JPH07311009A - Position detection device - Google Patents

Abstract

PURPOSE:To reduce the effect of reflected rays from an objective optical system, and thereby detect a position for alignment with high accuracy. CONSTITUTION:A laser beam LB from a laser beam source 1 is radiated on a wafer mark WM through those such as a cylindrical lens 2, a field stop 3, a second objective lens 4, a light transmitter receiver separation prism 5 composed of a polarized beam splitter, a first objective lens 7, a 1/4 wave length plate 6, a mirror 16 and a projection optical system 8. Diffracted light is incident on photodetectors 13A and 13B through those such as a projection optical system 8, the mirror 16, the 1/4 wave length plate 6, the first objective lens 7, and the light transmitter receiver separation prism 5. Reflected rays 15 from the first objective lens 7 transmit the light transmitter receiver separation prism 5 so as to be returned to the laser beam source 1 side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a position detecting device for detecting the position of a mark for position detection on an object to be inspected by self-illumination, and is particularly used for manufacturing a semiconductor element or a liquid crystal display element. It is suitable for application to an alignment system of a projection exposure apparatus that projects a pattern on a reticle onto a photosensitive substrate via a projection optical system.

[0002]

2. Description of the Related Art In an exposure apparatus such as a stepper or step-and-scan type projection exposure apparatus, a reticle (or photomask, etc.) on which a transfer pattern is formed and a wafer coated with a photoresist are used. (Or a glass plate or the like) is provided with an alignment device for performing alignment with high accuracy. In order to perform such alignment with high accuracy,
First, it is necessary to accurately detect the position of the alignment mark (wafer mark) on the wafer by the alignment system.

In this regard, the degree of roughness of the surface of the wafer changes due to exposure and subsequent processes, and
Since the step between the wafer mark and the peripheral underlying layer may be different depending on the layer (layer) on the wafer, it is difficult to accurately detect the positions of all the wafer marks with a single alignment system. Therefore, conventionally, the following alignment systems have been used according to the application.

LSA (Laser Step Alignment) type alignment system: This is a system which irradiates a laser beam on a wafer mark and measures the position of the wafer mark by using the diffracted / scattered light. It is widely used for more various process wafers.
An LSA type alignment system is disclosed in, for example, Japanese Patent Laid-Open No. 63-2.
It is disclosed in JP-A-29305, JP-A-5-226222, and JP-A-5-226224.

FIA (Field Image Alignment) system:
This is an image pickup device (vidicon tube or CCD) that takes an enlarged image of a wafer mark illuminated by light with a wide wavelength band using a halogen lamp or the like as a light source, and the obtained image pickup signal is image-processed to perform position measurement. It is a sensor and is effective for measuring asymmetric marks on the aluminum layer or wafer surface. FI
The A system is disclosed in, for example, Japanese Patent Laid-Open No. 4-273246.

LIA (Laser Interferometric Alignm)
ent) system: This is a method of irradiating a diffraction grating-shaped wafer mark with laser light whose frequency is slightly changed from two directions, causing two generated diffracted lights to interfere with each other, and determining the position information of the wafer mark from the phase of this interference light. Is a sensor for detecting. This LIA
The system is effective for a wafer mark having a low step or a wafer having a large surface roughness, and the detection principle of the LIA system is disclosed in Japanese Patent Laid-Open No.
It is disclosed in Japanese Patent No. 56818, Japanese Patent Laid-Open No. 2-116116, and the like.

FIG. 4 (a) shows a conventional LSA type alignment system. In FIG. 4 (a), the laser light source 1 is used.
As a result, the laser beam LB polarized in the direction parallel to the paper surface of FIG. 4A is emitted. This laser beam LB is
It is condensed by the cylindrical lens 2 in a direction perpendicular to the paper surface of FIG. The laser beam LB shaped into a slit by the field stop 3 is incident on the transmission / reception separation prism 5 including a deflection beam splitter via the second objective lens 4. Since the laser beam LB is P-polarized, the laser beam LB passes through the transmission / reception separation prism 5 as it is, and then is subjected to a test with a predetermined circular polarization through the quarter-wave plate 6, the first objective lens 7, and the projection optical system 8. The exposure surface 9a of the wafer 9 as a surface is irradiated. The field stop 3 is conjugate with the exposure surface 9a. Here, the Z axis is taken perpendicularly to the optical axis of the projection optical system 8, the X axis is taken in the direction perpendicular to the paper surface of FIG. 4A in the plane perpendicular to the Z axis, and the Z axis is taken to be the paper surface of FIG. 4A. Take the Y axis in the vertical direction.

A wafer mark for alignment is provided near each shot area on the exposure surface 9a.
As shown in (b), a predetermined wafer mark WM among them
A laser beam LB is irradiated as a slit-shaped light spot 10 extending in the X direction in the vicinity of. The wafer mark WM is a dot pattern arranged at a predetermined pitch in the X direction, and the wafer 9-is moved in the Y direction via a wafer stage (not shown) so that the light spot 1 is formed at the wafer mark WM.
When 0 is scanned, diffracted light is generated in the ± X directions when the wafer mark WM coincides with the light spot 10. In addition to this diffracted light, zero-order light is also generated.

In FIG. 4A, the 0th-order light LB (0) and the ± 1st-order diffracted lights LB1 (+1), LB (-1), which are circularly polarized light and which are generated from the exposure surface 9a, are the After passing through the projection optical system 8, the first objective lens 7, and the quarter-wave plate 6, the light returns to the light-transmitting / receiving-light separating prism 5. Since the light returned in this way is S-polarized light, it is reflected by the light-transmitting and receiving light separating prism 5, passes through the relay lens 11 once, and then goes to the light-receiving slit 12. The light receiving slit 12 has an opening 12 for the ± 1st order diffracted light.
a and 12b are bored, and photoelectric detectors 13A and 13B are arranged immediately after the openings 12a and 12b, respectively. At this time, the Fourier transform surface (pupil surface) of the first objective lens 7 is transferred to the photoelectric detectors 13A and 1A by the relay lens 11.
The photoelectric detectors 13A and 13A are relayed to the light receiving surface of 3B.
In B, the diffracted lights LB (-1) and LB (+1) are received, respectively, and the output signals of the photoelectric detectors 13A and 13B are added to the adder 1
4 is added and supplied to an alignment control system (not shown).

In the alignment control system, the Y coordinate of the wafer mark WM can be obtained from the Y coordinate of the wafer stage (not shown) when the sum signal supplied from the adder 14 reaches the peak value. Similarly, the coordinates of the wafer mark indicating the position in the X direction are also measured, and at the time of exposure, the corresponding shot area on the wafer 9 is positioned based on the thus measured X and Y coordinates.

[0011]

As described above, in the conventional alignment system, the light directed to the wafer 9 and the wafer 9 are provided by the transmission / reception separating prism 5 and the quarter wavelength plate 6.
It was separated from the reflected light from. However, in this method, when a small portion of the incident laser beam LB is reflected by the lens surface (for example, the surface 7a) of the first objective lens 7, the following inconvenience occurs.

Actually, even if each surface of the first objective lens 7 is provided with an antireflection coating, about 0.1% of the light incident on the first objective lens 7 is always reflected due to factors such as manufacturing tolerances. Resulting in. For example, considering the light beam 15 reflected on the surface 7a, since the reflected light beam 15 is already circularly polarized, it passes through the quarter-wave plate 6 to cause S It becomes polarized light. Therefore, the light beam 15 is reflected by the light-transmitting and receiving light separating prism 5 and enters the light-receiving optical system, and the photoelectric detector 13A
And the SN ratio of the photoelectric conversion signals of 13B deteriorates.

Further, in the projection optical system 8, there is a tendency to use a large number of lenses in order to improve the imaging performance with exposure light for exposing a pattern of a reticle (not shown) onto the wafer 9. is there. Further, the laser beam LB as the alignment light is a light in a wavelength band in which the photoresist on the wafer 9 is weakly photosensitive, and has a different wavelength band from the exposure light. Therefore, the transmittance of the projection optical system 8 for the laser beam LB is considerably low. For example,
The transmittance of the projection optical system 8 for the laser beam LB is 20.
Assuming that the light amount of the diffracted light generated at the wafer mark WM of the wafer 9 is about 17% of the light amount incident on the wafer mark WM, the photoelectric detectors 13A and 13B are represented by%.
The amount of light received at is 0.68 (= 0.2 × 0.17 ×) of the amount of light traveling from the transmitting / receiving separation prism 5 to the first objective lens 7.
It becomes about 0.2 × 100)%.

On the other hand, in the first objective lens 7, it is 0.1
% Reflected light is generated, the photoelectric detector 13
On the light-receiving surfaces of A and 13B, about 1/7 of the total amount of received light may be reflected light by the first objective lens 7, that is, noise light, and the position detection accuracy deteriorates.
Further, the intensity of the diffracted light may be lower depending on the state of the exposed surface of the wafer 9, and in this case, the SN ratio of the photoelectric detectors 13A and 13B is further deteriorated and the position detection cannot be performed. There is a fear.

Generally, the laser light source has a certain amount of output fluctuation, but when the SN ratio deteriorates in FIG. 4 (a), it becomes very susceptible to the output fluctuation of the laser light source 1. Therefore, the reproducibility of the wafer mark position detection result deteriorates. In view of such a point, the present invention reduces the influence of reflected light from the objective optical system,
An object of the present invention is to provide a position detection device that can detect the position of a mark for alignment (wafer mark) with higher accuracy.

[0016]

As shown in FIG. 1, for example, a position detecting device according to the present invention comprises a light source (1) for emitting illumination light and an illumination light emitted from this light source for inspection (9). ) Is arranged between the light source (1) and the objective optical system (7) and the objective optical system (7) for condensing on the mark (WM) for position detection on the above. An optical splitter (5) for separating the optical path of the illumination light and the optical path of the illumination light from the test object.
And photoelectric detection means (13A, 13B) for receiving the illumination light separated by the objective optical system (7) and the light splitter (5) after being reflected by the object to be inspected (9). In the device for detecting the position of the position detection mark (WM) on the object (9) based on the detection signals from these photoelectric detection means, the optical splitter (5) is a polarization beam splitter, and the objective optical A polarization state conversion member (1/4 wavelength plate 6) for changing the polarization state of the illumination light is provided between the system (7) and the object to be inspected (9), reflected by the object to be inspected, and the objective optical system. (7)
The polarization state of the illumination light, which is returned to the polarization beam splitter (5) through the polarization beam splitter (5) through the polarization state conversion member (6), is detected by photoelectric detection means (13A,
13B), which is the polarization state guided to 13B).

In this case, the light source (1) and the light splitting member (5)
A diaphragm (3) is disposed between the diaphragm and the diaphragm so that the illumination light reflected by the objective optical system (7) and traveling toward the light source (1) through the polarization beam splitter (5) is blocked by the diaphragm (3). In addition, it is desirable that the illumination light traveling from the light source (1) toward the diaphragm (3) be inclined with respect to the optical axis (AX) of the objective optical system (7).

[0018]

According to the present invention, since the polarization state varying means (6) is arranged between the objective optical system (7) and the object (9) to be inspected, the light source (1) is divided into the light splitter. After entering the objective optical system (7) via (5), the light reflected by the objective optical system (7) is directly returned to the light source (1) side via the light splitter (5). Therefore, since the reflected light from the objective optical system (7) does not enter the photoelectric detection means (13A, 13B), it is possible to perform position detection with high SN ratio and high accuracy.

The present invention is based on the TTL as shown in FIG.
When applied to a (through-the-lens) type alignment system, a projection optical system (8) is further arranged between the objective optical system (7) and the test object (9). In this case, the illumination light (LB) from the light source (1) is incident on the lens surface at a relatively large incident angle at a position largely decentered from the optical axis (8a) of the projection optical system (8). The optical path of the reflected light by the light projection optical system (8) is largely deviated from the optical path of the incident light. Therefore, the reflected light from the projection optical system (8) does not pose a problem.

However, it is desirable to further arrange the polarization state changing means (6) between the projection optical system (8) and the object (9) to be inspected. Further, a diaphragm (3) is arranged between the light source (1) and the light splitting member (5), and the illumination light traveling from the light source (1) to the diaphragm (3) is directed to the optical axis (AX of the objective optical system (7) system. ), The light source (1) is reflected by the objective optical system (7) and passes through the polarization beam splitter (5).
The illumination light directed to the side is blocked by the diaphragm (3). Therefore, when the light source (1) is a laser light source, back talk is reduced, and the stability of oscillation of the laser light source is increased.

[0021]

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. In the present embodiment, the present invention is applied to an alignment system of a TTL (through-the-lens) system and an LSA system. In FIG. 1, parts corresponding to those in FIG. The description is omitted.

FIG. 1 shows the alignment system of this embodiment,
1A is a front view thereof, and FIG. 1B is a plan view thereof (however, the reticle R is excluded). As shown in FIG. 1A, each shot area on the exposure surface 9a of the wafer 9 on which the pattern of the reticle R is coated with the photoresist through the projection optical system 8 by the exposure light from the illumination optical system (not shown). Is transcribed to. Z is parallel to the optical axis 8a of the projection optical system 8.
Taking the axis, the X axis is parallel to the plane of FIG. 1A and the Y axis is perpendicular to the plane of FIG. 1A in the plane perpendicular to the Z axis. In each shot area on the wafer 9, a wafer mark for the LSA system and for the X axis and a wafer mark for the Y axis are formed. In the following, a predetermined X-axis wafer mark WM among them will be detected.

In this embodiment, the laser beam LB emitted from the laser light source 1 and consisting of linearly polarized light which is polarized in a direction perpendicular to the paper surface of FIG. 1A, passes through the cylindrical lens 2 and has a slit shape of the field stop 3. The laser beam is irradiated onto the aperture of FIG. 1 and shaped into a laser beam having a vertically long cross section in the direction parallel to the paper surface of FIG. As the laser light source 1, for example, a He—Ne laser light source (oscillation wavelength: 633 nm) that oscillates in a wavelength band in which the photoresist on the wafer is weakly photosensitive can be used. Besides, a laser diode or the like that emits light in red or near infrared may be used.
In this embodiment, the center of the aperture of the field stop 3 is the second
The laser beam LB that coincides with the optical axes AX of the objective lens 4 and the first objective lens 7 and is incident on the field stop 3 is inclined at a predetermined angle ε with respect to the optical axis AX (details will be described later). When the width of the opening of the field stop 3 in the direction parallel to the paper surface of FIG. 1A is a, for example, the laser beam LB immediately after passing through the field stop 3 is parallel to the paper surface of FIG. The width in the direction is a, but in the drawing the laser beam LB
And the other diffracted lights respectively represent the loci of light at their centers.

The laser beam LB shaped in this way
Passes through the second objective lens 4 as P-polarized light and passes through the light-transmitting / receiving split prism 5 composed of a polarization beam splitter, and then goes to the first objective lens 7. Then, the laser beam LB condensed by the first objective lens 7 passes through the quarter-wave plate 6 as a polarization state conversion member to form an image of the field stop 3 on the conjugate plane P1 once, and then the reticle R. The laser beam LB reflected by the mirror 16 disposed between the projection optical system 8 and the projection optical system 8 and incident on the projection optical system 8 and emitted from the projection optical system 8 is a predetermined wafer on the exposure surface 9a of the wafer 9. A slit-shaped light spot 1 long in the X direction near the mark WM
It is focused as 0 (see FIG. 1B). At this time, 1
The optical axis of the / 4 wave plate 6 is approximately 45 ° with respect to the paper surface of FIG.
1/4 wavelength plate 6 because it is set to intersect with
The polarization state of the laser beam LB traveling toward the mirror 16 via is converted from linearly polarized light to predetermined circularly polarized light. Further, at the wavelength of the laser beam LB, the field stop 3 and the conjugate plane P1 are the second objective lens 4 and the first objective lens 7.
And the conjugate plane P1 and the exposure surface 9a of the wafer 9 are conjugate with respect to the projection optical system 8.

Next, the 0th-order light LB (0) from the exposure surface 9a by the laser beam LB and, for example, ± first-order diffracted lights LB (+1) and LB (-1) from the wafer mark WM are incident. The projection optical system 8 and the mirror 16 in the state of circularly polarized light in the direction opposite to
And enters the quarter wave plate 6. Then, the 0th-order light LB (0) becomes a linearly polarized light (S-polarized with respect to the transmitting / receiving separation prism 5) which is polarized in a direction parallel to the paper surface of FIG. First-order diffracted light LB (+1), LB (-
1) is reflected by the transmitting / receiving separation prism 5 via the first objective lens 7.

As shown in FIG. 1B, the 0th-order light LB (0) and the ± 1st-order diffracted lights LB (+1), LB (-1) reflected by the transmitting / receiving separation prism 5 are relay lenses. The light is condensed by 11 and intersects once, and then goes to the light receiving slit 12. The 0th-order light LB (0) is blocked by the light-receiving slit 12, and the ± 1st-order diffracted lights LB (+1) and LB (-1) pass through the openings 12a and 12b on the light-receiving slit 12 and are photoelectrically detected. The output signals of the photoelectric detectors 13A and 13B are incident on the detectors 13B and 13A, added by the adder 14, and supplied to an alignment control system (not shown). Photoelectric detector 13
The method of processing the output signals of A and 13B is the same as the conventional method.

As described above, in the present embodiment, 1/4
Since the wave plate 6 is provided between the first objective lens 7 and the projection optical system 8, the light beam 15 reflected by the surface 7a of the first objective lens 7 is sent as it is, as shown in FIG. The light passes through the light receiving / separating prism 5 and is returned to the second objective lens 4 side. Therefore, since the light beam 15 reflected by the first objective lens 7 does not enter the photoelectric detectors 13A and 13B, the SN ratio of the photoelectric conversion signals from the photoelectric detectors 13A and 13B is improved, and the position detection of the wafer mark WM is performed. Accuracy is improved.

However, since the light beam 15 reflected by the first objective lens 7 returns to the light transmitting system without entering the light receiving system, the laser light source 1 reflects the light beam 15 unless some measures are taken. The generated light beam 15 may return as backtalk, and the oscillation state of the laser light source 1 may become unstable. To avoid this, an isolator such as a Faraday rotator may be attached to the emission surface of the laser light source 1, for example. However, mounting the isolator increases the manufacturing cost.

Therefore, in this embodiment, in order to prevent the back talk from entering the laser light source 1 without increasing the manufacturing cost, as shown in FIG.
And the laser beam LB emitted from the cylindrical lens 2 in the direction conjugate with the X direction (non-measurement direction) on the wafer 9 with respect to the optical axis AX of the second objective lens 4 and the first objective lens 7. Crossed at. As a result, the laser beam LB is incident on the surface 7a of the first objective lens 7 at a position away from the optical axis AX, so that the surface 7a thereof is
The reflected light 15 from is returned to the transmitting / receiving separation prism 5 side with a deviation of an angle δ with respect to the direction of incidence (substantially parallel to the optical axis AX). Therefore, the reflected light 15 does not return to the laser light source 1 after entering the light-shielding portion of the field stop 3, and the laser light source 1 always oscillates stably.

As shown in FIG. 1A, when the angle formed by the light beam 15 reflected by the first objective lens 7 and the optical axis AX is δ, the focal length of the second objective lens 4 is f _2. ,
Laser beam LB on field stop 3 and reflected light beam 1
The deviation amount Δ1 from 5 is f ₂ · δ. Since the width of the reflected light beam 15 is actually a, the light beam 15 is blocked by the field stop 3 if the following expression can be satisfied.

Δ1 = f ₂ · δ> a (1) However, when this condition cannot be satisfied, FIG.
As shown in FIG. 3, between the laser light source 1 and the cylindrical lens 2, the first relay lens 17 having the focal length f _{4 in} order from the laser light source 1 side, the auxiliary field stop 18, and the focal length f ₃
It is also possible to provide a relay optical system including the second relay lens 19 of FIG. At this time, the optical axes of the first and second relay lenses 17 and 19 are aligned with the optical axis AX, but the center of the opening 18a of the auxiliary field stop 18 is decentered from the optical axis AX by a predetermined distance.

In FIG. 2, the laser beam LB emitted from the laser light source 1 is once condensed by the first relay lens 17 onto the circular aperture 18a on the auxiliary field stop 18, and the laser beam LB which has passed through the aperture 18a. However, the second relay lens 19 converts the light into a substantially parallel light beam and enters the cylindrical lens 2, and the light condensed by the cylindrical lens 2 in the direction perpendicular to the paper surface of FIG. Is incident at a predetermined inclination angle. At this time, the auxiliary field stop 18 and the field stop 3 are conjugate with respect to the measurement direction, and the magnification from the auxiliary field stop 18 to the field stop 3 is set as the enlargement magnification.

Therefore, even if the light beam 15 reflected by the first objective lens 7 passes through the aperture of the field stop 3, the light beam 15 passes through the cylindrical lens 2 and the second relay lens 19 and then the auxiliary field stop 18 is provided. Shut off by. Therefore, there is an advantage that the amount of back talk returning to the laser light source 1 is reduced and the stability of oscillation of the laser light source 1 is increased.

At this time, the cylindrical lens 2 (condensing method)
Focal length f_c) Has no refractive power in the non-measurement direction,
Ignore and think. And the focal length of the first objective lens 7.
F ₁Then, the focal length of the second objective lens 4 is f₂so
Therefore, the laser beam transmitted on the auxiliary field stop 18 is
The distance Δ2 between the beam LB and the reflected light beam 15 is
It is expressed as. Δ2 = δ · f₁f₃/ F₂ (2) Auxiliary of the light flux 15 at this time in the direction parallel to the paper surface of FIG.
Beam spot diameter on the field diaphragm 18 is BW, auxiliary field of view
If the diameter of the aperture 18a of the diaphragm 18 is b,
The conditions for completely shutting off by the auxiliary field stop 18 are as follows.
Like

Δ2 = δ · f ₁ f ₃ / f ₂ > (BW + b) / 2> BW (3) Next, a second embodiment of the present invention will be described with reference to FIG. In this embodiment, a TTL LIA (Laser Interferom) is used.
The present invention is applied to an etric Alignment) system.
However, in FIG. 3, parts corresponding to those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.

FIG. 3A shows the LIA system of this embodiment,
3A is a front view thereof, and FIG. 3B is a plan view thereof (however, the reticle R is excluded). As shown in FIG. 3B, the wafer marks to be detected in this embodiment are diffraction grating marks 26 arranged at a predetermined pitch in the Y direction. In FIG. 3B, the linearly polarized laser beam LB emitted from the laser light source 1 is split by the half mirror 20 into two laser beams LB1 and LB2. Then, one of the laser beams LB1 undergoes frequency modulation of frequency Δf ₁ by the first acousto-optic modulator (hereinafter referred to as “AOM”) 21A, and the relay lens 2
3 and the other laser beam LB2 is reflected by the mirror 22 and then transmitted by the second AOM 21B to the frequency Δ
It is subjected to the frequency modulation of f ₂ (≠ Δf ₁ ) and goes to the relay lens 23.

The laser beams LB1 and LB2 emitted from the relay lens 23 intersect once in the aperture of the field stop 24, and then pass through the second objective lens 4 and the transmitting / receiving separation prism 5 composed of a polarization beam splitter. , First
Go to the objective lens 7. Then, after the laser beams LB1 and LB2 condensed by the first objective lens 7 pass through the quarter-wave plate 6 as a polarization state conversion member to form an image of the field stop 24 on the conjugate plane P1 once, The laser beams LB1 and LB2 reflected by the mirror 16 and incident on the projection optical system 8 and emitted from the projection optical system 8 are irradiated near the diffraction grating mark 26 on the wafer 9 at a predetermined crossing angle (FIG. 3 (c)).

As shown in FIG. 3C, the + 1st-order diffracted light LB of the laser beam LB1 is emitted from the diffraction grating mark 26.
1 (+1), and -1st-order diffracted light LB2 of the laser beam LB2
(-1) is emitted as a heterodyne beam having a frequency difference of | Δf ₁ −Δf ₂ | almost vertically upward in parallel, and the + second-order diffracted light LB1 (+2) of the laser beam LB1 and the laser beam L
The heterodyne beam composed of the 0th-order light LB2 (0) of B2 is obliquely emitted in parallel, and the 0th-order light L of the laser beam LB1 is emitted.
B1 (0) and the −2nd order diffracted light LB of the laser beam LB2
A heterodyne beam consisting of 2 (-2) is obliquely emitted in parallel.

Returning to FIG. 3B, the diffraction grating mark 26
The three sets of heterodyne beams from 1 are transmitted through the projection optical system 8 and the mirror 16 in the state of circularly polarized light in the direction opposite to that at the time of incidence.
It is incident on the quarter wave plate 6. Then, the three sets of heterodyne beams that are S-polarized with respect to the transmission / reception separation prism 5 by the quarter-wave plate 6 are reflected by the transmission / reception separation prism 5 via the first objective lens 7, and then are relay lens 11
The light is collected by the light source, crosses once, and then goes to the light receiving slit 25. Then, the heterodyne beam LB1 (+1), LB
2 (-1) passes through the aperture 25a and enters the photoelectric detector 13C, and the heterodyne beams LB1 (+2) and LB2 (0) pass through the aperture 25b and enter the photoelectric detector 13B. (0) and LB2 (-2) pass through the opening 25a and enter the photoelectric detector 13A. Photoelectric detector 13A-
13C outputs beat signals obtained by photoelectrically converting the heterodyne beam, and the position of the diffraction grating mark 26 in the Y direction is detected based on these beat signals.

Also in this embodiment, as shown in FIG. 3A, the laser beam LB incident on the first objective lens 7 is inputted.
In 1 and LB2, the light beam 15 reflected by the surface 7a of the first objective lens 7 is P-polarized light and passes through the light-transmitting and receiving light separating prism 5 as it is toward the second objective lens 4. Therefore, the SN ratio in the photoelectric detectors 13A to 13C is improved, and the position detection accuracy of the diffraction grating mark 26 is improved.

In this LIA system, the reflected light is AOM2.
It will be returned to 1A and 21B, but AOM21A
21B and 21B, there is little tendency that the operation becomes unstable even if there is a returning light. Therefore, it is reflected by the first objective lens 7,
No special measures need to be taken for the light beam 15 returned through the light-transmitting / receiving light separating prism 5. However, when it is desired to prevent the luminous flux 15 from returning to the AOMs 21A and 21B side and further enhance the stability of the intensity of the laser beams LB1 and LB2, as shown in FIG. , LB2 are preferably incident on the field stop 24 with a predetermined angle ε1 with respect to the optical axis AX.
Also in this case, the angle ε1 determines the angle δ1 formed by the light beam 15 reflected on the surface 7a of the first objective lens 7 with respect to the optical axis AX. When the focal length of the second objective lens 4 is f2 and the aperture diameter of the field stop 24 is c, the luminous flux returning to the AOMs 21A and 21B can be almost ignored by satisfying the following expression.

Δ1 · f ₂ > c (3) In the above embodiment, the quarter-wave plate 6 is used as the polarization state converting member. However, by using, for example, a Faraday rotator, the reflected light The polarization direction may be orthogonal to the polarization direction of the incident light beam. Further, although the above-described embodiment applies the present invention to the LSA type alignment system or the LIA system, the present invention can also be applied to the FIA system which is an imaging type. Furthermore, TTL
Not only the system but also the TTR (through the reticle) system or the off-axis system alignment system can be similarly applied.

As described above, the present invention is not limited to the above-described embodiments, and various configurations can be adopted without departing from the gist of the present invention.

[0044]

According to the present invention, since the polarization state conversion member is provided between the objective optical system and the object to be inspected, the reflected light from the objective optical system is transmitted to the light source side through the light splitter. Will be returned. Therefore, since the reflected light from the objective optical system does not enter the photoelectric detecting means in the light receiving system, a signal having a good SN ratio can be obtained, and the position detection accuracy of the position detection mark can be improved.

Further, since the polarization state of the reflected light from the test object at a position closer to the test object is converted into a predetermined state (a state toward the photoelectric detecting means) with respect to the light splitter, the polarization state is changed. The length of a certain section is long. That is, the section of a state in which a plurality of polarization states are mixed (such as circular polarization) between the polarization state conversion member and the test object is shortened, and the characteristics such as antireflection coating of each optical member can be improved. Therefore, the reflected light from the test object can be efficiently guided to the photoelectric detection means.

Further, a diaphragm is arranged between the light source and the light splitting member so that the illumination light reflected by the objective optical system and directed to the light source through the light splitting member is blocked by the diaphragm. When the illumination light directed to the diaphragm is tilted with respect to the optical axis of the objective optical system, back talk is reduced even if the light source is a laser light source, so that the stability of oscillation of the laser light source is increased.

[Brief description of drawings]

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

FIG. 2 is a structural diagram with a part omitted showing a modified example in which a relay optical system is provided between a laser light source 1 and a cylindrical lens 2 in the first embodiment.

FIG. 3 is a configuration diagram showing a projection exposure apparatus to which a second embodiment of the position detecting apparatus according to the present invention is applied.

4A is a configuration diagram showing a main part of a projection exposure apparatus to which a conventional LSA system is applied, and FIG. 4B is an enlarged plan view showing a wafer mark and a light spot of the LSA system.

[Explanation of symbols]

 1 Laser Light Source 2 Cylindrical Lens 3 Field Stop 4 Second Objective Lens 5 Transmitting / Receiving Separation Prism (Polarizing Beam Splitter) 6 1/4 Wave Plate 7 1st Objective Lens 8 Projection Optical System R Reticle WM Wafer Mark 9 Wafer 11 Relay Lens 13A , 13B Photoelectric detector 17 First relay lens 18 Auxiliary field stop 19 Second relay lens

Claims (2)

[Claims] 1. A light source for emitting illumination light, an objective optical system for converging the illumination light emitted from the light source on a mark for position detection on an object, the light source and the objective optical system. An optical splitter that is disposed between the optical splitter and the optical splitter that separates the optical path of the illumination light to the test object and the optical path of the illumination light from the test object, and the objective optical system after being reflected by the test object. And a photoelectric detector that receives illumination light separated via the light splitter, and a device that detects the position of the mark for position detection based on a detection signal from the photoelectric detector. A polarization beam splitter is used as the light splitter, and a polarization state conversion member that changes the polarization state of the illumination light is provided between the objective optical system and the object to be inspected. Of the illumination light that is returned to the polarizing beam splitter through the system The polarization state,
A position detecting device, wherein a polarization state is introduced from the polarization beam splitter to the photoelectric detection means via the polarization state converting member. 2. A diaphragm is arranged between the light source and the light splitting member, and the light reflected by the objective optical system and directed to the light source side through the light splitter is blocked by the diaphragm. 2. The position detecting device according to claim 1, wherein the illumination light traveling from the light source to the diaphragm is inclined with respect to the optical axis of the objective optical system.