JPH11248419A - Interferometer and aligner having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an interferometer wherein degradation in measurement precision is suppressed to minimum, even if position or attitude of a measurement optical reflection mirror changes. SOLUTION: Related to an interferometer comprising a light source 1, a beam splitting means 3a for splitting the beam from the light source 1 into reference beams R and measurement beams M, a reflection mirror 7 for reflecting measurement beams M fitted to an object which is to be measured, and a photoelectric detector 10 for detecting the interference light caused by interference between the measurement beams M reflected on the reflection mirror 7 and the reference beams R, an aberration correcting mechanism 8 is placed on an optical path between the light source 1 and the photoelectric detector 10 so that wavefronts of the measurement beams M and reference beams R incident on the photoelectric detector 10 is axially symmetric about the optical axis of respective beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interferometer which is provided in an exposure apparatus used for manufacturing a semiconductor or a liquid crystal and measures a position and a posture of a stage on which a mask or a photosensitive substrate is mounted and moves with high accuracy. And an exposure apparatus having the same.

[0002]

2. Description of the Related Art In a projection exposure apparatus such as a semiconductor integrated circuit, it is necessary to control the position and orientation of a projection original such as a mask and a reticle and a photosensitive substrate such as a wafer and a glass plate with high precision. Since the mask and wafer are mounted on the mask stage and wafer stage, respectively,
In order to measure the positions and orientations of the mask and the wafer, it is necessary to measure the positions and orientations of both stages. For this purpose, an interferometer is mounted on both stages. This interferometer
A light beam splitting element that splits a light beam from a light source into reference light and measurement light, a measurement light reflecting mirror that is installed on a mask stage or a wafer stage and reflects measurement light, and a measurement light and a reference light from the measurement light reflection mirror And a photoelectric detector that receives the interference light generated by causing interference between the two and measures the position and orientation of the stage based on a signal from the photoelectric detector.

If the direction of the optical axis of the projection optical system is the Z direction, and the directions orthogonal to the Z direction and orthogonal to each other are the X and Y directions, the mask stage generally translates in the X and Y directions. It also moves in the direction of rotation about the Z axis. On the other hand, the wafer stage often moves in all directions. In other words, the waferage moves in the X direction, the Y direction, and the rotation direction around the Z axis in order to switch the exposure area and align with the pattern on the mask.
Move in the Z direction to achieve focusing. Further, the photosensitive surface of the wafer may have undulations, and even if the photosensitive surface of the wafer is flat, it is not necessarily parallel to the back surface. Then, in order to level the photosensitive surface in the exposure area, the mask stage moves in a rotation direction around the X axis and a rotation direction around the Y axis. In addition to the case where the stage is intentionally tilted as in the case of leveling, when the wafer stage is moved in the X direction, for example, for switching of the exposure area or scanning exposure, rotation around the X axis (rolling) is performed. , Rotation around Y axis (pitching), rotation around Z axis (yawing)
May be accompanied.

As described above, in particular, the wafer stage performs rotational movement in addition to parallel movement. Regarding the measurement error of the interferometer that occurs when the wafer stage changes its attitude with inclination, for example, Japanese Patent Application Laid-Open Nos. 5-272912 and 5-32
No. 6,364, an attention has been paid to Abbe error caused by a height shift between the optical axis of the interferometer and the wafer surface, and a method of adjusting the height shift to reduce the error has been proposed. In addition, while measuring the amount of displacement of the position of the wafer stage caused when the wafer stage is leveling-driven, the amount of displacement of the position of the wafer mark on the wafer mounted on the wafer stage is measured using an alignment sensor of the wafer. Detect
By comparing the displacement amounts obtained in this way, information on the correlation between the tilt amount of the wafer stage and the Abbe error is obtained, and a correction value according to the leveling amount is obtained with respect to the measurement value of the interferometer at the time of the leveling drive. A correction method of Abbe error such as addition is also proposed.

[0005]

When the wafer stage tilts due to leveling drive or the like, there are factors other than the above-mentioned height deviation that cause measurement errors in the interferometer. That is, in the interferometer mounted on the exposure apparatus, the light beam from the light source reaches the light beam splitting element via a number of optical components, and a certain amount of wavefront aberration is imparted to the light beam during this time. Thereafter, the light beam is split by the light beam splitting element into the reference light and the measurement light and reaches the photoelectric detector.However, since not so many optical components are arranged in the optical path from the light beam splitting element to the photoelectric detector, the light beam is interposed between them. The wavefront aberration given to the light beam is very small. Therefore, the reference light and the measurement light have substantially the same wavefront aberration when they are incident on the light receiving surface of the photoelectric detector.

FIG. 7A shows a cross section of a light beam on the light receiving surface of the photoelectric detector when the wafer stage is not tilted. At this time, since the wafer stage is not tilted, the positions of the light beams on the light receiving surface D of the reference light R and the measurement light M match, and therefore, the interference light I due to the interference between the two light beams also becomes
It occurs over the entire thickness of the luminous flux of the reference light R and the measurement light M, that is, has a sufficient thickness. FIG. 2B shows the phase φ between the reference light R and the measurement light M on the light receiving surface D. When the stage on which the measuring light reflecting mirror is attached moves in the direction of the measuring light, the phase difference Δφ between the reference light R and the measuring light M changes. By measuring this phase difference Δφ, the measuring light of the measuring light reflecting mirror is measured. You can know the position of the direction. Here, the positions of the reference light R and the measurement light M on the light receiving surface D coincide with each other, and the two light beams R and M enter the light receiving surface D with substantially the same wavefront aberration. , M have substantially the same value over the entire area of the interference light I. As described above, the interference light I
Has a sufficient thickness and the same brightness over the entire area, so that when the wafer stage is not tilted, it has a sufficient contrast even if the light beam incident on the light beam splitting element has a wavefront aberration. The interference light I is detected on the light receiving surface D. Therefore, the signal obtained by photoelectrically converting the signal, that is, the intensity of the interference signal is sufficiently strong.

However, when the wafer stage is tilted by leveling drive or the like, the measuring light reflecting mirror installed on the wafer stage is also tilted, and accordingly, the measuring light reflecting mirror receives reference light incident on the photoelectric detector from the measuring light reflecting mirror. Measurement light is shifted laterally. This lateral shift amount is determined by the tilt amount θ of the wafer stage,
Product L × θ with distance L from light splitting element to measuring light reflecting mirror
May be proportional to. FIG. 8A shows a cross section of a light beam on the light receiving surface of the photoelectric detector when the wafer stage is tilted. As shown in the figure, as the wafer stage is tilted, the measuring light M shifts laterally. Therefore, the area where the interference light I is generated on the light receiving surface D is narrowed, and the intensity of the interference signal obtained by photoelectric conversion is reduced.

FIG. 1B shows the phase φ of the reference light R and the measurement light M on the light receiving surface D. As the wafer stage is tilted, the measuring light M shifts laterally. However, since the reference light R and the measuring light M have a wavefront aberration, the phase difference Δφ between the two light beams is obtained.
Is a value different from the phase difference when the wafer stage is not tilted. Moreover, the phase difference Δφ between the two light beams is
The phase difference is not uniform in the region of the interference light I, but differs at each point in the region of the interference light I. Therefore, an error is caused in the measurement result, and at the same time, the intensity of the interference signal is reduced even when the interference light I is viewed only. As described above, if the wafer stage tilts when the reference light R and the measurement light M have a wavefront aberration, first, an error occurs in the measurement result. Second
In addition, since the area of the interference light I decreases and the interference signal in the area of the interference light I also decreases, the intensity of the interference signal decreases.

FIG. 9 shows a case where the wavefront aberration of the reference light R and the measurement light M is an axially symmetric aberration such as a spherical aberration. As shown in FIG. 3A, regardless of the aberration, when the wafer stage is tilted, the area of the interference light I is narrowed, and the intensity of the interference signal is reduced. In addition, FIG.
When the wafer stage is tilted as shown in FIG.
The phase difference Δφ between the measurement light M and the measurement light M is not uniform in the area of the interference light I, but the average value is equal to the phase difference when the wafer stage is not tilted except for the geometric displacement. Therefore, when the wavefront aberration of the reference light R and the measurement light M is an axially symmetric aberration, the measurement result does not cause a principle error, but the intensity of the interference signal decreases.

As described above, the aberration that causes a displacement in the average value of the phase difference Δφ between the reference light R and the measurement light M, and thus causes a fundamental error in the measurement result, occurs along the lateral shift direction such as coma. This is an aberration that is asymmetrical along the optical axis. The phase displacement of the interference light due to the aberration generally fluctuates in a complicated manner according to the overlapping region of the two light beams where the interference light is generated, that is, the lateral shift of the measurement light. If the wafer stage is tilted when the light flux of the interferometer has an aberration as described above, not only does the intensity of the interference signal decrease, thereby deteriorating the S / N ratio of the signal, but also changes the phase of the interference signal. This degrades the measurement accuracy of the interferometer and causes a practical error. Therefore, an object of the present invention is to provide an interferometer capable of minimizing deterioration in measurement accuracy even when the position or orientation of the measurement light reflecting mirror changes.

[0011]

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, that is, a light source, a light beam splitting means for splitting a light beam from the light source into reference light and measurement light, An interferometer, comprising: a reflecting mirror attached to a measurement target to reflect the measuring light; and a photoelectric detector that receives interference light generated by interference between the measuring light reflected by the reflecting mirror and the reference light. An aberration correction mechanism is interposed in the optical path between the light source and the photoelectric detector so that the wavefronts of the reference light and the measurement light incident on the detector are axially symmetric or plane waves with respect to the optical axis of each light flux. It is an interferometer characterized. The present invention also provides at least a light source and a photodetector disposed between the light source and the photodetector such that the wavefronts of the reference light and the measurement light incident on the photoelectric detector are axially symmetric or plane waves with respect to the optical axis of each light beam. An interferometer characterized in that a surface shape or a refractive index distribution of one optical member is formed.

The present invention also provides an illumination optical system for illuminating a pattern drawn on a mask, a mask stage on which the mask is mounted and moving, and a mask stage interferometer for measuring the position or orientation of the mask stage. A projection optical system that projects the image of the pattern on the mask onto a photosensitive substrate, a substrate stage that carries the photosensitive substrate and moves, and a substrate stage interferometer that measures the position or orientation of the substrate stage. An exposure apparatus having the above-mentioned interferometer as at least one of the mask stage interferometer and the substrate stage interferometer.

[0013]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of an interferometer according to the present invention, in which the present invention is applied to a double-pass interferometer DI. The parallel luminous flux emitted from the laser light source 1 passes through the two luminous flux generating device 2 and then enters the polarization beam splitter 3. Beam splitting surface 3 of polarization beam splitter 3
Assuming that polarized light whose electric vector oscillates in a direction parallel to the incident plane (a in FIG. 1) is P-polarized light and polarized light whose electric vector oscillates in a direction perpendicular to the incident plane is S-polarized light The generator 2 is configured to generate P-polarized light and S-polarized light having slightly different frequencies.

First, the S-polarized light component of the light incident on the polarizing beam splitter 3 is reflected by the light beam splitting surface 3a to become the reference light R, and exits the polarizing beam splitter 3 to be λ / 4.
The light enters the plate 4. The neutral axis of the λ / 4 plate 4 is arranged at an angle of 45 ° with respect to the page. Therefore, the reference light R
Is transmitted through the λ / 4 plate 4 and converted into circularly polarized light, reflected by the reference light reflecting mirror 5 and converted into circularly polarized light in the opposite direction as viewed in the traveling direction, and transmitted through the λ / 4 plate 4 again. The light is converted into P-polarized light and returns to the polarization beam splitter 3. Next, the P-polarized reference light R passes through the light beam splitting surface 3a, is reflected by the corner mirror 3b, returns to the light beam splitting surface 3a, passes through the light beam splitting surface 3a, and exits the polarization beam splitter 3.
Further, the reference light R, which is P-polarized light, transmits through the λ / 4 plate 4, is reflected by the reference light reflecting mirror 5, transmits again through the λ / 4 plate 4, and reciprocates through the λ / 4 plate 4 during this time. To return to the S-polarized light and return to the polarization beam splitter 3, where the light beam splitting surface 3a
And exits the polarization beam splitter 3.

On the other hand, the P-polarized light component of the light incident on the polarization beam splitter 3 passes through the light beam splitting surface 3a to become the measurement light M, exits the polarization beam splitter 3, and outputs λ / 4.
S is transmitted through the plate 6, reflected by the measuring light reflecting mirror 7 fixed to the object to be measured (not shown), transmitted again through the λ / 4 plate 6, and transmitted and reciprocated through the λ / 4 plate 6 during this time. The light is converted into polarized light and returns to the polarization beam splitter 3. Next, the S-polarized measurement light M is reflected by the light beam splitting surface 3a, reflected by the corner mirror 3b, returned to the light beam splitting surface 3a, reflected by the light beam splitting surface 3a, and emitted from the polarization beam splitter 3. Further, the measurement light M, which is S-polarized light, transmits through the λ / 4 plate 6, is reflected by the measurement light reflecting mirror 7, transmits again through the λ / 4 plate 6, and transmits and reciprocates through the λ / 4 plate 6 during this time. By P
The polarization beam returns to the polarization beam splitter 3 and returns to the polarization beam splitter 3, passes through the light beam splitting surface 3 a, and is emitted from the polarization beam splitter 3.

The reference light R and the measuring light M emitted from the polarizing beam splitter 3 pass through an aberration correcting mechanism 8 and pass through a polarizing plate 9 whose transmission axis is arranged at an angle of 45 ° with respect to the plane of the drawing. Heterodyne interference, photoelectric detector 10
Incident on the light receiving surface D of Since the photoelectric detector 10 receives the interference light generated in the area where the reference light R and the measurement light M overlap, the photoelectric detector 10 outputs a signal having a phase and a frequency corresponding to the position and speed of the measurement light reflecting mirror 7. Based on this signal, the position of the measuring light reflecting mirror 7, that is, the position of the measuring object can be measured.

When the measuring object is tilted, the measuring light reflecting mirror 7 is also tilted, and the measuring light M is shifted laterally with respect to the reference light R on the light receiving surface D of the photoelectric detector 10 according to the tilt.
The aberration correcting mechanism 8 disposed in front of the
By correcting the aberrations of the reference light R and the measurement light M passing through the optical system, it is possible to minimize the reduction of the light intensity and the phase displacement of the interference light due to the aberration, thereby preventing the measurement accuracy of the interferometer from being lowered. be able to.

FIG. 2 shows a specific example of the aberration correction mechanism 8. First, the aberration correction mechanism 8 shown in FIG. 1A is an approximately equal magnification afocal system including a positive lens 11 and a negative lens 12, and can correct coma aberration. That is, when the center of both lenses 11 and 12 is on the optical axis, no aberration is given to the light beam passing through this system, but by decentering either lens with respect to the optical axis, Coma is given to the light beam passing through this system. In this way, it is possible to cancel the coma aberration imparted to the light beam from the light source 1 to the photoelectric detector 10 by appropriately decentering the lenses in the afocal system. It is also possible to correct coma aberration in the direction of the paper by rotating the lenses 11 and 12 integrally in the plane of the paper, for example.

The aberration correcting mechanism 8 shown in FIG. 1B has a parallel plane plate 15 which is removably arranged in an optical path in an afocal system composed of a positive lens 13 and a positive lens 14. , Spherical aberration can be corrected. Even if there is spherical aberration, the average phase of the interference signal does not change, and thus does not cause a principle measurement error, but the S / N
Since the ratio is deteriorated, a practical measurement error is caused. Therefore, it is preferable that the spherical aberration is corrected and the light beam incident on the photoelectric detector is converted into a plane wave. The defocus of the wavefront generated at this time can be corrected by moving the afocal component lens back and forth along the optical axis. When a laser diode is converted into a parallel light beam by a collimator lens system and used for an interferometer, the defocus can be adjusted by moving the laser diode back and forth in the optical axis direction. Moving the lens back and forth is advantageous in terms of resolution in defocus adjustment.

The aberration correcting mechanism 8 shown in FIG. 1C is a combination of a convex cylindrical lens 16 and a concave cylindrical lens 17, and can correct astigmatism. Each of the convex cylindrical lens 16 and the concave cylindrical lens 17 is rotatably arranged around the optical axis, whereby the astigmatic difference can be corrected freely.

The above arrangement allows the correction amount of the wavefront aberration by the aberration correction mechanism 8 to be changed.
At least one of the optical members is movable, that is, detachable, inclined, eccentric or translatable.
On the other hand, the aberration correction mechanism 8 shown in FIG. 6D is obtained by performing fine unevenness processing on the surface shape of the parallel flat plate 18, thereby canceling any aberration.
The aberration correction can also be performed by changing the internal refractive index distribution of the parallel plane plate 18 in the optical axis direction or the optical axis vertical direction instead of processing the surface shape of the parallel plane plate 18.

In general, there is little aberration given to both light beams between the time when the reference light and the measurement light are separated by the polarizing beam splitter and the time when both light beams are integrated by the polarizing beam splitter. Therefore, the aberration correction mechanism 8
May be located anywhere as long as both light beams pass through the optical path. However, when the aberrations are different between the two light beams, the aberration correction mechanisms 8 may be arranged in the optical paths through which the two light beams individually pass. Further, instead of using the aberration correcting mechanism 8, the surface shape or the refractive index distribution of at least one optical member disposed between the light source 1 and the photoelectric detector 10 may be changed, that is, for example, the polarization may be changed. The aberration can also be corrected by changing the surface shape of the first entrance surface or the last exit surface of the beam splitter 3.

Next, FIG. 3 shows a second embodiment of the interferometer according to the present invention, in which the present invention is applied to a single-pass interferometer SI. Laser diode light source 2
The laser beam emitted from the collimator lens 21
Is converted into a parallel light beam, passes through the two light beam generation device 2,
The light passes through the aberration correcting mechanism 8 and enters the first polarization beam splitter 22. The two-beam generating device 2 can be configured to include, for example, an acousto-optic device. The S-polarized light component of the light incident on the first polarization beam splitter 22 is reflected by the light beam splitting surface 22 a to become the reference light R, and exits from the first polarization beam splitter 22. The reference light R enters the second polarization beam splitter 23, is reflected by the light beam combining surface 23a, and exits from the second polarization beam splitter 23. On the other hand, of the light incident on the first polarization beam splitter 22, the P-polarized light component is
The light passes through 2a and becomes the measurement light M, and is emitted from the first polarization beam splitter 22. The measurement light M is fixed to a measurement object (not shown), is reflected by a measurement light reflecting mirror 7 formed by a corner mirror, is incident on a second polarization beam splitter 23, and is transmitted through a light beam combining surface 23a. , From the second polarization beam splitter 23.

The reference light R and the measurement light M emitted from the second polarization beam splitter 23 pass through the polarizing plate 9 and enter the light receiving surface D of the photoelectric detector 10. The photoelectric detector 10
Since the interference light generated in the region where the reference light R and the measurement light M overlap is received, a signal having a phase and a frequency corresponding to the position and speed of the measurement light reflecting mirror 7 is output. Based on this signal, the position of the measuring light reflecting mirror 7, that is, the position of the object to be measured can be subjected to homodyne or heterodyne measurement. In the case of this embodiment, when the position of the measuring object moves in parallel in a plane direction orthogonal to the direction of the measuring light, the measuring light reflecting mirror 7 also moves in the same direction, and accordingly, on the light receiving surface D of the photoelectric detector 10. Although the measurement light M is shifted laterally with respect to the reference light R, the first
If the aberration of the reference light R and the measurement light M passing through the aberration corrector 8 is corrected by the aberration corrector 8 disposed in front of the polarization beam splitter 22, the light intensity of the interference light due to the aberration can be reduced and the phase can be reduced. The displacement can be kept to a minimum, and a decrease in measurement accuracy of the interferometer can be prevented.

Further, in this embodiment, a plane mirror 24 is detachably provided in the optical path immediately before the photoelectric detector 10, and the reflected light path when the plane mirror 24 is inserted into the optical path has an aberration measuring device 25. Is arranged. Note that, instead of the configuration in which the plane mirror 24 is inserted into and removed from the optical path, the aberration measuring device 25 itself may be inserted into and removed from the optical path. As the aberration measuring device 25, a device using a technique such as shearing interference or Shack-Hartmann interferometry can be used. Thus, the wavefront aberration of the light beam incident on the photoelectric detector 10 can be measured easily and with high accuracy. Therefore, the wavefront aberration of the light beam can be corrected using the aberration correction mechanism 8 based on the measured wavefront aberration. In particular, in the interferometer using the laser diode light source 20, the laser diode light source 20, the collimator lens 20, and the two-beam generating device 2 are united by incorporating the aberration correction mechanism 8 in advance, so that the parallel light emitted from this unit can be obtained. Correcting the wavefront aberration of the light beam is efficient in production.

FIGS. 4 to 6 show a scanning exposure apparatus according to an embodiment of the present invention. First, FIG. 4 shows the entire configuration of the exposure apparatus. A reticle 31 placed on a reticle stage 32 is uniformly illuminated by an illumination optical system 30. A reticle stage measuring mirror 33 is attached to the reticle stage 32, and the reticle stage measuring mirror 3
A reticle stage interferometer 34 is disposed opposite to the reticle stage 3. The luminous flux transmitted through the pattern on the reticle 31 is
An image is formed on the photosensitive surface of the wafer 36 placed on the wafer stage 37 by the projection optical system 35. Wafer stage 37
Is equipped with a wafer stage measuring mirror 38,
A wafer stage interferometer 39 is arranged to face the wafer stage measuring mirror 38. The reticle stage 32 and the wafer stage 37 scan synchronously in the Y direction at a speed ratio corresponding to the imaging magnification of the projection optical system 35, and thus the pattern of the reticle 31 is transferred to the wafer 36.

FIG. 5 shows the wafer stage interferometer 39. The light beam emitted from the HeNe Zeeman laser light source 1 passes through the two light beam generation device 2 and is split into two light beams by the beam splitter 40, and further split into four light beams by the beam splitters 41 and 42, each of which is first in the X direction. It is used as a light beam for the interferometer DI _X1 , the second interferometer DI _X2 , the Y-direction first interferometer DI _Y1 , and the second interferometer DI _Y2 . Each of these interferometers DI _{X1 to} DI _Y2 is constituted by a double-pass interferometer, and performs heterodyne measurement of the position of the wafer stage 37 in the X and Y directions and the rotation angle around the Z axis.

The photoelectric detector 10 of each of the interferometers DI _{X1 to} DI _Y2
Are arranged in front of the X-direction interferometers DI _X1 and DI _X2 . Therefore, even if the wafer stage 37 rotates around the Y-axis or the Z-axis, Regarding the interferometers DI _Y1 and DI _Y2 , even if the wafer stage 37 rotates around the X-axis or the Z-axis, it is possible to minimize the decrease in the measurement accuracy of the interferometer. Each aberration correction mechanism 8 corrects the aberration of the light beam incident on the photoelectric detector 10 for each photoelectric detector 10. For the adjustment, remove each photoelectric detector 10 or insert a reflecting mirror in front of the photoelectric detector 10 to take out a light beam, perform aberration measurement using an aberration measuring device for each light beam,
Correct the aberration. By performing such aberration correction, the measurement error due to the phase shift of the interference light caused by the aberration can be greatly reduced, particularly when the wafer stage 37 is driven for leveling, and the position and orientation control accuracy of the wafer stage 37 can be reduced. improves.

FIG. 6 shows a reticle wafer stage interferometer 3
4 is shown. The light beam emitted from the laser diode light source 20 is converted into parallel light by a collimator lens 21, and a two-beam light generating device 2 using an optical component such as an acousto-optic element generates a heterodyne parallel light beam. After the aberration is corrected by the aberration correcting mechanism 8, the light is split into two light by the beam splitter 43.
Further, one light beam is split by the beam splitter 44. The three light beams are used as light beams for the X-direction interferometer DI _X , the Y-direction first interferometer SI _Y1 , and the second interferometer SI _Y2 , respectively. Among interferometer DI _X for position measurement in the X direction which is the non-scanning direction perpendicular to the scanning direction Y is constituted by a double pass interferometer, the interferometer SI _Y1 for position measurement in the Y direction is a scanning direction, SI _Y2 is configured by a single-pass interferometer. In this manner, the position of the reticle stage 32 in the X and Y directions and the rotation angle around the Z axis are heterodyne-measured.

When the light beam from the laser diode light source 20 is heterodyneed, a large number of optical components such as an acousto-optic element are required. Wavefront aberration is increased. On the other hand, although the reticle stage 32 does not perform leveling drive, there is a positioning error in the conveyance when the reticle 31 is mounted on the reticle stage 32, and the reticle 3
Due to the writing position error of the pattern on the reticle with respect to the reticle outer shape, the measurement axis of the reticle stage interferometer 34 and the writing center of the reticle 31 may be greatly displaced in the XY plane. In this case, in order to eliminate Abbe error at the time of measurement, after mounting the reticle 31, the reticle stage 32 is rotated around the Z axis so that the measurement axis of the interferometer and the center of the reticle coincide, or XY. It will be moved horizontally in the plane.

Along with this rotational movement or horizontal movement, the measurement light is shifted laterally with respect to the reference light on the photoelectric detectors of all axes. In order to prevent a decrease in the light intensity of the interference light due to the aberration at the time of the lateral displacement, an aberration correction mechanism 8 is disposed between the two-beam generating device 2 and the beam splitter 43 to reduce the aberration of the heterodyne beam. to correct. By performing such aberration correction, the measurement error due to a decrease in the light intensity of the interference light caused by the aberration can be significantly reduced, particularly when the reticle stage 32 is rotationally driven or horizontally driven, and the position and orientation of the reticle stage 32 Control accuracy is improved.

[0032]

As described above, in the interferometer of the present invention, the aberration of the light beam of the interferometer is corrected by the aberration correcting mechanism. Therefore, even if the measurement light deviates laterally with respect to the reference light on the light receiving surface of the photoelectric detector due to a change in the position or posture of the measurement object, a decrease in the light intensity of the interference light or a phase shift caused by the aberration will occur. Can be kept to a minimum. As a result, it becomes possible to measure the position and orientation of the measurement target with high accuracy. In addition, by mounting such an interferometer on an exposure apparatus, control accuracy of the reticle stage and the wafer stage is improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of an interferometer according to the present invention.

FIG. 2 is a cross-sectional view illustrating a specific example of an aberration correction mechanism.

FIG. 3 is a configuration diagram showing a second embodiment of the interferometer according to the present invention.

FIG. 4 is an overall configuration diagram showing an exposure apparatus according to the present invention.

FIG. 5 is a plan view showing a wafer stage.

FIG. 6 is a plan view showing a reticle stage.

FIG. 7A is a diagram showing reference light and measurement light on the light receiving surface when the measurement light is not laterally shifted when there is a wavefront aberration, and FIG. 7B is a cross-sectional view taken along line AA in FIG. It is.

FIG. 8A is a diagram showing reference light and measurement light on the light receiving surface when the measurement light is laterally shifted when there is a wavefront aberration;
(B) It is the sectional view on the AA line in a figure.

9 is a diagram corresponding to FIG. 8 when the wavefront aberration is an axially symmetric aberration.

[Explanation of symbols]

DI: Double-pass interferometer SI: Single-pass interferometer R: Reference light M: Measurement light I: Interference light 1: Laser light source 2: Two light beam generator 3: Polarizing beam splitter 3a: Light beam splitting surface 3b: Corner mirrors 4, 6 Λ / 4 plate 5 Reference light reflecting mirror 7 Measurement light reflecting mirror 8 Aberration correction mechanism 9 Polarizing plate 10 Photoelectric detector 11 Positive lens 12 Negative lens 13, 14 Positive lens 15 Parallel plane plate DESCRIPTION OF SYMBOLS 16 ... Convex cylindrical lens 17 ... Concave cylindrical lens 18 ... Parallel plane plate 20 ... Laser diode light source 21 ... Collimator lens 22, 23 ... Polarization beam splitter 22a ... Light beam splitting surface 23a ... Light beam combining surface 24 ... Plane mirror 25 ... Aberration measuring device Reference Signs List 30 illumination optical system 31 reticle 32 reticle stage 33 reticle stage measurement mirror 34 reticle stage interferometer 35 projection optics System 36 ... Wafer 37 ... Wafer stage 38 ... Wafer stage measuring mirror 39 ... Wafer stage interferometer 40-44 ... Beam splitter

Continued on the front page (51) Int.Cl. ⁶ identification code FI H01L 21/30 525S

Claims (9)

[Claims] 1. A light source, a light beam splitting means for splitting a light beam from the light source into a reference light and a measuring light, a reflecting mirror attached to an object to be measured and reflecting the measuring light, and reflected by the reflecting mirror An interferometer having a photoelectric detector that receives interference light generated by interference between the measurement light and the reference light, wherein a wavefront of the reference light and the measurement light incident on the photoelectric detector is axially symmetric with respect to an optical axis of each light beam. An interferometer having an aberration correction mechanism interposed in an optical path between the light source and the photoelectric detector. 2. The interferometer according to claim 1, wherein the aberration correction mechanism is formed so that the wavefronts of the reference light and the measurement light incident on the photoelectric detector become plane waves. 3. The interferometer according to claim 1, wherein the aberration correcting mechanism is disposed in an optical path through which both the reference light and the measurement light pass. 4. The interferometer according to claim 1, wherein the aberration correction mechanism is configured to change a correction amount of a wavefront aberration by the aberration correction mechanism. 5. The interferometer according to claim 4, wherein the aberration correction mechanism has at least one optical member, and the optical member is movably disposed. 6. A light source, a light beam splitting means for splitting a light beam from the light source into a reference light and a measurement light, a reflecting mirror attached to an object to be measured and reflecting the measurement light, and reflected by the reflecting mirror An interferometer having a photoelectric detector that receives interference light generated by interference between the measurement light and the reference light, wherein a wavefront of the reference light and the measurement light incident on the photoelectric detector is axially symmetric with respect to an optical axis of each light beam. An interferometer, wherein a surface shape or a refractive index distribution of at least one optical member disposed between the light source and the photoelectric detector is formed such that: 7. The optical member according to claim 6, wherein the surface shape or the refractive index distribution of the optical member is formed such that the wavefronts of the reference light and the measurement light incident on the photoelectric detector become plane waves. Interferometer. 8. The interferometer according to claim 1, further comprising a wavefront measuring device for measuring a wavefront of the reference light or the measurement light incident on the photoelectric detector. 9. An illumination optical system for illuminating a pattern drawn on a mask, a mask stage on which the mask is mounted and moving, a mask stage interferometer for measuring the position or orientation of the mask stage, and An exposure apparatus comprising: a projection optical system that projects the image of the pattern onto a photosensitive substrate; a substrate stage that mounts and moves the photosensitive substrate; and a substrate stage interferometer that measures the position or orientation of the substrate stage. The exposure apparatus according to claim 1, wherein the interferometer according to any one of claims 1 to 8 is used as at least one of the mask stage interferometer and the substrate stage interferometer.