JPH0749926B2 - Alignment method and alignment device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention is applied to an exposure apparatus for manufacturing a semiconductor IC or LSI, a pattern evaluation apparatus, and the like, and is used for a suitable alignment method and its implementation. The present invention relates to a positioning device.

[Conventional technology]

With the miniaturization of semiconductor ICs and LSIs, it is essential to advance the technology for aligning the mask and the wafer with high precision in an apparatus that transfers the mask pattern to the wafer all at once or by the step-and-repeat method. It has become.

2. Description of the Related Art Conventionally, there is an apparatus that uses diffracted light from two diffraction gratings as shown in FIG. 4 as a device for performing minute displacement measurement or precise alignment using optical heterodyne interference (Japanese Patent Application No. 60-198966). . In FIG. 4, 13 is a two-wavelength orthogonal polarization laser light source which emits two wavelengths whose frequencies are slightly different from each other and whose polarization plane directions are orthogonal to each other.
Is a beam splitter, 2,2 'is a condenser lens, 3,3',
3 ″, 3 is a mirror, 4 is a polarization beam splitter, and 5,5 ′
Is a photodetector, 6 is a signal processing controller, 7 is a mask stage, 8 is a mask (first object), 9 is a transmissive diffraction grating (first diffraction grating), and 10 is a reflective diffraction grating (second diffraction grating). Diffraction grating), 11 is a wafer (second object), and 12 is a wafer stage.

In FIG. 4, a part of the light emitted from the two-wavelength orthogonal polarization laser light source 13 is taken out through the beam splitter 1, detected by the photodetector 5 through the condensing lens 2, and a signal processing controller as a reference beat signal. Enter in 6. On the other hand, 2
The light emitted from the wavelength orthogonal polarization laser light source 13 enters the polarization beam splitter 4 via the beam splitter 1 and the mirror 3. The polarization beam splitter 4 splits the light into two linearly polarized lights each having only a horizontal component or a vertical component and having slightly different frequencies,
The light enters the transmission diffraction grating 9 and the reflection diffraction grating 10 at desired incident angles via the mirrors 3'and 3 ", respectively. The diffracted light obtained from the diffraction gratings 9 and 10 is reflected by the mirror 3 and the condenser lens. The light is detected by the photodetector 5'through 2 ', and is input as a diffracted light beat signal to the signal processing control unit 6. The signal processing control unit 6 detects the phase difference between the reference beat signal and the diffracted light beat signal. , The holding / moving mechanism (not shown) is controlled so that the phase difference becomes 0 °, and the mask stage 7 and the wafer stage 12 are moved relative to each other, and the pattern on the mask surface is accurately positioned at a predetermined position on the wafer surface. Precise alignment between the mask 8 and the wafer 11 is performed so that they can be overlapped and exposed.

Next, a positioning method using the positioning device thus configured will be described with reference to FIG. In FIG. 5, 14 is a transmission type diffraction grating, 15 is a reflection type diffraction grating, and 16 and 1.
7 is two wavelengths of incident light whose frequencies are slightly different from each other, 18,
19 is the desired diffracted light, 16-1 and 17-1 are the -1st order transmission circuit light from the transmission type diffraction grating 14, 16-1 'and 17-1' are the 1st order reflection diffraction from the reflection type diffraction grating 15. Lights 16-2 and 17-2 are the −1st order transmitted diffracted light from the reflection type diffraction grating 15. P ₁ and P ₂ are the grating pitches of the transmission type diffraction grating 14 and the reflection type diffraction grating 15, respectively. Generally, when light of wavelength λ is incident on a diffraction grating having a grating pitch P, the diffracted light is θ = sin ⁻¹ (m
・ It becomes strong only in the direction of 2 / P) (m = 0, ± 1, ± 2,…),
Depending on the value of m, it is called m-th order diffracted light.

The angles of the ± 1st-order reflected diffracted lights of the diffraction gratings 14 and 15 are ψ ₋₁ = sin ⁻¹ (−λ ₁ / P, respectively) with respect to the direction in which the incident lights 16 and 17 are perpendicular to the diffraction grating surface. ₁ ), ψ ₊₁ = sin
^-1 (λ ₂ / P ₁ ), θ _-1 = sin ^-1 (-λ ₁ / P ₂ ), θ ₊₁ = sin ^-1
When (λ ₂ / P ₂ ), (ψ _-1 + θ _-1 ) and (ψ ₊₁ + θ)
₊₁ ) angle. Here, the wavelengths of the incident lights 16 and 17 are λ ₁ and λ ₂ , and the frequency difference Δf is a value of about several KHz to several hundreds MHz, which is very small compared to the speed of light C and two wavelengths λ.
_The ± first-order diffraction angles for ₁ and λ ₂ are almost equal. Therefore, ψ ₋₁ ≈ ψ ₊₁ and θ ₋₁ ≈ θ ₊₁ and (ψ _-1 + θ _-1 )
≈ (ψ ₊₁ + θ ₊₁ ).

By doing so, the incident light 1 incident on the diffraction gratings 14 and 15
6, 17 are respectively diffracted by the transmission type diffraction grating 14 to become −1st order transmission diffracted light 16-1, 17-1, which respectively enter the reflection type diffraction grating 15 at incident angles θ ₋₁ , θ ₊₁ . Here, they are respectively reflected and diffracted to become -1st-order reflected diffracted lights 16-1 'and 17-1'. The -1st-order reflected diffracted lights 16-1 'and 17-1' are diffracted lights that are diffracted in the vertical direction of the diffraction grating, and are optically synthesized and are zero-order transmitted and diffracted by the transmission type diffraction grating 14 to be desired. Diffracted light 18 becomes. On the other hand, a part of the incident light 16 and 17 that has entered the diffraction gratings 14 and 15 is 0-order transmission diffracted by the transmission diffraction grating 14 and enters the reflection diffraction grating 15, where it is reflected and diffracted to the -1st order. It becomes reflected diffracted light 16-2, 17-2,
The light enters the transmission diffraction grating 14 at incident angles ψ ₋₁ and ψ ₊₁ respectively. -1st order reflected diffracted light 16-2, 17-2 is a transmission type diffraction grating
The light is transmitted and diffracted by 14 and is combined with each other as the -1st-order transmitted diffracted light in the vertical direction with respect to the diffraction grating 14, and the desired diffracted light
It will be 19. Then, the photodetector 5'detects the beat signal due to the optical heterodyne interference from the desired diffracted lights 18 and 19, and the phase difference with the reference signal is measured to align the mask 8 and the wafer 11.

[Problems to be solved by the invention]

By the way, in the above-mentioned conventional method, the alignment point of the mask 8 and the wafer 11 is set as the coordinate origin of the mask 8 and the wafer 11, and the mask 8 and the wafer 11 with respect to the coordinate origin.
Where ΔM and ΔW are the small displacements of, respectively, between the phase difference Δφ between the reference signal and the beat signal and ΔM and ΔW, Therefore, a phase difference Δφ is generated for each minute displacement of ΔM and ΔW, and Δφ = 0 when ΔM = ΔW = 0, which is the alignment point. Therefore, when performing alignment, ΔM or ΔW must be set in advance.
It is necessary to set one of the coordinate origin positions, that is, the displacement amount to 0, and then perform the alignment control of the other coordinate origin position. Then, in order to set the displacement amount of either ΔM or ΔW in advance to the coordinate origin, the beat signal is detected by the heterodyne interference using only one of the diffraction grating 9 and the diffraction grating 10, and the beat signal is detected. Must be set so that the phase difference between the reference signal and the reference signal is 0 °.

However, since the setting is performed by single diffraction,
The incident angle is different from the case of double diffraction in the subsequent alignment, and therefore there is a drawback that an independent optical system for that is required.

Further, in this method, even when the relative positional displacement amount between the mask 8 and the wafer 11 is 0, when the mask 8 and the wafer 11 move in the same direction by the same amount, a phase difference Δφ occurs. That is, Δφ = 0 only when both the mask 8 and the wafer 11 are at the coordinate origin position.
It was difficult to apply as a method to perform relative alignment with 11.

Further, in this method, since the diffracted light diffracted doubly by the two diffraction gratings is detected, the intensity of the obtained diffracted light is weak.

The present invention has been made in view of the above circumstances. An object of the present invention is to directly extract the relative displacement amount of two objects as a phase difference signal to obtain a phase relationship based on absolute coordinates of the two objects. An object of the present invention is to provide a method capable of performing highly accurate alignment independently of the above, and an alignment device therefor.

[Means for solving problems]

According to the alignment method of the first invention, two wavelengths whose frequencies are slightly different from each other are respectively applied to the first diffraction grating provided on the first object and the second diffraction grating provided on the second object. Injecting monochromatic light, detecting optical heterodyne interference diffracted light generated from the first diffraction grating to generate a first beat signal, and detecting optical heterodyne interference diffracted light generated from the second diffraction grating. By generating a second beat signal and measuring the phase difference between the first and second beat signals, a diffraction grating pitch direction perpendicular to the diffraction grating lines of the diffraction gratings of the first and second objects is obtained. The feature is that the relative displacement amount is detected.

In addition, the alignment device of the second invention makes the first diffraction grating provided on the first object, the second diffraction grating provided on the second object, and the first and second objects relative to each other. A moving mechanism for moving the same, a light source for generating monochromatic light of two wavelengths whose frequencies are slightly different from each other, and a monochromatic light of two wavelengths generated from the light source for each of the first and second diffraction gratings. Angle adjusting means for making the light incident at an incident angle, first detecting means for detecting optical heterodyne interference diffracted light generated from the first diffraction grating, and generating a first beat signal, and the second diffraction grating. Second detection means for detecting the optical heterodyne interference diffracted light generated from the second beat signal and a control signal sent to the moving mechanism according to the first and second beat signals, and the first detection means. And the second object relatively It is characterized by comprising and a signal processing control means for aligning However in position.

[Action]

According to the present invention, incident light is incident on each of the first and second diffraction gratings, and the optical heterodyne interference diffracted light is detected independently from each of those diffraction gratings. Then, by measuring the phase difference of the beat signals respectively obtained from the interference lights, the relative alignment of the first and second objects in the diffraction grating pitch direction is performed.

〔Example〕

An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 shows a schematic configuration of an embodiment of an alignment apparatus according to the present invention, that is, an X-ray exposure apparatus for manufacturing a semiconductor IC or LSI. In FIG. 1, 20 is a two-wavelength orthogonal polarization laser light source (light source) that emits light of two wavelengths whose frequencies are slightly different from each other and whose polarization plane directions are orthogonal to each other, and 21,21 ′, 21 ″, 21 are mirrors. Of these mirrors, the mirrors 21 ', 21 "are adjustable in angle. 22 is a cylindrical lens, 23 is a polarization beam splitter, 24
Is a prismatic mirror, 25 and 25 'are condenser lenses, 26 and 26' are photodetectors (first and second detecting means), 27 is a signal processing control section (signal processing control means), and 28 is a mask stage. , 29 is a wafer stage, 30 is a mask (first object), 31 is a wafer (second object), 32 is a reflection type diffraction grating (first diffraction grating), and 33 is a monochromatic light incident / diffracted light extraction window. , 34 are reflection type diffraction gratings (second diffraction gratings), and 44, 44 'are polarizing plates. Here, the monochromatic light incident / diffracted light extraction window 33 is an opening provided in the mask 30, through which the incident light can be directly incident on the diffraction grating 34, and the diffraction from the diffraction grating 34 can be performed. The light can be taken out directly. Further, the mask stage 28 and the wafer stage 29
Constitute a moving mechanism for relatively moving the mask 30 and the wafer 31.

In FIG. 1, the light emitted from the two-wavelength orthogonal polarization laser light source 20 becomes an elliptical beam through the mirror 21 and the cylindrical lens 22, and the beam has only a horizontal component or a vertical component by the polarization beam splitter 23. It is split into two linearly polarized lights with slightly different frequencies, and the split lights are each reflected by the mirror 2
The light is incident on the reflective diffraction grating 32 and the reflective diffraction grating 34 at a desired incident angle via 1 ', 21 "(incident angle adjusting means).
In the example of FIG. 1, the reflection type diffraction gratings 32 and 34 are displaced in the grating line direction, and are arranged in the same elliptical beam of incident light of two wavelengths. Also, a reflection type diffraction grating
The diffraction grating pitches of 32 and 34 are made equal. Diffraction grating 3
The diffracted light obtained from 2 and the diffracted light obtained from the diffraction grating 34 through the monochromatic light incident / diffracted light extraction window 33 are mirror 21 (light combining means), prismatic mirror 24 (light separating means), and condenser lenses 25 and 25. ′ Is guided to the photodetectors 26 and 26 ′ via the polarizing plates 44 and 44 ′, respectively, and processed by the signal processing control unit 27 as a diffracted light beat signal. The signal processing control unit 27 detects the phase difference between both beat signals by using one of the beat signals of the diffracted light obtained from the reflection type diffraction gratings 32 and 34 as a reference beat signal, and the phase difference is 0. Mask stage 28 or wafer stage 2
9 is moved relative to the mask so that the pattern on the mask surface can be accurately overlapped at a predetermined position on the wafer surface for exposure.
A precise alignment between 30 and wafer 31 is provided.

Next, a positioning method using the positioning device thus configured will be described with reference to FIG. In FIG. 2, 35 is a reflection type diffraction grating (first diffraction grating), 36 is a reflection type diffraction grating (second diffraction grating), 37 and 38 are two wavelengths of incident light whose frequencies are slightly different from each other, 39 , 40 is diffracted light (optical heterodyne interference diffracted light), 41 is a mask (first object)
And a transparent thin film constituting the diffraction grating 35, 42 is a wafer, 43
Is an opaque thin film. Further, B ₁ -B ₁ ′ is the grating line direction of the second diffraction grating, B ₂ -B ₂ ′ is the grating line direction of the first diffraction grating, and A ₁ -A ₁ ′ is B ₁ -B ₁ ′. vertical grating pitch direction, a ₂ -A ₂ 'is B ₂ -B _2' perpendicular grating pitch direction, C ₁ -
C ₁ ′ is the direction perpendicular to the grating plane of the diffraction grating 36, and C ₂ −
C ₂ ′ is the direction perpendicular to the grating plane of the diffraction grating 35.
In the example of FIG. 2, the pitches of the first and second diffraction gratings 35 and 36 are made equal to P, and the diffraction grating 35 is B ₂ -B so as not to overlap with the grating surface of the diffraction grating 36. _The take-out window 33 (not shown in FIG. 2) is provided above the diffraction grating 36 in the vertical direction above the diffraction grating 36. The incident directions of the incident lights 37 and 38 are adjusted by adjusting the angles of the mirrors 21 ′ and 21 ″ with respect to the direction C ₁ −C ₁ ′ (or C ₂ −C ₂ ′) perpendicular to the diffraction grating. Are set to the angles θ ₋₁ = sin ⁻¹ (λ ₁ / P) and θ ₊₁ = sin ⁻¹ (λ ₂ / P) of the ± first-order reflected diffracted lights of the diffraction gratings 35 and 36, respectively. Here, the wavelengths of the incident lights 37 and 38 are λ ₁ and λ, respectively.
_2, the frequency difference Delta] f is the value of the order of several hundred MHz from a few KHz, Δf = C · the speed of light as _{C | 1 / λ 1 -1 /} λ 2 | for a next Δf << C θ _{- 1} ≈ θ ₊₁ .

By doing so, the incident light 3 incident on the diffraction gratings 35 and 36
Reference numerals 7 and 38 denote reflection diffraction gratings 35 and 36, respectively, which are -1st-order reflected and diffracted in a direction (C ₂ -C ₂ ′, C ₁ -C ₁ ′ direction) perpendicular to the grating surface, and are optically synthesized. The light becomes heterodyne interference diffracted lights 39 and 40, respectively. These optical heterodyne interference diffracted lights 39, 40 are diffracted lights diffracted by different diffraction gratings 35, 36, but since the incident angles of the incident lights 37, 38 are symmetrical with respect to the vertical direction of the grating surface, The diffraction gratings 35 and 36 are arranged in the vertical direction (C ₁ −C ₁ ′, C ₂ −C ₂ ′ direction) and the grating line direction (B ₁ −B ₁ ′, B ₂ −B ₂ ′ direction), respectively. However, the change in the optical path length of the incident light 37 and the incident light 38 until they are incident on the diffraction grating 35 or the diffraction grating 36 becomes equal, and the phase difference between the beat signals obtained from the diffracted lights 39 and 40 is determined by the diffraction grating. The phase shift does not affect the displacement of 35 and 36 in the vertical and grid line directions. That is, the phase difference between the beat signals obtained from the diffracted lights 39 and 40 is the diffraction grating 35 and the diffraction grating.
It changes only according to the spatial arrangement of 36 pitch directions (A ₂ −A ₂ ′, A ₁ −A ₁ ′ direction), that is, relative displacement. Then, the diffraction gratings 35 and 36 are arranged in the grating line direction (B ₁ -B
₁ 'or B ₂ -B _2' when it becomes aligned in the direction), the phase difference of the beat signal obtained from the diffracted light 39 and 40 becomes 0 degrees, the alignment is completed. Note that A ₁ −A ₁ ′ or A ₂
Let Δx be the relative displacement of the diffraction gratings 35 and 36 with respect to the −A ₂ ′ direction, and Δφ be the beat signal phase difference. The phase difference Δφ is 1/2 of the diffraction grating pitch.
Changes relative to the relative displacement.

As described above, according to the device of this embodiment, the first and second diffraction gratings provided on the first object and the second object are displaced in the grating line direction so as not to overlap each other in plan view. The optical heterodyne interference diffracted light obtained from the first diffraction grating and the optical heterodyne interference diffracted light obtained from the second diffraction grating can be detected completely independently. Then, by detecting the phase difference between the beat signals obtained from both diffracted lights, the first object and the second object are detected.
It is possible to directly and stably detect the phase difference corresponding to the relative displacement amount of the object in the diffraction grating pitch direction, and by setting the phase difference to 0 °, precise alignment can be stably performed.

In addition, the monochromatic light incident on the diffraction grating is set in the direction of the n-th order diffraction angle (n is a positive integer) symmetrical with respect to the vertical direction of the grating surface of the diffraction grating, and the first and second diffraction gratings are monochromatic. By arranging in the same spot of light, the phase shift of the diffracted light due to the change in the optical path length of the optical system until the monochromatic light enters the diffraction grating is the beat signal obtained by the first and second diffraction gratings. Since they appear as the same phase shift, they cancel each other out, and the influence of the phase shift does not appear. Therefore, it is not necessary to set the optical path lengths of the two-wavelength light with high accuracy, the optical system adjustment becomes easy, and the mechanical system becomes simple. Further, the phase shift due to the change in the optical path length due to the microvibration of the optical component or the like is canceled, and the highly stable phase difference signal can be taken out.

In the above embodiment, the case where one set of diffraction gratings is used is shown, but similar diffraction gratings are installed at two or more positions on the mask and the wafer surface, and the same method as in FIG. 1 is used. The beat signal of the diffracted light is detected using the mask stage and the wafer stage so as to eliminate the phase difference, so that the mask and the wafer are parallel to and perpendicular to the diffraction grating. 2-axis X, Y, and XY
It is also possible to perform alignment with respect to the three axes of the rotation axis θ of the XY plane centered on the Z axis perpendicular to the plane.

The first and second diffraction gratings may be either absorption type diffraction gratings or phase type diffraction gratings, and are not limited to binary diffraction gratings, and sinusoidal diffraction gratings, blazed diffraction gratings, etc. Various combinations are possible.

Further, in the above-mentioned embodiment, the opening was provided on the mask substrate as a monochromatic light incident / diffracted light extraction window, but in the case of a transparent thin film window through which incident light and diffracted light can pass without providing an opening. Can also obtain the same effect. Further, although the prism-shaped mirror is used to separate the two heterodyne interference diffracted lights, the same effect can be obtained by directly detecting with a two-divided detector.

Also, in the above, an example in which the first and second diffraction gratings are arranged so as to be displaced in the grating line direction has been shown, but the first and second diffraction gratings are arranged in a direction perpendicular to the grating line direction (grating pitch direction).
Similar effects can be obtained even when they are arranged in a staggered manner or when they are arranged in a staggered manner in both the lattice line direction and the lattice pitch direction.

Further, in the above, the first and second diffraction gratings are arranged in the same elliptical beam spot of the incident light.
Even when two monochromatic light beams of two wavelengths are independently incident on each diffraction grating, it is necessary to consider the phase difference due to the optical path length difference of each monochromatic light beam of two wavelengths incident on the first and second diffraction gratings. The same effect can be obtained.

Further, in the above, the example in which the grating pitches of the first and second diffraction gratings are made equal and the optical heterodyne interference light of the first-order diffracted light is used is shown, but generally, the n-th order diffracted light (n is a positive integer). The same effect can be obtained by using the optical heterodyne interference light of, and the n-th diffraction angle of the first diffraction grating is changed to that of the second diffraction grating by changing the pitches of the first and second diffraction gratings. It is set to be equal to the m-th order diffraction angle (m is a positive integer), and the optical heterodyne interference light of the n-th order diffracted light from the first diffraction grating and the optical heterodyne interference light of the m-th order diffracted light from the second diffraction grating are set. Even if used, the same effect can be obtained.

Further, by changing the incident direction and the outgoing direction, the ± 1st-order diffracted light (generally ± n-order diffracted light) is used for the vertical incidence of the two-wavelength monochromatic light on the first and second diffraction gratings, and the polarizing plate Of the + n-th order diffracted light and the −n-th order diffracted light, two diffracted lights having different frequencies are extracted and optically combined to obtain the optical heterodyne interference light from the first diffraction grating and the second diffraction grating. The same effect can be obtained by using the optical heterodyne interference light.

Further, in the above, either the optical heterodyne interference beat signal from the first diffraction grating or the optical heterodyne interference beat signal from the second diffraction grating is used as the reference beat signal, but as shown in FIG. In this method, a part of the laser light emitted from the two-wavelength orthogonal polarization laser light source 20 is separated in advance by a beam splitter or the like, and the two-wavelength laser light obtained by the separation is subjected to optical heterodyne interference with a polarizing plate to generate a reference beat signal. And this reference beat signal and the first
Detecting the phase difference between the optical heterodyne interference beat signal from the diffraction grating and the phase difference between the reference beat signal and the optical heterodyne interference beat signal from the second diffraction grating, and masking them so that both phase differences become equal. The same effect can be obtained in an apparatus that aligns the mask and the wafer by relatively moving the stage 28 or the wafer stage 29.

FIG. 3 shows another embodiment of the alignment apparatus according to the present invention. In FIG. 3, 45 is a two-wavelength orthogonal polarization laser light source, 46, 47, 48, 49, 50, 51, 52 are plane mirrors, 53 is a beam splitter, 54, 55 are polarized beam splitters, 56, 56 '.
Is a condenser lens, 57 and 57 'are polarizing plates, 58 and 58' are photodetectors,
59 and 59 'are preamplifiers, 60 is a detection signal processing unit, 61 is a position display unit, 62 is a stage drive unit, 63 is a first diffraction grating, and 64 is a
Is the second diffraction grating, 65 is the first object, 66 is the second object,
67 is a moving stage.

In this device, a part of the laser light emitted from the two-wavelength orthogonal polarization laser light source 45 is taken out through the plane mirror 46 and the beam splitter 53, and the polarization beam splitter is used.
54 is used to separate into P-polarized light and S-polarized light of two wavelengths,
The light is incident on the first diffraction grating 63 at a predetermined angle via the plane mirrors 47 and 48, and the two wavelengths of diffracted light from the diffraction grating 63 are optically combined to form a plane mirror 49, a condenser lens 56, and a polarized light. The light is detected by the photodetector 58 via the plate 57, and is input to the detection signal processing unit 60 through the preamplifier 59 as an optical heterodyne interference reference beat signal. On the other hand, the other laser light split by the beam splitter 53 is the polarized beam splitter.
55 is used to separate P-polarized light and S-polarized light of two wavelengths,
The light enters the second diffraction grating 64 at a predetermined angle via the plane mirrors 50 and 51. The two wavelengths of diffracted light from the diffraction grating 64 are optically combined to form a plane mirror 52, a condenser lens 56 ',
The light is detected by the photodetector 58 'through the polarizing plate 57', and is input to the detection signal processing unit 60 through the preamplifier 59 'as a diffracted light beat signal of optical heterodyne interference. The detection signal processing unit 60 detects the phase difference between the reference beat signal and the diffracted light beat signal, and the position display unit 61 displays the relative deviation amount between the diffraction grating 63 and the diffraction grating 64 corresponding to the phase difference. Further, a control signal is sent to the moving stage 67 via the stage drive unit 62 so that the phase difference becomes constant, and the second object 66 is servo-controlled to a predetermined position. That is, in the device of this embodiment,
By detecting the displacement amount of the second object 66 with respect to the first object 65 with reference to the position of the first object 65,
Alignment can be performed.

〔The invention's effect〕

As described in detail above, according to the present invention, monochromatic light of two wavelengths is incident on each of the first and second diffraction gratings provided on the first object and the second object, and both Since the diffracted light from the diffraction grating is detected and the phase difference of the beat signal generated from the interference light is measured, the relative alignment of both objects in the diffraction grating pitch direction is determined by their absolute coordinates. It can be performed regardless of the positional relationship. Therefore, it is possible to save the trouble of accurately setting either one of the objects at the reference position prior to the alignment, and prevent the alignment accuracy from deteriorating due to the setting error. Since there is no need for an independent optical system for the purpose, the device can be easily configured.

Further, according to the present invention, since the single-diffracted light from each diffraction grating is detected, the intensity of the obtained diffracted light is higher than that in the conventional case where the double-diffracted light is detected.

Furthermore, by disposing both diffraction gratings in the same beam spot of the incident light so that the same beam is incident on them, it is not necessary to accurately match the optical path lengths of the incident light incident on the respective diffraction gratings. It becomes possible to perform the alignment very easily.

The present invention can be applied not only to alignment but also to a device for measuring a minute displacement of an object, a coordinate position detection or control device, and the like.

[Brief description of drawings]

1 to 3 are views showing an embodiment of the present invention.
1 and 2 show an alignment apparatus according to an embodiment, FIG. 1 is a perspective view showing a schematic configuration thereof, and FIG. 2 is an enlarged perspective view of a diffraction grating portion. FIG. 3 is an elevational view showing a schematic configuration of a positioning device according to another embodiment of the present invention. 4 and 5 show a conventional alignment device, FIG. 4 is an elevational view showing a schematic configuration thereof, and FIG. 5 is an enlarged view of a diffraction grating portion thereof. 20: 2 wavelength orthogonal polarization laser light source (light source), 21 ', 21 "... mirror (incident angle adjusting means), 26 ... photodetector (first detecting means), 26' ... photodetector ( Second detection means), 27 ... Signal processing control section (signal processing control means), 28 ... Mask stage, 29 ... Wafer stage, 30,41 ... Mask (first object), 31,42 ... ... Wafer (second object), 32,35 ... Reflective diffraction grating (first diffraction grating), 34,36 ... Reflective diffraction grating (second diffraction grating), 37, 38 ... Incident light , 39,40 …… Diffracted light (optical heterodyne interference diffracted light), 45 …… 2-wavelength orthogonal polarization laser light source (light source), 47,48,50,51 …… Mirror (incident angle adjusting means), 58 …… Optical light Detector (first detection means), 58 '... Photodetector (second detection means), 60 ... Detection signal processing unit (signal processing control means), 63 ... First diffraction grating, 64 ... … Second time Folded grid, 65 ... first object, 66 ... second object, 67 ... moving stage (moving mechanism).

Claims (2)

[Claims] 1. A first diffraction grating and a second diffraction grating provided on a first object.
The monochromatic light of two wavelengths whose frequencies are slightly different from each other is incident on each of the second diffraction gratings provided on the object.
The optical heterodyne interference diffracted light generated from the first diffraction grating is detected to generate a first beat signal, and the optical heterodyne interference diffracted light generated from the second diffraction grating is detected to generate a second beat signal. By generating and measuring the phase difference between the first and second beat signals,
A method for alignment, comprising detecting a relative displacement amount in a diffraction grating pitch direction perpendicular to the diffraction grating lines of the diffraction gratings of the first and second objects. 2. A first diffraction grating provided on a first object, a second diffraction grating provided on a second object, and a moving mechanism for relatively moving the first and second objects. A light source for generating monochromatic light of two wavelengths having frequencies slightly different from each other, and a monochromatic light of two wavelengths generated from the light source for the first and second
Incident angle adjusting means for making each of the diffraction gratings incident at a predetermined incident angle, and a first detection for generating the first beat signal by detecting the optical heterodyne interference diffracted light generated from the first diffraction grating. Means, second detecting means for detecting the optical heterodyne interference diffracted light generated from the second diffraction grating to generate a second beat signal, and first detecting means generated by the first and second detecting means. And sends a control signal to the moving mechanism in response to the second beat signal,
An alignment apparatus comprising: signal processing control means for performing relative alignment by moving the first and second objects relative to each other.