JP2888233B2 - Position detecting apparatus, exposure apparatus and method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heterodyne interference type position detecting device, and is particularly suitable for a high-precision positioning device for a wafer, a mask or the like in a semiconductor manufacturing apparatus.

[0002]

2. Description of the Related Art In recent years, as an apparatus for transferring a fine pattern such as a semiconductor element onto a semiconductor wafer at a high resolution, a projection type exposure apparatus, a so-called stepper, has been frequently used. In particular, recently, it has been required to increase the density of LSIs manufactured thereby, and it is necessary to transfer a finer pattern onto a wafer. To address this,
Higher precision positioning (alignment) is essential.

Therefore, using heterodyne interferometry,
For example, Japanese Patent Application Laid-Open No.
It is disclosed in Japanese Patent Application Laid-Open No. 2-261003. This apparatus uses a Zeeman laser that emits a light beam containing P-polarized light and S-polarized light of slightly different frequencies as a light source for alignment (alignment). The light beam is split into two light beams of P-polarized light of frequency f1 and S-polarized light of frequency f2, and each of the split light beams passes through a respective reflecting mirror to form a diffraction grating mark formed on a reticle (mask) in a predetermined manner. Irradiation is performed in two directions.

A window is provided in the mask at a position adjacent to the diffraction grating mark, and a part of the light beam for irradiating the diffraction grating mark passes through the window to a predetermined two diffraction grating marks formed on the wafer. Irradiate in the direction. Diffracted light generated by irradiating each diffraction grating mark with light beams having different frequencies in two directions is caused to interfere with each other through a polarizing plate of a detection system, and two optical beat signals due to each interference are detected by a detector. Photoelectric detection.

Since the relative phase difference between the signals corresponds to the amount of displacement between the two light beams intersecting on the diffraction grating mark and the substrate, one of the detected optical beat signals is used as a reference signal. Highly accurate position detection is performed by relatively moving the reticle and the wafer so that the phase difference becomes zero.

[0006]

A polarization beam splitter or the like, which is one of the polarization splitting elements for splitting two orthogonally polarized lights having different frequencies supplied from the Zeeman laser light source described above, is used. Due to factors such as manufacturing errors now, polarized light incident on this
It is assumed that the directions of the polarization planes orthogonal to each other and the directions of the polarization planes that can be separated by the polarization beam splitter are slightly shifted. Then, the separated light fluxes include noise components of different frequencies polarized in a direction perpendicular to the main polarization component.

Further, even if the optical system of the above apparatus can be incorporated without a manufacturing error, the polarization splitting element such as a polarization beam splitter cannot strictly separate completely into P-polarized light and S-polarized light. As shown in FIG. 8, the separated polarized lights having different frequencies are noise components (sf1, sf1, sf1, sf1, s2) vertically polarized with respect to the respective main polarized components (Pf1 ′, Sf2 ′) in the same manner as described above. pf2).

For this reason, Japanese Patent Application Laid-Open No. Sho 62-261 mentioned above has been disclosed.
In the device disclosed in Japanese Patent Application Publication No. 003, when the light beam from the Zeeman laser light source is split into polarized light beams having different frequencies from each other by the polarizing beam splitter for the above-described reason,
Each of the divided polarized lights (Pf1 ', Sf2') slightly contains noise components (sf2, pf1) of different frequencies which are polarized in a direction perpendicular thereto.

Under these circumstances, the diffraction grating mark formed on the substrate is irradiated with two light beams in two directions, and the diffraction light from this diffraction grating mark is converted into two diffraction light beams by a polarizing plate or the like. If the main polarization directions are aligned and caused to interfere, the optical beat signal photoelectrically detected by the detector will contain a large error. In other words, when a noise component of a different frequency is mixed in each optical path split by the polarizing beam splitter and the light passes through a polarizing plate or the like, noise components of different frequencies polarized in the same direction as the main polarized component are mixed. At this point, there is a possibility that the light beam itself beats and a large error is included.

Further, there is a problem that a linearly polarized light beam is strictly deformed into elliptically polarized light when it passes through an optical member such as a polarization splitting element (a polarization beam splitter or the like) or a reflection mirror. For this reason, in the above-described conventional apparatus, the diffraction grating mark formed on the substrate is routed by each optical member until the diffraction grating mark is irradiated in two directions. In this process, for example, as shown in FIG. Main polarization component P at frequency f1
Noise component Prx (f1) of frequency f1 in the x direction perpendicular to ry (f1) and noise component Ny (f2) of frequency f2 in the y direction perpendicular to noise component Nx (f2) of frequency f2 Occurs.

This makes it possible to remove noise components (Prx (f1) and Nx (f2)) in the direction perpendicular to the main polarization direction, but to reduce noise in the same direction as the main polarization component Pry (f1). Since it is impossible to remove the component Ny (f2),
Until the diffraction grating mark is irradiated in two directions, the frequency f1
And the noise component Ny (f2) of the frequency f2 in the same direction as the main polarization component Pry (f1) beats, and the optical beat signal whose position is detected contains a fatal problem. There is.

Therefore, two diffracted lights photoelectrically detected by the detector due to the above-described problem will be analyzed. First, the amplitude D of the diffracted light having the main polarization component at the frequency f1 and the noise component at the frequency f2 slightly contained therein.
1 is

[0013]

(Equation 1)

On the other hand, the frequency f 2 together with the main polarization component of the frequency f 2 and the noise slightly contained therein,
The amplitude D2 of the diffracted light having the noise component of 1 is

[0015]

(Equation 2)

Can be expressed as However, the amplitude of the main polarization component of the frequency f1 which is often included in the diffracted light having the amplitude D1 is represented by U
1, the amplitude of the noise component of the frequency f2 slightly contained in the diffracted light of the amplitude D1 is V2, and the amplitude of the main polarization component of the frequency f2 frequently contained in the diffracted light of the amplitude D2 is U
2, the amplitude of the noise component of the frequency f1 slightly contained in the diffracted light of the amplitude D2 is V1, and the wave number is k1 (= 2πf1).
, K2 (= 2πf1), the phase change that occurs when polarized light of frequency f1 is diffracted by the diffraction grating is φ1, and the phase change that occurs when polarized light of frequency f2 is diffracted by the diffraction grating is φ2. And

According to the equations (1) and (2) obtained above, the intensity I of the optical beat signal photoelectrically detected by the detector is as follows.

[0018]

(Equation 3)

Expanding equation (3),

[0020]

(Equation 4)

## EQU1 ## Although the optical beat signal obtained by the equation (4) originally has only the phase component φ1 + φ2 indicating the information on the position of the diffraction grating, it also has another phase component, that is, (φ1−φ2). ) And (-φ1 + φ
2) is included. Therefore, U1, U2
Assuming that V1 and V2 are sufficiently small as compared with, the error e due to the phase component can be expressed by the following equation.

[0022]

(Equation 5)

As an example, the light intensity ratio of the polarization components in the directions orthogonal to each other included in each of the light beams divided into two by the above-described polarization beam splitter is 1: 1000 (| V2 |
Square of | U1 |, square of | U2 |: square of | V1 |), and U1 = U2, V1 = V2, the phase error e according to the above equation (5) becomes

[0024]

(Equation 6)

Thus, the optical beat signal photoelectrically detected is
It will include errors that cannot be ignored. The apparatus described in the above-mentioned prior art is designed to illuminate a diffraction grating mark formed on a substrate with two light beams having different frequencies in two directions and thereby reduce the pitch of interference fringes generated by the light beam to half. Each time the relative displacement between the two light fluxes and the substrate becomes １ ／ pitch, the phase difference between the optical beat signal including the position information of the diffraction grating mark and the optical beat signal for reference is set. Changes by 2π. That is, the relative displacement between the two light beams and the substrate corresponds to the phase difference, and the range that can be detected as the phase difference is 2π.

Therefore, when the pitch of the diffraction grating marks formed on the substrate is P and the above-described phase error e is converted into the relative deviation δ between the two light beams and the substrate, the following expression can be obtained.

[0027]

(Equation 7)

Now, assuming that the pitch P formed on the diffraction grating mark is 10 μm, the above-mentioned phase error of 3.6 ° is converted into a shift amount δ.

[0029]

(Equation 8)

This value is a large error which cannot be ignored. For example, when exposing a 4-megabit super LSI, it is necessary to print a line width of about 0.6 to 0.7 μm. A line width of about μm is required to be at least enough 1 (0.06 to 0.07 μm), but the error obtained by the equation (8) clearly shows that a stable alignment for exposing a 4-megabit VLSI is apparent. It becomes difficult.

As described above, since physical phenomena at a level which can be ignored so far have a great adverse effect on the alignment accuracy, the structure of the alignment optical system for detecting the position should be sufficiently taken into consideration to achieve high-precision alignment. It is necessary to eliminate all adverse factors. by the way,
There is a problem in that the incidence angles of two light beams, which should irradiate the diffraction grating mark formed on the substrate in two directions with a predetermined crossing angle, change due to manufacturing errors and the like.

Further, even if the crossing angle of the two light beams illuminating the diffraction grating mark formed on the substrate is set to a predetermined value, bright and dark interference fringes generated by interference on the diffraction grating mark are generated. There is also a problem that the generation (arrangement) direction and the grating arrangement (pitch) direction of the diffraction grating are relatively displaced in the rotation direction. The result of both, contrast,
It is difficult to obtain an optical beat signal with high reliability and stability, and it is difficult to perform highly accurate alignment.

Accordingly, an object of the present invention is to provide a high-performance position detecting device which can solve all the above problems, can obtain a stable optical beat signal with high reliability, and can detect a position with high accuracy. I have.

In order to achieve the above object, the present invention provides a diffraction mark formed on a substrate for position detection,
A position detecting device that irradiates two light beams having different frequencies from the alignment optical system from two directions, causes diffracted light generated by the two light beams to interfere with each other, and photoelectrically detects an optical beat signal due to the interference, irradiates a diffraction mark. Illumination light beam supply means for supplying an illumination light beam for performing the operation; light modulation means for dividing the illumination light beam into two and modulating the frequency of each of the two divided light beams by a predetermined value; alignment optics for the two modulated light beams And an optical path adjusting means for adjusting the intersection angle of two light beams that irradiate the diffraction mark formed on the substrate from two directions while moving the optical axis of the system therebetween.

Further, the apparatus has an alignment optical system for irradiating two illumination light beams from two different directions to the diffraction mark formed on the substrate whose position is to be detected, and a light receiving means for receiving the diffracted light from the diffraction mark. A position detecting device for detecting a position of a substrate based on a signal from a light receiving unit includes: a light modulating unit that modulates a frequency of two light beams by a predetermined amount; and an adjusting unit that adjusts an intersection angle of the two light beams. . A light source system that supplies alignment light in an exposure apparatus that exposes a pattern of a mask onto a substrate; a frequency modulation member that divides the alignment light into two and makes the frequencies of the two alignment lights different from each other; An irradiation optical system for irradiating the diffraction mark formed on the substrate with the two alignment lights from two different directions; and causing the diffraction light generated from the diffraction mark by the irradiation of the two alignments to interfere with each other to generate an optical beat signal due to the interference. A position detecting device for performing photoelectric detection; and an optical path adjusting member for adjusting an intersection angle of two alignment lights for irradiating the diffraction mark are provided. Further, in an exposure method for exposing a pattern of a mask onto a substrate, two alignment lights having different frequencies are irradiated onto alignment marks formed on the substrate from two different directions to interfere with diffracted light generated from the alignment marks. Then, the optical beat signal due to the interference is photoelectrically detected; and the intersection angle between the two alignment lights for irradiating the diffraction mark is adjusted. Also,
In a mark detection method for detecting a diffraction mark by causing diffraction light from a diffraction mark formed on a substrate for position detection to interfere with the diffraction mark, the diffraction mark is irradiated with two light beams from an alignment optical system from two directions. Modulating the frequency of each of the two light beams by a predetermined amount so as to obtain two light beams having different frequencies from each other; and causing the two light beams to travel across the optical axis of the alignment optical system. I decided that.

In a preferred configuration, the optical path adjusting means has a parallel flat plate with a variable inclination angle in at least one of the optical paths. [Operation] In the present invention, after separating the alignment light and independently modulating each light flux to a mutually different frequency,
By providing the optical path adjusting means, the two luminous fluxes modulated at mutually different frequencies are always maintained in a separated state,
Since the optical paths can be adjusted so that each light beam can travel on the optical paths separated in the alignment optical system, noise components that adversely affect the detection signal can be prevented from being mixed.

Therefore, it is guaranteed that a stable optical beat signal with high contrast and reliability is obtained, and more accurate alignment can be realized. In addition, since the optical path of the two light beams can be adjusted by this configuration, not only the intersection angle of the light beams that illuminates the diffraction grating mark on the substrate in two directions can be adjusted, but also the generation (arrangement) direction of interference fringes and the diffraction grating mark. This is extremely effective because it is possible to adjust a relative displacement amount in the rotation direction from the arrangement (pitch) direction.

[0038]

FIG. 1 is a diagram showing a schematic configuration of a position detecting device according to a first embodiment of the present invention, which will be described below in detail with reference to FIG. A reticle (mask) 1 having a predetermined circuit pattern and a diffraction grating mark RM for alignment is held on a reticle stage 2 that can move two-dimensionally. Each pattern on the reticle is imaged on a wafer (substrate) by the projection objective lens 3 under exposure light supplied from the illumination optical system 40. The diffraction grating mark R formed on the reticle also on the wafer
A diffraction grating mark WM similar to M is formed.

The wafer is attracted onto a stage which moves two-dimensionally in a step-and-repeat manner, and when the transfer of the pattern on the reticle in one shot area on the wafer is completed, the wafer is stepped to the next shot position. . Each stage is provided with an interferometer (not shown) for independently detecting the positions of the reticle stage 2 and the wafer stage 5 in the x direction, the y direction, and the rotation (θ) direction. This is performed by a drive motor (not shown).

The exposure light from the exposure optical system is
The light is reflected downward by the dichroic mirror 37 inclined at 45 ° above the reticle and illuminates the reticle 1 uniformly. Then, the pattern on the reticle uniformly illuminated forms an image of the pattern on the wafer by the projection lens 3 and is transferred. On the other hand, the alignment optical systems (10 to 31) for position detection are provided above the dichroic mirror, and the alignment optical systems will be described in detail below.

The illumination light for alignment having a long wavelength different from that of the exposure light is emitted from the laser light source 10 and then converted into circularly polarized light by the quarter-wave plate 11. Lens 1
The light beam passing through 2 is split by the polarizing beam splitter 13 into light beams of P-polarized light and S-polarized light so as to have the same light amount. The S-polarized light flux reflected by the polarization beam splitter 13 is incident on a first acoustic light modulator 15a (hereinafter simply referred to as AOM 15a), while the P-polarized light flux transmitted through the polarization beam splitter 13 passes through a reflection mirror 14. The second acousto-optic modulator 15b (hereinafter simply referred to as A
Called OM15b. ). Each AOM frequency-modulates the frequency of the P-polarized light beam to f1 and the frequency of the S-polarized light beam to f2 so that the relative frequency difference between the P-polarized light beam and the S-polarized light beam becomes Δf.

The s-polarized light flux modulated to the frequency f 1 by the AOM 15 a reaches the polarization beam splitter 18 via the parallel plane plate 16 a and the reflection mirror 17.
The P-polarized light flux modulated to the frequency f2 by the AOM 15b also reaches the beam splitter 18 via the plane parallel plate 16b. Here, each parallel plane plate (16a, 16b) functions as an optical path adjusting means, and is inclined with respect to the traveling direction of each light flux so that the two light fluxes modulated at mutually different frequencies are not combined again by the beam splitter 18. The inclination is set so that the amount of inclination can be adjusted.

As a result, each optical path of the two light beams that have been frequency-modulated by each AOM is shifted by a predetermined amount and passes through the polarization beam splitter 18 in a separated state. This polarization beam splitter 18 is arranged near the pupil position of the alignment optical system. In addition, each parallel plane plate (16
The functions a) and 16b) will be described later. The two light beams traveling in parallel in the separated state are rotated by 45 ° in the polarization direction by the half-wave plate 19, and the polarization beam splitter 20.
, The P-polarized light component in each light beam advances in the passing direction, and the S-polarized light component in each light beam advances in the reflection direction.

The two light beams transmitted through the polarizing beam splitter 20 form interference fringes flowing along the pitch direction on a reference diffraction grating 22 by a lens 21. The diffraction light passing through the diffraction grating 22 is used as a detector. At 23, it is photoelectrically detected as an optical beat signal for reference. On the other hand, the two light beams reflected by the polarization beam splitter 20 are transmitted to a relay system (24
a, 24b, 25) to reach a beam splitter 26 provided near the pupil position of the alignment optical system.

The two light beams that travel in parallel after passing through the beam splitter 26 pass through a parallel plane plate 35 provided at a variable tilt angle with respect to the optical axis of the alignment optical system in order to maintain telecentricity. Lens 36,
The diffraction grating mark RM on the reticle is illuminated via the dichroic mirror 37 in two directions having a predetermined crossing angle. At this time, the plane-parallel plate 35 for maintaining telecentricity is arranged in the pupil space of the alignment optical system, and it is more preferable that the plane-parallel plate is particularly arranged near this pupil position.

The parallel flat plate 35 may have a configuration in which a thick parallel flat plate for coarse adjustment and a thin parallel flat plate for fine adjustment are combined. When the chromatic aberration of the projection lens 3 is not corrected with respect to the alignment light, the objective lens 36 is constituted by a bifocal optical system proposed in Japanese Patent Application Laid-Open No. 63-283129 by the same applicant as the present invention. It is desirable to be done.

In this case, in order to split each of the two polarized light beams incident on the bifocal optical system into two components, the polarization direction of the incident light beam is arranged so as to be inclined with respect to the optical axis of the bifocal optical system. Then, one of the light beams traveling toward the first focal point forms an image on the reticle, and the other light beam traveling toward the second focal point forms an image at a position off the reticle. Image on the wafer through the

As shown in FIG. 2A, the reticle 1 is provided with an alignment light transmission window PO (hereinafter, referred to as a transmission window) in parallel with the diffraction grating mark RM. As shown in FIG. 2B, a diffraction grating mark WM having the same pitch as the diffraction grating mark formed on the reticle is formed on the wafer corresponding to the transmission window portion PO.

For this reason, a part of the alignment light illuminates the diffraction grating mark RM on the reticle in two directions having a predetermined crossing angle on the reticle, so that interference fringes flowing along the pitch direction of the diffraction grating. Occurs. The intersection angle of the two light beams is set in advance so that the ± first-order diffracted reflected light generated by the diffraction grating mark RM travels in the optical axis direction.

Accordingly, the ± 1st-order diffracted light generated from the diffraction grating mark RM is again transmitted to the dichroic mirror 37,
After passing through the objective lens 36, the parallel plane plate 36, the beam splitter 26, the lens 27, the beam splitter 2
Through 8, a field stop 32 is reached. This field stop 32
Is provided at a position conjugate with the reticle 1. Specifically, as shown by the oblique lines in FIG. 2C, only the diffracted light from the diffraction grating mark RM of the reticle 1 is transmitted.
An opening SRM is provided corresponding to the position of the diffraction grating mark RM.

For this reason, the diffracted light from the diffraction grating mark WM that has passed through the field stop 32 is filtered by the spatial filter 33 that cuts the zero-order light (specular reflection light), and the detector 34 detects the position information of the reticle 1. Is photoelectrically detected. On the other hand, a part of the alignment light beam that has passed through the transmission window PO on the reticle passes through the projection lens 3 to the diffraction grating mark WM on the wafer formed by the diffraction grating and has a predetermined intersection angle. ± 1st-order diffracted light generated by the mark WM and traveling along the optical axis is projected by the projection lens 3, the dichroic mirror 37, the objective lens 36, the parallel plane plate 35, the beam splitter 26, the lens 27, Beam splitter 28
, Reaches the field stop 29.

The field stop 29 is provided at a position conjugate with the wafer 4. More specifically, as shown by oblique lines in FIG. 2D, only the diffracted light from the diffraction grating mark WM of the wafer 4 is emitted. An opening SWM is provided corresponding to the position of the diffraction grating mark WM so as to allow transmission. Therefore, the diffracted light from the diffraction grating mark WM that has passed through the field stop 29 is filtered by the spatial filter 30 that cuts the zero-order light (specular reflection light), and the detector 31 includes the position information of the wafer 4. An optical beat signal is photoelectrically detected.

Each spatial filter (30, 33) is arranged at a position substantially 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, and the reticle and the wafer The 0th-order light (specular reflection light) from the diffraction grating mark formed above is cut off, and only the ± 1st-order diffraction light (diffraction light generated in the direction perpendicular to the diffraction grating of the reticle 1 and the wafer 4) is passed. Is set to

The detectors (31, 34) are arranged via the objective lens 36 and the lens 27 so as to be substantially conjugate with the reticle 1 and the wafer 4, respectively. When the reticle 1 and the wafer 4 are stopped at arbitrary positions in a state where they are not aligned, the three photoelectric signals obtained from the detectors (23, 31, 34) according to the present embodiment as described above are , Are both sinusoidal optical beat signals having the same frequency Δf, and are shifted from each other by a fixed phase difference. here,
The phase difference (± 180 °) between the respective optical beat signals from the reticle 1 and the wafer 4 is determined by the relative positional deviation within １ ／ of the grating pitch of the diffraction grating marks formed on the reticle 1 and the wafer 4. It corresponds uniquely.

When the reticle 1 and the wafer 4 move relative to each other in the grating arrangement direction, a signal of the same phase is obtained each time the relative positional shift amount becomes half the grating pitch of each diffraction grating mark (RM, WM). . For this reason, each diffraction grating mark (RM,
The main control system 51 performs pre-alignment with an accuracy equal to or less than the grating pitch of WM) １ ／ and the reticle stage 2 or the wafer stage 5 so that the phase difference obtained by the phase difference detection system 50 by the servo system 52 becomes zero. Is moved two-dimensionally to perform positioning, thereby achieving high-resolution position detection.

The reference optical beat signal obtained from the detector 23 is used as a reference signal, and the phase difference between this reference signal and each optical beat signal from each diffraction grating mark (RM, WM) becomes zero. Positioning may be performed as follows.
Further, it is of course possible to use a drive signal for driving each AOM (15a, 15b) as a reference signal.

Next, a description will be given of an embodiment in which the optical beat signal detected by photoelectric detection does not include an error. As shown in FIG. 3, the light beam supplied from the alignment light source 10 becomes circularly polarized light via the １１ wavelength plate 11, and is separated into S-polarized light and P-polarized light via the polarizing beam splitter 13. However, if the noise components (Δp, Δs) polarized in the direction perpendicular to the polarization direction of each of the separated light beams (S, P) are slightly included as described in the above problem, The polarization components of each light beam that has passed through the AOM (15a, 15b) are subjected to the same frequency modulation. After that, each light flux (Sf1 + Δpf1, Pf2 + Δsf)
2) parallel plane plates (16a, 16b) for adjusting the optical path,
A polarizing beam splitter 18 is provided via a reflection mirror 17.
Reach At this time, the polarization beam splitter 18
Each main polarization component is guided in a predetermined direction, and each noise component (Δpf
1, Δsf2) is guided in a different direction, so that each light beam passing through the same has a state in which only a substantially pure main polarization component exists.

When the light beams (Sf1 ', Pf2') passing through the polarizing beam splitter 18 pass through the half-wave plate 19, the polarization direction of each light beam is rotated by 45.degree. Reach the polarizing beam splitter 20 so as to be orthogonal to each other. Strictly speaking, the polarization beam splitter 20 splits the main polarization component Sf1 'having the frequency f1 not only into Pf1 "and Sf1" in the x and y directions, but also into the vertical direction in each split light beam. .DELTA.sf1 "and .DELTA.pf1" are mixed as noise components of the frequency f1.

On the other hand, the main polarization component Pf2 'of the frequency f2 is similarly divided not only into Pf2 "and Sf2" in the x and y directions, but also into the vertical direction in each of the divided light beams. Δsf2 ″ and Δp as noise components of f2
f2 ". The two light beams (Pf1", Pf1) transmitted through the polarizing beam splitter 20 are thus mixed.
2 "), the noise components (Δsf1", Δsf
2 ") are mixed, but each noise component (Δsf
1 ″, Δsf2 ″) is the corresponding main polarization component (Pf
1 ", Pf2"), there is no light beat in each light beam, and the light is photoelectrically detected as a reference signal via the lens 21, the reference diffraction grating 22, and the detector 23.

The reference optical beat signal obtained by the reference detector 23 is a highly reliable and stable photoelectric signal without including an error signal which has almost no adverse effect on accuracy. On the other hand, in the two light beams (Sf1 ", Sf2") reflected by the polarization beam splitter 20, the relay system (24, 25), the beam splitter 26, and the noise component (Δpf1 ”, Δpf2 ″) are mixed. The diffraction grating mark RM on the reticle via the plane parallel plate 35 and the objective lens 36 and the diffraction grating mark WM on the wafer via the projection lens are irradiated in two directions.

However, like the reference signal, the noise components (.DELTA.sf1 ", .DELTA.sf2") of each light beam have the same frequency as the corresponding main polarization components (Pf1 ", Pf2").
Since no beat occurs in each light beam, a highly reliable and stable signal containing only the reticle and wafer position information can be obtained for each signal that is photoelectrically detected. As described above, the light beams independently frequency-modulated by the AOM or the like are guided so as to be symmetrical with respect to the optical axis of the alignment optical system without intersecting again, and the diffraction grating marks (RM, WM) are moved in two directions. Is very effective because it does not include any light of a different frequency that causes a detection error.

Further, as described in the above problem, each optical member arranged in the alignment optical system of this embodiment may cause not only the main polarized light component but also the noise component to be transformed into elliptically polarized light. It is conceivable that the noise component slightly present in each light beam of the present embodiment shown in FIG.
Since the main polarization component has the same frequency, for example, as shown in FIG.
As shown in FIG. 5, even if there is a noise component Ny (f1) of the same frequency f1 in the same direction with respect to the main polarization component Pry (f1) of the frequency f1, each diffraction grating mark ( The two light fluxes do not beat before irradiating RM, WM), and a reliable and stable optical beat signal can be obtained in each detector (23, 31, 34).

Next, the function of each parallel plane plate (16a, 16b) as an optical path adjusting means will be described. As described above, the parallel plane plates (16a, 16b) not only ensure a state where the light beam is separated so as not to include an error signal in the light transmission system, and also each parallel plane plate (16a, 16b).
Since the optical path of each polarized light can be shifted in accordance with the amount of inclination of 6b), the plane-parallel plates (16a, 16a) can be shifted.
b) It is possible to adjust the optical paths so as to be separated in parallel with the optical axis of the alignment optical system provided rearward.

Therefore, the plane parallel plate (16a, 16a,
The optical path adjustment according to 16b) will be described in detail. The pupil plane Pu of the alignment optical system as shown in FIG. 5 exists at a position where the polarization beam splitters 18 and 20 are arranged. The pupil plane Pu has a spot (BS1) of two light beams from the light transmitting system.
, BS1) are formed across the optical axis. A pair of parallel plane plates (16a, 16b) provided above the pupil
Is provided so as to rotate about x and y axes as shown in the figure.

The beam spots (BS 1, BS 1) formed on the pupil plane Pu are reflected by the respective parallel plane plates (16 a, 16 a).
When b) is tilted about the x axis, it moves in the y direction, and when b) is tilted about the y axis, it moves in the x direction. For this reason, diffraction grating marks (WM, WM,
RM) can adjust the crossing angle of the two light beams irradiated on the two directions.

The crossing angle θ of the two light beams that irradiate each diffraction grating mark (WM, RM) in two directions is the incident angle (α, 2) of the two light beams that irradiate the diffraction grating mark (WM, RM) in two directions. β), the wavelength of the laser light source is λ,
The pitch of the diffraction grating is P, the order n1 of the diffracted light generated by the light beam irradiating the diffraction grating at the incident angle α (n1> 0), and the order n2 of the diffracted light generated by the light beam irradiating the diffraction grating at the incident angle β. If n2 <0), it is uniquely determined as in the following equation.

[0067]

(Equation 9)

For this reason, according to a predetermined intersection angle θ, each parallel flat plate (16a, 16b) is tilted about the y-axis,
Each beam spot (BS1, BS1) on the pupil plane Pu is represented by x
Adjust in the direction. Therefore, by simply changing the inclination of each parallel plane plate (16a, 16b), it is possible to adjust the crossing angle to an appropriate crossing angle according to the diffraction grating marks (WM, RM) having different pitches P, which is extremely effective. It is.

However, even if the intersection angle θ is adjusted, as shown in FIG.
(Array) direction and the diffraction grating mark (W
If the arrangement (pitch) direction of (M, RM) is largely deviated in the rotation direction, a high-contrast optical beat signal including accurate position information cannot be obtained. Therefore, it is necessary to further adjust the direction in which the interference fringes IF are generated (arranged) by moving the positions of the beam spots (BS1, BS2) formed on the pupil plane Pu so that the directions are parallel.

The flowing interference fringes IF formed on the diffraction grating marks (WM, RM) are formed in a direction perpendicular to a straight line connecting the two beam spots (BS1, BS2) on the pupil plane Pu. For this reason, as shown in FIG. 6B, for example, while maintaining a predetermined crossing angle, the grating perpendicular to the straight line connecting the two beam spots (BS1, BS2) is the grating of the grating marks (WM, RM). So that the direction
By tilting the parallel plane plate 16a around the x and y axes, the beam spot BS1 may be moved by .DELTA.X in the x direction and may be moved by .DELTA.Y in the y direction to correct the position of BS1 '.

Further, the generation (arrangement) direction of the interference fringes IF,
If the arrangement (pitch) direction of the diffraction grating marks (WM, RM) is slightly deviated in the rotation direction, for example, FIG.
As shown in (C), the one-dimensional parallel flat plate 16a is
The beam spot BS1 may be tilted about the axis and moved by .DELTA.Y in the y-direction to correct the position of BS1 ".

As described above, if at least one of the parallel plane plates (16a, 16b) is two-dimensionally inclined, the direction of generation (arrangement) of the interference fringes IF and the diffraction grating mark can be maintained while maintaining a predetermined intersection angle. This is effective because the arrangement (pitch) direction of (WM, RM) can be matched. In order to perform this automatically, the inclination of the parallel plane plates (16a, 16b) for adjusting the intersection angle, and the parallel plane plates (16a, 16a, It is preferable to perform the feedback control of the inclination of 16b).

More specifically, for example, when adjusting the crossing angle, the parallel plane plates (16a, 16a) as described above are used so that the contrast of the optically detected optical beat signal is maximized.
Also, when controlling the inclination of b) and adjusting the direction in which the interference fringes are generated and the arrangement direction of the diffraction grating marks, the parallel plane plate ( By controlling the inclinations of 16a and 16b), the deviation between them can be corrected.

As described above, in the present embodiment, the parallel plane plate whose inclination can be two-dimensionally varied is arranged in the alignment optical system for adjusting the optical path, but this parallel plane plate is provided in at least one of the optical paths. Is also good. Further, the number of the parallel plane plates is not limited, and a plurality of parallel plane plates which can be tilted in one-dimensional direction in each optical path may be provided in the alignment optical system.

In FIGS. 6B and 6C, the two beam spots are slightly separated from the optical axis, but have no effect on the detected optical beat signal. Also, interference fringes I
Generation (arrangement) direction of F and diffraction grating marks (WM, RM)
A configuration in which an image rotator is arranged in an alignment optical system may be applied to correct a shift amount in the rotation direction from the arrangement (pitch) direction.

Next, a modification of this embodiment will be described with reference to FIG. In this embodiment, the same members as those in FIG. 1 are given the same reference numerals. A light beam emitted from the laser light source 10 is split into two by a polarizing beam splitter 13 via a quarter-wave plate 11 and a lens 12, and is modulated to different frequencies by each AOM (15a, 15b).

The S-polarized light modulated to the frequency f 1 via the AOM 15 a reaches the prism 61 via the reflection mirror 17. On the other hand, the P-polarized light modulated to the frequency f2 via the AOM 15b becomes the S-polarized light by the half-wave plate 60,
The light reaches the prism 61 . The prism 61 is disposed in the vicinity of the pupil position, and has a partially transmitting surface 61b for transmitting a light beam having a frequency f1 through the AOM 15a, and a partially reflecting surface formed by vapor deposition or the like for reflecting S-polarized light having a frequency f2 through the AOM 15b. 61a.

Then, the respective S-polarized lights having different frequencies through the prism 61 pass through the half-wave plate 19. At this time, since the polarization directions of the light beams are uniform, if the half-wave plate 19 is rotated, the polarization beam splitter 20 and the reticle 1
The light amount of each light beam supplied to the light transmitting system for irradiating the wafer 4 can be adjusted.

At this time, since the amount of light required as reference light for photoelectric detection by the detector 23 is not required to be very large, it is sufficient. A light beam having a large amount of light is transmitted to each diffraction grating mark (R
M, WM). If a beam splitter is disposed instead of the polarization beam splitter 13 and the partially reflecting surface 61a of the prism 61 is formed of a metal film, the polarization plane of the light beam incident on the prism 61 is uniform, so that the half wavelength The plate 60 can be dispensed with.

At this time, the beam splitter divides the light beam from the laser light source 10 into two, and independently modulates the divided light beams by the AOMs (15a, 15b). Even if polarized light components of the same frequency are mixed in each light beam, there is no adverse effect on the optical beat signal that is photoelectrically detected. That is, since each light beam does not include a light beam component having a different frequency and is kept in a separated state, each diffraction grating mark (RM, WM) can be irradiated in two directions without beating.

The present invention is not limited to the embodiment described above, but is disclosed in Japanese Patent Application Laid-Open No. 60-1 by the same applicant as the present invention.
As proposed in Japanese Patent No. 30742, a configuration in which alignment light can be irradiated on a diffraction grating mark on a wafer in two directions through a projection lens without using a reticle may be applied, or a promixity method may be applied. can do.

[0082]

As described above, according to the present invention, since each light beam modulated to a different frequency does not include a light beam component of another frequency, each light beam can be placed on the reticle and the wafer. In the process of transmitting light to the diffraction grating mark formed in the above, it is possible to eliminate the cause of light beat. Thus, since the optical beat signal photoelectrically detected has purely information on the position of the reticle and the position of the wafer, highly accurate alignment is always guaranteed.

In addition, not only can the crossing angle of the two light beams irradiating the diffraction grating mark in two directions be adjusted, but also the deviation in the rotational direction between the fringe direction of the interference fringes generated by the two light beams and the grating direction of the diffraction grating can be adjusted. Since the correction can be performed, an optical beat signal with high contrast, stability, and reliability can be detected, so that highly accurate position detection can be realized. In addition, since a large frequency difference can be given to two light beams that illuminate each diffraction grating mark in two directions using an AOM or the like, throughput can be improved and high-resolution position detection can be realized.

[Brief description of the drawings]

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

2A is a plan view showing a shape of a diffraction grating mark RM on a reticle, and FIG. 2B is a plan view showing a diffraction grating mark W on a wafer.
A plan view showing the shape of M, (C) a plan view of a field stop for obtaining diffracted light from the diffraction grating mark RM on the reticle, and (D) a diffracted light from the diffraction grating mark WM on the wafer Plan view of a field stop for

FIG. 3 is a diagram showing only an alignment optical system;

FIG. 4 is a diagram showing a state in which a main polarization component and a noise component having the same frequency are elliptically polarized;

FIG. 5 is a diagram schematically showing the function of an optical path adjusting unit;

FIG. 6A is a diagram showing a state in which interference fringes and each diffraction grating mark are largely displaced, and FIG. 6B is a diagram showing a state in which the directions of the interference fringes and each diffraction grating mark are corrected and coincide with each other. (C) is a diagram showing a state in which the direction of the interference fringes slightly shifted and the direction of each diffraction grating mark has been corrected.

FIG. 7 is a diagram showing a schematic configuration of a projection exposure apparatus according to a modification of the present embodiment;

FIG. 8 is a diagram showing a function of a polarizing beam splitter;

FIG. 9 is a diagram illustrating a state in which a main polarization component and a noise component having a different frequency are elliptically polarized.

[Explanation of symbols]

 Reference Signs List 10 light source 13 polarization beam splitter 15a first acoustic light modulator 15b second acoustic light modulator 16a, 16b parallel plane plate 18 polarization beam splitter (beam splitter)

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-56818 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 11/00-11/30

Claims (7)

(57) [Claims] 1. A diffraction mark formed on a substrate for detecting a position is irradiated with two light beams having different frequencies from two directions from an alignment optical system to interfere with the diffracted light generated by the two light beams. A position detection device that photoelectrically detects an optical beat signal due to the interference; and an illumination light beam supply unit that supplies an illumination light beam for irradiating the diffraction mark; Light modulation means for modulating the frequency of each light beam by a predetermined value;
An optical path adjusting means for advancing the modulated two light beams across the optical axis of the alignment optical system and adjusting an intersection angle of the two light beams for irradiating the diffraction mark formed on the substrate from two directions; A position detecting device characterized by the above-mentioned. 2. The position detecting device according to claim 1, wherein said optical path adjusting means has a parallel flat plate with a variable tilt angle on at least one of the optical paths. 3. An alignment optical system for irradiating a diffraction mark formed on a substrate whose position is to be detected with two illuminating light beams from two different directions, and light receiving means for receiving diffracted light from the diffraction mark. A position detecting device that detects a position of the substrate based on a signal from the light receiving unit; a light modulating unit that modulates a frequency of the two light beams by a predetermined amount; and an adjusting unit that adjusts an intersection angle of the two light beams. Position detecting device characterized by having 4. An exposure apparatus for exposing a pattern on a mask onto a substrate, comprising: a light source system for supplying alignment light; and a frequency for dividing the alignment light into two and making the frequencies of the two alignment lights different from each other. A modulating member; an irradiating optical system for irradiating the two alignment lights to the diffraction marks formed on the substrate from two different directions; and a diffracted light generated from the diffraction marks by the two alignment irradiations. An exposure apparatus comprising: a position detection device that photoelectrically detects an optical beat signal due to the interference; and an optical path adjustment member that adjusts an intersection angle of the two alignment lights that irradiate the diffraction mark. 5. An exposure apparatus according to claim 4, wherein said optical path adjusting member has a parallel flat plate having a variable tilt angle on at least one of the optical paths. 6. An exposure method for exposing a pattern on a mask onto a substrate, comprising:
Irradiating the alignment mark formed on the substrate from the direction, causing the diffracted light generated from the alignment mark to interfere with each other, and photoelectrically detecting a light beat signal due to the interference; Adjusting an intersection angle of the alignment light. 7. A mark detection method for detecting a diffraction mark by interfering a diffraction light from a diffraction mark formed on a substrate for position detection, wherein two light beams from an alignment optical system are detected by the diffraction mark. To 2
Irradiating from a direction; modulating the frequency of each light beam of the two light beams by a predetermined amount in order to obtain two light beams having different frequencies from each other; and proceeding the two light beams across the optical axis of the alignment optical system. And a mark detection method.