JP3275273B2 - Alignment device and exposure device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alignment apparatus suitable for application to an alignment system of a projection exposure apparatus used for manufacturing, for example, a semiconductor element, a liquid crystal display element, a thin film magnetic head, and the like.

[0002]

2. Description of the Related Art When a semiconductor element, a liquid crystal display element, a thin film magnetic head, or the like is manufactured by photolithography, an image of a pattern of a photomask or a reticle (hereinafter, collectively referred to as a "reticle") is projected. And a projection exposure apparatus for transferring the image onto a photosensitive substrate via a photomask. Generally, a semiconductor element or the like is formed of a multi-layer pattern, and therefore, when manufacturing the same, it is necessary to transfer various reticle patterns on a photosensitive substrate in a predetermined order. As described above, when transferring another reticle circuit pattern to the photosensitive substrate on which the pattern has already been transferred to each shot area, alignment between each shot area of the photosensitive substrate and the reticle pattern to be exposed this time is performed. It needs to be done exactly.

As a method for accurately performing such an alignment, there is known a two-beam interference method using two laser beams as disclosed in, for example, JP-A-2-227603 and JP-A-2-272305. Have been. As shown in FIG. 8, in the two-beam interference method, a wafer mark WM composed of a phase-type diffraction grating is formed as an alignment mark near each shot area on a wafer 1 as a photosensitive substrate. X is the position measurement direction
In the direction, the wafer marks WM are formed at a pitch P in the X direction. The two laser beams LB1 and LB2 are symmetrically applied to the wafer mark WM via the projection optical system. In this case, the + 1st-order diffracted light LB11 from the wafer mark WM by the laser beam LB1 and the -1st-order diffracted light LB21 from the wafer mark WM by the laser beam LB2 are reflected parallel to each other and vertically upward from the wafer 1. The pitch P and the incident angles of the laser beams LB1 and LB2 are set.

[0004] A signal corresponding to the position of the wafer mark WM is obtained by causing the diffracted lights LB11 and LB21 to interfere with each other by an alignment optical system via a projection optical system and photoelectrically converting the interference light. And the laser beam LB1
In the case of the heterodyne system in which the frequencies of the signal 1 and the signal LB2 are different, the signal due to the interference becomes a signal of a predetermined beat frequency. By comparing the phase of this signal with the phase of the reference signal, the position of the wafer 1 in the X direction Can be accurately detected. Similarly, a wafer mark is formed in the Y direction orthogonal to the X direction, and the position in the Y direction is detected by the wafer mark. A reticle mark formed of an amplitude type diffraction grating or the like as an alignment mark is also formed on the reticle side, and the reticle mark is used to detect the position of the reticle. Then, the alignment is performed by directly or indirectly setting the wafer mark and the reticle mark in a predetermined positional relationship.

Next, a conventional example of a process for forming a wafer mark WM will be described. FIG. 9 shows the detailed configuration of the wafer mark WM. As shown in FIG. 9, when the wafer mark WM is formed, first, a pitch P is formed on the surface of the wafer 1 in the X direction.
Thus, a recess 1a is formed. Thereafter, a metal film 2 such as aluminum is deposited on the surface of the wafer 1 including the concave portion 1a by sputtering or vapor deposition, so that the concave portion 1a is formed.
Recesses 2a each having a width d and a pitch P in the X direction corresponding to
Is formed. In FIG. 9, the width d of the concave portion 2a is expressed as being narrow, but in the conventional wafer mark, the width d of the concave portion 2a is about 1/2 of the pitch P. Thus, the wafer mark WM is formed from the concave portions 2a arranged at the pitch P in the X direction.
Are formed. However, since the middle between two adjacent concave portions 2a can be said to be a convex portion, it can be said that the wafer mark WM is formed of convex portions arranged at a pitch P in the X direction. It can be said that the portions and the concave portions are formed by periodically arranging them in the measurement direction.

Conventionally, the polarization states of the laser beams LB1 and LB2 irradiated onto the wafer mark WM are both set to circular polarization states. FIG. 10 shows a conventional optical system (isolator) for separating a laser beam from the wafer mark WM from a laser beam from the wafer mark WM. In FIG. Two laser beams L
B1 and LB2 enter the polarization beam splitter 51. The polarization state of the laser beams LB1 and LB2 incident on the polarization beam splitter 51 is linearly polarized light in a direction parallel to the paper surface of FIG. 10, that is, linearly polarized light of P polarization with respect to the joint surface of the polarization beam splitter 51. Therefore, the laser beams LB1 and LB2 pass through the joining surface of the polarization beam splitter 51 as it is.

[0007] P passing through the polarizing beam splitter 51
The polarized laser beams LB1 and LB2 are
After passing through 2, the light becomes circularly polarized light, is reflected by the mirror 53, and is irradiated onto the wafer mark WM via, for example, a projection optical system. At this time, diffracted light diffracted vertically upward from the wafer mark WM (diffractive lights LB11 and LB21 in FIG. 8).
Is a circularly polarized light in the opposite direction, and the diffracted light of the circularly polarized light in the opposite direction passes through the projection optical system and the mirror 53 and is a quarter wavelength plate 52.
Incident on. Therefore, the diffracted light thus returned is 1 /
After passing through the four-wavelength plate 52, it is converted into S-polarized light,
The S-polarized diffracted light was totally reflected by the joint surface of the polarizing beam splitter 51 and was incident on the light receiving element 54. In this conventional example, by combining the polarization beam splitter 51 and the quarter-wave plate 52, the light amount loss was suppressed to the minimum.

[0008]

In the prior art as described above, as shown in FIG. 9, the bottom of each recess 2a of the wafer mark is not generally parallel to the measurement direction (X direction), but is Are formed asymmetrically with respect to. Therefore, the light reflected from the bottom of the concave portion 2a of the wafer mark has a predetermined direction. When the reflected light is detected and the position of the wafer mark is detected, the actual position of the wafer mark is measured. There is a disadvantage that an error occurs between the position and the position.

In order to eliminate such an error in the position detection result, the applicant of the present invention has disclosed in Japanese Patent Application Laid-Open No. 4-284370 that the wafer mark is a metal film and the width of the concave portion 2a in the measurement direction is determined by the wavelength of the laser beam. It has been proposed to make it less than about three times, especially less than about the wavelength. By the way, in the conventional example, the laser beams LB1, L
B2 is in a circularly polarized state, and electric vectors (electric field vectors) of the laser beams LB1 and LB2 in the measurement direction of the wafer mark include a polarization component in a direction parallel to the measurement direction and a polarization component in a direction perpendicular to the measurement direction. Have been. In this case, the polarization component in a direction perpendicular to the measurement direction of the wafer mark, that is, the direction perpendicular to the period (X direction) of the recess 2a, is absorbed and attenuated until it reaches the bottom of the recess 2a, but is parallel to the period of the recess 2a. The polarized light component has no attenuation and reaches the bottom of the concave portion 2a and is reflected. Therefore, the laser beam LB
If the wafer mark 1 and LB2 are irradiated with circularly polarized light, even if the width of the concave portion 2a in the measurement direction is set to about the wavelength of the laser beam, a measurement error due to the asymmetry of the concave portion 2a may occur. was there.

In view of the above, the present invention irradiates an alignment mark composed of concave portions periodically arranged in the alignment direction with light for position detection, and detects the position using light generated from the alignment mark. The purpose of the present invention is to reduce the influence of the asymmetry of the bottom of the concave portion in the alignment apparatus for performing the above.

[0011]

An alignment apparatus according to the present invention is formed on a test object (1) and arranged at a predetermined pitch in a predetermined measurement direction, as shown in FIGS. 1 and 2, for example. An alignment mark (W) composed of a row of concave portions (2a)
An irradiation optical system (12) for irradiating position detection light to M), and a light receiving optical system (12) for receiving light generated from the alignment mark (WM) by irradiation of the position detection light. The polarization state of the position detection light on the alignment mark (WM) is determined by measuring the concave portion.
The width in direction and / or the asymmetry of the bottom of the recess,
At least one of the alignment mark (WM) materials
This is linearly polarized light in a direction determined by the other and the arrangement direction of the concave portions .

In this case, when the alignment mark (WM) is formed of metal, the direction of the electric vector (electric field vector) of the position detecting light on the alignment mark (WM) is determined by the alignment mark (WM). Place )
It is desirable to be perpendicular to the fixed direction. However, when the alignment mark (WM) is formed of metal, the alignment mark (WM) of the position detection light is used.
The direction of the electric vector above to the location of the alignment mark
There are cases where the direction may be fixed . Further, it is desirable that the width of the concave portion (2a) of the alignment mark (WM) in a predetermined direction is about three times or less the wavelength of the position detecting light. Further, it is desirable to further include polarization state changing means for setting the direction of linearly polarized light on the alignment mark (WM) of the light for position detection. Also according to the invention
The exposure apparatus includes the alignment apparatus of the present invention.
A predetermined pattern is placed on the substrate positioned by the alignment device.
Transcribe the turn.

[0013]

According to the present invention, the position detecting light applied to the alignment mark (WM) is linearly polarized light. The linearly polarized light on the alignment mark (WM)
Direction is the width of the recess in the measurement direction and / or
Asymmetry at the bottom of the recess and the alignment mark (WM)
At least one of the above materials and the arrangement of the recesses
By setting the direction determined by the direction, the influence of the asymmetry of the bottom of the concave portion (2a) is reduced, and the position detection error is reduced.

When the alignment mark (WM) is formed of metal, the direction of the electric vector of the position detecting light on the alignment mark (WM) is determined by
When the alignment mark (WM) is perpendicular to the periodic direction, the following operation is achieved. That is, if the direction of the electric vector of the light for position detection is parallel to the inner surface of the concave portion (2a) (perpendicular to the periodic direction), the electrons on the inner surface of the concave portion (2a) also vibrate according to the vibration of the electric vector. Therefore, the light for position detection attenuates exponentially when propagating in the concave portion (2a). Therefore, even if the bottom of the concave portion (2a) is asymmetric, the influence of the asymmetry becomes very small, and the error in position detection becomes very small.

On the other hand, if the direction of the electric vector of the light for position detection is perpendicular to the inner surface of the concave portion (2a) (parallel to the periodic direction), the concave portion (2a) is not affected by the vibration of the electric vector. The electrons on the inner surface do not vibrate, and the light for position detection reaches the bottom of the recess (2a) without being attenuated even when propagating in the recess (2a). Therefore, it is affected by the asymmetry of the bottom of the concave portion (2a). However, when the width of the concave portion of the alignment mark is less than about three times the wavelength, and particularly narrower than the wavelength, the bottom of the concave portion (2a) of the alignment mark is formed symmetrically (it can be regarded as formed). Sometimes). At this time, since the light in the polarization state parallel to the periodic direction has no attenuation, the intensity of the diffracted light is larger than that of the polarized light perpendicular to the periodic direction, and the detection accuracy is improved. Further, depending on the alignment mark, it is better to make the periodic direction and the polarization direction coincide with each other.
As compared with the case (a) in which the direction along the groove and the polarization direction are made to coincide with each other, it may be advantageous in terms of the S / N ratio.

When the width of the concave portion (2a) is less than about three times the wavelength, particularly less than the wavelength, there is a problem that the intensity of the diffracted light is reduced. When the width of the concave portion becomes smaller than the wavelength, the bottom portion is formed symmetrically (may be regarded as formed)
Therefore, it does not depend on the polarization direction of the incident light. In this case, it is easier to obtain the amount of light if the light is incident in parallel than to make it perpendicular to the periodic direction of the alignment mark (WM).
/ N ratio is improved. Further, the width of the concave portion (2a) is set to 3
If it is about twice or less, the accuracy is further improved. In addition, a polarization state variable for setting the direction of the linearly polarized light on the alignment mark (WM) of the position detection light to a direction determined by the periodic direction of the alignment mark (WM) and the material of the alignment mark (WM). In the case where the means is provided, it is possible to reduce the amount of light for position detection reaching the bottom of the concave portion (2a) of the alignment mark (WM) even when the periodic direction and the material of the alignment mark (WM) change. it can.

Hereinafter, a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 shows a main part of a projection exposure apparatus provided with the alignment apparatus of this embodiment. In FIG. 2, a reticle R is held on a reticle holder 3 and a circuit pattern formed on the reticle R is not shown in the drawing. It is illuminated with exposure light IL from the optical system. The circuit pattern is reduced to, for example, 1/5 by the projection optical system 4,
The image is transferred onto the wafer 1 coated with a photosensitive material such as a resist. In the vicinity of each shot area of the wafer 1, a wafer mark WM as an alignment mark is formed at a predetermined pitch in the measurement direction.

FIG. 1 shows a wafer mark WM formed in the vicinity of each shot area of the wafer 1. In FIG. 1, a metal film 2 is formed on a wafer substrate (for example, a silicon substrate).
Are formed on the metal film 2 so as to form recesses 2a each having a width d at a pitch P in the X direction. Therefore, the periodic direction of the wafer mark WM is the X direction, and the X direction is also the measurement direction (alignment direction). In this example, the width d of the concave portion 2a in the X direction is set to be 3 times the wavelength λ of the position detecting light.
It is set to about twice or less, especially smaller than the wavelength λ. Thereby, the light for position detection is easily attenuated in the concave portion 2a.

Returning to FIG. 2, the wafer 1 is
Is placed on the wafer stage 6 via the. The wafer stage 6 includes an XY stage for positioning the wafer 1 in a two-dimensional plane perpendicular to the optical axis of the projection optical system 4 and a Z stage for positioning the wafer 1 in the optical axis direction. A movable mirror 7 is set on the wafer stage 6 and the coordinates of the XY stage in the wafer stage 6 are constantly measured by reflecting the laser beam of the laser interferometer 8 with the movable mirror 7. Further, by operating the wafer stage 6 via the driving device 9, for example, step-and-
Positioning of each shot area of the wafer 1 is performed by a repeat method.

The pattern already formed in each shot area on the wafer 1 and the reticle R pattern usually need to be aligned with an accuracy of about one fifth or less of the width of the pattern. In order to perform this alignment, a reference mark 10 is attached near the wafer 1 on the wafer stage 6, and an alignment microscope 11 having a light source of illumination light having the same wavelength as the exposure light IL is arranged above the reticle R. I do. Further, an alignment optical system 12 is arranged beside the projection optical system 4, and the position of the wafer mark WM on the wafer 1 is detected by the alignment optical system 12 (the details are disclosed in JP-A-2-272305 and the like). There).

Two laser beams LB 1 and LB 2 are emitted from the alignment optical system 12, and these laser beams are irradiated on the wafer 1 via the return mirror 13 and the projection optical system 4. In this case, the wafer mark WM
The incident angles of the two laser beams and the pitch P of the wafer mark WM are set so that the diffracted light LB0 is generated substantially vertically above the wafer 1 from above. The diffracted light LB0
Is a mixed light of the + 1st-order diffracted light of the laser beam LB1 and the -1st-order diffracted light of the laser beam LB2. The diffracted light LB0 enters the alignment optical system 12 via the projection optical system 4 and the return mirror 13.

In this case, the position of the two laser beams LB1 and LB2 irradiated onto the wafer 1 and the relative position between the reticle R and the reference mark 10 provided on the wafer stage 6 are determined by using an alignment microscope 11. Observing through the reticle R and detecting the same reference mark 10 with the alignment optical system 12 can be known.

FIG. 3 shows the alignment optical system 12 shown in FIG.
In FIG. 3, the laser beam LB emitted from the laser light source 14 is
5, the laser beam is divided into two laser beams LB1 and LB2. One laser beam LB1 enters the combining prism 20 via the first acousto-optic modulator (AOM) 16 and the right-angle prism 17, and the other laser beam LB1
B2 is incident on the combining prism 20 via the right-angle prism 18 and the second acousto-optic modulator (AOM) 19. The acousto-optic modulation elements 16 and 19 have different frequencies f
Driven at ₁ and f ₂ , acousto-optic modulators 16 and 19
+1 only order diffracted minute respective drive frequencies f ₁ and f ₂ frequency of the light diffracted increases by. These two + 1st-order diffracted lights having different frequencies (these are also called laser beams LB1 and LB2) are incident on the combining prism 20.

The laser beam LB1 transmitted through the synthesizing prism 20 and the laser beam LB2 reflected by the synthesizing prism 20 are focused on a reference grating 22 by an objective lens 21, and the light transmitted through the reference grating 22 is used as a reference grating. The two diffracted lights diffracted substantially vertically downward with respect to 22 are mixed by the light receiving element 23 and detected. On the other hand, the laser beam LB1 reflected by the combining prism 20 and the laser beam LB2 transmitted through the combining prism 20 pass through the polarizing beam splitter 24 and then pass through the objective lens 25.
And is incident on the return mirror 13 in FIG. At this time, the laser beams LB1 and LB2 incident on the polarization beam splitter 24 are linearly polarized light, and the polarization direction (the direction of the electric vector) is P-polarized with respect to the polarization beam splitter 24 (on the incident surface with respect to the joining surface of the polarization beam splitter 24). (Parallel direction).

Although not shown in FIG. 3, FIG.
As shown in FIG. 4, between the polarization beam splitter 24 and the objective lens 25, a Faraday rotator 28 for rotating the polarization direction by 45.degree.
A / 2 wavelength plate 29 is arranged. In FIG. 4, the P-polarized laser beam LB that has passed through the polarizing beam splitter 24 is shown.
1, LB2 enters the Faraday rotator 28. The laser beams LB1 and LB2 emitted from the Faraday rotator 28 are linearly polarized light polarized in a direction rotated by 45 ° from the polarization direction at the time of incidence. As the laser beams LB1 and LB2 further pass through the half-wave plate 29, the polarization directions of the laser beams LB1 and LB2 are further rotated by + 45 ° or −45 °.

The laser beam whose polarization state is set as described above is irradiated onto the wafer mark WM of FIG. 1 through the objective lens 25, the bending mirror 13, and the projection optical system 4. In this example, by adjusting the rotation angle of the half-wave plate 29, the polarization directions of the laser beams LB1 and LB2 irradiated onto the wafer mark WM in FIG. 1 are changed in the Y direction perpendicular to the periodic direction of the concave portion 2a. , The X direction which is a periodic direction.

The diffracted light LB0 diffracted almost vertically upward from the wafer mark WM passes through the projection optical system 4, the bending mirror 13, and the objective lens 25 while maintaining the linearly polarized light, and reaches the half-wave plate 29 in FIG. Incident. 1/2 wave plate 2
The diffracted light LB0 transmitted through 9 has a polarization direction of 4 as before.
A linearly polarized light beam rotated by 5 ° is incident on the Faraday rotator 28. The polarization direction of the diffracted light LB0 transmitted through the Faraday rotator 28 is further rotated by 45 °, and the polarization direction has been rotated 90 ° before returning to the polarization beam splitter 24. Therefore, the diffracted light L
B0 enters the polarization beam splitter 24 as an S-polarized laser beam, and is all reflected at the joint surface of the polarization beam splitter 24. Polarizing beam splitter 24
The diffracted light LB0 reflected by the light enters the light receiving element 26.

Returning to FIG. 3, the reference signal from the light receiving element 23 and the alignment signal from the light receiving element 26 are supplied to the alignment processing unit 27, respectively. Light receiving element 26
The alignment signal obtained by photoelectrically converting the diffracted light LB0 is a sine wave whose frequency is the frequency Δf of the difference between the respective drive frequencies f ₁ and f ₂ of the acousto-optic modulation elements 16 and 19, and is similarly received. The reference signal output from the element 23 is also a sine wave having a frequency Δf. By detecting the phase difference between the reference signal and the alignment signal, the position shift of the wafer 1 can be known. The amount of wafer displacement detected by the alignment processing unit 27 is sent to a main computer that controls the operation of the entire apparatus.

Next, the operation of this embodiment will be described with reference to FIG. FIG. 1 shows a wafer mark WM of the present embodiment. In FIG. 1, a laser beam irradiated on the wafer mark WM has been conventionally irradiated with circularly polarized light as shown by a circular arrow P3. On the other hand, the polarization state of the laser beam of the present example is linearly polarized light parallel to the periodic direction (X direction) of the concave portion 2a of the wafer mark WM as shown by the arrow P1, or the periodic direction of the concave portion 2a as shown by the arrow P2. It is a linearly polarized light perpendicular to.

When the wafer mark WM is composed of the concave portions 2a periodically formed in the X direction on the metal film 2 as in this embodiment, the linearly polarized laser beam applied to the wafer mark WM is The polarization direction (the direction of the electric vector) is set in the Y direction perpendicular to the X direction as shown by the arrow P2. Accordingly, when the laser beam passes through the concave portion 2a, the electrons on the side surfaces of the concave portion 2a also vibrate in the Y direction according to the vibration of the electric vector in the Y direction.
The laser beam decays exponentially rapidly. Therefore, the laser beam is almost attenuated before reaching the bottom of the recess 2a, and there is almost no reflected light from the bottom, and even when the bottom of the recess 2a is asymmetric in the X direction, the wafer mark WM is not removed. Is extremely small.

When the wafer mark WM has the concave portions 2a formed at a predetermined pitch in the Y direction, the polarization direction of the laser beam applied to the wafer mark WM is in the X direction perpendicular to the Y direction. Set. This allows
The error in the position detection result in the Y direction is also reduced. However, when the wafer mark WM is formed by periodically forming a concave portion in the X direction on a nonconductive object (such as an insulator), the polarization direction of the laser beam is not necessarily changed in the Y direction perpendicular to the X direction. You do not need to set it.

Next, in this embodiment, the wafer mark WM
A method of variously switching the polarization direction of the laser beam incident on the laser beam will be described. In this case, as shown in FIG. 4, the Faraday rotator 28 obtains a linearly polarized light beam rotated by 45 ° as described above. In order to make the linearly polarized beam rotated by 45 ° polarized and incident in a direction perpendicular or parallel to the periodic direction of the concave portion 2a of the wafer mark WM, a half-wave plate is used as a first method. 29 may be rotated. 1/2
By adjusting the rotation angle of the wave plate 29, a laser beam linearly polarized in a desired direction can be irradiated onto the wafer mark WM.

A second technique for setting the direction of linearly polarized light of the laser beam irradiated on the wafer mark WM to a desired direction uses a Pockels element instead of the half-wave plate 29 in FIG. That is. A Pockels element is an element that can change the angle of linearly polarized light of an emitted laser beam depending on the magnitude of an applied voltage. Accordingly, by applying a voltage that rotates, for example, ± 45 ° to the Pockels element to the incident light of the linearly polarized light rotated by 45 °, the Pockels element is perpendicular or parallel to the periodic direction of the concave portion 2a of the wafer mark WM. A linearly polarized beam polarized in the direction can be obtained.

Next, the alignment optical system 12 of this embodiment
The case where a laser diode is used as the laser light source 14 in FIG. 3 will be described with reference to FIG. FIG. 5 shows a laser diode 30. In FIG. 5, the spread of the laser beam output from the laser diode 30 in the direction of the electric field of the laser diode 30 is larger than that in the direction along the bonding surface. Therefore,
The cross-sectional shape of the laser beam emitted from the laser diode 30 is elliptical, and the laser beam is linearly polarized in a direction in which the width of the elliptical cross section is shorter.

In general, the sectional shape of the laser beam irradiated on the wafer mark WM in FIG. 1 is a parallelogram,
This cross-sectional shape is formed by a field slit placed at a position conjugate with the wafer. Therefore, when the laser diode 30 is used as a light source, the laser diode 3
By adjusting the longitudinal direction of the elliptical cross section of the laser beam emitted from zero so as to match the longitudinal direction of the field slit, loss of the light amount is reduced. In addition, the laser beam irradiated onto the wafer mark WM in FIG. 1 uses the laser diode 30 in FIG. 5 because the direction of the narrow cross section is generally set in the Y direction perpendicular to the periodic direction of the concave portion 2a. In the case, the concave portion 2 of the wafer mark WM is used.
There is an advantage that it is easy to obtain a linearly polarized beam polarized in the Y direction perpendicular to the period direction of a.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 6 shows a wafer mark WM formed on the wafer in the present embodiment. As shown in FIG. 6, a metal film 2 is deposited on the wafer and arranged on the metal film 2 at a pitch P1 in the X direction. And the concave portions 2b arranged at a pitch P2 (usually equal to the pitch P1) in the Y direction. The width of the concave portion 2a in the X direction is d1, the width of the concave portion 2b in the Y direction is d2, and the widths d1 and d2 are each 3 times the wavelength of the laser beam for position detection.
It is set to be narrower than about twice. The two-dimensional diffraction grating composed of these recesses 2a and 2b is used to obtain the wafer mark WM.
Is configured. In this example, two laser beams for position measurement in the X direction and Y
By mixing and irradiating two laser beams for position measurement in the X and Y directions, the X and Y directions of the wafer mark WM can be adjusted.
Direction position detection is performed simultaneously.

FIG. 7 shows a main part of the alignment optical system of the present embodiment. In FIG. 7, two parallel laser beams emitted from an optical system not shown (for example, the combining prism 20 in FIG. 3) are shown. LB1 and LB2 enter the polarization beam splitter 31 whose joining surface is perpendicular to the paper surface of FIG.
The laser beams LB1 and LB2 are linearly polarized in a direction inclined by 45 ° from the direction perpendicular to the plane of FIG. 7, and the S-polarized component (polarized component perpendicular to the plane of FIG. 7) of these laser beams is a polarized beam. A laser beam LB1 for position measurement in the X direction which is reflected by the joint surface of the splitter 31
X, LB2X. On the other hand, a P-polarized light component (a polarized light component parallel to the plane of FIG. 7) of these laser beams passes through the bonding surface of the polarizing beam splitter 31, and the laser beams LB1Y and LB1Y for position measurement in the Y direction.
Taken out as B2Y.

Laser beam LB1 for position measurement in Y direction
Y and LB2Y are a mirror 39a and a quarter-wave plate 33b.
And enters the polarization beam splitter 34b in the state of circularly polarized light. The S-polarized light component of the laser beams LB1Y and LB2Y is reflected by the polarizing beam splitter 34b, and enters the light receiving element 23b via an objective lens and a reference grating (not shown). On the other hand, the P-polarized light component passes through the polarization beam splitter 34b, further passes through the polarization beam splitter 35b, and then passes through the Faraday rotator 36b and the Pockels element 37b. The laser beams LB1Y and LB2Y whose polarization directions on the wafer mark WM have been adjusted to the optimum direction by the Faraday rotator 36b and the Pockels element 37b are reflected by the mirror 3
The light is reflected by 9b and is incident on a separation / combination mirror 38 composed of, for example, a polarization beam splitter.

The Db prism 32 rotates the optical axis by 90 ° so that the laser beams LB1X and LB2X for position measurement in the X direction are irradiated on the wafer mark WM in a direction crossing the direction orthogonal to the Y direction. Is done. Thereafter, the laser beams LB1X and LB2X are applied to the １ ／ wavelength plate 33a.
And enters the polarization beam splitter 34a in the state of circularly polarized light. The S-polarized light component of these laser beams is
The light is reflected by the polarization beam splitter 34a and enters the light receiving element 23a via an objective lens and a reference grating (not shown). On the other hand, the P-polarized light component is a polarized beam splitter 34a.
After passing through the polarization beam splitter 35a, the light passes through the Faraday rotator 36a and the Pockels element 37a. These Faraday rotators 36a
The laser beams LB1X and LB2X whose polarization directions on the wafer mark WM have been adjusted to the optimum direction by the Pockels element 37a are incident on the separation / combination mirror 38.

The four laser beams LB1X, LB2X and LB1Y, LB2 reflected by the separation / combination mirror 38
Y is irradiated onto the wafer mark WM in FIG. 6 via the objective lens 25, the turning mirror 40, and the projection optical system 4.
At this time, the optical axes of the laser beams LB1X and LB2X are orthogonal to the optical axes of the laser beams LB1Y and LB2Y, and the polarization directions are also orthogonal to each other. Wafer mark W
The laser beams LB1X and LB2X and the laser beams LB1Y and LB2Y applied to the light beam M, respectively, cause the diffracted light beams LB0X whose polarization directions are orthogonal to each other from the wafer mark WM.
And LB0Y are generated, and these diffracted lights enter the separation / combination mirror 38 via the projection optical system 4, the folding mirror 40, and the objective lens 25 in FIG.

Y reflected by the separating / combining mirror 38
The diffracted light LB0Y for measuring the position in the direction is reflected by a mirror 38b,
The light receiving element 26b passes through the Pockels element 37b, the Faraday rotator 36b, and the polarization beam splitter 35b.
Incident on. The reference signal for the Y direction output from the light receiving element 23b and the alignment signal for the Y direction output from the light receiving element 26b are supplied to the alignment processing unit 27, respectively. The diffracted light LB0X for position measurement in the X direction transmitted through the separating / combining mirror 38 is incident on the light receiving element 26a via the Pockels element 37a, the Faraday rotator 36a, and the polarization beam splitter 35a. The X-direction reference signal output from the light receiving element 23a and the X-direction alignment signal output from the light receiving element 26a are supplied to the alignment processing unit 27, respectively. The alignment processing unit 27 detects the positions of the wafer mark WM in FIG. 6 in the X and Y directions from the two sets of supplied signals.

In this embodiment, since the wafer mark WM in FIG. 6 is formed on the metal film 2, the laser beam for position measurement in the X direction (the laser beams LB1X, L in FIG. 7) is used.
B2X) is irradiated onto the wafer mark WM as linearly polarized light having a polarization direction of the Y direction. Further, a laser beam for position measurement in the Y direction (laser beams LB1Y and LB1 in FIG. 7).
B2Y) is irradiated on the wafer mark WM as linearly polarized light having a polarization direction of the X direction. As a result, the laser beam for position measurement is turned into the concave portions 2a and 2b of the wafer mark WM.
Decays sharply in and hardly reaches the bottom.
Therefore, even if the bottoms of the recesses 2a and 2b are asymmetric in the measurement direction, the error in the position detection result is small.

As in the case of the alignment optical system shown in FIG. 7, in order to simultaneously detect the positions in the X and Y directions, the following method can be considered. First, in the first method, the driving frequencies f ₁ and f ₁ for the acousto-optic modulator in the X direction and the Y direction.
Changing the frequency △ f ₂ of the difference, for receiving the alignment signal of the frequency difference △ f _y for alignment signal and the Y direction of the frequency difference △ f _x for the X-direction in one light-receiving element. Then, the photoelectric conversion signal output from the light receiving element, by separating into a component of the component and the frequency △ f _y frequency △ f _x at the frequency filter circuit, by performing position measurement of the X and Y directions at the same time Can be.

Further, in the second method, the pitch P1 in the X direction and the pitch P2 in the Y direction of the wafer mark WM shown in FIG.
(Usually equal to P1) are halved. When the pitch P1 (P2) of the wafer mark WM is halved, the diffraction angle of the laser beam applied to the wafer mark WM becomes 2
For example, the 0th-order diffracted light of the other laser beam LB2 and the + 1st-order diffracted light of the laser beam LB1 are emitted in the incident direction of one laser beam LB1. Similarly, in the incident direction of the laser beam LB2,
Zero-order diffracted light of laser beam LB1 and laser beam L
The -1st-order diffracted light of B2 is emitted overlapping. Therefore,
Since no diffracted light is generated vertically above the wafer mark WM, there is no mixing of the diffracted light for detecting the position in the X direction and the diffracted light for detecting the position in the Y direction.

In the above embodiment, the width of the concave portion of the alignment mark is set to about three times or less the alignment wavelength.
As long as the polarization direction of the alignment light (linearly polarized light) coincides with the direction perpendicular to the periodic direction, it is possible to reduce the effect of the asymmetry of the recess even if the width of the recess exceeds three times the wavelength. . In FIG. 1, the alignment mark (WM)
The width d of the concave portion 2a is, for example, 3 which is the wavelength of the alignment light.
When the wavelength is about twice or less, particularly when the wavelength is narrower than the wavelength, the bottom of the concave portion 2a may be considered to be formed symmetrically. In such a case, it is preferable that the polarization directions of the laser beams LB1 and LB2 applied to the alignment mark WM coincide with the X direction which is the periodic direction. At this time, since the bottom of the concave portion 2a is symmetrical, the position can be accurately detected even by using the diffracted light from the concave portion 2a. Therefore, Y perpendicular to the periodic direction
Compared to the case where the direction and the polarization direction match, the diffracted light intensity is increased by the amount that the diffracted light is not attenuated by the concave portion 2a.
That is, the advantage that the S / N ratio is improved is obtained.

Further, the width of the concave portion of the alignment mark,
It is preferable that the polarization direction of the alignment light be appropriately changed according to the degree of asymmetry of the bottom of the alignment light. That is, a first mode for matching the polarization direction to the direction perpendicular to the periodic direction and a second mode for matching the polarization direction to the periodic direction are prepared (for example, set in a control unit that controls the entire apparatus). One of the first mode and the second mode is selected according to the width of the concave portion of the alignment mark and / or the degree of asymmetry of the bottom thereof, and the polarization direction is adjusted (or confirmed) according to the selected mode. It is preferable to perform mark detection. For example, if the width of the concave portion of the alignment mark on the wafer exceeds the alignment wavelength, the first mode is selected, and if the width of the concave portion is smaller than the wavelength, the second mode is selected. At this time, even if the width of the concave portion is narrower than the wavelength, if there is asymmetry in the lower portion, it is desirable to make the polarization direction coincide with the direction perpendicular to the periodic direction.

The operator may select a mode according to the mark information (the width of the concave portion, whether or not the bottom is asymmetric, etc.) and set the mode via the keyboard, or the device itself. May be automatically selected according to the information written on the barcode of the wafer or the wafer cassette (the width of the concave portion, whether or not the bottom is asymmetric, or the name of the wafer, etc.). Further, for example, Japanese Patent Application Laid-Open No. 2-541
No. 03, JP-A-4-65603, an alignment mark is detected using an alignment sensor adopting an image processing method, and the asymmetry of the concave portion and the width of the concave portion determined from the detection result are determined. Mode selection may be performed accordingly. Note that the alignment sensor disclosed in the above publication irradiates an alignment mark with illumination light (for example, white light) having a predetermined wavelength width, and images the mark on an index plate arranged in a plane conjugate with the wafer. Image. Further, the image of the alignment mark and the image of the index mark on the index plate are formed on the light receiving surface of the image sensor by a relay lens system, and the relative displacement between the two marks is detected. In the above embodiment, 2
Although the description has been given by taking the alignment sensor adopting the light beam interference method as an example, the present invention may be applied to an alignment sensor adopting the image processing method as described above, and the same effect as the above embodiment is obtained. be able to.

Although the alignment system of the above embodiment employs the heterodyne system, for example, a homodyne system or two light beams having different polarization directions are irradiated on the alignment mark, and the diffracted light from the mark is detected. The same effect can be obtained by applying the present invention to a method of receiving light by causing interference through photons or the like. Also, not only the method of detecting the phase of the diffracted light from the alignment mark, for example, when performing position detection by a so-called laser step alignment method, or for an alignment apparatus of an image processing method using an image sensor, Exactly the same effect can be obtained by applying the present invention. For example, in the case of the laser step alignment method, an alignment mark and a slit-shaped probe light are relatively scanned, and the intensity of diffracted light emitted from the alignment mark in a predetermined direction by the probe light is measured. By detecting, position detection is performed.

In an actual process, for example, a photoresist layer having a predetermined thickness (about 1 μm) is formed on the metal film 2 shown in FIG. 1, but the present invention relates to the presence or absence of such a photoresist layer. However, it is effective against the asymmetry of the bottom of the concave portion of the alignment mark. As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

[0050]

According to the present invention, the polarization state of the position detecting light applied to the alignment mark is linearly polarized light. By setting the polarization direction of the light for position detection to a direction in which the light for position detection is attenuated in the concave portion of the alignment mark, the influence of the asymmetry of the bottom of the concave portion can be reduced. . Therefore, there is an advantage that the error of the position detection of the alignment mark can be reduced.

When the direction of the electric vector of the position detecting light on the alignment mark is made perpendicular to the periodic direction of the alignment mark when the alignment mark is formed of metal, When the width of the concave portion in the periodic direction is narrowed to, for example, about the wavelength of the position detecting light, the position detecting light rapidly attenuates in the concave portion. Therefore, the influence of the asymmetry of the bottom of the concave portion is reduced. However, when the bottom of the concave portion of the alignment mark is substantially symmetrical, the direction of the electric vector of the position detection light on the alignment mark is set to the periodic direction, so that the S / N of the detection signal is increased.
The ratio can be increased.

In particular, when the width of the concave portion of the alignment mark is set to about three times or less, particularly the wavelength or less, of the wavelength of the position detection light, the bottom of the concave portion is formed symmetrically. At this time, if the direction of the electric vector of the position detecting light on the alignment mark is parallel to the periodic direction of the alignment mark, the intensity of the diffracted light is maintained because there is no attenuation in the concave portion.
Further, when the polarization state changing means for setting the direction of the linearly polarized light on the alignment mark of the light for position detection to a direction determined by the periodic direction of the alignment mark is provided, the periodic direction of the alignment mark and Even when the material changes, the influence of the asymmetry of the bottom of the concave portion of the alignment mark can be reduced.

[Brief description of the drawings]

FIG. 1 is an enlarged plan view showing a wafer mark to be subjected to position detection in a first embodiment of the present invention .

FIG. 2 is a configuration diagram showing a main part of a projection exposure apparatus equipped with the alignment apparatus of the first embodiment.

FIG. 3 is a configuration diagram in which a part of an alignment optical system in FIG. 2 is omitted.

4 is a configuration diagram showing an optical system for separating a laser beam to a wafer mark and a laser beam from a wafer mark in the alignment optical system of FIG. 3;

FIG. 5 is a perspective view showing a laser diode as another example of the laser light source.

FIG. 6 is an enlarged plan view showing a wafer mark to be subjected to position detection in a second embodiment of the present invention.

FIG. 7 is a configuration diagram illustrating a main part of an alignment optical system according to a second embodiment.

FIG. 8 is a side view for explaining the principle of conventional wafer mark position detection.

FIG. 9 is a cross-sectional view for explaining a conventional manufacturing process of a wafer mark.

FIG. 10 is a configuration diagram showing an optical system for separating a laser beam to a wafer mark and a laser beam from a wafer mark in a conventional alignment optical system.

[Explanation of symbols]

 R Reticle 1 Wafer 2 Metal film 2a Depression 4 Projection optical system 10 Reference mark 11 Alignment microscope 12 Alignment optical system 14 Laser light source 16, 19 Acousto-optic modulation element 22 Reference grating 23, 26 Light receiving element 24 Polarizing beam splitter 27 Alignment processing unit 28 Faraday rotator 29 1/2 wave plate 32 Dove prism 36a, 36b Faraday rotator 37a, 37b Pockels element

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/027 G01B 11/00 G03F 9/00

Claims (11)

(57) [Claims] 1. A method according to claim 1, which is formed on an object to be measured and is performed in a predetermined measurement direction.
An irradiation optical system for irradiating position detection light to an alignment mark formed of concave portions arranged at a predetermined pitch; and a light receiving optical system for receiving light generated from the alignment mark by irradiation of the position detection light. The polarization state of the position detection light on the alignment mark is determined by changing the width of the concave portion in the measurement direction and / or
Is the asymmetry of the bottom of the recess and the alignment mark
And the arrangement of the recesses
An alignment apparatus, wherein the linearly polarized light has a direction determined by the direction. 2. The alignment mark is formed of metal.
When the alignment is performed, the alignment of the position detecting light is performed.
The direction of the electric vector on the
2. The apparatus according to claim 1, wherein the direction is perpendicular to the direction.
An alignment apparatus according to item 1. 3. The alignment mark is formed of metal.
And the width of the recess is smaller than the wavelength of the position detecting light.
When the distance is set to be narrower, the position detection light
The direction of the electric vector on the alignment mark,
2. The alignment apparatus according to claim 1 , wherein the alignment direction coincides with the measurement direction . 4. The width of the recess in the measurement direction is
The direction of polarization of the linearly polarized light on the alignment mark is set wider than the wavelength of the light for position detection.
In a direction perpendicular to the measurement direction.
2. The alignment apparatus according to claim 1 , wherein: 5. The width of the concave portion in the measurement direction is:
The direction of polarization of the linearly polarized light on the alignment mark is narrower than the wavelength of the position detection light.
2. The alignment apparatus according to claim 1 , wherein the distance is set to coincide with the measurement direction . 6. The width of the recess in the measurement direction is:
It is set narrower than the wavelength of the position detection light, and
If the asymmetry exists at the bottom of the alignment mark, the polarization direction of the linearly polarized light on the alignment mark
In a direction perpendicular to the measurement direction.
2. The alignment apparatus according to claim 1 , wherein: 7. The width of the recess in the measurement direction is
It is determined to be about three times or less the wavelength of the position detecting light.
The alignment device according to any one of claims 1 to 6, wherein: 8. The alignment of the position detecting light.
Variable polarization state hand to set the direction of linearly polarized light on the mark
The alignment device according to claim 1 , further comprising a step . 9. The apparatus according to claim 1, wherein said polarization state changing means is a half-wavelength light.
Plate or a Pockels element
Item 9. The alignment device according to item 8 . 10. A polarization state changing means, comprising:
Based on the mark information including the width and the asymmetry of the bottom of the recess
Automatically selecting the direction of the linearly polarized light.
The alignment device according to claim 8 or 9 , wherein 11. An alignment apparatus according to claim 1, further comprising: a substrate positioned by the alignment apparatus;
An exposure apparatus for transferring a predetermined pattern.