JP3994209B2 - Optical system inspection apparatus and inspection method, and alignment apparatus and projection exposure apparatus provided with the inspection apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an inspection apparatus and inspection method for an optical system, and an alignment apparatus and a projection exposure apparatus including the inspection apparatus, and more particularly to a projection optical system of a projection exposure apparatus used in a lithography process for manufacturing a semiconductor element, a liquid crystal display element, and the like. The alignment optical system of the alignment apparatus attached to the projection exposure apparatus, and the inspection of the aberration, the focal position, the optical axis deviation, etc. of the overlay measurement optical system of the overlay measurement apparatus for determining the alignment result; It relates to correction (adjustment).
[0002]
[Prior art]
2. Description of the Related Art Conventionally, in a projection exposure apparatus used in a lithography process for manufacturing semiconductor elements, liquid crystal display elements, and the like, a pattern formed on a mask is transferred onto a wafer that is a photosensitive substrate via a projection optical system. At this time, with respect to the pattern already formed on the wafer, the projection image of the mask pattern formed via the projection optical system is aligned (aligned) by an alignment device attached to the projection exposure apparatus, Perform overlay exposure. Further, the quality of the alignment result obtained by the alignment device is determined by an overlay measurement device that is internally or externally provided in the projection exposure apparatus.
[0003]
In this case, for example, if aberration remains in the projection optical system, the projection image of the mask pattern cannot be accurately formed, and a distorted transfer pattern is formed on the wafer. For example, if aberration remains in the alignment optical system of the alignment apparatus, accurate alignment between the mask and the wafer cannot be performed, and high-precision overlay exposure cannot be performed. Furthermore, with respect to the overlay measurement optical system of the overlay measurement apparatus, for example, if there is residual aberration, highly accurate overlay measurement cannot be performed.
[0004]
As described above, the projection optical system of the projection exposure apparatus, the alignment optical system of the alignment apparatus, and the overlay measurement optical system of the overlay measurement apparatus are set to a state as close to the ideal optical system as possible. The apparatus performance of the exposure apparatus, alignment apparatus, overlay measurement apparatus, etc. can be sufficiently exhibited. In recent years, it has become more and more important to accurately and simply inspect such aberrations, focal positions, and optical axis misalignments of the optical system, and to accurately correct or adjust according to the inspection results.
[0005]
Therefore, the applicant of the present invention is suitable for inspection of the projection optical system of the projection exposure apparatus, the alignment optical system of the alignment apparatus, and the overlay measurement optical system of the overlay measurement apparatus in JP-A-9-49781. Is proposing a simple inspection device. In this inspection apparatus, attention is paid to a change in image asymmetry that occurs, for example, when a phase pattern image is gradually defocused. Based on this change in asymmetry, coma aberration, spherical aberration, and luminous flux vignetting ( It is accurately inspected that the light beam is blocked.
[0006]
[Problems to be solved by the invention]
However, the inspection apparatus disclosed in Japanese Patent Application Laid-Open No. 9-49781 cannot accurately and easily inspect various aberrations other than coma and spherical aberration (with good reproducibility).
[0007]
The present invention has been made in view of the above-described problems, and provides an inspection apparatus and an inspection method that can accurately and easily inspect various aberrations, focal positions, optical axis deviations, and the like of an optical system. With the goal.
In addition, a projection exposure apparatus, an alignment apparatus, and an alignment apparatus that can exhibit sufficient apparatus performance by correcting or adjusting aberrations, a focal position, an optical axis shift, and the like of an optical system based on a detection result by the inspection apparatus of the present invention An object of the present invention is to provide an overlay measurement apparatus.
[0008]
[Means for Solving the Problems]
  In order to solve the above problem, in the first invention of the present invention, an illumination optical system for irradiating the phase pattern with illumination light and a light beam from the phase pattern are condensed to form an image of the phase pattern. In an inspection apparatus for inspecting an optical system having an imaging optical system for
  Image detecting means for detecting an image of the phase pattern formed through the optical system;
  Defocusing means for defocusing the image of the phase pattern detected by the image detection means;
  The asymmetry of the image corresponding to the edge of the phase pattern detected in each defocus state by the image detection means.A constant offset value B that is an index and does not depend on the defocus amount of the index β defined by the equation (1)Based onAnd saidThere is provided an inspection apparatus comprising inspection means for inspecting an inclination of a principal ray of the illumination light with respect to a normal line of a phase pattern forming surface.
β = Σ {V iL -V iR / (V max -V min )} / N (1)
Where V iL And V iR Is the left and right signal minimum values in the i-th period in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. max And V min Are the maximum and minimum values of the signal V, n is the number of periods of the distribution of the integrated signal ΣV, and Σ is a summation symbol from i = 1 to n.
[0009]
In the inspection apparatus according to the first aspect of the invention, the inspection unit includes an asymmetry of an image corresponding to an edge of the phase pattern detected in one or more defocus states by the image detection unit, and the phase pattern or the image. Based on the asymmetry of the image corresponding to the edge of the phase pattern detected in one or more defocus states in the image detection means with the detection means rotated 180 degrees around its detection center, It is preferable to inspect the optical system by correcting a detection error of an image asymmetry caused by a phase pattern or the image detecting means.
[0010]
  In the second invention of the present invention, an illumination optical system for irradiating the 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 In an inspection apparatus for inspecting an optical system having
  Image detecting means for detecting an image of the phase pattern formed through the optical system;
  Defocusing means for defocusing the image of the phase pattern detected by the image detection means,
  The phase pattern has a first phase pattern that repeats a periodic phase change along a detection direction of the image detection unit, and a phase amplitude distribution different from the first phase pattern, and is detected by the image detection unit. A second phase pattern that repeats a periodic phase change along the direction,
  The light intensity of the first phase pattern image corresponding to the phase advanced region of the first phase pattern and the image of the first phase pattern corresponding to the phase delayed region of the first phase pattern Light intensity andThe difference index α between the two becomes 0Corresponds to the first defocus position, the light intensity of the image of the second phase pattern corresponding to the phase advanced region of the second phase pattern, and the phase delayed region of the second phase pattern. The light intensity of the image of the second phase pattern;The difference index α between the two becomes 0The second defocus position andDifferenceIn accordance with the present invention, there is provided an inspection apparatus further comprising inspection means for inspecting the spherical aberration of the optical system.
α = Σ {V it -V io / (V it + V io )} / (2n) (2)
Where V io And V it Is an integral signal corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integral signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction, and n is the distribution of the integral signal ΣV. Σ is a summation symbol from i = 1 to n.
[0011]
  Furthermore, in the third invention of the present invention, an illumination optical system for irradiating the phase pattern with illumination light and an imaging optical system for condensing the light flux from the phase pattern to form an image of the phase pattern In an inspection apparatus for inspecting an optical system having
  Image detecting means for detecting an image of the phase pattern formed through the optical system;
  Defocusing means for defocusing the image of the phase pattern detected by the image detection means,
  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,
  The phase pattern is a phase pattern that repeats a periodic phase change along the detection direction of the image detection means,
  In the region where the phase intensity of the phase pattern image corresponding to the phase advanced region of the phase pattern illuminated under the first illumination condition set by the illumination aperture changing means and the phase of the phase of the phase pattern are delayed The light intensity of the corresponding image of the phase pattern andThe difference index α between the two becomes 0The first defocus position, the light intensity of the phase pattern image corresponding to the phase advanced region of the phase pattern illuminated under the second illumination condition set by the illumination aperture changing means, and the phase The light intensity of the image of the phase pattern corresponding to the phase lag region of the pattern;The difference index α between the two becomes 0The second defocus position andDifferenceIn accordance with the present invention, there is provided an inspection apparatus further comprising inspection means for inspecting the spherical aberration of the optical system.
α = Σ {V it -V io / (V it + V io )} / (2n) (2)
Where V io And V it Is an integral signal corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integral signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction, and n is the distribution of the integral signal ΣV. Σ is a summation symbol from i = 1 to n.
[0012]
  In the fourth invention of the present invention, an illumination optical system for irradiating the phase pattern with illumination light and an imaging optical system for condensing the light flux from the phase pattern to form an image of the phase pattern In an inspection apparatus for inspecting an optical system having
  Image detecting means for detecting an image of the phase pattern formed through the optical system;
  Defocusing means for defocusing the image of the phase pattern detected by the image detection means,
  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 phase pattern image corresponding to the phase advanced region of the phase pattern and the light intensity of the phase pattern image corresponding to the phase delayed region of the phase patternDefocus positions where α corresponding to each visual field position becomes 0 in the values of the difference index α between the visual system at a plurality of positions in the visual field of the optical systemThe optical system further includes inspection means for inspecting at least one of astigmatism on the optical axis, astigmatism, field curvature, and field tilt of the optical system. Provide inspection equipment.
α = Σ {V it -V io / (V it + V io )} / (2n) (2)
Where V io And V it Is an integral signal corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integral signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction, and n is the distribution of the integral signal ΣV. Σ is a summation symbol from i = 1 to n.
[0013]
In the inspection apparatus according to the first to fourth inventions and preferred embodiments of each invention, the illumination wavelength selection means for selecting the wavelength of the illumination light to be irradiated onto the phase pattern and the image from the phase pattern. Inspecting the optical system for light having a wavelength selected by the illumination wavelength selection means or the imaging light beam wavelength selection means, comprising at least one of imaging light beam wavelength selection means for selecting the wavelength of the light flux Is preferred.
In order to inspect the optical system for light of a selected wavelength, the phase pattern preferably has two or more phase patterns having different spectral reflectances or spectral transmittances.
[0014]
Moreover, it is preferable that the said phase pattern is a phase pattern of duty ratio which repeats a periodic phase change along the detection direction of the said image detection means to 1: 1. Further, the phase change amount Φ of the amplitude phase distribution of the transmission or reflection of the phase pattern is relative to the center wavelength of the light beam detected by the image detection unit.
Φ = π (2n−1) / 2 (n is a natural number)
It is preferable to satisfy the following conditions.
[0015]
Further, it is preferable that the defocusing unit moves at least one of the phase pattern, the whole or a part of the optical system, and the image detection unit along the optical axis of the optical system. Further, the defocusing means includes a light intensity of the phase pattern image corresponding to a phase advanced region of the phase pattern and a light intensity of the phase pattern image corresponding to a phase delayed region of the phase pattern. It is preferable that the defocus range of the image of the phase pattern detected by the image detecting means is defined around the defocus position where the two are equal.
[0016]
According to the fifth aspect of the present invention, from the alignment mark formed of the phase pattern provided on the mask on which the transfer pattern is formed or the phase pattern provided on the photosensitive substrate onto which the image of the transfer pattern is transferred. Alignment optics comprising an illumination optical system for irradiating illumination light to the alignment mark and an imaging optical system for condensing the 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 having a system,
In order to inspect the alignment optical system, the inspection apparatus according to the first to fourth inventions and preferred embodiments of each invention,
Aberration correction means for correcting the aberration of the imaging optical system based on inspection information of the alignment optical system by the inspection device, and for adjusting the in-focus position of the imaging optical system based on the inspection information Focusing position adjusting means, imaging for relatively displacing the position of the imaging aperture stop of the imaging optical system with respect to the optical axis in order to correct the vignetting of the imaging optical system based on the inspection information Aperture stop position adjusting means, and the position of the illumination aperture stop of the illumination optical system is displaced relative to the optical axis in order to correct the inclination of the principal ray of the illumination light with respect to the normal of the object plane of the imaging optical system There is provided an alignment apparatus further comprising at least one of illumination aperture stop position adjusting means.
According to another aspect of the present invention, in an exposure apparatus that exposes a transfer pattern formed on a mask onto a photosensitive substrate, the fifth invention is applied to position the mask or the photosensitive substrate. Preferably, an alignment device is provided.
[0017]
According to another aspect of the present invention, an illumination optical system for irradiating illumination light to the first pattern and the second pattern formed on the substrate, and a light flux from the first pattern and the second pattern And a superposition measuring optical system comprising an imaging optical system for forming an image of the first pattern and an image of the second pattern by focusing the light, and the first pattern and the second pattern In the overlay measurement device that measures the relative displacement of
In order to inspect the overlay measurement optical system, the inspection apparatus according to the first to fourth inventions and preferred embodiments of each invention,
Aberration correction means for correcting the aberration of the imaging optical system based on inspection information of the alignment optical system by the inspection device, and for adjusting the in-focus position of the imaging optical system based on the inspection information Focusing position adjusting means, imaging for relatively displacing the position of the imaging aperture stop of the imaging optical system with respect to the optical axis in order to correct the vignetting of the imaging optical system based on the inspection information Aperture stop position adjusting means, and the position of the illumination aperture stop of the illumination optical system is displaced relative to the optical axis in order to correct the inclination of the principal ray of the illumination light with respect to the normal of the object plane of the imaging optical system It is preferable to further include at least one of illumination aperture stop position adjusting means.
[0018]
According to another aspect of the present invention, in an exposure apparatus for exposing a transfer pattern formed on a mask onto a photosensitive substrate, the first pattern and the second pattern formed on the photosensitive substrate Preferably, the apparatus includes the overlay measurement device for measuring the relative displacement, and performs positioning correction of the mask or the photosensitive substrate based on the relative displacement information from the overlay measurement device.
[0019]
According to a sixth aspect of the present invention, there is provided an illumination optical system for irradiating a mask on which a transfer pattern is formed with illumination light, and a projection optical system for forming an image of the transfer pattern on a photosensitive substrate. In the projection exposure apparatus provided,
In order to inspect the illumination optical system and the projection optical system, the inspection apparatus according to the first to fourth inventions and preferred aspects of each invention is provided,
Aberration correction means for correcting aberration of the projection optical system based on inspection information of the illumination optical system and the projection optical system by the inspection device, and adjusting a focus position of the projection optical system based on the inspection information A focusing position adjusting means for adjusting the position of the imaging aperture stop of the projection optical system relative to the optical axis in order to correct the vignetting of the projection optical system based on the inspection information. An image aperture stop position adjusting unit, and a relative displacement of 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 of the object plane of the projection optical system There is provided a projection exposure apparatus further comprising at least one of illumination aperture stop position adjusting means.
[0020]
  According to a seventh aspect of the present invention, in a method for inspecting an optical system including an imaging optical system that forms an image of a predetermined phase pattern,
  Illuminating the phase pattern with illumination light,
  Detecting the image of the phase pattern at a plurality of different defocus positions in the optical axis direction of the imaging optical system;
  The asymmetry of the image corresponding to the edges of the phase pattern detected at the plurality of defocus positions.A constant offset value B that is an index and does not depend on the defocus amount of the index β defined by the equation (1)Based onAnd saidThere is provided an optical system inspection method for inspecting an inclination of a principal ray of the illumination light with respect to a normal line of a phase pattern forming surface.
β = Σ {V iL -V iR / (V max -V min )} / N (1)
Where V iL And V iR Is the left and right signal minimum values in the i-th period in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. max And V min Are the maximum and minimum values of the signal V, n is the number of periods of the distribution of the integrated signal ΣV, and Σ is a summation symbol from i = 1 to n.
[0021]
  According to an eighth aspect of the present invention, in a method for inspecting an optical system including an illumination optical system for irradiating illumination light to a phase pattern 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, a phase amplitude distribution different from the first phase pattern, and a periodic phase along the predetermined direction. A second phase pattern that repeats the change,
  Illuminating the phase pattern with illumination light through 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 first phase pattern image corresponding to the phase advanced region of the first phase pattern and the image of the first phase pattern corresponding to the phase delayed region of the first phase pattern Light intensity andThe difference index α between the two becomes 0Corresponds to the first defocus position, the light intensity of the image of the second phase pattern corresponding to the phase advanced region of the second phase pattern, and the phase delayed region of the second phase pattern. The light intensity of the image of the second phase pattern;The difference index α between the two becomes 0The second defocus position andDifferenceBased on the above, there is provided an inspection method of an optical system characterized by inspecting the spherical aberration of the optical system.
α = Σ {V it -V io / (V it + V io )} / (2n) (2)
Where V io And V it Is an integral signal corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integral signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction, and n is the distribution of the integral signal ΣV. Σ is a summation symbol from i = 1 to n.
[0022]
According to a preferred aspect of the eighth invention, the illumination optical system is configured to be capable of changing the amplitude distribution of the illumination light passing through the illumination aperture stop,
When detecting the first defocus position, the amplitude distribution of the illumination light at the illumination aperture stop is set to the first amplitude distribution,
When detecting the second defocus position, 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.
[0023]
  According to a ninth aspect of the present invention, in a method for inspecting an optical system including an imaging optical system that forms an image having a predetermined phase pattern,
  Illuminating the phase pattern with illumination light,
  Detecting an image of the phase pattern at a plurality of different defocus positions in an optical axis direction of the imaging optical system using an image detector having a predetermined detection direction;
  The phase pattern is a phase pattern that repeats a periodic phase change along the detection direction of the image detector,
  The light intensity of the phase pattern image corresponding to the phase advanced region of the phase pattern and the light intensity of the phase pattern image corresponding to the phase delayed phase of the phase pattern at the plurality of defocus positions. WhenDefocus positions where α corresponding to each visual field position becomes 0 in the values of the difference index α between the visual system at a plurality of positions in the visual field of the optical systemThe optical system inspection method is characterized by inspecting at least one of astigmatism on the optical axis, astigmatism, field curvature, and image plane tilt of the optical system.
α = Σ {V it -V io / (V it + V io )} / (2n) (2)
Where V io And V it Is an integral signal corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integral signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction, and n is the distribution of the integral signal ΣV. Σ is a summation symbol from i = 1 to n.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
In the inspection apparatus and inspection method of the present invention, as will be described with reference to FIGS. 3 and 4 in the embodiments described later, an index of image asymmetry corresponding to the edge of the phase pattern detected in each defocus state. Based on the change of β, in addition to coma aberration of the test optical system and luminous flux vignetting in the test optical system, the tilt of the chief ray of the illumination light with respect to the normal of the phase pattern forming surface, that is, the illumination telecentric can be easily performed In addition, the inspection can be performed quickly. Specifically, the tilt 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 coma aberration amount can be obtained based on the slope C of the straight line representing the index β that changes substantially linearly depending on the defocus amount Z. Furthermore, the amount of vignetting of the luminous flux can be obtained based on the amount of bending D of the broken line or the curved line representing the index β that changes to the shape of a bent line or a curved line depending on the defocus amount Z.
[0025]
In this case, based on the two asymmetry indices β1 and β2 detected in two states rotated 180 degrees around its detection center (eg based on its simple average value) It is possible to correct the detection error of the asymmetry index β of the image to be corrected. Further, based on two asymmetry indexes β1 and β2 detected in two states in which an image detection means such as a CCD is rotated 180 degrees around its detection center (for example, based on its simple average value), It is also possible to correct the detection error of the image asymmetry index β caused by the phase pattern.
[0026]
Further, in the inspection apparatus and inspection method of the present invention, the first phase pattern and the second phase pattern having different phase amplitude distributions (pitch) are used as described with reference to FIG. Thus, the spherical aberration of the optical system to be inspected can be inspected easily and quickly with good reproducibility. Specifically, the light intensity of the image corresponding to the phase-advanced region of the first phase pattern (for example, the convex portion of the reflective concavo-convex pattern) and the region of the phase of the first phase pattern delayed (for example, the reflective concavo-convex region The light intensity of the image corresponding to the first defocus position Z1 where the light intensity of the image corresponding to the (concave portion of the pattern) matches (index α = 0) and the phase-advanced region of the second phase pattern. And the second defocus position Z2 in which the light intensity of the image corresponding to the phase-lag region of the second phase pattern matches (index α = 0), the spherical aberration of the optical system to be tested And the correction state can be obtained.
[0027]
Furthermore, in the inspection apparatus and the inspection method of the present invention, as described with reference to FIG. 8 in the embodiments described later, the spherical surface of the optical system to be tested is used by using the same phase pattern for two different illumination conditions. Aberrations 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. The phase of the phase of the light intensity phase pattern of the image corresponding to the phase advanced region of the phase pattern illuminated with the first defocus position Z1 and the second illumination σ value (index α = 0) The magnitude and correction state of the spherical aberration of the optical system to be measured can be obtained based on the second defocus position Z2 at which the light intensity of the image corresponding to.
[0028]
Further, in the inspection apparatus and the inspection method of the present invention, as will be described with reference to FIGS. 7 and 8 in the embodiments described later, the image corresponding to the advanced region of the phase pattern in each defocus state is obtained. Based on the change in the index α of the difference between the light intensity and the light intensity of the image corresponding to the phase lag region of the phase pattern, the focal position of the test optical system, astigmatism on the optical axis, astigmatism, image At least one of the surface curvature and the image plane inclination can be easily and quickly inspected with high reproducibility.
[0029]
As described above, in the inspection apparatus and the inspection method of the present invention, the image asymmetry (index β) corresponding to the edge of the phase pattern in each defocus state and the difference in image intensity between the uneven portions of the phase pattern (index α). In addition to coma aberration, luminous flux vignetting, and illumination light tilt (illumination telecentric) in the optical system, spherical aberration, focal position, astigmatism on the optical axis, astigmatism, field curvature, and field tilt Can be easily and quickly inspected with good reproducibility. Then, based on the detected inspection information of the optical system, correction and adjustment related to the aberration and focus position of the optical system, position adjustment related to the illumination aperture stop and the imaging aperture stop, and the like are performed efficiently and appropriately. The system can be as close as possible to the ideal optical system.
[0030]
Therefore, by incorporating the inspection apparatus of the present invention into a projection exposure apparatus, alignment apparatus, overlay measurement apparatus, etc., an illumination optical system of the projection exposure apparatus, an alignment optical system of the projection optical system, and an alignment apparatus, and an overlay measurement apparatus In addition, the overlay measurement optical system can be inspected easily and quickly with good reproducibility, and sufficient apparatus performance can be achieved by correcting or adjusting the aberration, focal position, optical axis misalignment, etc. of the optical system based on the detection results of the inspection apparatus. It can be demonstrated. Specifically, the position detection error caused by the alignment optical system is reduced in the alignment apparatus, and the measurement error caused by the overlay measurement optical system is reduced in the overlay measurement apparatus. Further, in the projection exposure apparatus, the aberration of the projection optical system is corrected well and the focal position, the optical axis shift, etc. are adjusted well, so that the pattern transfer performance is improved and highly accurate overlay projection exposure is performed. It becomes possible.
[0031]
Embodiments of the present invention will be described below with reference to the accompanying 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. In the first embodiment, the alignment optical system (imaging optical system and illumination optical system) of the off-axis type alignment apparatus 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 parallel to the plane of FIG. 1 in the plane perpendicular to the optical axis, the Z axis and the X axis. The Y axis is set in a direction perpendicular to each other.
[0032]
The projection exposure apparatus shown in FIG. 1 includes an exposure illumination optical system (not shown) for uniformly illuminating a reticle R as a mask with appropriate exposure light. The reticle R is supported on the reticle stage 101 substantially parallel to the XY plane, and a circuit pattern to be transferred is formed in the pattern area PA.
The light transmitted through the reticle R reaches the wafer (or glass plate) W that is a photosensitive substrate through the projection optical system PL, and a pattern image of the reticle R is formed on the wafer W.
[0033]
The wafer W is supported on the Z stage 122 via the wafer holder 121 so as to be substantially parallel to 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 is further supported on the XY stage 123. Similarly, the XY stage 123 is driven two-dimensionally in the XY plane perpendicular to the optical axis of the projection optical system PL by the stage control system 124.
[0034]
In the projection exposure, it is necessary to optically align (align) the pattern area PA and each exposure area on the wafer W. Therefore, the position of the alignment step mark formed on the wafer W, that is, the position of the wafer mark WM in the reference coordinate system is detected, and alignment is performed based on the position information. Thus, the alignment apparatus of the present invention is used to detect and align the position of the wafer mark WM.
[0035]
The alignment apparatus shown in FIG. 1 includes a light source 103 such as a halogen lamp in order to supply illumination light (alignment light AL). Light from the 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 exit end of the light guide 104 is limited by the illumination aperture stop 127 as necessary, and then enters the condenser lens 129 as an illumination light beam having an appropriate cross-sectional shape.
[0036]
The alignment light AL that has passed through the condenser lens 129 is once condensed and then incident on the illumination relay lens 105 via an illumination field stop (not shown). The alignment light AL that has become parallel light through the illumination relay lens 105 passes through the half prism 106 and then enters the first objective lens 107. The alignment light AL collected by the first objective lens 107 is reflected downward by the reflecting surface of the reflecting prism 108 and then illuminates the wafer mark WM, which is an alignment mark formed on the wafer W.
[0037]
As described above, the light source 103, the light guide 104, the illumination aperture stop 127, the condenser lens 129, the illumination field stop (not shown), the illumination relay lens 105, the half prism 106, the first objective lens 107, and the reflection prism 108 are formed on the wafer. An illumination optical system for irradiating the mark WM with illumination light is configured.
[0038]
The reflected light from the wafer mark WM with respect to the illumination light enters the half prism 106 via the reflecting prism 108 and the first objective lens 107. The light reflected upward in the drawing 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 indicator plate 112 enters the XY branch half prism 115 via the relay lens system (113, 114). The light reflected by the XY branch half prism 115 enters the Y direction CCD 116, and the light transmitted through the XY branch half prism 115 enters the X direction CCD 117. An imaging aperture stop 130 is disposed in the parallel optical path of the relay lens system (113, 114) as necessary.
[0039]
As described above, the reflecting prism 108, the first objective lens 107, the half prism 106, the second objective lens 111, the indicator plate 112, the relay lens system (113, 114), the imaging aperture stop 130, and the half prism 115 are used as illumination light. An imaging optical system for forming a mark image based on the reflected light from the wafer mark WM is configured.
The Y-direction CCD 116 and the X-direction CCD 117 constitute image detection means for detecting a mark image formed through the imaging optical system.
[0040]
Thus, a mark image is formed together with the index pattern image of the index plate 112 on the imaging surfaces of the Y direction CCD 116 and the X direction CCD 117. Output signals from the Y direction CCD 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 signal processing (waveform processing) in the signal processing system 118 is supplied to the main control system 125.
[0041]
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 in accordance with the stage control signal to align 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 an input unit 126 such as a keyboard. Based on these commands, the main control system 125 drives the illumination aperture stop 127 via the drive system 128 or drives the imaging aperture stop 130 via the drive system 131. The main control system 125 drives the second objective lens 111 and the relay lens 113 based on an aberration correction command described later.
[0042]
As described above, the wafer mark WM is formed as an alignment mark on the wafer W. The wafer mark WM is a duty ratio that repeats a periodic phase change along the measurement direction of the CCD 116 or the measurement direction of the CCD 117, for example. Is a one-to-one phase pattern. Such a phase pattern can be formed into an accurate shape with a desired accuracy by, for example, etching a silicon wafer exposed by a projection exposure apparatus. In order to obtain sharp detection sensitivity in the aberration measurement of the optical system, which will be described later, the phase change amount Φ of the reflected amplitude phase distribution of the phase pattern is as follows with respect to the center wavelength of the light beam detected by the CCDs 116 and 117: It is desirable to satisfy formula (a).
Φ = π (2n−1) / 2 (n is a natural number) (a)
[0043]
FIG. 2 is a diagram in which an integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction is plotted with respect to the measurement direction S, and an asymmetry index β of the phase pattern image is obtained. It is a figure for demonstrating.
In the first embodiment, an image of the wafer mark WM consisting of a phase pattern is formed on the imaging surface of a CCD (116, 117) that is an imaging device. Therefore, in FIG. 2, an integration signal ΣV obtained by integrating the imaging signal V from the imaging element (116, 117) in the non-measurement direction is plotted with respect to the measurement direction S.
[0044]
As shown in FIG. 2, the integration signal ΣV changes along the measurement direction S every period 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 asymmetry of the phase pattern image, the left and right signal minimum values (the signal of the falling edge portion) in the i-th (second in FIG. 2) period in the distribution of the integral signal ΣV. Value) are ViL and ViR (i = 1, 2, 3,...), Respectively. In addition, the maximum value and the minimum value of the signal are Vmax and Vmin, respectively, in the entire region over each period except for both end portions of the integration signal ΣV.
[0045]
Then, an index β of asymmetry of the phase pattern image is obtained based on the following equation (1).
β = Σ {ViL−ViR / (Vmax−Vmin)} / n (1)
Here, n is the number of periods, and Σ is a summation symbol from i = 1 to n.
[0046]
3 and 4 show changes in the phase pattern image asymmetry index β and coma aberration in each defocus state obtained by the stage control system 124 appropriately driving the Z stage 122 based on the command of the main control system 125. It is a figure which shows the relationship with optical axis deviation.
In 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 deviation, as shown by a straight line L1 in FIG. The index β is 0 without depending on the defocus amount Z.
[0047]
Further, in the optical system to be tested (in this case, the illumination optical system), when the chief ray of the illumination light that irradiates the object surface (ie, the wafer surface) is inclined with respect to the normal of the object surface (hereinafter referred to as “illumination telecentric” 3), the index β takes a constant offset value B without depending on the defocus amount Z, as indicated by a straight line L2 in FIG. This offset value B is substantially proportional to the amount of inclination of the principal ray of illumination light with respect to the normal of the object plane, that is, the amount of illumination telecentricity.
[0048]
Further, when coma is present in the optical system to be measured (in this case, the imaging optical system), the index β is substantially linear depending on the defocus amount Z, as indicated by a straight line L3 in FIG. Changes. The slope C of the straight line L3 is substantially proportional to the coma aberration amount.
Further, when vignetting of the imaged light beam exists in the test optical system (also in this case, the image forming optical system), the index β is a broken line (in accordance with the change in the defocus amount Z, as shown in FIG. 4B). Or, a curve as indicated by a broken line (L4) is shown. The bending amount D of the bent line or curved line L4 is substantially proportional to the amount of vignetting of the imaging light beam.
[0049]
Thus, from the relationship between the index β obtained by defocusing the phase pattern image and the defocus amount Z, the illumination telecentricity is obtained by the offset value B, the coma aberration is obtained by the inclination value C, and the luminous flux vignetting is obtained from the bending amount D. 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 (1), the range of i = 1 to n may be limited. By limiting in this way, it is possible to inspect the illumination telecentricity, light flux vignetting, and coma aberration of the optical system under test at an arbitrary position on the object plane. Further, by performing the above-described inspection on each point of the visual field, it is possible to discriminate, for example, the eccentric coma aberration and the image height coma aberration in the detection visual field. The same applies to illumination telecentricity and luminous flux vignetting.
[0050]
FIG. 5 is a diagram in which an integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction is plotted with respect to the measurement direction S, and the phase pattern image corresponding to the concave portion of the phase pattern It is a figure for demonstrating the parameter | index (alpha) which quantified the difference between the image intensity of this and the image intensity of the phase pattern image corresponding to a convex part. As described above, FIG. 5 is a diagram corresponding to FIG. 2, but for the sake of simplification, an optical system to be tested that does not have coma aberration or luminous flux vignetting is assumed.
[0051]
As described above, in the first embodiment, an image of the wafer mark WM including a phase pattern is formed on the imaging surface of the CCD (116, 117) that is an imaging device. Therefore, in FIG. 5, similarly to FIG. 2, the integration signal ΣV obtained by integrating the imaging signal V from the imaging element (116, 117) in the non-measurement direction is plotted with respect to the measurement direction S. As shown in FIG. 5, the integration signal ΣV changes along the measurement direction S every period 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, the i th in the distribution of the integration signal ΣV. The integrated signal ΣV corresponding to the concave portion of the phase pattern is Vio (i = 1, 2, 3...), And the integrated signal ΣV corresponding to the convex portion of the i-th phase pattern is Vit (i = 1, 2, 3). ...).
[0052]
Then, an index α of the difference between the image intensity of the phase pattern image corresponding to the concave portion and the convex portion of the phase pattern is obtained by the following equation (2).
α = Σ {Vit−Vio / (Vit + Vio)} / (2n) (2)
Here, n is the number of periods, and Σ is a summation symbol from i = 1 to n.
[0053]
FIG. 6 shows images of phase pattern images respectively corresponding to the concave and convex portions of the phase pattern in each defocus state obtained by appropriately driving the Z stage 122 by the stage control system 124 based on the command of the main control system 125. It is a figure which shows the relationship between the change of the parameter | index (alpha) of the difference between intensity | strengths, and spherical aberration. In FIG. 6 and other related drawings (FIGS. 7 and 8), Z = 0 corresponds to the paraxial image plane position of the optical system to be measured. 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 substantially in proportion to the value of the defocus amount Z. That is, in the straight line L1 indicating the change of the index α, Z = 0 when α = 0.
[0054]
On the other hand, if there is overcorrected spherical aberration in the test optical system, the value of Z when α = 0 is negative on the straight lines L2 and L3 indicating the change of the index α. Further, the absolute value of Z when α = 0 increases in accordance with the magnitude of the spherical aberration amount. That is, the absolute value of Z when the straight line L2 indicating the change of the index α when the overcorrected spherical aberration exists is intersected with the Z axis (α = 0 axis) is overcorrected spherical aberration. Is larger than the absolute value of Z when the straight line L3 indicating the change in the index α when the angle α is relatively small intersects the Z axis. Thus, when there is an overcorrected spherical aberration, the defocus position 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 is the spherical surface. There is a tendency to move away from the paraxial image plane position of Z = 0 in the negative direction according to the magnitude of the aberration amount.
[0055]
Further, when there is undercorrected spherical aberration in the test optical system, the value of Z when α = 0 is positive in the straight lines L4 and L5 indicating changes in the index α. Further, the value of Z when α = 0 increases in accordance with the amount of spherical aberration. That is, when the straight line L4 indicating the change in the index α when the undercorrected spherical aberration is present relatively intersects with the Z axis (the axis of α = 0), the value of Z in the undercorrected spherical aberration is greater. The straight line L5 indicating the change of the index α when it exists relatively small is larger than the value of Z when it intersects the Z axis. Thus, when there is undercorrected 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 is the spherical surface. There is a tendency to move away from the paraxial image plane position of Z = 0 in the positive direction according to the magnitude of the aberration amount.
[0056]
FIG. 7 is a diagram showing the relationship between the defocus amount Z and the index α for two types of phase patterns having different periods. FIG. 7A shows the case where spherical aberration exists in the optical system to be tested. Respectively show the cases where there is no spherical aberration.
A phase pattern with a small period has a larger diffraction angle of diffracted light generated from the pattern than a phase pattern with a large period, and is more susceptible to spherical aberration. Therefore, when spherical aberration exists in the test optical system, the straight line L1 obtained with respect to the phase pattern with a longer period is located at the position Z2 where the straight line L2 obtained with respect to the phase pattern with a shorter period intersects the Z axis. Is farther from the paraxial image plane position of Z = 0 than the position Z1 at which it intersects the Z axis.
[0057]
On the other hand, when there is no spherical aberration in the test optical system, the straight line L1 obtained with respect to the phase pattern with a large period also exists at the position Z2 where the straight line L2 obtained with respect to the phase pattern with a small period intersects the Z axis. The position Z1 that intersects the Z axis also coincides with the paraxial image plane position at 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 sign of the difference (Z2-Z1) is the overcorrection and correction of the spherical aberration. It turns out that it corresponds to under. In other words, from the relationship between the index α obtained when the phase pattern image is defocused using two types of phase patterns having different periods and the defocus amount Z, the difference is determined based on the difference (Z2−Z1). The magnitude of the spherical aberration of the inspection optical system and its correction state can be obtained.
[0058]
FIG. 8 is a diagram showing the relationship between the defocus amount Z and the index α for the same phase pattern when illuminated with two types of illumination σ values. FIG. 8A shows spherical aberration in the test optical system. (B) shows the case where there is no spherical aberration. Here, the illumination σ refers to the ratio of the illumination numerical aperture to the imaging numerical aperture.
The illumination light beam from the phase pattern is more susceptible to the influence of spherical aberration in the illumination with a relatively large illumination σ value than in the illumination with a relatively small illumination σ value. Therefore, when spherical aberration exists in the test optical system, the straight line L1 obtained when the illumination σ value is smaller at the position Z2 where the straight line L2 ′ obtained when the illumination σ value is large intersects the Z axis. 'Is further away from the paraxial image plane position of Z = 0 than the position Z1 at which it intersects the Z axis.
[0059]
On the other hand, when there is no spherical aberration in the test optical system, the straight line L1 ′ obtained when the illumination σ value is small is also the position Z2 where the straight line L2 ′ obtained when the illumination σ value is large intersects the Z axis. The position Z1 that intersects the Z axis also coincides with the paraxial image plane position at Z = 0.
As described above, even when illuminating the same phase pattern with two types of illumination σ values, the difference (Z2−Z1) between Z2 and Z1 is the optical to be detected as in the case of using two types of phase patterns having different periods. It can be seen that the positive and negative signs of the difference (Z2−Z1) are proportional to the overcorrection and undercorrection of the spherical aberration, in proportion to the magnitude of the spherical aberration remaining in the system. 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 above difference (Z2−Z1) is obtained. Based on this, the magnitude of the spherical aberration of the test optical system and its correction state can be obtained.
[0060]
As can be easily understood from the description of FIGS. 7 and 8, in any case, when the optical system under test has no spherical aberration, the defocus position where the index α = 0 is the Z position on the paraxial image plane. is there. When the test optical system has spherical aberration, the first defocus position Z1 at which the index α = 0 with respect to the phase pattern (first illumination σ) of the first period and the phase of the second period Based on the second defocus position Z2 at which the index α = 0 with respect to the pattern (second illumination σ), the paraxial image plane position and the astigmatic difference on the optical axis can be obtained.
[0061]
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 in the field of view), in addition to the paraxial image plane position of the optical system to be examined and the astigmatic difference on the optical axis, astigmatism, image It becomes possible to inspect surface curvature and image plane inclination.
[0062]
In addition, an optical filter or the like is inserted in the optical path of the illumination optical system to select the wavelength of illumination light that irradiates the phase pattern, or two or more spectral reflectances (spectral transmittances in the case of a transmission type) are different. Prepare the phase pattern and select the wavelength of the reflected light from the phase pattern (or transmitted light in the case of the transmissive type), or insert an optical filter in the optical path of the imaging optical system to form the imaged light flux from the phase pattern It is possible to inspect the test optical system with respect to a desired wavelength. As a result, in addition to inspecting the various monochromatic aberrations already described for each wavelength, it is possible to inspect axial chromatic aberration and off-axis chromatic aberration.
[0063]
In the above description, the left and right minimum values ViL and ViR of the signal for one period are used when quantifying the asymmetry index β of the phase pattern image. However, as disclosed in Japanese Patent Application No. 7-20325 (Japanese Patent Laid-Open No. 8-213306) filed by the applicant of the present application, the widths of the left and right sagging edges in the signal for one cycle are used. It is also possible to quantify the asymmetry index β of the phase pattern image.
[0064]
Furthermore, regarding the index α of the difference between the image intensities of the phase pattern images corresponding to the convex portions and concave portions of the phase pattern, processing different from that of the present embodiment can be performed. FIG. 9 shows that the phase pattern image corresponding to the convex portion of the phase pattern matches the convex portion and the concave portion in the image intensity distribution of the phase pattern image when the image intensity of the phase pattern image corresponding to the concave portion matches. It is a figure which shows a mode that an angle | corner arises in the image intensity waveform to do. In this case, without directly obtaining the index α, a defocus position where an angle is generated in the image intensity waveform corresponding to the convex part and the concave part in the image intensity distribution of the phase pattern image may be adopted as the position Z1 or the position Z2. it can.
[0065]
Further, in order to ensure the accuracy when the index β is obtained, the image asymmetry index β1 corresponding to the edge of the phase pattern detected in one or a plurality of defocus states, and the phase pattern at the detection center Corresponding to the edge of the phase pattern detected in one or more defocused states (ie, in the present embodiment with the phase pattern rotated 180 degrees around the Z axis) It is desirable to detect the image asymmetry 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 the asymmetry index β of the phase pattern image when the test optical system is inspected, the detection error due to the asymmetry of the phase pattern itself can be corrected.
[0066]
Further, the image asymmetry index β1 corresponding to the edge of the phase pattern detected in one or a plurality of defocus states and the image sensor (CCDs 116 and 117 in this embodiment) are rotated by 180 degrees around the detection center. In this state, the image asymmetry index β2 corresponding to the edge of the phase pattern detected in one or a plurality of defocus states is detected, and the average value βave2 is obtained by the following equation (4). Is desirable.
βave2 = (β1 + β2) / 2 (4)
By using this average value βave2 as the asymmetry index β of the phase pattern image when the test optical system is inspected, the detection error due to the asymmetry of the image sensor itself can be corrected.
[0067]
The sensitivity of the index β obtained by defocusing the phase pattern image and the index α to the defocus amount Z depends on the illumination σ value, pattern pitch, duty ratio, taper, step, and the like. Therefore, it is desirable to control the inspection sensitivity so that an optimal inspection can be performed in an actual use state by appropriately selecting these parameters.
[0068]
Further, it is desirable to select an appropriate range centered on 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 way, it is possible to accurately grasp the mode of change of the index β.
Further, as the defocusing means, in addition to means for vertically driving the Z stage on which the wafer on which the phase pattern is formed is mounted, means for moving the entire optical system or part of the test optical system along the optical axis, and imaging means Means for moving at least one of them along the optical axis of the test optical system can be used.
[0069]
As described above, the phase pattern image is defocused by measuring the edge asymmetry index β of the phase pattern image and the image intensity difference index α of the uneven portion of the phase pattern image, thereby detecting coma aberration and decentration of the optical system to be detected. In addition to coma aberration, luminous flux vignetting, and tilting of illumination light, it is possible to inspect light of any wavelength such as spherical aberration, focal position, astigmatism on the optical axis, astigmatism, field curvature, and field tilt. Explained. Next, corrections and adjustments performed based on these inspection information (detection results), that is, corrections and adjustment methods related to the aberration and focus position of the optical system under test, and position adjustments related to the illumination aperture stop and imaging aperture stop The method will be described.
[0070]
First, in order to adjust the illumination telecentric (tilt of illumination light), the position of the illumination aperture stop 127 is adjusted. Specifically, the illumination aperture stop 127 is appropriately driven through the drive system 128 in a direction perpendicular to the optical axis or in a translational 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 a translational direction. Further, a light beam parallel moving means such as a plane-parallel plate may be provided in the optical path between the light guide 104 and the condenser lens 129 or in the optical path between the illumination relay lens 105 and the half prism 106. When a parallel plane plate is used as the light beam translation means, the illumination telecentricity can be adjusted by inclining the parallel plane plate.
[0071]
On the other hand, in order to adjust the vignetting of the imaging light beam, the position of the imaging aperture stop 130 is adjusted. Specifically, the imaging aperture stop 130 is appropriately driven in the direction perpendicular to the optical axis or in the translational direction via the drive system 131. Further, the plane-parallel plate is disposed in the optical path between the half prism 106 and the second objective lens 111 or in the optical path between the relay lens 113 and the relay lens 114 and on the wafer side of the imaging aperture stop 130. Such a light beam parallel movement means may be provided. When a parallel plane plate is used as the light beam parallel moving means, the vignetting of the imaging light beam can be adjusted by inclining the parallel plane plate.
[0072]
Furthermore, in order to correct the spherical aberration of the imaging optical system, for example, the second objective lens 111 and the relay lens 113 are 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. The spherical aberration can also be controlled by driving the Z stage to change the distance between the wafer W surface and the first objective lens 107. However, in this case, it is necessary to absorb the defocused portion of the image on the imaging surface of the CCD by appropriately translating the CCD in the optical axis direction.
[0073]
Further, the decentration coma aberration of the imaging optical system can be corrected by driving the entire lens system of the second objective lens 111 and the relay lens 113 or a part of the lenses to be decentered perpendicularly to the optical axis.
Note that in order to adjust the focus position (focal position), the Z stage may be appropriately driven in the optical axis direction. Further, 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.
[0074]
In addition, aberrations such as image height coma, field curvature, and field tilt rarely become a common problem in optical design considerations and manufacturing management. However, these aberrations can be corrected as necessary by changing the lens types of some lens systems of the imaging optical system and replacing them, or by decentering some lens systems. The correction of chromatic aberration is the same as these aberrations.
[0075]
FIG. 10 is a perspective view schematically showing a configuration of a projection exposure apparatus including an inspection apparatus according to the second embodiment of the present invention. In the first embodiment, the imaging optical system and illumination optical system of the off-axis type alignment apparatus attached to the projection exposure apparatus are inspected. In the second embodiment, the projection optical system of the projection exposure apparatus and Inspecting illumination optics. In the first embodiment, a CCD is used as the image detection means. In the second embodiment, a reference member having a slit and a photoelectric detector are used as the image detection 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, and the X axis and the Y axis are set to be orthogonal to each other in a plane perpendicular to the optical axis AX. .
[0076]
The projection exposure apparatus in FIG. 10 includes a light source LP made of, for example, an ultrahigh pressure mercury lamp. The light source LP is positioned at the first focal position of a condensing mirror (elliptical mirror) EM having a reflecting surface composed of a spheroidal surface. Therefore, the illumination light beam emitted from the light source LP forms a light source image (secondary light source) at the second focal position of the elliptical mirror EM.
[0077]
The light from the secondary light source passes through the collimating lens GL and the mirror M1, and then enters the fly-eye lens FL as a parallel light beam.
The light beam incident on the fly-eye lens FL is two-dimensionally divided by a plurality of lens elements constituting the fly-eye lens FL, and a plurality of light source images (that is, near the exit surface) at the rear focal position of the fly-eye lens FL (that is, near the exit surface). A tertiary light source).
[0078]
The light beams from the plurality of light source images are limited by the variable aperture stop 12 disposed 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 uniformly and uniformly illuminates the mask 14 on which the transfer pattern is formed.
Thus, 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.
[0079]
At the time of exposure, the light beam transmitted through the mask 14 reaches a wafer (not shown) which is a photosensitive substrate via the projection optical system 17. Thus, a pattern image of the mask 14 is formed on the wafer. The wafer moves along the optical axis AX direction of the XY stage 18 and the projection optical system 17 that can move two-dimensionally in an XY plane perpendicular to the optical axis AX (parallel to the Z direction) of the projection optical system 17. Supported on a possible Z stage 13. Therefore, by performing exposure while moving the wafer two-dimensionally, the pattern of the mask 14 can be sequentially transferred to each exposure region of the wafer.
[0080]
The projection exposure apparatus shown in FIG. 10 is provided with a grazing incidence light type autofocus system (22A, 22B). In the oblique incidence light type autofocus system, the light transmission system 22A irradiates light obliquely toward the surface of the wafer. The light regularly reflected on the wafer surface is received by the light receiving system 22B, and the position of the wafer in the Z direction is detected based on the change in position of the reflected light.
In this way, the wafer surface can be made to substantially coincide with the image plane of the projection optical system 17 (a plane conjugate with the mask 14) by the action of the autofocus system (22A, 22B).
[0081]
On the other hand, on inspection, a reference member PT and a light receiver 23 are installed on the XY stage 18 instead of the wafer. Then, the surface of the reference member PT is positioned at a predetermined defocus position with respect to the projection optical system 17 by the action of the autofocus system (22A, 22B) and the Z stage 13.
In this case, first, the autofocus system (22A, 22B) is used to make the surface of the reference member PT substantially coincide with the image plane of the projection optical system 17, and this position is 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) with reference to the paraxial image plane position (Z = 0). . Note that the pattern 16 and the projection optical system 17 can be moved in the Z direction to form a defocused state.
[0082]
In each defocus state, the light beam transmitted through the inspection phase pattern 16 formed on the mask 14 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 in each defocused state on the surface of the reference member PT. The light from the phase pattern image 16A enters the light receiver 23 through the slit 19 formed on the surface of the reference member PT.
The slit 19 is formed by, for example, a single slit pattern. Therefore, an electrical signal corresponding to the light intensity distribution of the phase pattern image 16A can be obtained in the light receiver 23 by a slit scanning method in which the phase pattern image 16A and the slit 19 are relatively moved in a predetermined direction.
[0083]
As described above, in the first embodiment, the CCD is used as the image detecting means, whereas in the second embodiment, the reference member PT having the slit 19 and the light receiver 23 are used as the image detecting means. However, the detection of the aberration based on the light intensity distribution of the obtained phase pattern image and the correction and adjustment of the aberration based on the detection information are the same as in the first embodiment. That is, in the second embodiment, as in the first embodiment, the phase pattern image edge asymmetry index β and the phase pattern unevenness image intensity difference index α are set while defocusing the phase pattern image. By measuring, in addition to coma aberration, decentering coma aberration, luminous flux vignetting, and tilt of illumination light of the optical system under test (projection optical system 17 and illumination optical system 11), spherical aberration, focal position, astigmatism on the optical axis Thus, it is possible to inspect light having an arbitrary wavelength such as astigmatism, field curvature, and field tilt. Further, based on the inspection information (detection result), it is possible to correct or adjust the aberration, the focus position, and the optical axis deviation of the optical system to be detected.
[0084]
For example, in the projection exposure apparatus of FIG. 10, in order to correct the spherical aberration and the coma aberration of the projection optical system 17, a lens sensitive to the spherical aberration and the coma aberration among the lens components constituting the projection optical system 17 is used. The optical axis AX is shifted (moved) or tilted (tilted). 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 the illumination telecentricity, the vignetting, etc., 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.
[0085]
Further, as a third embodiment of the present invention, the inspection apparatus of the present invention can be applied to the overlay measurement apparatus. The overlay measurement apparatus is an apparatus that is installed inside or outside the projection exposure apparatus, for example, and measures the relative positional deviation between the first pattern and the second pattern formed on the photosensitive substrate. The alignment optical system of the alignment apparatus described above and the overlay measurement optical system of the overlay measurement apparatus have optically similar configurations. Therefore, as in the case of the alignment apparatus, the aberration of the overlay measurement optical system can be inspected accurately and easily, and the aberration of the overlay measurement optical system can be favorably corrected based on the inspection information. .
[0086]
In the inspection apparatus and inspection method of the present invention, the detection of the asymmetry of the phase pattern image may be performed by an imaging method as in the first embodiment, or by a scanning method using a slit as in the second embodiment. You may go.
In addition, the present invention does not depend on a difference in illumination methods such as transmission illumination or epi-illumination (reflection illumination).
In addition, the inspection apparatus of the present invention can be applied not only to a projection exposure apparatus, an overlay measurement apparatus, and an alignment apparatus, but also to other general apparatuses having an optical system to be inspected.
[0087]
【The invention's effect】
As described above, according to the inspection apparatus and the inspection method of the present invention, in each defocus state, the image asymmetry (index β) corresponding to the edge of the phase pattern and the difference in the image intensity of the uneven portion of the phase pattern ( By measuring the index α), in addition to coma aberration, decentration coma aberration, luminous flux vignetting, tilt of illumination light (illumination telecentric), spherical aberration, focal position, astigmatism on optical axis, astigmatism, The curvature of field and the tilt of the field can be inspected easily and quickly with high reproducibility for light of an arbitrary wavelength. Then, based on the detected inspection information of the optical system, correction and adjustment related to the aberration and focus position of the optical system, position adjustment related to the illumination aperture stop and the imaging aperture stop, and the like are performed efficiently and appropriately. The system can be as close as possible to the ideal optical system.
[0088]
Therefore, by incorporating the inspection apparatus of the present invention into a projection exposure apparatus, alignment apparatus, overlay measurement apparatus, etc., an illumination optical system of the projection exposure apparatus, an alignment optical system of the projection optical system, and an alignment apparatus, and an overlay measurement apparatus In addition, the overlay measurement optical system can be inspected easily and quickly with good reproducibility, and sufficient apparatus performance can be achieved by correcting or adjusting the aberration, focal position, optical axis misalignment, etc. of the optical system based on the detection results of the inspection apparatus. It can be demonstrated. Specifically, the position detection error caused by the alignment optical system is reduced in the alignment apparatus, and the measurement error caused by the overlay measurement optical system is reduced in the overlay measurement apparatus. Further, in the projection exposure apparatus, the aberration of the projection optical system is corrected well and the focal position, the optical axis shift, etc. are adjusted well, so that the pattern transfer performance is improved and highly accurate overlay projection exposure is performed. It becomes possible.
[Brief description of the drawings]
FIG. 1 is a drawing 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, and an asymmetry index β of the phase pattern image is It is a figure for demonstrating.
FIG. 3 is a diagram illustrating a relationship between a change in an asymmetry index β of a phase pattern image in each defocus state, coma aberration, optical axis deviation, and the like.
FIG. 4 is a diagram illustrating a relationship between a change in an asymmetry index β of a phase pattern image in each defocus state, coma aberration, optical axis deviation, and the like.
FIG. 5 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, and the phase pattern image corresponding to a recess of the phase pattern It is a figure for demonstrating the parameter | index (alpha) which quantified the difference between the image intensity of this and the image intensity of the phase pattern image corresponding to a convex part.
FIG. 6 is a diagram showing a relationship between a change in index α of a difference between image intensities of phase pattern images corresponding to a concave portion and a convex portion of a phase pattern and spherical aberration in each defocus state.
7A and 7B are diagrams illustrating a relationship between a defocus amount Z and an index α with respect to two types of phase patterns having different periods, where FIG. 7A illustrates a case where spherical aberration exists in a test optical system; Respectively show the cases where there is no spherical aberration.
FIG. 8 is a diagram showing a relationship between a defocus amount Z and an index α with respect to the same phase pattern when illuminated with two types of illumination σ values. FIG. 8A shows a spherical aberration in a test optical system. (B) shows the case where there is no spherical aberration.
FIG. 9 corresponds to a convex portion and a concave portion in an image intensity distribution of the phase pattern image when 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. It is a figure which shows a mode that an angle | corner arises in the image intensity waveform to do.
FIG. 10 is a perspective view schematically showing a configuration of a projection exposure apparatus including an inspection apparatus 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 optics
12 Variable aperture stop
CL Codenser lens
13 Z stage
14 Mask
16 Inspection pattern
17 Projection optical system
18 XY stage
19 Slit
22 Oblique incident light autofocus system
23 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

Claims (10)

Inspection apparatus for inspecting 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 In
Image detecting means for detecting an image of the phase pattern formed through the optical system;
Defocusing means for defocusing the image of the phase pattern detected by the image detection means;
An index of asymmetry of the image corresponding to the edge of the phase pattern detected in each defocus state in the image detection means, and is a constant that does not depend on the defocus amount of the index β defined by Expression (1) An inspection apparatus comprising: inspection means for inspecting an inclination of a principal ray of the illumination light with respect to a normal line of the phase pattern forming surface based on an offset value B.
β = Σ {V iL −V iR / (V max −V min )} / n (1)
Here, V iL and V iR is the signal minimum value of the left and right in the i-th period in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image non-measurement direction, V max and V min is the maximum and minimum values of the signal V, n is the number of periods of the distribution of the integrated signal ΣV, and Σ is a summation symbol from i = 1 to n. Inspection apparatus for inspecting 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 In
Image detecting means for detecting an image of the phase pattern formed through the optical system;
Defocusing means for defocusing the image of the phase pattern detected by the image detection means,
The phase pattern has a first phase pattern that repeats a periodic phase change along a detection direction of the image detection unit, and a phase amplitude distribution different from the first phase pattern, and is detected by the image detection unit. A second phase pattern that repeats a periodic phase change along the direction,
The light intensity of the first phase pattern image corresponding to the phase advanced region of the first phase pattern and the image of the first phase pattern corresponding to the phase delayed region of the first phase pattern The first defocus position at which the difference index α between the first phase pattern and the second phase pattern is 0, and the second phase pattern image light intensity corresponding to the advanced phase region of the second phase pattern; Based on the difference from the second defocus position where the difference index α between the second phase pattern image and the light intensity of the second phase pattern image corresponding to the phase-lag region of the second phase pattern becomes zero. An inspection apparatus further comprising inspection means for inspecting the spherical aberration of the optical system.
α = Σ {V it −V io / (V it + V io )} / (2n) (2)
Here, V io and V it are integrated signals corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. , N is the number of periods of distribution of the integral signal ΣV, and Σ is a summation symbol from i = 1 to n. Inspection apparatus for inspecting 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 In
Image detecting means for detecting an image of the phase pattern formed through the optical system;
Defocusing means for defocusing the image of the phase pattern detected by the image detection means,
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,
The phase pattern is a phase pattern that repeats a periodic phase change along the detection direction of the image detection means,
In the region where the phase intensity of the phase pattern image corresponding to the phase advanced region of the phase pattern illuminated under the first illumination condition set by the illumination aperture changing means and the phase of the phase of the phase pattern are delayed A first defocus position where a difference index α between the light intensity of the image of the corresponding phase pattern is 0 and the second illumination condition set by the illumination aperture changing means is illuminated. The index α of the difference between the light intensity of the phase pattern image corresponding to the phase advanced region of the phase pattern and the light intensity of the phase pattern image corresponding to the phase delayed region of the phase pattern is 0. based on the difference between the second defocus position where the inspection apparatus characterized by further comprising an inspection means for inspecting the spherical aberration of the optical system.
α = Σ {V it −V io / (V it + V io )} / (2n) (2)
Here, V io and V it are integrated signals corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. , N is the number of periods of distribution of the integral signal ΣV, and Σ is a summation symbol from i = 1 to n. Inspection apparatus for inspecting 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 In
Image detecting means for detecting an image of the phase pattern formed through the optical system;
Defocusing means for defocusing the image of the phase pattern detected by the image detection means,
The phase pattern is a phase pattern that repeats a periodic phase change along the detection direction of the image detection means,
At each defocus state, the light intensity of the image of the phase pattern corresponding to the delay area of the phase of said light intensity of the image of the phase pattern phase pattern corresponding to a region advanced in phase of the phase pattern Astigmatism difference on the optical axis of the optical system based on defocus positions at which α corresponding to each visual field position becomes 0 at values at a plurality of positions in the visual field of the optical system. An inspection apparatus further comprising inspection means for inspecting at least one of astigmatism, field curvature, and field tilt.
α = Σ {V it −V io / (V it + V io )} / (2n) (2)
Here, V io and V it are integrated signals corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. , N is the number of periods of distribution of the integral signal ΣV, and Σ is a summation symbol from i = 1 to n. Illumination light is irradiated to a positioning mark made of a phase pattern provided on a mask on which a transfer pattern is formed or a positioning mark made of a phase pattern provided on a photosensitive substrate to which an image of the transfer pattern is transferred. An alignment optical system comprising: an illumination optical system for focusing; 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 device for positioning a conductive substrate,
The inspection apparatus according to any one of claims 1 to 4 for inspecting the alignment optical system,
Aberration correction means for correcting the aberration of the imaging optical system based on inspection information of the alignment optical system by the inspection device, and for adjusting the in-focus position of the imaging optical system based on the inspection information Focusing position adjusting means, imaging for relatively displacing the position of the imaging aperture stop of the imaging optical system with respect to the optical axis in order to correct the vignetting of the imaging optical system based on the inspection information Aperture stop position adjusting means, and the position of the illumination aperture stop of the illumination optical system is displaced relative to the optical axis in order to correct the inclination of the principal ray of the illumination light with respect to the normal of the object plane of the imaging optical system An alignment apparatus further comprising at least one of illumination aperture stop position adjusting means. In a projection exposure apparatus comprising an illumination optical system for irradiating illumination light onto 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, for inspecting the illumination optical system and the projection optical system,
Aberration correction means for correcting aberration of the projection optical system based on inspection information of the illumination optical system and the projection optical system by the inspection device, and adjusting a focus position of the projection optical system based on the inspection information A focusing position adjusting means for adjusting the position of the imaging aperture stop of the projection optical system relative to the optical axis in order to correct the vignetting of the projection optical system based on the inspection information. Image aperture stop position adjusting means, and relative displacement of 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 of the object plane of the projection optical system A projection exposure apparatus, further comprising at least one of illumination aperture stop position adjusting means. In a method for inspecting an optical system including an imaging optical system that forms an image of a predetermined phase pattern,
Illuminating the phase pattern with illumination light,
Detecting the image of the phase pattern at a plurality of different defocus positions in the optical axis direction of the imaging optical system;
A constant offset value B that is an index of asymmetry of the image corresponding to the edge of the phase pattern detected at the plurality of defocus positions and does not depend on the defocus amount of the index β defined by the equation (1). The inspection method of the optical system characterized by inspecting the inclination of the principal ray of the illumination light with respect to the normal line of the surface on which the phase pattern is formed.
β = Σ {V iL −V iR / (V max −V min )} / n (1)
Here, V iL and V iR is the signal minimum value of the left and right in the i-th period in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image non-measurement direction, V max and V min is the maximum and minimum values of the signal V, n is the number of periods of the distribution of the integrated signal ΣV, and Σ is a summation symbol from i = 1 to n. In a method for inspecting an optical system including an illumination optical system for irradiating illumination light to a phase pattern 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, a phase amplitude distribution different from the first phase pattern, and a periodic phase along the predetermined direction. A second phase pattern that repeats the change,
Illuminating the phase pattern with illumination light through 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 first phase pattern image corresponding to the phase advanced region of the first phase pattern and the image of the first phase pattern corresponding to the phase delayed region of the first phase pattern The first defocus position at which the difference index α between the first phase pattern and the second phase pattern is 0, and the second phase pattern image light intensity corresponding to the advanced phase region of the second phase pattern; Based on the difference from the second defocus position where the difference index α between the second phase pattern image and the light intensity of the second phase pattern image corresponding to the phase-lag region of the second phase pattern becomes zero. An inspection method for an optical system, comprising: inspecting a spherical aberration of the optical system.
α = Σ {V it −V io / (V it + V io )} / (2n) (2)
Here, V io and V it are integrated signals corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. , N is the number of periods of distribution of the integral signal ΣV, and Σ is a summation symbol from i = 1 to n. 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 amplitude distribution of the illumination light at the illumination aperture stop is set to the first amplitude distribution,
When detecting the second defocus position, 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. Item 9. An inspection method for an optical system according to Item 8 . In a method for inspecting an optical system including an imaging optical system that forms an image of a predetermined phase pattern,
Illuminating the phase pattern with illumination light,
Detecting an image of the phase pattern at a plurality of different defocus positions in an optical axis direction of the imaging optical system using an image detector having a predetermined detection direction;
The phase pattern is a phase pattern that repeats a periodic phase change along the detection direction of the image detector,
The light intensity of the phase pattern image corresponding to the phase advanced region of the phase pattern and the light intensity of the phase pattern image corresponding to the phase delayed phase of the phase pattern at the plurality of defocus positions. Of the difference index α between the optical system and the optical system based on the defocus position at which α corresponding to each visual field position becomes 0 in the values at a plurality of positions in the visual field of the optical system. An inspection method for an optical system, wherein at least one of point difference, astigmatism, field curvature, and field tilt is inspected.
α = Σ {V it −V io / (V it + V io )} / (2n) (2)
Here, V io and V it are integrated signals corresponding to the concave and convex portions of the i-th phase pattern in the distribution of the integrated signal ΣV obtained by integrating the signal V corresponding to the light intensity of the phase pattern image in the non-measurement direction. , N is the number of periods of distribution of the integral signal ΣV, and Σ is a summation symbol from i = 1 to n.

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