JPH0428217A - Positioning device - Google Patents

Abstract

PURPOSE:To make it possible to align two substances in a highly precise manner even when an exposing operation is being conducted by a method wherein an interference fringe is formed by interfering two-frequency alignment lights, having the wavelength differentiated from an exposing light, with each other, and the above-mentioned interference fringe is projected on the substances. CONSTITUTION:After the alignment light 10 emitted from a laser light source 9 has been split into two components in a split optical system 1, the light 10 is brought into a circularly polarized light. The split two-component light 10 is interfered by a downward-reflecting mirror 17 and it is made to irradiate on a reticle 1. Then, the alignment light 10, which passed through a correction optical system 18 is made incident on an alignment light deflection element 20, guided into exposure light flux and made incident on a projection lens 4. The light 10 which is made incident on the projection lens 4 is image-formed on a wafer alignment diffraction grating 6, and a progressing type interference fringe is formed again. A beat signal is picked up from the laser light source 9, the beat signal is led to outside an exposure light 8 by an element 20 through the lens 4, and it is inputted to a phase indicator together with the intensity signal of the diffracted beam 21 detected by a light detector 25. As a result, the amount of positional deviation of a wafer 2 can be recognized accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an alignment device used in, for example, an exposure apparatus that transfers a pattern on a reticle onto a wafer via a projection optical system.

BACKGROUND OF THE INVENTION In recent years, semiconductor devices have become extremely dense, and the dimensions of fine patterns of each element are on the verge of reaching 0.5 μm or less. In the exposure of such fine patterns, alignment between each exposure is extremely important in order to perform multiple overlapping exposures as required in semiconductor manufacturing, and the overlay accuracy is 0.1 μm. The following is required:

As a conventional positioning device, Japanese Patent Application Laid-Open No. 63-78004
The configuration described in the publication is known. Hereinafter, the conventional positioning device described in -1- will be explained with reference to the drawings.

FIG. 13 is a block diagram showing a conventional exposure apparatus.

In FIG. 13, coherent two-frequency alignment light emitted from a laser light source 101 is split into two beams by a mirror 102, and diffracted by a pair of first diffraction gratings 104a and 104b formed on a reticle 103. . Each diffracted light is the first. The spectral plane of the second lens systems 105a and 105b produces an appropriate light flux, and the spatial filter 1.0
6a, 106b, and further passes through the second lens system 1.07a, 107b and the projection optical system 108, and then onto the second pair of diffraction gratings 110a provided on the wafer 109''2. , 11. Project to Ob. These diffracted lights 111a and l1lb are transmitted to the projection optical system 108 in the opposite direction.
, second lens system 107a, 107b, and is guided to a photodetector] 12a112b. And wafer 10
When two beams of light are projected onto the second diffraction gratings 110a and 110b of 9'' from appropriate directions, the diffracted beams are diffracted in overlapping directions and interfere with each other. The intensity of this pair of interfering diffracted lights is detected by photodetectors 112a and 112b, and the detection results are compared by a comparator 113, and the control system 11
The reticle 103 and the wafer 109 can be aligned by moving the wafer 109 by driving 4 and selecting a location where the difference in intensity between the pair of diffracted light beams is zero.

On the other hand, the pattern on the reticle [03] is illuminated by a projection light source 115 and an illumination optical system 116, and its projected image is formed on the wafer 1091 via the projection lens 108.

Problems to be Solved by the Invention However, in the configuration of the conventional example shown below, the exposure light emitted from the projection light source 115 and the alignment light emitted from the laser beam #10 have approximately the same wavelength, and the projection optical System 1
It is only effective if 08 exhibits similarly good imaging performance for both. For example, for ultraviolet light such as excimer lasers, which are expected to become the mainstream exposure light in the future, the glass materials used to construct the refractive optical system are limited, so an achromatic projection optical system that corrects chromatic aberration is used. It is extremely difficult to configure. For this reason, the projection optical system 108 is designed to be sufficiently color corrected only at the exposure wavelength, and exhibits extremely large chromatic aberration for light of other wavelengths. For this reason, it is desirable that the wavelength of the alignment light is sufficiently close to the exposure wavelength. However, from the semiconductor manufacturing process,
It is desired that the alignment wavelength be sufficiently separated from the exposure wavelength. The reason for this is that with the use of a highly sensitive resist such as a chemically sensitized resist, there is a concern about exposure of the resist I by alignment light, and that the multi-layer For example, the dye-filled lens 1-, which prevents cysts and multiple reflections, absorbs alignment light close to the exposure wavelength. That is, for reasons related to the semiconductor manufacturing process, the wavelength of the alignment light must be sufficiently ahead of the exposure wavelength.

Therefore, with the configuration of the conventional example described above, there is a problem that it becomes difficult to align the reticle and the wafer with high precision.

The present invention solves the problems of the prior art as described above, and allows through-the-lens alignment light to be performed through a projection optical system using a diffraction grating even when a wavelength different from the exposure wavelength is used as the alignment light. In alignment (TTL alignment), an object is to provide an alignment device that can perform highly accurate alignment of a first and second object not only during exposure but also during exposure. That is.

Means for Solving the Problems The technical means of the present invention for solving the above problems is an alignment system provided on the first and second objects located on the object plane and the image plane of the projection optical system, respectively. mark and
A means for causing two-frequency coherent alignment light having a wavelength different from the exposure wavelength to interfere with each other using a two-layered object I, and a specific area where interference fringes are created by the first object. a correction optical system for correcting chromatic aberration of the projection optical system, and an alignment light deflection element that guides the two-layer alignment light so as not to block the exposure light and is placed between the correction optical system and the projection optical system. and a spatial filtering optical system for removing speckle patterns from the reflected light of the alignment mark of the second object, and a light detection means for detecting an optical beat signal from the light transmitted through the spatial filtering optical system. It is equipped with the following.

And, ``Two-layered 1. At least one of the alignment marks on the second object is a diffraction grating, and the first
It is preferable that the alignment mark on the object generates equal-bitch linear interference fringes by interference of two-frequency alignment light.

Further, the means for causing the two-frequency alignment light to interfere with each other on the object described in Description 1 includes a light source that emits a two-frequency coherent alignment light, and a light source that emits a two-frequency coherent alignment light, and two
It consists of a splitting optical system for splitting the frequency alignment light into two light beams, and a combining optical system for illuminating the two divided light beams at the same position on the first object, or one frequency alignment light. A light source that emits a coherent alignment light, a splitting optical system that divides the alignment light emitted from this light source into two beams and then uses the Doppler effect to create a difference in the frequency of the two beams, and a split optical system that uses the Doppler effect to differentiate the frequencies of the two beams. and a synthetic optical system for illuminating the same position on the first object.

Further, the synthetic optical system adjusts the pitch of interference fringes created by the alignment marks on the first object to absorb magnification errors of the correction optical system and the two-layer projection optical system, and , a polarizing optical element can be used in order for the splitting optical system to split the two-frequency coherent alignment light. Further, the alignment light deflection element can be formed using a dichroic mirror film that transmits exposure light and reflects alignment light.

Therefore, according to the present invention, two-frequency alignment lights having different wavelengths from the exposure light are caused to interfere with each other at the alignment mark on the first object to form arbitrary pinch interference fringes, An optical system that corrects this interference fringe, an alignment optical deflection element,
The image is projected onto a second object via a projection optical system. This second
After the speckle pattern is removed from the reflected light from the alignment mark on the object using a spatial filtering optical system,
The light is received by a photodetector. The relative positions of the first and second objects can be controlled and aligned based on a positional deviation signal obtained from a phase comparison of optical beat signals obtained by this photodetector. As mentioned above, the correction optical system can correct the chromatic aberration of the projection optical system in response to specific areas where interference fringes are created due to the interference of the alignment light, and the alignment light deflection element does not block the exposure light. The alignment light can be guided in this way.

EXAMPLES Hereinafter, examples of the present invention will be described with reference to the drawings.

First, a first embodiment of the present invention will be described. 1 to 8 show a positioning device according to a first embodiment of the present invention, in which FIG. 1 is an overall configuration diagram, FIG. 2 is an enlarged view of the section viewed from the is an enlarged view of the part shown by the arrow ■ in Figure 1, Figure 4 is a plan view of the reticle showing a specific area within the field of view of the projection lens that performs color correction, and Figure 5 is an enlarged view of the laser beam emitted from the laser light source. Polarization direction diagram, Figure 6 is a plan view for explaining the function of the spatial filter in the spatial filtering optical system,
FIGS. 7(a) and (b) are respectively a perspective view and a cross-sectional view of the alignment light deflection element, and FIGS. 8(a) to (dl) are for explaining the operation of the above embodiment; , (C) is an explanatory diagram of changes in the degree of overlap between interference fringes and alignment diffraction gratings on the wafer (second object), and (d) of the same figure is an explanatory diagram of the scan area.

In this embodiment, alignment of one axis in the X direction out of a three-axis alignment system of x, y, and θ will be described, but alignment can be performed in the same manner for other axes.

In the first M, 1 is the first object, which is the reticle of the exposure master, 2 is the wafer, which is the second object to which the pattern of the reticle 1 is exposed, 3 is the wafer stage that moves the wafer 2, and 4 is the projection lens ( The reticle 1 is placed on the object plane of the projection lens 4, and the image plane is placed on the object plane of the projection lens 4.
Wafer 2 is placed at L. Reference numeral 5 indicates an alignment mark provided on the wafer 2 (hereinafter referred to as an alignment blank), and 6 indicates an alignment mark provided on the wafer 2 (hereinafter referred to as an alignment diffraction grating). ),
7 is an illumination optical system, and 8 is exposure light transmitted through the illumination optical system 7. 9 is a light source for positioning, and the orthogonally polarized light 2
Alignment light 10 of two different frequencies (ff2) is emitted. 11 is a splitting optical system, which includes a polarizing beam splitter 12 that splits the alignment light 10 emitted from the laser light source 9;
Wave plate 1 that circularly polarizes f2 component alignment light 10
It consists of 3. 14 is a synthetic optical system, and a dividing optical system 1
Alignment of f, f2 components divided by 1]・light]0
It consists of a mirror 15 that reflects the light, and a fine adjustment mechanism 16 that adjusts the angle of the mirror 15. Reference numeral 17 indicates a reflection mirror that causes the alignment light 10 of f+ and f2 components reflected by the mirror 15 to interfere with each other and irradiates it onto the alignment blank 5 of the reticle 1. Reference numeral 18 indicates an alignment blank 5 that causes the alignment light 10 to interfere with the alignment light 10 for identification. Progressive interference fringes occurring in the area 1
A correction optical system 20 for correcting the chromatic aberration of the projection lens 4 corresponding to 9 (see FIG. 2) is disposed between the correction optical system 18 and the projection lens 4 so as not to block the exposure light 8. Alignment light deflection element for guiding alignment light 10, 2
1 is a diffracted light diffracted by the alignment diffraction grating 6 of the wafer 2''; 22 is a spatial filtering optical system having a spatial filter 23; , reflected mirror 17, mirror 2
Only the central portion of the diffracted light 21 reflected by the light source 4 is transmitted.

25 is a photodetector to which the diffracted light 21 transmitted through the spatial filtering optical system 22 is guided; 26 is a laser interferometer; and 27 is an L-shaped mirror provided on the wafer stage 3.

The above configuration will be explained in more detail along with its operation.

As shown in FIG. 5, the laser beams #9 for alignment are mutually orthogonally polarized and have frequencies of f4. This is an optical unit 7 that emits coherent alignment light 10 of r2, and in this embodiment, a Zeeman laser that obtains two frequencies by applying a magnetic field to a laser tube is used. In addition, such optical unidirectional devices include optical modulators that use ultrasonic waves that propagate in one direction, and devices that obtain two frequencies by using a rotating diffraction grating and shifting the frequency. can be used. Further, the frequency difference between f and f2 is generally several tens of kHz to several tens of MHz.

The alignment light 10 emitted from the laser light source 9 is split into an f1 component and an f2 component by a polarizing beam splitter 12 in a splitting optical system 11, and then converted from linearly polarized light to circularly polarized light by a wavelength plate 13. As the optical system 1, it is possible to use one using a dielectric multilayer film such as the polarizing beam splitter 12, or one using birefringence such as a Wollanston prism. Furthermore, if the alignment light 10 remains linearly polarized, it is susceptible to intensity fluctuations due to multiple reflections, and the alignment signal intensity margin during alignment of the wafer 2 is small, so it becomes circularly polarized.

The alignment light IO of the f, component and f2 component divided by the splitting optical system 11 is reflected from the mirror 15L in the combining optical system 14, and is interfered with by the reflection mirror 17 to produce the reticle. irradiated on top. The mirror 15 in the combining optical system 14 can be replaced with a prism or the like that utilizes total reflection. The alignment lights 10 of the fl and ft components that intersect on the alignment blank 5 interfere with each other, producing interference fringes. The angle of the mirror 15 is adjusted by the fine adjustment mechanism 16 so that the pinch of the interference fringes is about 4 μm, but for the reasons described later, the pinch of the interference fringes can be finely adjusted within a range of several percent. ing. Alignment light 1 of fl and f2 components
0 interfere with each other, but their frequencies are slightly different, so the interference fringes are unidirectional as shown in Figure 2.
・It will progress while vibrating at the frequency. Such interference fringes as traveling waves will be referred to as traveling interference fringes 19.

Exposure light 8 emitted from the KrF excimer laser is illuminated onto the reticle 1 via the illumination optical system 7.
is projected onto the Eva 2 by the projection lens 4. Since such a projection lens 4 is designed according to the exposure wavelength of the exposure light 8, the fl
, ft components of the alignment light 10, it is impossible to image the progressive interference fringes 19 on the wafer 2 using only the projection lens 4 because the chromatic aberration is too large.

However, the area on the reticle 1 where the progressive interference fringes 19 are formed is narrow, and it is possible to sufficiently correct the chromatic aberration of the projection lens 4 only in this specific area. Here, the correction optical system 18 corrects the chromatic aberration of the projection lens 4 in a specific area 29 (the same annular area in the figure) of the effective angle of view 28 of the projection lens 4, for example, as shown in FIG. Progressive interference fringes 19 created in a specific area 29 on the reticle 1 by the alignment light 10 of f, , f2 components emitted from the laser light source 9 are accurately projected and imaged onto the wafer 2. In addition, in FIG. 4, 3o indicates a pattern area.

” 1. To explain the correction optical system 18 in more detail,
The functions of the correction optical system 18 can be broadly divided into the following two types.

(1) Correcting aberrations of the projection lens 4 due to differences in wavelength.

Exposure light 8 (λ-2
The refractive index of synthetic quartz, etc. used for the projection lens 4 suitable for 48.5 nm) is thick (different) for ultraviolet light such as excimer laser light and visible light such as alignment light 10. Therefore, the alignment light 1 of the projection lens 4 is optimally designed to match the excimer laser light.
The chromatic aberration with respect to 0 is extremely large, and it is extremely difficult to design a correction optical system 18 that can color correct the entire angle of view 28 of the projection lens 4. Therefore, as in this embodiment, a correction optical system 18 is used that performs color correction on a very limited specific area 29 where the alignment blank 5 exists within the angle of view of the projection lens 4. Accordingly, the correction optical system 1
8 is considerably easier to design.

In this way, it becomes possible to project the traveling interference fringes 19 formed at the alignment wavelength onto the wafer 2'' by an optical system having small aberrations and sufficient MTF.

(2) Correcting the projection magnification between the reticle 1 and the wafer 2 with respect to the alignment light 10.

The projection lens 4 has a longer focal length for the alignment light 10 having a wavelength longer than the wavelength of the exposure light 8. For example, t
(The focal length of the projection lens 4 for the e-N e laser is several tens of times the KrF exposure wavelength, and of course the imaging magnification is also several tens of times (the imaging position is also different, of course). Therefore, it is often difficult to design the correction optical system 18 to make the projection magnification at the alignment light 10 equal to the projection magnification at the wavelength of the exposure light 8. Therefore, the projection magnification at the wavelength of the exposure light 8 is 5, it is preferable to suppress the projection magnification with the alignment light lO to about 1. On the other hand, the combined magnification of the correction optical system 8 and the projection lens 4 should be set to exactly 1 while completely correcting chromatic aberration. This means that manufacturing and assembling the lens is quite complicated, so it is necessary to provide another mechanism for correcting this composite magnification error.
It is. In other words, when the composite magnification is 1.01, if the fine adjustment mechanism 16 is adjusted so that the pitch of the progressive interference fringes 19 is 0.99 times, the progressive interference fringes projected onto the wafer 2 can be The pitch of the stripes 31 (see FIG. 3) remains unchanged.

Since the correction optical system 18 is normally arranged so as not to kick the exposure light 8, the alignment diffraction grating that is imaged onto the wafer 2-A by the correction optical system 18 has a conventional diffraction grating shown in FIG. Lattice 1.10a, 1.1. Like Ob, it is outside the exposure area 115 (-Since the alignment diffraction grating on the wafer is created by exposure, it exists within the exposure area 115). For this reason, the alignment position and the exposure position are different, and the alignment sequence (○If-Axis alignment (・) in which the wafer stage 3 is moved after alignment and moved to the exposure position is inevitable. In Siegen, the movement accuracy of the wafer stage 3 is included in the final overlay accuracy, so the device configuration-1
-1 disadvantage. For this reason, as mentioned above, the alignment I
~Alignment light deflection element 2 that guides the light 10 into the exposure light beam
0 between the correction optical system 18 and the projection lens 4, the alignment light 10 that has passed through the correction optical system]8
is incident on the alignment light deflection element 20, as shown in FIG. 7(a).
, (b), the light is reflected by the total reflection surface 32 and the gicroic mirror film 33 which are parallel to each other, and is guided into the exposure light beam and enters the projection lens 4. The guichroic mirror film 33 is designed to reflect the alignment light 10 and transmit the exposure light 8, so as not to deteriorate the imaging of the exposure light 8. The alignment light 10 incident on the projection lens 4 forms an image on a wafer positioning diffraction grating 61 within the exposure area, forming progressive interference fringes 31 again.

Since the combining optical system 14 is adjusted in advance so that the progressive interference fringes 31 are in the same pinch as the alignment-U diffraction grating 6 on the wafer 2, the progressive interference fringes 31 and the alignment diffraction grating 6 The intensity of the vertically diffracted light 21 generated by the beat frequency (f, and f.

frequency difference). Progressive lower striations 31
The intensity of the diffracted light 21 reaches its peak when it overlaps with the positioning diffraction grating 6, and the intensity of the diffracted light 21 reaches its lowest when the position is shifted by 180 degrees. In other words, the intensity of this diffracted light 21 includes positional shift information of the positioning diffraction grating 6 in the phase of the alternating current component. Therefore, a reference beat signal is extracted from the dual-frequency laser light source 9, and further, contrary to the above, it is guided to the exposure light 8 by the alignment light deflection element 20 via the projection lens 4,
Next, a correction optical system] 8, a reticle 1, a reflection mirror 17,
By inputting the intensity of the diffracted light 21 detected by the photodetector 25 via the mirror 24 and the spatial filtering optical system 22 (along with No. 8 to the phase meter), the amount of positional deviation of the wafer 2 can be accurately determined.

Here, the role of the spatial filtering optical system 22 will be explained. For example, if the surface of the wafer 2 is roughened by an aluminum pattern or the like, speckles from the aluminum pattern will be mixed into the diffracted light 21. The light pattern on the Fourier plane of the spatial filtering optical system 22 at this time is shown in FIG. From the figure, it can be seen that the speckled pattern 34 can be removed by using a spatial fill 23 that transmits only the central part.

In this embodiment, positional accuracy is extremely important when attaching the correction optical system 18 to the projection lens 4.

If the correction optical system 18 is misaligned for some reason, the alignment mark 5 on the reticle 1 and the wafer 2
-The conjugate relationship between L and the alignment mark 6 is shifted. Therefore, the correction optical system 18 must be firmly fixed to the projection lens 4 with long-term stability. To this end, it is effective to make the correction optical system 18 integral with the projection lens 4.

In addition, in this embodiment, alignment in one axis in the X direction has been described, but in an alignment system in three axes of
Since it is necessary not to impair the uniformity of the alignment light deflection element 20, the seventh IF (a
) and (b), a structure in which the side surfaces of a quadrangular pyramid are covered with a dichroic mirror film 33 can be used.

Furthermore, the above positional deviation detection method has a detection range that is only half the pitch of the alignment diffraction grating 6 on the wafer 2 due to the periodicity of the alignment marks used. Figures 1 and 8 show that the detection range can actually be made infinite by using the projected image of the alignment blank 5 and the beat signal intensity.
This will be explained with reference to the figures. The wafer 2 is placed on a wafer stage 3-hi that can be scanned at a constant speed, and the wafer stage 3 scans a scan area 35 (see FIG. 8(d)) that includes a position where the amount of positional deviation is assumed to be zero. shall be scanned. As shown in FIGS. 8(a), (b), and (C), the overlapping degree of the progressive interference fringes 31 and the alignment diffraction grating 6 changes (FIGS. 8(a), (b),
(C) corresponds to points A, B, and C in FIG. 8(d), respectively. ). At this time, the beat signal from the photodetector 25 is input to the amplitude detection circuit, and the wafer stage 3 at the time of scanning is
If the horizontal axis is the coordinates obtained by the laser interferometer 26 and the vertical axis is the amplitude of the beat signal, a pattern 141 that is close to a triangle as shown in FIG. 8(d) is generally obtained. By calculating the center position of this triangular pattern, it is possible to know the position of the wafer 2 with zero positional deviation. Although the detection accuracy at this time is not sufficient for the final alignment accuracy of wafer 2 and reticle 1, it has sufficient accuracy for rough alignment, and can be combined with the positional deviation detection method using phase detection described above. This makes it possible to construct an alignment system with an extremely wide detection range.

One feature of this positional deviation detection method is that the progressive interference fringes 19 are formed once in the form of a tickle II-, and then projected onto the wafer 2. Therefore, it is possible to perform not only the alignment of the wafer 2 but also the alignment of the reticle 1 at the same time. The device in this case is used as the second embodiment and the ninth embodiment
It is shown in Fig. 12.

9 to 12 show a positioning device according to a second embodiment of the present invention, FIG. 9 is an overall configuration diagram, and FIG.
The figure is an enlarged view of the X-arrow section in FIG. 9, and FIGS. 11 and 12 are layout diagrams of alignment marks on the reticle.

In this embodiment, diffracted light 37 from a positioning diffraction grating 36 provided on the reticle 1 (see FIG. 10) is used.
is detected by another photodetector 39 via another spatial filtering optics 38 . A field stop 40 provided in front of the photodetector 25 is used to guide only the light from the alignment blank 5 to the photodetector 25. Since the pitch of the progressive interference fringes 19 on the reticle 1 is finely adjusted by the combining optical system 14 for the above-mentioned reason, a pinch error may occur with respect to the positioning diffraction grating 36 of the reticle 1.

For this reason, it is desirable that the number of diffraction gratings in the positioning diffraction grating 36 of the reticle 1 be as small as possible. The reticle 1 generally has a Cr pattern drawn on quartz glass, and has high diffraction efficiency. Therefore, even if the area of the positioning diffraction grating 36 of the reticle l is somewhat small, it does not interfere with the photodetector 39 picking up the beat signal. FIG. 11 shows the positioning diffraction grating 36 of the reticle 1. When both the beat signals of the photodetector 25 and the photodetector 39 are detected, it becomes possible to align the reticle 1 and the wafer 2 relative to each other, and higher alignment accuracy can be expected than when aligning the reticle] and the wafer 2 alone (
Through-the-reticle alignment, or TTR alignment (1~). Furthermore, the arrangement of the reticle alignment diffraction grating 36 as shown in FIG. 12 can also be used. The feature of this positioning diffraction grating 36 is that even if the progressive interference fringes 19 rotate (the positioning diffraction grating 36
The object is to prevent errors from occurring in the detection of the amount of relative positional deviation between the wafer 1 and the reticle 2 even if a deviation occurs between the grating direction of the wafer 1 and the line direction of the progressive interference fringes 19. because,
Regardless of whether or not the progressive interference fringes 19 are rotated, the amount of detected positional deviation between the wafer 2 and reticle 1 is the same as that of the positioning diffraction grating 6 (assuming uniformity of the pattern of the positioning diffraction grating 6.36). This is represented by a center of gravity position of .36, and in the pattern shown in Fig. 12, wafer 2
This is because the positions of the centers of gravity of the alignment diffraction gratings 6 and 36 of the reticle 1 apparently coincide.

In this way, according to the present invention, the upper alignment blank 5 for a rejiku knife placed at a specific position is illuminated using the alignment light 10 of two coherent frequencies different from the exposure wavelength, and the progressive interference fringes 19 are formed. The correction optical system 18, the alignment light deflection element 2°, and the projection lens 4,
The diffraction light 21 is projected onto the positioning diffraction grating 6 on the wafer 2, passes through the spatial filtering optical system 22 and is guided to the photodetector 25, detects the beat signal, and examines its phase information. Based on the detected amount of positional deviation, the wafer stage 3 can be operated to eliminate the positional deviation and perform accurate alignment. Since the alignment completion position is the immediate exposure position, High overlay accuracy can be obtained.

Effects of the Invention As described above, according to the present invention, two-frequency alignment light having a different wavelength from that of the exposure light is caused to interfere with each other at the alignment mark of the first object. A pinch of interference fringes are formed, and these interference fringes are projected onto the second object via a correction optical system, an alignment light deflection element, and a projection optical system.

The speckle pattern of the reflected light from the positioning mark of the second object J- is removed by a spatial filtering optical system, and then the light is received by a photodetector. The relative positions of the first and second objects can be controlled and aligned based on a positional deviation signal obtained from a phase comparison of optical beat signals obtained by this photodetector. As mentioned above, the correction optical system can correct the chromatic aberration of the projection optical system in response to specific areas where interference fringes are created due to the interference of the alignment light, and the alignment light deflection element does not block the exposure light. Since the alignment light can be guided in such a manner that the first and second objects can be guided with high precision even during exposure as well as other times, even when using alignment light with a wavelength different from the exposure wavelength, 0n that can be aligned
- An Axis TTL alignment system can be constructed.

[Brief explanation of drawings]

1 to 8 show a positioning device according to a first embodiment of the present invention, in which FIG. 1 is an overall configuration diagram, FIG. 2 is an enlarged view of the first section viewed from the The figure is an enlarged view of the part shown by the ■ arrow in Figure 1, Figure 4 is a plan view of the reticle showing a specific area within the angle of view within the projection lens that performs color correction, and Figure 5 is the laser beam emitted from the laser light source. 6 is a plan view for explaining the function of the spatial filter in the spatial filtering optical system; FIGS. 7(a) and 7(b) are a perspective view and a cross-sectional view of the alignment light deflection element; FIG. Figures 8 (a) to (d) are for explaining the operation of the above embodiment;
(C) explains the change in the degree of overlap between the interference fringes on the wafer (second object) and the alignment diffraction grating.
) is an explanatory diagram of the scanning area, FIGS. 9 to 12 show the positioning device in the second embodiment of the present invention, FIG. 9 is an overall configuration diagram, and FIG. 10 is an illustration of the X arrow in FIG. The 11th and 12th views are enlarged views of the viewing section, the placement openings for positioning marks on the reticle, Figure 13 is an overall configuration diagram showing the conventional positioning device, and Figure 14 is the primers 1 to 1 of the present invention. FIG. 7 is an explanatory diagram showing the position of the alignment diffraction grating that is imaged on the wafer when no optical deflection element is used. 1... Reticle, 2... Wafer, 3...
... Wafer stage, 4 ... Projection lens, 5 ... Blank for positioning (positioning mark), 6 ... Diffraction grating for positioning (position alignment mark), 7... illumination optical system, 8...
...Exposure light, 9...Light source, 10. Alignment light, 11.....Divided optical system, 14.....
・Composition optical system, 18...Correction optical system, 19...
...Progressing interference fringes, 20...Alignment light deflection element, 21...Diffracted light, 22...
Spatial filtering optical system, 25... Photodetector, 2
6...Laser interference εI, 31...Progressing interference fringes, 36...Positioning diffraction grating, 37...
... Diffracted light, 38 ... Spatial filtering optical system, 39 ... Photodetector. Name of agent: Patent attorney Shigetaka Awano (1 person)

Claims (8)

[Claims] (1) Alignment marks provided on the first and second objects located on the object plane and the image plane of the projection optical system, respectively, and two-frequency coherent alignment light having a wavelength different from the exposure wavelength. means for causing interference with each other on the first object; a correction optical system that corrects chromatic aberration of the projection optical system corresponding to a specific area where interference fringes are formed on the first object; an alignment light deflection element disposed between the projection optical system and guiding the alignment light so as not to block the exposure light; and a spatial filtering element for removing speckle patterns from the reflected light of the alignment mark of the second object. A positioning device comprising an optical system and a light detection means for detecting an optical beat signal from light transmitted through the spatial filtering optical system. (2) The alignment device according to claim 1, wherein at least one of the alignment marks on the first and second objects is a diffraction grating. (3) The positioning apparatus according to claim 1 or 2, wherein the positioning mark on the first object generates linear interference fringes of equal pitch by interference of two-frequency alignment light. (4) A light source that emits two-frequency coherent alignment light, and a means for causing two-frequency alignment light to interfere with each other on the first object, and splits the two-frequency alignment light emitted from this light source into two light beams. 4. The positioning apparatus according to claim 1, further comprising a dividing optical system for illuminating the two divided light beams to the same position on the first object. (5) The means for interfering two-frequency alignment light with each other on the first object includes a light source that emits a single-frequency coherent alignment light, and after splitting the alignment light emitted from this light source into two beams, Doppler 4. Any one of claims 1 to 3, further comprising a splitting optical system that uses an effect to give a difference in frequency between the two light beams, and a combining optical system that illuminates the two split light beams at the same position on the first object. The alignment device described in . (6) Alignment according to claim 4 or 5, wherein the synthetic optical system adjusts the pitch of interference fringes created by the alignment marks on the first object and absorbs magnification errors of the correction optical system and the projection optical system. Device. (7) The positioning apparatus according to any one of claims 1 to 6, wherein the splitting optical system uses a polarizing optical element to split the two-frequency coherent alignment light. (8) The alignment device according to any one of claims 1 to 7, wherein the alignment light deflection element is formed using a dichroic mirror film that transmits exposure light and reflects alignment light.