JP2022129508A - Inspection device and wave surface aberration measurement method - Google Patents

Abstract

To provide an inspection device and a wave surface aberration measurement method that can measure the wave surface aberration instantly at high accuracy.SOLUTION: An inspection device 1 according to an embodiment includes a stage 10 on which a specimen 11 is disposed at the inspection and a point light source is disposed at the measurement of the aberration, an object lens 20 that transmits inspection light L1 resulting from reflection of illumination light L0 on the specimen 11 at the inspection, and measurement light L2 from the point light source at the measurement of the aberration, a pupil relay lens 21 that transmits the inspection light L1 and the measurement light L2 and has the focal distance longer than that of the object lens 20, a pupil relay lens 22 that forms an intermediate imaging surface between the pupil relay lens 21 and the pupil relay lens 22, a diffraction grating 40 that is disposed between the pupil relay lens 21 and the intermediate imaging surface and that diffracts the measurement light L2, a PDI plate 50 that is disposed in the vicinity within the focal depth of the intermediate imaging surface and that selectively transmits the diffraction light diffracted by the diffraction grating 40, a detector 30 that detects an image of the specimen, and a detector 60 that detects an interference image of the measurement light.SELECTED DRAWING: Figure 2

Description

The present invention relates to an inspection apparatus and wavefront aberration measuring method, and more particularly to an inspection apparatus and wavefront aberration measuring method for in-situ measuring wavefront aberration, which is imaging performance of an optical semiconductor inspection apparatus.

2. Description of the Related Art Optical inspection apparatuses for manufacturing semiconductor devices are becoming larger in scale as wavelengths are becoming shorter, numerical apertures are becoming higher, and functions are becoming more sophisticated. An optical inspection apparatus optically inspects a semiconductor device or the like using an optical microscope composed of an objective lens and an imaging lens. An objective lens and an imaging lens, which are adjusted with high precision by an apparatus manufacturer (Maker), are individually adjusted using dedicated wavefront aberration measuring equipment (so-called interferometer). However, the wavefront aberrations of the objective lens and the imaging lens are not quantitatively measured after mounting in an optical inspection device, after shipping and transportation, and after installation in a semiconductor manufacturing factory. Further, the aberration in the state in which the objective lens and the imaging lens are combined is not quantitatively measured due to structural limitations of the wavefront aberration measurement equipment that even the device manufacturer owns. Even after operation at a semiconductor production factory, even if some kind of impact is applied or if there is a performance change in the imaging optical system, it is only possible to determine the presence or absence of abnormalities in the sample observation image. Quantitative measurement of imaging performance in the semiconductor industry is becoming necessary from the viewpoint of semiconductor production management.

2. Description of the Related Art In a reduction projection system such as an exposure apparatus for manufacturing semiconductors, a projection lens is already combined because it is integrally constructed by an objective lens and an imaging lens. Wavefront aberration can also be measured integrally in-situ.

Patent Document 1 and Non-Patent Document 1 describe a method of exposing a special reticle and calculating wavefront aberration from a pattern image of a resist.

In FIG. 6 of Patent Document 2, a Shack-Hartmann sensor composed of a pinhole for generating a spherical wave is arranged in the reticle, and a pinhole, a relay lens, and a microlens array are placed on a wafer stage under a projection lens with a high numerical aperture. (Shack-Hartmann Sensor) describes a method for calculating wavefront aberration.

N. Farrar et al.: “In-situ measurement of lens aberrations,” Proc. SPIE, 4000 (2000) 18-29. H.Medecki,”Phase-shifting point diffraction interferometer”, OPTICS LETTERS / Vol. 21, No. 19 / October 1, 1996 M.Takeda,”Fourier-transform method of fringe-pattern analysis for computer-based topography and interferometry”,J.Opt.Soc.Am/Vol.72,No1/Jan 1982

U.S. Pat. No. 5,828,455 JP 2004-014865 A WO2000/065318

The methods of Non-Patent Document 1 and Patent Document 1 are premised on a resist image, and it is difficult to apply the concept to a semiconductor inspection apparatus. Furthermore, the method of Patent Document 2 is established by the limitation of a monochromatic high numerical aperture objective lens and a Shack-Hartmann sensor on the premise of a monochromatic wavelength. It is difficult to apply this method to an inspection apparatus that selects a wavelength band from within the range and uses multiple types of wavelength bands.

On the other hand, from the viewpoint of interferometric wavefront aberration measurement technology in general, there is a Fizeau-type wavefront aberration measurement facility that is often used by equipment manufacturers. However, this device is a large facility, difficult to move, and expensive. Moreover, it is a configuration that requires a reference surface. Therefore, there is also the problem that the measurement accuracy is rate-determined by the surface accuracy of the reference surface. Furthermore, in general, it is difficult to mount an inspection apparatus including a plurality of folding mirrors in its configuration on a wavefront aberration measurement facility in a state in which an imaging optical system is combined for measurement.

Non-Patent Document 2 and Patent Document 2 describe a wavefront aberration measurement technique called PS-PDI (Phase Shifting Point Diffraction Interferometry). The techniques described in these documents are characterized by using simple members, generating a reference wavefront with a simple pinhole, and measuring wavefront aberration with high accuracy. However, there is no report that the method of Patent Document 2 is embodied as an in-situ measurement of an inspection apparatus having an imaging optical system with a numerical aperture of 0.9 level.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides an inspection apparatus and a wavefront aberration measuring method capable of on-site measurement of wavefront aberration, which is imaging performance of an optical inspection apparatus, with high accuracy.

An inspection apparatus according to the present invention includes a stage on which a sample is placed during inspection and a point light source is placed during aberration measurement; illumination light that illuminates the sample during inspection transmits inspection light reflected by the sample; An objective lens that transmits measurement light emitted from the point light source during the aberration measurement, and a first lens that transmits the inspection light and the measurement light that have passed through the objective lens and functions as an imaging lens, A pupil plane is formed between the objective lens and the first lens, and the first lens has a focal length longer than the focal length of the objective lens, and the inspection light and the measurement are transmitted through the first lens. a second lens that transmits light, the second lens having an intermediate image plane formed between the first lens and the second lens; and the first lens and the intermediate image plane. a diffraction grating disposed between and diffracting the measurement light; a large hole and a small hole having an inner diameter smaller than that of the large hole; The hole is positioned on the optical axis of the measurement light, the small hole is separated from the large hole, and passes through a PDI plate that transmits the diffracted light diffracted by the diffraction grating, the second lens, and the tube lens. a first detector arranged on the imaging conjugate plane of the inspection light to detect the image of the sample; a second detector for detecting; and a mirror disposed between the second lens and the tube lens for switching between the inspection and the aberration measurement; The grating and the PDI plate are retracted from the optical path of the inspection light.

In the inspection apparatus, the magnification in the intermediate imaging plane determined by the ratio of the focal length of the objective lens to the focal length of the first lens may be 50 times or more.

In the above inspection apparatus, the gap between gratings of the diffraction grating, the large hole and the small hole may be hollow.

In the above inspection apparatus, the illumination light uses a plurality of inspection wavelengths, and the measurement light has a wavelength within the inspection wavelength band width of the illumination light, and is the center wavelength or the centroid of the inspection wavelength band of the illumination light. λ is the wavelength of the measurement light, NA is the numerical aperture of the objective lens, and the magnification of the intermediate imaging plane determined by the ratio between the focal length of the objective lens and the focal length of the first lens is Let M be the distance in the optical axis direction between the diffraction grating and the PDI plate, and let P be the pitch of each grating of the diffraction grating.
Φt>30・0.61・λ/(NA/M) (A)
and the inner diameter Φr of the small hole is
Φr<0.61 λ/(NA/M) (B)
and the distance D between the center of the large hole and the center of the small hole is
D = L tan (sin ^-1 (λ/P)) (C)
may be satisfied.

In the above inspection apparatus, the PDI plate includes a first large hole, a first small hole, a second large hole, and a second small hole so as to correspond to a plurality of inspection wavelengths; The measurement light includes a first measurement light having a first measurement wavelength corresponding to and a second measurement light having a second measurement wavelength corresponding to a second inspection wavelength, the first large hole, the first small hole and the second measurement light 1 measurement wavelength satisfies the formulas (A), (B) and (C), and the second large hole, the second small hole and the second measurement wavelength satisfy the formulas (A) and (B) and (C), when the measurement light is changed from the first measurement light to the second measurement light, the PDI plate is shifted to shift the first measurement light to the first large hole. And, the state in which the second measurement light is transmitted through the first small hole may be changed to the state in which the second measurement light is transmitted through the second large hole and the second small hole.

In the above inspection apparatus, the peripheral thickness a of the large hole and the small hole in the PDI plate is
a<λ/(NA/M) (D)
and the thickness of the portion of the PDI plate surrounding the peripheral edge may be twice or more the thickness a so as to increase the mechanical strength.

In the above inspection apparatus, when the point light source is moved in a plane perpendicular to the optical axis of the objective lens within the field of view of the objective lens, the PDI plate is adapted to move the point light source according to the amount of movement of the objective lens. The moving amount may be multiplied by the magnification of the intermediate imaging plane determined by the ratio of the focal length of the lens to the focal length of the first lens.

A wavefront aberration measurement method according to the present invention includes a stage on which a sample is arranged, an objective lens for transmitting inspection light reflected by the sample from illumination light that illuminates the sample, and the inspection light transmitted through the objective lens. a first lens for transmission, wherein a pupil plane is formed between the objective lens and the first lens, and the first lens has a longer focal length than the focal length of the objective lens; a second lens for transmitting the inspection light that has passed through the second lens, the second lens having an intermediate imaging plane formed between the first lens and the second lens; A wavefront aberration measurement method for an inspection apparatus, comprising: a first detector that is arranged on an imaging conjugate plane of inspection light and detects an image of the sample, the step of arranging a point light source on the stage; transmitting measurement light emitted from a point light source through the objective lens; transmitting the measurement light transmitted through the objective lens through the first lens; and forming the intermediate image with the first lens. a PDI in which a large hole and a small hole having an inner diameter smaller than the large hole are formed in the vicinity of the depth of focus of the intermediate imaging plane by diffracting the measurement light by arranging a diffraction grating between the surface and the PDI; disposing a plate so that the large hole is positioned on the optical axis of the measurement light, separating the small hole from the large hole, and allowing the diffracted light diffracted by the diffraction grating to pass through; and detecting an interference image of the measurement light transmitted through two lenses with a second detector arranged on a pupil conjugate plane of the measurement light.

In the wavefront aberration measuring method, the magnification on the intermediate imaging plane determined by the ratio of the focal length of the objective lens to the focal length of the first lens may be 50 times or more.

In the above-described wavefront aberration measuring method, the spaces between gratings of the diffraction grating, the large holes, and the small holes may be hollow.

In the wavefront aberration measurement method, the illumination light uses a plurality of inspection wavelengths, and the measurement light has a wavelength within the inspection wavelength band width of the illumination light, and is the center wavelength of the inspection wavelength band of the illumination light. or including the centroid wavelength, the wavelength of the measurement light is λ, the numerical aperture of the objective lens is NA, and the intermediate imaging plane determined by the ratio between the focal length of the objective lens and the focal length of the first lens Let M be the magnification, L be the distance between the diffraction grating and the PDI plate in the optical axis direction, and P be the pitch of each grating of the diffraction grating.
Φt>30・0.61・λ/(NA/M) (A)
is satisfied, and the inner diameter Φr of the small hole is
Φr<0.61 λ/(NA/M) (B)
and the distance D between the center of the large hole and the center of the small hole is
D = L tan (sin ^-1 (λ/P)) (C)
may be satisfied.

In the wavefront aberration measurement method, the PDI plate includes a first large hole, a first small hole, a second large hole, and a second small hole so as to correspond to a plurality of inspection wavelengths, and The measurement light includes a first measurement light having a first measurement wavelength corresponding to the first inspection wavelength and a second measurement light having a second measurement wavelength corresponding to the second inspection wavelength in the inspection light, and The hole, the first small hole and the first measurement wavelength satisfy the formulas (A), (B) and (C), and the second large hole, the second small hole and the second measurement wavelength are , (A), (B) and (C) are satisfied, the PDI plate is shifted when changing the measurement light from the first measurement light to the second measurement light, and The state in which the first measurement light is transmitted through the first large hole and the first small hole may be changed to the state in which the second measurement light is transmitted through the second large hole and the second small hole.

In the wavefront aberration measurement method, the thickness a of the periphery of the large hole and the small hole in the PDI plate is
a<λ/(NA/M) (D)
and the thickness of the portion surrounding the peripheral edge of the PDI plate may be twice or more the thickness a so as to increase the mechanical strength.

In the wavefront aberration measurement method, when the point light source is moved in a plane perpendicular to the optical axis of the objective lens within the field of view of the objective lens, the PDI plate is adjusted to the amount of movement of the point light source, The movement amount may be multiplied by the magnification of the intermediate imaging plane determined by the ratio of the focal length of the objective lens to the focal length of the first lens.

The present invention provides an inspection apparatus and a wavefront aberration measurement method capable of on-site measurement of wavefront aberration, which is imaging performance of an optical inspection apparatus, with high accuracy.

2 is a diagram illustrating the configuration of a sample inspection system in the inspection apparatus according to Embodiment 1. FIG. 4 is a diagram illustrating the configuration of a measurement optical system for measuring wavefront aberrations of an objective lens and a relay lens in the inspection apparatus according to Embodiment 1; FIG. 2 is a plan view illustrating a PDI plate in the inspection apparatus according to Embodiment 1. FIG. 2 is a plan view illustrating a null plate in the inspection device according to Embodiment 1. FIG. 2 is a flowchart illustrating an inspection method using the inspection apparatus according to Embodiment 1; FIG. FIG. 4 is a flowchart illustrating a wavefront aberration measurement method using the inspection apparatus according to Embodiment 1; FIG. 10 is a plan view illustrating a PDI plate in the inspection apparatus according to Embodiment 2; FIG. 11 is a plan view illustrating a PDI plate in the inspection apparatus according to Embodiment 3;

For clarity of explanation, the following descriptions and drawings are omitted and simplified as appropriate. Moreover, in each drawing, the same elements are denoted by the same reference numerals, and redundant description is omitted as necessary.

(Embodiment 1)
An inspection apparatus according to Embodiment 1 will be described below. The inspection apparatus of this embodiment has a sample inspection system for inspecting a sample such as a semiconductor device wafer and a measurement optical system for measuring wavefront aberration of an objective lens or the like provided in the inspection apparatus. First, <configuration of sample inspection system> will be described. Next, <configuration of aberration measurement optical system> will be described. Then, <specimen inspection method> and <wavefront aberration measurement method> using the inspection apparatus will be described.

<Configuration of sample inspection system>
FIG. 1 is a diagram illustrating the configuration of a sample inspection system in an inspection apparatus according to Embodiment 1. FIG. As shown in FIG. 1, the inspection apparatus 1 includes a light source (Light Source) LS, a beam splitter (Beam Splitter) BS, a stage (Stage) 10, an objective lens 20, a pupil relay lens (Relay Lens) 21, and a pupil relay lens 22. , a tube lens 23 and a detector 30 . The inspection apparatus 1 may appropriately include necessary optical members such as mirrors MR1 and MR2.

The light source LS is a UV lamp, an LPP light source (Laser Produced Plasma), or the like, and generates and emits illumination light L0. A part of the emitted illumination light L0 is reflected by the beam splitter BS and enters the objective lens 20 . The illumination light L<b>0 incident on the objective lens 20 passes through the objective lens 20 . At that time, the illumination light L0 is condensed by the objective lens 20 .

The stage 10 is arranged on the optical axis of the objective lens 20 . A sample 11 is placed on the stage 10 . The sample 11 is, for example, a wafer on which semiconductor devices are formed. Note that the sample 11 is not limited to a wafer on which semiconductor devices are formed, and may be a wafer such as a semiconductor substrate or a member for manufacturing a semiconductor device such as a photomask.

Here, for convenience of explanation of the inspection apparatus 1, an XYZ orthogonal coordinate axis system is introduced. The optical axis of the objective lens 20 is assumed to be the Z-axis direction, and the upper surface of the stage 10 is assumed to be the XY plane.

The illumination light L 0 condensed by the objective lens 20 illuminates the sample 11 . The illumination light L0 that has illuminated the sample 11 is reflected by the sample surface 15 of the sample 11 . The reflected light reflected by the sample surface 15 of the sample 11 is called inspection light L1. The inspection light L<b>1 enters the objective lens 20 . The inspection light L1 then passes through the objective lens 20 . At that time, the inspection light L1 is collimated by the objective lens 20 into parallel light. In this way, the objective lens 20 transmits the inspection light L1 that is the illumination light L0 that illuminates the sample 11 and is reflected by the sample 11 . A portion of the inspection light L1 transmitted through the objective lens 20 is transmitted by the beam splitter BS and enters the pupil relay lens 21 .

When the inspection light L1 enters the pupil relay lens 21, a pupil plane 25 is formed between the objective lens 20 and the pupil relay lens 21, forming a pupil image. If the pupil plane 25 is formed inside or outside the objective lens 20, it is difficult to insert a filter, a diaphragm, or the like. , a pupil image is formed on the focal plane 45 of the pupil relay lens 22, and a filter and a diaphragm are arranged on the pupil conjugate plane 45 on the main optical path on the reflection side of the MR2.

The focal length of the pupil relay lens 21 is, for example, about 50 times greater than the focal length of the objective lens 20 , and forms an enlarged image of the sample 11 on the intermediate imaging plane 35 . For example, if the magnification is 50 and the NA of the objective lens 20 is 0.9, the NA of the relay lens 21 is 0.9/50=0.018. Note that the NA of the objective lens 20 is not limited to these. For example, the NA of the objective lens 20 may be 0.85-0.9 or 0.9-0.95 depending on the case. The pupil relay lens 21 transmits the incident inspection light L1. At that time, the pupil relay lens 21 condenses the inspection light L1. As a result, an intermediate image of the sample 11 is formed on the intermediate imaging plane 35 between the pupil relay lens 21 and the pupil relay lens 22 .

Thus, the pupil relay lens 21 transmits the inspection light L<b>1 that has passed through the objective lens 20 and has a numerical aperture smaller than that of the objective lens 20 .

The pupil relay lens 22 transmits the inspection light L1 that has passed through the pupil relay lens 21 . At that time, the pupil relay lens 22 collimates the inspection light L1. An intermediate imaging plane 35 is formed between the pupil relay lens 21 and the pupil relay lens 22, and an intermediate image is formed. The inspection light L1 transmitted through the pupil relay lens 21 may be made incident on the pupil relay lens 22 after being reflected by a mirror MR1.

The magnification of the intermediate image on the intermediate imaging plane 35 is determined by the ratio between the focal length of the objective lens 20 and the focal length of the pupil relay lens 21 . The magnification of the intermediate image is, for example, 50 times or more, such as 50 to 70 times. Note that the magnification of the intermediate image is not limited to these.

The inspection light L1 transmitted through the pupil relay lens 22 becomes parallel light, for example. The inspection light L<b>1 that has passed through the pupil relay lens 22 enters the tube lens 23 . The inspection light L1 transmitted through the pupil relay lens 22 may be reflected by the mirror MR2 and then made incident on the tube lens 23 . A pupil conjugate plane 45 is formed between the pupil relay lens 22 and the tube lens 23 . A pupil conjugate plane 45 is also formed on the transmission side of MR2.

The tube lens 23 collects the inspection light L1 that has passed through the relay lens 22 . The tube lens 23 may include a plurality of lenses having different focal lengths. This makes it possible to achieve a plurality of imaging magnifications. The tube lens 23 may be used by switching lenses with different focal lengths. As a result, an imaging conjugate plane 55 is formed on the detection plane of the detector 30, and an image of the sample plane 15 on the sample 11 is formed.

The detector 30 is arranged on the imaging conjugate plane 55 of the inspection light L1 that has passed through the pupil relay lens 22 . For example, the tube lens 23 is placed on the imaging conjugate plane 55 where the inspection light L1 transmitted through the pupil relay lens 22 is imaged, and the detector 30 detects the image of the sample plane 15 on the sample 11. . The magnification of the image of the sample plane 15 on the detection plane of the detector 30 is, for example, 70 times to 300 times. Detector 30 may be, for example, a camera. Detector 30 may have an image sensor. For example, an image sensor records an image of the sample plane 15 .

The inspection device 1 may be, for example, a large microscope. Since the entire optical path in the inspection device 1 is long (eg, 3-5 [m]), the inspection device 1 may include several folding mirrors. The inspection apparatus 1 of the present embodiment causes the inspection light L1 to be introduced into the sample inspection system and observes the imaging conjugate plane 55 by retracting the folding mirror or the like from the optical path or semi-transmitting it. On the other hand, during aberration measurement, a point light source is placed on the sample surface 15 to emit light, the MR2 is retracted, measurement light is introduced into the aberration measurement optical system, and the pupil conjugate plane 45 can be observed with the detector 60. configuration.

<Configuration of aberration measurement system>
Next, the configuration of an aberration measurement system for measuring aberrations of the objective lens 20 and the pupil relay lens 21 will be described. FIG. 2 is a diagram illustrating the configuration of an aberration measurement system for measuring aberrations of the objective lens 20 and the pupil relay lens 21 in the inspection apparatus 1 according to the first embodiment. As shown in FIG. 2, when measuring the wavefront aberration of the objective lens 20 and the pupil relay lens 21, the inspection apparatus 1 includes a point light source generation unit 12, a diffraction grating 40, a PDI plate (Point Diffraction Interferometry Plate) 50, A detector 60 is provided.

The point light source generation unit 12 emits inspection light L2 including an ideal spherical wave 16. FIG. Thereby, the point light source generation unit 12 functions as a point light source. A point light source generation unit 12 is arranged on the stage 10 . Therefore, a sample 11 or a point light source is arranged on the stage 10 . The point light source generating unit 12 includes, for example, a laser light source (not shown), a lens (not shown) for collecting a laser beam emitted from the laser light source, and a pinhole 13 . A pinhole plate 14 may also be included.

One plate surface or pattern surface of the pinhole plate 14 faces the objective lens 20 . One plate surface of the pinhole plate 14 and the sample surface 15 of the sample 11 are arranged at the same position on the optical axis of the objective lens 20 . The inner diameter of the pinhole 13 is set to λ/(NA of the objective lens 20) or less. For example, when the wavelength of the laser beam (that is, the measurement light L2) is 355 [nm] and the NA of the objective lens 20 is 0.9, the inner diameter of the pinhole 13 is preferably 394 [nm] or less.

The laser light source is, for example, a DPSS laser (Diode Pumped Solid State Laser). The laser beam irradiates the other plate surface side of the pinhole plate 14 . Thereby, the laser beam passes through the pinhole 13 from the other plate surface side of the pinhole plate 14 . Therefore, the laser beam passes through the pinhole 13, and the diffracted measurement light L2 having an ideal spherical wave is emitted from the pinhole 13. FIG. In this manner, the point light source generation unit 12 emits measurement light L2, which is an ideal spherical wave, as a point light source.

The measurement light L2 emitted from the point light source generation unit 12 contains the spherical wave 16. As shown in FIG. The measurement light L2 containing the spherical wave 16 passes through the objective lens 20. FIG. At that time, the measurement light L2 is collimated by the objective lens 20 . For example, the inspection light L2 transmitted through the objective lens 20 is converted into parallel light. Thus, the objective lens 20 transmits the measurement light L2 emitted from the point light source.

If the objective lens 20 has no aberration, the measurement light L2 that has passed through the objective lens 20 becomes an ideal plane wave. However, the measurement light L2 that has passed through the objective lens 20 containing aberrations becomes a distorted plane wave 17 .

The measurement light L2 that has passed through the objective lens 20 enters the pupil relay lens 21 . A pupil plane 25 is formed between the objective lens 20 and the pupil relay lens 21 to form a pupil image. A pupil image of the measurement light L2 is relay-formed on the pupil plane 25 via the pupil relay lens 21 and the pupil relay lens 22 . The pupil relay lens 21 transmits and converges the measurement light L2. As a result, an intermediate imaging plane 35 is formed between the pupil relay lens 21 and the relay lens 22, and an intermediate image of the point light source is formed. Since the measurement light L2 incident on the pupil relay lens 21 is a distorted plane wave 17 including the aberration of the objective lens 20, the measurement light L2 transmitted through the pupil relay lens 21 contains a distorted spherical wave 18.

A diffraction grating (Grating) 40 is arranged between the pupil relay lens 21 and the intermediate imaging plane 35 . Although the diffraction grating 40 may be of a transmissive type or a reflective type, the transmissive type will be described in this embodiment. The diffraction grating 40 diffracts the inspection light L2 that has passed through the objective lens 20 and the pupil relay lens 21 into zero-order light, ±first-order light, ±second-order light, . . . , ±n-order light. Diffracted light of each order forms a focused spot on the intermediate imaging plane 35 .

The diffraction grating 40 can be moved in the grating pitch direction by steps of 0, 1/4, 1/2, and 3/4 of the grating pitch (Pitch) by a one-dimensional actuator (not shown). . For example, the actuator moves diffraction grating 40 in the Y-axis direction. Thereby, the phase of the +1st order (−1st order) diffracted light can be modulated to 0, π/2, π, and 3π/2.

As the transmission type diffraction grating 40, a grating formed in a line and space pattern on a thin plate is used. In the diffraction grating 40 in which a line-and-space pattern is formed on a light-shielding thin film on a glass substrate, spherical aberration, which is not inherent in the glass substrate, occurs due to the thickness of the glass substrate. Therefore, the transmission type diffraction grating 40 is preferably a thin plate on which a line-and-space grating is formed by photoetching or photoelectroforming. The spaces between gratings of such a diffraction grating 40 are hollow. That is, the space between the gratings of the diffraction grating 40 is air, a predetermined gas, or a space in which the pressure is reduced.

The minimum line-and-space dimension that can be formed by a photoetching or electroforming process is, for example, about several tens [μm]. In the inspection apparatus 1 of the present embodiment, the diffraction grating 40 is arranged in a space with a magnification of about 50 to 70 times. As a result, even the diffraction grating 40 with a line-and-space dimension of about several tens [μm] can satisfy the desired conditions. Therefore, it is not necessary to use a metal self-supporting film or the like having line-and-space dimensions on the order of nanometers for the diffraction grating 40, which is produced by an advanced and expensive process, and manufacturing costs can be reduced.

The PDI plate 50 is arranged in the vicinity of a predetermined range of the intermediate imaging plane 35 . The PDI plate 50 is plate-shaped. FIG. 3 is a plan view illustrating the PDI plate 50 in the inspection device 1 according to the first embodiment.

As shown in FIG. 3, the PDI plate 50 is formed with a plurality of holes. For example, the PDI plate 50 is formed with a large hole 51 and a small hole 52 having an inner diameter smaller than that of the large hole 51 . The large hole 51 and the small hole 52 are preferably through holes that penetrate the PDI plate 50 . That is, the large holes 51 and the small holes 52 are preferably hollow. Therefore, the insides of the large holes 51 and the small holes 52 are air, predetermined gas, or a space in which the pressure is reduced.

The large hole 51 is positioned on the optical axis of the measurement light L2. Specifically, the central axis of the large hole 51 is positioned on the optical axis of the measurement light L2. The small hole 52 is separated from the large hole 51 in the Y-axis direction. The center axis of the small hole 52 is located at the condensing point of the +1st order diffracted light or -1st order diffracted light.

The inspection light L2 containing the distorted spherical wave 18 is incident on the large hole 51 . The measurement light L2 that has passed through the large hole 51 still contains the distorted spherical wave 18 . The measurement light L2 that has passed through the large hole 51 is called a test wave (Test Wave) TW. On the other hand, the +1st order diffracted light or -1st order diffracted light of the measurement light L2 containing the distorted spherical wave 18 enters the small hole 52 . The measurement light L2 transmitted through the small hole 52 having an inner diameter as small as the pinhole 13 x intermediate image magnification is emitted from the small hole 52 as an ideal spherical wave 16 . Therefore, the measurement light L2 emitted from the small hole 52 is emitted as a reference wave RW. Thus, the PDI plate 50 transmits the diffracted light diffracted by the diffraction grating 40 through the large holes 51 and the small holes 52 .

The diameter Φr of the small hole 52 satisfies the following formula (1).

Φr<0.61 λ/(NA/M) (1)

Here, λ is the wavelength of the measurement light L2, NA is the NA of the objective lens 20 on the point light source generation unit 12 side, and M is the focal length of the objective lens 20 and the focal length of the pupil relay lens 21. is the magnification on the intermediate imaging plane 35 determined by the ratio of . The coefficient 0.61 is a coefficient representing the radius of a so-called Airy Disk. By satisfying the condition of formula (1), the reference wave 19 transmitted and diffracted through the small hole 52 is reset to the ideal spherical wave 16 as shown in the figure. For example, if the wavelength λ of the measurement light L2 is 355 [nm], the NA of the objective lens 20 on the point light source generation unit 12 side is 0.9, and the magnification M at the intermediate imaging plane 35 is 70, then Φr= 16.8 [μm]. This dimension is sufficiently formable by the above-described photoetching or electroforming process.

Also, the diameter Φt of the large hole 51 arranged on the optical axis satisfies the following equation (2).

Φt>30・0.61・λ/(NA/M) (2)

The measurement light L2 (zero-order light) transmitted through the objective lens 20 and the pupil relay lens 21 spreads on the surface of the PDI plate 50 due to aberration. The distortion of the measurement light L2 is correlated with aberration. Therefore, selection of the diameter of the large hole 51 is important. Here, 30 in equation (2) is a coefficient, and if this is increased, even high-order aberrations can be measured. However, in the case of the optical inspection device 1, about 30 is the minimum. For example, if the wavelength λ of the measurement light L2 is 355 [nm], the NA is 0.9, and the magnification M at the intermediate imaging plane 35 is 70, Φt is about 500 [μm].

Since the dimensions of the large holes 51 and the small holes 52 of the PDI plate 50 are several to several hundreds [μm], a normal patterning process on the glass substrate, or the above-described photoetching or electroforming process. However, it is possible to form When using a glass substrate on which the large hole 51 and the small hole 52 are formed, the substrate side is arranged on the emission side.

In the case of the PDI plate 50 formed by the patterning process, an antireflection coating may be applied to avoid multiple reflections on the front and back surfaces of the glass substrate. In the case of the PDI plate 50 formed by a photoetching or electroforming process, it is possible to prevent the generation of interference fringes due to unnecessary multiple reflections. The thickness (referred to as PDI plate thickness) preferably satisfies the formula (3).

PDI plate thickness <λ/(NA/M) (3)

For example, if the wavelength λ of the measurement light L2 is 355 [nm], the NA of the objective lens 20 is 0.9, and the magnification M at the intermediate imaging plane 35 is 70, then it is about 28 [μm]. Even in the process of photoetching or electroforming, if the thickness is thin, the mechanical strength may not be ensured. Therefore, a two-step structure in which only the peripheral edges of the large hole 51 and the small hole 52 are thin is desirable. For example, the thickness of the periphery of the large hole 51 and the small hole 52 in the PDI plate 50 is the PDI plate thickness, and the thickness of the portion surrounding the periphery of the PDI plate 50 is the PDI plate thickness so as to increase the mechanical strength. is preferably at least twice the As a result, loss of the amount of light can be suppressed while ensuring mechanical strength. Both the photoetching process and the electroforming process can be a two-stage process.

The test wave TW passing through the large hole 51 and the reference wave RW passing through the small hole 52 pass through the pupil relay lens 22 . Thus, the pupil relay lens 22 transmits the measurement light L2 including the test wave TW and the reference wave RW. The test wave TW and the reference wave RW form a one-dimensional inclined plane wave interference image (Fringe) on the detection plane of the detector 60 .

The detector 60 is arranged on the pupil conjugate plane 45 of the measurement light L2 that has passed through the pupil relay lens 22 . A detector 60 detects an interference image of the measurement light L2. Detector 60 may be, for example, a camera. Detector 60 may have an image sensor. For example, an image sensor records the aforementioned interference fringes.

Detector 60 may specifically be arranged ahead of mirror MR2 in FIG. When measuring with the aberration measurement system, the mirror MR2 is removed from the optical path. It is preferable not to arrange the detector 60 at the pupil conjugate plane 45 on the optical path of the MR2 reflection side of the sample inspection system. A pupil conjugate plane 45 on the optical path of the sample inspection system is usually equipped with a large number of diaphragms, optical filters, etc. as a switchable mechanism. Therefore, switching and driving these optical members to retreat from the optical path of the sample inspection system has a risk of affecting the imaging performance of the optical path of the sample inspection system. By arranging the detector 60 for recording the interference image on the pupil conjugate plane 45 in the aberration measurement system on the transmission side of the MR2, it is possible to suppress the influence on the main performance of the sample inspection system.

To obtain the wavefront aberration from the interference image, for example, a well-known interference image scanning (Fringe Scan) method is used. This acquires four interference images in four phases by shift driving that moves the diffraction grating 40 one-dimensionally. By a simple calculation of the four interference images, the wavefront aberration (unit: Waves divided by radium or 2π) can be obtained for each pixel of the detector 60 . In consideration of reproducibility of measurement, a plurality of interference images per phase may be averaged.

By the way, the obtained wavefront aberration also includes the aberration generated by the pupil relay lens 22 . A null plate 56 is used to remove this. FIG. 4 is a plan view illustrating the null plate 56 in the inspection device 1 according to the first embodiment.

As shown in FIG. 4, the null plate 56 has two small holes 57 and 58 formed therein. The small hole 57 is formed at the same position as the large hole 51 in the PDI plate 50 . The small hole 58 is formed at the same position as the small hole 52 in the PDI plate 50 . The inner diameter of the small hole 57 of the Null plate 56 is smaller than the inner diameter of the large hole 51 of the PDI plate 50 . The holes 57 and 58 of the Null plate 56 have the same inner diameter as the holes 52 of the PDI plate 50 .

A null plate 56 is placed instead of the PDI plate 50 . Then, using the small holes 57 and 58 of the null plate 56, interference image scanning is performed in the same manner as the PDI plate 50. FIG. Thereby, the aberration generated in the pupil relay lens 22 can be measured. By subtracting the aberration measured using the null plate 56 from the aberration measured using the PDI plate 50, the wavefront aberration generated by the objective lens 20 and the pupil relay lens 21 can be measured with high accuracy.

As a method of measuring the wavefront aberration from the interference image, there is also a method of Fourier transform from one interference image of one phase, which is described in Non-Patent Document 3. In this case, since an interference image with a finer pitch is required, the pitch of the grating in the diffraction grating 40 is set to 1/2 of that of the interference image scanning method, and the inclination angle of interference is doubled or more. There is a need. In general, the interference image scanning method is said to have higher accuracy than the Fourier method. However, it is important to select the optimal method because there are pros and cons.

In this embodiment, the diffraction grating 40 and the PDI plate 50 other than the point light source generation unit 12 arranged on the stage 10 are permanently installed, and these members are retracted from the optical path of the sample inspection system except during measurement. A possible mechanism is also possible. In the vicinity of the intermediate imaging plane 35 on which the diffraction grating 40 and the PDI plate 50 are arranged, normally there are no functional elements other than the field stop. For this reason, permanent installation is also possible because there is a margin in the installation space.

Also, the vicinity of the intermediate imaging plane 35 is, for example, a space magnified 50 to 70 times. Therefore, a relatively large spatial dimension can be ensured. Since the luminous flux is also NA/(50 to 70), unintended eclipse of the luminous flux can be avoided. The diffraction grating 40 and the PDI plate 50 can also be made into an integral mechanism, which improves the stability of the interferometric measurement system. Alternatively, the diffraction grating 40 and the PDI plate 50 other than the point light source generation unit 12 may be mounted only when measuring aberrations in terms of tools.

<Sample inspection method>
Next, the sample inspection method of this embodiment will be described with reference to a flow chart. FIG. 5 is a flow chart diagram illustrating a sample inspection method using the inspection apparatus 1 according to the first embodiment.

The sample 11 is placed on the stage 10 as shown in step S11 of FIG. Next, as shown in step S12, the illumination light L0 is collected by the objective lens 20 to illuminate the sample 11. FIG. Next, as shown in step S<b>13 , the illumination light L<b>0 is reflected by the sample 11 and the inspection light L<b>1 is transmitted through the objective lens 20 . At that time, the objective lens 20 converts the inspection light L1 into parallel light.

Next, as shown in step S14, the inspection light L1 is relayed through the pupil relay lens 21 and the pupil relay lens 22 so as to form an intermediate imaging plane 35 between the pupil relay lens 21 and the pupil relay lens 22. Let Next, as shown in step S15, the inspection light L1 transmitted through the pupil relay lens 22 is guided to the tube lens 23 by the mirror MR2. Next, as shown in step S16, the image of the sample 11 is detected by the detector 30 arranged on the imaging conjugate plane 55 of the inspection light L1 through the tube lens. In this manner, the inspection device 1 can inspect the sample 11 .

<Wavefront aberration measurement method>
Next, the wavefront aberration measurement method of this embodiment will be described with reference to the flow chart. FIG. 6 is a flow chart diagram illustrating a wavefront aberration measuring method using the inspection apparatus 1 according to the first embodiment.

A point light source is arranged on the stage 10 as shown in step S21 of FIG. Specifically, the point light source generation unit 12 is arranged on the stage 10 of the inspection apparatus 1 and the measurement light L2 is emitted from the point light source arranged at the same position as the sample surface 15 .

Next, as shown in step S22, the measurement light L2 emitted from the point light source is transmitted through the objective lens 20. FIG. As a result, the measurement light L2 becomes a distorted plane wave 17 including the aberration of the objective lens 20. FIG.

Next, as shown in step S<b>23 , the measurement light L<b>2 that has passed through the objective lens 20 is passed through the pupil relay lens 21 . As a result, the measurement light L2 becomes a distorted spherical wave 18 including aberrations of the objective lens 20 and the pupil relay lens 21 .

Next, as shown in step S24, the diffraction grating 40 is arranged between the pupil relay lens 21 and the intermediate imaging plane 35, and the diffraction grating 40 diffracts the measurement light.

Next, as shown in step S25, the PDI plate 50 formed with the large hole 51 and the small hole 52 is arranged near the intermediate imaging plane 35 within the depth of focus. At that time, the large hole 51 is positioned on the optical axis of the measurement light L2, and the small hole 52 is separated from the large hole 51. FIG. Diffracted light diffracted by the diffraction grating 40 is transmitted through the large hole 51 and the small hole 52 . Specifically, the 0th order light of the diffracted light is transmitted through the large hole 51 , and the +1st order light or −1st order light is transmitted through the small hole 52 .

Next, as shown in step S26, the mirror MR2 is retracted from the main optical path of the inspection apparatus 1 so that the measurement light L2 is guided to the pupil conjugate plane 45 on the detector 60 side in the latter stage.

Next, the measurement light is transmitted through the pupil relay lens 22 as shown in step S27. Then, the detector 60 arranged on the pupil conjugate plane 45 detects the interference image. Therefore, the aberration wavefronts of the objective lens 20 and the pupil relay lens 21 are measured from the interference image. In this way, the aberration wavefront can be measured.

Next, the effects of this embodiment will be described. The inspection apparatus 1 of this embodiment measures the wavefront aberration of the objective lens 20 and the pupil relay lens 21 by adding the point light source generation unit 12, the diffraction grating 40 and the PDI plate 50 to the inspection apparatus 1 for the sample 11. be able to. As a result, imaging performance can be improved on the spot without using expensive components, without affecting the optical path of the sample inspection system, and in a state where the objective lens 20 and pupil relay lens 21 are combined. can be measured.

Also, the NA of the objective lens 20 is made larger than the NA of the pupil relay lens 21 . Therefore, unlike a reduction optical system such as a stepper, it is an expansion optical system. Therefore, the magnification of the intermediate imaging plane 35 can be increased to 50 times or more, and a spatial margin can be provided. Therefore, optical members such as the diffraction grating 40 and the PDI plate 50 can be arranged on the intermediate imaging plane 35 .

Also, the line-and-space interval of the diffraction grating 40 and the dimensions of the large holes 51 and the small holes 52 of the PDI plate 50 can be increased to the order of several tens of microns. Therefore, the manufacturing cost of optical members such as the diffraction grating 40 and the PDI plate 50 can be reduced. As a result, the mechanical strength can be maintained even when the grating spaces of the diffraction grating 40, the large holes 51 and the small holes 52 are formed in the air.

By arranging the pupil relay lens 22, the detector 60 for detecting the interference image can be arranged on the pupil conjugate plane 45, and the interference image can be analyzed with high accuracy. Moreover, since the detector 60 can be arranged on the pupil conjugate plane 45, the inspection apparatus 1 can be made compact. The objective lens 20 and the pupil relay lenses 21 and 22 are optical members that are also used in the original semiconductor inspection, and are also used for aberration measurement in the present invention. It is configurable.

The inner diameter Φr of the small hole 52 is set by a formula including the measurement wavelength, the NA of the objective lens 20, and the intermediate image magnification. Thereby, the condition of the small hole 52 reset to the spherical wave 16 can be defined, and the reference wave RW can be approximated to the ideal spherical wave 16 . Therefore, wavefront aberration can be measured with high accuracy.

The peripheral thickness of the large hole 51 and the small hole 52 in the PDI plate 50 is set by a formula including the measurement wavelength, the NA of the objective lens 20, and the intermediate image magnification. This makes it possible to define the condition of the small hole 52 reset to the spherical wave 16 and bring the reference wave RW close to an ideal spherical wave. Therefore, wavefront aberration can be measured with high accuracy.

Furthermore, it becomes possible to manage the semiconductor production line using the actual measurement results on the spot. Further, optical elements such as an illumination pupil filter and an imaging pupil filter for improving the imaging performance of the inspection apparatus 1 can be designed using the aberration measurement results. In addition, it becomes possible to design measures for correcting differences in imaging performance among a plurality of inspection apparatuses 1 .

(Embodiment 2)
Next, an inspection apparatus according to Embodiment 2 will be described. The inspection apparatus 1 of Embodiment 1 described above inspects the sample 11 at an arbitrary wavelength and measures the wavefront aberration in the sample inspection system and the aberration measurement system on site. The inspection apparatus of this embodiment uses a plurality of wavelength bands (hereinafter referred to as bands) within a wide wavelength band to inspect the sample 11 and measure the wavefront aberration.

For example, the point light source generation unit 12 mounted on the stage 10 generates DPSS lasers with wavelengths of 266 [nm], 355 [nm], 375 [nm], 430 [nm], 457 [nm], 501 [nm], etc. may be used. These measurement laser wavelengths correspond to inspection wavelengths for semiconductor inspection. For example, the center wavelength of the inspection wavelength band is the measurement wavelength. The condenser lens and pinhole plate 14 in the point light source generation unit 12 may require design according to the wavelength. Therefore, the point light source generation unit 12 may be prepared for each wavelength. In the PDI plate 50, the diameters of the large holes 51 and the small holes 52 are formed according to the above formulas (1) and (2) according to the wavelength of the inspection light L2.

Also, the distance D (Spacing) between the center of the large hole 51 and the center of the small hole 52 is arranged according to the following equation (4) according to the wavelength of the inspection light L2.

D = L tan (sin ^-1 (λ/P)) (4)

Here, L indicates the distance in the optical axis direction between the diffraction grating 40 and the PDI plate 50, P indicates the grating pitch in the diffraction grating 40, and λ is the wavelength of the measurement light L12. For example, when L=70 [mm], P=30 [μm], and λ=266 [nm], D=0.6 [mm].

Since it is possible to select the diffracted light at D in the PDI plate 50, a common diffraction grating 40 can be used for each wavelength.

FIG. 7 is a plan view illustrating the PDI plate 50 in the inspection apparatus according to the second embodiment. As shown in FIG. 7, the PDI plate 50 has pairs of large holes 51 and small holes 52 corresponding to wavelengths λ1, λ2, and λ3 (λ1<λ2<λ3). For example, a large hole 511 and a small hole 521 are formed corresponding to the wavelength λ1, a large hole 512 and a small hole 522 are formed corresponding to the wavelength λ2, and a large hole 513 and a small hole 523 are formed corresponding to the wavelength λ3. formed. Depending on the wavelength, the PDI plate 50 is shifted in a direction perpendicular to the diffraction direction of the diffraction grating 40 (the Y-axis direction in the drawing).

Thus, in this embodiment, the PDI plate 50 includes large holes 511 , small holes 521 , large holes 512 , small holes 522 , large holes 513 and small holes 523 . The measurement light L2 includes a first measurement light with wavelength λ1, a second measurement light with wavelength λ2, and a third measurement light with wavelength λ3. The large hole 511, the small hole 521 and the wavelength λ1 satisfy the formulas (1), (2) and (4), and the large hole 512, the small hole 522 and the wavelength λ2 satisfy the formulas (1) and (2) and (4), and the large hole 513, the small hole 523 and the wavelength λ3 satisfy the formulas (1), (2) and (4). In this case, when the measurement light L2 is changed from the first measurement light to the second measurement light, the PDI plate 50 is shifted, and the state in which the first measurement light passes through the large hole 511 and the small hole 521 is changed to the second measurement light. The state is changed so that the measurement light passes through the large hole 512 and the small hole 522 . When the measurement light L2 is changed from the second measurement light to the third measurement light, the PDI plate 50 is shifted to shift the third measurement light from the state in which the second measurement light passes through the large hole 512 and the small hole 522. The state is changed to a state in which the hole 513 and the small hole 523 are transmitted.

According to this embodiment, since an optical material having wavelength dependence is not used, the inspection apparatus 1 using multiple wavelength bands can be used only by changing optical parameters such as the formulas (1) to (4) can be applied. Configurations and effects other than this are included in the description of the first embodiment.

(Embodiment 3)
Next, an inspection apparatus according to Embodiment 3 will be described. The inspection apparatus of this embodiment changes the image height to inspect the sample 11 and measure the wavefront aberration. Since the point light source generation unit 12 is arranged on the stage 10, by moving the stage 10, the image height for measuring and evaluating the aberration can be easily changed. Along with this, the PDI plate 50 is moved within the XY plane.

FIG. 8 is a plan view illustrating the PDI plate 50 in the inspection apparatus according to the third embodiment. As shown in FIG. 8, for example, when the coordinates of the pinhole 13 on the sample surface 15 in the point light source generation unit 12 are shifted by Δ in the Y-axis direction from the optical axis of the objective lens 20 (image height Y=Δ), The PDI plate 50 is also moved in the Y direction by M×Δ. where M is the magnification of the intermediate imaging plane. Let ΦS be the field of view of the objective lens 20 on the sample 11 . Then, the PDI plate 50 can move in the Y-axis direction by ±(S/2)×M. It is assumed that the diffraction grating 40 has a large effective area with respect to the image height swing.

As described above, in this embodiment, when the point light source is moved in the plane perpendicular to the optical axis of the objective lens 20 within the field of view of the objective lens 20, the PDI plate 50 changes the amount of movement of the point light source to It is moved by the amount of movement multiplied by the magnification of the intermediate imaging plane 35 .

According to this embodiment, the position of the point light source generation unit 12 on the XY plane and the position of the PDI plate 50 on the XY plane are linked to measure the wavefront aberration. Thereby, the wavefront aberration at an arbitrary image height within the field of view of the objective lens 20 can be measured. Configurations and effects other than this are included in the descriptions of the first and second embodiments.

The present invention is not limited to the above embodiments, and can be modified as appropriate without departing from the scope of the invention. For example, each configuration of Embodiments 1 to 3 can be combined with each other.

1 inspection device 10 stage 11 sample 12 point light source generation unit 13 pinhole 14 pinhole plate 15 sample surface 16 spherical wave 17 distorted plane wave 18 distorted spherical wave 20 objective lens 21 pupil relay lens 22 pupil relay lens 23 tube lens 25 pupil Surface 30 Detector 35 Intermediate imaging plane 40 Diffraction grating 45 Pupil conjugate plane 50 PDI plate 51 Large hole 52 Small hole 55 Imaging conjugate plane 56 Null plate 57, 58 Small hole 60 Detector BS Beam splitter L0 Illumination light L1 Inspection light L2 measurement light LS light sources MR1, MR2 mirror RW reference wave TW test wave

Claims (14)

a stage on which a sample is placed during inspection and a point light source is placed during aberration measurement;
an objective lens that transmits inspection light reflected by the sample from illumination light that illuminates the sample during the inspection, and that transmits measurement light emitted from the point light source during the aberration measurement;
A first lens that transmits the inspection light and the measurement light that have passed through the objective lens and functions as an imaging lens, wherein a pupil plane is formed between the objective lens and the first lens, and the the first lens having a focal length longer than the focal length of the objective lens;
a second lens that transmits the inspection light and the measurement light that have passed through the first lens, the second lens having an intermediate imaging plane formed between the first lens and the second lens; ,
a diffraction grating disposed between the first lens and the intermediate imaging plane for diffracting the measurement light;
A large hole and a small hole having an inner diameter smaller than that of the large hole are formed in the vicinity of the intermediate imaging plane within the depth of focus range, the large hole is positioned on the optical axis of the measurement light, and the small hole is formed. a PDI plate having holes spaced apart from the large holes and transmitting diffracted light diffracted by the diffraction grating;
a first detector arranged on an imaging conjugate plane of the inspection light that has passed through the second lens and the tube lens and detecting an image of the sample;
a second detector arranged on a pupil conjugate plane of the measurement light transmitted through the second lens and detecting an interference image of the measurement light;
a mirror disposed between the second lens and the tube lens for switching between the inspection and the aberration measurement;
and retracting the diffraction grating and the PDI plate from the optical path of the inspection light during the inspection;
inspection equipment. Magnification in the intermediate imaging plane determined by the ratio of the focal length of the objective lens to the focal length of the first lens is 50 times or more.
The inspection device according to claim 1. Between the gratings of the diffraction grating, the large holes and the small holes are hollow,
The inspection device according to claim 1 or 2. A plurality of inspection wavelengths are used for the illumination light,
The measurement light has a wavelength within the inspection wavelength band width of the illumination light and includes a central wavelength or a centroid wavelength of the inspection wavelength band of the illumination light, the wavelength of the measurement light is λ, and the aperture of the objective lens is Let NA be the number, let M be the magnification of the intermediate imaging plane determined by the ratio of the focal length of the objective lens to the focal length of the first lens, and let M be the optical axis direction between the diffraction grating and the PDI plate. L is the distance between and P is the pitch of each grating of the diffraction grating, the inner diameter Φt of the large hole is
Φt>30・0.61・λ/(NA/M) (A)
and the inner diameter Φr of the small hole is
Φr<0.61 λ/(NA/M) (B)
and the distance D between the center of the large hole and the center of the small hole is
D = L tan (sin ^-1 (λ/P)) (C)
satisfy the
The inspection device according to any one of claims 1 to 3. the PDI plate includes a first large hole, a first small hole, a second large hole and a second small hole so as to correspond to a plurality of inspection wavelengths;
the measurement light includes a first measurement light having a first measurement wavelength corresponding to the first inspection wavelength in the inspection light and a second measurement light having a second measurement wavelength corresponding to the second inspection wavelength;
The first large hole, the first small hole, and the first measurement wavelength satisfy formulas (A), (B), and (C), and the second large hole, the second small hole, and the first measurement wavelength satisfy formulas (A), (B), and (C). 2 measurement wavelength shifts the PDI plate when the measurement light is changed from the first measurement light to the second measurement light when formulas (A), (B), and (C) are satisfied; by moving the first measurement light from a state in which the first measurement light is transmitted through the first large hole and the first small hole to a state in which the second measurement light is transmitted through the second large hole and the second small hole;
The inspection device according to claim 4. The peripheral thickness a of the large hole and the small hole in the PDI plate is
a<λ/(NA/M) (D)
The filling,
The thickness of the portion surrounding the peripheral edge of the PDI plate is at least twice the thickness a so as to increase mechanical strength.
The inspection device according to claim 4 or 5. When the point light source is moved in a plane orthogonal to the optical axis of the objective lens within the field of view of the objective lens, the PDI plate has the focal length of the objective lens and the amount of movement of the point light source. moved by a movement amount multiplied by the magnification of the intermediate imaging plane determined by the ratio to the focal length of the first lens;
The inspection device according to any one of claims 1 to 6. a stage on which the sample is placed;
an objective lens that transmits inspection light reflected by the sample from illumination light that illuminates the sample;
A first lens for transmitting the inspection light that has passed through the objective lens, wherein a pupil plane is formed between the objective lens and the first lens and has a longer focal length than the focal length of the objective lens. the first lens;
a second lens that transmits the inspection light that has passed through the first lens, the second lens having an intermediate imaging plane formed between the first lens and the second lens;
a first detector arranged on the imaging conjugate plane of the inspection light transmitted through the second lens and detecting an image of the sample;
A wavefront aberration measurement method for an inspection apparatus comprising
placing a point light source on the stage;
a step of transmitting measurement light emitted from the point light source through the objective lens;
a step of transmitting the measurement light that has passed through the objective lens through the first lens;
placing a diffraction grating between the first lens and the intermediate imaging plane to diffract the measurement light;
A PDI plate having a large hole and a small hole smaller in inner diameter than the large hole is arranged near the intermediate imaging plane within the depth of focus, and the large hole is positioned on the optical axis of the measurement light. and separating the small holes from the large holes to transmit the diffracted light diffracted by the diffraction grating;
a step of detecting an interference image of the measurement light transmitted through the second lens with a second detector arranged on a pupil conjugate plane of the measurement light;
A wavefront aberration measurement method. The magnification in the intermediate imaging plane determined by the ratio of the focal length of the objective lens and the focal length of the first lens is 50 times or more,
The wavefront aberration measurement method according to claim 8. Between the gratings of the diffraction grating, the large holes and the small holes are hollow;
The wavefront aberration measuring method according to claim 8 or 9. A plurality of inspection wavelengths are used for the illumination light,
The measurement light has a wavelength within the inspection wavelength band width of the illumination light, and includes a center wavelength or a centroid wavelength of the inspection wavelength band of the illumination light,
Let λ be the wavelength of the measurement light, NA be the numerical aperture of the objective lens, M be the magnification of the intermediate imaging plane determined by the ratio between the focal length of the objective lens and the focal length of the first lens, and Assuming that the distance in the optical axis direction between the diffraction grating and the PDI plate is L, and the pitch of each grating of the diffraction grating is P, the inner diameter Φt of the large hole is:
Φt>30・0.61・λ/(NA/M) (A)
is satisfied, and the inner diameter Φr of the small hole is
Φr<0.61 λ/(NA/M) (B)
and the distance D between the center of the large hole and the center of the small hole is
D = L tan (sin ^-1 (λ/P)) (C)
to satisfy
The wavefront aberration measuring method according to any one of claims 8 to 10. The PDI plate includes a first large hole, a first small hole, a second large hole and a second small hole so as to correspond to a plurality of inspection wavelengths, and corresponds to the first inspection wavelength in the inspection light. The measurement light includes a first measurement light having a first measurement wavelength and a second measurement light having a second measurement wavelength corresponding to the second inspection wavelength in the inspection light,
The first large hole, the first small hole, and the first measurement wavelength satisfy formulas (A), (B), and (C), and the second large hole, the second small hole, and the first measurement wavelength satisfy formulas (A), (B), and (C). 2 When the measurement wavelength satisfies the formulas (A), (B), and (C), the PDI plate is shifted when changing the measurement light from the first measurement light to the second measurement light. by moving the first measurement light from a state in which the first measurement light is transmitted through the first large hole and the first small hole to a state in which the second measurement light is transmitted through the second large hole and the second small hole;
The wavefront aberration measurement method according to claim 11. The peripheral thickness a of the large hole and the small hole in the PDI plate is
a<λ/(NA/M) (D)
and
The thickness of the portion surrounding the peripheral edge of the PDI plate is set to be at least twice the thickness a so as to increase mechanical strength.
The wavefront aberration measuring method according to claim 11 or 12. When the point light source is moved in a plane orthogonal to the optical axis of the objective lens within the field of view of the objective lens, the PDI plate is adjusted to the amount of movement of the point light source and to the focal length of the objective lens. moving the amount of movement multiplied by the magnification of the intermediate imaging plane determined by the ratio to the focal length of the first lens;
The wavefront aberration measuring method according to any one of claims 8 to 13.

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