JPH09119811A - Alignment device, apparatus and method for exposure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an alignment device by which irradiation light is aligned at a desired angle so as to irradiate an object by a method wherein a plurality of irradiation optical systems by which a frequency modulator, a substrate and a reference mark are set to a mutually conjugate relationship are provided, a beam splitter is provided and a photoelectric detection means is provided. SOLUTION: The ± first-order light which is passed through a spatial filter 15 is transmitted through a beam splitter 20 so as to be incident on a bifocal optical system 21. P-polarized light which is radiated from the optical system 21 forms an image in a focal point 26a in the upper-part space of a reticle 1, and S-polarized light forms an image in a focal point 27a which agrees with a pattern face on the rear surface of the reticle 1. The focal point 26a conjugates with an image formation face 26b which agrees with the surface of a wafer 4 by a projection lens 3, and the focal point 27a conjugates with an image formation face 27b which is separated at the lower part from the surface of the wafer 4 by the lens 3. Reflected and diffracted light from a diffraction grating mark on the reticle 1 is reflected by the beam splitter 20 via the optical system 21 and the like so as to reach a photoelectric detector 25. The reflected and diffracted light from the diffraction grating mark on the wafer 4 is returned to its original optical path via the lens 3, and it is transmitted through the reticle 1 and the like so as to reach the detector 25.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positioning apparatus for a projection exposure apparatus used for manufacturing semiconductor elements and the like, and more particularly to a mask having an original image pattern, a semiconductor wafer to which this original image pattern is transferred, etc. The present invention relates to a device for relatively aligning the substrate with the substrate.

[0002]

2. Description of the Related Art In recent years, a projection type exposure apparatus (stepber) has been widely used as an apparatus for transferring a fine pattern of a semiconductor element or the like onto a semiconductor wafer with high resolution. Conventionally, in this type of stubber, alignment between a reticle (synonymous with a mask) and one sailboat region on the wafer, which is a so-called alignment method, is an alignment mark formed around the reticle circuit pattern and a shot on the wafer. It is known to simultaneously detect an alignment mark formed around the area.

In this alignment method, both the mark on the reticle and the mark on the wafer are detected with high accuracy, the relative positional deviation amount is obtained, and the reticle or the wafer is finely moved so as to correct this deviation amount. ing. Generally, in a projection type exposure apparatus, in order to form a reticle pattern on a wafer with high resolution, the projection optical system uses an illumination light for exposure (eg, g-line of wavelength 436 nm or i of wavelength 365 nm).
The current situation is that chromatic aberration is satisfactorily corrected only for the line). This means that in an alignment optical system that detects a reticle mark and a wafer mark via a projection optical system, the light for illuminating the mark is limited to the same wavelength as or very close to the wavelength of the exposure light. I do.

A resist layer is formed on the surface of the wafer in the exposure process, and a mark on the wafer is detected through the resist layer during alignment. In order to enable the formation of a pattern with higher resolution, it has been considered to adopt a multilayer resist structure or the like having a high absorption rate for exposure light and a low transmittance rate. In this case, the illumination light for alignment is attenuated before reaching the mark on the wafer, and the reflected light (specular reflection light, scattered light, diffracted light, etc.) from the mark is also attenuated. There arises a problem that the mark is not recognized by the alignment optical system with a sufficient amount of light.

Therefore, it is conceivable to use the light of the wavelength castle having a high transmittance for such a resist as the illumination light for alignment. For example, Japanese Patent Application Laid-Open No. 56-1102
As disclosed in Japanese Patent Publication No. 34-34, a small lens for chromatic aberration correction is provided in the alignment optical path between the reticle and the projection optical system, and even under light of a wavelength different from the exposure light,
A technique is known in which a mark on a reticle and a mark on a wafer are conjugated with each other. In this method, if the correction optical system is movable with respect to the projection optical system, the alignment accuracy is extremely reduced due to instability when setting the correction optical system. Stipulated. For this reason, the mark on the reticle is provided at a position sufficiently distant from the circuit pattern area so that the correction optical system does not block the negative part of the image formation light flux of the circuit pattern during exposure. On the other hand, among projection type exposure apparatuses, a stepper that repeats and exposes pattern images of a reticle sequentially on each of a plurality of shot areas on a wafer by a step-and-repeat method can align each shot area on the wafer. Is desirable.

By the way, the alignment accuracy is improved by increasing the detection resolution of the mark position, but at present, attention is paid to using a diffraction grating as a mark capable of the most accurate detection. . This is because the diffracted light generated from each of the grating formed as a mark on the chicle and the grating formed as a mark on the wafer is moved relative to the arrangement direction of the grating. The position difference between the reticle and the wafer is detected from the phase difference. As an example thereof, the one disclosed in Japanese Patent Publication No. 61-9733 is known. In addition, in the proximity method, optical information (sinusoidal intensity change) obtained by causing the diffracted light generated by the mask grating and the diffracted light generated by the wafer grating to interfere with each other.
There is also a method of detecting the positional deviation between the mask and the wafer on the basis of the above with a resolution of 1 / several tens to tens of minutes of the pitch of the diffraction grating.

In this case, it has been reported experimentally that alignment using a diffraction grating can provide a detection resolution of about several nm.

[0008]

In the case of the conventional projection exposure system having a correction optical system, the following problems occur. Usually 5 shots between each shot area on the wafer.
It is divided by scribe lines having a width of about 0 to 100 μm. If a mark attached to a certain shot area is provided at a position 100 μm away from the circuit pattern area on the scribing line, the reduction ratio of the projection optical system is reduced to 1 /.
Even if it is set to 10, the mark on the reticle is only 1000 μm (1 mm) away from the circuit pattern area on the reticle, and if the correction optical system is composed of a small lens, in order not to block the imaging optical path of the circuit pattern, It is necessary to prepare a lens system with a diameter of only 2 mm including the lens barrel. This is extremely impractical. Therefore, by solving this problem, even if the mark on the reticle is largely separated from the circuit pattern area, the configuration of the correction optical system is devised so that the conjugate state with the mark attached to the shot area on the wafer is maintained. Is Japanese Patent Sho 58-307
No. 36 publication.

However, Japanese Patent Laid-Open Publication No.
No. 34 or this Japanese Patent Publication No. 58-30736 cannot cope with the change in the size of the shot area on the wafer (that is, the size of the circuit pattern on the reticle), and in the end, Select either to adopt a configuration that moves the correction optical system (or its part), or to adopt a site alignment method in which the relative position between the reticle and the wafer is offset by a predetermined amount during alignment and during exposure. I had to do it.

On the other hand, although the alignment method using the diffraction grating can detect the mark position with high resolution, in the technique disclosed in Japanese Patent Publication No. 61-9733, there is a gap between the reticle and the projection optical system. Since an optical modulator or the like is provided in the alignment optical path of, the same problem as in the case where the correction optical system is provided occurs. As described above, although it is known that the alignment method that directly uses the periodic optical information uniquely determined by the periodic structure of the diffraction grating has high accuracy, it is applied to the projection exposure apparatus, particularly the stepper. For the practical structure of
Had not yet been considered.

[0011]

SUMMARY OF THE INVENTION The present invention solves various problems that occur when a positioning method using a diffraction grating is applied to a projection type exposure apparatus, and the stability and alignment accuracy of the apparatus are improved. It was done to satisfy both and. In the present invention, by illuminating the lattice mark on the substrate held on the movable stage and controlling the movement of the stage based on the photoelectric signal obtained by receiving the diffracted light generated from the lattice mark. In a device for aligning a substrate, a light source emitting a coherent beam for illuminating a grating mark on the substrate; a frequency for injecting the coherent beam to generate a pair of illumination beams having a predetermined frequency difference A modulator; a first irradiation optical system in which the frequency modulator and the substrate are conjugated to each other so as to irradiate the grating mark with a pair of illumination beams at a predetermined intersection angle; and the first irradiation optical system. A beam splitter disposed in the optical path of the system for splitting a pair of illumination beams; a frequency modulator and the beam modulator for illuminating the split pair of illumination beams on a reference grating at a predetermined crossing angle. A second irradiation optical system that makes the diffraction grating mutually conjugate with each other, and a first AC signal whose intensity changes at a cycle according to a predetermined frequency difference by receiving the interference light of two diffracted beams generated from the grating mark. And a photoelectric detection means for receiving interference light of two diffracted beams generated from the reference grating and outputting a second AC signal whose intensity changes at a frequency according to a predetermined frequency difference;
Measuring means for measuring the positional deviation amount of the grid mark with respect to the reference grating by measuring the phase difference between the AC signal and the second AC signal, and the movement of the stage is controlled based on the measured positional deviation amount. And a control system.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the structure of an alignment apparatus according to an embodiment of the present invention will be described with reference to FIG. A reticle 1 having a predetermined circuit pattern and a diffraction grating mark for alignment is held by a reticle slug 2 which is two-dimensionally movable. Each pattern on the reticle 1 is imaged on the wafer 4 under exposure light by the projection lens 3 which is telecentric on both sides. However, the projection lens 3 is satisfactorily corrected for chromatic aberration with respect to the wavelength of illumination light for exposure (g-line, i-line, etc.), and the reticle 1 and the wafer 4 are arranged so as to be conjugate to each other with respect to the wavelength of exposure. You. Diffraction grating marks similar to the grating marks formed on the chicle 1 are also formed on the wafer 4. The wafer 4 is attracted onto the stage 5 which moves two-dimensionally in a step-and-repeat manner. When the transfer exposure of the reticle 1 to one shot area on the wafer 4 is completed, the wafer 4 is stepped to the next shot position. A part of the reticle stage 2 has a laser light wave interference side length device (hereinafter referred to as an interferometer) 43 for detecting the position of the reticle 1 in the x direction, the y direction, and the rotation (a) direction in the horizontal plane. A movable mirror 6 that reflects the laser beam from is fixed. This interferometer 4
Reference numeral 3 has three side length laser beams for independently detecting the positions in the x direction, the y direction, and the white direction, but the illustration is omitted here for the sake of simplicity. The moving stroke of the reticle stage 2 is several millimeters or less, and the detection resolution of the interferometer 43 is set to about 0.01 μm, for example. On the other hand, a movable mirror 7 for reflecting the laser beam from the interferometer 45 for detecting the position of the wafer 4 in the horizontal direction in the horizontal plane is fixed to the negative part of the wafer stage 5. This interferometer 45 is also in the x direction,
Although two laser beams for shelf length are provided to detect the position in the y direction independently, the illustration is omitted here for simplification of the description. X direction of reticle stage 2,
Driving in the y and 6 directions is performed by the drive motor 42, and the two-dimensional movement of the wafer stage 5 is performed by the drive motor 46.

The illumination system for exposure is a mercury lamp 3
0, an elliptic mirror 31, an input lens group 32 including a condenser lens and an interference filter, an optical integrator (fly eye lens) 33, a mirror 34, a main condenser lens 35, a dichroic mirror 22, and the like. The dichroic mirror 22 is 45 above the reticle 1. The exposure light from the condenser lens 35 is vertically reflected downward to irradiate the reticle 1 uniformly. The dichroic mirror 22 has a reflectance of 90% or more with respect to the wavelength of the exposure light and 50% with respect to the wavelength of the illumination light for alignment (longer than the exposure light).
It has the above transmittance.

Next, the alignment system of this embodiment will be described. The illumination light for alignment is emitted from the laser light source 10, passes through a radial grating 11 in which a transmission type reference diffraction grating is radially formed, and passes through a Fourier transform lens 13 and a beam splitter 14 on a Fourier plane (of the alignment optical system). Reach the spatial filter 15 located on the pupil plane). The radial grating 11 is configured to be rotatable by a motor 12 at a substantially constant speed.
The laser light incident on the radial grating 11 is diffracted like 0th order light, ± 1st order light, ± 2nd order light.
Each spreads at a different diffraction angle. In FIG. 1, 0
Only the next light LBo, the + 1st order light + LB ₁ and the −1st order light −LB ₁ are shown. These 0th order light and ± 1st order light are spatial filters 1
5 are clearly separated and distributed, and only the 0th-order light LBo is blocked and the ± 1st-order lights are transmitted. The ± first-order light that has passed through the spatial filter 15 passes through the beam splitter 20 and enters the bifocal optical system 21. Although the bifocal optical system 21 is simply shown in FIG. 1, it is actually composed of a combination of a birefringent substance (quartz, calcite, etc.) and a telecentric objective lens for a microscope or the like. Different powers are given depending on the polarization components (P-polarized light and S-polarized light) of the ± first-order light. Therefore, one polarized light (e.g., P-polarized light) emitted from the bifocal optical system 21 is focused on the focal point 26a in the upper space of the reticle 1, and the other polarized light (e.g., S-polarized light) coincides with the pattern surface of the lower surface of the reticle 1. An image is formed on the focused focal point 27a. The other focal point of the bifocal optical system 21, that is, the plane conjugate with the focal points 26a and 27a on the laser light source 10 side is designated as the radial grating 11.
Here, the distance between the two focal points 26a and 27b of the bifocal optical system 21 in the optical axis direction corresponds to the amount of chromatic aberration on the reticle 1 side of the projection lens 3 at the wavelength of the alignment laser light. This focal plane 26a becomes conjugate with the back surface 26b which is the surface of the wafer 4 by the projection lens 3, and the focal plane 27a (reticle pattern surface) is spatially downwardly separated from the surface of the wafer 4 by the projection lens 3. Back surface 27
Becomes conjugate with b. The distance between the rear surfaces 26b and 27b corresponds to the amount of chromatic aberration on the wafer 4 side of the projection lens 3. Here, the distance between the rear surfaces 26b and 27b is Dw, and the focal plane 26
a and 27a, and the projection magnification of the projection lens 3 is 1 / M (usually M is 1, 25, 5, 10), Dr = M2. Dw. As the wavelength of the laser light for alignment becomes farther from the wavelength of the exposure light, Dw and Dr become larger according to the aberration characteristics of the projection lens 3. The depth of focus of this type of projection lens is extremely shallow, about ± 1 μm, and the distance Dw may reach several tens of μm depending on the wavelength of the alignment illumination light. The illumination light (laser light) for alignment is
It is desirable that the wavelength has almost no sensitivity to the resist coated on the substrate, but this is not necessarily the condition to be satisfied in the present invention. This is because the projection lens causes an extremely large aberration between the wavelength of the exposure light and the wavelength of the illumination light for alignment, and in particular, a large distortion is applied to the optical information itself from the diffraction grating mark on the wafer 4. Therefore, it is more important to give priority to determining the optimal illumination light for alignment in consideration of the aberration. Therefore, when the alignment illumination light irradiates the resist for a long time (for example, 1 minute or more), the wavelength may be weakly sensitive such that the resist is exposed (a thinning occurs after development).

The ± 1st-order light LB · (S-polarized light) of the alignment laser light is added to the + 1st-order light + LB ₁ and −1st-order light −LB on the diffraction grating mark portion of the reticle 1 on the focal plane 27a.
_The light enters from two directions at an angle of ₁ and forms an image. Further, the ± first-order light LB · (P-polarized light) from the focal plane 26 a that has passed through the transparent portion of the reticle 1 is transmitted through the projection lens 3 to the focal plane 26 a.
b, the +1 order light and -1
It forms an image by entering from two directions at an angle formed by the next light. Then, the diffracted light reflected from the diffraction grating mark of the reticle 1 is reflected by the beam splitter 20 via the dichroic mirror 22, the bifocal optical system 21, filtered by the spatial filter 23, and then the photoelectric detector 25 by the condenser lens 24. Reach Further, the diffracted light reflected from the diffraction grating mark on the wafer 4 returns to the original optical path through the projection lens 3, passes through the transparent portion of the reticle 1, and passes through the dichroic mirror 2.
It reaches the photoelectric detector 25 through the bifocal optical system 21, the beam splitter 20, the spatial filter 23, and the condenser lens 24. The spatial filter 23 is arranged at a position conjugate with the pupil plane of the alignment optical system, that is, at a position substantially conjugate with the pupil (exit pupil) of the projection lens 3, blocks the specular reflection light from the reticle 1 or the wafer 4, and It is defined that only the light diffracted in the direction perpendicular to the diffraction grating of the wafer 1 or the wafer 4 (the normal traverse direction of the surface) is transmitted. And photoelectric detector 2
The reticle 1 and the wafer 4 are arranged to be conjugate with each other via the bifocal optical system 21 and the lens 24.

The photoelectric signal obtained from the photoelectric detector 25 is the interference of the diffracted light from each of the two diffraction grating marks, and becomes a sinusoidal AC signal corresponding to the rotational speed of the radial grating 11. . By the way, the ± 1st order light and the 0th order light from the radial grating 11 are
Only the 0th order light is blocked by the spatial filter 16 which is transmitted through the beam splitter 14 and is arranged on the pupil (Fourier plane),
An image is formed on the reference diffraction grating 18 by the lens system (inverse Fourier transform lens) 17. The reference diffraction grating 18 is fixed on the apparatus. This diffraction grating 18
Also, the + _1st order light + LB ₁ and the −1st order light −LB ₁ are incident from two directions at a predetermined angle. The photoelectric detector 19 receives the diffracted light (or interference light) transmitted through the reference diffraction grating 18,
Outputs a sinusoidal photoelectric signal. The phase detection system 40 inputs the photoelectric signal from the photoelectric detector 26 and the photoelectric signal from the photoelectric detector 19, and detects the phase difference on the waveform of both signals. The detected phase difference (± 180.) Uniquely corresponds to the relative positional deviation amount within 1/2 of the grating pitch of the diffraction grating marks formed on the reticle 1 and the wafer 4, respectively.
The control system 41 provides information on the detected phase difference (position shift amount),
Interferometers 43, 45 obtained via servo system 44
Drive motors 42, 4 based on the position information from each of the
6 is controlled to perform relative alignment between the reticle 1 and the wafer 4.

As described above, in the overall structure of this embodiment, the part of the alignment optical system, especially the bifocal optical system 21 is movable to any position according to the arrangement of the alignment mark on the reticle 1, and what kind of mark is used. Mark detection is possible even with the arrangement. Further, since the exposure light and the alignment illumination light are separated by the dichroic mirror 22 obliquely provided above the reticle 1, it is possible to detect the mark even during the exposure operation. This means that even if the alignment between the reticle 1 and the wafer 4 is out of order due to some disturbance during the exposure, it can be detected immediately at that time. Further, it also means that the positioning servo between the reticle stage 2 and the wafer stage 5 can be executed in a closed loop even during the exposure operation based on the phase difference information from the phase detection system 40. The light source of the exposure light may be replaced with an excimer laser light source other than the mercury lamp.

Next, referring to FIG. 2, only the alignment system will be described.
The detailed configuration and the principle of alignment will be described. Second
In the figure, the same members as those in FIG.
Is attached. Radial grating (reference diffraction scale)
The laser beam formed from the laser light source 10 is
(Almost parallel light beam) LB is incident. This laser beam LB
Are polarized by the bifocal optical system 21 to be P-polarized light and S-polarized light.
When the light is separated into light and condensed at focal points 26a and 27a, P
The light intensity (light amount) of the polarized light and the S-polarized light has a predetermined ratio.
Has been adjusted as follows. Normally, the light reaching the wafer 4
However, the amount of light to the wafer 4 should be increased because
You. To do so, rotate the bifocal element around the optical axis.
Of the laser source and the radial grating 11
Insert a λ / 2 plate between them and rotate it around the optical axis
What is necessary is just to employ | adopt the structure which does. That is, by that
Light with polarized light reaching reticle 1 and polarized light reaching wafer 4
The quantity ratio can be adjusted to the optimal one. Well, radial gre
± 1 order light LBI from the lighting 11
Incident on the two-focal optical system 21 and + 1st-order light + LB ₁Is
+ LB of P polarization depending on polarization component_1PAnd + LB of S-polarized light_1S
And the diffraction angle with respect to the optical axis of the bifocal optical system 21
The reticle 1 is inclined by the determined angle. Similarly, -1
Next light-LB₁Also P-polarized -LB_1PAnd -LB of S-polarized light_1SWhen
+ 1st-order light (+ LB)_1P, + L
B_1SThe reticle 1 is reached at an angle symmetrical to that of the reticle 1. For P polarized light
As for the focal point 27a, that is, the diffraction grating
To form an image at the position of the peak RM, the primary light of P-polarized light + LB
_1P, -LB_1PCrosses at the diffraction grating mark RM.
Image). In FIG. 2, the grid arrangement direction of the mark RM is
In the horizontal direction in the paper plane, primary light + LB_1P, -LB_1Pof
The direction of tilt from each optical axis is also defined in the plane of FIG.
You. The reticle 1 has a diffraction grating as shown in FIG.
The mark RM and the transparent window Po are formed.
Light + LB_1P, -LB_1PAre both mark RM and window Po
Irradiate the reticle 1 with a size that covers. Fig. 3
The mark RM shown in (a) is in the x direction (grid arrangement direction).
Diffraction grating on wafer 4 used for position detection
The mark WM also corresponds to this, as shown in FIG.
ing. The mark WM is at the time of alignment (or at the time of exposure)
It is determined to be aligned with the position of the window Po of the reticle 1.
ing. Now, the first order of the S-polarized light emitted from the bifocal optical system 21
Light + LB_1S, -LB_1SIs formed once at the focal point 26a in space
After passing through the window Po of the reticle 1, the projection lens 3
To the diffraction grating mark WM of the wafer 4 via
The image is formed so as to enter from two directions. 3 projection lenses
S-polarized primary light + LB emitted from_1S, -LB_1SEach of
Is symmetric with respect to the grating arrangement direction of the diffraction grating mark WM.
Incident light. S-polarized primary light reaching wafer 4 +
LB_1S, -LB _1SIs large even if the angle formed by
Does not exceed the number of openings on the injection (wafer) side. still,
Reticle 1 and c for radial grating 11
Since the laser 4 and the laser 4 are arranged conjugate with each other,
Assuming that LB is a parallel light beam, each diffracted light beam + LB_1P,
-LB_1P, + LB_1S, -LB_1SAlso become a parallel light beam.

Here, the P-polarized primary light + LB _1P , -LB _1P
The behavior of the reticle 1 with respect to the mark RM will be described in detail with reference to FIG. FIG. 5 schematically shows the mark RM of the reticle 1, and it is assumed that the P-polarized primary light + LB _1P is incident on the mark RM at an angle of 6. At this time 1
The regular reflection light D _{1P of the} next light + LB _{1P on} the reticle 1 is also reflected at the angle 6. The light beam + LB _1P entering at an angle of 6 means that the light beam LB _1P has an angle of 6 and the specularly reflected light D
It means that it is incident on the reticle 1 in the opposite direction to _1P . Therefore, assuming that the grating pitch of the diffraction grating mark RM is P, the wavelength of the laser light beam LB is n, and n is an integer, the following (1)
The pitch P and the angle 8 are determined so as to satisfy the formula. sin θ = (λ / P) × n (1) If this equation (1) is satisfied, the primary light + LB _1P , −LB _1P
The diffracted light 104 of a specific order generated from the mark RM due to the irradiation of 1 travels in the direction perpendicular to the reticle 1, that is, in the direction along the optical axis of the bifocal optical system 21. Of course, other diffracted light 103 is also generated, but this travels in a different direction from the diffracted light 104.

By the way, the mark RM of the reticle 1 is irradiated from two directions so that the light fluxes + LB _1P and -LB _1P intersect each other, and both the light fluxes are emitted from the same laser light source 10. Two luminous fluxes + L above
The interference between B _1P and −LB _1P causes light and dark cotton, so-called interference fringes. Assuming that the radial grating 11 is stopped, the interference fringes are arranged at a predetermined pitch in the grid arrangement direction of the marks RM. The pitch of the interference fringes and the grating pitch of the mark RM are appropriately determined according to the required detection resolution. Therefore, the diffracted light 104 from the mark RM is generated by irradiating the mark RM with the interference fringes. Alternatively, one light beam + LB
_The diffracted light generated from the mark RM by the irradiation of _1P and the diffracted light generated from the mark RM by the irradiation of the other light beam −LB _1P return on the same optical path (on the axis of the bifocal optical system 21) and interfere with each other. It is also considered to have been done. In this way, the light flux LB _1P , −LB from the two different directions on the mark RM is
_{When 1P} is irradiated, interference fringes are generated on the mark RM,
If the radial grating 11 is rotating,
The interference fringes move (flow) in the grating arrangement direction of the marks RM. This is Radial Grating 1
This is because the clear field image formed by the primary light beams + LB ₁ and −LB ₁ of No. ₁ is formed on the mark RM of the reticle 1. Therefore, interference fringes on the mark RM (diffraction image projected by the bifocal optical system 21 of the radial grating 11)
The scanning of the beam causes the diffracted light 104 to repeatedly change in brightness and darkness. Therefore, the signal from the photoelectric detector 25 is a sinusoidal AC signal corresponding to the cycle of the light / dark change.

The above is the same in the relationship between the diffraction grating mark WM on the wafer 4 and the S-polarized light beams + LB _1S and -LB _1S, and the diffracted light 105 is emitted from the mark WM.
Occurs along the chief ray of the projection lens 3,
It reaches the photoelectric detector 25 through the window Po of the reticle 1. S-polarized light beam + L emitted from bifocal optical system 21
B _1S and -LB _1S are imaged so as to intersect at the focal point 26a, but are largely defocused at the mark RM of the reticle 1 and the window Po.

The photoelectric detector 25 is a bifocal optical system 21.
Although the mark RM and the mark WM are arranged so as to be conjugate with each other through the mark, in reality, as shown in FIG.
A mask member 25 'as shown in FIG. 3C is provided at a position conjugate with each of M and WM, and the diffracted light 104, 105 transmitted through the apertures A _P , A _S of the mask member 25'.
Is photoelectrically detected. Where aperture A
_P is the diffracted light 10 from the mark RM of the reticle 1, for example.
4 to extract the diffraction image, and the aperture A _S
Is for extracting a diffraction image by the diffracted light 105 from the mark WM of the wafer 1. Therefore, by providing the photoelectric detector 25 separately after each aperture A _P , A _S ,
The position detection of the reticle 1 by the mark RM and the position detection of the wafer 1 by the mark WM can be performed independently. The aperture A _P has an image of the mark RM of the reticle 1 illuminated by the P-polarized light beams + LB _1P and −LB _1P , but at the same time the S-polarized light beams + LB _1S and −LB _1S reflected and diffracted light are also in the background. It comes in as noise. Therefore, it is preferable that the aperture AP is provided with a polarizing plate that transmits P-polarized light, and the aperture A _S is provided with a polarizing plate that transmits S-polarized light. By doing so, crosstalk in which light from the wafer and light from the reticle are mixed in each of the two photoelectric detectors 25 is sufficiently reduced.

Here, the photoelectric signal of the diffracted light 104 obtained through the aperture A _P when the radial grating 11 is stopped will be analyzed. When n = ± 1 in the above equation (1), the grating pitch P is the same as the pitch of the reference grating of the radial grating 11 and the lens 1
There is a relationship of the magnification after formation through the third and second focus optical systems 21.
(Similarly, the grid pitch of the mark WM on the wafer 4 is also
It is related to the grating pitch P of the mark RM and the imaging magnification of the projection lens 3. Now, the light beam + L incident on the mark RM
The amplitude VR ^{+ of the} diffracted light generated by B _1P is given by the equation (2), and the amplitude VR ^{+ of the} diffracted light generated by the light beam −LB _1P
^- is given by the equation (3). VR ⁺ = a · sin [φ + 2π (x / P)] …… (2) VR ⁻ = a ′ · sin [φ-2π (x / P)] …… (3) where P is the grating pitch of the mark RM. And x is the amount of displacement of the marks RM in the lattice array direction. Since the two diffracted lights VR ⁺ and VR ⁻ which interfere with each other are photoelectrically detected, the change in the photoelectric signal (amplitude of the diffracted light 104) is expressed by the equation (4). │VR ^{+ +} VR ^- in ^{│ 2 = a 2 + a '} 2 +2 · a · a' · cos [4 [pi] (x / P)] ...... (4) where a ² + a ^'2 is signal bias (DC component) Yes, 2a · a ′ is the amplitude component of the signal change. As is apparent from equation (4), the photoelectric signal changes in a sine wave form when the radial grating 11 and the mark RM are relatively displaced in the lattice arrangement direction. The relative displacement x
However, each time x = P / 2 (half the grating pitch), the signal width changes by one cycle. On the other hand, the same applies to the diffracted light 105 from the mark WM on the wafer 4, (4)
It is expressed as an equation. Then, the alignment is completed by moving the reticle 1 or the wafer 4 so that the phase relationship between the two photoelectric signals matches. However, as can be seen from the equation (4), since each signal has a sine wave shape and the detectable phase difference is within a range of ± 180 °, the reticle 1 and the wafer 4 have the grating pitch P of the marks RM and WM in advance. It must be pre-aligned with an accuracy of 1/2 or less. When the radial grating 11 is stopped in this way, the amplitude level of the obtained photoelectric signal is changed to a sine wave shape only by moving the chipule 1 or the wafer 4.

By the way, when the radial grating 11 is rotated, the diffracted lights 104 and 105 become periodic (sinusoidal) light and dark information, and the obtained photoelectric signal assumes that the reticle 1 or the wafer 4 is stationary. Also becomes a sinusoidal AC signal. Therefore, in this case, the photoelectric signal (sine wave AC signal) from the photoelectric detector 19 shown in FIG. 1 is used as a basic signal, and the position of the diffracted light 104 from the mark RM is higher than that of the photoelectric signal (sine wave AC signal). The phase difference φ _r is detected by the phase detection system. Similarly, the phase difference φ _W between the photoelectric signal of the diffracted light 105 from the mark WM and the basic signal is detected. Then, if the difference between the phase differences φ _r and φ _W is obtained, the amount of deviation between the reticle 1 and the wafer W in the x direction can be known. This detection method is called a so-called optical heterodyne method, and if the reticle 1 and the wafer 4 are within the position error range of 1/2 of the grating pitch P, the positional deviation can be detected with high resolution even in a stationary state. , It is convenient to apply the closed-loop position servo so that a minute positional deviation does not occur while the pattern of the reticle 1 is exposed on the resist of the wafer 4. In this detection method, the reticle 1 or the wafer 4 is moved so that φ _r −φ _W becomes zero (or a predetermined value) to complete the alignment, and then the reticle 1 and the wafer 4 are relatively moved at the alignment position. Servo so as not to move
Can be locked.

In the above description of the present embodiment, only one set of alignment optical system is provided for detecting the positional deviation in the x direction.
Actually, two sets or three sets are required, and alignment in x direction, y direction, or alignment in x direction, y direction, 6 direction is performed. When arranging three sets of alignment optical systems, the mark arrangement on the wafer is, for example, the fourth arrangement.
The one shown in the figure is conceivable. FIG. 4 shows three diffraction grating marks WMx, WMy, WM6 associated with one shot area SA on the wafer. The marks WM white, WM
y is provided at both ends of the shot area, and both are used for detecting deviation in the y direction. A relative rotation error with respect to the reticle 1 is obtained for each shot from the difference between the deviation amounts of the marks WMy and WM8. The marks WMx, WMy, WM in FIG.
Although 6 is provided in the shot area, it may be provided on the scribe line (street line) SL.

As described above, in the present embodiment, the exposure light and the alignment illumination light are separated by the dichroic mirror 22, and the alignment optical system simultaneously observes the reticle and the wafer with the illumination light that does not easily expose the resist even during the exposure. I can do it. In addition, since the illumination light for alignment is bifocalized so as to correspond to the chromatic aberration amount of the projection lens by using the bifocal optical system, a correction optical system as in the past is provided in the alignment optical path between the reticle and the wafer. It is possible to directly detect the mark on the reticle and the mark on the wafer for high-precision alignment without the need to provide them. In addition, the alignment mark is a diffraction grating that can detect misalignment with high resolution, and a sinusoidal level change of the diffracted light generated according to the periodic structure of this diffraction grating is captured, so that a wavelength that is transparent to the resist is used. In combination with the use of the illumination light (non-photosensitive light), extremely stable and highly accurate positional deviation detection becomes possible. Further, in this embodiment, the radial grating is rotated so that two light fluxes + LB _1P , _−LB that illuminate the diffraction grating mark from two directions.
LB _1P (or + LB _1S , -LB _1S ) is provided with a phase difference to detect the positional deviation of the optical heterodyne method, but the laser beam LB is made a Zeeman laser and made incident on a fixed reference diffraction grating. Similarly, the optical heterodyne method can also be used to obtain two luminous fluxes, or to obtain two laser fluxes having slightly different frequencies using an ultrasonic photocopper (AOM) or the like. Come on. In particular, when an ultrasonic optical modulator is used, there is no need for a mechanical movable part such as radial grating, and the frequency difference due to modulation can be several steps larger than in the case of radial grating. There are advantages such as higher resolution.

In this embodiment, the wavelength of the exposure light is different from that of the alignment light, and the amount of chromatic aberration is large. Therefore, a detection optical system using a bifocal element is used. However, when the projection lens itself is aberration-corrected for the two wavelengths, a bifocal element is not required, and a telecentric objective lens achromatized at the two wavelengths is sufficient. Even in this case, the light receiving surface of the detection system can separate and receive the signal from the wafer and the signal from the reticle. This is because the wafer, reticle, and light receiving surface are each conjugate even under the wavelength of the alignment light.

Further, the wavelengths of the exposure light and the alignment light may be approximated. In this case, a large amount of chromatic aberration does not occur depending on the projection lens, but since the light source is substantially different, aberrations that may affect the alignment accuracy may remain. Therefore, the achromatized telecentric objective lens is used as the detection optical system. Is used. In such a case, if there is no light source that generates alignment light close to the wavelength of the exposure light, a laser beam can be made incident on the nonlinear crystal to generate a harmonic from the crystal, which can be used. In particular, in the case of an exposure apparatus using an excimer laser, there may be no laser that continuously oscillates at a wavelength close to the exposure wavelength. In such a case, it is preferable to use a nonlinear crystal to extract desired alignment light.

As described above, in this embodiment, a detection optical system such as a bifocal optical system is provided in the optical path of the illumination light of the alignment optical system, and the illumination light itself is double-focused (achromatic) corresponding to the amount of chromatic aberration. By doing so, it becomes unnecessary to provide a correction optical system between the mask (reticle) and the projection optical system. Therefore, despite the fact that the mark (diffraction grating) is detected with light having a wavelength different from the exposure light, various problems caused by the conventional correction optical system are eliminated, and extremely stable alignment can be performed. Further, in order to detect the relative positional deviation between the grating on the mask and the grating on the substrate, the bifocal optical system (so that the illumination light for alignment is emitted from two different directions with respect to the arrangement direction of each grating The alignment characteristics of the alignment illumination light incident on the detection optical system) are controlled. For this reason, regular reflection light and diffraction light (± first-order light, ± second-order light, etc.) generated from each grating are clearly separated, and misalignment between gratings using diffraction light can be accurately detected. Desired. Further, by making illumination light incident on the diffraction grating from two directions, the diffracted light generated by irradiation from one direction and the diffracted light generated by irradiation from the other direction are made to have the same optical path and interfere with each other. Therefore, the so-called optical heterodyne method can be easily adopted, the resolution of the positional deviation measurement becomes sufficiently high accuracy, and the measurement reproducibility and stability are sufficiently improved.

[0030]

As described above, according to the present invention, since the frequency modulator and the alignment object (substrate, reference grating) have a conjugate relationship, the alignment method using the diffraction grating
An alignment error does not occur even if the frequency modulator is displaced or air fluctuation occurs in the optical path between the frequency modulator and the alignment target. Therefore, it is possible to simultaneously satisfy the stability as a device and the alignment accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a projection exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of only an alignment system.

3A is a plan view showing a shape of a diffraction grating mark on a reticle, FIG. 3B is a plan view showing a shape of a diffraction grating mark on a wafer, and FIG. It is a top view which shows the shape of the provided mask member.

FIG. 4 is a plan view showing an arrangement of marks on a wafer.

FIG. 5 is a diagram showing how a laser beam is incident.

[Description of Signs of Main Parts]

 DESCRIPTION OF SYMBOLS 1 ... Reticle 3 ... Projection lens 4 ... Wafer 10 ... Laser light source 11 ... Radial grating 21 ... Bifocal optical system 25 ... Photoelectric detector 25 '... Mask member 30 ... Mercury lamp

[Procedure amendment]

[Submission date] December 5, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Name of invention

[Correction method] Change

[Correction contents]

Title: Positioning device, exposure device and exposure method

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0011

[Correction method] Change

[Correction contents]

[0011]

SUMMARY OF THE INVENTION The present invention solves various problems that occur when an alignment method using a diffraction grating is applied to an alignment apparatus or a projection exposure apparatus, and stability and alignment of the apparatus are achieved. This was done in order to satisfy both the improvement of accuracy and the accuracy. In the present invention, illuminating the mark on the substrate held on the movable stage,
In a device for aligning a substrate by controlling the movement of the stage based on a photoelectric signal obtained by receiving diffracted light generated from the mark, a light source that emits illumination light for illuminating the mark on the substrate. A frequency modulator that receives illumination light and generates a pair of illumination lights having a predetermined frequency difference; and a frequency modulator and a substrate for irradiating the mark with the pair of illumination light at a predetermined crossing angle A first irradiating optical system that makes the two mutually conjugate with each other; a beam splitter arranged in an optical path of the first irradiating optical system to split a pair of illuminating lights; see a pair of split illuminating lights A second irradiation optical system that makes the frequency modulator and the reference mark conjugate with each other in order to irradiate the mark at a predetermined crossing angle; Cycle according to frequency difference Photoelectric detection that outputs a first alternating-current signal whose intensity changes and also receives an interference light of two diffracted lights generated from a reference mark and outputs a second alternating-current signal whose intensity changes at a frequency according to a predetermined frequency difference. Means and first
Measuring means for measuring the positional deviation amount of the mark with respect to the reference mark by measuring the phase difference between the AC signal and the second AC signal; and controlling the movement of the stage based on the measured positional deviation amount. And a control system. In addition, the substrate is aligned by illuminating the mark on the substrate held on the movable stage and controlling the movement of the stage based on the photoelectric signal obtained by receiving the diffracted light generated from the mark. A light source that emits illumination light for illuminating the mark; two light flux generating means that emits the illumination light to generate a pair of illumination light, and a pair of illumination light to the mark at a predetermined intersection angle. An irradiation optical system for irradiating with a mark; photoelectric detection means for receiving interference light of two diffracted lights generated from the mark and outputting a photoelectric signal; measuring means for measuring the position of the mark based on the photoelectric signal; And a control system for controlling the movement of the stage based on the measured position of the mark. Further, in an exposure apparatus that transfers a mask pattern onto a substrate held on a movable stage, a light source that emits illumination light for illuminating a mark on the substrate; Two light flux generating means for generating light; a first irradiation optical system for irradiating the mark with a pair of illumination lights at a predetermined crossing angle;
A beam splitter arranged in the optical path of the first irradiation optical system to divide a pair of illumination light; a second irradiation optical system for emitting the divided pair of illumination light to a reference mark at a predetermined crossing angle And; receiving the interference light of two diffracted lights generated from the mark and outputting the first photoelectric signal, and receiving the interference light of two diffracted lights generated from the reference mark and outputting the second photoelectric signal. Photoelectric detecting means; measuring means for measuring the positional deviation amount of the mark with respect to the reference mark based on the first photoelectric signal and the second photoelectric signal; and controlling the movement of the stage based on the measured positional deviation amount. A control system for aligning the substrate and the mask was provided. Further, in the exposure method of transferring the pattern of the mask onto the substrate held on the movable stage, the illumination light from the light source is changed to 2
Incident on the light flux generating means; irradiating a pair of illumination light from the two light flux generating means with a predetermined frequency difference to the mark on the substrate through the first irradiation optical system; first irradiation Irradiating a pair of illumination light beams split by a beam splitter arranged in the optical path of the optical system to the reference mark via the second irradiation optical system;
The amount of positional deviation of the mark with respect to the reference mark is measured based on the interference light of one diffracted light and the interference light of the two diffracted light generated from the reference mark, and the movement of the stage is controlled based on the measured amount of positional deviation. By aligning the substrate with the mask. The exposure method according to claim 3, wherein the exposure relationship is established.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0012

[Correction method] Change

[Correction contents]

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Next, the structure of an alignment apparatus according to an embodiment of the present invention will be described with reference to FIG. A reticle 1 having a predetermined circuit pattern and a diffraction grating mark for alignment is held by a reticle slug 2 which is two-dimensionally movable. Each pattern on the reticle 1 is imaged on the wafer 4 under exposure light by the projection lens 3 which is telecentric on both sides. However, the projection lens 3 is satisfactorily corrected for chromatic aberration with respect to the wavelength of illumination light for exposure (g-line, i-line, etc.), and the reticle 1 and the wafer 4 are arranged so as to be conjugate to each other with respect to the wavelength of exposure. You. Diffraction grating marks similar to the grating marks formed on the chicle 1 are also formed on the wafer 4. The wafer 4 is attracted onto the stage 5 which moves two-dimensionally in a step-and-repeat manner. When the transfer exposure of the reticle 1 to one shot area on the wafer 4 is completed, the wafer 4 is stepped to the next shot position. Some of the reticle stage 2, x direction in the horizontal plane of the reticle 1, y-direction and rotation (theta) laser light waves for detecting the direction of the position interferometric side length unit (hereinafter referred to as an interferometer) 43 A movable mirror 6 that reflects the laser beam from is fixed. This interferometer 4
Reference numeral 3 has three side length laser beams for independently detecting the positions in the x-direction, the y-direction, and the θ- direction, but here, for simplification of description, the illustration is omitted. The moving stroke of the reticle stage 2 is several millimeters or less, and the detection resolution of the interferometer 43 is set to about 0.01 μm, for example. On the other hand, a movable mirror 7 for reflecting the laser beam from the interferometer 45 for detecting the position of the wafer 4 in the horizontal direction in the horizontal plane is fixed to the negative part of the wafer stage 5. This interferometer 45 is also in the x direction,
Although two laser beams for shelf length are provided to detect the position in the y direction independently, the illustration is omitted here for simplification of the description. X direction of reticle stage 2,
Driving in the y and 6 directions is performed by the drive motor 42, and the two-dimensional movement of the wafer stage 5 is performed by the drive motor 46.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction contents]

Next, the alignment system of this embodiment will be described. Illumination light for alignment are emitted from the laser light source 10, through the radial grating 11 formed a transmissive reference diffraction grating radially Fourier plane through the Fourier transform lens 13 and the beam-flop splitter 14 (the alignment optical system Reach the spatial filter 15 arranged on the pupil plane of the. The radial grating 11 is configured to be rotatable by a motor 12 at a substantially constant speed.
The laser light incident on the radial grating 11 is diffracted like 0th order light, ± 1st order light, ± 2nd order light.
Each spreads at a different diffraction angle. In FIG. 1, 0
Only the next light LBo, the + 1st order light + LB ₁ and the −1st order light −LB ₁ are shown. These 0th order light and ± 1st order light are spatial filters 1
5 are clearly separated and distributed, and only the 0th-order light LBo is blocked and the ± 1st-order lights are transmitted. The ± first-order light that has passed through the spatial filter 15 passes through the beam splitter 20 and enters the bifocal optical system 21. Although the bifocal optical system 21 is simply shown in FIG. 1, it is actually composed of a combination of a birefringent substance (quartz, calcite, etc.) and a telecentric objective lens for a microscope or the like. Different powers are given depending on the polarization components (P-polarized light and S-polarized light) of the ± first-order light. Thus bifocal optical system 21 while polarized light emitted (for example, P polarized light) focused on the focal point 26a of the upper space of les chicle 1, other polarization (e.g., S-polarized light) and the lower surface of the pattern surface of the reticle 1 An image is formed at the matched focal point 27a. The other focal point of the bifocal optical system 21, that is, the plane conjugate with the focal points 26a and 27a on the laser light source 10 side is designated as the radial grating 11.
Here, the distance between the two focal points 26a and 27b of the bifocal optical system 21 in the optical axis direction corresponds to the amount of chromatic aberration on the reticle 1 side of the projection lens 3 at the wavelength of the alignment laser light. This focal plane 26a becomes conjugate with the back surface 26b which is the surface of the wafer 4 by the projection lens 3, and the focal plane 27a (reticle pattern surface) is spatially downwardly separated from the surface of the wafer 4 by the projection lens 3. Back surface 27
Becomes conjugate with b. The distance between the rear surfaces 26b and 27b corresponds to the amount of chromatic aberration on the wafer 4 side of the projection lens 3. Here, the distance between the rear surfaces 26b and 27b is Dw, and the focal plane 26
a and 27a, and the projection magnification of the projection lens 3 is 1 / M (usually M is 1, 25, 5, 10), Dr = M2. Dw. As the wavelength of the laser light for alignment becomes farther from the wavelength of the exposure light, Dw and Dr become larger according to the aberration characteristics of the projection lens 3. The depth of focus of this type of projection lens is extremely shallow, about ± 1 μm, and the distance Dw may reach several tens of μm depending on the wavelength of the alignment illumination light. The illumination light (laser light) for alignment is
It is desirable that the wavelength has almost no sensitivity to the resist coated on the substrate, but this is not necessarily the condition to be satisfied in the present invention. This is because the projection lens causes an extremely large aberration between the wavelength of the exposure light and the wavelength of the illumination light for alignment, and in particular, a large distortion is applied to the optical information itself from the diffraction grating mark on the wafer 4. Therefore, it is more important to give priority to determining the optimal illumination light for alignment in consideration of the aberration. Therefore, when the alignment illumination light irradiates the resist for a long time (for example, 1 minute or more), the wavelength may be weakly sensitive such that the resist is exposed (a thinning occurs after development).

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0015

[Correction method] Change

[Correction contents]

The ± 1st-order light LB · (S-polarized light) of the alignment laser light is added to the + 1st-order light + LB ₁ and −1st-order light −LB on the diffraction grating mark portion of the reticle 1 on the focal plane 27a.
_The light enters from two directions at an angle of ₁ and forms an image. Further, the ± first-order light LB · (P-polarized light) from the focal plane 26 a that has passed through the transparent portion of the reticle 1 is transmitted through the projection lens 3 to the focal plane 26 a.
b, the +1 order light and -1
It forms an image by entering from two directions at an angle formed by the next light. Then, the diffracted light reflected from the diffraction grating mark of the reticle 1 is reflected by the beam splitter 20 via the dichroic mirror 22, the bifocal optical system 21, filtered by the spatial filter 23, and then the photoelectric detector 25 by the condenser lens 24. Reach Further, the diffracted light reflected from the diffraction grating mark on the wafer 4 returns to the original optical path through the projection lens 3, passes through the transparent portion of the reticle 1, and passes through the dichroic mirror 2.
It reaches the photoelectric detector 25 through the bifocal optical system 21, the beam splitter 20, the spatial filter 23, and the condenser lens 24. The spatial filter 23 is arranged at a position conjugate with the pupil plane of the alignment optical system, that is, at a position substantially conjugate with the pupil (exit pupil) of the projection lens 3, blocks the specular reflection light from the reticle 1 or the wafer 4, and It is defined to pass only light diffracted in the vertical (law line direction of the surface) in the diffraction grating of 1 or wafer 4. And photoelectric detector 2
The reticle 1 and the wafer 4 are arranged to be conjugate with each other via the bifocal optical system 21 and the lens 24.

[Procedure amendment 7]

[Document name to be amended] Statement

[Name of item to be corrected] 0025

[Correction method] Change

[Correction contents]

In the above description of the present embodiment, only one set of alignment optical system is provided for detecting the positional deviation in the x direction.
Actually, two sets or three sets are required, and alignment in x direction, y direction, or alignment in x direction, y direction, θ direction is performed. When arranging three sets of alignment optical systems, the mark arrangement on the wafer is, for example, the fourth arrangement.
The one shown in the figure is conceivable. FIG. 4 shows three diffraction grating marks WMx, WMy, WM θ associated with one shot area SA on the wafer, and the marks WM white, WM
y is provided at both ends of the shot area, and both are used for detecting deviation in the y direction. Mark WMy, relative rotation error of the reticle 1 every shot from the difference between the amount of deviation of the WM theta is determined. The marks WMx, WMy, WM in FIG.
Although θ is provided in the shot area, it may be provided on the scribe line (street line) SL.

[Procedure amendment 8]

[Document name to be amended] Statement

[Correction target item name] 0030

[Correction method] Change

[Correction contents]

[0030]

As described above, according to the present invention, the object to be aligned (the substrate and the reference grating) is illuminated with a pair of illumination lights from the two light flux generating means provided separately from the light source. It is possible to irradiate the alignment target with the illumination light at a desired angle. In addition, since the alignment target (substrate, reference grating) has a conjugate relationship with the frequency modulator, in the alignment method using the diffraction grating, the frequency modulator is displaced or the frequency modulator and the alignment target are aligned. Since there is no alignment error even if air fluctuations occur in the optical path between and, the frequency modulator and the alignment target (substrate, reference grating) have a conjugate relationship, so in the alignment method using the diffraction grating, An alignment error does not occur even if the frequency modulator is displaced or air fluctuation occurs in the optical path between the frequency modulator and the alignment target. Therefore, it is possible to simultaneously satisfy the stability as a device and the alignment accuracy.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 21/30 525R 525K

Claims (1)

[Claims] 1. Illuminating a grating mark on a substrate held on a movable stage, and controlling movement of the stage based on a photoelectric signal obtained by receiving diffracted light generated from the grating mark. An apparatus for aligning the substrate by means of a light source for emitting a coherent beam for illuminating a grating mark on the substrate; a pair of illumination beams for injecting the coherent beam and having a predetermined frequency difference A frequency modulator for generating a pair of illumination beams for irradiating the pair of illumination beams to the grating mark at a predetermined crossing angle, and a first irradiation optical system for making the frequency modulator and the substrate conjugate with each other. When;
A beam splitter disposed in the optical path of the first irradiation optical system for splitting the pair of illumination beams; and for illuminating the split pair of illumination beams on a reference grating at a predetermined crossing angle. A second irradiation optical system that makes the frequency modulator and the reference grating mutually conjugate with each other; receives interference light of two diffracted beams generated from the grating mark, and responds to the predetermined frequency difference. A first AC signal whose intensity changes periodically, and a second AC signal whose intensity changes at a frequency corresponding to the predetermined frequency difference by receiving interference light of two diffracted beams generated from the reference grating. Photoelectric detecting means for outputting; measuring means for measuring a positional deviation amount of the lattice mark with respect to the reference lattice by measuring a phase difference between the first AC signal and the second AC signal;
And a control system that controls the movement of the stage based on the measured amount of positional deviation.