JP2008153675A - Optical performance measuring method of projection optical system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical performance measuring method of a projection optical system, by which the optical performance of the projection optical system can be measured on its main body. <P>SOLUTION: The method for measuring the optical performance of the projection optical system measures the optical performance of the projection optical system with an interferometer mounted on an exposure apparatus, wherein the exposure apparatus includes: an illumination system for illuminating a first object with an exposure light from an exposure light source; and the projection optical system for projecting a pattern of the first object onto a second object. The method includes steps of: generating a reference light based on the exposure light passed through the projection optical system from the exposure light source; and observing interference fringes formed by making the exposure light that has passed through the reference light and the projection optical system interfere with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for measuring optical performance of a projection optical system. For example, when manufacturing a semiconductor device such as an IC or LSI, an imaging device such as a CCD, a display device such as a liquid crystal panel, or a device such as a magnetic head, a mask or reticle ( Suitable for a projection exposure apparatus used in a lithography process to obtain a highly integrated device by projecting or scanning exposure of an electronic circuit pattern on a surface via a projection optical system onto a wafer surface (hereinafter collectively referred to as “reticle”) It is.

  Conventionally, when a device such as a semiconductor device or a liquid crystal panel is manufactured using a photolithography technique, a pattern on a reticle surface is exposed to a photosensitive material such as a wafer or a glass plate coated with a photoresist or the like via a projection optical system. Exposure transfer on the substrate.

  In recent years, higher integration of devices such as ICs and LSIs has been accelerated, and the progress of microfabrication technology of semiconductor wafers accompanying this has been remarkable. As a projection exposure apparatus that forms the center of this microfabrication technology, an equal magnification projection exposure apparatus (mirror projection aligner) that performs exposure while scanning a mask and a photosensitive substrate with respect to an equal magnification mirror optical system having an arc-shaped exposure area, There is a reduction projection exposure apparatus (stepper) that forms a pattern image of a mask on a photosensitive substrate by a refractive optical system and exposes the photosensitive substrate by a step-and-repeat method.

  Recently, as the resolution of a projection optical system mounted on a projection exposure apparatus has been increased, strict demands have also been made for aberration correction of the projection optical system. Therefore, it is indispensable to measure and inspect the optical performance of the projection optical system after the projection optical system is mounted on the exposure apparatus body.

  For this reason, conventionally, in order to inspect the performance of the projection optical system on the main body of the exposure apparatus, particularly aberrations, a plurality of light-shielding patterns (line and space, etc.) are provided on the light transmitting portion on the reticle, and this pattern is actually printed on the wafer. The resist image is observed and examined using an electron microscope or the like.

  As a method of inspecting the optical performance of the projection optical system, a method of inspecting and inspecting a resist image baked on a wafer using an electron microscope is a method for inspecting a resist image after performing complicated operations such as an exposure process and a development process. In order to obtain the inspection, the inspection becomes complicated, and as a result, the entire inspection requires a long time.

  In addition, a high-precision measuring device is necessary for the inspection of the resist image, and the only existing device is a scanning electron microscope (SEM). However, there is a problem that the measurement system of the SEM changes depending on the optical axis alignment accuracy of the electron optical system, the degree of internal vacuum, etc., and there is a difference in measurement values due to individual differences among workers and the state of the apparatus.

  In addition, since the resist image formed on the wafer is inspected, if there is an error in the resist process (coating or developing), the inspection accuracy is poor, and particularly the inspection reproducibility is poor. Furthermore, since it is necessary to perform baking for each illumination condition used for actual device baking, there is still a problem that a large amount of labor is required for inspection.

  In recent years, with the progress of device miniaturization, projection optical systems are required to maintain higher optical performance. For example, a slight change in the optical performance of the projection optical system during transportation is measured at the time of installation, and it is necessary to readjust after the installation so that the optical performance is optimal.

  On the other hand, it is becoming necessary to reduce the change in the optical performance of the projection optical system due to the change in the illumination conditions as much as possible. Therefore, it is becoming necessary to easily measure the performance of the projection optical system under various illumination conditions on the exposure apparatus body in a short time.

  Further, in the actual exposure process, there is a problem that the projection optical system is warmed by the illumination system together with the exposure, and the image performance is changed. In this case, since there is no means for performing wavefront aberration measurement and image evaluation of the projection optical system and no means for adjustment on the exposure apparatus, only the processing such as stopping the operation of the apparatus can be performed at present.

An optical performance measurement method for a projection optical system according to a first aspect of the present invention includes an illumination system that illuminates a first object with exposure light from an exposure light source, and a projection optical system that projects a pattern of the first object onto a second object. In an optical performance measurement method for a projection optical system, the optical performance of the projection optical system is measured with an interferometer mounted on the exposure apparatus.
Observing interference fringes formed by generating reference light from exposure light from the exposure light source that has passed through the projection optical system and causing the reference light to interfere with the exposure light that has passed through the projection optical system It is characterized by having steps.

  ADVANTAGE OF THE INVENTION According to this invention, the optical performance measuring method of the projection optical system which can measure the optical performance of a projection optical system on a main body can be provided.

  FIG. 1 is a schematic view of the essential portions of Embodiment 1 of a projection exposure apparatus equipped with an interferometer used in the optical performance measurement method for a projection optical system of the present invention. The projection exposure apparatus according to this embodiment is applied to a normal stepper or a scanning type (scan type) stepper (projection exposure apparatus).

  In FIG. 1, for example, a light beam emitted from an exposure light source 1 such as an excimer laser (ArF excimer laser, KrF excimer laser) is converted into a beam shape symmetric with respect to the optical axis by a beam shaping optical system 2, and is transmitted to an optical path switching mirror 3. It is guiding light. The optical path switching mirror 3 is disposed outside the optical path during normal exposure. The light beam emitted from the beam shaping optical system 2 enters the incoherent unit 4, reduces coherence, passes through the illumination optical system 5, and illuminates the reticle (first object) surface 15. Each element 2, 4, 5 constitutes one element of the illumination system. A projection lens 16 projects a pattern on the reticle surface 15 onto a wafer (second object) surface 17.

  Next, the configuration of the interferometer of this embodiment will be described.

  The optical path switching mirror 3 is disposed in the optical path other than during exposure. The exposure light beam from the beam shaping optical system 2 is reflected by the optical path switching mirror 3, guided to the routing optical system 6, and guided to the vicinity of the interferometer 29 disposed in the vicinity of the reticle surface 15. Here, the routing optical system 6 is normally composed of a plurality of reflecting mirrors, but may be guided using a fiber. In that case, a polarization plane preserving fiber is preferable. The light beam emitted from the drawing optical system 6 is collected at one point by the condenser lens 7. Here, a pinhole 8 is disposed in the vicinity of the focal point of the condenser lens 7. The light beam that has passed through the pinhole 8 is converted into parallel light by the collimator lens 9. Here, the diameter of the pinhole 8 is set to be about the same as the Airy disk determined by the numerical aperture of the collimator lens 9. As a result, the light beam emitted from the pinhole 8 is an almost ideal spherical wave. The collimator lens 9 is designed and manufactured with almost no aberration. Therefore, the light beam from the collimator lens 9 is emitted as an almost ideal plane wave. The parallel light from the collimator lens 9 is reflected by the half mirror 10 and guided to the plane mirror 11 and the collimator lens 12 disposed on the XYZ stage 13.

  The path of the light beam to the collimator lens 12 will be described in detail with reference to FIG. The light beam 206 reflected by the half mirror 10 is bent in the y-axis direction by the fixed mirror 204 and then reflected in the x-axis direction by the mirror 205 disposed on the y stage 201. Further, the direction is changed in the z-axis direction by the mirror 11 arranged on the x stage 202, and the light is condensed on the reticle surface 15 in FIG. 1 by the collimator lens 12 arranged on the z stage 203. By following the path described above and moving the XYZ stage 13, the light beam reflected from the half mirror 10 can be condensed at an arbitrary point on the surface of the reticle 15. Here, the XYZ stage 13 is moved so that the collimator lens 12 is inserted and removed from the optical path. The light beam condensed on the reticle surface 15 is re-imaged on the wafer surface 17 by the projection lens 16.

  Here, on the wafer stage (XYZ stage) 19 or inside, a spherical mirror 20 is disposed as a reflecting means. Here, the center of curvature of the spherical mirror 20 substantially coincides with that on the wafer surface 17. The light beam from the projection lens 16 is reflected by the spherical mirror 20, travels substantially the same optical path, travels backward to the projection lens 16, the collimator lens 12, and the mirrors 11, 205, 204, and returns to the interferometer half mirror 10 again. The light passes through and enters the half mirror 21.

  The spherical mirror 20 may be a plane mirror. The plane mirror at this time is made to substantially coincide with the wafer surface 17. Alternatively, the plane mirror may be driven to the image forming position of the projection lens 16 to reflect the light beam at the vertex.

  The interferometer 29 in the first embodiment is a radial share type. The light of the exposure light source mounted on the exposure apparatus has a short coherence distance, and the optical path lengths of the reference light beam and the test light beam must be matched to perform interference measurement. For example, when the light source 1 is an excimer laser, the beam width from the light source such as an i-line stepper is about several nanometers by the interference filter, so that the coherence distance is several tens of μm. . Therefore, the optical path length difference between the reference light and the test light is adjusted within the interferometer 29 to be equal to or less than the above-described interference distance.

  Next, the inside of the interferometer 29 will be described in detail. First, the half mirror 21 divides the light into transmitted light and reflected light so that the intensity is approximately 1: 1. The reflected light beam is reflected by the mirror 22, and the central portion is expanded by the beam expander 23. For example, the magnification of the beam expander 23 is usually 10 times or more. The light beam whose center is enlarged by the beam expander 23 passes through the half mirror 24, is collected by the lens 27 as a reference light beam, and enters the surface of the CCD camera 28.

  On the other hand, the transmitted light beam from the half mirror 21 is reflected by the mirror 25, further reflected by the half mirror 24, collected by the lens 27, and incident on the surface of the CCD camera 28. Overlapping interference fringes are formed. The interference fringes observed here are that the central part of the test light beam is magnified by the beam expander 23, so that the reference light beam can be regarded as an ideal wavefront, and therefore the test lens (projection lens) 16 and the intermediate optical system (collimation). Information on the sum of wavefront aberration and shape error of the meter lens 12, spherical mirror 20, mirror, etc.). Accordingly, the wavefront aberration and the shape error of the intermediate optical system are measured in advance with another interferometer, or the so-called system error measuring method (the spherical mirror 20 is arranged under the condenser lens 12 and 0 degrees , 180 degrees and vertex reflection, wavefront aberration is measured, and the wavefront aberration of the spherical mirror 20 and other optical system is obtained by calculation) and measured through the projection lens 16 described above. Subtracted from wavefront aberration.

  In order to accurately measure the wavefront aberration, a so-called fringe scan method may be used. The modulation of the phase required in the fringe scanning method may be performed by changing the optical path length of the test light path of the test light, for example, by moving the mirror 25 by the wavelength by the PZT element 26. Alternatively, the mirror 22 on the reference light path side may be moved.

  A so-called electronic moire method may be used as a fringe processing method for interference fringes. In this case, the PZT element 26 is not required, and so-called carrier stripes may be generated by tilting the mirror 25, for example.

  In this embodiment, by driving a predetermined lens in the projection lens 16 in the optical axis direction, the direction orthogonal to the optical axis, or the tilt direction from the wavefront aberration of the projection lens 16 measured by this optical performance measurement method, for example, Correction of spherical aberration, coma aberration, astigmatism, etc. is performed.

  FIG. 3 is a schematic diagram of a main part of an interferometer 302 according to Embodiment 2 of the present invention.

  In this embodiment, the interferometer 29 in FIG. 1 is a Mach-Zehnder type lateral shear interferometer 302. Only the light beam transmitted through the half mirror 21 is transmitted to the plane parallel plate 301 inclined slightly, and the light beam is shifted laterally. Then, the light is reflected by the mirror 25 and is incident on the half mirror 24. On the other hand, the light beam reflected by the half mirror 21 that has not been laterally shifted is reflected by the mirror 22, is incident on the half mirror 24, is caused to interfere with the previously laterally shifted light beam, and the interference fringes are observed by the CCD camera 28. The observed interference fringes are differential values of the sum of wavefront aberrations of the projection lens 16 and other optical systems. Therefore, if this is integrated and the wavefront aberration corresponding to the system error is subtracted as in the first embodiment, the wavefront aberration of only the projection optical system (projection lens) 16 can be obtained. If the optical path length is adjusted on either the transmission side or the reflection side of the half mirror 21, interference measurement can be sufficiently performed even with an Ex laser with a short coherence distance, i-line with a spectral width of several nm, or the like.

  FIG. 4 is a diagram for explaining a part of the interferometer according to the third embodiment of the present invention.

  The interferometer in this embodiment is also a lateral shear type interferometer. A light beam transmitted through the half mirror 10 in FIG. The reflected light beams from the front and back surfaces of the plane parallel plate 401 are made to interfere. Since the light beams from the front and back surfaces are shifted laterally with respect to the traveling direction, the interference fringes observed as in the second embodiment are the differential values of the wavefront aberration of the sum of the projection lens 16 and other optical systems. . Therefore, the wavefront aberration of only the projection lens 16 is obtained by similarly integrating and subtracting the wavefront aberration corresponding to the system error.

  In the configuration of the present embodiment, the test optical path and the reference optical path are the same common optical path up to the CCD camera surface 28, and extremely stable measurement is possible. Since the optical path length difference between the reference light and the test light is equivalent to about twice the thickness of the parallel flat plate 401, it is effective when an excimer laser having a coherence distance of about several centimeters is used as the light source.

  FIG. 5 is a schematic diagram of a main part of an interferometer according to Embodiment 4 of the present invention.

  In the present embodiment, the interferometer 29 in FIG. 1 is a modified Twiman Green interferometer 501. The light beam that has passed through the half mirror 21 is collected on the spatial filter 505 by the collimator lens 504, and after passing through the spatial filter 505, is reflected by the spherical mirror 506 having the center of curvature in the pinhole of the spatial filter 505 and again. Condensed and transmitted above. The pinhole diameter of the spatial filter 505 is set to be equivalent to an Airy disk determined by the numerical aperture of the collimator lens 504. As a result, the re-emitted light from the collimator lens 504 becomes an almost aberration-free plane wave and is reflected by the half mirror 21 to be used as a reference wave (strictly speaking, the output wave surface from the collimator lens 504 has a collimator lens 504 with a wave front. Transmitted wavefront aberration is included).

  On the other hand, the light beam reflected by the half mirror 21 is reflected by the plane mirror 502, passes through the half mirror 21, becomes a test wave, interferes with the reference wave, and forms an interference fringe on the camera 508 by the imaging lens 507. Observed.

  At this time, as in the first embodiment, the plane mirror 502 is moved by about the wavelength by the PZT element 503 and subjected to fringe processing by a so-called fringe scan method. Here, as described in the first embodiment, the electronic moire method may be used as the fringe processing method. In this case, the plane mirror 502 may be tilted in advance to generate carrier stripes.

  FIG. 6 is a schematic view of the essential portions of Embodiment 5 of the present invention.

  In each of the embodiments described above, the interferometer is configured on the reticle (first object) side. However, in the present embodiment, the interferometer is configured on the wafer stage (second object) side, and the spherical mirror is positioned on the reticle 14 side. 605 is arranged.

  In the case of this embodiment, the light from the exposure light source 1 is routed through the beam shaping optical system to the optical system 602 and guided to the interferometer 29 by the optical path switching mirror 601 during wavefront measurement. The measurement optical path is simply the reverse of the optical path in FIG. 1, and is basically the same. As the interferometer 29, the radial shear type interferometer 29 of the same type as in the first embodiment is used, but a lateral shear type or a Twiman Green type as shown in FIGS. 3, 4 and 5 may be used.

  By disposing the interferometer 29 on the wafer stage side as in the present embodiment, it is possible to move away from the illumination optical system 5, and it is less susceptible to heat, and more stable interference measurement is possible. Further, since the NA of the collimator lens 604 is larger than the NA of the spherical mirror 605, the shape (system error) of the entire surface of the spherical mirror 605 can be obtained at the time of system error measurement by the so-called system error measurement method. When the interferometer is arranged on the reticle side, the shape of the spherical mirror can be obtained only for one part of NA actually used).

  FIG. 7 is a schematic view of the essential portions of Embodiment 6 of the present invention.

  In this embodiment, the light beam from the light source 1 is guided to the wafer stage side by the condenser lens 604 via the beam shaping optical system 2, the optical path switching mirror 601, the drawing optical system 602, and the mirrors 701 and 603, and collected on the wafer surface 17. I am making it light. Then, the light beam from the wafer surface 17 is imaged on the reticle surface 15 by the projection optical system 16, and the wavefront aberration is measured by the interferometer 29 similar to that shown in FIG. 1 in which the light beam therefrom is arranged on the reticle side. Yes. In the present embodiment, a single-pass interferometer is configured to guide the light beam that has once passed through the projection optical system 16 to the interferometer.

  FIG. 8 is a schematic view of the essential portions of Embodiment 7 of the present invention.

  In this embodiment, the light beam from the exposure light source 1 is guided to the reticle 15 side by the beam shaping optical system 2, the switching mirror 5, the drawing optical system 6, the mirror 801, and the lens 802, and is condensed on the surface of the reticle 15. Then, the wavefront aberration is measured by an interferometer 29 similar to that shown in FIG. 1 in which the light beam imaged on the wafer 17 by the projection optical system 16 is arranged on the wafer 17 side. In this embodiment, a single-path interferometer is configured as in the fifth embodiment, but there is a difference in the arrangement of the interferometer.

  In the first, second, third, fourth, and sixth embodiments in which the interferometer is disposed on the reticle side in each of the embodiments described above, the collimator lenses 12 and 703 that guide the light flux from the reticle surface to the interferometer are as follows. You may share with the objective lens of the TTR alignment scope mounted in the exposure apparatus. In this case, a half mirror or a switching mirror may be arranged after passing through the collimator lens to switch between wavefront measurement and alignment observation.

  In any of the embodiments described above, the collimator lens at the time of wavefront measurement obtained by the rotationally asymmetric component of the wavefront obtained by wavefront measurement, particularly the tilt component and rotationally symmetric component, particularly the defocus component and the length measuring device. 12 and the XYZ coordinates of the spherical mirror 20 can determine the field curvature and distortion of the projection lens 16.

  In the present invention, an interval adjustment mechanism and an eccentricity adjustment mechanism provided in the projection lens 16 based on the wavefront aberration, field curvature, and distortion of the projection lens 16 measured by the interferometer shown in the first to seventh embodiments. Etc. to adjust / control the desired aberration amount.

  As described above, according to each embodiment, an interferometer that can easily and accurately measure and inspect the optical performance of the projection optical system in a short time under various illumination conditions on the projection exposure apparatus main body is installed. The projection exposure apparatus can be achieved.

Schematic diagram of main parts of Embodiment 1 of the present invention Detailed view showing path of light flux to reticle surface in FIG. Explanatory drawing of the interferometer which concerns on Embodiment 2 of this invention Explanatory drawing of the interferometer which concerns on Embodiment 3 of this invention Explanatory drawing of the interferometer which concerns on Embodiment 4 of this invention. Main part schematic of Embodiment 5 of this invention Main part schematic of Embodiment 6 of this invention Main part schematic of Embodiment 7 of this invention

Explanation of symbols

1: Exposure light source 2: Beam shaping optical system 3: Optical path switching mirror 4: Incoherent unit 5: Illumination optical system 6: Drawing optical system 7: Condensing lens 8: Spatial filter 9: Collimator lens 10: Half mirror 11 : Reflection mirror 12: Collimator lens 13: XYZ stage 14: Collimator unit 15: Reticle surface 16: Projection lens 17: Wafer surface 18: Wafer chuck 19: Wafer stage 20: Spherical mirror 21: Half mirror 22: Reflection mirror 23 : Beam expander 24: Half mirror 25: Reflection mirror 26: PZT element 27: Imaging lens 28: CCD camera 201: y stage 202: x stage 203: z stage 204: reflection mirror 205: reflection mirror 206: half mirror 10 Light from 301: Parallel plane plate with wedge 302: Lateral shear type interferometer 401: Parallel plane plate with wedge 402: Lateral shear type interferometer 501: Modified twiman green type interferometer 502: Plane mirror 503: PZT element 504: Condensing lens 505: Spatial filter 506: Spherical mirror 507: Imaging lens 508: CCD camera 601: Optical path switching mirror 602: Drawing optical system 603: Reflection mirror 604: Condensing lens 605: Reflection mirror 701: Reflection mirror 702: Reflection mirror 703: Collimator lens 704: Collimator unit 801: Reflection mirror 802: Condensing lens 803: Condensing lens unit 804: Collimator lens 805: Reflection mirror

Claims (1)

An exposure apparatus comprising: an illumination system that illuminates a first object with exposure light from an exposure light source; and a projection optical system that projects a pattern of the first object onto a second object. In the optical performance measurement method of the projection optical system that measures with an interferometer mounted on the apparatus,
Observing interference fringes formed by generating reference light from exposure light from the exposure light source that has passed through the projection optical system and causing the reference light to interfere with the exposure light that has passed through the projection optical system And a step of measuring the optical performance of the projection optical system.