JP2008252128A - Projection exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exposure device capable of directly measuring the wave aberration of a projection optical system in a projection exposure device on the projection exposure device. <P>SOLUTION: The device is provided with a projection optical system projecting the pattern of a first object on a second object and an interferometer measuring the optical characteristics of the projection optical system. The interferometer includes an objective lens by which light from an illumination source is led from the first and second object sides to the projection optical system. The objective lens is disposed independently of the other lenses of the interferometer and can move along the surface of the first object, the surface having the pattern. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a projection exposure apparatus for manufacturing semiconductors, and more particularly to a projection exposure apparatus for manufacturing semiconductors used in a lithography process for manufacturing semiconductor elements and liquid crystal display elements.

  Along with the increase in the density of integrated circuits, projection exposure apparatuses for manufacturing semiconductors are required to project and expose a circuit pattern on a reticle surface onto a wafer surface with high resolution. In order to achieve high resolution, the projection optical system of the projection exposure system has a higher NA and shorter wavelength, and the projection exposure system with NA 0.6 using a KrF excimer laser (λ = 248 nm) as the light source has a resolution of 0.18 μm. It came to realize resolution power.

  Furthermore, in recent years, super-resolution exposure technology using deformed illumination such as annular illumination and quadrupole illumination has been developed, and the resolution is about to reach 0.15 to 0.1 μm.

  In order to manufacture a high-resolution projection optical system, precise adjustment is required after the projection optical system is assembled. In other words, the projection optical system performs optical evaluations such as spherical aberration, coma aberration, distortion, and exposure magnification, and adjusts the distance and decentration between predetermined lenses and lens groups to pursue performance that satisfies the specifications. The optical performance is evaluated by projecting a mask pattern image onto a resist (photosensitive member) coated on a photosensitive substrate such as a wafer, developing it, and observing the obtained resist image.

  As another method, the wavefront aberration of the projection optical system is also measured using an interferometer, but a special device is required.

  As described above, in the conventional projection exposure apparatus, it is necessary to check the quality of the resist image in order to adjust the final lens performance of the projection optical system. However, determining the quality of a resist image requires a very complicated process of printing a pattern on a resist-coated wafer, developing the pattern, and observing the resist image with a scanning electron microscope (SEM). there were.

  In addition, after the optical adjustment and evaluation are completed, the projection optical system is mounted on the projection exposure apparatus after fixing the lens and the lens group so as not to change. Therefore, the projection exposure optical system cannot be adjusted after the projection optical system is mounted on the projection exposure apparatus. However, in the actual wafer exposure process, there is a problem that the projection optical system is warmed by the illumination light along with the exposure, and the image performance changes.

  Conventionally, there is no means for measuring the wavefront aberration of the projection optical system after it is mounted on the projection exposure apparatus, and therefore the target of readjustment of image performance cannot be determined, so only measures such as stopping the apparatus and suppressing changes can be performed. Is the current situation.

In view of the above problems, the present invention includes mounting an interferometer for measuring optical characteristics of a projection optical system on a projection exposure apparatus body, and directly measuring the optical characteristics of the projection optical system on the projection exposure apparatus body. It is characterized by being possible.

  The specific configuration of each claim is as follows.

A projection exposure apparatus according to a first aspect of the present invention includes: a projection optical system that projects a pattern of a first object onto a second object; and an interferometer that measures optical characteristics of the projection optical system,
The interferometer includes an objective lens that guides light from a light source from the first object side or the second object side to the projection optical system, and the objective lens is independent of other lenses of the interferometer. The pattern of the first object is movable along the surface on which the pattern is located.

  The invention of claim 2 is characterized in that, in the invention of claim 1, the interferometer uses the light reflected by the final surface of the objective lens as a reference light.

  According to a third aspect of the present invention, in the first aspect of the invention, the interferometer includes a half mirror that divides the light from the light source into two lights, and a mirror that reflects the light transmitted through the half mirror as reference light. The light reflected by the half mirror is guided to the objective lens.

  According to a fourth aspect of the present invention, there is provided the illumination optical system according to the first aspect of the invention, wherein the first object is illuminated with exposure light from an exposure light source, and the light source of the interferometer is a light source different from the exposure light source. It is characterized by being.

  According to a fifth aspect of the present invention, in the invention of the fourth aspect, the objective lens collects and diverges light from the light source of the interferometer that converges and diverges on a surface on which the pattern of the first object is located. It is characterized by doing.

  According to the present invention, it is possible to provide an exposure apparatus that can perform exposure while maintaining imaging performance at a high level.

  FIG. 1 is a schematic diagram of a projection exposure apparatus according to Embodiment 1 of the present invention, in which the present invention is applied to an excimer stepper having an exposure wavelength of 248 nm.

  In the figure, reference numeral 1 denotes a KrF excimer laser which is a light source for exposure. The light emitted from the light source 1 is shaped into a beam shape symmetric with respect to the optical axis by the beam shaping optical system 2. The light having a reduced coherence distance by the incoherent unit 3 irradiates the reticle (first object) 15 through the illumination optical system 4. A desired pattern is drawn on the reticle 15, and an image is formed on the wafer (second object) 17 by the projection optical system 16. A chuck 18 for mounting the wafer 17 is fixed to the stage 19. In addition to the above, the projection exposure apparatus is equipped with an alignment detection system, a focus detection system, and the like, which are omitted in FIG. 1 for the sake of simplicity. The reticle 15 is also referred to as “reticle pattern equivalent position 15” or “first object plane 15”. The wafer 17 is also referred to as “imaging position 17” or “second object plane 17”.

  Next, the configuration of the interferometer for wavefront measurement of the projection optical system, which is a feature of the present invention, will be described. FIG. 1 shows an embodiment in which a Fizeau interferometer is configured on the reticle side.

  In general, when the exposure light source is an excimer laser, the coherence distance is about several tens of millimeters, whereas the total length of the projection optical system to be measured is about 1000 mm, and a Fizeau interferometer cannot be constructed. Therefore, the present invention is characterized in that a dedicated light source different from the exposure light source is arranged as the light source of the interferometer for wavefront measurement of the projection optical system.

  6 is a dedicated light source for the interferometer. Since the exposure wavelength is 248 nm, a beam of 248 nm, which is the second harmonic of the Ar laser, is used in this embodiment. The Ar laser beam forms a parallel beam by a collimator lens 9 through a condensing system 7 and a pinhole 8 via a mirror. Since 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, the light beam emitted from the pinhole 8 becomes an almost ideal spherical wave. Since the collimator lens 9 is designed and manufactured with substantially no aberration, it is considered that the light beam emitted from the collimator lens 9 is emitted as an ideal plane wave. In the configuration of FIG. 1, the light from the light source 6 of the interferometer may be guided to the pinhole 8 using a polarization maintaining fiber. The formed parallel beam enters the objective lens 12 through the half mirror 10 and the mirror 11. The mirror 11 and the objective lens 12 are held on the XYZ stage 5. Here, the objective lens 12 guides light from the light source 6 to the projection optical system 16 from the reticle 15 side.

  As a means for aligning the reticle 15 and the wafer 17, a TTR alignment scope for detecting the position of the wafer 17 through the reticle 15 is held and mounted on the stepper by a mechanism that can be driven to an arbitrary position on the reticle 15. In this embodiment, this TTR alignment scope is also used as the objective lens 12 for the interferometer. For this reason, the objective lens 12 is movable along the surface (reticle pattern equivalent position 15) on which the pattern of the reticle 15 is located, independently of the other lenses of the interferometer.

  When the TTR alignment scope is used as a detection optical system, the objective lens 12 for the interferometer is retracted out of the exposure light beam of the projection optical system 16 during exposure, and moves into the optical path of the projection optical system during wavefront aberration measurement It can be performed. Therefore, if a mechanism capable of driving the objective lens of the TTR alignment scope to an arbitrary position on the reticle (first object plane) is used, a plurality of points in the screen of the exposure area can be measured.

  The radius of curvature of the final surface on the reticle side of the objective lens 12 is the same as the distance to the reticle pattern corresponding position 15, and the reflected light from the final surface is condensed as reference light via the mirror 11 and the half mirror 10. The light is guided to the CCD light receiving surface 28 through the system 27.

On the other hand, the beam that has passed through the objective lens 12 forms an image at the position 15 corresponding to the reticle pattern, and then forms an image again at the position of the wafer (second object plane) 17 by the projection optical system 16. A spherical mirror 20 is disposed on the stage 19, and the radius of curvature of the spherical mirror 20 is matched with the distance from the imaging position 17 of the projection optical system. Accordingly, the light reflected by the spherical mirror 20 is condensed again at the imaging position 17 of the projection optical system 16 and returns to the projection optical system 16, and the light collection system 27 is passed through the objective lens 12, the mirror 11, and the half mirror 10. As described above, the light is guided to the CCD light receiving surface 28. Since the beam that has passed through the projection optical system 16 interferes with the reference beam reflected by the final surface of the objective lens 12, the wavefront of the projection optical system can be measured. Here, the objective lens 12 condenses on the surface where the pattern surface of the reticle 15 is located, and the diverging light is converted into parallel light.

  In addition, although the concave mirror type is shown as the spherical mirror 20, an interferometer can also be configured by a convex mirror type spherical mirror. At this time, the center position of the convex mirror coincides with the imaging position 17, and the position to be placed is opposite to the concave mirror. Further, as a plane mirror, even if the vertex is reflected, only a rotationally symmetric component of wavefront aberration can be obtained.

  The wavefront error of the interferometer itself, such as the final surface of the objective lens 12, the spherical mirror 20, etc., is obtained by measuring the wavefront in advance using the system error method in order to distinguish it from the wavefront aberration of the projection optical system 16 to be measured. It is necessary to keep it. By correcting the wavefront error by subtracting it from the measurement result of the projection optical system 16, the wavefront of the projection optical system 16 can be obtained accurately.

  In order to further improve the measurement accuracy, the fringe scan method is used for the measurement of the interferometer. A fringe scan can be realized by driving the PZT elements in the 19 wafer stages 19 and moving the mirror 20 about the wavelength in the direction of the optical axis to perform phase modulation of the wavefront. As the moving means in the optical axis direction of the spherical mirror 20, the focusing moving means of the projection exposure apparatus can be used.

  Information on the wavefront aberration at the measurement point can be obtained from the measurement of the wavefront of the projection optical system. Furthermore, if the objective lens 12 obtained from the length measuring device at the time of wavefront measurement, the rotationally asymmetric component of the wavefront aberration obtained by measuring the XYZ coordinates of the spherical mirror 20 and the wavefront of the projection optical system 16, and the rotationally symmetric component are combined, It is also possible to determine the field curvature and distortion, which are the relationship between the measurement points of the projection optical system.

  The curvature of field of the projection optical system can be obtained by wavefront measurement of a plurality of points in the screen of the projection optical system. That is, if the coordinate position of the detection optical system of the interferometer at the time of wavefront measurement, the wavefront measured by the interferometer, and the coordinate position of the spherical mirror 20 with respect to the optical axis direction of the projection optical system 16 are known, the information of the plurality of points can be obtained. The field curvature can be calculated. A particularly important wavefront aberration component in the calculation of the field curvature is a rotationally symmetric power component (defocus component) of the measured wavefront.

  The distortion of the projection optical system 16 can also be obtained by wavefront measurement of a plurality of points in the screen of the projection optical system. That is, if the coordinate position of the detection optical system of the interferometer at the time of wavefront measurement, the wavefront measured by the interferometer, and the coordinate position of the spherical mirror 20 in the direction orthogonal to the optical axis of the projection optical system 16 are known, the multiple points The distortion of the projection optical system can be calculated from the above information. A component of wavefront aberration that is particularly important in the calculation of distortion is a rotationally asymmetric component (tilt component) of the measured wavefront.

  If a predetermined lens in the projection optical system 16 is driven from the measurement result, the aberration of the projection optical system can be adjusted and controlled to a desired state.

  FIG. 2 is a schematic diagram of Embodiment 2 of the present invention. This embodiment has an excimer stepper configuration with an exposure wavelength of 248 nm as in the first embodiment, but is characterized in that a Twiman-Green interferometer is configured on the reticle side.

  6 is a light source for the interferometer, which extracts a 248 nm beam that is the second harmonic of the Ar laser. The laser beam is converted into a parallel beam by an optical system 9 through a condensing system 7 and a pinhole 8 via a mirror. The parallel beam is divided into two beams by the half mirror 10. The beam that has passed through the half mirror 10 is reflected by the mirror 29 as a reference beam. This time, after being reflected by the half mirror 10, it passes through the condensing system 27 and is guided to the CCD light receiving surface 28.

  On the other hand, the beam reflected by the half mirror 10 enters the objective lens 13 via the mirror 11. The beam that has passed through the objective lens 13 forms an image at the position 15 corresponding to the reticle pattern, and then forms an image again at the position of the wafer 17 by the projection optical system 16. A spherical mirror 20 is disposed on the stage 19, and the radius of curvature of the spherical mirror 20 matches the distance from the imaging position 17 of the projection optical system 16. Therefore, the light reflected by the spherical mirror 20 is condensed again at the image forming position of the projection optical system 16 and returns to the projection optical system 16, and passes through the condenser system 27 via the objective lens 13, the mirror 11, and the half mirror 10. To the CCD light receiving surface 28. The beam that has passed through the projection optical system 16 interferes with the aforementioned reference beam, and the wavefront of the projection optical system can be measured.

The correction of the measured wavefront system error, the use of fringe scanning for improving measurement accuracy, the use of a convex mirror type spherical mirror, the calculation of the aberration of the projection optical system, and the like are the same as in the first embodiment. By driving a predetermined lens in the projection optical system 16 based on the measurement result of the wavefront, the aberration amount of the projection optical system can be adjusted and controlled to a desired state.

  FIG. 3 is a schematic diagram of Embodiment 3 of the present invention.

  As in the first embodiment, the present embodiment is characterized by an excimer stepper having an exposure wavelength of 248 nm and a radial shear type interferometer on the reticle side.

  6 is a light source for the interferometer, which extracts a 248 nm beam that is the second harmonic of the Ar laser. The laser beam passes through a condensing system 7 and a pinhole 8 via a mirror, and a parallel beam is formed by the optical system 9. This parallel beam is reflected by the half mirror 10 and enters the objective lens 13 via the mirror 11. The beam that has passed through the objective lens 13 forms an image at the position 15 corresponding to the reticle pattern, and then forms an image again at the position of the wafer 17 by the projection optical system 16. A spherical mirror 20 is disposed on the stage 19, and the radius of curvature of the spherical mirror 20 matches the distance from the imaging position 17 of the projection optical system 16. Therefore, the light reflected by the spherical mirror 20 is condensed again at the imaging position 17 of the projection optical system 16 and returns to the projection optical system 16, and passes through the objective lens 13, the mirror 11, and the half mirror 10, and thereafter in the interferometer. Led to.

  The beam incident on the interferometer is split into two beams by the 1: 1 half mirror 21. The reflected beam is expanded by the beam expander 23 via the mirror 22. A magnification of 10 times or more is usually used. Since the beam is expanded, the beam can be regarded as an almost ideal plane wave, and is guided to the CCD light receiving surface 28 through the half mirror 24 and the condensing system 27 as a reference beam.

  On the other hand, the beam transmitted through the half mirror 21 is reflected as a measurement beam by the mirror 25 and the half mirror 24 and is combined with the reference beam, and is guided to the CCD light receiving surface 28 through the condensing system 27. For fine adjustment of the interferometer, the mirror 25 is disposed on a mechanism 26 capable of adjusting tilt and parallel eccentricity. The measurement beam interferes with the aforementioned reference beam, and the wavefront of the projection optical system 16 can be measured.

The correction of the measured wavefront system error, the use of a convex mirror type spherical mirror, the calculation of the aberration of the projection optical system, and the like are the same as in the first embodiment. By driving a predetermined lens in the projection optical system 16 based on the measurement result of the wavefront, the aberration amount of the projection optical system can be adjusted and controlled to a desired state.

  FIG. 4 is a schematic diagram of Embodiment 4 of the present invention. As in the first embodiment, this embodiment is characterized in that a Fizeau interferometer is formed on the wafer side based on the configuration of an excimer stepper with an exposure wavelength of 248 nm.

  6 is a light source for the interferometer, which extracts a 248 nm beam that is the second harmonic of the Ar laser. The laser beam passes through a condensing system 7 and a pinhole 8 via a mirror, and a parallel beam is formed by the optical system 9. The parallel beam is incident on the objective lens 32 via the half mirror 10 and the mirror 31. The radius of curvature of the final surface of the objective lens 32 on the wafer side is the same as the distance to the imaging position 17 on the wafer side of the projection optical system 16, and the reflected light from the final surface is used as a reference light for the mirror 31 and the half mirror 10. Through the condensing system 27 and led to the CCD light receiving surface 28.

  On the other hand, the beam transmitted through the objective lens 32 forms an image on the wafer 17 and then forms an image again at the position 15 corresponding to the reticle pattern by the projection optical system 16. A spherical mirror 33 is disposed on the stage 34 on the reticle side, and the radius of curvature of the spherical mirror 33 is made to coincide with the distance from the imaging position 15 of the reticle pattern of the projection optical system 16. Therefore, the light reflected by the spherical mirror 33 is condensed again at the position 15 corresponding to the reticle pattern of the projection optical system 16 and returns to the projection optical system 16, and is collected through the objective lens 32, the mirror 31 and the half mirror 10. To the CCD light receiving surface 28. The beam that has passed through the projection optical system 16 interferes with the reference beam reflected by the final surface of the objective lens 32 described above, and the wavefront of the projection optical system 16 can be measured.

  Since the detection optical system is configured on the wafer side, it is possible to measure a plurality of points in the screen of the exposure region using the XY movability of the wafer stage. As the wafer stage moves, the reticle-side spherical mirror 33 is moved to a predetermined position by the stage. Therefore, not only the measurement of the wavefront of each point but also the wavefront aberration such as the field curvature and distortion of the projection optical meter can be calculated and obtained from the measurement data of a plurality of points.

  The correction of the measured wavefront system error, the use of fringe scanning for improving the measurement accuracy, the calculation of the aberration of the projection optical system, and the like are the same as in the first embodiment. Further, a modification in which a convex mirror type spherical mirror is arranged on the reticle side can be prepared in advance. However, in the case of the present embodiment, fringe scanning is realized by driving the PZT element in the stage 34 on the reticle side and moving the mirror 33 about the wavelength in the optical axis direction to perform phase modulation of the wavefront. A fringe scan can also be realized by driving the PZT element in the wafer stage 19 and moving the objective lens 32 by about the wavelength in the optical axis direction to perform phase modulation of the wavefront.

  By driving a predetermined lens in the projection optical system 16 based on the measurement result of the wavefront, the aberration amount of the projection optical system can be adjusted and controlled to a desired state.

  FIG. 5 is a schematic diagram of Embodiment 5 of the present invention.

  As in the first embodiment, the present embodiment is characterized by an excimer stepper having an exposure wavelength of 248 nm and a single-pass radial shear interferometer on the reticle side.

  6 is a light source for the interferometer, which extracts a 248 nm beam that is the second harmonic of the Ar laser. The laser beam enters the objective lens 13 via the mirror 11. The beam transmitted through the objective lens 13 is imaged on the wafer 17 and then imaged at the reticle pattern corresponding position 15 by the projection optical system 16. The light imaged at the position 15 corresponding to the reticle pattern is guided into the subsequent interferometer through the objective lens 13, the mirror 11, and the half mirror 10.

  The beam incident on the interferometer is split into two beams by the 1: 1 half mirror 21. The reflected beam is expanded by the beam expander 23 via the mirror 22. A magnification of 10 times or more is usually used. Since the beam is expanded, the beam can be regarded as an almost ideal plane wave, and is guided to the CCD light receiving surface 28 through the half mirror 24 and the condensing system 27 as a reference beam.

  On the other hand, the beam transmitted through the half mirror 21 is reflected as a measurement beam by the mirror 25 and the half mirror 24 and is combined with the reference beam, and is guided to the CCD light receiving surface 28 through the condensing system 27. For fine adjustment of the interferometer, the mirror 25 is disposed on a mechanism 26 that can adjust tilt and parallel eccentricity. The measurement beam interferes with the aforementioned reference beam, and the wavefront of the projection optical system 16 can be measured.

  Correction of the measured wavefront system error, calculation of the aberration of the projection optical system, and the like are the same as in the first embodiment. By driving a predetermined lens in the projection optical system 16 from the measurement result of the wavefront, the aberration amount of the projection optical system 16 can be adjusted and controlled to a desired state.

  As described above, in the present invention, the wavefront measurement of the projection optical system can be performed on the projection exposure apparatus body by mounting the interferometer for measuring the optical characteristics of the projection optical system on the projection exposure apparatus body.

  By measuring the optical characteristics of the projection optical system on the projection exposure apparatus main body, it becomes possible to check the state of the projection optical system on the spot, and the correspondence according to the state of the projection optical system can be performed on the projection exposure apparatus main body. It became possible to take.

  That is, it is possible to determine, for example, whether to correct the aberration state of the projection optical system or stop the apparatus according to the measurement result of the optical characteristics. Therefore, it is possible to perform exposure while maintaining the imaging performance of the projection exposure apparatus at a high level, and it is possible to obtain a great effect in the manufacture of semiconductor elements.

The figure which shows the structure of the projection exposure apparatus of Embodiment 1 of this invention. The figure which shows the structure of the projection exposure apparatus of Embodiment 2 of this invention. The figure which shows the structure of the projection exposure apparatus of Embodiment 3 of this invention. The figure which shows the structure of the projection exposure apparatus of Embodiment 4 of this invention. The figure which shows the structure of the projection exposure apparatus of Embodiment 5 of this invention.

Explanation of symbols

1 Light source for exposure
2 beam shaping optics
3 Incoherent unit
4 Lighting system
5 XYZ stage
6 Light source for wavefront measurement
7 Condensing lens
8 pinhole
9 Collimator lens
10 half mirror
11 Mirror
12 Objective lens
13 Objective lens
15 Reticle (Reticle pattern equivalent position)
16 Projection optics
17 Wafer (imaging position)
18 Wafer chuck
19 Wafer stage
20 Spherical mirror
21 half mirror
22 mirror
23 Beam Expander
24 half mirror
25 mirror
26 Mirror eccentricity adjustment mechanism
27 Condensing lens
28 CCD receiver
31 mirror
32 Objective lens
33 Spherical mirror

Claims (5)

A projection optical system that projects a pattern of the first object onto the second object;
An interferometer for measuring optical characteristics of the projection optical system,
The interferometer includes an objective lens that guides light from a light source from the first object side or the second object side to the projection optical system,
The projection exposure apparatus, wherein the objective lens is movable along a plane on which the pattern of the first object is located, independently of other lenses of the interferometer.   The projection exposure apparatus according to claim 1, wherein the interferometer uses light reflected by a final surface of the objective lens as reference light.   The interferometer includes a half mirror that divides light from the light source into two lights, and a mirror that reflects light that has passed through the half mirror as reference light, and the light reflected by the half mirror is The projection exposure apparatus according to claim 1, wherein the projection exposure apparatus is guided to an objective lens. An illumination optical system that illuminates the first object with exposure light from an exposure light source;
The projection exposure apparatus according to claim 1, wherein the light source of the interferometer is a light source different from the exposure light source. 5. The projection exposure apparatus according to claim 4, wherein the objective lens collimates the light from the light source of the interferometer that converges and diverges on a surface on which the pattern of the first object is located. .