affected by measurement accuracy (reproducibility) of the laser interferometer itself.

Further, according to the present invention, since a plurality of TTR alignment systems can be simultaneously operated using the group of fiducial marks, it is also possible to implement beam positioning, tele-centric checking and focus checking at the same time, which are necessary upon the an object lens of the TTR alignment system being moved, resulting in an advantage of increasing a throughput in setting of the TTR alignment system.

Claims

1. A projection optical apparatus comprising:

a projection optical system for projectively focusing a pattern image of a mask under illumination by a light of first wavelength characteristic onto a sensitive substrate,

a stage for holding said sensitive substrate,

a fiducial plate disposed on said stage,

first mark detection means for illuminating a light of second wavelength characteristic different from said first wavelength characteristic, through a first mark area formed on said mask and said projection optical system, onto said sensitive substrate or a second mark area formed on said fiducial plate, and then detecting optical information produced from said second mark area,

a fourth mark area formed on said sensitive substrate or said fiducial plate and arranged in a predetermined positional relationship relative to said second mark area,

a third mark area formed on said mask and arranged in a predetermined positional relationship relative to said first mark area,

second mark detection means for illuminating said light of first wavelength characteristic onto said fourth mark area through said third mark area and said projection optical system, and then detecting optical information produced from said fourth mark area, under a condition that said first mark detection means is detecting the optical information produced from said second mark area, and

error detection means for detecting detection errors due to a distortion at respective positions in the view field of said projection optical system where said first mark area and said second mark area are present, based on the detected results by said first mark detection means and said second mark detection means.

2. A projection optical apparatus according to claim 1, wherein:

said first mark detection means has a first object lens system movable depending on position change of said first mark area on said mask, and

the a uniform mark pattern is formed in said second mark area over a movable range of said first object lens system.

3. A projection optical apparatus comprising:

a projection optical system disposed between first and second planes such that said first and second planes are optically conjugate to each other under a first wavelength characteristic,

alignment mark means including first and third mark means disposed on said first plane with a predetermined positional relationship therebetween, and second and fourth mark means disposed on said second plane with a predetermined positional relationship therebetween;

first mark detection means for illuminating a light of second wavelength characteristic different from said first wavelength characteristic onto said second mark means through said first mark means and said projection optical system, and then detecting first optical information produced from said second mark means,

second mark detection means for illuminating said light of first wavelength characteristic onto said fourth mark means through said third mark means and said projection optical system, and then detecting second optical information produced from said fourth mark means, and

means for creating information of alignment errors developed between said first and second planes in the directions enough to define a plane, based on said first and second optical information.

4. A projection exposure apparatus for exposing a pattern area of a mask irradiated with first illumination light onto a substrate through a projection optical system, the apparatus comprising:

(a) a movable stare supporting the substrate and moving in a predetermined plane perpendicular to an optical axis of said projection optical system;

(b) a mask holder supporting the mask which has a mask mark formed at a peripheral position of the pattern area;

(c) a fiducial plate mounted on said movable stage and having first and second fiducial marks on its top face, the first fiducial mark being aligned through said projection optical system with the mask mark when said movable stage is located at a predetermined reference position with respect to the image field of said projection optical system;

(d) a first alignment system irradiating the mask mark and the first fiducial mark with the first illumination light and receiving a light from the mask mark and a light from the first fiducial mark through said projection optical system, to detect a positional relationship between the mask mark and the first fiducial mark, when said movable stage is; located near the reference position; and

(e) a second alignment system including a predetermined detecting reference, irradiating the second fiducial mark with second illumination light which has different wavelength from the first illumination light and receiving a light from the second fiducial mark through said projection optical system, to detect a positional relationship between the detecting reference and the second fiducial mark, when said movable stage is located near the reference position.5. A projection exposure apparatus for exposing a pattern area of a mask irradiated with first illumination light onto a substrate through a projection optical system, the apparatus comprising:

(a) a movable stage supporting the substrate and moving in a plane perpendicular to an optical axis of said projection optical system;

(b) a fiducial plate fixedly mounted on a portion of said movable stage and having first and second fiducial patterns on its surface, said first and second fiducial patterns being arranged with predetermined positional relationship;

(c) a first alignment optical system detecting a light from said first fiducial pattern through said projection optical system and a peripheral portion of the pattern area of said mask and a light from a mask mark formed within the peripheral portion of said mask, when said mask mark and the first fiducial pattern are irradiated with a light of a same wavelength as the first illumination light;

(d) a controller driving and positioning said movable stage so that the first fiducial pattern is substantially aligned with the mask mark and simultaneously the second fiducial pattern is located at a predetermined position in the image field of said projection optical system; and

(e) a second alignment optical system detecting a light from the second fiducial pattern through said projection optical system, when the second fiducial pattern is irradiated with a light having different wavelength than the first illumination light;

wherein said movable stage is stationary until said first and second alignment optical systems complete the light detecting

operations.6. A method for examining a variation of the base line distance between a center point of a reticle and a detecting center of an alignment system which detects positional deviation of a mark formed on a substrate for aligning the substrate through a projection optical system, the method comprising the steps of:

(a) providing a fiducial plate within the image field of said projection optical system instead of the substrate, said fiducial plate having a first fiducial mark to be aligned with a reticle mark through said projection optical system and a second fiducial mark disposed at a predetermined positional relationship with respect to the first fiducial mark;

(b) positioning said fiducial plate at a reference position so that the first fiducial mark and the reticle mark are substantially aligned with each other through said projection optical system; and

(c) detecting the positional deviation between the detecting center of said alignment system and the second fiducial mark to determine the variation of said base line distance while said fiducial plate is stationary at the

reference position.7. A method for aligning a substrate and a mask having a circuit pattern, and for exposing a an image of the circuit pattern onto the substrate through a projection optical system, the method comprising the steps of:

(a) detecting a mask mark formed on the mask and a first fiducial mark disposed on a movable stage through said projection optical system with a first alignment system using a first wavelength of light and, substantially at the same time, detecting a second fiducial mark disposed on said movable stage through said projection optical system with a second alignment system using a different wavelength of light, when said movable stage is stationary at a baseline measurement position;

(b) determining a positional relationship between a detecting reference of said second alignment system and the circuit pattern of the mask in an image field of said projection optical system based on detection results obtained in step (a);

(c) detecting an alignment mark formed on the substrate, which is mounted on said movable stage, with said second alignment system;

(d) determining a positional relationship between the detecting reference of paid second alignment system and the alignment mark of the substrate in the image field of said projection optical system based on a detection result obtained in step (c); and

(e) positioning said movable stage to alit a shot area of the substrate and the image of the circuit pattern based on the positional relationships determined in steps (b) and (d), and exposing the shot area of the

substrate.8. A method according to claim 7, wherein, in the step (a), said first alignment system generates a first deviation signal representing a positional relationship of the mask mark and the first fiducial mark and, substantially at the game time, said second alignment system generates a second deviation signal representing a positional relationship of the detecting reference of said second

alignment system and the second fiducial mark.9. A method according to claim 7, wherein the substrate has first and second X-direction alignment marks and first and second Y-direction alignment marks, and said second alignment system includes a first objective lens for detecting the first X-direction aliment mark, a second objective lens for detecting the first Y-direction alignment mark, a third objective lens for detecting the second X-direction alignment mark, and a fourth objective lens for detecting the second Y-direction alignment mark.10. A method according to claim 9, wherein the step (c) includes detecting at least one of said first and second X-direction alignment marks and at least one of said first and second Y-direction alignment marks, and the step (d) includes determining positional relationships between the detecting reference of said alignment system and each of said one X-direction alignment mark and said one Y-direction alignment mark.11. A method according to claim 7, wherein the steps (a) and (b) are performed after operation of an adjustment unit which adjusts a magnification or a distortion characteristic of said

projection optical system.12. A projection exposure apparatus comprising:

a projection optical system disposed between a mask and a substrate to project on the substrate an illumination light irradiating the mask;

a plate having fiducial marking formed thereon and disposed in an image field of said projection optical system;

a first alignment system irradiating a portion of said fiducial marking with a first alignment light different from said illumination light in wavelength to detect optical information produced from said fiducial marking through said projection optical system;

a second alignment system irradiating a portion of said fiducial marking with a second alignment light having substantially the same wavelength as said illumination light through said projection optical system to detect a positional relationship between said mask and said plate; and

an alignment controller connected to said first and second alignment systems to detect an offset amount of said first alignment system caused

by said projection optical system.13. An apparatus according to claim 12, wherein

said fiducial marking includes two mark patterns disposed at a predetermined positional relationship so that said two mark patterns are detected substantially at the same time by said first and second alignment systems, respectively.14. An apparatus according to claim 12, wherein

said first alignment system includes a photodetector which receives, through a mark area on said mask, diffraction light produced from said fiducial marking and passing through said projection optical system.15. An apparatus according to claim 12, further comprising:

an adjustment unit connected to said projection optical system to adjust an optical characteristic of said projection optical system,

wherein said alignment controller determines the offset amount of said first alignment system after an adjustment of said optical characteristic.16. A projection exposure apparatus comprising:

a projection optical system disposed between a mask and a substrate to project on the substrate an illumination light irradiating the mask;

a first alignment system irradiating a first fiducial mark with a first alignment light different from said illumination light in wavelength to detect optical information produced from said first fiducial mark through said projection optical system;

a second alignment system irradiating a second fiducial mark with a second alignment light having substantially the same wavelength as said illumination light through said projection optical system to detect a positional relationship between said second fiducial mark and a mark on said mask; and

a plate disposed on a substrate side with respect to said projection optical system, said first and second fiducial marks being formed on said plate at a predetermined positional relationship so that said first and second alignment systems respectively detect said first and second

fiducial marks substantially at the same time.17. An apparatus according to claim 16, further comprising:

an alignment controller connected to said first and second alignment systems to determine a base line amount of said first alignment system.18. A projection exposure method for protecting an illumination light irradiating a mask through a projection optical system on a substrate to transfer a pattern of said mask onto said substrate, comprising the steps of:

disposing a plate formed with a first fiducial mark and a second fiducial mark in an image field of said projection optical system;

detecting said first fiducial mark through said projection optical system by a first alignment system which uses a first beam different from said illumination light in wavelength;

detecting said second fiducial mark through said projection optical system by a second alignment system which uses a second beam having substantially the same wavelength as said illumination light; and

determining a base line amount of said first alignment system based on outputs of said first and second alignment systems.19. A method according to claim 18, wherein

said step of detecting said first fiducial mark by said first alignment system and said step of detecting said second fiducial mark by said second alignment system are performed substantially at the same time.20. A method according to claim 19, wherein

said plate is substantially at rest during said steps of detecting said first and second fiducial marks.21. A method according to claim 18, wherein

said base line amount of said first alignment system is determined after an adjustment of an optical characteristic of said projection optical system or a position of said first alignment system.22. A projection exposure method for protecting an illumination light irradiating a mask through a projection optical system on a substrate to transfer a pattern of said mask on said substrate, comprising the steps of:

disposing a plate formed with fiducial marking in an image field of said projection optical system;

detecting said fiducial marking through said projection optical system by a first alignment system which uses a first beam different from said illumination light in wavelength and by a second alignment system which uses a second beam having substantially the same wavelength as said illumination light, respectively; and

determining a base line amount of said first alignment system based on outputs of said first and second alignment systems.