JP2008172004A - Aberration evaluating method, adjusting method, exposure device, exposure method and device manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aberration evaluating method for compensating influence of comparatively large warpage and distortion of a thin film in a slit substrate and highly precisely evaluating wavefront aberration of an optical system to be inspected by a space image measuring method. <P>SOLUTION: The aberration evaluating method for evaluating wavefront aberration of the optical system to be inspected is provided with an approximation process (S12) for approximating a wavefront deviation amount by a function of a coordinate in a radius vector direction on a plurality of radius vector directions passing through a center of an ejection pupil face of the optical system to be inspected, a correction process (S13) for offset-correcting a plurality of functions obtained through the approximation process so that the wavefront deviation amount becomes almost zero at the center of the ejection pupil face, and an expression process (S14) for expressing wavefront aberration of the optical system to be inspected on the ejection pupil face based on wavefront deviation amount data obtained through the correction process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aberration evaluation method, an adjustment method, an exposure apparatus, an exposure method, and a device manufacturing method, and more particularly to evaluation of wavefront aberration of a projection optical system mounted on an EUVL exposure apparatus.

  Batch exposure type that transfers the pattern of a reticle (or photomask, etc.) onto a wafer (or glass plate, etc.) coated with a photosensitive material via a projection optical system in a lithography process for manufacturing devices such as semiconductor elements Projection exposure apparatuses (steppers and the like) and scanning exposure type projection exposure apparatuses (scanning steppers and the like) are used. As the integration degree and fineness of semiconductor elements and the like are further improved, the accuracy of imaging characteristics required for the projection optical system of the exposure apparatus is also increasing. In order to obtain high-precision imaging characteristics, it is necessary to control (adjust) the imaging characteristics of the projection optical system, and as a precondition, the imaging of the projection optical system in the state mounted on the exposure device (on-body state) It is necessary to measure the characteristics with high accuracy.

  As a conventional method for measuring the imaging characteristics of the projection optical system in an on-body state, a spatial image of the measurement mark of the test mask illuminated with exposure light is formed by the projection optical system, and the spatial image of the measurement mark (projection image) A method of measuring the light intensity distribution of the projection optical system and evaluating the wavefront aberration of the projection optical system based on the measurement result (hereinafter referred to as “aerial image measurement method”) has been proposed (see, for example, Patent Document 1). Another conventional aerial image measurement method is to illuminate a plurality of diffraction gratings and measure the light intensity distribution of the aerial image of each diffraction grating obtained via the projection optical system at a plurality of defocus positions. A method for evaluating the wavefront aberration of the projection optical system based on the measurement result has also been proposed (see, for example, Patent Document 2).

  In recent years, a technique of EUVL (Extreme UltraViolet Lithography) has been attracting attention as a next-generation exposure method (exposure apparatus) for semiconductor patterning corresponding to higher precision. In the EUVL exposure apparatus, EUV (Extreme UltraViolet) light having a wavelength of about 5 to 20 nm as compared with a conventional exposure method using a KrF excimer laser light having a wavelength of 248 nm or an ArF excimer laser light having a wavelength of 193 nm. Is used.

JP-A-10-170399 JP 2001-57337 A

  When applying the above-described aerial image measurement method according to the prior art to the projection optical system of an EUVL exposure apparatus, it is necessary to use a substrate in which a fine slit pattern is formed on a thin film as a slit substrate placed on a wafer stage There is. On the other hand, for example, in an exposure apparatus using excimer laser light, a substrate in which a fine slit pattern is formed on a glass plate can be used as the slit substrate placed on the wafer stage. That is, the excimer laser exposure apparatus can use a flat and low-strain slit substrate (glass substrate), but the EUVL exposure apparatus uses a slit substrate (thin film) having relatively large deflection and distortion.

  The aerial image measurement method measures the amount of positional deviation with respect to the design value of the horizontal position of the aerial image and the amount of positional deviation with respect to the design value of the focus position. This is a technique for evaluating (calculating) the wavefront aberration of an optical system. When the conventional aerial image measurement method is applied to the projection optical system mounted on the EUVL exposure apparatus, the wavefront aberration of the projection optical system can be evaluated with high accuracy due to the relatively large deflection and distortion of the thin film of the slit substrate. It is difficult to evaluate the imaging performance of the projection optical system with high accuracy.

  The present invention has been made in view of the above-described problems, and compensates for the effects of relatively large deflections and distortions of the thin film of the slit substrate, so that the wavefront aberration of the optical system to be detected can be accurately determined by the aerial image measurement method. It is an object to provide an aberration evaluation method that can be evaluated.

  In addition, the present invention provides an adjustment method that can satisfactorily optically adjust the test optical system based on the aberration evaluation obtained by the aberration evaluation method that evaluates the wavefront aberration of the test optical system with high accuracy. For the purpose.

  The present invention also provides an exposure apparatus, an exposure method, and a device manufacturing method capable of performing good projection exposure using a projection optical system that is optically adjusted by an adjustment method that optically adjusts a test optical system. The purpose is to provide.

In order to solve the above problems, in the first embodiment of the present invention, in the aberration evaluation method for evaluating the wavefront aberration of the optical system to be tested,
For a plurality of radial directions passing through the center of the exit pupil plane of the test optical system, an approximation step for approximating the wavefront deviation amount as a function of the radial direction coordinates,
A correction step of offset correcting each of the plurality of functions obtained through the approximating step so that a wavefront deviation amount becomes substantially zero at the center of the exit pupil plane;
An aberration evaluation method comprising: expressing a wavefront aberration of the optical system under test on the exit pupil plane based on the offset-corrected wavefront deviation amount data obtained through the correction step I will provide a.

  According to a second aspect of the present invention, there is provided an adjustment method characterized in that the test optical system is optically adjusted based on an evaluation result obtained by the aberration evaluation method of the first aspect.

  According to a third aspect of the present invention, a test optical system optically adjusted by the adjustment method of the second aspect is provided as a projection optical system for projecting and exposing a predetermined pattern onto a photosensitive substrate. An exposure apparatus is provided.

  According to a fourth aspect of the present invention, there is provided an exposure method characterized in that an image of a predetermined pattern is projected and exposed onto a photosensitive substrate using the test optical system optically adjusted by the adjustment method of the second aspect. To do.

In the fifth embodiment of the present invention, using the exposure apparatus of the third embodiment, an exposure step of exposing the predetermined pattern to the photosensitive substrate;
And a developing process for developing the photosensitive substrate that has undergone the exposure process.

  The aberration evaluation method of the present invention compensates for the effects of relatively large deflection and distortion of the thin film of the slit substrate by the effect of offset correction that makes the wavefront deviation at the center of the exit pupil plane of the optical system to be tested substantially zero. Thus, the wavefront aberration of the test optical system can be evaluated with high accuracy by the aerial image measurement method. Therefore, in the present invention, it is possible to satisfactorily optically adjust the test optical system based on the aberration evaluation obtained by the aberration evaluation method for accurately evaluating the wavefront aberration of the test optical system. As a result, in the present invention, it is possible to perform good projection exposure using a test optical system that is optically adjusted well, and thus to manufacture a good device.

  Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 is a view schematically showing the overall configuration of an exposure apparatus to which an aberration evaluation method according to an embodiment of the present invention is applied. FIG. 2 is a diagram schematically showing the internal configuration of the light source, illumination optical system, and projection optical system of FIG. In FIG. 1, the Z axis along the optical axis direction of the projection optical system, that is, the normal direction of the wafer as the photosensitive substrate, the Y axis in the direction parallel to the paper surface of FIG. The X axis is set in the direction perpendicular to the paper surface of FIG.

  Referring to FIG. 1, the exposure apparatus of this embodiment includes, for example, a laser plasma light source 1 as a light source for supplying exposure light. The light emitted from the light source 1 enters the illumination optical system 2 via a wavelength selection filter (not shown). Here, the wavelength selection filter has a characteristic of selectively transmitting only EUV light having a predetermined wavelength (for example, 13.4 nm or 11.5 nm) from light supplied from the light source 1 and blocking transmission of other wavelength light. . The EUV light 3 that has passed through the wavelength selection filter illuminates a reflective mask (reticle) M on which a pattern to be transferred is formed, via an illumination optical system 2 and a plane reflecting mirror 4 as an optical path deflecting mirror.

  The mask M is held by a mask stage 5 that can move along the Y direction so that its pattern surface extends along the XY plane. The movement of the mask stage 5 is configured to be measured by a laser interferometer 6. The light from the illuminated pattern of the mask M forms an image of the mask pattern on the wafer W, which is a photosensitive substrate, via the reflective projection optical system PL. That is, on the wafer W, as will be described later, for example, an arcuate still exposure region (effective exposure region) that is symmetrical with respect to the Y axis is formed.

  The wafer W is held by a wafer stage 7 that can move two-dimensionally along the X and Y directions so that the exposure surface extends along the XY plane. The movement of the wafer stage 7 is configured to be measured by the laser interferometer 8 as in the mask stage 5. Thus, scanning exposure (scan exposure) is performed while the mask stage 5 and the wafer stage 7 are moved along the Y direction, that is, while the mask M and the wafer W are moved relative to the projection optical system PL along the Y direction. As a result, the pattern of the mask M is transferred to one rectangular shot area of the wafer W.

  At this time, when the projection magnification (transfer magnification) of the projection optical system PL is, for example, 1/4, the moving speed of the wafer stage 7 is set to 1/4 of the moving speed of the mask stage 5 to perform synchronous scanning. Further, by repeating scanning exposure while moving the wafer stage 7 two-dimensionally along the X direction and the Y direction, the pattern of the mask M is sequentially transferred to each shot area of the wafer W.

  Referring to FIG. 2, the laser plasma light source 1 shown in FIG. 1 includes a laser light source 11, a condenser lens 12, a nozzle 14, an elliptical reflecting mirror 15, and a duct 16. Light (non-EUV light) emitted from the laser light source 11 is condensed on the gas target 13 via the condenser lens 12. Here, a high-pressure gas made of, for example, xenon (Xe) is supplied from the nozzle 14, and the gas injected from the nozzle 14 forms the gas target 13. The gas target 13 obtains energy from the focused laser beam, turns it into plasma, and emits EUV light. The gas target 13 is positioned at the first focal point of the elliptical reflecting mirror 15.

  Therefore, the EUV light emitted from the laser plasma light source 1 is collected at the second focal point of the elliptical reflecting mirror 15. On the other hand, the gas that has finished emitting light is sucked through the duct 16 and guided to the outside. The EUV light collected at the second focal point of the elliptical reflecting mirror 15 becomes a substantially parallel light beam via the concave reflecting mirror 17 and is guided to an optical integrator 18 including a pair of fly-eye mirrors 18a and 18b. The fly-eye mirrors 18a and 18b are configured by, for example, arranging a large number of concave mirror elements having an arcuate outer shape vertically and horizontally and densely. For the detailed configuration and operation of the fly-eye mirrors 18a and 18b, reference can be made to, for example, Japanese Patent Application Laid-Open No. 11-312638.

  Thus, a substantial surface light source having a predetermined shape is formed in the vicinity of the exit surface of the optical integrator 18, that is, in the vicinity of the reflection surface of the second fly-eye mirror 18b. Here, the substantial surface light source is the exit pupil position of the illumination optical system 2 (reference numeral 2 is not shown in FIG. 2: 17, 18a, 18b, 19a, 19b) or its vicinity, that is, the incidence of the projection optical system PL. It is formed on or near a surface optically conjugate with the pupil. Light from a substantial surface light source is emitted from the illumination optical system 2 via a condenser optical system 19 (reference numeral 19 is not shown: 19a, 19b) configured by a convex reflecting mirror 19a and a concave reflecting mirror 19b. The

  The light emitted from the illumination optical system 2 is deflected by the plane reflecting mirror 4, and then passes through the arc-shaped opening (light transmission portion) of the field stop 21 disposed substantially parallel to and close to the mask M. Thus, an arcuate illumination area is formed on the mask M. Thus, the light source 1 (11 to 16), the illumination optical system 2 (17 to 19), the planar reflecting mirror 4, and the field stop 21 are illumination systems for Koehler illumination of the mask M provided with a predetermined pattern. It is composed.

  The light from the illuminated pattern of the mask M forms an image of the mask pattern in an arcuate static exposure region on the wafer W via the projection optical system PL. The projection optical system PL forms on the wafer W a first reflective imaging optical system for forming an intermediate image of the mask M pattern and an image of the mask pattern intermediate image (secondary image of the mask M pattern). And a second reflection imaging optical system. The first reflective imaging optical system is constituted by four reflecting mirrors M1 to M4, and the second reflective imaging optical system is constituted by two reflecting mirrors M5 and M6. The projection optical system PL is an optical system telecentric on the wafer side (image side).

  FIG. 3 is a diagram schematically illustrating one scanning exposure in the exposure apparatus of the present embodiment. Referring to FIG. 3, in the exposure apparatus of the present embodiment, an arcuate still exposure region (effective exposure region) that is symmetric with respect to the Y axis so as to correspond to the arcuate effective imaging region and effective field of the projection optical system PL. ) ER is formed. This arc-shaped static exposure region ER is a scanning start position indicated by a solid line in the figure when the pattern of the mask M is transferred to one rectangular shot region SR of the wafer W by one scanning exposure (scan exposure). To a scanning end position indicated by a broken line in the figure.

  In the exposure apparatus of this embodiment, in order to perform good projection exposure while maintaining the imaging characteristics of the projection optical system PL with high accuracy, for example, the wavefront aberration of the projection optical system PL is reduced in an on-body state by an aerial image measurement method. It is necessary to measure and evaluate from time to time. The aberration evaluation method according to the present embodiment will be described below with reference to the flowchart of FIG. In the aberration evaluation method of the present embodiment, the amount of wavefront deviation is measured at a plurality of positions on the exit pupil plane (hereinafter, also simply referred to as “pupil plane”) of the projection optical system PL that is the test optical system (S11).

  In the measurement step S11, as shown in FIG. 5, the test mask TM is set on the mask stage 5, and the slit substrate 31 set on the wafer stage 7 is positioned with respect to the projection optical system PL. A photodetector 32 is provided directly below the slit substrate 31, and the output of the photodetector 32 is connected to the input of the processing system 33. As shown in FIG. 6, the test mask TM is formed with test marks made of, for example, line and space patterns (hereinafter also referred to as “L & S patterns” for short) arranged in four directions. Yes. In the L & S pattern, the line portion is a region that reflects light, and the space portion is a region that does not reflect light.

  Specifically, the test mask TM includes a Y direction L & S pattern 61 whose pitch direction matches the Y direction, an X direction L & S pattern 62 whose pitch direction matches the X direction, and a pitch direction of + Y direction and −X direction. A first oblique direction L & S pattern 63 that coincides with the first oblique direction forming 45 degrees and a second oblique direction L & S pattern 64 that coincides with the second oblique direction whose pitch direction forms 45 degrees with the + Y direction and the + X direction are formed. Has been.

  The Y direction L & S pattern 61 includes, for example, six types of L & S patterns having different pitches. That is, in the Y direction L & S pattern, the left L & S pattern 61a in the drawing has the smallest pitch, the rightmost L & S pattern 61f in the drawing has the largest pitch, and the L & S pattern from the left side in the drawing to the right side in the drawing. The pitches 61b to 61e increase monotonously. The X direction L & S pattern 62, the first oblique direction L & S pattern 63, and the second oblique direction L & S pattern 64 also have basically the same pattern configuration as the Y direction L & S pattern 61, although the arrangement direction is different.

  In the slit substrate 31, as shown in FIG. 7, a slit pattern corresponding to the test mark of FIG. 6 is formed on the thin film. Specifically, on the thin film of the slit substrate 31, an X-direction slit pattern 71 elongated along the X direction, a Y-direction slit pattern 72 elongated along the Y direction, and 45 degrees with the + Y direction and the + X direction. A second oblique direction slit pattern 73 that is elongated along the second oblique direction is formed, and a first oblique direction slit pattern 74 that is elongated along the first oblique direction that forms 45 degrees with the + Y direction and the −X direction. ing.

  In the measurement step S11, the Y direction L & S pattern 61 of the test mask TM is illuminated, and the aerial image of the Y direction L & S pattern 61 formed via the projection optical system PL is moved in the Y direction by the X direction slit pattern 71 of the slit substrate 31. Light that has passed through the X-direction slit pattern 71 is detected by the photodetector 32 while scanning. This scanning detection is performed a plurality of times while changing the position of the slit substrate 31 in the Z direction. Similarly, the X direction L & S pattern 62 of the test mask TM is illuminated, and the aerial image of the X direction L & S pattern 62 formed via the projection optical system PL is scanned in the X direction by the Y direction slit pattern 72 of the slit substrate 31. Meanwhile, the light that has passed through the Y-direction slit pattern 72 is detected by the photodetector 32. This scanning detection is performed a plurality of times while changing the position of the slit substrate 31 in the Z direction.

  Further, the first oblique direction L & S pattern 63 of the test mask TM is illuminated, and an aerial image of the first oblique direction L & S pattern 63 formed via the projection optical system PL is represented by the second oblique direction slit pattern 73 of the slit substrate 31. Light that has passed through the second oblique slit pattern 73 is detected by the photodetector 32 while scanning in the first oblique direction. This scanning detection is performed a plurality of times while changing the position of the slit substrate 31 in the Z direction. Further, the second oblique direction L & S pattern 64 of the test mask TM is illuminated, and the aerial image of the second oblique direction L & S pattern 64 formed via the projection optical system PL is represented by the first oblique direction slit pattern 74 of the slit substrate 31. Light that has passed through the first oblique slit pattern 74 is detected by the photodetector 32 while scanning in the second oblique direction. This scanning detection is performed a plurality of times while changing the position of the slit substrate 31 in the Z direction.

  In this way, the processing system 33 measures the light intensity distribution of the projection space image of various L & S patterns having different pitches and arrangement directions (pitch directions) based on the output from the light detector 32, and the horizontal direction of this space image. A horizontal position displacement amount with respect to the design value of the position (position on the XY plane) and a focus position displacement amount with respect to the design value of the focus position (position in the Z direction) are obtained, and the projection optical system PL is obtained based on these position displacement information The amount of wavefront deviation at the sample point on the pupil plane is calculated. FIG. 8 is a diagram schematically showing sample points on the pupil plane of the projection optical system PL.

  Based on the light intensity distribution of the aerial image of the L & S pattern 61a having the smallest pitch among the Y-direction L & S patterns 61, the outermost side in the Y-direction region 81 extending in the Y direction through the center of the pupil plane of the projection optical system PL. The wavefront deviation amount at the pair of sample points 81a is obtained. Further, based on the light intensity distribution of the aerial image of the L & S pattern 61f having the largest pitch among the Y-direction L & S pattern 61, the wavefront deviation amount at the innermost pair of sample points 81f in the Y-direction region 81 is obtained. Furthermore, based on the light intensity distributions of the aerial images of the other Y-direction L & S patterns 61b to 61e, the wavefront deviation amounts at the other sample points 81b to 81e in the Y-direction region 81 are obtained. FIG. 9A shows a change in the amount of wavefront deviation at each sample point in the Y direction region 81.

  Similarly, based on the light intensity distribution of the aerial image of the X-direction L & S pattern 62, the wavefront deviation amount at each sample point in the X-direction region 82 extending in the X-direction through the center of the pupil plane of the projection optical system PL is obtained. It is done. FIG. 9B shows a change in the amount of wavefront deviation at each sample point in the X direction region 82. Further, based on the light intensity distribution of the aerial image of the first oblique direction L & S pattern 63, at each sample point in the first oblique direction region 83 extending elongated in the first oblique direction through the center of the pupil plane of the projection optical system PL. The amount of wavefront deviation is obtained. FIG. 9C shows a change in the amount of wavefront deviation at each sample point in the first oblique direction region 83. FIG.

  Further, based on the light intensity distribution of the aerial image of the second oblique direction L & S pattern 64, at each sample point in the second oblique direction region 84 extending elongated in the second oblique direction through the center of the pupil plane of the projection optical system PL. The amount of wavefront deviation is obtained. FIG. 9D shows a change in the amount of wavefront deviation at each sample point in the second oblique direction region 84. As described above, in the measurement step S11, the wavefront deviation amounts at a plurality of positions on the exit pupil plane of the projection optical system PL are measured based on the aerial image formed via the projection optical system PL.

  Next, in the aberration evaluation method of the present embodiment, the amount of wavefront deviation is determined in the radial direction for a plurality of radial directions (four radial directions in the example of the present embodiment) passing through the center of the exit pupil plane of the projection optical system PL. (S12). Specifically, in the approximation step S12, the amount of wavefront deviation of the sample points 81a to 81f in the Y-direction region 81 extending linearly along the Y direction on the pupil plane of the projection optical system PL is calculated using, for example, the least square method. It is approximated by a function of radial coordinate.

  As an example, the amount of wavefront deviation of the sample points 81a to 81f in the Y direction region 81 is approximated by least squares with a cubic function of the coordinate in the radial direction. Similarly, the amount of wavefront deviation of the sample points 82a to 82f (reference numerals not shown) in the X direction region 82 is approximated by least squares with a cubic function of the coordinate in the radial direction. Further, the wavefront deviation amounts of the sample points 83a to 83f (reference numerals not shown) in the first oblique direction region 83 are approximated by least squares by a cubic function of the coordinate in the radial direction. Further, the amount of wavefront deviation of the sample points 84a to 84f (reference numerals not shown) in the second oblique direction region 84 is approximated by least squares with a cubic function of the coordinate in the radial direction.

  Referring to FIGS. 9A to 9D, it can be seen that the wavefront deviation amount at the center of the pupil plane is not zero for each radial direction passing through the center of the pupil plane of the projection optical system PL. Originally, the wavefront deviation amount on the pupil plane is a deviation quantity based on the center of the pupil plane, so the wavefront deviation amount at the center of the pupil plane should be zero without depending on the radial direction. Here, the reason why the wavefront deviation amount at the center of the pupil plane does not become zero in each radial direction is due to an error caused by a relatively large deflection or distortion of the thin film of the slit substrate 31. That is, due to the influence of the relatively large deflection and distortion of the thin film of the slit substrate 31, the measurement result regarding the horizontal position shift and the focus position shift of the aerial image has an error depending on the direction of the slit pattern. The amount of wavefront deviation at the sample point has an error depending on the direction of the slit pattern.

  Therefore, in the aberration evaluation method of the present embodiment, the amount of wavefront deviation becomes substantially zero at the center of the exit pupil plane of the projection optical system PL in order to compensate for the influence of relatively large deflection and distortion of the thin film of the slit substrate 31. As described above, offset correction is performed on each of a plurality of functions (four cubic functions in the example of the present embodiment) obtained through the approximation step S12 (S13). As an example, FIG. 10 shows how a cubic function obtained by least square approximation of the amount of wavefront deviation of each sample point in the X direction region 82 is offset corrected.

  Referring to the diagram on the left side of FIG. 10, the wavefront deviation amount at each sample point in the X direction region 82 is represented by a point, and the wavefront deviation amount at each sample point in the X direction region 82 is obtained by least square approximation. The cubic function is represented by a continuous curve. In the offset correction step S13, the wavefront deviation amount at the center of the pupil plane of the cubic function obtained in the approximation step S12 is obtained, and the wavefront deviation amount at the center of the pupil plane is used as the offset amount, and the cubic function obtained in the approximation step S12. Subtract the amount of offset uniformly from. As a result, as shown in the diagram on the right side of FIG. 10, wavefront deviation amount data that has been offset-corrected so that the wavefront deviation amount at the center of the pupil plane in the X direction region 82 becomes zero is obtained.

  FIG. 11B shows the wavefront deviation amount of each sample point corresponding to the cubic function whose offset is corrected in the X direction region 82. Similarly, for the Y-direction region 81, the first oblique direction region 83, and the second oblique direction region 84, a cubic function that is offset-corrected so that the wavefront deviation amount at the center of the pupil plane becomes zero is obtained. 11A, 11C, and 11D, each sample corresponding to a cubic function offset-corrected for the Y-direction region 81, the first oblique direction region 83, and the second oblique direction region 84. The amount of wavefront deviation of a point is shown, respectively.

  Finally, in the aberration evaluation method of the present embodiment, the wavefront aberration of the projection optical system PL on the exit pupil plane is expressed based on the wavefront deviation amount data obtained through the offset correction step S13 (S14). In the expressing step S14, as an example, the wavefront aberration of the projection optical system PL is expressed using a Zernike polynomial that is an orthonormal function sequence in a circular area normalized by the exit pupil plane. The coefficient of each term of the Zernike polynomial is called a Zernike coefficient and is used as an index for evaluating the imaging performance of the projection optical system. The Zernike coefficient is obtained by using, for example, a method of least square approximation.

  Hereinafter, basic matters regarding the Zernike polynomial representing the distribution of wavefront aberration in the pupil plane will be described. In the Zernike polynomial expression, pupil polar coordinates (ρ, θ) are used as the coordinate system on the pupil plane, and Zernike cylindrical functions are used as the orthogonal function system. That is, the wavefront aberration W (ρ, θ) is developed as shown in the following equation (a) using Zernike's cylindrical function Zi (ρ, θ).

W (ρ, θ) = ΣCi · Zi (ρ, θ)
= C2 · Z2 (ρ, θ) +... + Cn · Zn (ρ, θ) (a)

  Here, Ci is a coefficient of each term of the Zernike polynomial, that is, a Zernike coefficient. Hereinafter, among the function system Zi (ρ, θ) of each term of the Zernike polynomial, the functions Z2 to Z37 according to the second term to the 37th term are shown in the following table (1).

Table (1)
Z2: ρcosθ
Z3: ρsinθ
Z4: 2ρ ² −1
Z5: ρ ² cos2θ
Z6: ρ ² sin2θ
Z7: (3ρ ² −2) ρcosθ
Z8: (3ρ ² −2) ρsinθ
Z9: 6ρ ⁴ -6ρ ² +1
Z10: ρ ³ cos3θ
Z11: ρ ³ sin3θ
Z12: (4ρ ² -3) ρ ² cos2θ
Z13: (4ρ ² -3) ρ ² sin2θ
Z14: (10ρ ⁴ -12ρ ² +3) ρcosθ
Z15: (10ρ ⁴ −12ρ ² +3) ρsinθ
Z16: 20ρ ⁶ −30ρ ⁴ + 12ρ ² −1
Z17: ρ ⁴ cos4θ
Z18: ρ ⁴ sin4θ
Z19: (5ρ ² -4) ρ ³ cos3θ
Z20: (5ρ ² -4) ρ ³ sin3θ
Z21: (15ρ ⁴ −20ρ ² +6) ρ ² cos 2θ
Z22: (15ρ ⁴ −20ρ ² +6) ρ ² sin2θ
Z23: (35ρ ⁶ -60ρ ⁴ + 30ρ ² -4) ρcosθ
Z24: (35ρ ⁶ -60ρ ⁴ + 30ρ ² -4) ρsinθ
Z25: 70ρ ⁸ −140ρ ⁶ + 90ρ ⁴ −20ρ ² +1
Z26: ρ ⁵ cos 5θ
Z27: ρ ⁵ sin5θ
Z28: (6ρ ² -5) ρ ⁴ cos4θ
Z29: (6ρ ² -5) ρ ⁴ sin4θ
Z30: (21ρ ⁴ −30ρ ² +10) ρ ³ cos 3θ
Z31: (21ρ ⁴ −30ρ ² +10) ρ ³ sin3θ
Z32: (56ρ ⁶ −104ρ ⁴ + 60ρ ² −10) ρ ² cos 2θ
Z33: (56ρ ⁶ −104ρ ⁴ + 60ρ ² −10) ρ ² sin2θ
Z34: (126ρ ⁸ −280ρ ⁶ + 210ρ ⁴ −60ρ ² +5) ρcosθ
Z35: (126ρ ⁸ −280ρ ⁶ + 210ρ ⁴ −60ρ ² +5) ρsinθ
Z36: 252ρ ¹⁰ −630ρ ⁸ + 560ρ ⁶ −210ρ ⁴ + 30ρ ² −1
Z37: 924ρ ¹² −2772ρ ¹⁰ + 3150ρ ⁸ −1680ρ ⁶ + 420ρ ⁴
-42ρ ² -1

  In the aberration evaluation method of the present embodiment, the amount of wavefront deviation at each sample point of the exit pupil plane of the projection optical system PL is measured by a normal aerial image measurement method, and a plurality of radial directions passing through the center of the exit pupil plane are measured. The measured wavefront deviation is approximated by a function of the radial coordinate. Then, the plurality of approximate functions are offset-corrected so that the wavefront deviation amount becomes substantially zero at the center of the exit pupil plane, and the wavefront aberration of the projection optical system PL on the exit pupil plane is based on the offset-corrected wavefront deviation amount data. Is expressed by a Zernike polynomial.

  As described above, in the aberration evaluation method of this embodiment, the effect of the relatively large deflection or distortion of the thin film of the slit substrate 31 is compensated by the effect of offset correction that makes the wavefront deviation amount at the center of the exit pupil plane substantially zero. Thus, the wavefront aberration of the projection optical system PL can be evaluated with high accuracy by the aerial image measurement method. Therefore, in the exposure apparatus of the present embodiment, the projection optical system PL can be optically adjusted well based on the aberration evaluation obtained by the aberration evaluation method that evaluates the wavefront aberration of the projection optical system PL with high accuracy. As a result, the exposure apparatus of the present embodiment can perform good projection exposure using the projection optical system PL that has been optically adjusted.

  In the above description, a plurality of positions on the exit pupil plane of the optical system to be tested prior to the approximation step of approximating the wavefront deviation amount for a plurality of radial directions passing through the center of the exit pupil plane of the test optical system. It is assumed that a measurement process for measuring the amount of wavefront deviation is performed. However, the present invention is not limited to this, and a modification in which the above approximation process is performed on the wavefront deviation amount data obtained by a method other than measurement is also possible.

  In the EUVL exposure apparatus according to the above-described embodiment, a laser plasma light source is used as a light source for supplying EUV light. However, without being limited thereto, other suitable light sources that supply EUV light, such as synchrotron radiation (SOR) light sources, can also be used.

  In the above-described embodiment, the present invention is applied to the projection optical system mounted on the EUVL exposure apparatus using the reflective mask M. However, the present invention is not limited to this, and general optical optics The present invention can also be applied to the evaluation of the wavefront aberration of the system.

  In the exposure apparatus according to the above-described embodiment, the illumination system illuminates the mask (illumination process), and exposes the transfer pattern formed on the mask using the projection optical system onto the photosensitive substrate (exposure process). Microdevices (semiconductor elements, imaging elements, liquid crystal display elements, thin film magnetic heads, etc.) can be manufactured. Hereinafter, referring to the flowchart of FIG. 12 for an example of a technique for obtaining a semiconductor device as a micro device by forming a predetermined circuit pattern on a wafer or the like as a photosensitive substrate using the exposure apparatus of this embodiment. I will explain.

  First, in step 301 of FIG. 12, a metal film is deposited on one lot of wafers. In the next step 302, a photoresist is applied on the metal film on the one lot of wafers. Thereafter, in step 303, using the exposure apparatus of the present embodiment, the pattern image on the mask (reticle) is sequentially exposed and transferred to each shot area on the wafer of the one lot via the projection optical system. .

  Thereafter, in step 304, the photoresist on the one lot of wafers is developed, and in step 305, the resist pattern is etched on the one lot of wafers to form a pattern on the mask. Corresponding circuit patterns are formed in each shot area on each wafer. Thereafter, a device pattern such as a semiconductor element is manufactured by forming a circuit pattern of an upper layer. According to the semiconductor device manufacturing method described above, a semiconductor device having an extremely fine circuit pattern can be obtained with high throughput.

It is a figure which shows schematically the whole exposure apparatus structure to which the aberration evaluation method concerning embodiment of this invention is applied. It is a figure which shows schematically the internal structure of the light source of FIG. 1, an illumination optical system, and a projection optical system. It is a figure which illustrates schematically one scanning exposure in the exposure apparatus of this embodiment. It is a flowchart explaining the aberration evaluation method concerning this embodiment. It is a figure which shows roughly the apparatus structure which implements the aberration evaluation method of this embodiment. It is a figure which shows schematically the test mark formed in the test mask. It is a figure which shows roughly the slit pattern formed on the thin film of a slit board | substrate. It is a figure which shows typically the sample point on the pupil surface of a projection optical system. It is a figure which shows the change of the wavefront deviation | shift amount in each sample point on the pupil plane of a projection optical system. It is a figure which shows a mode that the cubic correction obtained by carrying out the least square approximation of the wavefront deviation | shift amount of each sample point in a X direction area | region is carrying out an offset correction. The wavefront deviation | shift amount of each sample point corresponding to the cubic function by which offset correction was carried out is shown. It is a figure which shows the flowchart about an example of the method at the time of obtaining the semiconductor device as a microdevice.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser plasma light source 2 Illumination optical system 5 Mask stage 7 Wafer stage 11 Laser light source 13 Gas target 14 Nozzle 15 Elliptical reflection mirrors 18a and 18b Fly eye mirror 21 Field stop 31 Slit substrate 32 Photo detector 33 Processing system M Mask TM Test mask PL projection optical system W wafer

Claims (10)

In the aberration evaluation method for evaluating the wavefront aberration of the test optical system,
For a plurality of radial directions passing through the center of the exit pupil plane of the test optical system, an approximation step for approximating the wavefront deviation amount as a function of the radial direction coordinates,
A correction step of offset correcting each of the plurality of functions obtained through the approximating step so that a wavefront deviation amount becomes substantially zero at the center of the exit pupil plane;
An aberration evaluation method comprising: expressing a wavefront aberration of the optical system under test on the exit pupil plane based on the offset-corrected wavefront deviation amount data obtained through the correction step . The aberration evaluation method according to claim 1, wherein in the expressing step, the wavefront aberration of the optical system to be measured is expressed by a function of two-dimensional coordinates on the exit pupil plane. 3. The aberration evaluation method according to claim 1, wherein in the approximating step, the amount of wavefront deviation is approximated by a function of a coordinate in a radial direction using a least square method. 4. The aberration evaluation method according to claim 1, wherein in the expressing step, the wavefront aberration of the optical system to be measured is expressed using a Zernike polynomial on the exit pupil plane. 5. A measurement step of measuring the amount of wavefront deviation at a plurality of positions on the exit pupil plane,
5. The aberration evaluation method according to claim 1, wherein, in the approximating step, the amount of wavefront deviation obtained in the measuring step is approximated by a function of a coordinate in a radial direction. 6. The aberration according to claim 5, wherein, in the measuring step, wavefront deviation amounts at a plurality of positions on the exit pupil plane are measured based on an aerial image formed through the test optical system. Evaluation methods. An adjustment method, wherein the test optical system is optically adjusted based on an evaluation result obtained by the aberration evaluation method according to claim 1. An exposure apparatus comprising a test optical system optically adjusted by the adjustment method according to claim 7 as a projection optical system for projecting and exposing a predetermined pattern onto a photosensitive substrate. An exposure method comprising: projecting and exposing a predetermined pattern image onto a photosensitive substrate using the test optical system optically adjusted by the adjustment method according to claim 7. An exposure process for exposing the predetermined pattern to the photosensitive substrate using the exposure apparatus according to claim 8;
And a development step of developing the photosensitive substrate that has undergone the exposure step.

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