JPH11258487A - Regulating method for optical system and optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reulate an optical system with excellent reproducibility in an actual using state or a state corresponding to that. SOLUTION: In this regulating method, an image of a phase pattern 4 having at least one projected part T and one recessed part B is focused by an inspected optical system 3, and a distance Δx between the image focusing position XT of a light quantity tilting part on a projected side and an image focusing position XB of the light quantity tilting part on a recessed side is obtained about the position XE of the extreme value IE of a light quantity I produced in a boundary E between the image of the projected part T and the image of the recessed part B in the phase pattern 4, and then the distance ΔX is obtained in a plurality of states where the defocused quantity ΔZ of an image in the phase pattern 4 is mutually different, and the optical regulation of the inspected optical system 3 is carried out on a relation between the defocused quantity ΔZ and the distance ΔX.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection optical system and an alignment optical system provided in a projection exposure apparatus used in a manufacturing process of a semiconductor, a liquid crystal, or the like, or an overlay provided inside or outside a projection exposure apparatus. The present invention relates to inspection and adjustment of an aberration state and an optical adjustment state of an optical system such as a measurement optical system used in a measurement device.

[0002]

2. Description of the Related Art Conventionally, in a projection exposure apparatus used in a photolithography process for manufacturing a semiconductor device or a liquid crystal display device, a pattern formed on a projection original such as a mask or a reticle is transferred to a wafer or a wafer through a projection optical system. It is transferred to a photosensitive substrate such as a glass plate multiple times. That is, a pattern image already transferred onto the wafer is aligned with a projection image of a mask pattern formed via a projection optical system by an alignment apparatus (alignment optical system), and overlay exposure is performed. Further, whether the alignment is good or not is determined by an overlay measuring device provided inside or outside the projection exposure apparatus.

[0003] In this case, if the optical adjustment of the projection optical system is insufficient or the aberration remains in the projection optical system, the projected image of the mask pattern is not accurately formed, and there is distortion on the wafer. A transfer pattern is formed. In addition, if the optical axis of the alignment device is insufficiently adjusted, or if aberrations remain in the optical system of the alignment device, accurate alignment between the mask and the wafer cannot be performed, resulting in high accuracy. Overlay exposure cannot be performed. Further, with respect to the overlay measurement device, if there is a poor optical axis adjustment or residual aberration, it is not possible to perform an overlay measurement with high accuracy.

Therefore, a plurality of light-shielding patterns formed on the light transmitting portion of the mask are transferred onto a wafer via a projection optical system, and the amount of asymmetry of a resist image formed on the wafer is observed using an electron microscope. Conventionally, a method for inspecting the aberration of the projection optical system has been adopted. Further, Japanese Patent Application Laid-Open No.
No. 18957 discloses a method of detecting a spatial image of a mask light-shielding pattern formed via a projection optical system,
A method for inspecting an asymmetric aberration of a projection optical system is disclosed. Further, regarding the optical axis adjustment, see Japanese Patent Application Laid-Open No. 6-6909.
No. 7, JP-A-6-132197 and the like disclose a method for correcting optical axis shift and optical axis inclination.

[0005]

However, of the above-mentioned conventional techniques, in the method of observing a resist image using an electron microscope, it is necessary to actually form a resist image on a wafer. For this reason, a complicated process took a long time before the inspection. In addition, a scanning electron microscope is usually used for inspection of the resist image, but the reproducibility of the inspection is not good because the resolution of the scanning electron microscope changes depending on individual differences between operators and the state of the apparatus. . Further, Japanese Unexamined Patent Publication No.
In the method using an aerial image disclosed in Japanese Patent Publication No. 118957, sufficient accuracy cannot be obtained unless the illumination σ (the ratio of the illumination numerical aperture to the imaging numerical aperture) is reduced. However, when the illumination σ is changed, the manner in which the light beam contributes to the wavefront aberration of the projection optical system changes. For this reason, the aberration obtained based on the aerial image obtained when the illumination σ is reduced is different from the aberration in the actual use state.

Further, the optical axis adjusting methods disclosed in Japanese Patent Application Laid-Open Nos. 6-69097 and 6-132197, etc., need not clearly distinguish between telecentricity of an optical system and vignetting of a light beam. Has been adjusted. Therefore, both the telecentricity and the vignetting of the light beam could not be adjusted sufficiently. Therefore, an object of the present invention is to provide a method of adjusting an optical system that can adjust an optical system with good reproducibility in an actual use state or a state similar thereto, and an optical device provided with the adjustment method is provided. The task is to provide.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, that is, an image of a phase pattern having at least one convex portion and one concave portion is formed by an optical system to be measured. With respect to the position of the extreme value of the amount of light generated at the boundary between the image of the convex portion and the image of the concave portion of the phase pattern, the image forming position of the light amount inclined portion on the convex side and the image formation of the light amount inclined portion on the concave side The distance from the position is obtained, the distance is obtained in a plurality of states where the defocus amounts of the images of the phase pattern are different from each other, and the optical adjustment of the test optical system is performed based on the relationship between the defocus amount and the distance. This is a method for adjusting an optical system.

The present invention also provides an illumination optical system for illuminating a phase pattern, an imaging optical system for forming an image of the phase pattern, and a position where the phase pattern image is formed by the imaging optical system. An optical device having a photoelectric detection means, the extreme of the output signal level from the photoelectric detection means occurring at the boundary between the image of the convex portion and the image of the concave portion of the phase pattern. A first position is detected based on one of the two different signal ramps forming the position of the value, and a different position forming the extreme position of the output signal level is detected. Signal processing means for detecting a second position based on the other one of the two signal inclination parts, and the photoelectric detection means for detecting an image of the phase pattern formed by the imaging optical system. Defocus means for defocusing the phase pattern image with respect to the photoelectric detection means formed by the defocus means according to each defocus state of the image of the phase pattern. An optical device comprising a position displacement detection system for detecting a difference between a position and the second position. This optical device can be used as an overlay measuring device for measuring a positional deviation between two predetermined portions of the phase pattern, and a position for detecting the position of the phase pattern. It can also be used as a detection device.

[0009]

Embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a first embodiment of an optical device to which the method for adjusting an optical system according to the present invention is applied. The light beam emitted from the light source 1 is reflected by the half mirror 2, passes through the objective lens 3 serving as the optical system to be tested, and uniformly illuminates the phase pattern 4. The phase pattern 4 is mounted on a Z stage 5 that moves up and down in the optical axis z direction of the objective lens 3. The light beam emitted from the phase pattern 4 passes through the objective lens 3 and the half mirror 2, and then forms an image on a CCD 6 serving as a photoelectric detection unit. The electric signal obtained by the CCD 6 and the position signal of the Z stage 5 in the z direction are sent to the signal processing means 7.

FIG. 2 shows the relationship between the pattern direction x of the phase pattern and the light intensity I of the image. Convex part T of phase pattern 4
Light intensity I _T of the image of the increases in response to the reflectivity of the convex portion T. Similarly, the light intensity I _B of the image of the concave portion B of the phase pattern 4
Becomes higher corresponding to the reflectance of the concave portion B. However the light intensity I _E of the image of the boundary E between the convex portion T and concave portion B after passing through the pupil of the light beam is scattered or diffracted objective lens 3 at the boundary E and phase pattern surface, interference in a predetermined image plane it is, reduced as compared to the light intensity I _B of the image of the light intensity I _T and recess B of the image of the convex portion T to. As a result, the distribution of the light intensity I has a minimum value at a position x _E of the image of the boundary E between the convex portion T and concave portion B,
Thus the position protrusion side light amount inclined portion to the convex portion side with respect to x _E I _Ti of the minimum value (i = 1~n: n is the measurement number data) have, have a concave side light amount inclined portion I _Bi on the concave side become.

In this embodiment, the convex portion side light amount inclined portion I
From the position x _Ti of _Ti, the average position x _T, x _T = determined by? X _Ti / n, similarly, the position x of the concave side light amount inclined portion I _Bi
From _Bi, its average position x _B, determined by x _B = Σx _Bi / n, both distance [Delta] x, is determined by Δx = x _B -X _T. Note that the distance Δx is obtained by the position displacement detection system 7 a in the signal processing means 7. As the position displacement detection system 7a, for example, a differential amplifier can be used.

[0012] Figure 3 is a convex portion, or an example of a logic for determining the location x _i of the light intensity gradient portion I _i of the concave side. The amount of the image of the boundary E between the convex portion T and concave portion B and I _E, the maximum value of the amount of light that occurs on the opposite side and I _a is the boundary E with respect to the amount of light inclined portion. The light amount obtained by apportioning the light amounts _IE and _Ia at an appropriate ratio is I _i
And For example, when apportioned equally ratio becomes _{I i = (I E + I} a) / 2. The position where the light quantity I _i is given is the position x _i of the light quantity inclined portion I _i .

FIG. 4 shows that the CCD 6 is moved up and down the Z stage 5.
5 shows the result of measuring the distance Δx between the position of the convex-side light amount inclined portion and the position of the concave-side light amount inclined portion while defocusing the position of the image of the pattern 4. Figure 4
(A) shows a case where the objective lens 3 has no coma aberration, no vignetting, and no inclination of the optical axis of the illumination light with respect to the pattern 4. In this case, the distance Δx becomes Δx = 0 regardless of the defocus amount Δz. FIG. 4 (b)
A case where coma aberration exists in the objective lens 3 is shown. In this case, when the defocus amount Δz increases from the in-focus state, the distance Δx increases or decreases in proportion thereto. The proportionality constant can be positive or negative. Therefore, a line representing the relationship between the defocus amount Δz and the distance Δx is represented by Δx =
It becomes a straight line inclined by a certain angle α with respect to the straight line representing 0, and this angle α represents an index of coma aberration. As for the angle, for example, the counterclockwise direction is positive.

FIG. 4C shows a case where the light beam vignetting exists in the objective lens 3. In this case, when the absolute value of the defocus amount Δz increases from the focused state, the distance Δx increases or decreases in proportion to the absolute value. The proportionality constant can be positive or negative. Therefore, the straight line representing the relationship between the defocus amount Δz and the distance Δx is bent in the in-focus state, and is Δ on the front pin (the state where the imaging surface of the CCD 6 is closer to the objective lens 3 than the in-focus position).
It becomes a straight line that is inclined by a certain angle φ with respect to the straight line representing x = 0, and is Δ on the rear focus (the state where the imaging surface of the CCD 6 is on the opposite side of the objective lens 3 from the in-focus position).
It becomes a straight line inclined by -φ with respect to the straight line representing x = 0, and this angle φ represents the index of the luminous flux vignetting.

FIG. 4D shows a case where both the coma aberration and the luminous flux vignetting are present in the objective lens 3. In this case, on the front focus side, the straight line is inclined by a certain angle β with respect to the straight line representing Δx = 0. The breakdown is that it is inclined by α due to coma, and φ due to vignetting.
Β = α + φ. On the rear focus side, the straight line is inclined by a certain angle γ with respect to the straight line representing Δx = 0. The breakdown is as follows: γ = α−φ because the light is tilted by α due to coma and further tilted by −φ due to light flux vignetting.

Therefore, the inclination angle β on the front pin side,
By measuring the inclination angle γ on the rear focus side, α = (β + γ) / 2 and φ = (β−γ) / 2 to obtain the coma aberration index α of the objective lens 3 and the luminous flux vignetting. And the index φ of Based on this result, the coma aberration and the luminous flux vignetting of the test optical system are eliminated by eccentrically adjusting the lens components and the aperture stop constituting the objective lens 3 so that α = 0 and φ = 0. Can be. Also, when the optical axis of the test optical system is inclined with respect to the pattern 4 (that is, when the illumination light irradiates the pattern obliquely, the projection side light amount due to the shadow due to the step of the phase pattern at the boundary E). the average position x _T itself inclined portion, as the average position x _B of the recess side light amount ramps each change, although the distance Δx between the two occurs,
The distance Δx between the two does not change with respect to the defocus amount Δz. That is, by detecting a constant Δx with respect to Δz, it is possible to measure the amount of inclination of the optical axis of the optical system to be measured with respect to the object plane. It is possible to eliminate the inclination of the optical axis with respect to the object plane.

In this embodiment, in order to defocus the image of the phase pattern 4 on the imaging surface of the CCD 6, Z
Although the phase pattern 4 is moved in the optical axis z direction by the stage 5, as another method, the imaging surface of the CCD 6 can be moved in the optical axis direction, or the objective lens 3 can be moved in the optical axis z direction. it can. In addition, in order to optimize the detection sensitivity of the coma aberration of the optical system to be inspected, the luminous flux vignetting, and the tilt of the optical axis with respect to the object surface, the illumination conditions such as the defocus range, illumination σ (coherence factor) and illumination wavelength, and phase pattern It is desirable to control the detection sensitivity by changing the shape.

Next, FIG. 5 shows a second embodiment of the present invention.
In this embodiment, the method of the present invention is applied to an overlay measuring apparatus. A light beam emitted from the light source 1 is reflected by the half mirror 2 and transmitted through the first objective lens 8 to form a first mark WM1 and a second mark WM formed on the wafer W.
Illuminate 2 uniformly. The first objective lens 8 includes a driving device 8a
Is configured to move in the optical axis z direction by
In this embodiment, a piezo element is used as the driving device 8a. Further, the wafer W is mounted on an XY stage 9 that moves in an xy plane direction orthogonal to the optical axis z of the first objective lens 8. First mark WM1 formed on wafer W
And the second mark WM2 are both phase patterns, and both marks WM1 and WM2 are marks formed on the wafer W by different exposure processes. This overlay measurement device is a device that detects a positional shift between the marks WM1 and WM2.

The light beams emitted from both marks WM1 and WM2 pass through the first objective lens 8 and the half mirror 2, and pass through the second objective lens 8 and the half mirror 2.
After passing through the objective lens 10, the images of both marks WM1, WM2 are formed at the wafer conjugate position 11. Also, one or a group of lenses 10a constituting the second objective lens 10
Are arranged eccentrically in the xy plane direction orthogonal to the optical axis z by the driving device 10b. Wafer conjugate position 1
After passing through the first relay lens 12, the aperture stop 13, and the second relay lens 14,
Re-image on D6. The aperture stop 13 includes a driving device 13a.
Eccentrically in the xy plane direction orthogonal to the optical axis z. The electric signal obtained by the CCD 6 and the position signal of the first objective lens 8 in the z direction are sent to the signal processing means 7.

In the present embodiment, the first driving device 8a
By moving the objective lens 8 in the z direction, the defocus amount Δz
In a plurality of different states, images of the first mark WM1 and the second mark WM2 formed on the wafer W are captured.
And as in the previous embodiment, it obtains the distance Δx between the average position x _B of the average position x _T and a recess side light amount inclined portion of the protrusion side light amount inclined portion of the both marks WM1, WM2, defocus amount Δ
From the relationship between z and the distance Δx, an index α of coma aberration, an index φ of light flux vignetting, and an index Δx of optical axis inclination are obtained. Then, the driving device 10b moves the lens 10a in the second objective lens in the xy plane direction so as to eliminate the coma aberration, and the driving device 13 so as to eliminate the light beam vignetting.
The aperture stop 13 is moved in the xy plane direction by a.
Further, for example, the eccentricity of the light source 1 is adjusted so that the optical axis tilt is eliminated. Thus, the optical adjustment of the test optical system arranged in the optical path from the wafer W to the CCD 6 can be performed.

FIG. 6 shows a third embodiment of the present invention.
In this embodiment, the method of the present invention is applied to a projection optical system and an off-axis alignment optical system attached thereto. Exposure light emitted from an unillustrated illumination optical system uniformly illuminates the reticle R. A circuit pattern RP to be transferred to the wafer W and a reticle mark RM for positioning the reticle R are drawn on the reticle R. The light beam transmitted through the circuit pattern RP is transmitted to the projection optical system 1.
5 to form an image on the wafer W, whereby the circuit pattern RP on the reticle is transferred to the photosensitive surface on the wafer W. One or one group of lenses 1 constituting the projection optical system 15
Reference numeral 5a denotes an eccentrically arranged xy plane perpendicular to the optical axis z.
b is also arranged eccentrically in the xy plane direction orthogonal to the optical axis z.

On the wafer W, a wafer mark WM for positioning the wafer W is drawn. An XYZ stage 1 that can move in the x, y, and z directions
6. An opening is arranged on the XYZ stage 16 at the same height as the photosensitive surface of the wafer W, and a photoelectric detector 17 is arranged so as to measure the amount of light flux passing through the opening. X of the XYZ stage 16,
The positions in the y and z directions are measured by the interferometer 18. On the other hand, the configuration of the off-axis alignment optical system is the same as that of the second embodiment. However, at the conjugate position 11 of the wafer W, an index plate serving as an index for measuring the position of the wafer mark WM is arranged. The entire device is controlled by a computing device 19, and one of the computing devices 19
As one element, a signal processing means 7 is provided.

In this embodiment, the optical adjustment of the projection optical system 15 is performed as follows. That is, the XYZ stage 16
Then, the photoelectric detector 17 is moved in the z direction, and the opening is placed in a plurality of states having different defocus amounts Δz. Then, at that height, the opening is set to x-
The output of the photoelectric detector 17 is measured while scanning in the y-plane. And as in the previous embodiment, if the phase pattern is a circuit pattern RP, determine the distance Δx between the average position x _B of the average position x _T and a recess side light amount inclined portion of the convex portion side light amount inclined portion, di From the relationship between the focus amount Δz and the distance Δx, an index α of the coma aberration, an index φ of the light beam vignetting, and an index Δx of the optical axis inclination are obtained. Then, the lens 15a in the projection optical system is moved in the xy plane direction so that coma aberration is eliminated, and the aperture stop 15b is moved x so that light beam vignetting is eliminated.
-Move in the y-plane direction. Further, the eccentricity of the light source of the illumination optical system (not shown) is adjusted so that the optical axis tilt is eliminated. Thus, the optical adjustment of the test optical system, that is, the projection optical system 15 arranged on the optical path from the reticle R to the photoelectric detector 17 can be performed. On the other hand, the optical adjustment of the off-axis alignment optical system is performed in the same manner as in the second embodiment.

[0024]

As described above, according to the method and apparatus of the present invention, the coma aberration of the optical system, the vignetting of the light beam and the inclination of the optical axis with respect to the object plane can be easily and accurately determined. By using the aberration correcting means and the optical axis adjusting means mounted on the system, it is possible to adjust the coma aberration, the luminous flux vignetting, and the optical axis inclination with high accuracy. In particular, it is useful for aberration correction and optical axis adjustment of a measurement optical system of an overlay measurement device used for semiconductor manufacturing, a projection optical system and an alignment optical system of an exposure device.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a light amount distribution of an image of a phase pattern.

FIG. 3 is an explanatory diagram showing one method for determining the position of a light amount inclined portion.

FIG. 4 is an explanatory diagram showing a relationship between a defocus amount Δz and a distance Δx between a convex portion side light amount inclined portion and a concave side light amount inclined portion.

FIG. 5 is a configuration diagram showing a second embodiment of the present invention.

FIG. 6 is a configuration diagram showing a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Half mirror 3 ... Objective lens 4 ... Phase pattern 5 ... Z stage 6 ... CCD 7 ... Signal processing means 7a ... Position displacement detection system 8 ... First objective lens 8a ... Driving device 9 ... XY stage 10 ... 2 Objective lens 10a Lens 10b Driving device 11 Wafer conjugate position 12 First relay lens 13 Aperture stop 13a Driving device 14 Second relay lens 15 Projection optical system 15a Lens 15b Aperture stop 16 XYZ Stage 17 Photoelectric detector 18 Interferometer 19 Computing device W Wafer WM, WM1, WM
2 wafer mark R reticle RP circuit pattern RM reticle mark z optical axis

Claims (10)

[Claims] An image of a phase pattern having at least one protrusion and one recess is formed by an optical system to be measured, and a light amount generated at a boundary between the image of the protrusion and the image of the recess of the phase pattern. The distance between the image forming position of the light amount inclined portion on the convex side and the image forming position of the light amount inclined portion on the concave side with respect to the position of the extremum is obtained. Wherein the distance is obtained, and the optical adjustment of the optical system to be measured is performed based on the relationship between the defocus amount and the distance. 2. The imaging position of the light amount inclined portion on the convex portion side or the concave portion side is a light amount obtained by proportionally dividing an extreme value of the light amount generated before and after the light amount inclined portion by a predetermined ratio. The method for adjusting an optical system according to claim 1, wherein the value is obtained based on a position. 3. The method according to claim 1, wherein coma aberration adjustment, luminous flux vignetting adjustment, or inclination adjustment of the optical axis with respect to the object plane is performed based on the relationship between the defocus amount and the distance. 3. The method for adjusting an optical system according to 1 or 2. 4. An illumination optical system for illuminating a phase pattern, an imaging optical system for forming an image of the phase pattern, and a photoelectric detector disposed at a position where the phase pattern image is formed by the imaging optical system. The position of the extremum of the output signal level with respect to the position of the extremum of the output signal level from the photoelectric detection means, which is generated at the boundary between the image of the convex portion and the image of the concave portion of the phase pattern. The first of one of two different signal ramps forming
A first position is detected based on the signal ramp, and a second position is detected based on the other second signal ramp of the two different signal ramps forming the extreme position of the output signal level. Signal processing means for detecting a position; and defocus means for defocusing the image of the phase pattern formed by the imaging optical system with respect to the photoelectric detection means. A position displacement detection system that detects a difference between the first position and the second position according to each defocus state of the image of the phase pattern with respect to the photoelectric detection unit formed by the focusing unit. Characteristic optical device. 5. The apparatus according to claim 1, wherein the defocusing means moves at least one of the phase pattern, the imaging optical system, and the photoelectric detection means in an optical axis direction of the imaging optical system. The optical device according to claim 4. 6. The optical apparatus according to claim 4, wherein the illumination optical system includes a unit that changes an illumination state of the phase pattern. 7. The imaging optical system according to claim 4, wherein said imaging optical system has means for adjusting coma of said imaging optical system.
7. The optical device according to 5 or 6. 8. The illumination optical system or the imaging optical system according to claim 4, wherein the illumination optical system or the imaging optical system has means for adjusting an optical axis of the illumination optical system or the imaging optical system. Optical device. 9. An exposure illumination system for illuminating a mask with exposure light, a projection system for projecting a transfer pattern on the mask onto a substrate, and an alignment system for detecting a position of a phase pattern formed on the substrate. In the exposure apparatus, the alignment system includes: a position detection illumination system that illuminates a phase pattern; a detection optical system that forms an image of the phase pattern; and the phase pattern image is formed by the detection optical system. Photoelectric detection means arranged at a position, with respect to the position of the extreme value of the output signal level from the photoelectric detection means occurring at the boundary between the image of the convex portion and the image of the concave portion of the phase pattern, the extreme value of the output signal level Of one of the two different signal ramps forming the position
A first position is detected based on the signal ramp, and a second position is detected based on the other second signal ramp of the two different signal ramps forming the extreme position of the output signal level. Signal processing means for detecting a position; and defocus means for defocusing the image of the phase pattern formed by the imaging optical system with respect to the photoelectric detection means. A position displacement detection system that detects a difference between the first position and the second position according to each defocus state of the image of the phase pattern with respect to the photoelectric detection unit formed by the focusing unit. Exposure equipment characterized. 10. An exposure apparatus, comprising: an exposure illumination system for illuminating a mask with exposure light; and a projection system for projecting a transfer pattern on the exposure mask onto a substrate. An inspection device to be inspected is arranged, wherein the inspection device photoelectrically detects an image of a phase pattern of the inspection mask different from the exposure mask through the projection system, Regarding the position of the extreme value of the output signal level from the photoelectric detection means occurring at the boundary between the image and the image of the concave portion, one of two different signal slopes forming the extreme position of the output signal level First
A first position is detected based on the signal ramp, and a second position is detected based on the other second signal ramp of the two different signal ramps forming the extreme position of the output signal level. Signal processing means for detecting a position; and defocus means for defocusing the image of the phase pattern formed by the imaging optical system with respect to the photoelectric detection means. A position displacement detection system that detects a difference between the first position and the second position according to each defocus state of the image of the phase pattern with respect to the photoelectric detection unit formed by the focusing unit. Exposure equipment characterized.