JP2554626B2 - Positioning method and positioner using diffraction grating - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an alignment method used in an exposure apparatus or a pattern evaluation apparatus for manufacturing semiconductor ICs or LSIs, and an alignment apparatus used for implementing the same. It is about.

[Conventional technology]

Along with the miniaturization of semiconductor ICs and LSIs, in a device that transfers a mask pattern to a wafer all at once, or in a device that performs exposure transfer by a step-and-repeat method, the progress of technology for aligning a mask and a wafer with high precision is It has become indispensable.

As a method of performing alignment using a diffraction grating, for example, there is a double diffraction grating method introduced in J. Vac. Sci. Technol., Vol. 19, No. 4, 1981, P. 214.

FIGS. 5 (a) to 5 (c) show an example of an apparatus for alignment using this double diffraction grating. FIG. 5 (a) is an elevational sectional view of the whole, and FIG. 5 (b) is (a). FIG. 3C is a partial vertical cross-sectional view as seen from a direction orthogonal to, and FIG. In FIG. 5, laser light source 1
The laser light emitted from the
The mask mark 5 formed on the mask 4 held by the vacuum suction holder 3 is made incident on the mask mark 5 from its normal direction, and after passing through it, the fine adjustment stage 7 on the coarse adjustment stage 6
Wafer mark 9 made on the wafer 8 held on
Is reflected by and passes through the mask mark 5 again.

The mask mark 5 and the wafer mark 9 are diffraction grating patterns. As shown in (c), the former is a transmissive transparent thin film 10 such as a nitride film on which an opaque thin film 11 such as Au or Ta is formed. The formed one, the latter one, is a reflection type one in which the diffraction grating pattern is formed by etching the surface of the wafer 8 stepwise.

Of the light diffracted by the mask mark 5 and the wafer mark 9, only the + 1st-order diffracted light and the -1st-order diffracted light diffracted in a direction symmetrical to the incident light are photoelectrically converted.
Positions are adjusted by photoelectric conversion of the respective diffraction intensities I ₊₁ and I ₋₁ , and detection of the change of the subtraction intensity ΔI = I ₊₁ −I ₋₁ .

[Problems to be solved by the invention]

However, as shown in FIG.
In the method of perpendicularly entering the diffraction grating, that is, the mask mark 5, a means for entering the light from the normal direction of the mask mark 5, that is, an optical component such as the mirror 2 is applied to the surface on which the mask mark 5 is formed, that is, the grating surface. On the other hand, it was necessary to set it vertically upward. Therefore, the mask 4 and the wafer 8 are aligned by the alignment device as shown in FIG.
In a device for exposing and transferring a mask pattern of LSI or the like onto a wafer surface after aligning and, when mask mark 5 and wafer mark 9 are arranged in a chip made of a pattern of LSI or the like, a mirror is used for pattern transfer. 2 is included in the exposure area and interferes with the exposure, and there is a drawback that part of the pattern in the chip is not transferred.

This will be described in more detail with reference to FIGS. 6 (a) to 6 (c). FIG. 6A shows a mask portion of an apparatus for aligning a mask with a double diffraction grating to expose a mask pattern, FIG. 6B shows the mask mark portion of the diffraction grating, and FIG. ) Shows the mask mark part seen from the direction orthogonal to the direction. In FIG. 6, 14 is a mask, 14 'is a wafer, 15 is a mirror, 16 and 17 are photoelectric converters, 18 is a mask mark made of a diffraction grating, 18' is a wafer mark made of a diffraction grating, and a shaded area 19 is shown. Is an LSI pattern area, and 20 is an exposure area through which the exposure light passes, and shows an example in the case of matching with the LSI pattern area 19. 21 is incident light, 22 is + 1st order diffracted light, 23 is −1st order diffracted light, 24 is a transparent thin film, and 25 is an opaque thin film. BB ′ is the grating line direction of the diffraction grating,
A-A 'is a direction perpendicular to the grid line direction and is called a grid pitch direction. C-C 'is the direction normal to the grating surface forming the diffraction grating. The ± 1st-order diffracted lights 22 and 23 are mask marks 18
At a predetermined angle determined by the pitch P of the diffraction grating and the wavelength λ of the incident light 21 in the grating pitch direction (AA 'direction) of the diffraction grating with respect to the normal direction (CC' direction) of the grating surface of ψ =
Since it is diffracted by sin ⁻¹ (± 2 / P), it is possible to detect the diffracted lights 22 and 23 by disposing the photoelectric converters 16 and 17 outside the exposure area 20. However, in order to make the incident light 21 incident from the direction normal to the lattice plane of the mask mark 18, the mirror 15 is set to the exposure area 20.
Since it needs to be arranged inside, the shadow of the mirror 15 is formed on the surface of the LSI pattern area 19 during exposure, which hinders transfer of the LSI pattern.

As a method of solving this problem, a method of retracting the mirror 15 to the outside of the exposure area at the time of exposure or a mask mark is used.
There is a method of arranging the 18 and the wafer mark 18 'outside the LSI pattern area 19, but in the former case, a mechanism system and a control system for accurately retracting optical parts such as the mirror 15 are required, and the apparatus becomes complicated. To do. Alternatively, there is a drawback that it is difficult to perform highly accurate alignment because the servo during exposure is impossible. In the latter method, for example, in step-and-repeat exposure, when the mask mark 18 and the wafer mark 18 ′ are arranged outside the LSI pattern area 19, it is necessary to secure a large scribe line. Reduces yield. On the other hand, a method of using the scribe line of the chip separated by one step may be considered, but in any case, in order to eliminate the influence of the shadow of the mirror 15 from the LSI pattern area 19, the mark should be placed far away. Since they have to be arranged, there is a drawback that the alignment accuracy is deteriorated.

[Means for solving problems]

In order to solve the above-mentioned problems, the scope of claims 1
Positioning method described in the above paragraph, or Claim 3
The alignment device according to the item 1 is a method or device for relatively aligning a first object provided with a first diffraction grating and a second object provided with a second diffraction grating. , Two monochromatic lights having slightly different frequencies are subjected to hederodyne interference to generate a reference beat signal, and the two monochromatic lights are formed on a surface forming the first diffraction grating or the second diffraction grating. And a surface including the normal direction of the first surface and the line direction of the first diffraction grating or the second diffraction grating as the second surface, and the first surface and the second surface. A plane perpendicular to the plane is defined as a third plane, which is symmetric with respect to the second plane and is not included in the third plane in two directions, or the first plane within the second plane. By making the light incident from a diagonal direction that is deviated by a predetermined angle with respect to the normal line, , Or two diffracted lights emitted in the two symmetrical directions are heterodyne-interfered to generate a diffracted light beat signal, and based on a phase change between the reference beat signal and the diffracted light beat signal, the first and It is characterized in that the second object is moved by relative movement to be aligned.

Further, the alignment method according to claim 2 or the alignment device according to claim 4 includes a first object provided with a first diffraction grating and a second diffraction element. A method or device for relatively aligning with a second object provided with a grating, wherein two monochromatic lights having slightly different frequencies are supplied to the first diffraction grating or the second diffraction grating.
The surface forming the diffraction grating is a first surface, and the surface including the normal direction of the first surface and the first diffraction grating or the line direction of the second diffraction grating is a second surface, A plane perpendicular to the first surface and the second surface is defined as a third surface, which is symmetric with respect to the second surface and is not included in the third surface, or the second direction. Is incident on the first and second diffraction gratings from an oblique direction that is deviated by a predetermined angle with respect to the normal line of the first surface within the plane, and then from the first diffraction grating to the oblique direction or the symmetry. 2 emitted in two directions
The two diffracted lights are heterodyne interfered with each other to generate a first beat signal, and the two diffracted lights emitted from the second diffraction grating in the oblique direction or the two symmetrical directions are heterodyne interfered with each other to generate a second beat signal. Is generated, and the first and second objects are relatively moved and aligned based on the phase change between the first beat signal and the second beat signal.

[Work]

According to the above configuration, an oblique incidence unit for monochromatic light (for example,
An exposure area through which exposure light that exposes a chip area such as an LSI pattern including a diffraction grating passes through an optical component such as a mirror) or a diffracted light detection unit (for example, a photoelectric converter such as a photodiode) that detects diffracted light. Placed outside. For this reason, the optical component or the photoelectric converter does not interfere with the exposure at the time of exposure, and a complicated mechanical system for retracting the optical component, the photoelectric converter, etc. is not required. Also,
Since the alignment of the first object and the second object is performed based on the phase change between the reference beat signal and the diffracted light beat signal or the phase change between the first beat signal and the second beat signal. Highly accurate alignment is possible.

〔Example〕

Hereinafter, an embodiment of the present invention will be described with reference to FIGS. 1 to 4.

FIG. 1 shows a mask portion in an alignment apparatus of a first embodiment of the present invention, (a) is a perspective view thereof,
(B) is a view of the mask mark portion formed of a diffraction grating as viewed from the grating line direction, and (c) is a view of the same as viewed from the grating pitch direction. In FIG. 1, reference numeral 26 is a mask, 26 'is a wafer, 27 is a mirror, 28 and 29 are photoelectric converters, 30 is a mask mark made of a diffraction grating, 30' is a wafer mark made of a diffraction grating, and 31 shown by hatching is an LSI. Pattern area, 32 is exposure area, 3
3 is incident light, 34 is + 1st order diffracted light, 35 is −1st order diffracted light, 36
Is a transparent thin film and 37 is an opaque thin film. A-A 'is the pitch direction of the diffraction grating, BB' is the grating line direction of the diffraction grating, and CC 'is the normal direction of the grating surface of the diffraction grating. θ is an angle formed by the incident light 33 with respect to the normal direction CC ′.

In this device, the incident light 33 is obliquely incident on the diffraction grating 30 by the mirror 27. Here, the incident direction is B'O
In the plane C ', the direction is perpendicular to the line segment A-A' and has a predetermined angle .theta. With the line segment C-C '. That is, the mask 26
It is a direction perpendicular to the grating pitch direction of the mask mark 30 formed of the upper diffraction grating and forming a predetermined angle θ on the grating line direction B ′ side with respect to the normal line direction of the grating surface. Therefore, although the ± first-order diffracted lights 34 and 35 are diffracted at symmetrical angles on the opposite side of the direction of the incident light 33 with respect to the normal direction CC ′, as shown in FIG. As shown in FIG. 1 (b), when viewed from the grating line direction B'of the diffraction grating, the light is diffracted in the symmetrical first-order diffraction angle direction with the normal direction CC 'as the center. That is, with respect to the displacement of the diffraction grating in the grating pitch direction,
By obtaining the sum signal or the difference signal of the light intensity signals of the first-order diffracted lights 34, 35, the wafer 26 'and the mask 26
Can be aligned with.

On the other hand, the mirror 27 that determines the incident direction and the photoelectric converters 28 and 29 have a diffraction grating mark 3 whose incident direction and diffraction direction are different.
Since it has a predetermined angle θ or a first-order diffraction angle with the direction CC ′ perpendicular to 0, it can be arranged outside the exposure area 32 through which the exposure light passes, and the diffraction grating mark Even if 30 is formed in the pattern area 31 such as LSI, the mirror 2
7. The photoelectric converters 28 and 29 do not interfere with the exposure. Therefore, the diffraction grating mark 30 can be arranged close to the LSI pattern region 31, and the alignment can be performed with higher precision than the method of forming the mark 30 outside the pattern region 31 and performing the alignment. In addition, the mechanism control system is not required so that the mirror 27, the photoelectric converters 28, 29, etc. can be retracted so as not to interfere with the exposure at the time of exposure, the detection optical system and the mechanism control system can be simplified, and the LSI pattern area 31 It is possible to easily configure the detection optical system and mechanism control system even when multiple diffraction grating marks are formed on the surface to perform high-level alignment such as mask rotation correction in addition to x and y displacement. Is.

FIG. 2 shows a second embodiment of the present invention, in which the directions of incident light and diffracted light are different from those of the first embodiment. In FIG. 2, 38 and 39 are incident lights whose wavelengths are slightly different from each other, 40 and 41 are mirrors, and 42 is light folding light from the diffraction grating mark 30, which is a combined light of the diffracted lights of the incident lights 38 and 39. is there. By detecting the combined diffracted light 42 by the photoelectric converter 43, a beat signal due to heterodyne interference can be obtained, and alignment can be performed by utilizing the transfer change of the beat signal corresponding to the displacement of the diffraction grating mark 30 or 30 '. it can.

FIG. 3 shows a third embodiment of the present invention. As an example of a positioning device using a pair of diffraction gratings, a semiconductor IC
An outline of the configuration of an X-ray exposure apparatus for manufacturing an LSI or LSI will be shown. In FIG. 3, reference numeral 44 denotes a light beam having two wavelengths whose frequencies are slightly different from each other and whose polarization plane directions are orthogonal to each other.
Wavelength orthogonal polarization laser light source, 45 is beam splitter,
46, 46 'are condenser lenses, 47, 47', 47 ", 47 are mirrors, 48
Is a polarization beam splitter, 49 and 49 'are photodetectors, 50 is a signal processing control unit, 51 is a mask stage, 52 is a mask, and 53 is a mask.
Is a transmission type diffraction grating, 54 is a reflection type diffraction grating, 55 is a wafer,
56 is a wafer stage, and 78 and 78 'are polarizing plates. The mask stage 51 and the wafer stage 56 are the mask 52
And a moving table that relatively moves the wafer 55.

In the device shown in FIG. 3, a part of the light emitted from the two-wavelength orthogonal polarization laser light source 44 is converted into a beam splitter.
The light is taken out via 45, is detected through heterodyne interference by the photodetector 49 through the condenser lens 46 and the polarizing plate 78, and is input to the signal processing control unit 50 as a reference beat signal. On the other hand, the light emitted from the two-wavelength orthogonal polarization laser light source 44 enters the polarization beam splitter 48 via the beam splitter 45. The polarization beam splitter 48 splits the light into two linearly polarized lights, each having only a horizontal component or a vertical component, and having slightly different frequencies. The mirrors 47, 47 ",
The light enters the transmission diffraction grating 53 and the reflection diffraction grating 54 at a predetermined incident angle via 47. Here mirror 47 ″, 47
The incident angle can be adjusted to a predetermined value by adjusting the direction of. The desired diffracted light obtained from the diffraction gratings 53 and 54 is passed through a mirror 47 ', a condenser lens 46', and a polarizing plate 78 'to form a photodetector.
It is detected by causing the heterodyne interference by 49 ', and is input to the signal processing control unit 50 as a diffracted light beat signal. The signal processing control unit 50 detects the phase difference between the reference beat signal and the diffracted light beat signal, controls the mask stage 51 and the wafer stage 56 so that the phase difference becomes 0 °, and the pattern on the mask surface is Precise alignment between the mask 52 and the wafer 55 is carried out so that exposure can be performed accurately overlapping a predetermined position on the wafer surface.

Here, the direction of the diffracted light from the diffraction gratings 53, 54 detected by the photodetector 49 'via the mirror 47' and the condenser lens 46 'is the pitch direction of the diffraction gratings 53, 54 (A-A' direction). ), And the grating direction of the diffraction gratings 53 and 54 (B-
It has a predetermined angle with respect to the B'direction). Further, the two lights, which are incident on the diffraction gratings 53 and 54 and are separated by the polarization beam splitter 48 and whose frequencies are slightly different from each other, are diffracted by the diffraction gratings 53 and 54, respectively, and are reflected by the mirror 4
The incident angle is set so that the diffracted lights are optically combined on the optical path consisting of 7 ', the condenser lens 46', and the photodetector 49 '. Therefore, the mirrors 47 ′, 47 ″, 47 can be set outside the X-ray spatial area for transferring the pattern on the mask 52 onto the surface of the wafer 55, that is, outside the X-ray exposure area. The X-ray exposure optical system can be completely separated, and the moving mechanism system such as the mirrors 47 ', 47 ", 47 is unnecessary. In addition, since the diffraction grating can be arranged in the exposure area, highly accurate alignment is possible.

FIG. 4 is a diagram showing a diffraction grating portion of an alignment device according to a fourth embodiment of the present invention. In FIG. 4, 57 and 58 are incident lights whose wavelengths are slightly different from each other, 59 is a spot shape of the incident light, 60 is a monochromatic light incident / diffracted light extraction window, 61 is a mask mark made of a diffraction grating, and 62 is diffraction. A wafer mark composed of a lattice, 63 is a mask, 64 is a wafer, and 65 and 66 are synthetic diffracted light.

In FIG. 4, the incident directions of the incident lights 57 and 58 are the same as the directions shown in FIG. 2, and the grating line direction BB ′ is different from the normal direction CC ′ of the surface forming the diffraction grating. It is a direction inclining to the B side by an angle θ and an angle ± first-order diffraction angle symmetrically with respect to the BOC ′ plane. Then, the grating pitches of the diffraction gratings 61 and 62 are made equal, and the window 60 is provided in the mask portion above the diffraction grating 62 in the vertical direction, and the diffraction grating 62 and the diffraction grating 62 are on the B ′ side in the BB ′ direction. By arranging the diffraction grating 61 formed to be shifted in parallel to the same beam of the incident lights 57 and 58, the respective −1st order diffracted lights from the diffraction gratings 61 and 62 with respect to the incident lights 57 and 58 are In contrast to the normal direction CC ′ of the surface forming 61, 62, the lattice line direction (BB ′)
Direction) on the B ′ side in the direction of the angle θ, and become combined diffracted lights 65 and 66, respectively. Therefore, by detecting the combined diffracted lights 65 and 66 by the photoelectric converters (first beat signal generation means and second beat signal generation means),
A beat signal due to the two heterodyne interferences is obtained, and the alignment can be performed by utilizing the phase difference change between the two beat signals corresponding to the relative displacement of the diffraction gratings 61 and 62 in the AA 'direction.

In the third and fourth embodiments, in the configurations shown in FIGS. 3 and 4, light is incident on the diffraction grating from two directions and diffracted light in one direction is detected. As is clear from the relationship between the embodiment (see FIG. 1) and the second embodiment (see FIG. 2), light is made incident on the diffraction grating from one direction and diffracted light in two directions is detected respectively. It goes without saying that it may be configured as.

〔The invention's effect〕

As described in detail above, according to the present invention, the monochromatic light is incident on the diffraction grating in the oblique direction or the diffracted light is detected in the oblique direction. Therefore, it is not necessary to set an optical component or the like for setting the incident direction of the mirror or the photoelectric converter in the vertical direction, or for detecting the diffracted light. Therefore, if it is applied to the upper side of the diffraction grating surface in the vertical direction, for example, when there is a region through which X-rays pass in X-ray exposure (that is, an exposure region), the above optical components or the like interfere with the exposure. It is extremely effective because it does not require any complicated mechanism system for retracting the above-mentioned optical components and the like. Further, the alignment of the first object and the second object is performed based on the phase change between the reference beat signal and the diffracted light beat signal or the phase change between the first beat signal and the second beat signal. Therefore, the alignment can be performed with high accuracy. Incidentally, the present invention is not only a device for alignment, but a device for measuring a minute displacement of a certain object,
It can also be applied to coordinate position detection and control devices and the like.

[Brief description of drawings]

1 to 4 are views showing an embodiment of the present invention.
FIG. 1 is a diagram showing a configuration of a mask portion of the alignment apparatus of the first embodiment, in which (a) is a perspective view, (b),
(C) is an enlarged view of the mask mark portion viewed from the B′-B direction and the AA ′ direction, respectively. FIG. 2 is a diagram showing the configuration of the mask portion of the alignment apparatus of the second embodiment, in which (a) is a perspective view and (b) and (c) are B '.
It is an enlarged view of the mask mark part seen from the -B direction and the AA 'direction. FIG. 3 is a perspective view showing the overall schematic configuration of the alignment apparatus of the third embodiment, and FIG. 4 is a perspective view showing the diffraction grating portion of the alignment apparatus of the fourth embodiment. FIGS. 5 and 6 show a conventional alignment device using a double diffraction grating. FIG. 5 (a) is an overall vertical sectional view, and FIG. 5 (b) is orthogonal to (a). FIG. 5 (c) is an enlarged view showing the alignment diffraction grating mark, FIG. 6 (a) is a perspective view showing the structure of the mask portion, and FIG. , (C) are in the B′-B direction,
FIG. 6 is an enlarged view of a mask mark portion viewed from the AA ′ direction. 26,52,63 ... Mask (first object), 26 ', 55,64 ... Wafer (second object), 30,61 ... Mask mark (first diffraction grating), 30', 62 ...... Wafer mark (second diffraction grating) 53 ...... Transmission type diffraction grating (first diffraction grating), 54 ...... Reflective type diffraction grating (second diffraction grating), 27,40,41,47 ″, 47 ... Mirror (incident angle adjusting means), 28, 29, 43 ... Photoelectric converter, 49 ... Photodetector (reference beat signal generating means), 49 '... Photodetector (diffractive light beat signal generating means) ), 33,38,39,57,58 ... Incident light, 34,35,42,65,66 ... Diffracted light, 44 ... Light source, 50 ... Signal processing control section (signal processing control means), 51 …… Mask stage, 56 …… Wafer stage.

Claims (4)

(57) [Claims] 1. A method for relatively aligning a first object provided with a first diffraction grating and a second object provided with a second diffraction grating, wherein the frequencies are slightly different. A reference beat signal is generated by causing two different monochromatic lights to interfere with each other by hederodyne, and the two monochromatic lights are combined with the first diffraction grating or the second diffraction grating.
The surface forming the diffraction grating is a first surface, and the surface including the normal direction of the first surface and the first diffraction grating or the line direction of the second diffraction grating is a second surface, A plane perpendicular to the first surface and the second surface is defined as a third surface, which is symmetric with respect to the second surface and is not included in the third surface, or the second direction. Of the diffracted light emitted in the oblique direction or in the symmetrical two directions by causing the diffracted light to enter the oblique direction with a predetermined angle deviation with respect to the normal line of the first surface in the plane A diffracted light beat signal is generated in accordance with the phase change between the reference beat signal and the diffracted light beat signal, and the first and second objects are relatively moved and aligned. Positioning method using a grid. 2. A method for relatively aligning a first object provided with a first diffraction grating and a second object provided with a second diffraction grating, wherein the frequencies are slightly different. Two different monochromatic lights are used as the first surface, which is the surface forming the first diffraction grating or the second diffraction grating, and the normal direction of the first surface and the first diffraction grating, or the second diffraction grating. A plane including the line direction of the diffraction grating is a second plane, and a plane perpendicular to the first plane and the second plane is a third plane, which is symmetric with respect to the second plane. And to the first and second diffraction gratings from two directions not included in the third surface, or an oblique direction deviated by a predetermined angle with respect to the normal line of the first surface in the second surface. Two diffracted lights that enter and are emitted from the first diffraction grating in the oblique direction or the two symmetrical directions are heterodiffused. The first beat signal is generated by the in-interference, and the two diffracted lights emitted from the second diffraction grating in the oblique direction or the two symmetrical directions are heterodyne-interfered to generate the second beat signal. A diffraction grating alignment method for generating and aligning the first and second objects relative to each other based on a phase change between the first beat signal and the second beat signal. . 3. A device for relatively aligning a first object provided with a first diffraction grating and a second object provided with a second diffraction grating, the device being arranged in accordance with a control signal. A moving table that relatively moves the first object and the second object, a light source that emits two monochromatic lights having slightly different frequencies, and a reference beat signal by heterodyne interfering the two monochromatic lights. A reference beat signal generating means for generating the two monochromatic lights, and the first diffraction grating or the second monochromatic light.
The surface forming the diffraction grating is a first surface, and the surface including the normal direction of the first surface and the first diffraction grating or the line direction of the second diffraction grating is a second surface, A plane perpendicular to the first surface and the second surface is defined as a third surface, which is symmetric with respect to the second surface and is not included in the third surface, or the second direction. Of incident diffracted light emitted in the oblique direction or in the two symmetrical directions. A diffracted light beat signal generation unit that generates a diffracted light beat signal by causing heterodyne interference, and sends the control signal to the movement table based on a phase change between the reference beat signal and the diffracted light beat signal, Align the first and second objects by moving them relative to each other Alignment apparatus according to a diffraction grating, characterized by comprising and a signal processing control unit. 4. An apparatus for relatively aligning a first object provided with a first diffraction grating and a second object provided with a second diffraction grating, which is responsive to a control signal. A moving table that relatively moves the first object and the second object, and a surface that forms the first diffraction grating or the second diffraction grating with two monochromatic lights having slightly different frequencies. Is a first surface, and a surface including the normal direction of the first surface and the line direction of the first diffraction grating or the second diffraction grating is a second surface, and the first surface and the first surface The surface perpendicular to the second surface is defined as a third surface, and the surface is symmetrical with respect to the second surface and not included in the third surface, or in the second surface. Incident angle adjusting means for making the light incident on the first and second surfaces from an oblique direction which is deviated by a predetermined angle with respect to the normal of the surface. First beat signal generating means for generating a first beat signal by heterodyne interfering two diffracted lights emitted from the first diffraction grating in the oblique direction or in the two symmetrical directions; Second beat signal generating means for generating a second beat signal by heterodyne interfering two diffracted lights emitted from the diffraction grating in the oblique direction or in the two symmetrical directions. Of the beat signal and the second beat signal based on the phase change, the control signal is sent to the moving table, and the first and second objects are relatively moved and aligned. Alignment device using a diffraction grating.