JP2008064770A - Fizeau type interferometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aspherical interferometer of high reproducibility in measurement. <P>SOLUTION: This Fizeau type interferometer for measuring the shape of an optical surface of an optical element comprises a reference surface of the aspherical shape and a holding member for integrally holding the reference surface and the optical surface in a state where the reference surface is made adjacent to the optical surface. Then, light from the optical surface and light from the reference surface are made to interfere with each other. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a surface shape measuring interferometer for measuring the surface shape of an optical element constituting a projection optical system suitable for an exposure apparatus called EUVL, which uses soft X-rays having a wavelength of around 10 nm as exposure light.

  Conventionally, light of 193 nm or more has been used as exposure light in a lithography apparatus used when a device such as a semiconductor element, a liquid crystal display element, or a thin film magnetic head is manufactured by a lithography process. The surface of the lens used for the projection optical system in such a lithography apparatus is usually a spherical surface, and the shape accuracy of the lens surface is 1 to 2 nm RMS.

  In recent years, the miniaturization of patterns on semiconductor circuit elements has progressed, and in order to achieve further miniaturization, there has been a demand for an exposure apparatus that uses a shorter wavelength than ever before. Soft X-rays having a wavelength of 11 to 13 nm are required. There is a demand for development and manufacture of the projection exposure apparatus used.

  In this soft X-ray wavelength region, a lens (refractive optical element) cannot be used for absorption, and a reflection type projection optical system consisting entirely of a reflective surface must be used as the projection optical system. Further, in the soft X-ray wavelength range, only about 70% of the reflectance of the reflecting surface can be expected, so that only three to six reflecting surfaces in the projection optical system can be used.

  Therefore, in the projection optical system, in order to make an optical system free from aberrations with a small number of reflecting surfaces, all the reflecting surfaces are made aspherical. Here, in the case of a projection optical system using four reflecting surfaces, 0.23 nm RMS is required as the shape accuracy of the reflecting surfaces. As a method for forming this aspherical shape, it is conceivable that an actual surface shape is measured using an interferometer, and the shape is made with a correction polishing machine in order to make this surface shape a desired shape.

  However, the measurement accuracy of the conventional interferometer for surface shape measurement is 0.3 nmRMS with repeatability, 1 nmRMS with spherical accuracy, and 10 nmRMS with aspherical accuracy, which cannot satisfy the required accuracy. As a result, a projection optical system with desired performance could not be manufactured.

  Accordingly, an object of the present invention is to obtain an aspherical interferometer with good reproducibility.

In order to achieve the above object, a Fizeau interferometer according to the present invention is a Fizeau interferometer for measuring the shape of the optical surface of an optical element, for example, as shown in FIG.
An aspherical reference surface;
A holding member that integrally holds the reference surface and the optical surface in a state in which the reference surface and the optical surface are close to each other;
The light from the optical surface interferes with the light from the reference surface.

Further, the Fizeau interferometer according to a preferred embodiment of the present invention is the above Fizeau interferometer,
A light source that supplies light toward the reference surface and the optical surface, and has a main body that interferes with the light via the reference surface and the optical surface;
The holding member and the main body are spatially separated.

Further, the Fizeau interferometer according to a preferred embodiment of the present invention is the above Fizeau interferometer,
The distance between the reference surface and the optical surface is 1 mm or less.

Further, the Fizeau interferometer according to a preferred embodiment of the present invention is the above Fizeau interferometer,
The distance between the reference surface and the optical surface is variable.

Further, the Fizeau interferometer according to a preferred embodiment of the present invention is the above Fizeau interferometer,
A position detection system for detecting a positional relationship between the reference surface and the optical surface is further included.

Further, the Fizeau interferometer according to a preferred embodiment of the present invention is the above Fizeau interferometer,
The interval between the reference surface and the optical surface is fixed and is 10 μm or less.

  According to the present invention, it is possible to obtain an aspherical interferometer with good reproducibility, to achieve highly accurate wavefront aberration measurement, and to improve the absolute accuracy of surface accuracy measurement in an aspherical interferometer. it can. It is also possible to produce a projection optical system with excellent performance.

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[First Embodiment]
FIG. 1 is a diagram showing an interferometer according to the first embodiment, and FIG. 2 is a diagram showing a main part of the interferometer of FIG. The interferometer of the first embodiment shown in FIG. 1 is an interferometer for measuring an aspherical shape.

  In FIG. 1, laser light from a laser 1 becomes parallel light having a desired diameter via a lens system and enters a null element 2. The null element 2 emits a wavefront having a shape substantially equal to the shape of the test surface, and the wavefront converted into a predetermined aspheric shape has an aspheric reference surface 3 and an aspheric test surface 4. Perpendicularly incident on Here, the aspherical reference surface 3 has substantially the same shape as the aspherical test surface (the concavities and convexities are reversed), and the incident light is amplitude-divided on the surface to detect one wavefront. The light wave is directed to the surface 4 and the other wavefront is returned to the original optical path as a reference wavefront.

  The aspherical reference surface 3 is disposed close to the test surface 4, and at this time, the aspherical reference surface 3 and the test surface 4 have complementary shapes. The aspherical reference surface 3 and the test surface 4 are integrally supported by a holder 6.

  Now, the light from the aspherical reference surface 3 is reflected by the test surface 4 and enters the aspherical reference surface 3 again as a measurement wavefront.

  The reference wavefront and the measurement wavefront described above are detected from an imaging element such as a CCD after being emitted from an optical element having an aspherical reference surface 3, incident on a null element 2 and reflected by a beam splitter. Interference fringes are formed on the detection surface of the device 5. By processing the interference fringes with a computer, the shape error of the test surface can be measured.

  In the interferometer of FIG. 1, the main body that houses from the light source 1 to the null element 2 and the holder 6 are supported by separate members so as to be spatially separated.

  The interferometer of FIG. 1 is basically a Fizeau interferometer, and a conventional Fizeau interferometer will be described below as a comparative example in order to explain this advantage.

[Comparative example]
FIG. 20 is a diagram illustrating an example of a conventional Fizeau interferometer. In FIG. 20, the laser light from the laser 1 passes through the lens system and is converted into parallel light having a predetermined diameter, and then enters the Fizeau plate 7. The back surface of the Fizeau plate 7 is polished to a highly accurate plane, and a part of the incident light is reflected by this back surface to become reference light having a plane wave. The light that has passed through the Fizeau plate 7 passes through a null element 8 that converts a plane wave into a desired aspherical wavefront, and then enters the aspherical test surface 4 perpendicularly. The light reflected by the test surface 4 returns to the original optical path, overlaps with the reference light, and forms interference fringes on the CCD 5. The shape error can be measured by processing the interference fringes with a computer.

  The first problem of the interferometer shown as a comparative example is that the absolute accuracy is deteriorated by the null element 8. As the null element 8, a null lens (Computer genarated Hologram) or a combination of several high-precision lenses is usually used, but an error of about 10 nm RMS occurs due to a manufacturing error. Further, in the interferometer of the comparative example, since the reference surface (the back surface of the Fizeau plate 7) and the test surface 4 are separated from each other, the reproducibility is 0.3 nm RMS because it is easily affected by vibration and air fluctuation. Low. Further, when performing aspherical measurement, alignment between the null element 8 and the test surface 4 is important. Therefore, if the alignment accuracy is poor, the measurement reproducibility deteriorates by several nm.

  The causes of poor interferometer measurement reproducibility are air fluctuation, vibration, sound, air pressure fluctuation, temperature fluctuation, detector noise, fringe scanning nonlinearity error and scanning amplitude error, sample position repeatability, sample There are reproducibility of distortion of the sample by the holder, aberration of the optical system, and the like. Among these, air fluctuation, vibration, sound, atmospheric pressure fluctuation, temperature fluctuation, and aberration of the optical system are greatly increased by bringing the test surface and the reference surface close together and integrated as in the embodiment of FIG. Can be reduced.

  In particular, in the case of the embodiment of FIG. 1, the measurement accuracy is not affected by the accuracy of the null device 2 or the alignment accuracy of the null device 2 and the test surface 4 while using the null device 2. is there. In the embodiment of FIG. 1, the null element 2 has a function of giving the aspherical reference surface 3 a wavefront having an aspherical shape that is substantially the same as the aspherical shape. This is because it does not have a function of directly giving an aspherical wavefront. Therefore, in the embodiment of FIG. 1, the null element 2 is not an essential configuration, but it is preferable to use the null element 2 in order to further improve the measurement accuracy.

  In the embodiment of FIG. 1, the position reproducibility of the sample is assured by a position sensor (such as an electronic micrometer) (not shown) arranged around the object to be tested. It is improved by adopting a three-point or multi-point support structure.

  Further, since the test surface and the reference surface are brought close to each other, it is easy to detect an alignment error, and high-precision alignment is possible. Detector noise can be reduced sufficiently by cooling the detector and accumulating data that overcomes it. The non-linear error and amplitude error of fringe scanning (fringe scanning) can be eliminated by using a digital piezo and further increasing the number of buckets of fringe scanning and performing signal processing. By adopting the above-described configuration in the embodiment of FIG. 1, it is possible to reduce the repeatability to 0.05 nm RMS or less and the measurement repeatability including alignment error and change with time to 0.1 nm RMS or less.

  The remaining problem with this interferometer is the absolute accuracy, which depends on the surface accuracy of the reference aspheric surface. This error is the systematic error of this interferometer. This correction (calibration) will be described later.

  As described above, the interferometer of the embodiment of FIG. 1 is basically a Fizeau interferometer, but differs from the conventional Fizeau interferometer in the following points. The Fizeau surface is an aspherical surface, and the shape is reverse to the test surface, and the test surface is arranged close to the Fizeau surface. The lens with the Fizeau surface has a structure separated from this optical system, and has a structure integrated with the test object. With this configuration, repeatability and measurement reproducibility can be significantly improved over conventional interferometers such as the comparative example.

  2 is a diagram showing an example of the configuration of the holder 6 in the interferometer of FIG. 1, and FIG. 2 (A) is an example in which the distance between the test surface 4 and the aspherical reference surface 3 is configured to be variable, FIG. (B) shows an example in which the interval is fixed.

  In FIG. 2A, the reference element having the aspherical reference surface 3 is held by a holder 43 separately from the interferometer body. A piezo element 41 is provided on the holder 43, and a test surface holder 43 that holds the test surface 4 is placed on the holder 43 via the piezo element 41. By driving the piezo element 41, the distance between the aspherical reference surface 3 and the test surface 4 can be adjusted. Furthermore, it can also be used for fringe scanning, which is a conventional means of interference fringe analysis.

  In the example of FIG. 2B, the reference element having the aspheric reference surface 3 is held by the holder 43 in the same manner as in the example of FIG. The difference is that 42 is directly deposited. The thickness of these spacers 42 is 1 to 3 μm, and the thickness is the same at all three locations. In addition, the spacer 42 is provided so as to divide the circumference around the vertical direction in the drawing in FIG. 2B into three equal parts. The test surface 4 is placed on the three spacers 42, whereby the distance between the aspherical reference surface 3 and the test surface 4 can be kept constant, and distortion of the test surface 4 due to gravity is also caused. Can always be constant. In the case of FIG. 2B, fringe scanning for interference fringe analysis can be achieved by making the wavelength of the laser variable. In this case, the interferometer may not be affected by mechanical vibrations. Disappear.

  The holding method of the test surface 4 is preferably the same as the holding method in the optical system composed of the optical element having the test surface 4, and the posture of the test surface in the optical system with respect to gravity. Is preferably held in the same posture. As a result, it is possible to perform measurement in the presence of a change in the surface shape due to distortion of the test surface when it is actually incorporated into the optical system.

  Further, the distance between the aspherical reference surface 3 and the test surface is preferably 1 mm or less. If this interval exceeds 1 mm, the influence of air fluctuation, vibration, sound, atmospheric pressure fluctuation, temperature fluctuation, and aberration of the optical system becomes large, resulting in deterioration of measurement accuracy. In order to further improve the measurement accuracy, it is preferable to set the distance between the aspherical reference surface 3 and the test surface to 100 μm or less.

  2B, when the distance between the aspherical reference surface 3 and the test surface 4 is fixed, the distance between the aspherical reference surface 3 and the test surface 4 should be set to 10 μm or less. Is preferred.

[Modification of First Embodiment]
In the example of FIG. 2A described above, the interval between the test surface 4 and the aspherical reference surface 3 may be detected by the following method.

  FIG. 3 is a diagram illustrating a modification of the first embodiment. In FIG. 3, members having the same functions as those in the example of FIG. In the following description, in order to simplify the description, the portions common to FIG. 1 will not be described.

  3 is different from the example of FIG. 1 in that shearing interferometers 50 to 54 are provided on the back side of the test surface 4 (the side opposite to the aspherical reference surface 3). This shearing interferometer guides the light from the white light source 50 to the test surface 4 and the aspherical reference surface 3 via the beam splitter 51, and reflects the light reflected by the test surface 4 and the reference surface 3. After passing the light through the beam splitter 51, the light is shifted laterally by a birefringent member 52 such as a Wollaston prism and passed through the analyzer 53 to form an interference pattern on the CCD 54. Here, by monitoring the change in the interference pattern on the CCD 54, the distance between the test surface 4 and the aspherical reference surface 3 can be detected. In the modified example of FIG. 3, it goes without saying that the optical element having the test surface 4 is made of a light-transmitting material, such as quartz or zero-dur.

[Interferometer Calibration Method of First Embodiment]
The interferometer calibration method according to the first embodiment will be described below with reference to FIG. FIG. 4 is a flowchart for explaining the calibration method.

  Before executing step S1 in FIG. 4, first, aspheric processing is performed with a surface accuracy of about 10 nm RMS by a known technique.

<Step S1>
In step S1, the surface shape of the aspherical surface is measured using the interferometer of the first embodiment. Note that the interferometer of the first embodiment may be used from the time of the above aspherical surface processing. At the time of this measurement, the test surface is rotated little by little around the optical axis with respect to the reference surface, or data is taken while rotating the reference surface little by little around the optical axis with respect to the test surface. It is preferred to average to minimize asymmetric systematic errors (reference plane errors).

<Step S2>
In step S2, correction polishing of the aspherical shape is performed using the measurement data of step S1 so that the aspherical shape becomes the design data. A small tool polishing apparatus for performing this correction polishing is shown in FIG. In FIG. 5, the small tool polishing apparatus has a polishing head 63 having a rotating polisher 61 and a coil spring 62 that presses the polisher 61 with a predetermined pressure, and rotates an optical element having a test surface 4. Polishing is performed by applying a constant load from a direction perpendicular to the surface of the test surface. The polishing amount is proportional to the residence time of the polisher 61 (the time for the polisher 61 to remain at a predetermined position for polishing). Here, as in step S1, the shape of the surface to be measured is measured using the interferometer of FIG. 1, and as a result, if the measured aspherical shape is different from that of the design data, side small tool polishing is performed. The surface shape of the test surface 4 is corrected by the apparatus. By repeating this measurement / correction process, the measured aspheric shape can be matched with the designed aspheric shape.

<Step S3>
In step S3, the optical element having the test surface 4 obtained in step S2 is incorporated into the optical system.

<Step S4>
In step S4, the wavefront aberration of the optical system assembled in step S3 is measured. In measuring the wavefront aberration, a PDI (Point Diffraction Interferometer) using an undulator of SOR (Synchrotron Orbital Radiation) as a light source is used. Since this interferometer has a short measurement wavelength of 13 nm, it can measure the wavefront aberration of the optical system with a high accuracy of 0.13 nm RMS or less. The configuration of this interferometer will be described in the embodiments shown in FIGS.

<Step S5>
In step S5, the cause of the wavefront aberration measured in step S4 is decomposed into an alignment error (for each aspheric surface) and a shape error for each surface.

  Specifically, for example, by using an automatic correction program for an existing optical system, the position of the surface to be tested (spacing, inclination, shift) and the shape of the surface to be measured are variables on the computer, and the measured value of the wavefront aberration As an initial value, optimization is performed so that the wavefront aberration approaches zero. The difference between the position and shape of the test surface when optimized and the position and shape of the test surface before optimization correspond to alignment error (position error) and shape error, respectively.

<Step S6>
In step S6, it is determined whether or not the alignment error obtained in step S5 is a sufficiently small amount. If it is not a sufficiently small amount, the process proceeds to step S7, and if it is a sufficiently small amount, the process proceeds to step S8. .

<Step S7>
In step S7, the optical elements in the optical system are adjusted based on the alignment error obtained in step S5, and the process proceeds to step S4.

  Here, steps S4 to S7 are repeated until the alignment error obtained in step S5 becomes sufficiently small.

<Step S8>
If it is determined in step S6 that the alignment error is sufficiently small, the process proceeds to step S8. In step S8, the shape error (the shape error resolved in the latest step S5) in the final wavefront aberration (the wavefront aberration obtained in the latest step S4) and the final measurement in step S2 are performed. Find the difference from the aspherical shape data. This difference corresponds to the systematic error that the interferometer of the first embodiment has. This error corresponds to the shape error of the reference surface (Fizeau surface) in an aspheric (Fizeau type) interferometer.

<Step S9>
In step S8, the aspherical shape data finally measured in step S2 is corrected by the systematic error obtained in step S8, and the small aspherical shape data is corrected based on the corrected aspherical shape data. The test surface 4 is reprocessed using a tool polishing apparatus. At this time, it goes without saying that the optical element having the test surface 4 is removed from the optical system.

<Step S10>
After executing the above steps S1 to S9, the optical system is reassembled and the wavefront aberration is measured. The measurement value is again decomposed into an alignment error and a shape error of each surface, and it is confirmed that the shape error is small.

  The series of operations of aspherical surface processing, optical system assembly, wavefront aberration measurement, and aspherical interferometer systematic error determination as described above are repeated many times, and the systematic error of the aspherical interferometer is driven. If this error is large (for example, 2 nm RMS or more), correction of the aspherical interferometer (correction of the surface shape of the aspherical reference surface) is also necessary.

  If the systematic error of the interferometer obtained by this procedure is always corrected from the measured value in the subsequent measurement processing and used as the data of the modified polishing machine, highly accurate aspherical processing is possible.

  In the interferometer according to the first embodiment, since the measurement accuracy of the interferometer, particularly reproducibility, is excellent, the above-described calibration method is extremely effective.

  If a systematic error is confirmed in subsequent measurements such as wavefront aberration measurement using the exposure wavelength during mass production, the systematic error is corrected each time so that it always approaches the true value.

  In the processing measurement according to the present invention, after the aspherical surface processing, a reflection film must be attached to each surface before assembling the optical system and measuring the wavefront aberration. When a reflective film is attached or peeled off (for correction polishing), the shape of the surface may change due to the stress of the film. The reproducibility of this change needs to be 0.1 nm RMS or less, but this is not possible. However, surface changes are mostly second-order and fourth-order components (power component, third-order spherical aberration component), and high-order components are small. Regarding the change in the surface of the second-order and fourth-order components, it can be compensated by adjusting the space between the surfaces if the size is a certain size. In other words, the reproducibility of the surface change related to only the higher order component may be suppressed to 0.1 nm RMS or less. This can be suppressed by sufficiently reducing the stress of the film.

[Second Embodiment]
Next, a wavefront aberration measuring apparatus according to the second embodiment of the present invention will be described with reference to FIGS. The wavefront aberration measuring apparatus of the second embodiment measures the wavefront aberration of the projection optical system using the exposure wavelength of soft X-rays. Here, FIGS. 6 and 7 are diagrams for explaining the principle of the wavefront aberration measuring machine of the second embodiment.

  In FIG. 6A, light from an undulator of SOR (Synchrotron Orbital Radiation) passes through a spectroscope (not shown) to become quasi-monochromatic light 11 having a wavelength of about 13 nm. After being condensed by the condenser mirror, it enters the pinhole 12. The pinhole 12 has an opening sufficiently smaller than the size of the Airy disk determined from the numerical aperture on the incident side (pinhole 12 side) of the optical system 13 to be tested. The size of the Airy disk is given by 0.6λ / NA, where NA is the incident-side numerical aperture of the optical system 13 to be tested and λ is the wavelength of the quasi-monochromatic light 11.

  Accordingly, light having a wavefront that can be regarded as an ideal spherical wave is emitted from the pinhole 12. The light from the pinhole 12 enters the optical system 13 to be tested and reaches the semipermeable membrane 14 with a pinhole disposed at the image forming position. At this time, the pinhole 12 and the semipermeable membrane 14 with a pinhole are conjugated with each other with respect to the test optical system 13, and object points and image points when the test optical system 13 is actually used. Placed in position.

  As shown in FIG. 6 (B), the semipermeable membrane 14 with pinholes includes a semipermeable membrane 14b provided on a substrate 14c having optical transparency with respect to the radiant light having the wavelength of the quasi-monochromatic light 11, and a semipermeable membrane 14b. It consists of the opening part 14a in which the permeable film 14b is not provided. Therefore, a part of the wavefront incident on the semipermeable membrane with pinhole 14 passes through without breaking the wavefront shape, but another part is diffracted at the opening 14a. Here, if the size of the opening 14a is sufficiently small, the diffracted light from the opening 14a can be regarded as an ideal spherical wave.

  Returning to FIG. 6A, a CCD 15 is disposed on the exit side (opposite side of the optical system 13 to be tested) of the semipermeable membrane 14 with a pinhole, and on the imaging surface of the CCD 15 from the opening 14a. Interference fringes are formed by the interference between the ideal spherical wave and the transmitted wavefront from the semipermeable membrane 14b. At this time, the transmitted wavefront from the semipermeable membrane 14b is a wavefront having a shape corresponding to the wavefront aberration of the optical system 13 to be tested, and the interference fringes on the CCD 15 are ideal spherical waves (from the opening 14a) of the transmitted wavefront. The shape is in accordance with the deviation from the wavefront. Therefore, by analyzing the interference fringes, the wavefront aberration of the test optical system 13 can be obtained.

  7 (A) to 7 (C) are the measurement techniques shown in FIGS. 6 (A) and 6 (B) with higher accuracy. 7A to 7C, members having functions similar to those in FIGS. 6A and 6B are denoted by the same reference numerals. 7A is different from the wavefront aberration measuring device shown in FIG. 6A in that a pinhole plate 17 is disposed instead of the semipermeable membrane 14 with pinholes, and the pinholes 12 and the pinholes are arranged. The diffraction grating 16 is inserted between the plate 17 and the plate 17.

  FIG. 7C is a diagram showing the configuration of the pinhole plate 17, and FIG. 7B is a diagram for explaining the functions of the diffraction grating 16 and the pinhole plate 17. In FIG. 7B, the pinhole plate 17 has a minute opening 17a functioning as a pinhole and an opening 17b larger than the minute opening. At this time, as shown in FIG. 7C, the minute opening 17a and the opening 17b are transmitted through the diffraction grating 16 when the pinhole plate 17 is at the imaging position of the optical system 13 to be tested. The minute opening 17 a is positioned in the optical path of the folded light, and the opening 17 b is positioned in the optical path of the first-order diffracted light that has passed through the diffraction grating 16.

  Accordingly, the 0th-order diffracted light from the diffraction grating 16 passing through the minute opening 17a is diffracted by the minute opening 17a as a pinhole, converted into an ideal spherical wave, and travels toward the CCD 15. The first-order diffracted light from the diffraction grating 16 toward the opening 17b is measurement light having wavefront aberration of the optical system 13 to be tested, passes through the opening 17b while maintaining this wavefront, and travels toward the CCD 15. Here, the 0th-order diffracted light and the 1st-order diffracted light from the diffraction grating 16 have wavefronts corresponding to the wavefront aberration of the optical system 13 to be tested. The light passing through the minute opening 17a serving as a pinhole is converted into an ideal spherical wave, but the light passing through the opening 17b is not affected by diffraction at the opening 17b, and the wavefront A wavefront having a shape corresponding to the aberration is maintained. Accordingly, an interference fringe is formed on the imaging surface of the CCD 15 due to interference between an ideal spherical wave from the minute opening 17a and a measurement wavefront from the opening 17b. Here, the interference fringes on the imaging surface of the CCD 15 have a shape corresponding to the deviation of the measurement wavefront from the ideal spherical wave, and the interference fringes are analyzed by analyzing the interference fringes as in FIGS. The wavefront aberration of the test optical system 13 can be obtained. In FIG. 7, fringe scanning for high-precision measurement can be performed by moving the diffraction grating 16. In the example of FIG. 7, the diffraction grating 16 is disposed in the optical path between the optical system 13 to be tested and the pinhole plate 17 with an opening, but the diffraction grating 16 has the pinhole plate 12 and the opening. It may be arranged in the optical path between the pinhole plate 17 and may be arranged, for example, between the pinhole plate 12 and the test optical system 13. In the example of FIG. 7, two diffracted lights of the 0th-order diffracted light and the 1st-order diffracted light by the diffraction grating 16 are used. However, this diffracted light is not limited to two. It is not limited to combinations.

  The interferometer of the second embodiment measures the wavefront aberration of the optical system under test based on the principle described above, and its configuration is shown in FIG. In FIG. 8, members having the same functions as those in FIGS. 6 and 7 are given the same reference numerals.

  The interferometer shown in FIGS. 6 and 7 can measure only one aberration on the image plane of the optical system 13 to be tested. Measurement at a plurality of image points is necessary to accurately know the aberration of the optical system. 6 and 7, in order to perform measurement at a plurality of image points, measurement is performed by moving the pinhole 12, the semipermeable membrane with pinhole 14 or the pinhole plate 17 to a predetermined position. Can be considered. In this case, since the pinhole is very small, the moving mechanism that moves the pinhole is affected by vibration, and in particular, there is a possibility that light cannot be stably passed through the pinhole on the imaging surface side. It can be very difficult. In addition, when the pinhole is moved, it is difficult to accurately measure the position of the opening of the pinhole, and in particular, the aberration at the position of the imaging point, that is, the accuracy of distortion measurement may not be sufficient. is there.

  Therefore, in the second embodiment shown in FIG. 8, a pinhole array plate 25 in which pinholes are two-dimensionally arranged is used.

  In FIG. 8, light from an undulator of SOR (Synchrotron Orbital Radiation) passes through a spectroscope (not shown) to become quasi-monochromatic light 11 having a wavelength of about 13 nm, and is a condensing mirror. After being condensed at 35, it is incident on the pinhole array plate 25. In the example of FIG. 8, unlike the wavefront aberration measuring machine shown in FIGS. 6 and 7, the light is incident from the image plane side of the optical system 13 to be tested. The reason will be described later.

  As shown in FIG. 9A, the pinhole array plate 25 has an Airy disk size (0.6λ / NA, λ: quasi-monochromatic) determined from the incident-side numerical aperture (image-side numerical aperture) NA of the optical system 13 to be tested. Pinholes 25a each having an opening sufficiently smaller than the wavelength of the light 11 are arranged in a matrix. The position of the pinhole 25a corresponds to the image point position of the optical system 13 to be measured.

  Returning to FIG. 8, the condensing mirror 35 is provided on a stage 33 that can move along the in-image direction of the optical system 13 to be tested. By moving the stage 33, a pinhole array is provided. One of the plurality of pinholes 25a on the plate 25 can be selectively illuminated. This illuminated pinhole 25a corresponds to a measurement point. Needless to say, the incident position of the quasi-monochromatic light 11 on the condenser mirror 25 is changed as the stage 33 moves. Further, instead of one of the plurality of pinholes 25a, a plurality may be illuminated together.

  Now, a pinhole array plate 26 with an opening as shown in FIG. 9B is arranged at an image forming position of the pinhole array plate 25 by the optical system 13 to be tested. The pinhole array plate 26 with openings has a plurality of pinholes 26a provided in a matrix at the respective image forming positions of the plurality of pinholes 25a of the pinhole array plate 25, and a predetermined number of pinholes 26a. And a plurality of openings 26b provided in a matrix at intervals of. Here, each of the plurality of pinholes 26a has the same function as the pinhole 17a of FIG. 7, and each of the plurality of openings has the same function as the opening 17b of FIG. Yes.

  Light having a wavefront that can be regarded as an ideal spherical wave is emitted from the illuminated pinhole 25 a and is incident on the optical system 13 to be tested. The light from the test optical system 13 is diffracted by the diffraction grating 16, and the 0th-order diffracted light is a pinhole 26a corresponding to the illuminated pinhole 25a among the plurality of pinholes 26a of the pinhole array plate 26 with openings. The first-order diffracted light reaches the opening 26b corresponding to the illuminated pinhole 25a among the plurality of pinholes 26a of the pinhole array plate 26 with the opening. The light passing through the pinhole 26a and the light passing through the opening 26b cause interference with each other.

  Now, on the exit side of the pinhole plate 26 with an opening, a CCD 15 mounted on a stage 34 that is movable along the in-plane direction of the optical system 13 to be tested is disposed. The stage 34 is configured to move in conjunction with the stage 33 described above, and the CCD 15 expects only the pinhole 26a and the opening 26b corresponding to the illuminated pinhole 25a. Therefore, an interference fringe is formed on the CCD 15 by light from only the pinhole 26a and the opening 26b corresponding to the illuminated pinhole 25a, and the interference fringe is analyzed to analyze the illumination of the illuminated pinhole 25a. The wavefront aberration at the position on the image plane can be obtained.

  In the embodiment of FIG. 8, a pinhole array plate 25 as a first pinhole member and a pinhole array plate 26 with an opening as a second pinhole member are fixed to the optical system 13 to be tested. Therefore, the measurement is not affected by vibration caused by the movement of the stages 33 and 34, and stable measurement is possible.

  The pinhole array plate 25 is placed on a vertical stage 36 that allows the pinhole array plate 25 to be finely moved along the optical axis direction of the test optical system 13. It is fixed to the stand that supports The pinhole array plate 26 with an opening is placed on an XY stage 37 that can be finely moved along the object plane direction of the optical system 13 to be tested. The XY stage 37 is attached to the gantry via a piezo. Here, focus adjustment can be achieved by moving the pinhole array plate 25 by the vertical stage 36, and by moving the XY stage 37, the position of the pinhole 26a can be adjusted when there is distortion in the optical system under test. it can. Here, the XY stage 37 is provided with a minute displacement sensor such as a length measuring interferometer, and the distortion of the optical system 13 to be measured can be measured by the output from the minute displacement sensor. In this example, the positions of the plurality of pinholes 25a of the pinhole array plate 25 and the plurality of pinholes 26a of the pinhole array plate 26 with openings are accurately measured in advance using a coordinate measuring machine. .

  In the example of FIG. 8, the position of the pinhole 26a is moved. However, since this moving stroke is a minute amount, the pinhole 26a can be positioned with high accuracy. Further, in the example of FIG. 8, since the pinhole 26a is moved on the object plane side of the test optical system 13, when the test optical system 13 has a reduction magnification of -1 / β, the test optical Compared with the case where the pinhole 25a on the image plane side of the system 13 is moved, the positioning accuracy of the pinhole 26a can be loosened by | −1 / β | times.

  As described above, in the example of FIG. 8, the pinhole 25a is not configured to move, and the amount of movement of the pinhole 26a is within a range in which the positioning accuracy can be maintained. The accuracy of the aberration measurement, that is, distortion measurement can be sufficient.

  In the above example, the plurality of pinholes 25a corresponding to the wavefront aberration measurement point positions of the test optical system 13 are arranged in a matrix. However, the arrangement of the pinholes is not limited to the matrix. For example, when the visual field (exposure area) 13A of the test optical system 13 has an arc shape as shown in FIG. 10, a predetermined height along the object height (image height) in the test optical system 13 is set. A pinhole array plate 250 may be used in which the pinholes 250a are arranged at intervals and the pinholes 250a are arranged at a predetermined interval along another object height (image height). In this case, it goes without saying that the arrangement of the pinholes and openings in the pinhole array plate with openings is also matched to the pinhole 250a.

  In the example of FIG. 8, the diffraction grating 16 is disposed in the optical path between the optical system 13 to be tested and the pinhole array plate 26 with an opening, but the diffraction grating 16 has an opening with the pinhole array plate 12. It may be arranged in the optical path between the parted pinhole array plate 26 and may be arranged, for example, between the pinhole array plate 25 and the test optical system 13. In the example of FIG. 8, two diffracted lights of the 0th-order diffracted light and the 1st-order diffracted light by the diffraction grating 16 are used. However, this diffracted light is not limited to two. It is not limited to combinations.

[Third Embodiment]
Next, a wavefront aberration measuring apparatus according to the third embodiment of the present invention will be described with reference to FIG. The wavefront aberration measuring machine of the third embodiment measures the wavefront aberration of the projection optical system using the exposure wavelength of soft X-rays. In FIG. 11, members having the same functions as those shown in FIGS. 6 to 10 are denoted by the same reference numerals.

  In FIG. 11 (A), the light from the undulator of SOR (Synchrotron Orbital Radiation) becomes quasi-monochromatic light 11 having a wavelength of about 13 nm through a spectroscope (not shown). After being condensed by the condenser mirror, it enters the pinhole 12. The pinhole 12 is sufficiently larger than the size of the Airy disc (0.6λ / NA, λ: wavelength of the quasi-monochromatic light 11) determined from the numerical aperture NA on the incident side (pinhole 12 side) of the optical system 13 to be tested. It has a small opening. Accordingly, light having a wavefront that can be regarded as an ideal spherical wave is emitted from the pinhole 12.

  In the third embodiment, between the image forming position of the test optical system 13 (a position conjugate with the pinhole 12 by the test optical system 13) and the test optical system 13, FIG. As shown, a Hartmann plate 23 having a plurality of openings 23a is arranged.

  Returning to FIG. 11 (A), the light flux from the pinhole 12 emitted from the optical system 13 to be tested becomes a light beam group having the same number as the number of the openings 23a by the plurality of openings 23a of the Hartmann plate 23. Head to the imaging position. This light beam is once condensed at the image forming position and then reaches the CCD 15 in a spread state. A group of light rays through the plurality of openings 23a in the Hartmann plate 23 corresponds to light rays that pass through each section when the pupil plane of the test optical system 13 is divided into a plurality of sections. If the position where the light beam (light beam group) reaches is detected, the lateral aberration of the test optical system 13 can be obtained, and the wavefront aberration of the test optical system 13 can be calculated from this lateral aberration.

  In addition, although the arrangement | positioning of the several opening part 23a provided on the Hartmann plate 23 is made into the matrix form in the example of FIG. 11 (B), it is not restricted to this arrangement | positioning. In the example of FIG. 11, the Hartmann plate 23 is arranged between the test optical system 13 and the imaging position of the test optical system 13. The position of the Hartmann plate 23 is the pinhole plate 12. Between the pinhole plate 12 and the test optical system 13, for example.

[Fourth Embodiment]
Next, a wavefront aberration measuring machine according to the fourth embodiment of the present invention will be described with reference to FIG. In the second and third embodiments described above, the wavefront aberration measuring machine uses a SOR undulator as a light source. However, if the SOR undulator is used as a light source, the accuracy can be extremely high. The size becomes too large, making it very difficult to use in ordinary factories. In the following fourth embodiment, a laser plasma X-ray source (LPX) is used as a light source instead of the SOR undulator. A laser plasma X-ray source (LPX) generates high-temperature plasma from a target when a powerful pulse laser is focused on the target, and uses X-rays contained in the plasma. In the present embodiment, the radiated light from the laser plasma X-ray source is dispersed with a spectroscope to extract only light having a predetermined wavelength (for example, 13 nm), and this is used as the light source of the wavefront aberration measuring machine.

  Since the luminance of the laser plasma X-ray source (LPX) is orders of magnitude smaller than that of the SOR undulator, the fourth embodiment has one aperture in the second and third examples. The pinhole made of is replaced with a pinhole group in which a plurality of openings are integrated in a minute region.

  In FIG. 12A, a laser light source 18 supplies pulse laser light having a wavelength in the infrared region to the visible region, and for example, a YAG laser or an excimer laser by semiconductor laser excitation can be applied. This laser beam is condensed on the target 19 by a condensing optical system. The target 19 receives a high-intensity laser beam, becomes high temperature, is excited into a plasma state, and emits X-rays 20 when transitioning to a low potential state. When the X-ray 20 passes through a spectroscope (not shown), only 13 nm quasi-monochromatic light is extracted and irradiates a pinhole group on the pinhole member 21 through a condenser mirror.

  Here, as shown in FIG. 12B, the pinhole member 21 has a pinhole group 21a composed of a plurality of minute openings in a minute region at the measurement point position of the optical system 13 to be measured. Although FIG. 12B illustrates the pinhole group 21a having only four minute openings, the actual pinhole group 21a includes 100 or more minute openings. The size of these minute openings is the size of the Airy disk (0.6λ / NA, λ: wavelength of the quasi-monochromatic light 11) determined by the numerical aperture NA on the incident side (pinhole member 21 side) of the optical system 13 to be tested. ) Is sufficiently smaller than. In the example of FIG. 12B, a plurality of pinhole groups 21a are formed on the pinhole member 21, and the positions where the pinhole groups 21a are formed are objects to be measured by the optical system to be measured. What is necessary is just to determine according to an upper position.

  Returning to FIG. 12A, the entire region of one pinhole group 21a on the pinhole member 21 is illuminated with quasi-monochromatic light. A plurality of ideal spherical waves are generated from a large number of minute openings of the illuminated pinhole group 21a. After passing through the test optical system 13, the plurality of ideal spherical waves are condensed toward an imaging position that is a position conjugate with the pinhole member 21 related to the test optical system 13.

  Although not shown in FIG. 12, in the present embodiment, one of the plurality of pinhole groups 21a on the pinhole member 21 is selectively illuminated as in the second embodiment described above. .

  In the example of FIG. 12, a diffraction grating 16 is arranged between the test optical system 13 and the imaging position, and light emitted from the test optical system 13 and passing through the diffraction grating 16 is diffracted by this diffraction grating 16. It is diffracted by the grating 16 and travels toward the pinhole member 22.

  FIG. 12C is a diagram showing the configuration of the pinhole member 22, and the pinhole member 22 is provided in a one-to-one correspondence with the minute openings of each of the plurality of pinhole groups 21 a on the pinhole member 21. In addition, a pinhole group 22a composed of a plurality of minute openings and a plurality of openings 22b provided in a one-to-one correspondence with the plurality of pinhole groups 21a. That is, one opening 22b corresponds to one pinhole group 21a composed of a plurality of minute openings.

  At this time, the plurality of pinhole groups 21 a and the plurality of openings 22 b are configured such that the optical path of the 0th-order diffracted light that has passed through the diffraction grating 16 when the pinhole member 22 is disposed at the imaging position of the optical system 13 to be tested. The pinhole group 22a is located at the same position, and the opening 22b is located in the optical path of the first-order diffracted light that has passed through the diffraction grating 16.

  Therefore, an ideal spherical wave group from the illuminated pinhole group 21a among the plurality of pinhole groups 21a is diffracted by the diffraction grating 16 after passing through the test optical system 13. Of this diffracted light, the 0th-order diffracted light reaches the pinhole 22 a corresponding to the illuminated pinhole group 21 a among the plurality of pinhole groups 22 a on the pinhole member 22. The first-order diffracted light reaches the opening 22b corresponding to the illuminated pinhole group 21a among the plurality of openings 22b on the pinhole member 22. These 0th-order and 1st-order diffracted lights have a wavefront having a shape corresponding to the wavefront aberration of the optical system 13 under test. The 0th-order diffracted light passing through the pinhole group 22a is diffracted by the pinhole group 22a. The second ideal spherical wave group is converted. In addition, the first-order diffracted light that passes through the opening 22b is emitted from the opening 22b without being affected by diffraction by the opening 22b. These second ideal spherical wave group and the light from the opening 22b interfere with each other.

  Therefore, an ideal spherical wave group from the pinhole group 22a and an opening 22b are formed on the imaging surface of the CCD 15 arranged on the exit side of the pinhole member 22 (on the side opposite to the optical system 13 to be tested). Interference fringes due to interference with the wavefront are formed. Here, the interference fringes on the imaging surface of the CCD 15 have a shape corresponding to the deviation of the wavefront passing through the test optical system 13 from the ideal spherical wave, and by analyzing the interference fringes in the same manner as in the above example. The wavefront aberration of the test optical system 13 can be obtained.

  Although not shown in FIG. 12A, as in the second embodiment described above, from the pinhole group 22a and the opening 22b corresponding to the selectively illuminated pinhole group 21a. The CCD 15 is configured to be movable along the image plane direction of the test optical system 13 so that light can be received. Thereby, it is possible to measure wavefront aberrations at a plurality of measurement points in the object plane (image plane) of the test optical system.

  As described above, according to the fourth embodiment, it is possible to provide a wavefront aberration measuring machine that can be used in general factories.

  In the example of FIG. 12, the diffraction grating 16 is disposed in the optical path between the optical system 13 to be tested and the pinhole member 22, but the diffraction grating 16 is formed between the pinhole member 21 and the pinhole member 22. For example, it may be disposed between the pinhole member 21 and the test optical system 13. In the example of FIG. 12, two diffracted lights of the 0th-order diffracted light and the 1st-order diffracted light by the diffraction grating 16 are used, but this diffracted light is not limited to two, and the 0th-order and 1st-order diffracted lights It is not limited to combinations.

[Fifth Embodiment]
In the fourth embodiment described above, the pinhole groups 21a and 22a are provided with a large number of minute openings in a predetermined minute region. Instead, for example, as shown in FIG. In addition, a pinhole group 210a in which a large number of minute openings are arranged in a predetermined one-dimensional direction may be used. In this case, in order to correspond to a plurality of measurement points in the object plane (image plane) of the test optical system 13, the pinhole member 210 includes a plurality of pinhole groups 210a arranged in a matrix. Although FIG. 13A illustrates the pinhole group 210a having only four minute openings, the actual pinhole group 210a includes 100 or more minute openings. The size of these minute apertures is the size of the Airy disk (0.6λ / NA, λ: wavelength of the quasi-monochromatic light 11) determined by the numerical aperture NA on the incident side (pinhole member 210 side) of the optical system 13 to be tested. ) Is sufficiently smaller than.

  When this pinhole member 210 is used instead of the pinhole member 21, a pinhole member 220 shown in FIG. 13B is used instead of the pinhole member 22. This pinhole member 220 includes a plurality of pinholes 220a each having a plurality of minute openings provided in a one-to-one correspondence with the minute openings included in each of the plurality of pinhole groups 210a on the pinhole member 210, and a plurality of pinholes. And a plurality of openings 220b provided in one-to-one correspondence with the group 210a. Here, each of the plurality of pinhole groups 220a includes a large number of minute openings arranged along a predetermined one-dimensional direction. Further, one opening 22b corresponds to one pinhole group 21a composed of a plurality of minute openings.

  As described above, when the pinhole group is composed of a plurality of minute openings arranged along a predetermined one-dimensional direction, it is possible to reduce noise caused by light mixing between the plurality of minute openings. Further improvement in measurement accuracy can be achieved.

  The arrangement pitch of the plurality of minute openings arranged along a predetermined one-dimensional direction is 10 to 25 times the radius of the Airy disk determined by the numerical aperture on the pinhole member 210 side of the optical system 13 to be tested. It is more preferable that it is about 16 to 20 times.

[Sixth Embodiment]
Instead of the pinhole groups 21a and 22a in the fourth embodiment described above, slit-shaped openings can be used. 14A and 14B are views showing a slit member provided with a plurality of slit-shaped openings.

  In FIG. 14A, the slit member 211 has a plurality of slit-shaped openings 211a arranged in a matrix so as to correspond to a plurality of measurement points in the object plane (image plane) of the optical system 13 to be tested. I have. Here, the slit shape in the present embodiment refers to a shape extending in a predetermined one-dimensional direction, and the overall shape is not limited to a rectangular shape. The width in the short direction of the slit-shaped opening 211a is the size of the Airy disc (0.6λ / NA, λ: determined by the numerical aperture NA on the incident side (pinhole member 210 side) of the optical system 13 to be measured. The wavelength is sufficiently smaller than the wavelength of the quasi-monochromatic light 11. Therefore, when the slit-shaped opening 211a is illuminated, an ideal spherical wave (ideal one-dimensional spherical wave) is emitted from the cross-sectional direction along the short direction.

  When this slit member 211 is used instead of the pinhole member 21, a slit member 221 shown in FIG. 14B is used instead of the pinhole member 22. The slit member 221 includes a plurality of slit-shaped openings 221 a provided in a one-to-one correspondence with the plurality of slit-shaped openings 211 a on the slit member 211, and a plurality of slit-shaped openings 211 a on the slit member 211. And a plurality of openings 221b provided in a one-to-one correspondence.

  The operation when these slit members 211 and 221 are incorporated in the wavefront aberration measuring machine of the fourth embodiment shown in FIG. 12 will be described below.

  First, among the plurality of slit-shaped openings 211a, one slit-shaped opening 211a corresponding to a desired measurement point is illuminated by light from the laser plasma X-ray source. From the illuminated slit-shaped opening 211a, an ideal one-dimensional spherical wave is generated in the slit short direction. The ideal one-dimensional spherical wave passes through the test optical system 13 and is diffracted by the diffraction grating 16, so that the zero-order diffracted light reaches the slit-shaped opening 221 a of the slit member 221, and the first-order diffracted light is slit member 221. To the opening 221b.

  Here, an ideal one-dimensional spherical wave is generated from the slit-shaped opening 221a in the slit short direction, and a wavefront having a shape corresponding to the wavefront aberration of the optical system 13 to be tested passes through the opening 221b. These ideal one-dimensional spherical waves and the wavefront from the opening interfere with each other to form interference fringes on the CCD 15. By analyzing the interference fringes, the wavefront aberration of the test optical system 13 can be measured. In the sixth embodiment, the measurement accuracy along the longitudinal direction of the slit may be reduced. In this case, the slit members 211 and 221 and the test optical system 13 can be relatively rotated. A plurality of slit-shaped openings having different longitudinal directions may be provided instead of the slit-shaped openings 211a and 221a in FIG.

  As described above, by using the slit-shaped opening, the amount of light can be further improved as compared with the case of using a pinhole having one minute opening or a pinhole group including a plurality of minute openings. This configuration corresponds to a shearing interferometer.

  Here, the slit member 221 in FIG. 14 uses two diffracted lights of the 0th-order diffracted light and the 1st-order diffracted light among the diffracted lights by the diffraction grating 16, but is limited to the combination of the 0th-order and the first-order. I can't.

[Seventh Embodiment]
In the wavefront aberration measuring apparatus according to the seventh embodiment shown in FIG. 15, the light source of the third embodiment shown in FIG. 11 is replaced with an SOR (Synchrotron Orbital Radiation) undulator. This is a modification using a laser plasma X-ray source.

  In FIG. 15, a laser light source 18 supplies pulsed laser light having a wavelength in the infrared region to the visible region, and for example, a YAG laser or excimer laser by semiconductor laser excitation can be applied. This laser beam is condensed on the target 19 by a condensing optical system. The target 19 receives a high-intensity laser beam, becomes high temperature, is excited into a plasma state, and emits X-rays 20 when transitioning to a low potential state. When the X-ray 20 passes through a spectroscope (not shown), only 13 nm quasi-monochromatic light is extracted, and irradiates the pinhole member 24 via a condenser mirror.

  This pinhole member 24 is sufficiently larger than the diameter (0.6λ / NA, λ: wavelength of quasi-monochromatic light) of the Airy disk determined from the numerical aperture NA on the incident side (pinhole member 24 side) of the optical system 13 to be tested. Have a large (more than 10 times) opening. Here, the opening of the pinhole member 24 is illuminated with a uniform amount of light in the object plane direction of the test optical system 13 and with a uniform amount of light within the cross-sectional direction of the light beam incident on the opening of the pinhole member 24. If possible, it is not necessary to make the size of the opening sufficiently smaller than the Airy disk as in the above-described embodiment.

  In the present embodiment, the illumination is performed with a uniform light amount in the in-object direction of the optical system 13 to be measured and with a uniform light amount in the cross-sectional direction of the light beam incident on the opening of the pinhole member 24. A large opening pinhole can be used.

  Also in the seventh embodiment, light having a wavefront that can be regarded as an ideal spherical wave is emitted from the opening of the pinhole member 24.

  In the seventh embodiment, as in the third embodiment described above, the imaging position of the test optical system 13 (the position conjugate with the pinhole 12 by the test optical system 13), the test optical system 13, and A Hartmann plate 23 having a plurality of openings is disposed between the two.

  The light beam emitted from the opening of the pinhole member 24 emitted from the test optical system 13 becomes a light beam group having the same number as the number of openings by the plurality of openings of the Hartmann plate 23 and travels toward the imaging position. This light beam is once condensed at the image forming position and then reaches the CCD 15 in a spread state. A group of light rays through the plurality of openings in the Hartmann plate 23 corresponds to light rays that pass through each section when the pupil plane of the test optical system 13 is divided into a plurality of sections. If the position where the (ray group) reaches is detected, the lateral aberration of the test optical system 13 can be obtained, and the wavefront aberration of the test optical system 13 can be calculated from this lateral aberration.

[Eighth Embodiment]
In the above-described embodiment, a light source that supplies a soft X-ray wavelength region is used as a light source. However, when adjusting and assembling an optical system in a normal factory, a normal laser light source is used instead of an X-ray source. It is convenient to use.

  Hereinafter, as an eighth embodiment, a wavefront aberration measuring machine using a laser light source will be described with reference to FIGS. Here, FIG. 16 is a diagram for explaining the principle of the eighth embodiment.

  In FIG. 16A, a laser light source 18 supplies laser light having a predetermined wavelength. This laser light is divided by the beam splitter BS, and one of the divided light beams is guided to the first pinhole 12 having a minute aperture through the bending mirror and the condenser lens. The first pinhole 12 is disposed at the image plane position of the test optical system 13, and the size of the minute aperture is determined from the numerical aperture NA on the exit side (pinhole 12 side) of the test optical system 13. The size is sufficiently smaller than the determined Airy disk diameter (0.6λ / NA, λ: wavelength of laser light). Accordingly, the first ideal spherical wave is generated from the minute opening of the first pinhole 12.

  The first ideal spherical wave from the first pinhole 12 passes through the test optical system 13 and is a pinhole mirror 30 disposed at a position conjugate with the first pinhole with respect to the test optical system 13. Led to.

  As shown in FIG. 16B, the pinhole mirror 30 includes a light-transmitting substrate 30c, a reflecting surface 30b provided on the substrate 30c, and an opening 30a that is a region where the reflecting surface 30b is not provided. It consists of. The size of the opening 30a of the pinhole mirror 30 is also the diameter of the Airy disk (0.6λ / NA, λ: laser beam) determined from the numerical aperture NA on the exit side (pinhole mirror 30 side) of the optical system 13 to be tested. The wavelength is sufficiently smaller than the wavelength.

  Now, referring back to FIG. 16A, of the light beams divided by the beam splitter BS, the other light beam passes through the condensing lens 28 and then is a pinhole disposed on the object plane of the optical system 13 to be tested. The light is guided to the back surface of the mirror 30 (the side opposite to the reflecting surface 30b) in a condensed state.

  Therefore, in the pinhole mirror 30, when the light beam from the back surface of the pinhole mirror 30 passes through the opening 30a, a second ideal spherical wave is generated. When the light beam that has passed through the test optical system 13 is reflected by the reflection surface 30 b of the pinhole mirror 30, the reflected light has a wavefront having a shape corresponding to the wavefront aberration of the test optical system 13.

  The second ideal spherical wave from the opening 30 a of the pinhole mirror 30 and the reflected light from the reflection surface 30 b of the pinhole mirror 30 reach the CCD 29 via the lens, and on the imaging surface of the CCD 29. Interference fringes are formed.

  The interference fringes on the imaging surface of the CCD 29 have a shape corresponding to the deviation of the wavefront that has passed through the test optical system 13 from the ideal spherical wave. By analyzing the interference fringes, the wavefront aberration of the test optical system 13 is reduced. Can be sought.

  In the principle diagram of the eighth embodiment shown in FIG. 16, a predetermined point on the object plane (image plane) of the optical system 13 to be measured is set as a measurement point. However, when measuring a plurality of measurement points, In place of the pinhole 12 of FIG. 16, a pinhole array plate 31 in which a plurality of openings are arranged in a predetermined arrangement is used, and a plurality of openings and reflecting surfaces are used instead of the pinhole mirror 30 of FIG. What is necessary is just to use the pinhole mirror array 32 which has.

  Hereinafter, an eighth embodiment in which the wavefront aberration of the optical system 13 to be measured can be measured at a plurality of measurement points will be described with reference to FIG. In FIG. 17, members having the same functions as those shown in FIG.

  In FIG. 17, a laser beam having a predetermined wavelength from the laser light source 27 is split by a beam splitter BS. One light beam split by the beam splitter BS passes through a bending mirror and a condenser lens provided in a stage 33 movable in the image plane direction of the test optical system 13 to the pinhole array 31 in order. Reach.

  As shown in FIG. 18A, the pinhole array 31 has a plurality of openings 31a arranged in a matrix. The positions of the plurality of openings 31a correspond to the positions of the measurement points of the optical system 13 to be measured. Here, each of the plurality of openings 31a has an Airy disk diameter (0.6λ / NA, λ: wavelength of the laser beam) determined from the numerical aperture NA on the exit side (pinhole array 31 side) of the optical system 13 to be tested. ) Is sufficiently smaller than. Accordingly, an ideal spherical wave is generated from the opening 31 a of the pinhole array 31.

  Returning to FIG. 17, by moving the stage 33, one of the plurality of openings 31 a on the pinhole array 31 is selectively illuminated. Needless to say, the incident position of the laser beam on the bending mirror is changed as the stage 33 moves. Further, instead of one of the plurality of openings 31a, a plurality may be illuminated together.

  Now, the ideal spherical wave from the pinhole array 31 passes through the test optical system 13 and is then guided to the pinhole mirror array 32 at a position conjugate with the pinhole array 31 with respect to the test optical system 13.

  As shown in FIG. 18B, the pinhole mirror array 32 is provided with a reflective surface 30b so that a plurality of openings 32a are arranged in a matrix, and the reflective surface 30b is provided in the openings 32a. Absent. Here, the size of each of the plurality of openings 32a of the pinhole mirror array 32 is the diameter (0...) Of the Airy disk determined from the numerical aperture NA on the emission side (pinhole mirror array 32 side) of the optical system 13 to be tested. 6λ / NA, where λ is the wavelength of the laser beam).

  Now, referring back to FIG. 17, among the light beams divided by the beam splitter BS, the other light beam passes through the bending mirror 38 and the condensing lens 28 in order, and is then disposed on the object plane of the optical system 13 to be tested. The light is guided to the back surface of the pinhole mirror array 32 (on the side opposite to the reflection surface 32b) in a condensed state.

  Therefore, in the pinhole mirror array 32, an ideal spherical wave is generated when the light beam from the back surface of the pinhole mirror array 32 passes through the opening 32a. When the light beam that has passed through the test optical system 13 is reflected by the reflection surface 32 b of the pinhole mirror array 32, the reflected light has a wavefront having a shape corresponding to the wavefront aberration of the test optical system 13.

  The ideal spherical wave from the opening 32 a of the pinhole mirror array 32 and the reflected light from the reflection surface 32 b of the pinhole mirror 32 reach the CCD 29 via the bending mirror and lens, and on the imaging surface of the CCD 29. Interference fringes are formed at. The interference fringes on the imaging surface of the CCD 29 have a shape corresponding to the deviation of the wavefront that has passed through the test optical system 13 from the ideal spherical wave. By analyzing the interference fringes, the wavefront aberration of the test optical system 13 is reduced. Can be sought.

  In the eighth embodiment shown in FIG. 17, the CCD 29 is arranged along the in-plane direction of the test optical system 13 together with the optical system for guiding light from the pinhole mirror array 32 to the CCD 29 and the condenser lens 28. It is mounted on a movable stage 34. The stage 34 is configured to move in conjunction with the stage 33 described above, and the CCD 29 expects only the opening 32b corresponding to the illuminated opening 31a. Therefore, on the CCD 29, light generated from the illuminated opening 31a and passing through the test optical system 13 and diffracted light from the opening 32a on the pinhole mirror array 32 corresponding to the illuminated opening 31a. Interference fringes are formed due to interference. Therefore, by analyzing the interference fringes, the wavefront aberration at the measurement point where the illuminated opening 31a is located can be obtained.

  As described above, also in the eighth embodiment, stable measurement can be performed without being affected by the vibration caused by the movement of the stages 33 and 34 during the measurement.

  The pinhole array 31 is placed on a vertical stage 36 that allows the pinhole array 31 to be finely moved along the optical axis direction of the test optical system 13. The stage 36 supports the test optical system 13. It is fixed to the mount. The pinhole mirror array 32 is placed on an XY stage 37 that can be finely moved along the object plane direction of the optical system 13 to be tested. The XY stage 37 is attached to the gantry via a piezo. Here, the focus adjustment can be achieved by the movement of the pinhole array 31 by the vertical stage 36, and the position of the opening 32a can be adjusted by moving the XY stage 37 when there is distortion in the test optical system.

  Here, the XY stage 37 is provided with a minute displacement sensor such as a length measuring interferometer, and the distortion of the optical system 13 to be measured can be measured by the output from the minute displacement sensor. Also in this example, the positions of the plurality of openings 31a of the pinhole array 31 and the plurality of openings 32a of the pinhole mirror array 32 are accurately measured in advance using a coordinate measuring machine.

  In the eighth embodiment, the bending mirror 38 is configured to be able to vibrate, and due to this vibration, the optical path length between the optical paths divided into two by the beam splitter BS changes. Thereby, fringe scanning (fringe scanning) when performing high-accuracy measurement can be performed.

[Comparative example]
FIG. 19 is a diagram illustrating a configuration of a comparative example of the eighth embodiment. In the comparative example shown in FIG. 19, the light source of the wavefront aberration measuring machine shown in FIG. 6 is an ultraviolet laser. As described above, the shorter the wavelength of the light source of the wavefront aberration measuring instrument, the higher the measurement accuracy. However, in the ultraviolet laser, the wavelength differs by about 20 times from the wavelength used by the optical system 13 to be tested. In the example, the accuracy is 20 times worse than that of FIG.

  On the other hand, in the wavefront aberration measuring instrument of the eighth embodiment, since the reference wavefront is routed through a different optical path from the measurement wavefront, measurement with higher accuracy than the comparative example of FIG. 19 is possible. Thus, in the eighth embodiment, it is possible to measure wavefront aberration with high accuracy without using an X-ray source.

  Note that the wavefront aberration measuring machines of the second to eighth embodiments described above can be incorporated into an exposure apparatus. In particular, the wavefront aberration measuring machines of the second and third embodiments are suitable when the SOR undulator is used as the exposure light because the light source unit can be shared with the exposure light source. In the fourth to seventh embodiments, When a laser plasma X-ray source is used as the exposure wavelength, it is preferable because the light source unit can be shared with the exposure light source. In the wavefront aberration measuring apparatus according to the eighth embodiment, it is necessary to prepare a laser light source separately from the exposure light source, and this laser light source is shared with an alignment system light source or an autofocus light source in the exposure apparatus. It is also possible. In addition, in the wavefront aberration measuring apparatus of each embodiment, when shared with the light source in the exposure apparatus, a unit in which a CCD as a detector is housed can be provided detachably from the exposure apparatus. In this case, it is possible to measure the wavefront aberration of the projection optical system if the unit is attached to the exposure apparatus at the time of maintenance or the like, so that it is not necessary to provide a wavefront aberration measuring device for each exposure apparatus. The cost reduction can be measured.

  In the second to seventh embodiments described above, a CCD is applied as a detector. Instead, a member (for example, a fluorescent plate) having a function of converting emitted light in a soft X-ray region into visible light. May be provided at the position of the detector, and visible light from this member may be detected by a detector such as a CCD.

  In the above-described embodiment, a method of manufacturing a projection optical system in an exposure apparatus that uses soft X-rays having a wavelength of around 10 nm as exposure light, a wavefront aberration measuring machine suitable for measuring the wavefront aberration of the projection optical system, and the projection optical system Although a surface shape measuring interferometer suitable for measuring the surface shape of the reflecting surface in the system and a calibration method of the interferometer have been described, the present invention is not limited to the wavelength of this soft X-ray. Absent. For example, it can be applied not only to a projection optical system for hard X-rays having a wavelength shorter than that of soft X-rays, a wavefront aberration measuring machine, and an interferometer for measuring the surface shape of an optical element of a projection optical system for hard X-rays. The present invention can also be applied in a vacuum ultraviolet region (100 nm to 200 nm) having a wavelength longer than that of soft X-rays. Here, if applied to the surface shape measurement of the optical elements of the vacuum ultraviolet projection optical system, wavefront aberration measuring machine, and vacuum ultraviolet projection optical system, measurement and manufacture with extremely higher accuracy than conventional ones can be achieved. It becomes possible.

  As described above, the present invention is not limited to the above-described embodiment, and can take various configurations without departing from the gist of the present invention.

It is a figure which shows the structure of the interferometer concerning the 1st Embodiment of this invention. It is a figure which shows the principal part of the interferometer of 1st Embodiment. It is a figure which shows the modification of the interferometer of 1st Embodiment. It is a flowchart which shows the calibration method of the interferometer of 1st Embodiment. It is a figure which shows the structure of the correction grinding machine used in the calibration method of the interferometer of 1st Embodiment. It is a figure for demonstrating the principle of the interferometer of 2nd Embodiment. It is a figure for demonstrating the principle of the interferometer of 2nd Embodiment. It is a figure which shows the structure of the interferometer of 2nd Embodiment. It is a figure which shows the principal part in the interferometer of 2nd Embodiment. It is a figure which shows the modification of the principal part in the interferometer of 2nd Embodiment. It is a figure which shows the structure of the interferometer of 3rd Embodiment. It is a figure which shows the structure of the interferometer of 4th Embodiment. It is a figure which shows the principal part in the interferometer of 5th Embodiment. It is a figure which shows the principal part in the interferometer of 6th Embodiment. It is a figure which shows the structure of the interferometer of 7th Embodiment. It is a figure for demonstrating the principle of 8th Embodiment. It is a figure which shows the structure of the interferometer of 8th Embodiment. It is a figure which shows the principal part in the interferometer of 8th Embodiment. It is a figure which shows the structure of the interferometer of a comparative example. It is a figure which shows the structure of the interferometer of a comparative example.

Explanation of symbols

1: Light source 2: Null element 3: Aspherical reference surface 4: Test surface 5: CCD

Claims (6)

In a Fizeau interferometer for measuring the shape of the optical surface of an optical element,
An aspherical reference surface;
A holding member that integrally holds the reference surface and the optical surface in a state in which the reference surface and the optical surface are close to each other;
A Fizeau interferometer characterized in that light from the optical surface interferes with light from the reference surface. A light source that supplies light toward the reference surface and the optical surface, and has a main body that interferes with the light via the reference surface and the optical surface;
The Fizeau interferometer according to claim 1, wherein the holding member and the main body are spatially separated. The Fizeau interferometer according to claim 1 or 2, wherein a distance between the reference surface and the optical surface is 1 mm or less. 4. The Fizeau-interferometer according to claim 1, wherein a distance between the reference surface and the optical surface is variable. 5. The Fizeau interferometer according to claim 4, further comprising a position detection system for detecting a positional relationship between the reference surface and the optical surface. 4. The Fizeau interferometer according to claim 1, wherein a distance between the reference surface and the optical surface is fixed and 10 μm or less. 5.

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