JP2010025609A - Wavefront generation optical system and wavefront aberration measuring system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a light flux having an excellent wavefront shape regardless of a polarization state of an illumination light flux. <P>SOLUTION: A wavefront generation optical system includes a pinhole mask (14) for generating a spherical light wave, and a phase plate (16) for compensation arranged on the emission side of the pinhole mask (14). A phase shift distribution imparted to two polarized components of each mutually-different incident light by the phase plate (16) for compensation is set to be a distribution for compensating or reducing a phase shift distribution imparted to the two polarized components of the incident light by the pinhole mask (14). <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a wavefront generating optical system that generates a spherical light wave, and a wavefront aberration measuring apparatus that measures the wavefront aberration of a test optical system.

  In an optical measurement device (see Patent Document 1 or the like) such as a wavefront aberration measurement device or an interference measurement device, a pinhole mask may be used as an optical element for generating measurement light. This is because the light beam (transmitted light beam) emitted from the pinhole mask becomes an ideal spherical wave with the pinhole position as the wave source, regardless of the wavefront shape of the light beam (illumination light beam) that illuminates the pinhole.

Incidentally, some projection lenses, microscope objective lenses, etc. of semiconductor exposure apparatuses have an object-side numerical aperture exceeding 1.0 (immersion lens). When these lenses are measured, they are transmitted through a pinhole mask. In order to increase the effective numerical aperture of the light beam, it is necessary to make the radius of the pinhole extremely small.
Japanese Patent Laid-Open No. 2004-14865

  However, it has been found that if the radius of the pinhole is made smaller than a certain value, the wavefront shape of the transmitted light beam may be significantly deteriorated depending on the polarization state of the illumination light beam.

  Therefore, an object of the present invention is suitable for measuring a wavefront generating optical system capable of generating a light beam having a good wavefront shape regardless of the polarization state of the illumination light beam and a test optical system having a high numerical aperture with high accuracy. Another object is to provide a wavefront aberration measuring apparatus.

  A wavefront generating optical system that exemplifies the present invention includes a pinhole mask for generating a spherical light wave, and a compensation phase plate disposed on the exit side of the pinhole mask, and the compensation phase plate is configured to transmit incident light to each other. The phase shift distribution given to two different polarization components is set to a distribution that cancels or reduces the phase shift distribution given to the two polarization components of incident light by the pinhole mask.

  In addition, a wavefront aberration measuring apparatus exemplifying the present invention includes the above-described wavefront generation optical system and an illumination optical system that causes the wavefront generation optical system to generate a measurement light beam by illuminating the pinhole mask of the wavefront generation optical system And detection means for detecting the wavefront shape of the measurement light beam generated by the wavefront generation optical system and passed through the optical system to be measured.

  INDUSTRIAL APPLICABILITY According to the present invention, it is suitable for measuring a wavefront generating optical system capable of generating a light beam having a favorable wavefront shape regardless of the polarization state of the illumination light beam and a test optical system having a high numerical aperture with high accuracy. A wavefront aberration measuring apparatus is realized.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described. This embodiment is an embodiment of a wavefront aberration measuring apparatus using a Mach-Zehnder interferometer.

  FIG. 1 is a configuration diagram of a wavefront aberration measuring apparatus according to the present embodiment. As shown in FIG. 1, the wavefront aberration measuring apparatus of the present embodiment includes a laser light source 11, a beam expander 12, a polarizing plate 13, beam splitters BS1 and BS2, a transmissive pinhole mask 14 for generating spherical waves, and a birefringent element. Compensation plate 16, mirrors M <b> 1 and M <b> 2, image sensor 17 and the like are arranged. Among these, between the pinhole mask 14 and the compensation plate 16, the optical system 15 to be measured is arranged. The test optical system 15 is supported by a support mechanism (not shown).

  Here, the test optical system 15 is an immersion microscope objective lens (infinity system) having an object-side numerical aperture of 1 or more, and the used wavelength range of the test optical system 15 is visible light (about 400 nm to about 700 nm). Assume that

  The laser light source 11 emits a laser beam having a wavelength used by the optical system 15 to be measured or a wavelength in the vicinity thereof. Laser light emitted from the laser light source 11 is linearly polarized light. The laser light is converted into a light beam having a large diameter by the beam expander 12 and enters the polarizing plate 13 as a plane wave.

  Here, it is assumed that the direction of the transmission axis of the polarizing plate 13 is set so that the polarization direction of the incident light beam is the direction indicated by the symbol y in FIG. The light beam that has passed through the polarizing plate 13 is split into two light beams by the beam splitter BS1.

  One light beam branched by the beam splitter BS1 illuminates the pinhole mask 14 from the front. Of the illumination light beam, the light beam that has passed through the pinhole of the pinhole mask 14 becomes a spherical wave and enters the test optical system 15 from the object side. Note that the object-side focal plane of the test optical system 15 is located in the vicinity of the pinhole mask 14, and the optical axis of the test optical system 15 is the center line of the pinhole formed in the pinhole mask 14. Match.

  The light beam incident on the test optical system 15 changes its wavefront shape under the influence of the aberration of the test optical system 15 and then exits to the image side of the test optical system 15. The light beam enters the compensation plate 16, receives the birefringence action of the compensation plate 16, changes its wavefront shape, and then enters the mirror M 1. When the light beam is reflected by the mirror M 1 and then enters the beam splitter BS 2, the light beam is reflected by the beam splitter BS 2 and enters the image sensor 17.

  Hereinafter, the light beam that passes through the beam splitter BS1, the pinhole mask 14, the test optical system 15, the compensation plate 16, the mirror M1, and the beam splitter BS2 and then enters the image sensor 17 is referred to as “measurement light beam”.

  The other light beam branched by the beam splitter BS1 enters the mirror M2, is reflected by the mirror M2, and then enters the beam splitter BS2. The light beam passes through the beam splitter BS2 and then enters the image sensor 17. Hereinafter, the light beam that passes through the beam splitter BS1, the mirror M2, and the beam splitter BS2 in this order and then enters the image sensor 17 is referred to as a “reference light beam”.

  The reference light beam incident on the image sensor 17 causes interference fringes on the image sensor 17 together with the measurement light beam incident on the image sensor 17. The luminance distribution of the interference fringes represents a difference in wavefront between the measurement light beam and the reference light beam. When the image sensor 17 captures the interference fringes and generates image data, the image sensor 17 outputs the image data to a computer (not shown). The computer analyzes the image data and calculates the wavefront aberration of the test optical system 15 (the amount of wavefront deformation of the measurement light beam before and after passing through the test optical system 15).

  FIG. 2 is a schematic view of a cross section obtained by cutting the periphery of the pinhole mask 14 of the present embodiment along a plane including the optical axis and parallel to the paper surface of FIG. Here, only the pinhole mask 14 and the test optical system 15 will be described, and the compensation plate 16 will be described in detail later.

  As shown in FIG. 2, the pinhole mask 14 is formed by forming a light shielding film 14b having a circular opening corresponding to the pinhole 14c on the transparent substrate 14a so that the shape error of the transparent substrate 14a does not affect the measurement light flux. The side of the film 14b is directed to the test optical system 15. Since the light shielding film 14b has a constant thickness, the pinhole 14c has a cylindrical shape.

  The transparent substrate 14a of the pinhole mask 14 is a substrate (for example, a glass substrate) transparent to the wavelength of the laser light source 11 (see FIG. 1), and the light shielding film 14b of the pinhole mask 14 is the laser light source 11 (FIG. 1). (See, for example, a chromium film). For the production of such a pinhole mask 14, for example, photolithography can be applied. The optical path between the pinhole mask 14 and the test optical system 15 is filled with an immersion liquid 20 such as oil.

  Hereinafter, the design data of each part is assumed as follows.

-Object-side numerical aperture of optical system 15 to be tested ... 1.4
Refractive index on the image side of the test optical system 15 ... 1 (= refractive index of air)
The wavelength of the laser light source 11: 535 nm
Illuminating luminous flux of the pinhole mask 14: plane wave perpendicularly incident on the pinhole mask 14 Refractive index on the light source side of the pinhole mask 14 1 (= refractive index of air)
-Refractive index of the transparent substrate 14a of the pinhole mask 14 ... 1.5
-Refractive index of the light shielding film 14b of the pinhole mask 14 ... 2.75 + 4.46i
-Thickness of the light shielding film 14b of the pinhole mask 14 ... 200 nm
-Diameter of pinhole 14c of pinhole mask 14 ... 200 nm
-Refractive index of immersion liquid 20 ... 1.5
According to the above design data, since the object-side numerical aperture of the optical system 15 to be tested is 1 or more, the effective numerical aperture of the transmitted light beam of the pinhole mask 14 needs to be 1 or more.

  Here, according to the well-known Fourier optics, when a pinhole having a radius r is vertically illuminated with a plane wave having a wavelength λ, the amplitude of the diffracted light having a diffraction angle of zero among the transmitted light fluxes of the pinhole is the largest. The larger the folding angle, the smaller the amplitude, and the amplitude of the diffracted light diffracted in the direction corresponding to the numerical aperture of about 0.61 × λ / r becomes zero.

  Therefore, if it is assumed that the allowable variation in amplitude is within 3/4 of the maximum amplitude, the effective numerical aperture of the transmitted light through the pinhole is about 0.47 × λ / r. Therefore, if it is attempted to increase the effective numerical aperture to 1 or more under the assumption, the radius r of the pinhole needs to be 47% or less of the wavelength λ (Condition 1).

  In that respect, according to the above design data, the radius of the pinhole 14c is 100 nm, which is 47% or less of the wavelength (535 nm) of the laser light source 11. That is, according to the design data, condition 1 is satisfied.

  Here, it is assumed that the allowable variation in amplitude is within 3/4 of the maximum amplitude, but it may be as severe as within 1/2 of the maximum amplitude. If the effective numerical aperture is to be made 1 or more under the assumption, the radius r of the pinhole needs to be 35% or less of the wavelength λ (Condition 2).

  In that respect, according to the above design data, the radius of the pinhole 14c is 100 nm, which is 35% or less of the wavelength (535 nm) of the laser light source 11. That is, according to the design data, condition 2 is satisfied.

  FIG. 3 is data showing the wavefront shape of the transmitted light flux of the pinhole mask 14. This data is obtained by analyzing the design data by the FDTD method, and is data of the wavefront shape at a sufficiently far distance of the transmitted light beam.

  The symbol Δ in FIG. 3 indicates the relative phase with reference to the ideal spherical wave, and that Δ is positive (upward in the figure) indicates that the phase is advanced compared to the ideal spherical wave. Show. Reference sign y indicates the polarization direction of the illumination light beam, and reference sign x indicates a polarization direction that is 90 ° different from the polarization direction of the illumination light beam.

  As shown in FIG. 3, the wavefront shape of the light beam transmitted through the pinhole mask 14 is not rotationally symmetric and depends on the polarization direction (here, the y direction) of the illumination light beam. Specifically, the wavefront shape is a saddle shape having an azimuth angle dependency approximately proportional to cos 2θ when the diffraction angle of the diffracted light constituting the wavefront is set to θ.

  Therefore, if the transmitted light beam of the pinhole mask 14 is used as a measurement light beam as it is, it becomes difficult to accurately measure the wavefront aberration of the optical system 15 (see FIG. 1). The problem is particularly serious when the measurement is performed while rotating the polarizing plate 13 of FIG. 1 to change the polarization direction of the illumination light beam. In this case, it is impossible to distinguish whether the change in the measurement result depends on the aberration of the optical system 15 to be measured or the change in the wavefront shape of the transmitted light beam. Further, when the illumination light beam is changed from linearly polarized light to non-polarized light, the wavefront shape of the transmitted light beam is deformed, so that the same difficulty occurs.

  FIG. 4 is a diagram for explaining the reason why the wavefront shape of the transmitted light beam of the pinhole mask 14 is not rotationally symmetric, and is a schematic diagram when the wavefront of the transmitted light beam is viewed from the front (from the optical axis direction).

The symbol y in FIG. 4 indicates the polarization direction of the illumination light beam, and the symbol x indicates the polarization direction that is 90 ° different from the polarization direction of the illumination light beam. The sign S _y in Figure 4, the y-direction and parallel to a plane including the optical axis is a cross-section is cut at the wavefront, symbols S _x is cut wavefront in the x-direction and parallel to a plane including the optical axis It is a cross section made.

Here, attention is paid to four diffracted lights Lφ ₁ , Lφ ₂ , Lr ₁ , and Lr ₂ having the same diffraction angle among the diffracted lights constituting the wavefront of the transmitted light flux. The diffracted lights Lφ ₁ and Lφ ₂ are diffracted lights to the cross section S _x , and the diffracted lights Lr ₁ and Lr ₂ are diffracted lights to the cross section S _y .

Since the polarization direction of the illumination light beam is the y direction as described above, the polarization direction of the diffracted lights Lφ ₁ and Lφ ₂ to the cross section S _x corresponds to the circumferential direction (φ direction) of the pinhole 14c. On the other hand, the polarization direction of the diffracted lights Lr ₁ and Lr ₂ to the cross section S _y corresponds to the radial direction (r direction) of the pinhole 14c.

Therefore, the angle formed by the polarization direction of the diffracted lights Lφ ₁ and Lφ ₂ with respect to the wall surface of the pinhole 14c and the angle formed by the polarization direction of the diffracted lights Lr ₁ and Lr ₂ with respect to the wall surface of the pinhole 14c are mutually different. Different.

Therefore, the phase amount given by the diffracted lights Lφ ₁ and Lφ ₂ from the pinhole 14c is different from the phase quantity given by the diffracted lights Lr ₁ and Lr ₂ from the pinhole 14c.

  That is, the phase amount that the pinhole mask 14 gives to each diffracted light depends on the polarization direction of the diffracted light. Such polarization dependency of the pinhole mask 14 is the reason why the wavefront shape of the transmitted light beam is non-rotationally symmetric. Incidentally, even if the shape error of the pinhole 14c is zero, the wavefront shape of the transmitted light beam is non-rotationally symmetric.

Hereinafter, the light polarized in the r direction (radial direction of the pinhole 14c) like the diffracted lights Lr ₁ and Lr ₂ shown in FIG. 4 is referred to as “r-polarized component Lr”, and the diffracted lights Lφ ₁ and Lφ ₂ The light polarized in the φ direction (circumferential direction of the pinhole 14c) is referred to as “φ polarization component Lφ”.

  FIG. 5 is data showing the distribution of the phase Δr that the pinhole mask 14 gives to the r-polarized component Lr and the distribution of the phase Δφ that the pinhole mask 14 gives to the φ-polarized component Lφ. This data was also obtained by analyzing the design data by the FDTD method, and only the distribution in the r direction is shown here. The horizontal axis in FIG. 5 represents the diffraction angle θ in the unit of numerical aperture (n · sin θ), and the vertical axis in FIG. 5 represents the relative phase with the phases Δr and Δφ as a reference with respect to the ideal spherical wave. It is expressed by (phase advance amount).

  In FIG. 5, the diffracted light having a diffraction angle θ of zero tends to be slightly different from the other diffracted light because there is a slight amount of light that passes through the light shielding film 14b of the pinhole mask 14. However, it can be ignored when the light shielding film 14b is sufficiently thick.

  For reference, FIG. 6 shows data comparing the distribution of the amplitude Ir given to the r-polarized component Lr by the pinhole mask 14 and the distribution of the amplitude Iφ given to the φ-polarized component Lφ. This data was also obtained by analyzing the design data by the FDTD method, and only the distribution in the r direction is shown here.

  As shown in FIG. 5, the distribution of the phase Δr and the distribution of the phase Δφ are different from each other, and the phase Δr advances between the phase Δr and the phase Δφ. Further, the phase difference Δ ′ between the phase Δr and the phase Δφ is more conspicuous as the diffraction angle θ is larger, and particularly when the diffraction angle θ is maximum (here, when the numerical aperture is 1.35). The phase difference Δ ′ reaches 0.45 rad (= 0.07λ).

  Therefore, if the polarizing plate 13 is rotated by 90 ° and the polarization direction of the illumination light beam of the pinhole mask 14 is changed from the y direction to the x direction, the wavefront of the transmitted light beam of the pinhole mask 14 is 0. Deform 45 rad (= 0.07λ). Such a wavefront deformation amount is a level that cannot be ignored for the optical system 15 to be tested.

  FIG. 7 shows data indicating the distribution of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light beam. This data is calculated based on the data of FIG. 5, and only the distribution in the r direction is shown here. The horizontal axis in FIG. 7 is the same as the horizontal axis in FIG. 5, and the vertical axis in FIG. 7 is the phase difference Δ ′ (= Δr−Δφ).

  The manufacturer suppresses the polarization dependence of the pinhole mask 14 by designing the uneven pattern of the compensation plate 16 according to the distribution of the phase difference Δ ′ shown in FIG.

  FIG. 8 is a schematic view of the compensation plate 16 viewed from the optical axis direction.

  The compensation plate 16 is formed by forming a concavo-convex pattern on a substrate (for example, a glass substrate) transparent to the wavelength of the laser light source 11 (see FIG. 1) at a pitch less than the wavelength of the laser light source 1 (see FIG. 1). 2 is a structural birefringent element, and the surface on which the concave / convex pattern is formed is directed to the side opposite to the optical system 15 to be tested as shown in FIG. 2 (however, the concave / convex pattern shown in FIG. Not necessarily the same thing). For the production of such a compensation plate 16, for example, photolithography can be applied.

  Further, the arrangement place of the compensation plate 16 is in the vicinity of the pupil of the detection optical system 15 as shown in FIG. For example, the compensation plate 16 is disposed on the image side of the test optical system 15 and as close to the test optical system 15 as possible. In this way, when the arrangement position of the compensation plate 16 is set in the vicinity of the pupil of the optical system 15 to be measured, the incident angle of the light beam with respect to the compensation plate 16 is reduced, so that the degree of freedom in arranging the compensation plate 16 in the optical axis direction is increased. In addition, the performance of the compensation plate 16 can be maximized.

  Further, the formation pitch (structure period) of the unevenness in the compensation plate 16 is substantially uniform over the entire surface of the compensation plate 16, and the step between the concave and convex portions of the uneven pattern is also uniform over the entire surface of the compensation plate 16. It is.

  Hereinafter, the design data of the compensation plate 16 is assumed as follows.

-Refractive index of compensation plate 16 ... 1.5
-Refractive index of the concave portion of the compensation plate 16 ... 1 (= refractive index of air)
-Concavity and convexity formation pitch of compensation plate 16 ... 250 nm
-Step between concave and convex of compensation plate 16 ... 350 nm
However, the direction of the slow axis of the compensation plate 16 is set according to the sign of the phase difference Δ ′ (see FIG. 7), and the distribution of the duty ratio of the concave / convex pattern (the width of the convex portion: the width of the concave portion) is It is set according to the magnitude distribution of the phase difference Δ ′ (see FIG. 7).

  As shown in FIG. 7, the sign of the phase difference Δ ′ is “positive”. This indicates that the pinhole mask 14 tends to advance the phase of the r-polarized component Lr rather than the φ-polarized component Lφ. Accordingly, the direction of the slow axis of the compensation plate 16 is set to the r direction as shown by a thin line in FIG.

  Further, as shown in FIG. 7, since the magnitude of the phase difference Δ ′ depends on the diffraction angle θ, that is, the position in the r direction, the duty ratio of the concavo-convex pattern of the compensation plate 16 is a plurality of regions A1 having different r positions. , A2, and A3 are set to different values.

  First, the region A1 is a ring-shaped region located on the outermost periphery of the compensation plate 16 and is a diffracted light incident region having a numerical aperture exceeding 1.3. As shown in FIG. 7, since the phase difference Δ ′ of about 0.4 to 0.5 rad is given from the pinhole mask 14 to the incident light beam with respect to the region A1, the phase difference Δ ″ that the region A1 gives to the incident light beam is also 0. It is desirable to be about 4 to 0.5 rad.

  Therefore, the duty ratio of the concavo-convex pattern in the region A1 is set to 1: 1. As described above, since the refractive index of the convex portion is 1.5, the refractive index of the concave portion is 1, and the step between the concave portion and the convex portion is 350 nm, the phase difference given to the incident light beam by the region A1 having a duty ratio of 1: 1. Δ ″ is 35 nm, that is, about 0.065λ (= 0.4 rad).

  Next, the region A2 is a ring-shaped region located inside the region A1, and is an incident region of diffracted light corresponding to a numerical aperture of 1.15 to 1.3. As shown in FIG. 7, since the phase difference Δ ′ of about 0.15 to 0.4 rad is given from the pinhole mask 14 to the incident light beam with respect to the region A2, the phase difference Δ ″ given to the incident light beam by the region A2 is also zero. It is desirable to be about 15 to 0.4 rad.

  Therefore, the duty ratio of the concavo-convex pattern in the region A2 is set to 1: 3. As described above, since the refractive index of the convex portion is 1.5, the refractive index of the concave portion is 1, and the step between the concave portion and the convex portion is 350 nm, the region A2 where the duty ratio of the concave and convex pattern is 1: 3 is the incident light flux. The phase difference Δ ″ to be applied is about 0.045λ (= 0.28 rad).

  Next, the region A3 is a circular region inside the region A2, and is a diffracted light incident region corresponding to a numerical aperture of less than 1.15. As shown in FIG. 7, since the incident light flux to the area A3 is only given a phase difference Δ ′ of about 0 to 0.15 rad from the pinhole mask 14, the phase difference Δ ″ given to the incident light flux by the area A3 is also 0 to 0. .About 15 rad is sufficient.

  Therefore, the duty ratio of the concavo-convex pattern in the region A3 is set to 0: 1. The phase difference Δ ″ that the region A3 gives to the incident light flux is zero.

  FIG. 9 is a diagram showing the distribution of the phase difference Δ ″ that the compensator 16 gives to the incident light beam. Here, only the distribution in the r direction is shown. The horizontal axis of FIG. 9 is the same as the horizontal axis of FIG. The vertical axis in FIG. 9 represents the phase difference Δ ″ as the phase delay amount of the r-polarized component Lr with the phase of the φ-polarized component Lφ as a reference. The dotted line in FIG. 9 shows the distribution of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light beam.

  As shown in FIG. 9, the distribution of the phase difference Δ ″ that the compensator 16 gives to the incident light beam has a shape similar to the distribution of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light beam. Is within 0.025λ within the range of the effective numerical aperture (here, the numerical aperture of 1.40 or less).

  Therefore, the phase difference that the entire wavefront generating optical system including the pinhole mask 14 and the compensation plate 16 gives between the r-polarized component Lr and the φ-polarized component Lφ of the incident light beam is within 0.025λ. This value is about 1/3 or less of the phase difference Δ ′ (see FIG. 7) that the single pinhole mask 14 gives between the r-polarized component Lr and the φ-polarized component Lφ of the incident light beam.

  Therefore, in this apparatus using the compensation plate 16 in combination with the pinhole mask 14, the influence of the polarization dependence of the pinhole mask 14 on the measurement can be suppressed to about 1/3 or less. Therefore, the measurement accuracy of the present apparatus is reliably increased.

  In this embodiment, the distribution curve in the r direction of the duty ratio of the concavo-convex pattern is stepped (see FIG. 9), but may be a polygonal line or a curved line. In any case, it is desirable to make the distribution curve of the phase difference Δ ″ that the compensator 16 gives to the incident light beam closer to the distribution curve of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light beam.

  In the present embodiment, the concave / convex pattern of the compensation plate 16 is set according to the design data of the pinhole mask 14, but may be set according to the actual measurement data of the pinhole mask 14. Alternatively, it may be set according to both the design data and actual measurement data of the pinhole mask 14. Incidentally, the actual measurement data of the pinhole mask 14 may be acquired from the pinhole mask 14 or a sample thereof by a manufacturer of the apparatus using a precise shape measuring apparatus such as an electron microscope. If the concavo-convex pattern of the compensation plate 16 is set according to the actual measurement data of the pinhole mask 14, not only the influence of the polarization dependency of the pinhole mask 14 on the measurement but also the influence of the shape error of the pinhole mask 14 on the measurement. Can also be suppressed.

  When the concave / convex pattern of the compensation plate 16 is set according to the measurement data of the pinhole mask 14, the manufacturer determines the distribution of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light flux in the r direction (θ direction). It is desirable to check over both the φ direction.

  Further, the compensation plate 16 of the present embodiment is given only the function of reducing (or canceling out) the distribution of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light beam. A function of reducing (or canceling) the deviation of the wavefront imparted to the incident light beam from the ideal spherical surface may be provided. Alternatively, another compensation plate provided with a function of reducing (or canceling) deviation from the ideal spherical surface may be prepared separately from the compensation plate 16 and used together with the compensation plate 16.

  Further, although the pinhole mask 14 of the present embodiment is a transmission type pinhole mask, a reflection type pinhole mask may be used.

  Further, although the principle of the Mach-Zehnder interferometer is applied to the wavefront aberration measuring apparatus of the present embodiment, other principles may be applied.

  Further, the optical system to be tested of the wavefront aberration measuring apparatus according to the present embodiment is a microscope objective lens, but may be another type of imaging optical system such as a projection optical system for photolithography. However, in any case, it is desirable that the compensation plate 16 is disposed near the pupil of the optical system to be examined. This apparatus is particularly effective when the object-side numerical aperture of the test optical system is 1 or more (that is, when the test optical system is an immersion lens).

[Second Embodiment]
Hereinafter, a second embodiment of the present invention will be described.

  Here, only differences from the first embodiment will be described. The difference is that the arrangement position of the compensation plate is changed from the image side of the test optical system 15 to the object side.

  FIG. 10 is a schematic view of a cross section obtained by cutting the periphery of the pinhole mask 14 of the present embodiment along a plane that includes the optical axis and is parallel to the paper surface of FIG. As shown in FIG. 10, the compensation plate 16 ′ of this embodiment is disposed between the pinhole mask 14 and the test optical system 15, and the concave / convex pattern faces the test optical system 15 side. .

  In this way, care should be taken when placing the compensation plate 16 ′ away from the pupil of the optical system 15 to be tested, since the degree of freedom in placement is reduced. Further, the concave / convex pattern of the compensation plate 16 'needs to be set in advance to be suitable for the placement destination of the compensation plate 16'. That is, the manufacturer obtains the distribution of the phase difference Δ ′ of the wavefront formed by the transmitted light beam of the pinhole mask 14 at the position where the compensation plate 16 ′ is arranged, and the compensation plate 16 ′ has a distribution according to the distribution of the phase difference Δ ′. It is necessary to set an uneven pattern.

  Therefore, it is assumed that the compensation plate 16 ′ of the present embodiment is previously positioned and fixed with respect to the pinhole mask 14. Reference numeral 24 in FIG. 10 denotes a wavefront generating optical system in which the compensation plate 16 ′ and the pinhole mask 14 are fixed to each other. The wavefront generating optical system 24 includes, for example, a ring frame 20 that fixes the pinhole mask 14 and the compensation plate 16 ′ from the outer peripheral side, and the ring frame 20 keeps the distance between the pinhole mask 14 and the compensation plate 16 ′ constant. Keep on.

  In the wavefront generating optical system 24, at least the optical path portion of the gap between the pinhole mask 14 and the compensation plate 16 ′ is filled with the immersion liquid 20. However, since it is difficult to fill only the optical path portion with the immersion liquid 20, the entire gap between the pinhole mask 14 and the compensation plate 16 ′ is filled with the immersion liquid 20, and the gap prevents outside air (air) from entering. It is desirable that the ring frame 20 be sealed.

  The optical path between the compensation plate 16 ′ and the optical system 15 to be tested is also filled with the immersion liquid 20. However, the inside of the fine recesses formed on the surface of the compensation plate 16 ′ is left as air, and the surfaces of all the protrusions are covered in close contact with the transparent cover 24 b so that there is no gap. The transparent cover 24b is a parallel flat plate (for example, a glass plate) that is transparent to at least the wavelength of the laser light source 11 (see FIG. 1). The transparent cover 24b is also held by the ring frame 20 together with the compensation plate 16 'from the outer peripheral side.

[Third Embodiment]
Hereinafter, a third embodiment will be described. The present embodiment is an embodiment relating to calibration of a Shack-Hartmann wavefront aberration measuring apparatus.

  FIG. 11 is a configuration diagram at the time of measurement of the wavefront aberration measuring apparatus of the present embodiment. As shown in FIG. 11, a laser light source 31, a beam expander 32, a polarizing plate 13, a test reticle Rt having a function of a pinhole mask, and a detection optical system 31 are arranged in the wavefront aberration measuring apparatus of this embodiment. In the detection optical system 31, a relay lens 34, a microlens array 36, and an image sensor 37 are arranged.

  At the time of measurement, the test optical system 35 is disposed between the test reticle Rt and the detection optical system 31. The test optical system 35 is, for example, a projection optical system for photolithography.

  The laser light source 31 emits a laser beam having a wavelength used by the optical system to be tested 35 or a wavelength in the vicinity thereof. Laser light emitted from the laser light source 31 is linearly polarized light. The laser light emitted from the laser light source 31 is converted into a light beam having a large diameter by the beam expander 32, and enters the polarizing plate 33 as a plane wave. The light beam that has passed through the polarizing plate 33 illuminates the test reticle Rt. Of the illumination light beam, the light beam that has passed through the test reticle Rt becomes a spherical wave, and enters the test optical system 35 as a measurement light beam from the object side. Note that the object-side focal plane of the optical system to be tested 35 is located in the vicinity of the test reticle Rt.

  The light beam emitted from the test optical system 35 forms an image on the image plane of the test optical system 35 and then diverges again, is converted into a parallel light beam by the relay lens 34, and enters the microlens array 36. The parallel light beam incident on the microlens array 36 is divided into wavefronts to form a secondary image array on the image sensor 37. When the image sensor 37 captures the secondary image array and generates image data, it outputs the image data to a computer (not shown). Based on the image data and calibration data (described later) stored in advance, the computer calculates the wavefront aberration of the test optical system 35 (the amount of wavefront deformation of the measurement light beam before and after passing through the test optical system 35).

  FIG. 12 is a configuration diagram at the time of calibration of the wavefront aberration measuring apparatus of the present embodiment.

  The calibration target is the relay lens 34. At the time of calibration, the test reticle Rt and the test optical system 35 are removed from the optical path, and instead, a transmissive pinhole mask 14 ′ for generating a spherical wave and a compensation plate 16 ″ that is a birefringent element are arranged.

  The pinhole mask 14 ′ is disposed on the front focal plane of the relay lens 34, and the compensator 16 ″ is disposed near the pupil of the relay lens 34, that is, between the relay lens 34 and the microlens array 36. In the parallel luminous flux.

  The pinhole mask 14 ′ has the same configuration as the pinhole mask 14 of the first embodiment, and the transparent substrate of the pinhole mask 14 ′ is a substrate that is transparent with respect to the wavelength of the laser light source 31. The light shielding film of the hole mask 14 ′ is a film that is opaque to the wavelength of the laser light source 31.

  The compensation plate 16 ″ has the same configuration as the compensation plate 16 of the first embodiment, and the pinhole mask 14 ′ gives the r-polarized light component Lr in the direction of the slow axis of the uneven pattern of the compensation plate 16 ″. The distribution of the duty ratio of the concavo-convex pattern of the compensation plate 16 ″ is set according to the delay relationship between the phase and the phase given to the φ polarization component Lφ, and the distribution of the phase difference Δ ′ given to the incident light beam by the pinhole mask 14 ′ These settings give the compensation plate 16 ″ a function of suppressing the polarization dependence of the pinhole mask 14 ′.

  In the calibration, image data is output from the image sensor 37 to the computer in the state shown in FIG. Based on the image data, the computer generates and stores calibration data for the relay lens 34 (the amount of wavefront deformation of the light beam before and after passing through the relay lens 34).

  In the above calibration, the compensation plate 16 ″ is used together with the pinhole mask 14 ′, so that the influence of the polarization dependency of the pinhole mask 14 ′ on the calibration can be suppressed. Therefore, the measurement performed in the state shown in FIG.

  Although the numerical aperture of the relay lens 34 has not been described in the present embodiment, when the numerical aperture of the relay lens 34 is 1 or more (when the relay lens 34 is an immersion lens), the relay lens 34 The optical path between the pinhole mask 14 'is filled with immersion liquid. Incidentally, this embodiment is also particularly effective when the numerical aperture of the relay lens 34 is 1 or more.

  In this embodiment, the same wavefront generating optical system as that of the first embodiment is used for calibration of the Shack-Hartmann wavefront aberration measuring apparatus (that is, the wavefront generating optical system in which the compensator is disposed near the pupil of the test optical system). However, a wavefront generating optical system similar to that of the second embodiment (that is, a wavefront generating optical system in which the compensator is disposed near the pinhole mask) may be applied.

[Supplement of Wavefront Generating Optical System etc. Exemplifying the Present Invention]
In the above-described wavefront generating optical system illustrating the present invention, the compensation phase plate may be a structural birefringent element in which a concavo-convex pattern is formed at a pitch less than the use wavelength of the wavefront generating optical system. .

  Further, the phase shift distribution given to the two polarization components by the compensating phase plate may be a rotationally symmetric distribution around the optical axis.

  Further, the radius r of the pinhole formed in the pinhole mask may satisfy the equation r <0.47λ with respect to the wavelength λ used for the pinhole mask.

  In the above-described wavefront aberration measuring apparatus exemplifying the present invention, the compensation phase plate of the wavefront generating optical system may be disposed near the pupil of the optical system to be measured.

  The object-side numerical aperture of the optical system to be tested may be 1 or more.

It is a block diagram of the wavefront aberration measuring apparatus of 1st Embodiment. It is a schematic diagram of the cross section which cut | disconnects the periphery of the pinhole mask 14 of 1st Embodiment in the plane parallel to the paper surface of FIG. 1 including an optical axis. This is data indicating the wavefront shape of the transmitted light flux of the pinhole mask. It is a figure explaining the reason why the wavefront shape of the transmitted light beam of the pinhole mask is not rotationally symmetric. This is data indicating the distribution in the r direction of the phase Δr that the pinhole mask 14 gives to the r polarization component Lr and the distribution in the r direction of the phase Δφ that the pinhole mask 14 gives to the φ polarization component Lφ. This is data indicating the distribution in the r direction of the amplitude Ir given to the r-polarized light component Lr by the pinhole mask 14 and the distribution in the r direction of the amplitude Iφ given to the φ-polarized light component Lφ by the pinhole mask 14. This is data indicating the distribution in the r direction of the phase difference Δ ′ that the pinhole mask 14 gives to the incident light beam. It is the schematic diagram which looked at the compensation plate 16 from the optical axis direction. It is a figure which shows distribution of the r direction of phase difference (DELTA) '' which the compensating plate 16 gives to an incident light beam. It is a schematic diagram of the cross section which cut | disconnects the periphery of the pinhole mask 14 of 2nd Embodiment by the plane parallel to the paper surface of FIG. 1 including an optical axis. It is a block diagram at the time of the measurement of the wavefront aberration measuring apparatus of 3rd Embodiment. It is a block diagram at the time of calibration of the wavefront aberration measuring apparatus of 3rd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Laser light source 11, 12 ... Beam expander, 13 ... Polarizing plate, BS1, BS2 ... Beam splitter, 14 ... Pinhole mask, 16 ... Compensation plate, M1, M2 ... Mirror, 17 ... Image sensor, 15 ... Test Optical system

Claims (7)

A pinhole mask for generating a spherical light wave, and a compensation phase plate disposed on the exit side of the pinhole mask,
The phase shift distribution that the compensating phase plate gives to two different polarization components of incident light is:
A wavefront generating optical system, wherein the pinhole mask is set to a distribution that cancels or reduces a phase shift distribution given to the two polarization components of incident light. The wavefront generating optical system according to claim 1,
The compensation phase plate is
A wavefront generating optical system, wherein the wavefront generating optical system is a structural birefringent element in which a concavo-convex pattern is formed with a pitch less than a wavelength used by the wavefront generating optical system. The wavefront generating optical system according to claim 1 or 2,
The phase shift distribution given to the two polarization components by the compensation phase plate is:
A wavefront generating optical system characterized by having a rotationally symmetric distribution around the optical axis. In the wavefront generating optical system according to claim 1,
A wavefront generating optical system characterized in that a radius r of a pinhole formed in the pinhole mask satisfies an expression of r <0.47λ with respect to a use wavelength λ of the pinhole mask. The wavefront generating optical system according to any one of claims 1 to 4,
An illumination optical system that generates a measurement light beam in the wavefront generation optical system by illuminating the pinhole mask of the wavefront generation optical system;
Detection means for detecting the wavefront shape of the measurement light beam generated by the wavefront generation optical system and passed through the test optical system;
A wavefront aberration measuring device for an optical system, comprising: In the wavefront aberration measuring device according to claim 5,
The placement destination of the compensation phase plate of the wavefront generating optical system is:
A wavefront aberration measuring apparatus, wherein the wavefront aberration measuring apparatus is in the vicinity of the pupil of the test optical system. In the wavefront aberration measuring device according to claim 5 or 6,
The object-side numerical aperture of the test optical system is
A wavefront aberration measuring apparatus characterized by being 1 or more.

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