JP2000077295A - Apparatus and method for inspecting optical system, aligner having the inspecting apparatus and projection aligner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily inspect various astigmatisms, focal positions, optical axis deviations, etc., of an optical system. SOLUTION: An optical system, having illumination optical systems 103-108 for radiating an illumination light on a phase pattern WM and image forming optical systems 107-115 for forming image of the phase pattern is inspected. It comprises means 116, 117 for detecting the image of the phase pattern formed through this optical system and a means 122 for defocusing the image of the phase pattern detected in the image inspecting means. The coma aberration of the optical system, shading of the light flux in the optical system and inclination of the main light beam of the illumination light with respect to the normal to a phase pattern forming plane W are inspected, based on the change in the asymmetry of an image corresponding to the edge of the phase pattern which is respectively detected in a defocused condition in the image detecting means.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inspection apparatus and an inspection method for an optical system, an alignment apparatus and a projection exposure apparatus having the inspection apparatus, and more particularly to a projection apparatus used in a lithography process for manufacturing a semiconductor element, a liquid crystal display element and the like. The projection optical system of the exposure apparatus, the alignment optical system of the alignment apparatus attached to the projection exposure apparatus, the aberration, the focal position of the overlay measurement optical system of the overlay measurement apparatus for determining the alignment result, The present invention relates to inspection and correction (adjustment) of optical axis deviation and the like.

[0002]

2. Description of the Related Art Conventionally, in a projection exposure apparatus used in a lithography process for manufacturing a semiconductor element, a liquid crystal display element, or the like, a pattern formed on a mask is transferred onto a wafer as a photosensitive substrate via a projection optical system. At this time, a projection image of a mask pattern formed via a projection optical system is aligned (aligned) with a pattern already formed on the wafer by a positioning device attached to a projection exposure apparatus. Perform overlay exposure. Furthermore, the quality of the alignment result by the positioning device is determined by an overlay measurement device provided inside or outside the projection exposure device.

In this case, for example, if an aberration remains in the projection optical system, the projected image of the mask pattern cannot be formed accurately, and a transfer pattern with distortion is formed on the wafer. Further, for example, if aberration remains in the alignment optical system of the alignment device, accurate alignment between the mask and the wafer cannot be performed, and high-accuracy overlay exposure cannot be performed. Further, with respect to the overlay measurement optical system of the overlay measurement apparatus, for example, if there is residual aberration, it is not possible to perform overlay measurement with high accuracy.

As described above, by setting the projection optical system of the projection exposure apparatus, the alignment optical system of the positioning apparatus, and the overlay measurement optical system of the overlay measurement apparatus as close as possible to the ideal optical system. For the first time, the performance of the apparatus such as the projection exposure apparatus, the alignment apparatus, and the overlay measurement apparatus can be sufficiently exhibited. In recent years, it has become increasingly important to accurately and simply inspect such aberrations, focal positions, optical axis shifts, and the like of the optical system, and to precisely correct or adjust according to the inspection results.

Accordingly, the present applicant has disclosed in Japanese Patent Laid-Open No. 9-4978.
In Japanese Patent Laid-Open No. 1 (1994), an inspection apparatus suitable for inspection of a projection optical system of a projection exposure apparatus, an alignment optical system of a positioning apparatus, and an overlay measurement optical system of an overlay measurement apparatus is proposed. In this inspection apparatus, for example, attention is paid to a change in asymmetry of an image generated when an image of a phase pattern is gradually defocused, and based on the change in asymmetry, mainly coma aberration, spherical aberration, and light flux vignetting ( The light beam is interrupted).

[0006]

However, the inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 9-49781 inspects various aberrations other than coma and spherical aberration accurately (with good reproducibility) and simply. I couldn't do that.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an inspection apparatus and an inspection method capable of accurately and easily inspecting various aberrations, a focal position, an optical axis shift, and the like of an optical system. The purpose is to provide. In addition, aberrations of the optical system based on the detection result by the inspection device of the present invention,
It is an object of the present invention to provide a projection exposure apparatus, a positioning apparatus, and an overlay measuring apparatus that can exhibit sufficient apparatus performance by correcting or adjusting a focal position, an optical axis shift, and the like.

[0008]

According to a first aspect of the present invention, there is provided an illumination optical system for irradiating illumination light on a phase pattern and a light beam from the phase pattern. In an inspection apparatus for inspecting an optical system having an imaging optical system for forming an image of the phase pattern, an image detection unit for detecting an image of the phase pattern formed via the optical system, A defocusing unit for defocusing the image of the phase pattern detected by the image detection unit; and an asymmetry of an image corresponding to an edge of the phase pattern detected in each defocused state by the image detection unit. Based on the change in the coma aberration of the optical system, the vignetting of the light beam in the optical system, and the inclination of the principal ray of the illumination light with respect to the normal to the surface on which the phase pattern is formed. It provides a test apparatus characterized by comprising an inspection means for 査.

In the inspection apparatus according to a first aspect of the present invention, the inspection means includes an asymmetry of an image corresponding to an edge of the phase pattern detected in one or a plurality of defocused states by the image detection means; Alternatively, based on the asymmetry of the image corresponding to the edge of the phase pattern detected in one or a plurality of defocused states by the image detecting means in a state where the image detecting means is rotated by 180 degrees around the detection center. It is preferable that the optical system is inspected by correcting a detection error of asymmetry of an image caused by the phase pattern or the image detecting means.

According to a second aspect of the present invention, there is provided an illumination optical system for irradiating the phase pattern with illumination light, and an illumination optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. In an inspection apparatus for inspecting an optical system having an image optical system, an image detection unit for detecting an image of the phase pattern formed via the optical system, and the phase pattern detected by the image detection unit Defocusing means for defocusing the image of the first phase pattern, wherein the phase pattern repeats a periodic phase change along a detection direction of the image detection means, and the first phase pattern A second phase pattern having a phase amplitude distribution different from that of the first phase pattern and repeating a periodic phase change along the detection direction of the image detecting means. The light intensity of the image of the first phase pattern corresponding to the region and the light intensity of the image of the first phase pattern corresponding to the region where the phase of the first phase pattern is delayed are respectively predetermined light intensities. A first defocus position, a light intensity of the image of the second phase pattern corresponding to a region where the phase of the second phase pattern is advanced, and a region where the phase of the second phase pattern is delayed. Inspection means for inspecting the spherical aberration of the optical system based on the light intensity of the image of the second phase pattern corresponding to the second phase pattern and the second defocus position at which the light intensity becomes a predetermined light intensity. An inspection device is provided.

Further, according to a third aspect of the present invention, there is provided an illumination optical system for irradiating the phase pattern with illumination light, and an illumination optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. In an inspection apparatus for inspecting an optical system having an image optical system, an image detection unit for detecting an image of the phase pattern formed via the optical system, and the phase pattern detected by the image detection unit Defocusing means for defocusing the image of
The illumination optical system is provided with illumination aperture changing means for changing the amplitude distribution of the illumination light passing through the illumination aperture stop, and the phase pattern is periodically arranged along a detection direction of the image detection means. A light intensity of an image of the phase pattern corresponding to a region where the phase of the phase pattern illuminated under the first illumination condition set by the illumination aperture changing unit is a phase pattern that repeats a phase change; The first light intensity of the image of the phase pattern corresponding to the region where the phase of the phase pattern is delayed becomes a predetermined light intensity;
Defocus position, light intensity of an image of the phase pattern corresponding to a region where the phase of the phase pattern illuminated under the second illumination condition set by the illumination aperture changing means, and the phase pattern The light intensity of the image of the phase pattern corresponding to the region where the phase is delayed and the second defocus position at which the respective light intensity becomes a predetermined light intensity,
An inspection apparatus is provided, further comprising an inspection unit for inspecting a spherical aberration of the optical system.

According to a fourth aspect of the present invention, there is provided an illumination optical system for irradiating the phase pattern with illumination light, and an illumination optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. In an inspection apparatus for inspecting an optical system having an image optical system, an image detection unit for detecting an image of the phase pattern formed via the optical system, and the phase pattern detected by the image detection unit Defocus means for defocusing the image of the, the phase pattern is a phase pattern that repeats a periodic phase change along the detection direction of the image detection means, in each defocus state, The light intensity of the image of the phase pattern corresponding to the region where the phase of the phase pattern is advanced, and the light intensity of the image of the phase pattern corresponding to the region where the phase of the phase pattern is delayed. Based on the change in the difference between the focal position of the optical system, the optical axis astigmatism, astigmatism, field curvature,
And an inspection device for inspecting at least one of the image plane tilt.

In the inspection apparatus according to the first to fourth inventions and the preferred embodiments of each invention, the illumination wavelength selecting means for selecting the wavelength of the illumination light to be applied to the phase pattern and the phase pattern are used. And at least one of imaging light flux wavelength selection means for selecting the wavelength of the imaging light flux, the optical system for light having a wavelength selected by the illumination wavelength selection means or the imaging light flux wavelength selection means. Inspection is preferred. Also,
Preferably, to inspect the optical system for light of a selected wavelength, the phase pattern has two or more phase patterns having different spectral reflectances or transmittances.

Further, it is preferable that the phase pattern is a phase pattern having a duty ratio of 1 to 1 that repeats a periodic phase change along a detection direction of the image detecting means. Further, the phase change amount Φ of the transmission or reflection amplitude phase distribution of the phase pattern is represented by Φ = π (2n−1) / 2 (n is a natural number) with respect to the center wavelength of the light beam detected by the image detection means. It is preferable to satisfy the following condition.

It is preferable that the defocus means moves at least one of the phase pattern, the whole or a part of the optical system, and the image detecting means along an optical axis of the optical system. . In addition, the defocusing unit may include a light intensity of an image of the phase pattern corresponding to a region where the phase of the phase pattern is advanced and a light intensity of an image of the phase pattern corresponding to a region where the phase of the phase pattern is delayed. It is preferable to define a defocus range of an image of the phase pattern detected by the image detecting means, with a defocus position at which is equal to the center as a center.

According to a fifth aspect of the present invention, there is provided an alignment mark comprising a phase pattern provided on a mask on which a transfer pattern is formed, or provided on a photosensitive substrate onto which an image of the transfer pattern is transferred. An illumination optical system for irradiating the alignment mark composed of the phase pattern with illumination light, and an imaging optical system for condensing a light beam from the alignment mark to form an image of the alignment mark. In an alignment apparatus for positioning the mask or the photosensitive substrate, the inspection apparatus according to the first to fourth inventions and preferred embodiments of each invention for inspecting the alignment optical system. An inspection device for correcting aberrations of the imaging optical system based on inspection information of the alignment optical system by the inspection device. Correction means, focus position adjustment means for adjusting the focus position of the imaging optical system based on the inspection information, and the focusing means for correcting light flux vignetting of the imaging optical system based on the inspection information. Imaging aperture stop position adjusting means for relatively displacing the position of the imaging aperture stop of the image optical system with respect to the optical axis, and adjusting the inclination of the principal ray of the illumination light with respect to the normal to the object plane of the imaging optical system. A position alignment device is provided, further comprising at least one of illumination aperture stop position adjusting means for relatively displacing the position of the illumination aperture stop of the illumination optical system with respect to an optical axis for correction. I do. According to another aspect of the present invention, there is provided an exposure apparatus for exposing a transfer pattern formed on a mask onto a photosensitive substrate according to the fifth aspect of the present invention for positioning the mask or the photosensitive substrate. It is preferable to have a positioning device.

According to another aspect of the present invention, an illumination optical system for irradiating the first pattern and the second pattern formed on the substrate with illumination light, the first pattern and the second pattern are provided. And an imaging optical system for focusing the light beam from the first pattern image and the second pattern image to form an image of the first pattern,
In an overlay measurement apparatus for measuring a relative positional deviation between the first pattern and the second pattern, the overlay measurement apparatus according to the first to fourth inventions and preferred aspects of each invention for inspecting the overlay measurement optical system. Equipped with an inspection device,
An aberration correction unit for correcting aberration of the imaging optical system based on inspection information of the alignment optical system by the inspection device; and an adjusting unit for adjusting a focus position of the imaging optical system based on the inspection information. An in-focus position adjusting means for forming an image-forming aperture stop of the image-forming optical system to relatively displace the position of an image-forming aperture stop with respect to an optical axis in order to correct a light beam vignetting of the image-forming optical system based on the inspection information; Aperture stop position adjusting means for displacing the position of the illumination aperture stop of the illumination optical system relative to the optical axis in order to correct the inclination of the principal ray of the illumination light with respect to the normal to the object plane of the imaging optical system It is preferable that at least one of the illumination aperture stop position adjusting means is further provided.

According to another aspect of the present invention, there is provided an exposure apparatus for exposing a transfer pattern formed on a mask to a photosensitive substrate, wherein the first pattern formed on the photosensitive substrate is exposed.
The apparatus is provided with the overlay measuring device for measuring the relative positional displacement between the pattern and the second pattern, and performs the position correction of the mask or the photosensitive substrate based on the relative positional displacement information from the overlay measuring device. Is preferred.

According to a sixth aspect of the present invention, there is provided an illumination optical system for irradiating illumination light to a mask on which a transfer pattern is formed, and a projection optical system for forming an image of the transfer pattern on a photosensitive substrate. And a projection exposure apparatus comprising:
Inspection devices for inspecting the illumination optical system and the projection optical system according to the first to fourth inventions and preferred embodiments of each invention are provided, and inspection information of the illumination optical system and the projection optical system by the inspection device is provided. Aberration correction means for correcting the aberration of the projection optical system based on the focus position adjustment means for adjusting the focus position of the projection optical system based on the inspection information, Image-forming aperture stop position adjusting means for relatively displacing the position of the image-forming aperture stop of the projection optical system with respect to the optical axis in order to correct vignetting of the projection optical system, and a method of measuring the object plane of the projection optical system At least one of illumination aperture stop position adjusting means for relatively displacing the position of the illumination aperture stop of the illumination optical system with respect to the optical axis in order to correct the inclination of the principal ray of the illumination light with respect to a line; To provide a projection exposure apparatus characterized by comprising the al.

According to a seventh aspect of the present invention, in a method for inspecting an optical system including an imaging optical system for forming an image of a predetermined phase pattern, the phase pattern is irradiated with illumination light. Detecting the image of the phase pattern at a plurality of different defocus positions in the optical axis direction of the image optical system, based on a change in asymmetry of an image corresponding to an edge of the phase pattern detected at the plurality of defocus positions. hand,
An inspection method for an optical system is provided, which comprises inspecting coma aberration of the optical system, vignetting of the light beam in the optical system, and an inclination of a principal ray of the illumination light with respect to a normal to a surface on which the phase pattern is formed.

According to an eighth aspect of the present invention, there is provided a method for inspecting an optical system including an illumination optical system for irradiating a phase pattern with illumination light and an imaging optical system for forming an image of the phase pattern. The phase pattern has a first phase pattern that repeats a periodic phase change along a predetermined direction, and a phase amplitude distribution different from the first phase pattern, A second phase pattern that repeats a phase change, irradiating the phase pattern with illumination light through the illumination optical system, and detecting an image of the phase pattern having a detection direction along the predetermined direction. The light intensity of the image of the first phase pattern corresponding to the region where the phase of the first phase pattern is advanced and the region corresponding to the region where the phase of the first phase pattern is delayed The first place A first defocus position at which the light intensity of the image of the pattern becomes a predetermined light intensity, and a light intensity of the image of the second phase pattern corresponding to a region where the phase of the second phase pattern is advanced. The optical system based on the second defocus position where the light intensity of the image of the second phase pattern corresponding to the region where the phase of the second phase pattern is delayed and the predetermined light intensity. And a method for inspecting an optical system characterized by inspecting spherical aberration of the optical system.

According to a preferred aspect of the eighth invention,
The illumination optical system is configured to be able to change an amplitude distribution of the illumination light passing through an illumination aperture stop, and when detecting the first defocus position, an amplitude of the illumination light at the illumination aperture stop is detected. Setting the distribution to a first amplitude distribution,
When the defocus position is detected, the amplitude distribution of the illumination light at the illumination aperture stop is set to a second amplitude distribution different from the first amplitude distribution.

According to a ninth aspect of the present invention, in a method for inspecting an optical system including an image forming optical system for forming an image of a predetermined phase pattern, the phase pattern is irradiated with illumination light. An image of the phase pattern is detected at a plurality of different defocus positions in an optical axis direction of the imaging optical system using an image detector having a detection direction, and the phase pattern extends along a detection direction of the image detector. A phase pattern that repeats a periodic phase change, and at the plurality of defocus positions, the light intensity of the image of the phase pattern corresponding to a region where the phase of the phase pattern has advanced, and the phase of the phase pattern. Based on the change in the difference between the light intensity of the image of the phase pattern corresponding to the delayed region, the focal position of the optical system, astigmatism on the optical axis, astigmatism, field curvature, and image plane tilt Our Even without providing an inspection method of an optical system, characterized by inspecting one.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In an inspection apparatus and an inspection method according to the present invention, as will be described later with reference to FIGS. Based on the change in the index β of the asymmetry of the image to be formed, in addition to the coma aberration of the test optical system and the light beam vignetting in the test optical system, the inclination of the principal ray of the illumination light with respect to the normal to the phase pattern forming surface, that is, The illumination telecentric can be easily and quickly inspected with good reproducibility.
Specifically, the inclination amount of the principal ray of the illumination light, that is, the illumination telecentric amount can be obtained based on the constant offset value B of the index β that does not depend on the defocus amount Z. Further, the amount of coma aberration can be obtained based on the slope C of a straight line representing the index β that changes almost linearly depending on the defocus amount Z. Further, the vignetting amount of the light beam can be obtained based on the bending amount D of the polygonal line or the curved line representing the index β that changes in a polygonal line or a curved line depending on the defocus amount Z.

In this case, based on two asymmetry indices β1 and β2 detected in two states where the phase pattern is rotated by 180 degrees around the detection center (for example, based on the simple average value), The detection error of the index β of the asymmetry of the image caused by the pattern can be corrected. Further, based on two asymmetry indices β1 and β2 detected in two states in which an image detecting means such as a CCD is rotated by 180 degrees around the detection center (for example, based on a simple average value thereof), It is also possible to correct the detection error of the index β of the image asymmetry caused by the phase pattern.

Further, according to the inspection apparatus and the inspection method of the present invention, as will be described later with reference to FIG. 7 in an embodiment, a first phase pattern and a second phase pattern having different phase amplitude distributions (pitches) are provided. By using the above, the spherical aberration of the optical system to be inspected can be easily and quickly inspected with good reproducibility. Specifically, the light intensity of the image corresponding to the region where the phase of the first phase pattern is advanced (for example, the convex portion of the reflection type uneven pattern) and the region where the phase of the first phase pattern is delayed (for example, the reflection type unevenness) The first defocus position Z1 at which the light intensity of the image corresponding to the concave portion of the pattern coincides (the index α = 0), and the light intensity of the image corresponding to the advanced phase region of the second phase pattern And the light intensity of the image corresponding to the phase delayed region of the second phase pattern matches (index α =
0) based on the second defocus position Z2.
The magnitude and correction state of the spherical aberration of the test optical system can be obtained.

Further, according to the inspection apparatus and the inspection method of the present invention, as will be described later with reference to FIG. The spherical aberration of the system can be inspected easily and quickly with good reproducibility. Specifically, the light intensity of the image corresponding to the phase advanced region of the phase pattern illuminated with the first illumination σ value matches the light intensity of the image corresponding to the phase delayed region of the phase pattern. A region where the phase of the light intensity phase pattern of the image corresponding to the region where the phase of the phase pattern illuminated with the second illumination σ value is advanced is the first defocus position Z1 (indicator α = 0) and the region where the phase is delayed. The magnitude and the correction state of the spherical aberration of the optical system to be measured can be obtained based on the second defocus position Z2 where the light intensity of the image corresponding to the second optical axis coincides.

Further, in the inspection apparatus and the inspection method of the present invention, as will be described later with reference to FIGS. The focus position of the optical system to be measured, the astigmatic difference on the optical axis, the astigmatism, based on the change in the index α of the difference between the light intensity of the image to be reproduced and the light intensity of the image corresponding to the phase delayed region of the phase pattern. It is possible to easily and quickly inspect at least one of the aberration, the field curvature, and the image plane inclination with good reproducibility.

As described above, according to the inspection apparatus and the inspection method of the present invention, in each defocus state, the asymmetry (index β) of the image corresponding to the edge of the phase pattern and the difference in the image intensity of the uneven portion of the phase pattern (index β) are obtained. By measuring the index α), in addition to coma of the optical system, luminous flux vignetting, inclination of illumination light (illumination telecentricity), spherical aberration, focal position, astigmatism on the optical axis, astigmatism, field curvature, It is possible to easily and quickly inspect the image plane inclination with good reproducibility. Then, based on the detected inspection information of the optical system, correction and adjustment of the aberration and the focusing position of the optical system, and position adjustment of the illumination aperture stop and the imaging aperture stop, etc., are performed efficiently and appropriately, so that the optical The system can be made as close as possible to an ideal optical system.

Therefore, by incorporating the inspection apparatus of the present invention into a projection exposure apparatus, a positioning apparatus, an overlay measuring apparatus, and the like, the illumination optical system of the projection exposure apparatus, the alignment optical system of the projection optical system and the alignment apparatus, and the overlay optical apparatus. It is sufficient to inspect the overlay measurement optical system of the overlay measurement device easily and quickly with good reproducibility, and correct or adjust the aberration, focal position, optical axis deviation, etc. of the optical system based on the detection result by the inspection device. Apparatus performance can be exhibited. Specifically, the position alignment device reduces the position detection error caused by the alignment optical system, and the overlay measurement device reduces the measurement error caused by the overlay measurement optical system. Further, in the projection exposure apparatus, aberrations of the projection optical system are satisfactorily corrected, and the focal position and optical axis deviation thereof are well adjusted, so that the pattern transfer performance is improved and the overlay projection exposure with high accuracy is performed. It becomes possible.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a view schematically showing a configuration of a projection exposure apparatus including an inspection apparatus according to a first embodiment of the present invention. In the first embodiment, the alignment optical system (imaging optical system and illumination optical system) of the off-axis type alignment device attached to the projection exposure apparatus is inspected.
In FIG. 1, the Z axis is parallel to the optical axis of the projection optical system PL of the projection exposure apparatus, the X axis is a direction parallel to the plane of FIG. 1 in a plane perpendicular to the optical axis, the Z axis and the X axis. The Y-axis is set in a direction perpendicular to.

The projection exposure apparatus shown in FIG. 1 includes an exposure illumination optical system (not shown) for uniformly illuminating the reticle R as a mask with appropriate exposure light. The reticle R is supported substantially parallel to the XY plane on the reticle stage 101, and a circuit pattern to be transferred is formed in its pattern area PA. The light transmitted through the reticle R reaches the wafer (or glass plate) W as a photosensitive substrate via the projection optical system PL, and a pattern image of the reticle R is formed on the wafer W.

The wafer W is supported on the Z stage 122 via the wafer holder 121 substantially in parallel with the XY plane. The Z stage 122 is driven by the stage control system 124 along the optical axis of the projection optical system PL. The Z stage 122 further
It is supported on an XY stage 123. The XY stage 123 is also two-dimensionally driven by the stage control system 124 in an XY plane perpendicular to the optical axis of the projection optical system PL.

At the time of projection exposure, it is necessary to optically align (align) the pattern area PA with each exposure area on the wafer W. Therefore, the position of the alignment step mark formed on the wafer W, that is, the wafer mark WM in the reference coordinate system is detected, and alignment is performed based on the position information. As described above, the alignment device of the present invention is used to detect and align the position of the wafer mark WM.

The alignment device shown in FIG. 1 includes a light source 103 such as a halogen lamp for supplying illumination light (alignment light AL). Light source 103
Is guided to a predetermined position via a light guide 104 such as an optical fiber. The illumination light emitted from the emission end of the light guide 104 is restricted by the illumination aperture stop 127 as necessary, and then enters the condenser lens 129 as an illumination light flux having an appropriate cross-sectional shape.

The alignment light AL passing through the condenser lens 129 is once converged, and then enters the illumination relay lens 105 via an illumination field stop (not shown). The alignment light AL converted into parallel light via the illumination relay lens 105 passes through the half prism 106, and then enters the first objective lens 107. First objective lens 107
The alignment light AL condensed by the reflection prism 10
After being reflected by the reflecting surface 8 downward in the figure, the wafer mark WM serving as an alignment mark formed on the wafer W is illuminated.

As described above, the light source 103 and the light guide 1
04, illumination aperture stop 127, condenser lens 12
9, illumination field stop (not shown), illumination relay lens 10
5, the half prism 106, the first objective lens 107, and the reflection prism 108 constitute an illumination optical system for irradiating the wafer mark WM with illumination light.

The reflected light from the wafer mark WM with respect to the illumination light is reflected by the reflecting prism 108 and the first objective lens 10.
7, the light enters the half prism 106. The light reflected upward in the figure by the half prism 106 forms an image of the wafer mark WM on the index plate 112 via the second objective lens 111. The light passing through the index plate 112 enters the XY branch half prism 115 via the relay lens system (113, 114). The light reflected by the XY branching half prism 115 is transmitted to the Y-direction CCD 116.
The light transmitted through the XY branch half prism 115 is incident on the X-direction CCD 117. In the parallel optical path of the relay lens system (113, 114), an imaging aperture stop 130 is arranged as necessary.

As described above, the reflecting prism 108, the first objective lens 107, the half prism 106, the second objective lens 111, the index plate 112, the relay lens system (113, 1)
14), imaging aperture stop 130 and half prism 11
Reference numeral 5 constitutes an imaging optical system for forming a mark image based on reflected light from the wafer mark WM with respect to the illumination light. In addition, CCD 116 for Y direction and C for X direction
The CD 117 constitutes image detection means for detecting a mark image formed via the imaging optical system.

Thus, the Y-direction CCD 116 and X
The mark image is displayed on the imaging surface of the direction CCD 117 on the index plate 1.
It is formed together with 12 index pattern images. C for Y direction
Output signals from the CD 116 and the X-direction CCD 117 are supplied to a signal processing system 118. Further, the position information of the wafer mark WM obtained by the signal processing (waveform processing) in the signal processing system 118 is supplied to the main control system 125.

The main control system 125 outputs a stage control signal to the stage control system 124 based on the position information of the wafer mark WM from the signal processing system 118. The stage control system 124 appropriately drives the XY stage 123 according to the stage control signal to perform alignment of the wafer W. Note that a command for the illumination aperture stop 127 and a command for the imaging aperture stop 130 are supplied to the main control system 125 via input means 126 such as a keyboard. The main control system 125 drives the illumination aperture stop 127 via the drive system 128 and drives the imaging aperture stop 130 via the drive system 131 based on these commands. Further, the main control system 125 drives the second objective lens 111 and the relay lens 113 based on an aberration correction command described later.

As described above, the wafer mark WM is formed as an alignment mark on the wafer W. The wafer mark WM has a periodic phase change along the measurement direction of the CCD 116 or the measurement direction of the CCD 117, for example. This is a phase pattern in which the duty ratio to be repeated is 1: 1. Such a phase pattern can be formed into a precise shape with desired accuracy by, for example, etching a silicon wafer exposed by a projection exposure apparatus. In order to obtain a sharp detection sensitivity in the measurement of the aberration of the optical system to be described later, the phase change amount Φ of the reflection amplitude / phase distribution of the phase pattern must be
The following equation (a) is used for the center wavelength of the light beam detected in step (17).
It is desirable to satisfy Φ = π (2n-1) / 2 (n is a natural number) (a)

FIG. 2 is a diagram in which an integrated signal ΔV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction is plotted in the measurement direction S, and shows the asymmetry of the phase pattern image. FIG. 6 is a diagram for explaining an index β. In the first embodiment, an image of the wafer mark WM composed of a phase pattern is formed on the imaging surface of the CCD (116, 117) that is the imaging device. Therefore, in FIG. 2, the image sensor (11
6, 117) is plotted in the measurement direction S with respect to the measurement direction S.

As shown in FIG. 2, the integration signal ΔV has a period BP (B: magnification of the imaging optical system, P:
It changes for each phase pattern WM on the wafer. In the first embodiment, in order to quantify the asymmetry of the phase pattern image, the minimum value of the left and right signals (the signal at the falling edge portion) in the i-th (second in FIG. 2) cycle in the distribution of the integrated signal ΣV ) Are ViL and ViR (i = 1, 2, 3,...), Respectively. Also, in the entire region over each period except for both end portions of the integration signal ΔV,
The maximum and minimum values of the signal are Vmax and Vmi, respectively.
Let n.

Then, the index β of the asymmetry of the phase pattern image is obtained based on the following equation (1). β = {ViL−ViR / (Vmax−Vmin)} / n (1) where n is the number of periods, and Σ is a sum symbol for i = 1 to n.

FIGS. 3 and 4 show the change in the index β of the asymmetry of the phase pattern image in each defocus state obtained by the stage control system 124 appropriately driving the Z stage 122 based on a command from the main control system 125. FIG. 4 is a diagram illustrating a relationship between the optical axis, coma aberration, optical axis shift, and the like. FIG. 3A shows an ideal optical adjustment state in which the test optical system (in this case, the imaging optical system and the illumination optical system) has no residual aberration and no optical axis shift.
In this case, as shown by the straight line L1, the index β is 0 without depending on the defocus amount Z.

In the case where the principal ray of the illumination light irradiating the object surface (that is, the wafer surface) in the optical system to be inspected (in this case, the illumination optical system) is inclined with respect to the normal to the object surface (hereinafter, referred to as the "light"). In the case where “there is an illumination telecentric”, as shown by a straight line L2 in FIG. 3B, the index β is set to a constant offset value B without depending on the defocus amount Z.
Take. This offset value B is substantially proportional to the inclination amount of the principal ray of the illumination light with respect to the normal to the object plane, that is, the illumination telecentricity.

Further, when a coma exists in the optical system to be measured (in this case, the imaging optical system), the index β depends on the defocus amount Z as shown by a straight line L3 in FIG. It shows an almost linear change. The slope C of the straight line L3 is substantially proportional to the amount of coma. Further, when there is vignetting of the image forming light beam in the optical system to be inspected (also in this case, the image forming optical system), as shown in FIG. Or a curved curve as shown by a broken line) L4. The amount of bending D of the broken line or curved line L4 is substantially proportional to the amount of vignetting of the image forming light beam.

Thus, based on the relationship between the index β obtained by defocusing the phase pattern image and the defocus amount Z, the illumination telecentricity is calculated by the offset value B, and the inclination value C
, The light beam vignetting can be obtained from the bending amount D. In the above description, the region where the phase pattern image is detected may be limited to a desired range. That is, in equation (1), i = 1 to n
May be limited. By limiting in this way, it is possible to inspect illumination telecentricity, luminous flux vignetting, and coma of the optical system to be inspected at an arbitrary position on the object plane. Further, by performing the above-described inspection on each point of the visual field, for example, it is possible to determine the eccentric coma aberration and the image height coma aberration in the detection visual field. The same applies to the illumination telecentric and luminous flux vignetting.

FIG. 5 is a diagram in which an integrated signal ΔV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction is plotted in the measurement direction S, and corresponds to the concave portion of the phase pattern. An index α that quantifies the difference between the image intensity of the phase pattern image and the image intensity of the phase pattern image corresponding to the projection.
FIG. As described above, FIG. 5 is a diagram corresponding to FIG. 2, but for simplicity, a test optical system free of coma aberration and light beam vignetting is exemplarily assumed.

As described above, in the first embodiment, the image of the wafer mark WM composed of the phase pattern is formed on the imaging surface of the CCD (116, 117) as the imaging device. Therefore, in FIG. 5, similarly to FIG.
117) is plotted in the measurement direction S with respect to the measurement direction S. FIG.
As shown in the figure, the integrated signal ΣV changes along the measurement direction S at every cycle BP (B: magnification of the imaging optical system; P: pitch of the phase pattern WM on the wafer). In the first embodiment, in order to quantify the difference between the image intensity of the phase pattern image corresponding to the concave portion of the phase pattern and the image intensity of the phase pattern image corresponding to the convex portion, i
The integral signal ΔV corresponding to the concave portion of the
io (i = 1, 2, 3,...), and the integrated signal ΣV corresponding to the projection of the i-th phase pattern is Vit (i = 1, 2, 2,...).
3 ...).

Then, an index α of a difference between the image intensities of the phase pattern images corresponding to the concave portions and the convex portions of the phase pattern is obtained by the following equation (2). α = {Vit−Vio / (Vit + Vio)} / (2n) (2) where n is the number of periods, and Σ is a sum symbol for i = 1 to n.

FIG. 6 shows phase patterns corresponding to the concave and convex portions of the phase pattern in each defocused state obtained by the stage control system 124 appropriately driving the Z stage 122 based on a command from the main control system 125. FIG. 7 is a diagram illustrating a relationship between a change in an index α of a difference between image intensities of images and spherical aberration. In FIG. 6 and other related figures (FIGS. 7 and 8), Z = 0 corresponds to the paraxial image plane position of the test optical system. Further, α = 0 corresponds to a state where the image intensity of the phase pattern image corresponding to the concave portion of the phase pattern is equal to the image intensity of the phase pattern image corresponding to the convex portion. When there is no spherical aberration in the test optical system (in this case, the imaging optical system), the index α changes almost directly in proportion to the value of the defocus amount Z. That is, the index α
, When α = 0, Z = 0.

On the other hand, when overcorrected spherical aberration exists in the test optical system, a straight line L indicating a change in the index α is obtained.
In 2 and L3, the value of Z when α = 0 is negative. The absolute value of Z when α = 0 increases according to the magnitude of the spherical aberration. That is, the absolute value of Z when the straight line L2 indicating the change of the index α intersects the Z axis (the axis of α = 0) when the overcorrected spherical aberration is relatively large is determined by the overcorrected spherical aberration. Is relatively small, the straight line L3 indicating the change in the index α is Z
It is larger than the absolute value of Z when it intersects the axis. As described above, when there is overcorrected spherical aberration, the defocus position where the image intensity of the phase pattern image corresponding to the concave portion of the phase pattern and the image intensity of the phase pattern image corresponding to the convex portion are equal to the spherical position. According to the magnitude of the aberration amount, Z =
It tends to move away from the paraxial image plane position of 0 in the negative direction.

When the undercorrected spherical aberration exists in the optical system to be measured, a straight line L indicating a change in the index α is obtained.
At 4 and L5, the value of Z when α = 0 is positive. The value of Z when α = 0 increases in accordance with the magnitude of the spherical aberration amount. That is, when the straight line L4 indicating the change of the index α when the undercorrected spherical aberration is relatively large intersects the Z axis (the axis of α = 0),
Is larger than the value of Z when the straight line L5 indicating the change in the index α when the undercorrected spherical aberration is relatively small intersects the Z axis. As described above, when the undercorrected spherical aberration exists, the defocus position at which the image intensity of the phase pattern image corresponding to the concave portion of the phase pattern is equal to the image intensity of the phase pattern image corresponding to the convex portion is set to the spherical position. It tends to move away from the paraxial image plane position of Z = 0 in the positive direction according to the magnitude of the aberration amount.

FIGS. 7A and 7B show the relationship between the defocus amount Z and the index α for two types of phase patterns having different periods. FIG. 7A shows a case where spherical aberration exists in the optical system to be measured. (B) shows the case where there is no spherical aberration. A phase pattern with a smaller cycle has a larger diffraction angle of diffracted light generated from the pattern than a phase pattern with a larger cycle, and is more susceptible to spherical aberration. Therefore, when spherical aberration exists in the test optical system, the position Z2 where the straight line L2 obtained for the phase pattern with a small cycle intersects with the Z axis is closer to the straight line L1 obtained for the phase pattern with a large cycle. Is farther from the paraxial image plane position of Z = 0 than the position Z1 intersecting the Z axis.

On the other hand, when there is no spherical aberration in the test optical system, the position Z2 at which the straight line L2 obtained for the phase pattern with a small period intersects the Z axis is also obtained for the phase pattern with a large period. The position Z1 where the straight line L1 intersects the Z axis also matches the paraxial image plane position where Z = 0. From the above, the difference (Z2-Z1) between Z2 and Z1 is proportional to the magnitude of the spherical aberration remaining in the test optical system, and the difference (Z2
It can be seen that the positive and negative signs of 2-Z1) correspond to overcorrection and undercorrection of spherical aberration. In other words, from the relationship between the index α and the defocus amount Z obtained when the phase pattern image is defocused using two types of phase patterns having different periods, the difference (Z2-Z
Based on 1), the magnitude of the spherical aberration of the test optical system and its correction state can be obtained.

FIG. 8 shows a defocus amount Z and an index α for the same phase pattern when illuminated with two types of illumination σ values.
(A) shows the case where spherical aberration exists in the test optical system, and (b) shows the case where spherical aberration does not exist. Here, the illumination σ refers to the ratio of the illumination numerical aperture to the imaging numerical aperture. Lighting σ
Illumination with a relatively large value is more susceptible to spherical aberration than the illumination with a relatively small illumination σ value. Therefore, when the test optical system has a spherical aberration, the position Z2 where the straight line L2 ′ obtained when the illumination σ value is large intersects the Z axis is the straight line L1 obtained when the illumination σ value is small. 'Is farther from the paraxial image plane position of Z = 0 than the position Z1 where it intersects the Z axis.

On the other hand, when there is no spherical aberration in the optical system to be tested, a straight line L obtained when the illumination σ value is large is obtained.
The position Z2 at which 2 ′ intersects the Z axis, and the position Z1 at which the straight line L1 ′ obtained when the illumination σ value is small intersects the Z axis,
This coincides with the paraxial image plane position of Z = 0. As described above, even when the same phase pattern is illuminated with two types of illumination σ values, the difference (Z2-Z1) between Z2 and Z1 is the same as that of the two types of phase patterns having different periods. Proportional to the magnitude of the spherical aberration remaining in the system, and the difference (Z
It can be seen that the positive and negative signs of 2-Z1) correspond to overcorrection and undercorrection of spherical aberration. In other words, from the relationship between the index α and the defocus amount Z obtained when the phase pattern image is defocused by illuminating the same phase pattern with two types of illumination σ values, the difference (Z2
−Z1), the magnitude of the spherical aberration of the test optical system and the correction state thereof can be obtained.

As can be easily understood from the description of FIGS. 7 and 8, in any case, when there is no spherical aberration in the test optical system, the defocus position where the index α = 0 is on the paraxial image plane. The Z position. If the test optical system has spherical aberration, the phase pattern of the first cycle (first illumination σ)
Defocus position Z1 at which index α = 0 with respect to
And the second defocus position Z2 at which the index α = 0 with respect to the phase pattern (second illumination σ) of the second period, the paraxial image plane position and the astigmatic difference on the optical axis are obtained. be able to.

In the above description, the region for detecting the phase pattern image may be limited to a desired range. That is, in the formula (2), the range of i = 1 to n may be limited. By limiting in this way (by performing the above-described inspection for each point of the field of view), in addition to the paraxial image plane position of the optical system to be tested and the astigmatic difference on the optical axis, astigmatism, image It becomes possible to inspect surface curvature and image plane inclination.

Further, an optical filter or the like is inserted into the optical path of the illumination optical system to select the wavelength of the illumination light for irradiating the phase pattern, or to change the spectral reflectance (spectral transmittance in the case of the transmission type). Prepare two or more phase patterns to select the wavelength of reflected light (transmitted light in the case of transmission type) from the phase pattern, or insert an optical filter into the optical path of the imaging optical system to By selecting the wavelength of the imaging light beam, it becomes possible to inspect the optical system to be inspected for a desired wavelength. As a result, it is possible to inspect longitudinal chromatic aberration and off-axis chromatic aberration in addition to inspecting various types of monochromatic aberration and the like described above for each wavelength.

In the above description, the left and right minimum values ViL and ViR of the signal for one cycle are used when quantifying the index β of the asymmetry of the phase pattern image. However,
As disclosed in Japanese Patent Application No. 7-20325 (Japanese Patent Application Laid-Open No. 8-213306) filed by the present applicant, a phase pattern is obtained by using the widths of left and right falling edges in one cycle of a signal. The index of image asymmetry β can also be quantified.

Further, a process different from that of the present embodiment can be performed for the index α of the difference between the image intensities of the phase pattern images corresponding to the projections and depressions of the phase pattern, respectively. FIG. 9 shows a case where the image intensity of the phase pattern image corresponding to the convex portion of the phase pattern matches the image intensity of the phase pattern image corresponding to the concave portion, and the image intensity distribution of the phase pattern image corresponds to the convex portion and the concave portion. FIG. 4 is a diagram showing a state in which a corner occurs in an image intensity waveform that changes. In this case, without directly obtaining the index α, a defocus position where an angle occurs in the image intensity waveform corresponding to the convex portion and the concave portion in the image intensity distribution of the phase pattern image may be adopted as the position Z1 or the position Z2. it can.

Further, in order to secure the accuracy when obtaining the index β, the index β1 of the asymmetry of the image corresponding to the edge of the phase pattern detected in one or more defocus states and the phase pattern 18 around the detection center
Asymmetry of an image corresponding to an edge of the phase pattern detected in one or a plurality of defocused states in a state where the phase pattern is rotated by 0 degrees (that is, in the present embodiment, the phase pattern is rotated by 180 degrees around the Z axis). It is desirable to detect the sex index β2 and obtain the average value βave1 by the following equation (3). βave1 = (β1 + β2) / 2 (3) By using this average value βave1 as an index β of asymmetry of the phase pattern image when inspecting the optical system to be inspected,
Detection errors due to asymmetry of the phase pattern itself can be corrected.

Further, an index β1 of asymmetry of the image corresponding to the edge of the phase pattern detected in one or a plurality of defocused states, and an image sensor (in this embodiment, a CCD 116)
And 117) are rotated by 180 degrees around the detection center, and an index β2 of the asymmetry of the image corresponding to the edge of the phase pattern detected in one or more defocus states is detected. It is desirable to calculate the average value βave2 by the following equation (4). βave2 = (β1 + β2) / 2 (4) By using this average value βave2 as an index β of asymmetry of the phase pattern image when inspecting the optical system to be inspected,
It is possible to correct a detection error due to the asymmetry of the imaging element itself.

The sensitivity of the index β and the index α obtained by defocusing the phase pattern image to the defocus amount Z includes the illumination σ value, the pattern pitch, the duty ratio,
It depends on the taper, step, etc. Therefore, it is desirable to control the inspection sensitivity by appropriately selecting these parameters so that an optimum inspection can be performed in an actual use state.

It is desirable to select an appropriate range around the Z position where the index α is 0 as the defocus range when the phase pattern image is defocused. By selecting the defocus range in this manner, the manner of change of the index β can be accurately grasped. In addition, as a defocus means, in addition to a means for vertically driving a Z stage on which a wafer on which a phase pattern is formed,
Means for moving the optical system to be inspected along the entire or partial optical axis, and means for moving at least one of the imaging units along the optical axis of the optical system to be inspected can be used.

As described above, while the phase pattern image is defocused, the index β of the asymmetry of the edge of the phase pattern image and the index α of the difference in the image intensity of the uneven portion of the phase pattern are measured, whereby the frame of the optical system to be inspected is measured. In addition to aberration, eccentric coma, luminous flux vignetting, and illumination light inclination, inspection is performed on light with arbitrary wavelengths such as spherical aberration, focal position, astigmatism on the optical axis, astigmatism, field curvature, and field inclination. Explained what can be done. Next, correction and adjustment performed based on the inspection information (detection result), that is, a method of correcting and adjusting the aberration and the focusing position of the optical system to be inspected, and adjusting the position of the illumination aperture stop and the imaging aperture stop The method will be described.

First, to adjust the illumination telecentricity (the inclination of the illumination light), the position of the illumination aperture stop 127 is adjusted.
Specifically, the illumination aperture stop 127 is transmitted via the drive system 128.
Is appropriately driven in a direction perpendicular to the optical axis or in a translation direction. When the exit end of the light guide 104 also serves as an illumination aperture stop, the light guide 104 is appropriately driven in a direction perpendicular to the optical axis or in a translation direction. Further, the light guide 104 and the condenser lens 129
In the optical path between the illumination relay lens 105 and the half prism 106, a light beam parallel moving means such as a plane parallel plate may be provided. When a parallel plane plate is used as the light beam parallel movement means, the illumination telecentric can be adjusted by tilting the parallel plane plate.

On the other hand, to adjust the vignetting of the image forming light beam, the position of the image forming aperture stop 130 is adjusted. Specifically, the imaging aperture stop 130 is appropriately driven in a direction perpendicular to the optical axis or in a translation direction via the drive system 131. Also,
In the optical path between the half prism 106 and the second objective lens 111, or between the relay lens 113 and the relay lens 1
14, a light beam parallel moving means such as a plane parallel plate may be provided in the optical path on the wafer side of the imaging aperture stop 130. When a parallel plane plate is used as the light beam parallel movement means, the vignetting of the image forming light beam can be adjusted by inclining the parallel plane plate.

Further, in order to correct the spherical aberration of the imaging optical system, for example, the second objective lens 111 and the relay lens 1
13 is appropriately driven along the optical axis. Alternatively, the spherical aberration of the imaging optical system can be corrected by changing the distance between the second objective lens 111 and the relay lens 113. Further, the Z stage is driven so that the wafer W surface and the first
The spherical aberration can also be controlled by changing the distance from the objective lens 107. However, in this case, the defocus of the image on the imaging surface of the CCD must be absorbed by appropriately translating the CCD in the optical axis direction.

The decentering coma of the imaging optical system is
The correction can be performed by eccentrically driving the entire or a part of the lens system of the objective lens 111 and the relay lens 113 perpendicularly to the optical axis. It should be noted that in order to adjust the focus position (focal position), the Z stage may be appropriately driven in the optical axis direction. In order to correct the astigmatic difference on the optical axis, at least one of the CCD in the X direction and the CCD in the Y direction may be appropriately moved along the optical axis direction.

Further, aberrations such as image height coma, field curvature, and field tilt rarely cause problems in optical design considerations and manufacturing management. However, these aberrations can be corrected as necessary by changing and replacing the lens type of some lens systems of the imaging optical system, or by decentering some lens systems. The correction of chromatic aberration is similar to these aberrations.

FIG. 10 is a perspective view schematically showing a configuration of a projection exposure apparatus provided with an inspection apparatus according to a second embodiment of the present invention. In the first embodiment, the imaging optical system and the illumination optical system of the off-axis type alignment device attached to the projection exposure apparatus are inspected. However, in the second embodiment, the projection optical system and the projection optical system of the projection exposure apparatus are inspected. Inspecting the illumination optics. In the first embodiment, a CCD is used as the image detecting means. In the second embodiment, a reference member having a slit and a photoelectric detector are used as the image detecting means. In FIG. 10, the Z axis is set parallel to the optical axis AX of the projection optical system PL of the projection exposure apparatus so that the X axis and the Y axis are orthogonal to each other in a plane perpendicular to the optical axis AX. .

The projection exposure apparatus shown in FIG. 10 includes a light source LP composed of, for example, an ultra-high pressure mercury lamp. Light source LP
Is positioned at a first focal position of a condenser mirror (elliptical mirror) EM having a reflection surface composed of a spheroid. Therefore, the illumination light beam emitted from the light source LP is reflected by the elliptical mirror EM.
A light source image (secondary light source) is formed at the second focal position.

The light from the secondary light source is
After passing through the L and the mirror M1, it becomes a parallel light beam and enters the fly-eye lens FL. The light beam incident on the fly-eye lens FL is two-dimensionally split by a plurality of lens elements constituting the fly-eye lens FL, and the rear focal position of the fly-eye lens FL (ie, near the exit surface)
A plurality of light source images (tertiary light sources).

Light beams from a plurality of light source images are restricted by the variable aperture stop 12 arranged on the exit surface of the fly-eye lens FL, and then enter the condenser lens CL via the mirror M2. The light condensed through the condenser lens CL is transferred to a mask 14 on which a transfer pattern is formed.
Are uniformly illuminated in a superimposed manner. As described above, the light source PL, the elliptical mirror EM, the collimating lens GL, the mirror M1, the fly-eye lens FL, the variable aperture stop 12, the mirror M2, and the condenser lens CL constitute the illumination optical system 11.

At the time of exposure, a light beam transmitted through the mask 14 reaches a wafer (not shown) as a photosensitive substrate via the projection optical system 17. Thus, the mask 14 is formed on the wafer.
Is formed. The wafer has a projection optical system 17.
On an XY stage 18 movable two-dimensionally in an XY plane perpendicular to an optical axis AX (parallel to the Z direction) and a Z stage 13 movable along the optical axis AX direction of the projection optical system 17. Supported. Therefore, by performing exposure while moving the wafer two-dimensionally, the pattern of the mask 14 can be sequentially transferred to each exposure area of the wafer.

The projection exposure apparatus shown in FIG. 10 is provided with an oblique incident light type autofocus system (22A, 22B). In the oblique incident light type autofocus system, the light transmission system 22A irradiates light obliquely toward the surface of the wafer. The light specularly reflected on the wafer surface is received by the light receiving system 22B, and the position in the Z direction of the wafer is detected based on a change in the position of the reflected light. Thus, the auto focus system (22
A, 22B), the wafer surface can be made substantially coincident with the image forming plane (plane conjugate with the mask 14) of the projection optical system 17 during exposure.

On the other hand, upon inspection, a reference member PT and a photodetector 23 are set on the XY stage 18 instead of the wafer. Then, the auto focus system (22A, 2
2B) and the action of the Z stage 13, the reference member P
The surface of T is positioned at a predetermined defocus position with respect to the projection optical system 17. In this case, first, the surface of the reference member PT is made substantially coincident with the imaging plane of the projection optical system 17 by using the autofocus system (22A, 22B), and this position is set to the paraxial image plane position (Z = 0). ). Next, the surface of the reference member PT can be positioned at a predetermined defocus position by driving the Z stage 13 by a predetermined amount Z (defocus amount) based on the paraxial image plane position (Z = 0). . The defocus state can be formed by moving the pattern 16 and the projection optical system 17 in the Z direction.

In each defocus state, the mask 14
The light beam transmitted through the inspection phase pattern 16 formed on the reference member PT reaches the surface of the reference member PT via the projection optical system 17. Thus, the inspection phase pattern image 16A of the mask 14 is formed on the surface of the reference member PT in each defocused state. Light from the phase pattern image 16A passes through the slit 19 formed on the surface of the reference
3 is incident. The slit 19 is formed by, for example, one slit pattern. Therefore, an electric signal corresponding to the light intensity distribution of the phase pattern image 16A can be obtained in the light receiver 23 by the slit scan method in which the phase pattern image 16A and the slit 19 are relatively moved in a predetermined direction.

As described above, the CCD is used as the image detecting means in the first embodiment, whereas the reference member P having the slit 19 is used as the image detecting means in the second embodiment.
Although T and the photodetector 23 are used, detection of aberration and the like based on the light intensity distribution of the obtained phase pattern image and correction and adjustment of the aberration and the like based on the detected information are the same as in the first embodiment. That is, in the second embodiment, similarly to the first embodiment, while defocusing the phase pattern image, the index β of the asymmetry of the edge of the phase pattern image and the index α of the difference in the image intensity of the uneven portion of the phase pattern are set. By measuring, the test optical system (projection optical system 17 and illumination optical system 1)
In addition to 1) coma aberration, eccentric coma aberration, luminous flux vignetting, illumination light inclination, spherical aberration, focal position, astigmatism on the optical axis, astigmatism, field curvature, and light of any wavelength of image plane inclination Inspections can be performed. Further, based on the inspection information (detection result), it is possible to correct or adjust the aberration, the in-focus position, and the optical axis shift of the optical system to be inspected.

For example, in the projection exposure apparatus shown in FIG. 10, in order to correct the spherical aberration and the coma of the projection optical system 17, the lens components constituting the projection optical system 17 are sensitive to the spherical aberration and the coma. Lens AX
Is shifted (moved) or tilted (inclined) with respect to. Further, other aberrations of the projection optical system 17 can be processed in the same way as in the first embodiment. On the other hand, in the projection exposure apparatus shown in FIG. 10, in order to properly adjust illumination telecentricity, luminous flux vignetting, and the like, the variable aperture stop 12 and the aperture stop in the projection optical system 17 are appropriately driven with respect to the optical axis AX.

As a third embodiment of the present invention, the inspection apparatus of the present invention can be applied to an overlay measuring apparatus. The overlay measurement device is, for example, a device that is provided inside or outside of a projection exposure apparatus, and that measures a relative positional deviation between a first pattern and a second pattern formed on a photosensitive substrate. The alignment optical system of the alignment device and the overlay measurement optical system of the overlay measurement device have optically similar configurations. Therefore, as in the case of the positioning device, it is possible to accurately and easily inspect the aberration and the like of the overlay measurement optical system, and satisfactorily correct the aberration and the like of the overlay measurement optical system based on the inspection information. .

In the inspection apparatus and the inspection method of the present invention, the asymmetry of the phase pattern image may be detected by an imaging method as in the first embodiment, or may be detected by a slit as in the second embodiment. The scanning may be performed. Further, the present invention does not depend on a difference in illumination method such as transmission illumination or epi-illumination (reflection illumination). Further, the inspection apparatus of the present invention can be applied to not only a projection exposure apparatus, an overlay measurement apparatus, and a positioning apparatus but also other general apparatuses having an optical system to be inspected.

[0087]

As described above, according to the inspection apparatus and the inspection method of the present invention, in each defocus state, the asymmetry (index β) of the image corresponding to the edge of the phase pattern and the unevenness of the phase pattern are obtained. Difference in image intensity (index α)
In addition to the coma, eccentric coma, luminous flux vignetting, tilt of illumination light (illumination telecentricity), spherical aberration, focal position, astigmatism on the optical axis, astigmatism,
The curvature of field and the inclination of the image plane can be easily and quickly inspected with good reproducibility for light having an arbitrary wavelength. Then, based on the detected inspection information of the optical system, correction and adjustment of the aberration and the focusing position of the optical system, and position adjustment of the illumination aperture stop and the imaging aperture stop, etc., are performed efficiently and appropriately, so that the optical The system can be made as close as possible to an ideal optical system.

Therefore, by incorporating the inspection apparatus of the present invention into a projection exposure apparatus, a positioning apparatus, and an overlay measuring apparatus, the illumination optical system of the projection exposure apparatus, the alignment optical system of the projection optical system and the alignment apparatus, and the overlay optical apparatus. It is sufficient to inspect the overlay measurement optical system of the overlay measurement device easily and quickly with good reproducibility, and correct or adjust the aberration, focal position, optical axis deviation, etc. of the optical system based on the detection result by the inspection device. Apparatus performance can be exhibited. Specifically, the position alignment device reduces the position detection error caused by the alignment optical system, and the overlay measurement device reduces the measurement error caused by the overlay measurement optical system. Further, in the projection exposure apparatus, aberrations of the projection optical system are satisfactorily corrected, and the focal position and optical axis deviation thereof are well adjusted, so that the pattern transfer performance is improved and the overlay projection exposure with high accuracy is performed. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a view schematically showing a configuration of a projection exposure apparatus provided with an inspection apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram in which an integrated signal ΣV obtained by integrating a signal V corresponding to the light intensity of a phase pattern image in a non-measurement direction is plotted with respect to a measurement direction S; It is a figure for explaining.

FIG. 3 is a diagram illustrating a relationship between a change in an index β of asymmetry of a phase pattern image in each defocus state, a coma aberration, an optical axis shift, and the like.

FIG. 4 is a diagram illustrating a relationship between a change in an index β of asymmetry of a phase pattern image in each defocus state, a coma aberration, an optical axis shift, and the like.

FIG. 5 is a diagram in which an integrated signal ΔV obtained by integrating a signal V corresponding to the light intensity of the phase pattern image in a non-measurement direction is plotted in a measurement direction S, and the phase pattern image corresponding to a concave portion of the phase pattern; FIG. 8 is a diagram for explaining an index α quantifying a difference between the image intensity of the phase pattern image corresponding to the convex portion and the image intensity of the convex portion.

FIG. 6 is a diagram showing a relationship between a change in an index α of a difference between image intensities of phase pattern images respectively corresponding to concave portions and convex portions of a phase pattern and spherical aberration in each defocus state.

FIG. 7 is a diagram illustrating a relationship between a defocus amount Z and an index α for two types of phase patterns having different periods,
(A) shows a case where spherical aberration exists in the test optical system, and (b) shows a case where spherical aberration does not exist.

8A and 8B are diagrams showing a relationship between a defocus amount Z and an index α for the same phase pattern when illuminated with two kinds of illumination σ values, and FIG. (B) shows the case where there is no spherical aberration.

FIG. 9 shows a case where the image intensity of the phase pattern image corresponding to the convex portion of the phase pattern matches the image intensity of the phase pattern image corresponding to the concave portion, and the image intensity distribution of the phase pattern image corresponds to the convex portion and the concave portion. FIG. 4 is a diagram showing a state in which a corner occurs in an image intensity waveform that changes.

FIG. 10 is a perspective view schematically showing a configuration of a projection exposure apparatus including an inspection device according to a second embodiment of the present invention.

[Explanation of symbols]

 LP light source EM elliptical mirror GL collimating lens FL fly-eye lens 11 illumination optical system 12 variable aperture stop CL condenser lens 13 Z stage 14 mask 16 inspection pattern 17 projection optical system 18 XY stage 19 slit 22 oblique incident light type autofocus System 23 Light receiver 104 Light guide 106 Half prism 107 Objective lens 111 Second objective lens 115 Branch prism 116, 117 CCD 118 Signal processing system 121 XY stage 122 Z stage 127 Illumination aperture stop 130 Imaging aperture stop

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G03F 7/20 521 G03F 7/20 521 9/00 9/00 H H01L 21/30 502V 516A (72) Invention Person Masahiro Nakagawa 3-2-3 Marunouchi, Chiyoda-ku, Tokyo F-term in Nikon Corporation (reference) 2G086 EE12 HH01 HH06 2H052 AA03 AB14 AB17 AC02 AC07 AC31 AF06 BA02 BA09 BA12 2H087 KA09 KA21 QA02 QA06 5F046 DA04 CC05 DB08 DC10 DC12 EA07 EB01 EB02 EC03 FA03 FA07 FA10 FB06 FB09 FB13 FC04 FC05

Claims (10)

[Claims] 1. An optical system comprising: an illumination optical system for irradiating a phase pattern with illumination light; and an imaging optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. An inspection device for detecting an image of the phase pattern formed via the optical system, and an image detection device for defocusing the image of the phase pattern detected by the image detection device. Defocusing means, based on a change in asymmetry of an image corresponding to the edge of the phase pattern detected in each defocused state in the image detection means, coma of the optical system, light flux vignetting in the optical system, And an inspection unit for inspecting the inclination of the principal ray of the illumination light with respect to the normal to the phase pattern formation surface. 2. An optical system comprising: an illumination optical system for irradiating a phase pattern with illumination light; and an imaging optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. An inspection device for detecting an image of the phase pattern formed via the optical system, and an image detection device for defocusing the image of the phase pattern detected by the image detection device. A first phase pattern that repeats a periodic phase change along a detection direction of the image detection means;
A second phase pattern having a phase amplitude distribution different from the first phase pattern and repeating a periodic phase change along the detection direction of the image detecting means; and a phase of the first phase pattern. The light intensity of the image of the first phase pattern corresponding to the region where the phase has advanced and the light intensity of the image of the first phase pattern corresponding to the region where the phase of the first phase pattern is delayed are respectively predetermined. A first defocus position at which the light intensity of the first phase pattern becomes light intensity, a light intensity of an image of the second phase pattern corresponding to a region where the phase of the second phase pattern is advanced, and a phase of the second phase pattern. Inspection means for inspecting the spherical aberration of the optical system based on the light intensity of the image of the second phase pattern corresponding to the delayed region and the second defocus position at which the light intensity becomes a predetermined light intensity Is further equipped An inspection device characterized by the above-mentioned. 3. An optical system having an illumination optical system for irradiating a phase pattern with illumination light and an imaging optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. An inspection device for detecting an image of the phase pattern formed via the optical system, and an image detection device for defocusing the image of the phase pattern detected by the image detection device. A defocusing unit, wherein the illumination optical system is provided with an illumination aperture changing unit for changing an amplitude distribution of the illumination light passing through an illumination aperture stop, and the phase pattern is detected by the image detection unit. A phase pattern that repeats a periodic phase change along a direction; and a phase pattern of the phase pattern illuminated under the first illumination condition set by the illumination aperture changing unit. First defocusing in which the light intensity of the image of the phase pattern corresponding to the shifted region and the light intensity of the image of the phase pattern corresponding to the region where the phase of the phase pattern lags become predetermined light intensity, respectively. A position, a light intensity of an image of the phase pattern corresponding to a region where a phase of the phase pattern illuminated under the second illumination condition set by the illumination aperture changing unit, and a phase of the phase pattern Inspection means for inspecting the spherical aberration of the optical system based on the light intensity of the image of the phase pattern corresponding to the delayed region and the second defocus position at which the light intensity becomes a predetermined light intensity. An inspection apparatus characterized in that: 4. An optical system having an illumination optical system for irradiating a phase pattern with illumination light and an imaging optical system for condensing a light beam from the phase pattern to form an image of the phase pattern. An inspection device for detecting an image of the phase pattern formed via the optical system, and an image detection device for defocusing the image of the phase pattern detected by the image detection device. Defocusing means, wherein the phase pattern is a phase pattern that repeats a periodic phase change along a detection direction of the image detection means, and in each defocused state, an area where the phase of the phase pattern has advanced. Light intensity of the image of the phase pattern corresponding to
The focal position of the optical system, astigmatism on the optical axis, astigmatism, field curvature based on a change in the difference between the phase pattern image and the light intensity of the image of the phase pattern corresponding to the phase delayed region of the phase pattern. And an inspection device for inspecting at least one of the image plane inclination and the image plane inclination. 5. An alignment mark comprising a phase pattern provided on a mask on which a transfer pattern is formed or an alignment mark comprising a phase pattern provided on a photosensitive substrate onto which an image of the transfer pattern is transferred. An illumination optical system for irradiating illumination light, and an alignment optical system including an imaging optical system for condensing a light beam from the alignment mark and forming an image of the alignment mark, A positioning device for positioning the mask or the photosensitive substrate, comprising: the inspection device according to any one of claims 1 to 4 for inspecting the alignment optical system; Aberration correcting means for correcting aberrations of the imaging optical system based on inspection information of the alignment optical system, and the imaging light based on the inspection information A focus position adjusting means for adjusting a focus position of the system, and a position of an image forming aperture stop of the image forming optical system for correcting a light beam vignetting of the image forming optical system based on the inspection information. Imaging aperture stop position adjusting means for causing relative displacement with respect to the illumination aperture stop of the illumination optical system for correcting the inclination of the principal ray of the illumination light with respect to the normal to the object plane of the imaging optical system. An alignment device, further comprising at least one of illumination aperture stop position adjustment means for displacing the position relative to the optical axis. 6. A projection exposure apparatus comprising: an illumination optical system for irradiating illumination light on a mask on which a transfer pattern is formed; and a projection optical system for forming an image of the transfer pattern on a photosensitive substrate. The inspection apparatus according to any one of claims 1 to 4, which inspects the illumination optical system and the projection optical system, wherein inspection information of the illumination optical system and the projection optical system by the inspection apparatus is provided. Aberration correction means for correcting the aberration of the projection optical system based on the focus position adjustment means for adjusting the focus position of the projection optical system based on the inspection information, Image-forming aperture stop position adjusting means for relatively displacing the position of the image-forming aperture stop of the projection optical system with respect to the optical axis in order to correct vignetting of the projection optical system, and a method of measuring the object plane of the projection optical system On the line The illumination optical system further comprises at least one of illumination aperture stop position adjusting means for relatively displacing the position of the illumination aperture stop of the illumination optical system with respect to the optical axis in order to correct the inclination of the principal ray of the illumination light. A projection exposure apparatus characterized by the above-mentioned. 7. A method for inspecting an optical system including an imaging optical system that forms an image of a predetermined phase pattern, comprising: irradiating the phase pattern with illumination light; Detecting an image of the phase pattern at a defocus position, based on a change in asymmetry of an image corresponding to an edge of the phase pattern detected at the plurality of defocus positions, the coma of the optical system, An inspection method for an optical system, comprising: inspecting a light beam vignetting in an optical system and an inclination of a principal ray of the illumination light with respect to a normal to a surface on which the phase pattern is formed. 8. A method for inspecting an optical system including an illumination optical system for irradiating a phase pattern with illumination light and an imaging optical system for forming an image of the phase pattern, wherein the phase pattern is formed along a predetermined direction. And a second phase pattern having a phase amplitude distribution different from the first phase pattern and repeating a periodic phase change along the predetermined direction. Irradiating the phase pattern with illumination light via the illumination optical system, detecting an image of the phase pattern using an image detector having a detection direction along the predetermined direction, The light intensity of the image of the first phase pattern corresponding to the region where the phase of the phase pattern is advanced, and the light of the image of the first phase pattern corresponding to the region where the phase of the first phase pattern is delayed Strength and strength A first defocus position at which a predetermined light intensity is obtained, a light intensity of an image of the second phase pattern corresponding to a region where the phase of the second phase pattern advances, and a second phase pattern Inspecting the spherical aberration of the optical system based on the light intensity of the image of the second phase pattern corresponding to the region where the phase is delayed and the second defocus position where the light intensity becomes a predetermined light intensity. An inspection method for an optical system, comprising: 9. The illumination optical system is configured to be capable of changing an amplitude distribution of the illumination light passing through an illumination aperture stop. When detecting the first defocus position, the illumination optical system uses an illumination aperture. When the amplitude distribution of the illumination light is set to a first amplitude distribution, and when the second defocus position is detected, the amplitude distribution of the illumination light at the illumination aperture stop is defined as the first amplitude distribution. The inspection method for an optical system according to claim 7, wherein the first and second amplitude distributions are set to different second amplitude distributions. 10. A method for inspecting an optical system including an imaging optical system for forming an image of a predetermined phase pattern, comprising: irradiating the phase pattern with illumination light; and using an image detector having a predetermined detection direction. Detecting an image of the phase pattern at a plurality of different defocus positions in the optical axis direction of the imaging optical system, wherein the phase pattern is a phase pattern that repeats a periodic phase change along a detection direction of the image detector. In the plurality of defocus positions, the light intensity of the image of the phase pattern corresponding to the region where the phase of the phase pattern is advanced, and the phase pattern corresponding to the region where the phase of the phase pattern is delayed. Inspection of at least one of a focal position of the optical system, astigmatism on the optical axis, astigmatism, curvature of field, and inclination of the image plane is performed based on a change in a difference from the light intensity of the image. Method of inspecting an optical system characterized by.