JPH09153451A - Aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To minimize the positioning error due to the relative displacement between fixed mirrors of a laser interferometer by compensating for effects of the displacement detected through a projection optical system using two reference members. SOLUTION: The relative displacement between a fixed mirror 7 substantially integral with a reference mark 3a on the mask side and a fixed mirror 5a integral with a reference mark 14 on the wafer side is detected by a heterodyne displacement detector through a projection optical system 4. Based on the detected displacement and the reading of a laser interferometer for a wafer stage, a control unit 20 supplies a mask stage drive 21 and a wafer stage drive 19 with signals that have undergone compensation for effects of the detected relative displacement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus used in a photolithography process for manufacturing, for example, a semiconductor element or a liquid crystal display element, and more particularly to a mask in an exposure apparatus of a step scan type or a step and repeat type. Regarding alignment with a photosensitive substrate.

[0002]

2. Description of the Related Art An exposure apparatus currently in practical use incorporates an alignment system for optically aligning a mask with a photosensitive substrate (wafer, glass plate or the like). As such an alignment system, for example, an off-axis imaging system alignment system is known. The imaging system alignment system is
It is also called an A (Field Image Alignment) system.

In an off-axis type FIA system, a wafer image pickup system detects a wafer mark, and a mask image pickup system different from the wafer image pickup system detects a mask mark without using a projection optical system. The alignment operation using the off-axis FIA system will be briefly described below. First, prior to exposure, the wafer position is detected by detecting the wafer mark by an off-axis FIA system fixed to the projection optical system. The offset between the projection optical system and the off-axis FIA system is measured in advance by another appropriate means.

Next, the wafer stage, and thus the wafer, is positioned at a predetermined position with respect to the projection optical system based on the wafer position detection result and the offset measured in advance. In this way, exposure is performed in a state where the wafer is aligned (aligned) with the projection optical system. In this case, at the time of positioning the wafer stage, a wafer stage interferometer having a fixed mirror connected to the projection optical system is used. Therefore, the wafer stage fixed mirror connected to the projection optical system serves as a reference for positioning the wafer stage.

In a step scan type exposure apparatus that exposes each shot area of a wafer while scanning the mask and the wafer with respect to a projection optical system, the mask is also held on a movable mask stage. in this case,
The off-axis FIA system detects the mask mark and positions the mask stage. When positioning the mask stage, a mask stage interferometer having a fixed mirror fixed to a mask stage holder connected to the projection optical system is used. Therefore, also in the case of the mask stage, the fixed mirror for the mask stage connected to the projection optical system serves as a positioning reference.

[0006]

In the conventional exposure apparatus as described above, the position control of the wafer and the mask during exposure depends only on the wafer stage interferometer and the mask stage interferometer, respectively. In other words, in each interferometer, when the reference fixed mirror is displaced with respect to the projection optical system, an alignment error, that is, an alignment error between the wafer and the mask occurs, and as a result, the transfer accuracy deteriorates.

Particularly, in the step-scan type exposure apparatus, the movement of the mask during the scanning operation is large, and vibration occurs in the entire apparatus. Due to this vibration, each fixed mirror serving as a positioning reference for the wafer stage and the mask stage is likely to be relatively displaced, or each fixed mirror is relatively displaced with respect to the projection optical system. As a result, as described above, an alignment error occurs between the mask and the wafer.

Even in a step-and-repeat type exposure apparatus in which only the wafer is two-dimensionally scanned and successively transferred to each shot area of the wafer, the above-mentioned vibration may cause a positioning error. further,
In the step scan type exposure device,
Both the mask and the wafer move with respect to the projection optics. Therefore, when attempting to align the mask and the wafer during exposure, it is necessary to form a mask mark over the entire surface of the mask.

The present invention has been made in view of the above-mentioned problems, and it is possible to suppress the alignment error caused by the displacement of the fixed mirror of the interferometer due to the vibration of the entire apparatus and perform the exposure with high precision alignment. The purpose is to provide a device.

[0010]

In order to solve the above-mentioned problems, in the present invention, projection optics for forming an image of a predetermined pattern formed on a mask on a photosensitive substrate based on exposure light. In an exposure apparatus comprising a system and a substrate stage that holds the substrate and is movable in a predetermined plane with respect to the projection optical system, a substrate stage position detection member formed on the substrate stage and the projection Based on the first reference member fixedly provided at a predetermined position on the substrate side of the optical system,
A relative displacement of a substrate stage position detection system for detecting the position of the substrate stage, a second reference member fixed at a predetermined position on the mask side of the projection optical system, and the first reference member is detected. And a relative displacement detection system for detecting the relative displacement detection system, wherein the relative displacement detection system detects at least the first reference member of the first reference member and the second reference member via the projection optical system. An exposure apparatus is provided.

According to a preferred aspect of the present invention, a mask stage which holds the mask and is movable in a predetermined plane with respect to the projection optical system, and a mask stage position detecting member formed on the mask stage. , And a mask stage position detection system for detecting the position of the mask stage based on the second reference member.

In this case, the substrate stage position detecting member is a first movable mirror fixed to the substrate stage, and the first reference member is formed between the projection optical system and the substrate. A first movable mirror fixed to the mask stage, the first stage having a first reference mark and a first fixed mirror integrally formed with the first reference mark; The second reference member has a second reference mark formed between the projection optical system and the mask, and a second reference mark formed integrally with the second reference mark.
A fixed mirror; and the substrate stage position detection system with respect to the first reference member based on the interference between the length measurement beam passing through the first moving mirror and the reference beam passing through the first fixed mirror. The mask stage position detection system includes an interferometer for a substrate that detects the position of the substrate stage, and the mask stage position detection system detects interference between a measurement beam that passes through the second movable mirror and a reference beam that passes through the second fixed mirror. On the basis of this, a mask interferometer that detects the position of the mask stage with respect to the first reference member is used, and the relative displacement detection system projects the relative displacement between the first reference mark and the second reference mark. It is preferable to detect via an optical system.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In an exposure apparatus, a substrate stage position detection member formed on a substrate stage and a first reference member fixedly provided at a predetermined position on the substrate side of a projection optical system are used as a substrate stage position detector. Detect the position. Further, in a normal case, the position of the mask stage is detected based on the mask stage position detection member formed on the mask stage and the second reference member fixedly provided at a predetermined position on the mask side of the projection optical system. In the present invention, the relative displacement between the first reference member and the second reference member is detected by detecting at least the first reference member of the first reference member and the second reference member via the projection optical system. To do.

According to a specific embodiment, the positions of the substrate stage and the mask stage are measured by, for example, separately provided laser interferometers. In this case, in the substrate stage laser interferometer, the substrate stage position detection member is the first movable mirror fixed to the substrate stage. Further, the first reference member has, for example, a first reference mark formed between the projection optical system and the substrate, and a first fixed mirror integrally formed with the first reference mark. On the other hand, in the mask stage laser interferometer, the mask stage position detection member is the second movable mirror fixed to the mask stage. The second reference member includes, for example, a second reference mark formed between the projection optical system and the mask, and the second reference mark.
And a second fixed mirror integrally formed with the reference mark.

Then, in each interferometer, the positions of the substrate stage and the mask stage are respectively detected based on the interference between the length measurement beam with respect to the reflecting surface of the movable mirror and the reference beam with respect to the reflecting surface of the fixed mirror. In this embodiment, according to the present invention, the relative displacement detection system allows the relative positioning of the first reference mark integrally formed with the first fixed mirror and the second reference mark integrally formed with the second fixed mirror. The displacement is detected via the projection optical system.

As described above, according to the present invention, the relative displacement between the first reference mark and the second reference mark, that is, the relative displacement between the first fixed mirror and the second fixed mirror is detected and detected through the projection optical system. By correcting the influence of the relative displacement, the mask and the substrate can be aligned with high accuracy. In other words, based on the measurement result of each interferometer and the relative displacement between the first fixed mirror and the second fixed mirror, it is equivalent to the alignment by the so-called TTL (through the lens) method via the projection optical system. It is possible to perform highly accurate alignment.

Therefore, in the present invention, the exposure apparatus vibrates due to the scanning operation during the exposure to cause relative displacement between the first fixed mirror and the second fixed mirror, or the projection optical system and each fixed mirror. Even if a relative displacement occurs between and, high-precision alignment can be performed at any time during exposure. By setting the first reference mark and the second reference mark substantially conjugate with the substrate surface and the mask surface, respectively, the first reference mark and the second reference mark can be formed in a state close to a favorable image forming state of the projection optical system. The relative displacement of can be detected more accurately.

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a view schematically showing a configuration of an exposure apparatus according to an embodiment of the present invention. It should be noted that the present embodiment is an example in which the present invention is applied to a scanning exposure apparatus of a so-called step scan system, which performs exposure while moving a mask and a wafer relative to a projection optical system. FIG.
Then, the z-axis is parallel to the optical axis of the projection optical system 4, the x-axis is parallel to the plane of FIG. 1 in the plane perpendicular to the optical axis, and the y-axis is parallel to the z-axis and the x-axis. Each axis is set.

The illustrated exposure apparatus is an excimer laser beam (wavelength 249 nm) using, for example, KrF or ArF as a medium.
Alternatively, an illumination optical system 18 for uniformly illuminating the mask 16 with exposure light such as (193 nm) is provided. The mask 16 is held on the mask stage 2, and the mask stage 2 is connected to the projection optical system 4 by a mask stage holder 6
Supported by The mask stage 2 is two-dimensionally driven by the drive system 21 in the xy plane perpendicular to the optical axis of the projection optical system 4. The x-direction movement amount and the y-direction movement amount of the mask stage 2 are constantly measured by the mask stage laser interferometer 11. The output of the laser interferometer 11 is supplied to the control system 20.

For example, the light transmitted through the mask 16 on which the circuit pattern is formed reaches the wafer 17 which is a photosensitive substrate via the projection optical system 4, and a pattern image of the mask 16 is formed on the wafer 17. The wafer 17 is held on the wafer stage 8 via a wafer holder (not shown). The wafer stage 8 is two-dimensionally driven by a drive system 19 in an xy plane perpendicular to the optical axis of the projection optical system 4. And
The x-direction movement amount and the y-direction movement amount of the wafer stage 8 are constantly measured by the wafer stage laser interferometer 9. The output of the laser interferometer 9 is supplied to the control system 20.

Thus, the mask 1 for the projection optical system 4 is
The pattern of the mask 16 can be transferred to one exposure region on the wafer 17 by performing scan exposure while moving the 6 and the wafer 17 relatively in the x direction (scanning direction). Then, the pattern of the mask 16 can be sequentially transferred to each exposure region of the wafer 17 by repeating the above-described scan exposure while sequentially driving the wafer 17 two-dimensionally in the xy plane.

As described above, the exposure apparatus of FIG. 1 is provided with the laser interferometer 9 as the main body of the wafer stage position detection system for detecting the position of the wafer stage 8.
The measurement beam emitted from the laser interferometer 9 is incident on the movable mirror 8 a fixed to the wafer stage 8. On the other hand, the reference beam from the laser interferometer 9 is incident on the fixed mirror 5a formed on the reference body 5 made of an optical member provided at the lower end of the projection optical system 4.

The return light from the movable mirror 8a and the return light from the fixed mirror 5a enter the laser interferometer 9 after being combined. The laser interferometer 9 detects the amount of movement of the wafer stage 8 and thus the position of the wafer stage 8 based on the interference of the combined light. Further, the exposure apparatus of FIG. 1 includes a laser interferometer 11 as a main body of a mask stage position detection system for detecting the position of the mask stage 2. The measurement beam emitted from the laser interferometer 11 is incident on the movable mirror 2 a fixed to the mask stage 2. On the other hand, the reference beam from the laser interferometer 11 enters a fixed mirror 7 fixed to the mask stage holder 6 (connected to the projection optical system 4).

The return light from the movable mirror 2a and the return light from the fixed mirror 7 are incident on the laser interferometer 11 after being combined. In the laser interferometer 11, the movement amount of the mask stage 2 and thus the mask stage 2 is determined based on the interference of the combined light.
Detect the position of. In this way, the laser interferometer 11 can position the mask stage 2, and the laser interferometer 9 can position the wafer stage 8. The initial positioning of the mask stage 2 and the initial positioning of the wafer stage 8 are performed prior to exposure by a wafer position detection system and a mask position detection system (not shown).

In this embodiment, a so-called heterodyne type relative displacement detection system detects the relative displacement between the fixed mirror 7 and the fixed mirror 5a via the projection optical system 4. For the detailed configuration of the heterodyne type relative displacement detection system, see Japanese Patent Application Laid-Open No. HEI-1.
-212436. The relative displacement detection system includes a laser light source 1 that supplies detection light having a wavelength substantially longer than the exposure light. The detection light from the laser light source 1 illuminates a local area including the mask-side reference mark 3a formed on the reference body 3 fixed to the mask stage holder 6. The mask-side reference mark 3a is a diffraction grating formed at a predetermined pitch along a predetermined measurement direction,
It is formed at a position that is substantially conjugate with the pattern forming surface of the mask 16.

The first-order transmitted diffracted light and the 0th-order transmitted light from the mask-side reference mark 3a with respect to the detected light are, as indicated by arrows in the figure, as light including the optical information of the mask-side reference mark 3a, and the mirror 10 and After passing through the half mirror 12, the light enters the projection optical system 4. The light that has passed through the projection optical system 4 enters a reference body 5 connected to the wafer side of the projection optical system 4 in the optical path between the projection optical system 4 and the wafer 17.

FIG. 2 is a diagram schematically showing the structure of the wafer side reference body 5 of FIG. As shown in FIG. 2, the wafer-side reference body 5 is made of a glass block such as quartz, and a fixed mirror 5a is formed on its side surface. On the upper surface of the reference body 5, for example, the reference mark 1 is formed by etching the chrome surface.
4 are formed. The reference mark 14 is a diffraction grating formed at a predetermined pitch along a predetermined measurement direction that is optically coincident with the measurement direction of the mask-side reference mark 3a, for example, the x direction and the y direction.

The reference mark 14 is formed at a position which is substantially conjugate with the exposed surface of the wafer 17. As described above, the wafer-side reference mark 14 and the mask-side reference mark 3 a are arranged substantially optically conjugate with respect to the projection optical system 4. In the projection optical system 4, a correction optical element (PGC) 13 for correcting the chromatic aberration with respect to the detection light in the projection optical system 4 whose aberration has been corrected with respect to the exposure light.
Is provided. The correction optical element 13 is, for example, a transparent substrate having a diffraction grating formed at a predetermined position. Further, on the lower surface of the reference body 5, a thin film having a characteristic of transmitting the exposure light and reflecting the detection light is formed.

In this way, the detection light incident on the reference body 5 is
After being reflected on the lower surface, the local area including the wafer-side reference mark 14 formed on the upper surface is illuminated. Of the detection light incident on the wafer-side reference mark 14, the first-order reflected diffracted light from the wafer-side reference mark 14 and the mask-side reference mark 3 with respect to the 0th-order transmitted light from the mask-side reference mark 3a.
Wafer side reference mark 1 for the first-order transmitted diffracted light from a.
The 0th-order reflected light (regularly reflected light) from No. 4 is the light of the reference body 5 as the light including the optical information of the mask side reference mark 3a and the optical information of the wafer side reference mark 14 as shown by the arrow in the figure. After being reflected by the lower surface, it is incident on the projection optical system 4 again. The 0th-order reflected light and the 1st-order reflected diffracted light from the wafer side reference mark 14 via the projection optical system 4 are reflected by the half mirror 12 and then detected by the photodetectors 15a and 15b, respectively. Output signals from the photodetectors 15a and 15b are supplied to the control system 20.

The control system 20 scans the wafer-side reference mark 14 in a predetermined direction by the detection light passing through the mask-side reference mark 3a by swinging the mirror 10, and in synchronization with this scanning, the photodetector 15a and the photodetector 15a. The output signal from 15b is taken in. Thus, in the control system 20, the photodetector 1
Based on the output signals from 5a and 15b, the relative displacement between the mask-side reference mark 3a and the wafer-side reference mark 14 and, by extension, the relative displacement between the wafer-side fixed mirror 5a and the mask-side fixed mirror 7 is detected.

To reduce the difference between the relative displacement between the mask-side reference mark 3a and the wafer-side reference mark 14 and the relative displacement between the wafer-side fixed mirror 5a and the mask-side fixed mirror 7, that is, the error, the reference body 5 should be used. It is desirable that the fixed mirror 5a, the reference body 3, and the fixed mirror 7 are separately formed so as to be as close as possible, or integrally formed of a member having a low expansion coefficient.

In FIG. 1, the reference body 5 on the wafer side and the fixed mirror 5a on the wafer side are integrally formed, and the reference body 3 on the mask side and the fixed mirror 7 on the mask side are formed separately from each other. Has been done. However, even if the reference body 3 and the fixed mirror 7 are separated from each other, they are connected through a structure having a high rigidity and a low expansion coefficient, and the temperature change is suppressed to be small, whereby the above error can be sufficiently suppressed. it can.

As described above, in this embodiment, the relative displacement between the fixed mirror 7 substantially integrated with the mask side reference mark 3a and the wafer side fixed mirror 5a integrated with the wafer side reference mark 14 is measured. It is detected via the projection optical system 4. Control system 2
At 0, the detected relative displacement, the measurement value of the wafer stage laser interferometer 9 and the mask stage laser interferometer 11 are detected.
A drive signal in which the influence of the detected relative displacement is corrected based on the measured value of 1 is supplied to the mask stage drive system 21 and the wafer stage drive system 19, respectively.

As described above, in this embodiment, based on the measurement results of the interferometers 9 and 11 and the relative displacement between the fixed mirror 7 and the fixed mirror 3a, the position by the TTL method via the projection optical system 4 is used. It is possible to perform high-precision alignment equivalent to alignment. Therefore, even if a relative displacement occurs between the fixed mirror 7 and the fixed mirror 3a or a relative displacement occurs between the projection optical system 4 and each of the fixed mirrors 7 and 3a due to the scanning operation during exposure, It is possible to perform highly accurate alignment at any time by correcting the influence of relative displacement. That is, since alignment marks formed on the mask or the wafer are not used in the alignment by the relative displacement detection system and each interferometer, highly accurate alignment can be performed at any time even during exposure.

In the above embodiment, a heterodyne type detection system is used as the relative displacement detection system. However, in addition to this method, for example, a two-beam interference method for detecting a reference mark by irradiating a reference mark formed of a diffraction grating with coherent two light beams from a predetermined direction, that is, LI
It is also possible to use a detection system of A (Laser Interferometric Alignment) method.

Further, in the above-mentioned embodiment, the example in which the present invention is applied to the step-scan type scanning exposure apparatus is shown, but it is obvious that the present invention can be applied to other general exposure apparatuses. is there. Further, in the above embodiment,
An example in which the present invention is applied to an exposure apparatus that uses excimer laser light as exposure light has been shown, but the present invention can be applied to general exposure apparatuses that use other exposure light.

Further, in the above-described embodiment, the initial setting of the mask and wafer positioning is performed in Japanese Patent Application No. 7-15857.
It can be performed by the off-axis optical system disclosed in the specification No. 0 and the drawings. In this case, by using the reference body 5 of the above-described embodiment and the reference body 2 disclosed in the above-mentioned publication in common, it is possible to perform more accurate alignment.

In the above embodiment, the mask stage is movable. However, even when the mask stage is fixed and there is no mask-side interferometer, the relative displacement between the mask-side reference mark and the wafer-side reference mark fixed on the mask stage holder is detected by the projection optical system. Accurate alignment is possible.

[0039]

As described above, according to the present invention, the first reference member (the fixed mirror 5a and the reference mark 3a in the embodiment) and the second reference member (the fixed mirror 7 and the reference mark 1 in the embodiment).
The relative displacement with respect to 4) is detected through the projection optical system, and the influence of the detected relative displacement is corrected, so that the mask and the substrate can be aligned with high accuracy. That is, highly accurate alignment equivalent to alignment by the TTL (through the lens) method can be performed at any time even during exposure.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of an exposure apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing a configuration of a wafer-side reference body 5 of FIG.

[Explanation of symbols]

 1 Laser Light Source 2 Mask Stage 3 Mask Side Reference Body 3a Mask Side Reference Mark 4 Projection Optical System 5 Wafer Side Reference Body 5a Wafer Side Fixed Mirror 6 Mask Stage Holder 7 Mask Side Fixed Mirror 8 Wafer Stage 9 Wafer Stage Laser Interferometer 10 Mirror 11 Mask Stage Laser Interferometer 12 Half Mirror 13 Correction Optical Element 14 Wafer Side Reference Mark 15 Photodetector 16 Mask 17 Wafer 18 Illumination Optical System 19 Wafer Stage Drive System 20 Control System 21 Mask Stage Drive System

Claims (6)

[Claims] 1. A projection optical system for forming an image of a predetermined pattern formed on a mask on a photosensitive substrate based on exposure light, and a projection optical system which holds the substrate and which is predetermined for the projection optical system. In an exposure apparatus including a substrate stage movable in a plane, a substrate stage position detection member formed on the substrate stage and a first reference member fixedly provided at a predetermined position on the substrate side of the projection optical system. A substrate stage position detection system for detecting the position of the substrate stage, and a second fixed on a mask side of the projection optical system.
A relative displacement detection system for detecting relative displacement between a reference member and the first reference member, wherein the relative displacement detection system is at least the first reference member and the second reference member. 1. An exposure apparatus, wherein one reference member is detected via the projection optical system. 2. A mask stage which holds the mask and is movable in a predetermined plane with respect to the projection optical system, a mask stage position detection member formed on the mask stage, and the second reference member. The exposure apparatus according to claim 1, further comprising a mask stage position detection system for detecting the position of the mask stage based on the above. 3. The substrate stage position detection member is a first movable mirror fixed to the substrate stage, and the first reference member is a first movable mirror formed between the projection optical system and the substrate. One reference mark and a first fixed mirror integrally formed with the first reference mark, wherein the mask stage position detection member is a second movable mirror fixed to the mask stage, The second reference member has a second reference mark formed between the projection optical system and the mask, and a second fixed mirror integrally formed with the second reference mark, and the substrate stage A position detection system for a substrate that detects the position of the substrate stage with respect to the first reference member based on the interference between the length measurement beam passing through the first movable mirror and the reference beam passing through the first fixed mirror. It consists of an interferometer, The image position detection system detects the position of the mask stage with respect to the first reference member based on the interference between the measurement beam passing through the second movable mirror and the reference beam passing through the second fixed mirror. A mask interferometer, wherein the relative displacement detection system includes the first reference mark and the second reference mark.
The exposure apparatus according to claim 2, wherein the relative displacement with respect to the reference mark is detected via the projection optical system. 4. The first reference mark is formed of a first diffraction grating having a predetermined pitch along a predetermined direction, and the second reference mark has a predetermined pitch along a predetermined direction. It is formed of two diffraction gratings, and the relative displacement detection system irradiates the first diffraction grating and the second diffraction grating with detection light, and based on the diffracted light from the first diffraction grating and the second diffraction grating. The exposure apparatus according to claim 3, wherein a relative displacement between the first diffraction grating and the second diffraction grating is detected. 5. The first reference member is connected to the substrate side of the projection optical system, and at least one of the first diffraction grating and the second diffraction grating is located at a position optically conjugate with the substrate. And the relative displacement detection system irradiates the first diffraction grating with detection light that has passed through the second diffraction grating and the projection optical system,
The exposure apparatus according to claim 4, wherein the relative displacement between the first diffraction grating and the second diffraction grating is detected based on the diffracted light that has passed through the first diffraction grating and the second diffraction grating. . 6. The first reference member has a first surface facing the projection optical system and a second surface facing the substrate, and the first diffraction grating faces the projection optical system. Which is formed on the first surface, and the detection light is reflected by the second surface via the second diffraction grating and the projection optical system, and then irradiates the first diffraction grating on the first surface. 6. The method according to claim 5, wherein
3. The exposure apparatus according to claim 1.