JPH06241726A - Position detection device - Google Patents

Abstract

PURPOSE:To provide a position detection device having simple constitution and a sing a heterodyne interference method. CONSTITUTION:Light flux Lo from a white light source 10 is made to be incident on an acoustic/optic modulation element (AOM) 17 in parallel to wave front of the progressive wave in AOM<17, so that two light fluxes occurring symmetrically to light axis in Raman-Nath diffraction in AOM17, Lo(1), LO(-1), are led to a beam splitter 28 through relay optical system 18a, 18b, relay optical system 26, 27, etc. The two light fluxes penetrating through the beam splitter 28 irradiate a diffraction lattice mark RM on a reticle 1 through an objective lens 38. Then, the two light fluxes passing through a window in the vicinity of the diffraction lattice mark RM irradiate a diffraction lattice mark WM on a wafer through an objective lens 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterodyne type position detecting device, and is particularly suitable for application to a position aligning device for highly accurately aligning a wafer or a mask in a semiconductor manufacturing apparatus. is there.

[0002]

2. Description of the Related Art In recent years, a pattern image of a photomask or a reticle (generally referred to as a "reticle" hereinafter) is projected in order to form a fine pattern of a semiconductor device or a liquid crystal display device with high resolution by using a photolithography technique. A projection exposure apparatus (for example, a so-called stepper) that transfers images onto a photosensitive substrate via an optical system is often used. For example, in the case of manufacturing a semiconductor element, it has been particularly required recently to increase the density of a circuit pattern to be manufactured, and a projection exposure apparatus is also required to accurately transfer a finer pattern onto a wafer. ing.

Further, since a semiconductor element is generally formed by stacking a large number of layers of circuit patterns on a wafer, when transferring the circuit patterns to the second and subsequent layers on the wafer, the circuits that have been formed by that time. It is necessary to perform highly accurate alignment between the pattern and the pattern of the reticle to be transferred. As the density of the circuit pattern to be manufactured as described above increases, it is required to improve the alignment accuracy.

As a position detecting device for detecting the position of a reticle and / or a wafer with high accuracy when performing alignment with such high accuracy, for example, Japanese Patent Laid-Open No. 62-26100.
Japanese Patent No. 3 discloses an apparatus that performs highly accurate position detection by using the heterodyne interferometry. This position detecting device uses a Zeeman laser light source that emits a light beam including a P-polarized component and an S-polarized component that have slightly different frequencies as a light source for position detection. In this case, the light beam from the Zeeman laser light source is split into a P-polarized light beam having a frequency f ₁ and an S-polarized component light beam having a frequency f ₂ by a polarization beam splitter, and each of the thus split light beams is reflected. The diffraction grating mark as an alignment mark formed on the reticle is irradiated from two predetermined directions via the mirror. Further, a transmission window is provided on the reticle at a position adjacent to the diffraction grating mark, and a part of the light beam irradiated on the diffraction grating mark is part of the alignment mark formed on the wafer through the transmission window. The above diffraction grating mark is irradiated from two predetermined directions.

By irradiating each diffraction grating mark with two light fluxes having different frequencies from two directions in this way, diffracted lights generated from each diffraction grating mark are caused to interfere with each other through the polarizing plate of the detection system, and The interference light of 1 is photoelectrically converted by a photoelectric detector to obtain two optical beat signals. At this time, the relative phase difference between the two optical beat signals is the amount of deviation between the position of the two light beams intersecting on the diffraction grating mark on the reticle and the position of the two light beams intersecting on the diffraction grating mark on the wafer. To cope with this, for example, by using one of the detected optical beat signals as a reference signal, the reticle and the wafer are relatively moved so that the phase difference becomes a predetermined amount (for example, zero). Alignment is performed.

However, this Japanese Patent Laid-Open No. 62-2610
In the position detecting device disclosed in Japanese Patent Laid-Open No. 03-2003, it is difficult to completely separate the P-polarized component and the S-polarized component, and for example, a light beam with an original frequency f ₁ applied to a diffraction grating mark has a frequency f. There is a disadvantage that the light flux of ₂ is mixed and the obtained optical beat signal has a poor SN ratio. Therefore, in Japanese Patent Laid-Open No. 2-227604, another position detecting device has been proposed which performs position detection with a good SN ratio by using the heterodyne interferometry.

In this position detecting device, a light beam from a laser light source is split into two by a beam splitter or the like, and then each light beam is passed through two different acousto-optic modulators (AOMs) so that the two light beams have a frequency difference. Have.
Then, the two light beams having different frequency differences from each other are applied to the diffraction grating marks on the reticle and the wafer from two directions, and the diffracted lights generated from the diffraction grating marks in the same direction are caused to interfere with each other. Of the interference light is photoelectrically converted by a photoelectric detector to obtain two optical beat signals, and highly accurate relative alignment between the reticle and the wafer is realized by using these two optical beat signals. According to this configuration, the light beams of different frequencies are not mixed, and the position detection is performed with a good SN ratio.

[0008]

However, in the position detecting device by the heterodyne interferometry method disclosed in Japanese Patent Laid-Open No. 2-227604, in order to generate two light beams (heterodyne beams) having different frequencies from each other. , An optical member (a beam splitter or the like) for splitting a light beam from a laser light source, and two acousto-optic modulators for giving a frequency difference to two light beams emitted from this optical member are used, and the structure is There was the inconvenience of being complicated and large. In addition, in a configuration in which two light fluxes having different frequencies are obtained by arranging two acousto-optic modulators, it is difficult to adjust each optical member, and it is difficult to keep the position detection accuracy within a predetermined allowable value. There was also.

Further, in the position detecting device by the heterodyne interferometry method disclosed in the above-mentioned Japanese Patent Laid-Open No. 2-227604, the light beam from the laser light source is split to generate two light beams (heterodyne beams) having different frequencies. At that time, the optical path difference between the two divided light fluxes was larger than the wavelength. Therefore, in principle, there is no choice but to use monochromatic light such as a laser beam as the light for position detection, and even if a resist (photosensitive material) is applied on the wafer to transfer the circuit pattern on the reticle. However, if the alignment is attempted by using the above, there is a disadvantage that the alignment accuracy is lowered due to the adverse effect of the thin film interference due to the resist.

Further, in general, as a wafer undergoes each process, the cross-sectional shape of the alignment mark collapses and the cross-sectional shape becomes asymmetric. In this case, in the method of aligning using the interference of monochromatic light such as a laser beam,
Since the cross-sectional shape of the alignment mark becomes asymmetric, there is a disadvantage that the position detection accuracy of the alignment mark is reduced.

In view of the above-mentioned problems, it is an object of the present invention to provide a position detecting device using the heterodyne interferometry which has a relatively simple structure and facilitates adjustment of each optical member. Furthermore,
The present invention reduces the detection error due to thin film interference of light for position detection on the photosensitive material on the substrate onto which the pattern of the reticle is transferred and the detection error due to the asymmetry of the alignment mark to achieve highly accurate position detection. Another object of the present invention is to provide a position detection device using the heterodyne interferometry capable of performing the above.

[0012]

A position detecting device according to the present invention has two different frequencies as shown in FIG. 1, for example.
Two light flux generating means for generating a light flux and two light fluxes for the diffraction grating (RM, WM) formed on the object (1, 4) by condensing the two light fluxes from the two light flux generating means. Objective optical system (38 or 38, 3) for irradiating the light from two predetermined directions
And a detector (36, 33) for photoelectrically detecting the diffracted lights generated from the diffraction gratings (RM, WM) via the objective optical system (38 or 38, 3), and 1,4)
In the position detecting device for detecting the position of the light source, the two light flux generating means diffracts and diffracts the light flux supplied from the light source means (10 to 12) that supplies the light flux of a single wavelength or a plurality of wavelengths. Frequency difference generation means (17) for generating two light fluxes having a predetermined frequency difference from the light flux from the light source means by using the traveling wave to be modulated, and frequency difference generation from the light source means (10-12) The luminous flux supplied to the means (17) is made incident parallel to the wavefront of the traveling wave, and two diffracted lights of different orders generated by the traveling wave and having different frequencies are generated in the objective optical system ( 38 or 38, 3).

Further, for example, as shown in FIG. 6, the two-beam generating means is a relay optical system () for collecting two light beams of respective wavelengths having a predetermined frequency difference generated by the frequency difference generating means (17). 18a, 18b) and a traveling wave that diffracts and modulates the two light fluxes condensed by this relay optical system, and gives a second second frequency difference to the two light fluxes from the relay optical system. It is desirable to have a frequency difference generating means (60).

[0014]

According to the present invention, the light source means (10 to 1)
The luminous flux supplied from 2) is frequency difference generating means (17).
It is incident parallel to the wave front of the traveling wave inside. Assuming that the frequency difference generating means (17) is, for example, an acousto-optic modulator, as shown in FIG.
The light flux from 2) is incident parallel to the wavefront of the traveling wave of the ultrasonic wave generated in the acousto-optic modulator (17). Then, the incident light flux causes so-called Raman-Nath diffraction. That is, the 0th-order light from the acousto-optic modulator (17) is emitted parallel to the incident optical axis, and the ± n-order (n = 1, 2, ...) Diffracted light is diffracted symmetrically with respect to the incident optical axis. The two light beams of the same order (± n order) are uniformly ± nf (f is an acousto-optic modulator (1
7) The frequency of the ultrasonic wave in) is modulated.

Therefore, for example, in the case of ± 1st-order diffracted light, these two light beams become a heterodyne beam having a frequency difference of 2f. The position of the heterodyne interferometry can be detected by using these two light beams. In this case, by using the Raman-Nass diffraction, one acousto-optic modulator (17) can perform the two functions of dividing the luminous flux and imparting a frequency difference, thus simplifying the configuration of the device. And it is miniaturized.

Further, in the present invention, by using Raman-Nass diffraction, light of a plurality of wavelengths (multi-wavelength light) can also be used as light for position detection. To explain this, it is assumed that the frequency difference generating means (17) is an acousto-optic modulator. In this case, the light source means (10
A light flux including light of a plurality of wavelengths supplied from 12) enters parallel to the wavefront of the traveling wave of the ultrasonic wave in the acousto-optic modulator (17). Then, due to Raman-Nass diffraction, the ± n-order (n = 1.2 ...) Diffracted light is diffracted symmetrically with respect to the incident optical axis in the light flux of each wavelength, and the two light fluxes of the same order of each wavelength are uniform. Receive ± nf modulation. For example, in the case of ± first-order diffracted light, these two light beams become a heterodyne beam having a frequency difference of 2f. When these two light fluxes are relayed and re-imaged, there is no optical path difference between the two light fluxes for each wavelength, so at the re-imaging point, each wavelength has the same pitch,
Interference fringes flow in the same phase.

Therefore, the diffraction gratings (RM, WM) on the object to be inspected (1, 4) are illuminated from two directions at different predetermined angles for each wavelength, and this diffraction is performed. The interference fringes for each wavelength formed on the grating by the two light fluxes of each wavelength have no phase difference at all and almost completely match each other. Therefore,
Since the optical beat signal including the position information of the diffraction grating (RM, WM) can be superimposed and detected in a state in which the phase (phase of the optical beat signal) is aligned for each wavelength, the diffraction grating is obtained by the averaging effect of the detection signal. It is possible to detect the position with high accuracy while suppressing the adverse effect due to the asymmetry of (RM, WM). Moreover, since the diffraction grating (WM) on the object to be inspected (4) is irradiated with multi-wavelength light, there is also an adverse effect due to thin film interference of the photosensitive material (eg resist) on the object to be inspected (4). Can be suppressed.

Further, the acousto-optic modulator is, for example, several 10M.
Since it is driven at Hz, when only one acousto-optic modulator is used, the frequency difference between the obtained two light beams may become too large. On the other hand, for example, as shown in FIG. 7, the two-beam generating means condenses the two-beams of each wavelength having the predetermined frequency difference generated by the frequency difference generating means (17) ( 18a, 18b),
By using the traveling wave that diffracts and modulates the two light fluxes condensed by this relay optical system,
When it has the 2nd frequency difference production | generation means (60) which gives a predetermined 2nd frequency difference to a light beam, the frequency difference given by the frequency difference production | generation means (17) and the 2nd frequency difference production | generation means (60). ) And the frequency difference given by () are made to have opposite signs and the sizes are slightly different, the diffraction grating (RM, W
It is possible to easily set the frequency difference between the two light fluxes irradiated to M) to an appropriate value.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the position detecting device according to the present invention will be described below with reference to FIGS. FIG. 1 shows a schematic configuration of a projection exposure apparatus provided with the position detection apparatus of this embodiment. In FIG. 1, a transfer circuit pattern and an alignment circuit provided in the peripheral portion of the circuit pattern are used. The reticle 1 having the diffraction grating mark RM is 2
It is held on a reticle stage 2 which is dimensionally movable. The pattern formation surface of the reticle 1 is arranged so as to be conjugate with the exposure surface of the wafer 4 with respect to the projection objective lens 3.

An illumination optical system 40 is arranged obliquely above the reticle 1, and the exposure light from the illumination optical system 40 is reticle 1.
The reticle 1 is reflected downward by a dichroic mirror 6 obliquely installed at an inclination angle of 45 ° above, and illuminates the reticle 1 with a uniform illuminance distribution. The pattern on the reticle 1 illuminated in this way is transferred onto the wafer 4 by the projection objective lens 3. Diffraction grating marks WM for alignment similar to the diffraction grating marks RM formed on the reticle 1 are formed in the vicinity of each shot area on the wafer 4.

The wafer 4 is held on the wafer stage 5 which moves two-dimensionally by the step-and-repeat method, and when the transfer of the reticle pattern onto one shot area on the wafer 4 is completed, the next wafer 4 is transferred. Shot area is stepped to the exposure field of the projection objective lens 3. Reticle stage 2 and wafer stage 5
Each stage is provided with an interferometer (not shown) for independently detecting the position in the x direction, the y direction, and the rotational direction (θ direction) in each stage. Driving of each stage in each direction is performed by a drive motor (not shown). Done.

On the other hand, an alignment optical system for detecting the positions of the diffraction grating mark RM and the diffraction grating mark WM is provided above the dichroic mirror 6.
In this alignment optical system, the white light source 10 is a light source such as a Xe lamp or a halogen lamp that supplies light in a wavelength band different from the exposure light. White light from the white light source 10 is converted into a parallel light flux L ₀ by passing through a variable aperture 11 having a variable aperture and a condenser lens 12, and then a bandpass filter 13 for extracting light in a predetermined wavelength range. The light is incident on an acousto-optic modulator (hereinafter referred to as “AOM”) 17 in parallel to the wavefront of the traveling wave (details will be described later).

The AOM 17 is a high frequency signal S having a frequency f _1.
F ₁ is driven in, the light beam L ₀ in a predetermined wavelength region AO
Raman-Nasu diffraction effect by M17. here,
When the frequency of the light beam L ₀ in a predetermined wavelength band and f _0, 1 order diffracted light L ₀ of the light beam L ₀ (1) (hereinafter, referred to as "light beam L ₀ (1)".) By AOM17 (f ₀ + subjected to frequency modulation of f _1), -1-order diffracted light L ₀ of the light beam L ₀ (-1) (hereinafter referred to as "light beam L
₀ (-1) ". ) Undergoes frequency modulation of (f ₀ -f ₁ ) by the AOM 17.

Thereafter, the luminous flux L ₀ (1) and the luminous flux L ₀ (-1) are
After passing through the lens 18 a, the reflection mirror 20, the lens 18 b, and the lens 21, the beam splitter 22 divides the beam into two. A spatial filter 19 for extracting the first-order diffracted light L ₀ (1) and the −1st-order diffracted light L ₀ (-1) is provided between the relay optical system including the lenses 18a and 18b. Has been.

Light flux L transmitted through the beam splitter 22
₀ (1) and the light beam L ₀ (-1) are condensed by the lens 23, and on the reference diffraction grating 24 provided at this condensing position,
Interference fringes that flow along the pitch direction are formed. Then, the diffracted light passing through the diffraction grating 24 is photoelectrically detected by the detector 25 as an optical beat signal for reference. On the other hand, the light flux L ₀ (1) and the light flux L ₀ (-1) reflected by the beam splitter 22 are relay optical systems (26a, 26b, 27),
It passes through the beam splitter 28 and the plane-parallel plate 37.
The plane-parallel plate 37 is provided at the pupil conjugate position of the projection objective lens 3 or in the vicinity thereof so that the tilt angle is variable with respect to the optical axis of the alignment optical system, and has a function of maintaining telecentricity. Instead of the parallel flat plate 37, a member having a combination of a thick parallel flat plate for rough adjustment and a thin parallel flat plate for fine adjustment may be used.

The light flux L ₀ (1) and the light flux L ₀ (-1) that have passed through the plane-parallel plate 37 are passed through the objective lens 38 and the dichroic mirror 6 from two directions having a predetermined crossing angle on the reticle 1. Illuminate the diffraction grating mark RM. When the projection objective lens 3 is not corrected for chromatic aberration with respect to the alignment light, the objective lens 38 is disclosed in JP-A-63-283.
It is desirable to use a bifocal optical system proposed in Japanese Patent No. 129. As a result, the two light beams incident on the bifocal optical system are split into polarized light beams orthogonal to each other,
One polarized light beam toward the first focal point is condensed on the reticle, and the other polarized light beam toward the second focal point is condensed on the wafer.

The light beam L ₀ (1) and the light beam L ₀ (-1) illuminate the diffraction grating mark RM on the reticle. The reticle 1 has a diffraction grating mark RM as shown in FIG. A transmission window P ₀ for alignment light is provided in parallel with the RM, and the transmission window P ₀ is formed on the wafer 4 as shown in FIG.
_The diffraction grating mark WM is formed at a position corresponding to ₀ .

[0028] Then, the crossing angle when the light beam L ₀ (1) and the light beam L ₀ of the (-1) illuminate the diffraction grating mark RM from two directions, the pitch of the diffraction grating mark RM P _RM, from the light source 10 The reference wavelength of the supplied light is λ ₀ , the luminous flux L ₀ (1) or the luminous flux L ₀
When the incident angle with respect to the diffraction grating mark RM of (-1) is θ _RM , it is set so as to satisfy the relationship of (1) sin θ _RM = λ ₀ / P _RM .

As a result, the ± first-order diffracted light generated from the diffraction grating mark RM passes through the dichroic mirror 6, the objective lens 38, and the plane-parallel plate 37 again, is reflected by the beam splitter 28, and then the lens 29 and the beam. The field stop 34 is reached via the splitter 30. The field stop 34 is provided at a position conjugate with the reticle 1,
Specifically, as shown by the hatched portion in FIG. 3A, the opening S _RM is formed at a position conjugate with the diffraction grating mark RM so that only the diffracted light from the diffractive child mark RM of the reticle 1 passes through.
Is provided. The diffracted light from the diffraction grating mark RM that has passed through the field stop 34 is filtered by the spatial filter 35 that cuts the 0th-order diffracted light, and only the ± 1st-order diffracted light reaches the detector 36. The optical beat signal including the position information of is detected photoelectrically.

On the other hand, in FIG. 1, a part of the light flux L ₀ (1) and the light flux L ₀ (-1) that have passed through the transmission window P ₀ of the reticle 1 is transferred onto the wafer 4 via the projection objective lens 3. Illuminate the diffraction grating mark WM of from 2 directions with a predetermined crossing angle,
As a result, interference fringes that flow along the pitch direction are formed on the diffraction grating mark WM. Then, the normal direction of the diffraction grating mark WM (the optical axis direction of the projection objective lens 3)
The -1-order diffracted light of the light beam L ₀ (1), the light beam L ₀ (-1) +
First-order diffracted light is generated, respectively.

[0031] Here, intersection angle when the light beam L ₀ (1) and that the light beam L ₀ (-1) illuminate the diffraction grating mark WM from two directions, the pitch of the diffraction grating mark WM P _WM, the light source 10 The reference wavelength of the light supplied from λ ₀ , the luminous flux L ₀ (1) or the luminous flux L ₀
When the incident angle of (-1) with respect to the diffraction grating WM is θ _WM , it is set so as to satisfy the relationship of (2) sin θ _WM = λ ₀ / P _WM .

As a result, the ± first-order diffracted light generated from the diffraction grating mark WM is again projected by the projection objective lens 3 and the transmission window P.
_After passing through the dichroic mirror 6, the objective lens 38, and the plane-parallel plate 37 and being reflected by the beam splitter 28 (see FIG. 2A), it reaches the field stop 31 through the lens 29 and the beam splitter 30. This field stop 3
1 is provided at a position conjugate with the wafer 4, and specifically, as shown by the hatched portion in FIG. 3B, only the diffracted light from the diffraction grating mark WM on the wafer 4 is allowed to pass therethrough. The opening S _WM is provided at a position conjugate with the diffraction grating mark WM.

Therefore, the diffracted light from the diffraction grating mark WM that has passed through the field stop 31 is filtered by the spatial filter 32 that cuts the 0th-order diffracted light to ± 1.
Only the next-order diffracted light reaches the detector 33, and the detector 33 photoelectrically detects the optical beat signal including the position information on the wafer 4. Here, each spatial filter (32, 35) is arranged at a position substantially conjugate with the pupil of the alignment optical system, that is, a position substantially conjugate with the pupil (exit pupil) of the projection objective lens 3, and on the reticle 1 and the wafer 4. Diffraction grating mark (R
± 0th order diffracted light (specular reflection light) from M, WM) is blocked,
It is set to pass only the first-order diffracted light (reticle 1, diffracted light generated in the direction perpendicular to the diffraction grating mark on the wafer 4). In addition, the detector 33 and the detector 3
The objective lens 6 and the lens 29 are arranged so as to be substantially conjugate with the reticle 1 and the wafer 4, respectively.

With the configuration of the alignment optical system described above, the three signals obtained from the detectors (25, 33, 36) have the same frequency Δf (= | 2f).
₁ |) containing the sinusoidal optical beat signal, and the three optical signals are electrically Fourier transformed by the optical beat signal extraction unit (Fourier transform circuit) in the phase difference detection system 50 of FIG. Three sinusoidal optical beat signals of frequency Δf are accurately extracted.

Now, assuming that the reticle 1 and the wafer 4 are stopped at arbitrary positions without being aligned,
This optical beat signal is shifted by a certain phase. Here, the phase difference (within ± 180 °) of each optical beat signal from the reticle 1 and the wafer 4 is the relative position within 1/2 of the grating pitch of the diffraction grating marks formed on the reticle 1 and the wafer 4, respectively. It corresponds to the amount of deviation uniquely.

Therefore, when the reticle 1 and the wafer 4 move relative to the grating arrangement direction, the relative positional deviation amount is prealigned with an accuracy of 1/2 or less of the grating pitch of each diffraction grating mark (RM, WM). Then, the main control system 51 moves the reticle stage 2 or the wafer stage 5 two-dimensionally so that the phase difference obtained by the phase difference detection system 50 by the servo system 52 becomes zero or a predetermined value, and the alignment is performed. As a result, highly accurate alignment is performed.

The reference optical beat signal obtained by the detector 25 is used as a reference signal, and the phase difference between the reference signal and the optical beat signal from each diffraction grating mark (RM, WM) is zero or predetermined. You may align so that it may become the value of. Further, a drive signal for driving the AOM 17 can be used as a reference signal. Next, in the first embodiment shown in FIG. 1, a more specific configuration and principle of a portion that generates two light fluxes having different frequencies will be described with reference to FIG.

FIG. 4 shows the acousto-optic modulator (AO) shown in FIG.
Indicates M) 17, as shown in FIG. 4, the white light L ₀ is A
The light enters the OM 17 parallel to the wavefront of the traveling wave. As a result, diffracted light of each order is generated for each wavefront due to the diffracting action (Raman-Nass diffraction) of the AOM 17.

At this time, when the diffraction angle of the Nth-order diffracted light of the incident light of the wavelength λ is φ ₁ and the pitch of the traveling wave is Λ ₁ , the following equation is established. (3) sin φ ₁ = Nλ / Λ _{1 Further} , regarding the pitch Λ ₁ of the traveling wave, the following equation holds when the traveling wave velocity is v ₁ and the frequency is f ₁ .

(4) Λ ₁ = v ₁ / f ₁ Therefore, for the ± 1st order diffracted light, the equation (3) is as follows. (5) sin φ ₁ = f ₁ λ / v ₁

Now, let us consider the diffraction angles of the ± first-order lights L ₀ (1) and L ₀ (-1) passing through the spatial filter 19 of FIG. For example, the reference wavelength λ ₀ of the irradiation light is 633 nm and the wavelength width is ± 5.
When the traveling wave pitch Λ ₁ of 0 nm and the AOM 17 is 40 μm, the diffraction angle of the ± first-order light with respect to the light with the shortest wavelength of 583 nm is 0.835 °, and the diffraction angle with respect to the light with the longest 683 nm is 0.978 °. Become. Therefore, 583-68
With 3 nm light, the diffraction angle of the ± 1st order light is 0.835 ° to 0.
It is distributed in the range of 978 °. These lights are AOM17
Is diffracted by the traveling wave, the diffracted light is modulated by the frequency of the traveling wave.

Next, referring to FIG. 5, Raman-Nus
Optical frequency modulation by diffraction will be described. In FIG.
Drive signal SF of AOM17₁ Traveling wave of ultrasonic waves
Angle θ between the wave front and the incident light_i Is 0 °. And
Drive signal SF of AOM17₁ Traveling wave of ultrasonic waves
The angle between the wavefront of the and the diffracted light is θ_d Incident on AOM17
The wave vector of the incident light_i >, By AOM17
The wave number vector of the diffracted light is <K_d >,drive
Signal SF₁ The wave number vector of the ultrasonic wave by <K _S >age
Are shown respectively.

In the case of Raman-Nass diffraction, the angle θ _d is small, and each vector has an approximately isosceles triangular relationship as shown in FIG. Therefore, if the wavelength of light is λ, the refractive index of the AOM 17 is n, the frequency of the ultrasonic wave is f ₁ , and the velocity of the ultrasonic wave (traveling wave) traversing the inside of the AOM 17 is v ₁ , the vector <K
The absolute values of _i >, <K _d >, and <K _S > are expressed as follows.

(6) | <K _i > | = 2πn / λ (7) | <K _d > | = 2πn / λ (8) | <K _S > | = 2πf ₁ / v ₁ Also, the progress of ultrasonic waves. If the wavelength of the wave is Λ ₁ , the following relation holds. (9) sin θ _d = λ / Λ ₁ (10) | <K _S > | = sin θ _d · | <K _d > |

From the above equations (9) and (10), the following equation (11)
Can be calculated. (11) | <K _S > | = 2πn / Λ ₁ As is clear from the equation (11), as long as the Raman-Nass diffraction condition is satisfied, │ <K _S > |
It can be understood that the light having a constant size is subjected to the same frequency modulation (f ₁ ) regardless of the wavelength of the light.

Therefore, the luminous flux incident on the AOM 17
L₀ Let f be the frequency of ₀ First-order diffracted light L
₀(1) is (f + f) for each wavelength₁) (= F₁) Same frequency modulation
Light flux L₀ -1st order diffracted light L₀(-1) is for each wavelength
(F-f₁) (= F₂) Same frequency modulation. Like this
And a frequency F having a predetermined wavelength range₁ First-order diffracted light L₀(1)
And a frequency F having a predetermined wavelength range₂ -1st order diffracted light L
₀(-1) and for each diffraction grating (24, RM, WM)
Irradiation can be performed symmetrically under different incident angles for each wavelength of light
Therefore, in the vertical direction of each diffraction grating (24, RM, WM)
The ± 1st order diffracted light of each wavelength can always be generated.
As a result, the ± 1st-order diffracted light of each wavelength causes a predetermined frequency Δ
f (= | F₁-F₂| = | 2f₁Generate a beat light containing
You can Therefore, the predetermined frequency Δf (= | F₁-
F₂| = | 2f₁Each of the multi-wavelength beat light including |
(25, 33, 36) photoelectric detection (each diffraction pattern)
(Multiple beat lights including the position information of the child are detected for each wavelength)
Because of the averaging effect of the beat light of each wavelength,
Multi-wavelength while suppressing the asymmetry of each diffraction grating mark
Effects of resist thin film interference due to light (shadows such as changes in light intensity)
Of high accuracy by heterodyne interferometry
The liment can be achieved.

Moreover, since the light diffracted by the AOM 17 travels symmetrically with respect to the optical axis thereafter, in principle, no optical path length difference occurs between the divided light beams. That is, two-beam interference is possible even with white light having a short interference distance. Further, since the wavefronts of the divided light fluxes are aligned in a state where the phase difference is zero, it is possible not only to perform highly accurate alignment but also to realize an easy and compact device.

By the way, in the first embodiment, the AOM
± 1st-order diffracted light L that has undergone optical modulation that is emitted symmetrically from 17
₀ (1), L ₀ (-1) is used as a luminous flux for alignment,
The ± 1st-order diffracted lights L ₀ (1) and L ₀ (-1) are reflected by each diffraction grating (2
4, RM, WM), the beat light signal of a predetermined frequency Δf (= | 2f ₁ |) generated by irradiating from two directions, each detector (25, 33, 36) and phase difference detection Optical beat signal extraction unit (Fourier transform circuit) in system 50
And the extracted signal is used as an alignment signal. This makes it possible to achieve highly accurate alignment due to heterodyne interference.

Further, in the first embodiment shown in FIGS. 1 and 4, the ± first-order diffracted light split and generated by the Raman-Nus diffracting action of the AOM 17 is used as two light beams for position detection with respect to the position detection mark. However, the present invention is not limited to this. For example, the diffracted light of two arbitrary orders generated by the acousto-optic element 17 may be applied to the position detection mark from two directions as two light beams for position detection.

Next, referring to FIGS. 6 to 8, the second embodiment of the present invention will be described.
Examples will be described. 6, members having the same functions as those of the first embodiment shown in FIG. 1 are designated by the same reference numerals and detailed description thereof will be omitted. The present embodiment is different from the first embodiment in that the second acousto-optic element 60 (hereinafter, referred to as "the second acousto-optic element 60") is provided between the relay optical system (18a, 18b) and the condenser lens 21.
It is called "AOM60". ) Is provided, a spatial filter 61 is provided between the condenser lens 21 and the beam splitter 22, and the lenses 18a and 18b are attached to the first AOM.
17 (first acousto-optic modulator) to the second AOM
This is a function as a relay optical system that relays to the diffraction point of 60 (second acousto-optic modulator).

In this embodiment, the first AOM
By making the high frequency signal SF ₁ applied to 17 and the high frequency signal SF ₂ applied to the second AOM 60 reverse to each other, the finally obtained beat frequency is lowered (to 1 MHz or less) to facilitate electric signal processing. ing. Now, Fig. 6
, The white light from the white light source 10 that supplies light in a wavelength band (multi-wavelength) different from the exposure light is
The light enters the first AOM 17 via the condenser lens 12 and the bandpass filter 13. At that time, the first AO
The incident light is made to enter the wavefront of the traveling wave in parallel so that Raman-Nass diffraction occurs at M17.

The first AOM 17 has a frequency f₁ The first of
High frequency signal SF₁ Is driven by the specified wavelength range
Luminous flux L₀ Light flux L which is the first-order diffracted light of₀(1) and -1 next time
Light flux L that is broken light₀(-1) is the first AOM17
By (f₀+ f₁) And (f₀-f₁) Frequency modulation
It After that, the luminous flux L₀(1) and luminous flux L₀(-1) is for lens 1
8a, the reflection mirror 20, the lens 18b, and the second A
The light is symmetrically incident on the OM 60 at the same incident angle. Na
The sky placed in the relay optical system (18a, 18b)
± 1 from the first AOM 17 by the inter-filter 19
Diffracted light L₀(1), L ₀(-1) is extracted.

In this case, the light is incident on the second AOM 60 of this example.
Luminous flux L₀(1) and luminous flux L₀For (-1), the acoustic bra
Make sure that the conditions for the Gag diffraction are satisfied. Second AOM6
0 is the frequency f from the opposite direction to the first AOM 17.₂ The first
2 high frequency signals SF₂ Driven by the specified wavelength range
Luminous flux L₀(1) -1st-order diffracted light L₀(1, -1) (Hereafter, "Luminous flux L
₀(1, -1) ". ) Is due to the second AOM60
(F₀+ f₁-f₂) (= F₁ ) Frequency modulation,
Luminous flux L in wavelength range₀(-1) + 1st order diffracted light L₀(-1,1) (or less
Below, "Luminous flux L₀(-1,1) ". ) Is the second AOM
By 60 (f₀-f₁+ f₂) (= F₂ ) Frequency modulation
Kick After that, the luminous flux L₀(1, -1) and L₀(-1,1) is that
After passing through each lens 21, the beam splitter 22
It is divided into two. In addition, between the relay optical system (21, 23)
Is equipped with a spatial filter 61.
Second-order diffracted light L from the second AOM 60₀(1, -1) and +1
Diffracted light L₀(-1,1) and are extracted.

As described above, the light beams split into two by the beam splitter 22 are finally detected by the detectors (25, 33, 36) as in the first embodiment shown in FIG. Since photoelectric detection is performed, a more detailed description is omitted. In this embodiment, from the photoelectric signals photoelectrically detected by the detectors (25, 33, 36), a predetermined frequency Δf (= | F ₁ −F ₂ | = | 2 (f ₁ − The beat signals of f ₂ ) |) are extracted by the optical beat signal extraction unit (Fourier transform circuit) in the phase difference detection system 50, and alignment is performed based on these signals.

As described above, in this embodiment, two AOMs are used.
AOM of both sides is configured by arranging 17,60 in series.
On the other hand, since the high frequency signals SF ₁ and SF ₂ are applied from the opposite direction, the frequency of the beat signal photoelectrically detected by each detector (25, 33, 36) can be lowered to 1 MHz or less at which signal processing is easy. It will be possible. For example, the first AOM1
7 is a first high frequency signal SF having a frequency f ₁ of 100 MHz
Driven by ₁ , the second AOM 60 is the first AOM 1
Assuming that the second high frequency signal SF ₂ having the frequency f ₂ of 99.9 MHz is driven from the direction opposite to the direction 7, the one light flux L ₀ (1,
The frequency of (-1) becomes F ₁ (= f ₀ + f ₁ -f ₂ ), and the second A
The frequency of the other light flux L ₀ (-1,1) that has passed through the OM 60 is F
₂ (= f ₀ −f ₁ + f ₂ ).

Therefore, these two light fluxes L ₀ (1, -1) and L
Each diffraction grating (24, RM, WM) by irradiation of ₀ (-1,1)
The frequency Δf of the beat light generated in is 200 kHz
(= | F ₁ −F ₂ | = | 2 (f ₁ −f ₂ ) |), and the beat frequency can be easily processed for signal processing. Next, FIG.
In the second embodiment shown in FIG.
A more specific configuration of the portion that generates the light flux will be described with reference to FIG. 7.

As shown in FIG. 8, in the second embodiment, the first
The AOM 17 and the second AOM 60 are arranged in series,
The diffraction point of the first AOM 17 (high-frequency signal SF₁ Progress
Path) and the diffraction point of the second AOM 60 (high-frequency signal SF₂ of
Relay optical system (18a, 18)
b) is provided. And of white light (multi-wavelength light)
Luminous flux L₀ Enters the first AOM 17 parallel to its traveling wavefront
Shoot. As a result, the luminous flux L ₀ By the first AOM17
Raman-Nass diffraction.

The first AOM 17 has a first high frequency signal f.₁ 
Is driven by, and the luminous flux L₀ First-order diffracted light L₀(1) is
(F₀+ f₁), The light flux L₀ -1st order diffraction
Light L ₀(-1) is (f₀-f₁) Frequency modulation of both beams
L₀(1), L₀(-1) are angles φ with respect to the incident optical axis.₁ 
Only symmetrically with respect to the traveling wavefront and symmetrically with respect to the first A
Ejected from OM17.

The light beams L ₀ (1) and L ₀ (-1) which have been optically modulated by the first AOM 17 are transmitted to the first relay optical system (18).
a, 18b) and the angle φ with respect to the optical axis direction.
The light enters the second AOM 60 symmetrically under the condition of ₃ . The second AOM 60 is driven by the _second high-frequency signal f ₂ from the opposite direction to the first AOM 17, and the luminous flux L ₀ (1) is −1 of −1.
The first-order diffracted light L ₀ (1, -1) undergoes frequency modulation of (f ₀ + f ₁ -f ₂ ) (= F ₁ ), and the first-order diffracted light L ₀ (-1,1) of the light flux L ₀ (-1) is received. ) Undergoes frequency modulation of (f ₀ -f ₁ + f ₂ ) (= F ₂ ), and both light fluxes L ₀ (1, -1) and L ₀ (-1,1) have an incident angle φ ₃ and It is ejected symmetrically from the second AOM 60 under the same angle φ ₃ . That is, both light fluxes L ₀ (1, -1) and L ₀ (-1,1) undergo acoustic Bragg diffraction by the second AOM 60.

Here, the diffraction angle by acoustic Bragg diffraction of the second AOM 60 is set to θ _b2 (= 2φ ₃ ) and the second AO 60 is set.
The velocity of the ultrasonic wave (traveling wave) traversing the M60 is v ₂ , the ultrasonic frequency of the high-frequency signal SF ₂ is f ₂ , the wavelength of the light is λ, and the wavelength of the ultrasonic wave (traveling wave) traversing the second AOM 60 is Λ
_{When set to 2} , the relationships of the following expressions (12) and (13) are established.

(12) Λ ₂ = v ₂ / f ₂ (13) sin θ _b2 = λ / Λ _{2 From} these equations (12) and (13), the second AOM6
The diffraction angle θ _b2 (= 2φ ₃ ) due to 0 is finally given by the following equation (1
It becomes like 4). (14) sin θ _b2 = f ₂ λ / v ₂ (or sin 2φ ₃
= F ₂ λ / v ₂ ) Further, when the magnification of the relay optical system (18a, 18b) is β ₁ and the relay optical system (18a, 18b) satisfies the sine condition, the following equation (15) The relationship is established.

(15) β ₁ = (sin φ ₁ ) / (sin φ ₃ ) ≈ (2sin φ ₁ ) / (sin 2φ ₃ ) Therefore, from equation (5), equation (14) and equation (15), Equation (16) is derived. (16) β ₁ = 2 · (v ₂ f ₁ ) / (v ₁ f ₂ ) As described above, in the second embodiment shown in FIGS. 6 and 7, the relay optical system (18a, 18b) has the above-mentioned structure. It is preferably configured so as to satisfy the equation (16).

The first and second AOMs (17, 6)
0) are made of the same material, and the frequency difference between the first and second high-frequency signals (f ₂ , f ₁ ) is about several tens kHz,
Beta ₁ of the equation (16) is, since the beta ₁ ≒ 2, the relay optical system (18a, 18b) magnification beta ₁ of may be constituted by 2-fold. As described above, according to the second embodiment, the predetermined frequency Δ
Multi-wavelength beat light including f (= | 2 (f ₁ -f ₂ ) |) is photoelectrically detected by each detector (25, 33, 36) (beat light including position information of each diffraction grating is detected). Since multiple detections can be made for each wavelength), while suppressing the influence of the asymmetry of each diffraction grating mark by the averaging effect of the beat light of each wavelength,
High-precision alignment can be achieved by the heterodyne interference method that can eliminate the influence of thin film interference of the resist on the wafer 4 due to multi-wavelength light, and the beat frequency can be significantly reduced, so that the signal processing system can be simplified.

Furthermore, since white light (multi-wavelength light) travels symmetrically and in parallel in each relay optical system and each AOM, an optical path length difference does not theoretically occur between the divided light beams. That is, two-beam interference is possible even with a light beam having a short coherence length such as white light. Further, since the wavefronts of the divided light fluxes are uniform, that is, the mutual phase difference is zero, not only highly accurate alignment is possible, but also an easy and compact device can be realized.

By the way, in the second embodiment, the first and second optical axes of the relay optical system (18a, 18b) are arranged relative to the optical axis.
Is generated by irradiating the diffracted light that travels symmetrically through the AOM (17, 60) as a luminous flux for alignment and irradiating the two diffracted lights to the respective diffraction gratings (24, RM, WM) from two directions. Predetermined frequency Δf (= | 2 (f
_1- f ₂ ) |) beat signal is detected by each detector (25, 3
(3, 36) and the optical beat signal extraction unit (Fourier transform circuit) in the phase difference detection system 50, and this extracted signal is used for alignment for the reason described below.

In this embodiment, as shown in FIGS. 8A and 8B, the light beam L ₀ is present on the optical path A of the first-order diffracted light L ₀ (1, -1) by the optical modulation of the second AOM 60. 0 of (-1)
Order diffracted light L ₀ (-1, 0) is mixed, the -1st-order diffracted light L ₀ (-1,1)
Luminous flux of the light path on B L ₀ (1) of the zero-order diffracted light L ₀ (1, 0) will be mixed. At this time, the 0th-order diffracted light L ₀ (1, ₀ ) of the light flux L ₀ (1)
0) and the 0th-order diffracted light L ₀ (-1,0) of the light flux L ₀ (-1) are not subjected to frequency modulation by the second AOM 60 at each wavelength, and have a frequency (f ₀ ± f ₁ ) respectively. Have.

Therefore, in the optical path A, the frequency (f₀+ f₁-f
₂) First-order diffracted light L₀(1, -1) and frequency (f₀-f₁) 0 next time
Origami L₀(-1,0) and the frequency (f₀-f
₁+ f ₂) -First-order diffracted light L₀(-1,1) and frequency (f₀+ f₁)of
0th-order diffracted light L₀Since (1,0) is mixed, these are each diffraction
Irradiation from two directions on the grating (24, RM, WM)
As a result, the vertical direction of each diffraction grating (24, RM, WM)
Directional beat light with various beat frequencies is generated.
Be done. Then, beat light with various beat frequencies is simply
Signals photoelectrically converted by each detector (25, 33, 36)
Alignment based on various beat frequencies
Signal becomes a noise signal and adversely affects the detection accuracy.
Or even the problem that alignment is not possible
It

Therefore, first, the beat light having various beat frequencies generated by the optical modulation of the second AOM 60 will be examined. The frequencies of the diffracted lights are summarized and shown. In the optical path A, the frequency of the first-order diffracted light L ₀ (1, -1): f ₀ + f ₁ −f ₂ (I) 0-th order diffracted light L ₀ (-1 , 0) frequency: f ₀ −f ₁ (II) In optical path B, frequency of −1st order diffracted light L ₀ (-1,1): f ₀ −f ₁ + f ₂ …… (I ′) 0 next time The frequency of the broken light L ₀ (1,0) is f ₀ + f ₁ (II ').

Therefore, each frequency of the beat light generated by the combination of each diffracted light traveling on the optical path A and each diffracted light traveling on the optical path B is the absolute difference between (I) and (I ′). From the value, | (f ₀ + f ₁ −f ₂ ) − (f ₀ −f ₁ + f ₂ ) | = 2 | f ₁ −f ₂ | ...... [1] The difference between (I) and (II ′) From the absolute value, | (f ₀ + f ₁ −f ₂ ) −f ₀ + f ₁ | = | 2f ₁ −f ₂ | ...... [2] From the absolute value of the difference between (II) and (I ′), | than the absolute value of the difference between ...... (3) and (II) and (II '), 2 | | - f 0 -f 1 (f 0 -f 1 + f 2) | = | f 2 f 1 | ...... [ 4], the beat light photoelectrically detected by the detectors (25, 33, 36) contains three beat frequencies [1] to [3].

Therefore, what can be used as the beat frequency for alignment is that there is no common beat frequency among these beat frequencies. Therefore, in this embodiment, the luminous flux L ₀ (1, -1) is used. And the luminous flux L ₀ (-1,1) are combined to generate only one 2 | f _1-
A signal having a beat frequency of f ₂ | is extracted by an optical beat signal extraction unit (Fourier transform circuit) in the phase difference detection system 50.

As a result, even if the beat lights having various beat frequencies are photoelectrically detected by the detectors (25, 33, 36), the predetermined beats extracted by the optical beat signal extraction section (Fourier transform circuit) are obtained. Based on the signal of frequency 2 | f ₁ -f ₂ |, highly accurate alignment due to heterodyne interference can be achieved. In the second embodiment, the first
Of at least one of the AOM 17 and the second AOM 60 is set in a rotated state so that the traveling direction of the traveling wave across the first AOM 17 is different from the traveling direction of the traveling wave of the second AOM 60. Then, as shown in FIG.
Unnecessary diffracted light L traveling on the optical path A of the light flux L ₀ (1, -1)
₀ (-1,0) and unnecessary diffracted light L ₀ (1,0) traveling on the optical path B of the light beam L ₀ (-1,1) can be separated, and these unnecessary diffracted light L ₀ ( -1,0) and L ₀ (1,0) can be filtered by the spatial filter 61 of FIG.

Next, the structure of FIG. 6 is developed to develop the light source 10
Consider a case where n acousto-optic modulators (AOMs) are arranged in series and the relay optical system is arranged between adjacent AOMs. Considering the frequency B _{f of the} beat light to be extracted in this configuration, the diffracted light that travels symmetrically with respect to the optical axis of each relay optical system may be used as the irradiation light flux for alignment. B _f is generally expressed by the following equation (17).

(17) B _f = | 2 (f ₁ + f ₂ + f ₃
+ ... + f _n ) | where f _i is the i-th (i = 1 to n) AO from the light source side
It is the drive frequency of M, and the sign when the drive signal is applied from the first direction is positive, and the sign when the drive signal is applied from the second direction opposite to the first direction is negative. Further, in this case, the magnification β ₁ of the first relay optical system is as shown in the equation (16), and the magnification β _i of the i-th relay optical system is as shown in the following equation (18) (where i = 2, 3, ...).

(18) B _i = (v _{i + 1} f _i ) / (v _i f _{i + 1} ) In the second embodiment shown in FIGS. 6 to 8, the first AOM is used.
Two beams of ± first-order diffracted light that are split and generated by the Raman-Nass diffraction action of 17 are made incident on the second AOM 60, and the second AOM 60
For detecting the position of two light beams, the first-order diffracted light of one of the two light beams diffracted through the OM60 and the -1st-order diffracted light of the other light beam of the two light beams diffracted through the second AOM60 An example in which the mark is irradiated from two directions is shown, but the mark is not limited to this. For example, the two diffracted lights of arbitrary orders generated by the first AOM 17 are used for position detection.
It may be incident on the second AOM 60 as a light beam, and
The diffracted light of any order of one of the two light beams diffracted via the second AOM60 and the other order of the other light beam of the two light beams diffracted via the second AOM60 The diffracted light and the two light beams for position detection may be applied to the position detection mark from two directions.

By the way, in each of the embodiments described above, a white light source 10 such as a Xe lamp or a halogen lamp, a variable aperture 11 and the like.
Also, the condenser lens 12 is used as the light source means, and the white light L ₀ (multi-wavelength light) from this light source means is made incident on the AOM 17. However, as shown in FIG. 9, a plurality of laser light sources 100, 1 that emit light of different wavelengths from each other are used.
Light beams 01 and 102 are applied to a blazed diffraction grating 103 having a sawtooth cross section at different incident angles, and light beams L having different wavelengths from the laser light sources 100, 101, and 102 are combined. A light source system that emits ₀ may be used as the light source means.

Further, in each of the embodiments shown in FIGS. 1 and 6, the photoelectric beat signals are photoelectrically detected by the detectors (25, 33, 36) to the optical beat signal extraction section in the phase difference detection system 50. The beat signal having a predetermined frequency is extracted by the detectors (25, 33, 36) and the phase difference detection system 50.
An optical beat signal extraction unit (Fourier transform circuit) is arranged between the electric paths of the detectors (25, 33,
The photoelectric signals photoelectrically detected in 36) may be independently Fourier-transformed.

In the above embodiment, white light (multi-wavelength light) is used as the light for detecting the position of the diffraction gratings RM and WM, but monochromatic light may be used as the light for detecting the position. . For example, when a laser light source that supplies light of a single wavelength (monochromatic) is used as the light source means, there arises a problem of thin film interference due to the resist on the wafer 4, but by utilizing Raman-Nass diffraction, the entire device can be used. The advantage remains that the structure can be simplified and the device can be easily adjusted.

Further, in each of the above-described embodiments, the alignment by the heterodyne interferometry method is performed by using the ± first-order diffracted light of two light beams diffracted by irradiating the alignment mark (RM, WM) from two directions. However, for example, as disclosed in Japanese Patent Application Laid-Open No. 2-133913, the pitch of the alignment marks (RM, WM) of each embodiment is halved to illuminate one of the alignment marks (RM, WM). 0th-order diffracted light and alignment mark (R
Alignment by the heterodyne interferometry may be performed using the second-order diffracted light (or the −second-order diffracted light) of one light beam illuminating M, WM) as the detection light. Furthermore, JP-A-4-78
As disclosed in Japanese Patent Publication No. 14, the diffracted light generated by illuminating the alignment mark RM on the reticle with the first light flux from the first direction and in the direction opposite to the first direction, and the diffracted light on the reticle. The alignment mark RM is illuminated with a second light flux from a second direction different from the first direction, and the second light flux is emitted from the second direction.
The diffracted light generated in the direction opposite to the direction of is used as the detection light, and the two diffracted detection lights are caused to interfere by the diffraction grating arranged at the wafer conjugate position in the alignment optical system, and the interference light is As a configuration for detecting with a detector, alignment by the heterodyne interferometry may be performed.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that various configurations can be adopted without departing from the gist of the present invention.

[0080]

According to the present invention, since Raman-Nass diffraction is utilized, two functions of dividing a light beam and giving a frequency difference are executed by one frequency difference generating means, and one frequency difference generating means is used. A frequency difference is given to the two light beams by the frequency difference generating means. Therefore, there are advantages that the configuration of the entire apparatus can be simplified and downsized, and that the positional relationship of the optical members can be easily adjusted.

When light fluxes of a plurality of wavelengths are used as the light for position detection, an optical beat signal of white light (multi-wavelength light) is obtained. Therefore, an optical beat signal of each wavelength, that is, a plurality of light rays is obtained. Due to the averaging effect by the beat signal, it is possible to suppress the adverse effect due to the asymmetry of each diffraction grating mark and the reduction in the light amount of the detection light generated by the step structure of the diffraction grating mark. Moreover, since the diffraction grating mark on the test object is illuminated by white light (multi-wavelength light), even if a photosensitive material such as a resist is coated on the test object, the influence of thin film interference by the resist etc. It is possible to achieve highly accurate position detection by the heterodyne interferometry while eliminating the above.

Further, since white light (multi-wavelength light) enters the frequency difference generating means and is diffracted, it travels through each optical system symmetrically and in parallel with respect to the optical axis. Optical path length difference does not occur in principle. Therefore, since the wavefronts between the divided light beams are aligned, not only highly accurate alignment is possible, but also an easy-adjustable and compact device can be realized. In addition, the two-light flux generating means diffracts and diffracts the two light fluxes condensed by the relay optical system and the relay optical system that condenses the two light fluxes of each wavelength having the predetermined frequency difference generated by the frequency difference generating means. A second wave that gives a predetermined second frequency difference to the two light beams from the relay optical system by using the traveling wave to be modulated.
When the frequency difference generating means is included, the frequency difference between the two light fluxes is reduced to a level at which signal processing is easy by applying frequency differences of opposite signs whose magnitudes are slightly different by the two frequency difference generating means. There is an advantage that you can beat down.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a projection exposure apparatus to which a first embodiment of a position detection device according to the present invention is applied.

FIG. 2A is a plan view showing a diffraction grating mark on a reticle and a transmission window, and FIG. 2B is a plan view showing a diffraction grating mark on a wafer.

FIG. 3A is a plan view showing a field stop for a reticle-side diffraction grating mark provided in an alignment optical system;
(B) is a plan view showing a field stop for the diffraction grating mark on the wafer side.

FIG. 4 is a diagram for explaining the operation of the acousto-optic modulator 17 in the first example.

FIG. 5 is an explanatory view of the principle of Raman-Nass diffraction by an acousto-optic modulator.

FIG. 6 is a schematic configuration diagram showing a projection exposure apparatus according to a second embodiment of the present invention.

FIG. 7 shows two acousto-optic modulators 1 in the second embodiment.
It is a figure with which explanation of operation of 7 and 60 is offered.

FIG. 8 is a diagram showing how noise light is generated by the acousto-optic modulator of the second embodiment.

FIG. 9 is a configuration diagram showing another example of a light source that supplies light of a plurality of wavelengths.

[Explanation of symbols]

 RM Reticle side diffraction grating mark WM Wafer side diffraction grating mark 1 Reticle 3 Projection objective lens 4 Wafer 10 White light source 11 Variable aperture 12 Condenser lens 13 Bandpass filter 17,60 Acousto-optic modulator (AOM) 18a, 18b Relay optics System 19,61 Spatial filter 38 Objective lens

Claims (2)

[Claims] 1. A two-beam generation means for generating two light beams having different frequencies, and two light beams from a diffraction grating formed on a test object by converging the two light beams from the two-beam generation means. Has an objective optical system for irradiating light from two predetermined directions and a detector for photoelectrically detecting diffracted lights generated from the diffraction grating via the objective optical system, and detects the position of the object to be inspected. In the position detecting device, the two-beam generation means uses light source means for supplying a light flux having a single wavelength or a plurality of wavelengths, and a traveling wave for diffracting and modulating the light flux supplied from the light source means, Frequency difference generating means for generating two light fluxes having a predetermined frequency difference from the light flux from the light source means, and the light flux supplied from the light source means to the frequency difference generating means is converted into a wavefront of the traveling wave. Incident parallel to it,
A position detecting device having a structure in which two diffracted lights of different orders having different frequencies generated by the traveling wave are guided to the objective optical system. 2. The two-beam generation means includes two wavelengths of each wavelength having a predetermined frequency difference generated by the frequency difference generation means.
A relay optical system that condenses the light flux and a traveling wave that diffracts and modulates the two light fluxes condensed by the relay optical system are used to generate a predetermined second frequency difference between the two light fluxes from the relay optical system. The position detecting device according to claim 1, further comprising: a second frequency difference generating means for giving the second frequency difference.