Patent Publication Number: US-2023152213-A1

Title: Ellipsometer and apparatus for inspecting semiconductor device including the ellipsometer

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based on and claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2021-187562, filed on Nov. 18, 2021, in the Japanese Patent Office and Korean Patent Application No. 10-2022-0009233, filed on Jan. 21, 2022 in the Korean Intellectual Property Office, the disclosures of which are incorporated by reference herein in their entireties. 
     BACKGROUND 
     The inventive concepts relate to apparatuses for inspecting a semiconductor device, and more particularly, to apparatuses for inspecting a semiconductor device by using an ellipsometer. 
     In ellipsometry, because automatic measurement was made possible by Aspnes et al. in 1975, measurement time has been significantly shortened and precision has been greatly improved, and spectral ellipsometry that makes measurement by multiple wavelengths is also being put to practical use. In non-destructive measurement of thin films and microstructures, ellipsometry is widely used in semiconductor manufacturing processes by taking advantage of the characteristic of measuring dimensions, such as film thickness, and optical constants, such as refractive index with high precision. 
     SUMMARY 
     The inventive concepts provide ellipsometers capable of improving a throughput calculating ellipsometry coefficients (ψ, Δ) even when performing measurement with a combination of a light source having a wide wavelength band and a spectrometer, and/or apparatuses for inspecting a semiconductor device including the ellipsometer. 
     In addition, the problems to be solved by the inventive concepts are not limited to the problems mentioned above, and other problems m be clearly understood by those skilled in the art from the following description. 
     According to an example embodiment, an ellipsometer may include a polarizing optical element unit configured to separate reflected light into two polarization components, the two polarization components having polarization directions that are orthogonal to each other in radial direction with respect to an optical axis of a condensing optical system of the reflected light, the reflected light being light reflected front a measurement surface of a sample when illumination light illuminate the measurement surface of the sample, the illumination light comprising at least one of linear polarization, circular polarization, or elliptical polarization, with respect to the two polarization components, an analyzer unit configured to transmit components in a direction, which is different from each of the polarization directions of the two polarization components, to make the two polarization components interfere with each other, and to form an interference fringe in a them of a concentric circle, an image detector configured to detect the interference fringe, and processing circuitry configured to calculate ellipsometry coefficients ψ and Δ from the detected interference fringe. 
     According to an example embodiment, an ellipsometer may include a polarizing optical element unit configured to separate reflected light reflected light into two linear polarization components, the two linear polarization components having polarization directions that are orthogonal to each other, the reflected light being light reflected from a measurement surface of a sample when illumination light comprising, linear polarization illuminates the measurement surface of the sample, with respect to the two linear polarization components, an analyzer unit configured to transmit components in a direction, which is different from each of the polarization directions of the two linear polarization components, to make the two linear polarization components interfere with each other, and form an interference fringe in a form of a stripe, an image detector configured to detect the interference fringe, and processing circuitry configured to calculate ellipsometry coefficients ψ and Δ from the detected interference fringe. A stripe pitch of the interference fringe may have a same value at a plurality of wavelengths of the illumination light. 
     According to an example embodiment, an apparatus for inspecting a semiconductor device may include an ellipsometer, a stage configured to receive thereon the semiconductor device as an inspection target is disposed and an environment chamber configured to isolate a part of the ellipsometer and the stage from an external environment. The ellipsometer may include a polarizing optical element unit configured to separate two polarization components of reflected light in a polarization direction, the two polarization components being orthogonal to each other in a radial direction with respect to an optical axis of an optical system of the reflected light, the reflected light being light reflected from a measurement surface of a sample when illumination light illuminate the measurement surface of the sample, the illumination light comprising at least one of linear polarization, circular polarization, or elliptical polarization, with respect to the two polarization components, an analyzer unit configured to transmit components of a direction, which is different from the polarization direction of each of two polarization components, to make the two polarization components interfere with the components each other and to form an interference fringe in a concentric circle, all image, detector configured to detect the interference fringe, and processing circuitry configured to calculate ellipsometry coefficients ψ and Δ from the detected interference fringe. 
     According to an example embodiment, an ellipsometer may include an illumination optical system configured to illuminate a sample with illumination light comprising at least one of linear polarization, circular polarization, or elliptical polarization, a condensing optical system configured to condense reflected light, the reflected light being light reflected from a measurement surface of the sample when the illumination light illuminates the measurement surface of the sample, a polarizing optical element unit configured to separate the reflected light into two polarization components, the two polarization components having polarization directions that are orthogonal to each other or separate the two polarization components in a radial direction with respect to an optical axis of the condensing optical system, and a light receiving optical system comprising an analyzer unit, the light receiving optical system configured to calculate ellipsometry coefficients ψ and Δ from an interference fringe formed through the analyzer unit. With respect to the two polarization components, the analyzer unit may be configured to transmit components of a direction, which is different from each of the polarization directions of the two polarization components to make the two polarization components interfere with each other, and to form an interference fringe in a form of a stripe Or a concentric circle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some example embodiments of the inventive concepts will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG.  1    is a configuration diagram schematically showing an ellipsometer according to a comparative example; 
         FIG.  2    is a photograph showing an interference fringe on an image detector in the ellipsometer of  FIG.  1   ; 
         FIG.  3    illustrates photographs showing interference fringes when widths of wavelengths are the same in illumination light of a long wavelength, a medium wavelength, and a short wavelength in the ellipsometer of  FIG.  1   ; 
         FIG.  4    is a configuration diagram schematically showing an ellipsometer according to an example embodiment of the inventive concepts; 
         FIG.  5    is a graph showing linear polarization transmitting through an analyzer unit in the ellipsometer of  FIG.  4   ; 
         FIG.  6    is a photograph of reflected light interfering on an image detector in the ellipsometer of  FIG.  4    with respect to an interference fringe, and conceptual diagrams of X polarization and Y polarization; 
         FIGS.  7  to  9    are conceptual diagrams of a method of analyzing an interference fringe of reflected light interfering on the image detector in the ellipsometer of  FIG.  4   ; 
         FIG.  10    is photographs of interference fringes of reflected light interfering on an image detector in the ellipsometer of  FIG.  4    and the ellipsometer of  FIG.  1   ; 
         FIG.  11    is a perspective view showing an arrangement of an illumination optical system a condensing optical system, and a pupil plane in the ellipsometer of  FIG.  4   ; 
         FIG.  12    is a conceptual diagram showing a relationship between a location on a pupil plane, an angle of incidence of light to a sample, and an azimuth of incidence in the ellipsometer of  FIG.  4   ; 
         FIG.  13    is a configuration diagram schematically illustrating an apparatus for inspecting a semiconductor device including an ellipsometer according to an example embodiment of the inventive concepts; 
         FIG.  14    is a configuration diagram schematically showing an ellipsometer according to an example embodiment of the inventive concepts; 
         FIG.  15    is a photograph of an interference fringe of reflected light interfering on an image detector in the ellipsometer of  FIG.  14   , and conceptual diagrams of radial polarization and the azimuth polarization; 
         FIG.  16    is a conceptual diagram of a polarizing optical element unit in the ellipsometer of  FIG.  14   ; 
         FIG.  17    is a configuration diagram schematically showing an ellipsometer according to an example embodiment of the inventive concepts; 
         FIG.  18    is a photograph of an interference fringe of reflected light interfering on an image detector in the ellipsometer of  FIG.  17   , and conceptual diagrams of radial polarization and azimuth polarization; 
         FIG.  19    is a conceptual diagram of a polarizing optical element ellipse of  FIG.  17   ; 
         FIGS.  20  to  23    are conceptual diagrams of polarizing optical element units according to modification examples in the ellipsometer of  FIG.  17   ; 
         FIG.  24    is a configuration diagram schematically showing an ellipsometer according to an example embodiment of the inventive concepts; 
         FIG.  25    is a photograph of an interference fringe of reflected light interfering on an image detector in the ellipsometer of  FIG.  24   , and conceptual diagrams of X polarization and Y polarization; 
         FIG.  26    is a graph showing the wavelength dependence of birefringence in each material of a birefringent crystal; and 
         FIG.  27    is a conceptual diagram of a polarizing optical element unit in the ellipsometer of  FIG.  24   . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, some example embodiments of the inventive concepts will be described in detail with reference to the accompanying drawings. The same reference numerals are used for the same components in the drawings, and redundant descriptions thereof are omitted. 
     Currently, as an optical critical dimension (OCD) measuring apparatus that measures a dimension of a microstructure with a line width equal to or less than 10 nm of a circuit pattern on a wafer, a length measuring scanning electron-beam microscope (SEM) or atomic force microscope (AFM) is used in a complementary form. In addition, in the last 10 years, semiconductor circuit structures, such as fin field-effect transistors (finFETs) in logic semiconductors and a 3D-NAND in memory semiconductors, have progressed to three-dimensionalization and become more complex. Most OCDs use spectral ellipsometry as a measurement principle and in order to obtain the dimension of a semiconductor circuit structure that is a measurement target or the optical constant of a constituent material of semiconductor circuit that is a measurement target, a method is taken to obtain a solution by creating a model and fitting the model to a measurement result using the dimension or optical constant of the measurement target as a floating parameter. For this reason, when the structure of the target to be sought becomes complicated, the number of floating parameters may increase, For example, in the current measurement with respect to the OCD of finFET, it is desired to use about 20 to about 30 floating parameters. Ellipsometry generally obtains two values of ψ and Δ as ellipsometry coefficients, which are measurement results, but both the ellipsometry coefficients ψ and Δ are wavelength dependent. For this reason, in the case of spectral ellipsometry, the ellipsometry coefficients ψ and Δ may be expressed as ψ(λ) and Δ(λ), respectively. 
     In order to obtain a solution of the dimension, it is at least desired for the fitting of the model to obtain a larger number of ellipsometry coefficients ψ, Δ than the number of floating parameters, through measurement. As a problem that occurs when the number of floating parameters is large, there are cases where the fitting converges with a combination of floating parameters different from the actual dimension. This is a problem called coupling, and in order to avoid this, it is effective or desirable to perform fitting by measuring the ellipsometry coefficients ψ, Δ having different dependencies on the floating parameters. Therefore, in addition to wavelength, it is desirable to perform ellipsometry measurements at different angles of incidence and azimuth of incidence, and use the ellipsometry coefficients ψ, Δ having different dependencies on each other for fitting the model with respect to the above floating parameters. 
     In addition, from the viewpoint of measurement sensitivity, in illumination light to a semiconductor wafer, the Brewster angle at which the reflectance of P polarization is 0 has the highest measurement sensitivity. For this reason, in the ellipsometry measurement, the Brewster angle is often performed as an angle of incidence. This angle of incidence may correspond to approximately 60° to 75° in the semiconductor circuit structure. When performing measurement with such an oblique incidence, spectral ellipsometry measurement is often performed using an oblique incidence optical system specialized for a single angle of incidence and azimuth of incidence. However, in order to avoid the coupling problem described above, there is a growing demand for an optical system capable of responding to a plurality of angles of incidence or azimuth of incidence. 
     In response to such a request, when the optical system or semiconductor wafer is moved for each measurement, there is a problem in that a measurement time greatly increases. For this reason, by using an objective lens having a large numerical aperture (NA) including the Brewster angle described above, measurement light is simultaneously incident from a wide range of angle of incidence and azimuth of incidence. Then, ellipsometry measurement is performed by deriving reflected light from the semiconductor wafer onto an exit pupil of an objective lens. Such a combination of a pupil image measurement optical system and the ellipsometry measurement may be ideal. However, even in this case, in a configuration in which a rotation compensator is combined with a rotation analyzer, as is the case for general methods of ellipsometry measurement, the measurement time for each wavelength may be equal, to or greater than 1 second due to the limitation of an obtained pupil image transmission speed. In addition, when spectral ellipsometry measurement using illumination fight of 100 wavelengths or more is performed, the measurement time may be unrealistic for the OCD measurement apparatus in a semiconductor manufacturing process. 
     An ellipsometer used in the OCD measurement apparatus in the semiconductor manufacturing process typically needs a measurement time of 1 second to several seconds to measure one point. Within the time allotted for measurement, only several to tens of points are usually measured in the wafer, and thus yield deterioration due to as partial film thickness change or line width change in the wafer may be missed. Some reasons for this are that (1) a certain number of measurement points are desired in synchronization with modulation by the rotation compensator or phase modulation element, (2) in the case of spectroscopic measurement, it is desired to measure an amount of light divided by each wavelength in a dispersion element, such as a diffraction grating at a high S/N ratio, and further (3) in the case if Mueller matrix ellipsometry, the measurement needs to be performed while switching several types of polarization states in the illumination light. 
     In this regard, in order to shorten the measurement time of ellipsometry while increasing measurement points in the wafer, it is desired to speed up a movable portion such as the rotation compensator. However, stability and heat generation become obstacles, and it is difficult to improve the throughput of ellipsometry coefficient measurement for OCD measurement, etc. 
       FIG.  1    is a configuration diagram schematically showing an ellipsometer  101  according to a comparative example. 
     Referring to  FIG.  1   , the ellipsometer  101  of the comparative example may make two orthogonal polarization components interfere on an image detector  142  by using a Nomarski prism  131 . Then, an analysis apparatus  143  may obtain ψ and Δ from the amplitude and phase of a generated interference fringe. By using such a method, the practical application of the OCD apparatus with a high stability due to the absence of the movable portion is expected while realizing a high throughput, in the semiconductor manufacturing process. 
     Meanwhile, an illumination optical system  110  includes a light source  111 , a spectrometer  112 , a fiber  113 , an illumination lens  114 , a polarizer  115 , a beam splitter  116 , and an objective lens  117 , and may illuminate a sample  50  with illumination light L 1 . A condensing optical system  120  includes the objective lens  117 , the beam splitter  116 , and relay lenses  121  and  122 , and may condense reflected light R 1  reflected from the sample  50 . A polarizing optical element  130  may include the Nomarski prism  131 , and a light receiving optical system  140  may include an analyzer unit  141 , an image detector  142 , and the analysis apparatus  143 . 
     This method may obtain and A from a single image without obtaining a Stokes parameter, which is common in ellipsometry measurement. For this reason, the measurement efficiency is relatively good, and spectral ellipsometry is also possible by combining the ellipsometer  101  with a high-speed spectrometer. By applying this measurement principle to pupil image measurement using the objective lens  117  of a large NA, ellipsometry information of multiple angles of incidence and azimuth of incidence may be obtained simultaneously, and ideal performance may be realized or approximated for a measurement apparatus in the semiconductor manufacturing process. 
       FIG.  2    is a photograph showing an interference fringe on the image detector  142  in the ellipsometer  101  of  FIG.  1   . In the graph, the x-axis represents a location of the interference fringe on the image detector  142 , and the y-axis represents the intensity of light of the interference fringe. 
     Referring to  FIG.  2   , the ellipsometer  101  of  FIG.  1    may form the interference fringe of vertical stripes on the image detector  142  by, for example, interfering X polarization and Y polarization. On the vertical line transmitting through the center of the image detector  142 , an optical path length difference between the X polarization and the Y polarization is 0. When a width of a wavelength is wide, the contrast of the interference fringes on both sides deteriorates. 
     As described above, because partial coherent light is used as the illumination light L 1 , when the number of interference fringes formed on the pupil increases, as shown in  FIG.  2   , in regions on the left and right sides where the optical path length difference of two polarization components is large, the contrast of the interference fringe deteriorates. The phenomenon that the contrast of the interference fringes deteriorates in the region where the optical path length difference is large means that there is an upper limit on the number of available interference fringes. 
       FIG.  3    illustrates photographs showing interference fringes when widths of the wavelengths are the same in illumination light of a long: wavelength, a medium wavelength, and a short wavelength in the ellipsometer  101  of  FIG.  1   . 
     Referring to  FIG.  3   , when widths of the wavelengths are the same, because the number of interference fringes of the short wavelength increases, the shorter the wavelength, the lower the contrast of the interference fringes. In order to avoid this problem, it is desired to reduce a polarization separation angle by the Nomarski prism  131  or to narrow the wavelength width upon Measurement at the short wavelength. However, in the former case, especially on the long wavelength side, because a stripe space widens, a measurement resolution on the pupil may deteriorate. In the latter case, a side effect of decreasing an amount of light at the short wavelength may occur. 
     Therefore, even upon measurement with a combination of a light source having a wide wavelength band and a spectrometer, an ellipsometer capable of suppressing a decrease in resolution due to the widening of the stripe space and a decrease in the amount of light due to narrowing the width of wavelength of a spectrometer, and improving a throughput calculating the ellipsometry coefficients ψ and Δ is desired. 
       FIG.  4    is a configuration diagram schematically showing art ellipsometer  1  according to an example embodiment of the inventive concepts. 
     Referring to  FIG.  4   , the ellipsometer  1  of the present example embodiment may include an illumination optical system  10 , a condensing optical system  20 , a polarizing optical element unit  30 , and a light receiving optical system  40 . The ellipsometer  1  may receive the reflected light R 1  reflected from the sample  50  when the illumination light L 1  illuminates the sample  150 , to obtain the ellipsometry coefficients ψ and Δ. 
     The illumination optical system  10  may illuminate the sample  50  with the illumination light L 1  including a linear polarization. The illumination optical system  10  may include a light source  11 , a spectrometer  12 , a fiber  13 , an illumination lens  14 , a polarizer unit  15 , a beam splitter  16 , and an objective lens  17 . 
     The light source  11  may generate the illumination light L 1 . The illumination light L 1  generated by the light source  11  may include light having a broadband wavelength. The illumination light L 1  may be, for example, white light. However, the illumination light L 1  generated by the light source  11  is not limited to white light. For example, the illumination light L 1  may include monochromatic light having a specific wavelength or light having a specific wavelength width. The illumination light L 1  generated by the light source  11  may be incident on the spectrometer  12 . 
     The spectrometer  12  may extract and emit light having a specific wavelength width from the incident illumination light L 1 . The spectrometer  12  may emit light with a center wavelength of 400 nm having a wavelength width of, for example, 10 nm. The illumination light L 1  emitted from the spectrometer  12  may be incident on the fiber  13 . 
     The fiber  13  may be a light guide member having one end and the other end in a cable shape. The illumination light L 1  incident on one end of the fiber  13  may be emitted from the other end of the fiber  13 . The illumination light L 1  emitted from the other end of the fiber  13  may be incident on the illumination lens  14 . 
     The illumination lens  14  may be, for example, a convex lens. The illumination lens  14  may change an angular distribution of the incident illumination light L 1  and irradiate the illumination light L 1  to the polarizer unit  15 . For example, the illumination lens  14  may convert the illumination light L 1  emitted from the other end of the fiber  13  into parallel light. In addition, the illumination lens  14  may make the illumination light L 1  convened into the parallel light be incident on the polarizer unit  15 . 
     The illumination light L 1  generated by the light source  11  may be incident on the polarizer unit  15 . The polarizer unit  15  may include, for example, a linear polarizer H 1  that generates the linear polarization. Accordingly, the polarizer unit  15  may transmit the illumination light L 1  including the linear polarization in one direction. For example, the polarizer unit  15  may emit the illumination light L 1  of the linear polarization of which polarization direction is inclined by 45° with respect to a surface to the beam splitter  16 . 
     The beam splitter  16  may reflect a part of the incident illumination light L 1  and transmit a part thereof. The beam splitter  16  may reflect a part of the incident illumination light L 1  toward the objective lens  17 . The illumination light L 1  reflected by the beam splitter  16  may be incident on the objective lens  17 . 
     The objective lens  17  may illuminate the sample  50  with the illumination light L 1  including the linear polarization. The objective lens  17  may illuminate the sample  50  by condensing the illumination light L 1  reflected by the beam splitter  16  in a dotted shape. The objective lens  17  has an NA. The objective lens  17  may illuminate the specimen  50  from all angles and all directions within the NA. The NA of the objective lens  17  may be a value, for example, equal to or greater than 0.95, including the Brewster&#39;s angle with respect to the sample  50 . 
     The objective lens  17  may transmit the illumination light L 1  and the reflected light R 1  reflected from a measurement surface of the sample  50  by the illumination light L 1 . In the ellipsometer  1  of the present example embodiment, an optical axis C of the illumination light L 1  incident on the sample  50  and an optical axis C of the reflected light R 1  reflected from the sample  50  may be orthogonal to the measurement surface of the sample  50 . 
     Here, for convenience of description of the ellipsometer  1  of the present example embodiment, an XYZ rectangular coordinate axis system is introduced. A Z-axis direction is defined as the optical axis C. Two directions orthogonal to the Z-axis direction and orthogonal to each other are defined as an X-axis direction and a Y-axis direction. 
     The illumination light L 1  illuminating the sample  50  may include a linear polarization in one direction. The illumination light L 1  including the linear polarization in one direction may be incident on the measurement surface of the sample  50  while being condensed. Therefore, in the case of the illumination light L 1 , which is full polarization and linear polarization, when the optical axis C is orthogonal to the measurement surface of the sample  50 , according to a direction incident on the measurement surface the illumination L 1  may include part of P polarization and part of S polarization. The part of the P polarization in the illumination light L 1  may be reflected as the P polarization. The part of the S polarization in the illumination light L 1  may be reflected as the S polarization. 
     The condensing optical system  20  may condense the reflected light R 1  from reflected from the sample  50 . The condensing optical system  20  may include the objective lens  17 , the beam splitter  16 , and relay lenses  21  and  22 . The objective lens  17  is a member of the illumination optical system  10  as well as a member of the condensing optical system  20 . The reflected light R 1  reflected from the sample  50  may transmit through a pupil location  23  of the objective lens  17 . Further, the pupil location  23  may be reimaged on the image detector  42  by the relay lenses  21  and  22 . As described above, the condensing optical system  20  may image an exit pupil of the objective lens  17  on the image detector  42 . The objective lens  17  may transmit the reflected light R 1  reflected from the sample  50  by the illumination light L 1  to be incident on the beam splitter  16 . 
     The beam splitter  16  may transmit part of the incident reflected light R 1 . For example, the reflected light R 1  transmitting through the beam splitter  16  may be incident on the lower relay lens  21 . 
     The lower relay lens  21  may condense the reflected light R 1  that transmitted through the beam splitter  16  to form an image, and then make the reflected light R 1  be incident on the upper relay lens  12 . The upper relay leas  22  may transmit the incident reflected light R 1  to be incident on the polarizing optical element unit  30 . 
     The polarizing optical element emit  30  may separate the reflected light R 1  into two linear polarization components, where the two linear polarization components of the reflected light R 1  has polarization directions that are orthogonal to each other in a radial direction with respect to the optical axis C of the condensing, optical system  20  of the reflected light R 1 . The reflected light R 1  is light reflected from the measurement surface of the sample  50  when the light L 1  including the linear polarization illuminates the measurement surface of the sample. The polarizing optical element unit  30  may include, for example, a Wollaston lens. Also, as shown in  FIG.  4   , the polarizing optical element unit  30  may include a plurality of Wollaston lenses W 10  and W 20 . The lower Wollaston lens W 10  may include two birefringent crystals W 11  and W 12 . The upper Wollaston lens W 20  may also include two birefringent crystals W 21  and W 22 . 
     The first birefringent crystal W 11  may include a uniaxial birefringent crystal. The first birefringent crystal W 11  may have an incidence surface having a planar shape and an exit surface haying a concave spherical shape. The first birefringent crystal W 11  may have a crystal optical axis in the X-axis direction. The second birefringent crystal W 12  may include a uniaxial birefringent crystal. The second birefringent crystal W 12  may have an incidence surface having a convex spherical shape and an exit surface having a planar shape. The second birefringent crystal W 12  may have a crystal optical axis in the Y-axis direction. Accordingly, the lower Wollaston lens W 12  may include two uniaxial birefringent crystals having a spherical shape to fit each other. A crystal optical axis of each of the uniaxial birefringent crystals of the lower Wollaston lens W 10  may be orthogonal to the optical axis C of the condensing optical system  20  and the crystal optical axes of the uniaxial birefringent crystals of the lower Wollaston lens W 10  may be orthogonal to each other. 
     The third birefringent crystal W 21  may include a uniaxial birefringent crystal. The third birefringent crystal W 21  may have an incidence surface having a planar shape and an exit surface having a concave spherical shape. The third birefringent crystal W 21  may have a crystal optical axis in the Y-axis direction. The fourth birefringent crystal W 22  may include a uniaxial birefringent crystal. The fourth birefringent crystal W 22  may have an incident surface having a convex spherical shape and an exit surface having a planar shape. The fourth birefringent crystal W 22  may have a crystal optical axis in the X-axis direction. Accordingly, the upper Wollaston lens W 20  may include two uniaxial birefringent crystals having a spherical shape to fit each other. A crystal optical axis of each of the uniaxial birefringent crystals of the upper Wollaston lens W 20  is orthogonal to the optical axis C of the condensing optical system  20  and the crystal optical axes of the uniaxial birefringent crystals of the upper Wollaston lens W 20  may be orthogonal to each other. 
     Each of the birefringent crystals W 11 , W 12 , W 21 , and W 22  may include any one of quartz, magnesium fluoride, sapphire, calcite, or Alpha-Barium Borate (αBBO) as a material. In the polarizing optical element unit  30 , the Wollaston lenses W 10  and W 20  may have a refractive power of 0. Accordingly, the polarizing optical element unit  30  may not condense or diffuse the reflected light R 1 . 
     In the lower Wollaston lens W 10 , the crystal optical axis of the first birefringent crystal W 11  and the crystal optical axis of the second birefringent crystal W 12  may be arranged to be perpendicular to each other kind orthogonal to the optical axis C. For example, the crystal optical axis of the first birefringent crystal W 11  may be in the X-axis direction, and the crystal optical axis of the second birefringent crystal W 12  may be in the Y-axis direction. Accordingly, two perpendicular polarizations (X polarization and Y polarization in  FIG.  4   ) may be radially separated with respect to the optical axis C and proceed in different directions. For example, the X polarization may be separated outwardly away from the optical axis C than the Y polarization. The Y polarization may be separated inwardly closer to the optical axis C than the X polarization. 
     The polarizing optical element unit  30  may further include another set of upper Wollaston lenses W 20 . In the upper Wollaston lens W 20 , the crystal optical axis of the third birefringent crystal W 21  and the crystal optical axis of the fourth birefringent crystal W 22  may be arranged to be perpendicular to each other and orthogonal to the optical axis C. However, in the upper Wollaston lens W 20 , the crystal optical axis of each of the birefringent crystals may be opposite to the crystal optical axis of each of the birefringent crystals of the lower Wollaston lens W 10 . For example, the crystal optical axis of the third birefringent crystal W 21  may be in the Y-axis direction, and the crystal optical axis of the fourth birthing-era crystal W 22  may be in the X-axis direction. Accordingly, the arrangement and radius of curvature of two sets of Wollaston lenses W 10  and W 20  may be designed such that the respective polarizations are separated in opposite directions, and the two polarizations become the same point again on the image detector  42 . Accordingly, two polarization components of the reflected light R 1  transmitted through the polarizing optical element unit  30  and the analyzer unit  41  may be detected at the same point on the image detector  42 . 
     The light receiving optical system  40  may receive the reflected light R 1  to calculate the ellipsometry coefficients ψ and Δ. The light receiving optical system  40  may include an analyzer unit  41 , an image detector  42 , and an analysis apparatus  43 . The analyzer unit  41  may include, for example, a linear polarizer H 2  that transmits a linear polarization component in a certain direction. 
       FIG.  5    is a graph showing linear polarization transmitting through the analyzer unit  41  in the ellipsometer  1  of  FIG.  4   .  FIG.  5    will be described with reference to  FIG.  4   . 
     Referring to  FIG.  5   , the analyzer unit  41  may transmit components of linear polarization of a 45° inclined direction with respect to a polarization direction in the X direction and a polarization direction in the Y direction separated by the polarizing optical element unit  30 . Accordingly, the analyzer unit  41  may transmit the polarization component of the 45° inclined direction with respect to the X direction among the linear polarizations having the polarization direction in the X direction. In addition, the analyzer unit  41  may transmit the polarization component of the  45  inclined direction with respect to the Y direction among the linear polarizations having the polarization direction in the Y direction. As described above, the analyzer unit  41  such as the linear polarizer H 2  may be disposed between the upper Wollaston lens W 20  and the image detector  42 . A transmission axis direction of the linear polarizer H 2  may be arranged in an azimuth that is intermediate (45°) of the optical axis of each of the two uniaxial birefringent crystals forming the Wollaston lenses W 10  and W 20 . Accordingly, the analyzer unit  41  may make two orthogonal polarization components interfere with each other by transmitting a component in a direction different from each polarization direction, and form an interference fringe in the form of a concentric circle. That is, the two polarization components may interfere with each other while being emitted as polarization components polarized in the same direction (the 45° inclined direction) by transmitting through the analyzer unit  41 . 
     The image detector  42  may receive the incident reflected light R 1 . The image detector  42  may be disposed at a pupil conjugate location  24  that is conjugate with the pupil location  23  of the objective lens  17 . The reflected light R 1  may include polarization components in the same direction in two linear polarizations orthogonal to each other. Accordingly, the reflected light R 1  may interfere on the image detector  42 . Accordingly, the interference fringe in the form of a concentric circle may be formed on the image detector  42 . The image detector  42  may detect an interference fringe of each polarization component that transmitted through the analyzer unit  41 . 
       FIG.  6    is a photograph of an interference fringe of reflected light interfering on the image detector  42  in the ellipsometer  1  of  FIG.  4   , and conceptual diagrams of X polarization and Y polarization.  FIG.  6    will be described with reference to  FIG.  4   . 
     Referring to  FIG.  6   , the interference fringe on the image detector  42  may have a shape of a concentric circle. In the ellipsometer  1  of the present example embodiment, such an interference fringe in the form of a concentric circle is called a Wollaston lens interference fringe. The Wollaston lens interference fringe may be formed by interference between X polarization and Y polarization. In the Wollaston lens interference fringe, a stripe space near the center may be large, and may be fine at the end of the pupil corresponding to light incident at the Brewster&#39;s angle. The Wollaston lens interference fringe may have a location where an optical path length difference between X polarization and Y polarization is 0 in a circular shape in a peripheral region of the image detector  42 . 
       FIGS.  7  to  9    are conceptual diagrams of a method of analyzing an interference fringe of reflected light interfering on the image detector  42  in the ellipsometer  1  of  FIG.  4   .  FIGS.  7  to  9    will be described with reference to  FIG.  4   . 
     Referring to  FIG.  7   , the analysis apparatus  43  may obtain an image detected on the image detector  42 . The analysis apparatus  43  may convert the coordinates into polar coordinates so that the center of a concentric circle becomes a coordinate origin with respect to the obtained image including the interference fringe in the form of a concentric circle of point symmetry. Next, the analysis apparatus  43  may represent the image after coordinate conversion in two-dimensional (2D) coordinates having a radius and an azimuth (polar angle) of a polar coordinate system as axes. The analysis apparatus  43  may perform a 2D Fourier transform on an image on a 2D coordinate plane, divide the frequency space image after transformation into a DC component and an AC component, and trim the components. 
     Referring to  FIG.  8   , the analysis apparatus  43  may perform an inverse Fourier transform on the DC component after shifting a peak location to the coordinate origin. In addition, as shown in  FIG.  9   , the analysis apparatus  43  may perform an inverse Fourier transform on the AC component after shifting the peak location to the coordinate origin. The analyzer  43  may obtain a first AC component, which is an amplitude component, and a second AC component, which is a phase component from the AC component. The obtained second AC component may correspond) to Δ of ellipsometry measurement as it is, ψ of ellipsometry measurement may be calculated from Equation (1) below. Here, DC represents a DC component, and AC amplitude represents the second AC component. As described above, the analysis apparatus  43  may calculate the ellipsometry coefficients ψ and Δ from the detected interference fringes based on a result of the inverse Fourier transform. 
       ψ=tan −1 [DC/AC amplitude±√{(DC/AC amplitude) 2 −1}]  Equation (1)
 
     Hereinafter, the effect of the ellipsometer  1  of the present example embodiment will be described. 
       FIG.  10    is photographs of interference fringes of reflected light interfering on an image detector in the ellipsometer  1  of  FIG.  4    and the ellipsometer  101  of  FIG.  1   .  FIG.  10    will be described with reference to  FIGS.  1  and  4   . 
     Referring to  FIG.  10   , in the ellipsometers  1  and  101  using the interference fringes of the present example embodiment and the comparative example, respectively, light used tor measurement may be partial coherent light temporally and spatially. Therefore, in a place where an optical path length difference of two interfering polarized light increases, the contrast of the interference fringes may significantly deteriorate. For this reason, the number of interference fringes firmed in the pupil has an upper limit depending on a wavelength width and/or a field of view. 
     As shown in  FIG.  10   , in order to compare the first interference fringes in the form of a concentric circle formed in the ellipsometer  1  of the present example embodiment and the second interference fringes formed in the ellipsometer  101  of the comparative example. for example, both the first and second interference fringes have the same number of snipes of about 5. Then, in the ellipsometer  101  of the comparative example, the interference fringes may be equally spaced within the pupil. On the other hand, in the ellipsometer  1  of the present example embodiment, the interference fringes may be sparse near the center and dense near the periphery. In addition, the width including the same five interference fringes may correspond to a pupil diameter in the ellipsometer  101  of the comparative example, but may correspond to a pupil radius in the ellipsometer  1  of the present example embodiment. Accordingly, the ellipsometer  1  of the present example embodiment may arrange the interference fringes twice as densely as the ellipsometer  101  of the comparative example. For example, near the periphery of the pupil, the interference fringes may be formed several to ten times as densely as possible. 
     Hereinafter, the technical advantages and/or effects of the pupil in ellipsometry measurement is described. 
       FIG.  11    is a perspective view showing an arrangement of an illumination optical system, a condensing optical system, and a pupil plane in the ellipsometer  1  of  FIG.  4   , and shows a relationship between a location on the pupil plane, and an angle of incidence of light and an azimuth of incidence to the sample  50 .  FIG.  11    will be described with reference to  FIG.  4   . 
     Referring to  FIG.  11   , the light perpendicularly incident on the sample  50  may arrive near the center of the pupil. On the other hand, near the periphery of the pupil, the light incident on the sample  50  at a large angle of incidence may arrive. In ellipsometry measurements, the obliquely incident light of the latter may be more important. For example, ellipsometry measurement using the illumination light L 1  near the Brewster&#39;s angle having an angle of incidence of 60° to 75° may have the highest sensitivity. Further, because the illumination light L 1  having such an angle of incidence has a large dependence on the angle of incidence and the azimuth of incidence, the illumination light L 1  may be measured with relatively high resolution. 
       FIG.  12    is a conceptual diagram showing a relationship between a location on a pupil plane, and an angle of incidence of light and an azimuth of incidence to a sample in the ellipsometer  1  of  FIG.  4   .  FIG.  12    will be described with reference to  FIG.  4   . 
     Referring to  FIG.  12   , NA=0.95, which is the upper limit of an NA of the general objective lens  17 , may correspond to an angle of incidence of 72°, and may substantially include the Brewster angle. NA=0.7 may correspond to an angle of incidence of 45°. The ellipsometer  1  of the present example embodiment may form a dense interference fringe near the periphery on the pupil because the periphery is more important for ellipsometry measurements. Therefore, for example, in high-precision measurement of a semiconductor manufacturing process, the ellipsometer  1  may be widely used. 
     As described above, the ellipsometer  1  of the present example embodiment may have a characteristic measurement principle for calculating ψ and Δ from an interference fringe in the form of a concentric circle formed as two different polarized pieces of light. For example, in the case of performing spectral ellipsometry measurement by combining a broadband light source and a spectrometer, the resolution of the pupil may improve and the amount of light may increase, and thus a measurement time may shorten. Accordingly, a throughput may improve while a measurement precision improves. 
       FIG.  13    is a configuration diagram schematically illustrating an apparatus IA for inspecting a semiconductor device including the ellipsometer  1  according to an example embodiment of the inventive concepts.  FIG.  13    will be described with reference to  FIG.  1   , and the descriptions already given with reference to  FIGS.  1  to  12    will be briefly provided or omitted. 
     Referring to  FIG.  13   , the apparatus  1 A for inspecting the semiconductor device including the ellipsometer  1  of the present example embodiment (hereinafter, simply referred to as ‘apparatus  1 A for inspecting the semiconductor device’) may include the ellipsometer  1 , a base  80 , and an isolator  81 , an optical surface plate  82 , a stage  83 , a wafer holder  84 , a frame  85 , an environment chamber  86 , a temperature controller unit  87 , and an automatic substrate transfer device  88 . The ellipsometer  1  may be, for example, the ellipsometer  1  of  FIG.  4   . Accordingly, the ellipsometer  1  may include the illumination optical system  10 , the condensing optical system  20 , the polarizing optical element unit  30 , and the light receiving optical system  40 . 
     The base  80  may be a pedestal serving as a foundation. The isolator  81  installed on the base  80  may remove vibration from the floor. The optical surface plate  82  may be installed on the isolator  81 . The stage  83  and the frame  85  may be disposed on the optical surface plate  82 . The sample  50 , such as a silicon (Si) wafer mounted on the wafer holder  84 , may be mounted on the stage  83 . The frame  85  may fix an optical system. The environment chamber  86  may isolate several members of the ellipsometer  1  (e.g., the base  80 , the isolator  81 , the optical surface plate  82 , the stage  83 , the wafer holder  84 , and the frame  85 ) from an external environment. Meanwhile, in  FIG.  13   , the light source  11  and the spectrometer  12  of the illumination optical system  10 , and the analysis apparatus  43  that are not included in the environment chamber  86  are separately illustrated outside the environment chamber  86 . The temperature controller unit  87  may maintain the inside of the environment chamber  86  at a certain temperature. The automatic substrate transfer device  88  may transfer the sample  50 . 
     The analysis apparatus  43  of the ellipsometer  1  may acquire an image from the image detector  42 , such as a camera, and may perform processing of ellipsometry measurement. The analysis apparatus  43  may include a control unit  91 , such as a computer or processing, circuitry, a grabber board  92  that acquires and processes an image from the image detector  42 , a stage controller  93  that controls the stage  83  on which the sample  50  is mounted, and a light source-spectrometer controller  94  that controls the light source  11  and the spectrometer  12 . In other words, the analysis apparatus  43  may include processing circuitry such as hardware including logic circuits; a hardware/software combination such as a processor executing software; or a combination thereof. For example, the processing circuitry more specifically may include, but is not limited to, a central processing unit (CPU), an arithmetic logic unit (ALU), a digital signal processor, a microcomputer, a field programmable gate array (FPGA), a System-on-Chip (SoC), a programmable logic unit, a microprocessor, application-specific integrated circuit (ASIC), etc. 
     The apparatus  1 A for inspecting the semiconductor device of the present example embodiment may include the ellipsometer  1  of  FIG.  4   . Accordingly, the apparatus  1 A for inspecting the semiconductor device may improve a measurement accuracy and improve a throughput in the inspection of the semiconductor device. For example, in CD measurement and overlay evaluation in the semiconductor manufacturing process, the apparatus  1 A for inspecting the semiconductor device may perform even distribution evaluation within a shot on a wafer, within a chip, and within a memory-cell, instead of measuring several points within a single wafer so far. Thereby, the apparatus  1 A for inspecting the semiconductor device may contribute to improving a manufacturing yield and productivity of the semiconductor device, and may also contribute to cost reduction of the semiconductor device. Other configurations and effects are the same as those described with respect to the ellipsometer  1  of  FIG.  4   . 
       FIG.  14    is a configuration diagram schematically showing an ellipsometer  2  according to an example embodiment of the inventive concepts. The descriptions already given with reference to  FIGS.  1  to  12    will be briefly provided or omitted. 
     Referring to  FIG.  14   , the ellipsometer  2  of the present example embodiment may be different from the ellipsometer  1  of  FIG.  4    in that illumination light L 1  including circular polarization is used. For example, the ellipsometer  2  of the present example embodiment may include a polarizer unit  18 . The polarizer unit  18  may include a circular polarizer that generates the circular polarization that rotates in any one of a left rotation and a right rotation with respect to an optical axis of the illumination light L 1 . The circular polarizer of the polarizer unit  18  may include a linear polarizer H 1  and a λ/4 wave plate H 3 . 
     In addition, the ellipsometer  2  of the present example embodiment may include an analyzer unit  44 . The analyzer unit  44  may include a circular polarizer that transmits a circular polarization component that rotates in any one of a left rotation and a right rotation. The circular polarizer of the analyzer unit  44  may include a linear polarizer H 2  and a λ/4 wave plate H 4 . 
     Furthermore, the ellipsometer  2  of the present example embodiment may include a polarizing optical element unit  31 . The polarizing optical element unit  31  may include a birefringent crystal F 1 . The birefringent crystal F 1  may be disposed at a location where the reflected light R 1  is condensed or diffused in the condensing optical system  20 . For example, the birefringent crystal F 1  may be disposed between the lower relay lens  21  and the upper relay lens  22  at a location where the reflected light R 1  diffuses. The birefringent crystal F 1  may have a parallel plane plate shape. Accordingly, the birefringent crystal F 1  may include two parallel plate surfaces. The birefringent crystal F 1  may be a uniaxial birefringent crystal. A crystal optical axis of the birefringent crystal F 1  may be disposed in a direction orthogonal to a plate surface. The birefringent crystal F 1  may be disposed so that the plate plane is orthogonal to the optical axis. Accordingly, the crystal optical axis of the birefringent crystal F 1  may be parallel to the optical axis C of the condensing optical system  20 . The birefringent crystal F 1  may include, for example, αBB) as a material. In addition, the birefringent crystal F 1  may include any one of quartz, magnesium fluoride, sapphire, or calcite. 
     In the ellipsometer  2  of the present example embodiment, the illumination light L 1  converted into parallel light by the illumination lens  14  includes linear polarization while transmitting through the linear polarizer H 1 . Thereafter, the illumination light L 1  including the linear polarization may become the illumination light L 1  including the circular polarization by transmitting through the  214  wave plate H 3 . Also, according to an example embodiment, the illumination light L 1  may include elliptical polarization. 
     The illumination light L 1  may transmit through the objective lens  17  via the beam splitter  16 . Thereby, the illumination light L 1  may illuminate the sample  50  from all angles and all azimuths within an NA of the objective lens  17 . In this case, the NA of the objective lens  17  may be greater than or equal to a value including the Brewster angle of the sample  50 . 
     The reflected light R 1  reflected from the sample  50  may include radial polarization and azimuth polarization. The reflected light R 1  may transmit through the pupil location  23  of the objective lens  17 . The pupil conjugation location  24 , which is conjugate with the pupil location  23 , may be imaged on the image detector  42  by the relay lenses  21  and  22 . 
       FIG.  15    is a photograph of an interference fringe of reflected light interfering on an image detector in the ellipsometer  2  of  FIG.  14   , and conceptual diagrams of radial polarization and azimuth polarization.  FIG.  15    will be described with reference to  FIG.  14   . 
     Referring to  FIG.  15   , the action when the radial polarization and azimuth polarization included in the reflected light R 1  transmit through the birefringent crystal F 1  is considered. First, the azimuth polarization is always perpendicular to a crystal optical axis of the birefringent crystal F 1 . Accordingly, the azimuth polarization may be ordinary light. Meanwhile, in the radial polarization, a polarization direction is inclined with respect to the optical axis C. For this reason, radial polarization may include extraordinary light in which an electric field is parallel to the crystal optical axis of the birefringent crystal F 1 . 
       FIG.  16    is a conceptual diagram of the polarizing optical element unit  31  in the ellipsometer  2  of  FIG.  14   , in which the linear polarizer H 2  and the λ/4 wave plate H 4  of the analyzer unit  44  are omitted, to explain a propagation state of each of radial polarization and azimuth polarization. 
     Referring to  FIG.  16   , in the polarizing optical element unit  31  of the ellipsometer  2  of the present example embodiment, the radial polarization and azimuth polarization that transmit through the birefringent crystal F 1  may be relatively different in a traveling direction and a phase according to a difference in refractive index. That is, the radial polarization including extraordinary light may be diffused in a direction away from the optical axis C than the azimuth polarization including ordinary light. Meanwhile, after transmitting through the birefringent crystal F 1 , radial polarization and azimuth polarization may be shifted parallel to each other. 
     Then, after transmitting through the upper relay lens  22 , radial polarization and azimuth polarization may return to the same point on the image detector  42  (On the pupil). Here, it should be noted that a phase difference between two polarizations is also delayed by a different amount. On the optical axis C, radial polarization and azimuth polarization are in the same phase, but the phase may be different toward the periphery of the image detector  42  (on the pupil). 
     The analyzer unit  44  including the λ/4 wave plate H 4  and the linear polarizer H 2  may be disposed between the image detector  42  and the upper relay lens  22 . The analyzer unit  44  may transmit only a common polarization component of radial polarization and azimuth polarization. Accordingly, the radial polarization and azimuth polarization transmitted through the analyzer unit  44  may cause interference, and thus, an interference fringe in the form of a concentric circle may be formed on the image detector  42 . Here, the radial polarization may correspond to P polarization on the sample  50 , such as a semiconductor wafer, for example, and the azimuth polarization may correspond to S polarization on the sample  50 . Accordingly, the ellipsometer  2  of the present example embodiment may enable ellipsometry measurement on the P polarization and S polarization in all directions, and enable high-sensitivity measurement due to its symmetry without depending on a structure of a measurement target. Other configurations and effects are the same as those described with respect to the ellipsometer  1  of  FIG.  4    and the apparatus  1 A for inspecting the semiconductor device of  FIG.  13   . 
       FIG.  17    is a configuration diagram schematically showing an ellipsometer  3  according to an example embodiment of the inventive concepts. The descriptions already given with reference to  FIGS.  1  to  16    will be briefly provided or omitted. 
     Referring to  FIG.  17   , in the ellipsometer  2  of  FIG.  14   , a location where an optical path length difference between radial polarization and azimuthal polarization is 0 is on the optical axis C of the condensing optical system  20 . Meanwhile, in the ellipsometer  3  of the present example embodiment, the location where the optical path length difference between the radial polarization and the azimuth polarization is 0 may be arranged more peripherally on the pupil, whereby the number of stripes in the interference fringe may be densely measured. 
     For example, the ellipsometer  3  of the present example embodiment may include a polarizing optical element unit  32 . The polarizing optical element unit  32  may include an upper birefringent crystal F 2  in addition to the lower birefringent crystal F 1 . The upper birefringent crystal F 2  may be disposed between the upper relay lens  22  and the analyzer unit  44 . The upper birefringent crystal F 2  has a plate shape having an incident surface and an exit surface. The incident surface may have a concave cone shape and the exit surface may have a convex cone shape. The upper birefringent crystal F 2  may have a double-sided axicon lens shape. The upper birefringent crystal F 2  may include a uniaxial birefringent crystal. The crystal optical axis of the upper birefringent crystal F 2  may be parallel to the optical axis C of the condensing optical system  20 . 
     The upper birefringent crystal F 2  may have a birefringence opposite to that of the lower birefringent crystal FL For example, the lower birefringent crystal F 1  and the upper birefringent crystal F 2  may have opposite birefringence of a refractive index n 0  of ordinary light (hereinafter referred to as n 0 )&lt;a refractive index n e  of extraordinary light (hereinafter referred to as n e ), and n 0 &gt;n e . For example, when the lower birefringent crystal F 1  is a negative crystal (n 0 &gt;n e ), the upper birefringent crystal F 2  may be a positive crystal (n 0 &lt;n e ). Conversely, when the lower birefringent crystal H is the positive crystal (n 0 &lt;n e ) the upper birefringent crystal F 2  may be the negative crystal (n 0 &gt;n e ). 
       FIG.  18    is a photograph of an interference fringe of reflected light interfering on the image detector  42  in the ellipsometer  3  of  FIG.  17   , and conceptual diagrams of radial polarization and azimuth polarization, and  FIG.  19    is a conceptual diagram of the polar zing optical element unit  32  in the ellipsometer  3  of  FIG.  17   . 
     Referring to  FIGS.  18  and  19   , by adding the upper birefringent crystal F 2  to the lower birefringent crystal F 1 , on the image detector  42 , a location where an optical path length difference between radial polarization and azimuth polarization is 0 may be, moved to a location outside the optical axis C. Meanwhile, in  FIG.  19   , the linear polarizer H 2  and the λ/4 wave plate H 4  of the analyzer unit  44  are omitted, in order to explain a propagation state of each of radial polarization and azimuth polarization. 
       FIGS.  20  to  23    are conceptual diagrams of polarizing optical element units  33  to  36  according to modification examples in the ellipsometer  3  of  FIG.  17   .  FIGS.  20  to  23    will be described with reference to  FIG.  17   , and the descriptions already given with reference to  FIGS.  17  to  19    will be briefly provided or omitted. 
     Even when the polarizing optical element units  33  to  36  of  FIGS.  20  to  23    have a different configuration from that of the polarizing optical element unit  32  of  FIG.  19   , by the same principle as that of the polarizing optical element unit  32  of  FIG.  19   , interference fringes in the form of a concentric circle in radial polarization and azimuth polarization may be formed tiara the image detector  42 . 
     Referring to  FIG.  20   , the polarizing optical element unit  33  according to a first modification example may include the lower birefringent crystal F 1  and an upper birefringent crystal F 3 . For example, in the configuration of the polarizing optical element unit  32  of the ellipsometer  3  of  FIG.  17   , the polarizing optical element unit  33  of the first modification may omit the upper birefringent crystal  12 , and the upper birefringent crystal F 3  may be disposed between the lower birefringent crystal F 1  and the upper relay lens  22 . Accordingly, the upper birefringent crystal  13  may be disposed in a region where the reflected light R 1  of the condensing optical system  20  is condensed or diffused. The upper birefringent crystal F 3  may include a uniaxial birefringement crystal having a parallel plane plate shape. The upper birefringent crystal F 3  may include two parallel plate surfaces. The crystal optical axis of the upper birefringent crystal F 3  may be orthogonal to the plate surface. The upper birefringent crystal F 3  may be disposed such that the plate surface thereof is orthogonal to the optical axis C of the condensing optical system  20 . The crystal optical axis of the upper birefringent crystal F 3  may be parallel to the optical axis C. 
     The upper birefringent crystal F 3  may have a birefringence opposite to that of the lower birefringent crystal F 1 . For example, the lower birefringent crystal F 1  and the upper birefringent crystal F 3  may have opposite birefringence of n 0 &lt;n e  and n 0 &gt;n e . For example, when the lower birefringent crystal F 1  is a negative crystal (n 0 &gt;n e ), the upper birefringent crystal F 3  may be a positive crystal (n 0 &lt;n e ). Conversely, when the lower birefringent crystal F 1  is the positive crystal (n 0 &lt;n e ), the upper birefringent crystal F 3  may be the negative crystal (n 0 &gt;n e ). 
     Referring to  FIG.  21   , the polarizing optical element unit  34  of a second modification example may include the upper birefringent crystal F 2  having a double-sided axicon lens shape and a lower birefringent crystal F 4  having a meniscus lens shape. For example, in the configuration of the polarizing optical element unit  32  of the ellipsometer  3  in  FIG.  17   , the polarizing optical element unit  34  of the second modification example may include the lower birefringent crystal F 4  between the lower relay lens  24  and the upper relay lens  22 , instead of the lower birefringent crystal F 1 . Accordingly, the lower birefringent crystal F 4  may be disposed in a region where the reflected light R 1  of the condensing optical system  20  is condensed or diffused. The lower birefringent crystal F 4  may include an incident surface and an exit surface. The lower birefringent crystal F 4  may have the incident surface having a concave spherical shape and the exit surface having a convex spherical shape. The lower birefringent crystal F 4  may include a uniaxial birefringent crystal. The crystal optical axis of the lower birefringent crystal F 4  may be arranged so as to be parallel to the optical axis C the condensing optical system  20 . 
     The lower birefringent crystal F 4  may have a birefringence opposite to that of the upper birefringent crystal F 2 . For example, the upper birefringent crystal F 2  and the lower birefringent crystal F 4  may have opposite birefringence of n 0 &lt;n e  and n 0 &gt;n e . For example, when the upper birefringent crystal F 2  is a negative crystal (n 0 &gt;n e ), the lower birefringent crystal F 4  may be a positive crystal (n 0 &lt;n e ). Conversely, when the upper birefringent crystal F 2  is the positive crystal (n 0 &lt;n e ), the lower birefringent crystal F 4  may be the negative crystal (n 0 &gt;n e ). 
     Referring to  FIG.  22   , the polarizing optical element unit  35  of the third modified example may include the lower birefringent crystal F 1 , an upper birefringent crystal F 5 , and axicon lenses  25  and  26 . For example, in the configuration of the ellipsometer  3  in  FIG.  17   , the polarizing optical element unit  35  of a third modification example may have a configuration in which an upper birefringent crystal F 5  having a parallel plane plate shape is disposed between the concave-convex axicon lenses  25  and  26 , instead of the upper birefringent crystal F 2  having a double-sided axicon lens shape. The upper birefringent crystal F 5  may include a uniaxial birefringent crystal having the parallel plane plate shape. The upper birefringent crystal F 5  may include two parallel plate surfaces. The crystal optical axis of the upper birefringent crystal F 5  may be orthogonal to the plate surface. The upper birefringent crystal F 5  may be disposed such that the plate surface thereof is orthogonal to the optical axis C of the condensing optical system  20 . The crystal optical axis of the upper birefringent crystal F 5  may be parallel to the optical axis C. 
     The lower axicon lens  25  may be disposed between the upper relay lens  22  and the upper birefringent crystal F 5 . Accordingly, the lower axicon lens  25  may be disposed on an incident surface side of the upper birefringent crystal F 5 . The lower axicon lens  25  may include, for example, glass, as a material. The lower axicon lens  25  may have an incident surface having a concave cone shape and an exit surface having a planar shape. 
     The upper axicon lens  26  may be disposed between the upper birefringent crystal F 5  and the analyzer unit  44 . Accordingly, the upper axicon lens  26  may be disposed on an exit surface side of the upper birefringent crystal F 5 . The upper axicon lens  26  may include, for example, glass, as a material. The upper axicon lens  26  may have an incident surface having a planar shape and an exit surface having a convex conical shape. 
     The upper birefringent crystal F 5  may have a birefringence opposite to that of the lower birefringent crystal F 1 . For example, the lower birefringent crystal F 1  and the upper birefringent crystal F 5  may have opposite birefringence of n 0 &lt;n e  and n 0 &gt;n e . For example, when the lower birefringent crystal F 1  is a negative crystal (n 0 &gt;n e ), the upper birefringent crystal F 5  may be a positive crystal (n 0 &lt;n e ). Conversely, when the lower birefringent crystal F 1  is the positive crystal (n 0 &lt;n e ), the upper birefringent crystal F 5  may be the negative crystal (n 0 &gt;n e ). 
     Referring to  FIG.  23   , the polarizing optical element unit  36  according to a fourth modification example may include the upper birefringent crystal F 2 , a lower birefringent crystal F 6 , and an intermediate birefringent crystal F 7 . For example, in the configuration of the ellipsometer  3  in  FIG.  17   , the polarizing optical element unit  36  of the fourth modification example may include the lower birefringent crystal F 6  and the intermediate birefringement crystal F 7 , instead of the lower birefringent crystal F 1 . Accordingly, the lower birefringent crystal F 6  and the intermediate birefringent crystal F 7  may be disposed in a region where the reflected light R 1  of the light converging optical system  20  is condensed or diffused. The lower birefringent crystal F 6  and the intermediate birefringent crystal F 7  may include a uniaxial birefringent crystal having a parallel plane plate shape. Each of the lower birefringent crystal F 6  and the intermediate birefringent crystal F 7  may include two parallel plate surfaces. The crystal optical axis of the lower birefringent crystal F 6  and the crystal optical axis of the intermediate birefringent crystal F 7  may be parallel to the plate surface. The lower birefringent crystal F 6  and the intermediate birefringent crystal F 7  may be disposed such that the plate surface is orthogonal to the optical axis C of the light converging optical system  20 . The crystal optical axis of the lower birefringent crystal F 6  and the crystal optical axis of the intermediate birefringent crystal F 7  may be orthogonal to the optical axis C of the condensing optical system  20  and may be orthogonal to each other. 
     The lower birefringent crystal F 6  and the middle birefringent crystal F 7  may have opposite birefringence to that of the upper birefringent crystal F 2 . For example, the lower birefringent crystal F 6  and the intermediate birefringent crystal F 7 , and the upper birefringent crystal F 2  may have opposite birefringence of n 0 &lt;n e  and n 0 &gt;n e . For example, when the lower birefringent crystal F 6  and the intermediate birefringent crystal F 7  are negative crystals (n 0 &gt;n e ), the upper birefringent crystal F 2  may be a positive crystal (n 0 &lt;n e ). Conversely, when the lower birefringent crystal F 6  and the intermediate birefringent crystal F 7  are the positive crystals (n 0 &lt;n e ), the upper birefringent crystal F 2  may be the negative crystal (n 0 &gt;n e ). As described above, in the ellipsometer  3  of  FIG.  17    and the first to fourth modification examples, the polarizing optical element units  32  to  36  may include a plurality of birefringent crystals having birefringence of n 0 &lt;n e  and n 0 &gt;n e . Other configurations and effects are the same as those described with respect to the ellipsometer  1  of  FIG.  4   , the apparatus  1 A for inspecting the semiconductor device of  FIG.  13   , and/or the ellipsometer  2  of  FIG.  14   . 
       FIG.  24    is a configuration diagram schematically showing an ellipsometer  4  according to an example embodiment of the inventive concepts. The descriptions already given with reference to  FIGS.  1  to  23    will be briefly provided or omitted. 
     Referring to  FIG.  24   , in the ellipsometer  4  of the present example embodiment, the polarizer unit  15  may include the linear polarizer H 1 , and the analyzer unit  41  may include the linear polarizer H 2 . The polarizing optical element unit  37  may include Nomarski prisms  131  and  132 . For example, the polarizing optical element unit  37  may include the lower Nomarski prism  131  including a uniaxial birefringent crystal having a positive birefringence of n 0 &lt;n e  and as uniaxial birefringent crystal having as negative birefringence of n 0 &gt;n e , and the upper Nomarski prism  132  including a uniaxial birefringent crystal having positive birefringence and a uniaxial birefringent crystal having negative birefringence. Accordingly, the polarizing optical element unit  37  may separate the reflected light R 1  in which the illumination light L 1  including linear polarization is reflected from a measurement surface of the sample  50  into two linear polarization components in a linear polarization direction orthogonal to each other. The analyzer unit  41  may form an interference fringe by transmitting through and interfering with two linear polarization components in a direction different from each polarization direction. The image detector  42  may detect the interference fringe. The analysis apparatus  43  may calculate the ellipsometry coefficients ψ, Δ from the detected interference fringes. 
       FIG.  25    is a photograph of an interference fringe of reflected light interfering on the image detector  42  in the ellipsometer  4  of  FIG.  24   , and conceptual diagrams of X polarization and Y polarization, along with a photograph of an interference fringe of reflected light interfering on an image detector in the ellipsometer  101  of  FIG.  1   .  FIG.  25    will be described with reference to  FIG.  24    together. 
     Referring to  FIG.  25   , unlike the ellipsometers  1  to  3  of  FIGS.  4 ,  14 , and  17   , the ellipsometer  4  of the present example embodiment may form the interference fringe of X polarization and Y polarization as vertical stripes in one-dimensional shape on the pupil. However, by using two or more types of crystals having different birefringence, a separation angle of two polarizations may be changed for each wavelength. For example, the Nomarski prisms  131  and  132  may be arranged so that the separation angle of two polarizations immediately before the image detector  42  is relatively large at a long wavelength side and relatively small at a short wavelength side. Accordingly, the ellipsometer  4  of the present example embodiment includes the achromatic Nomarski prism  132 , thereby suppressing a decrease in the contrast at both ends in the X-axis direction compared to the ellipsometer  101  of the comparative example. As described above, a Change in the space of the interference fringes due to a difference in the wavelength may be reduced. Therefore, even in measurement using a broadband light source, it may be possible to narrow the space of the interference fringes or to widen the wavelength width compared to the existing methods. 
       FIG.  26    is a graph showing the wavelength dependence of birefringence in each material of a birefringent crystal, where the x-axis represents wavelength and the y-axis represents birefringence. 
     Referring to  FIG.  26   , the graph shows the wavelength dependence of a polarization separation angle in the case where a value of (n 0 −n e )/{(n 0 +n e )/2} is normalized to be 1 when the wavelength is 400 nm, and a Nomarski prism is configured of at least one material of αBBO, quartz, magnesium fluoride (MgF 2 ), sapphire (Al 2 O 3 ), or calcite. As shown in the graph, magnesium fluoride may have a relatively small wavelength dependence of the polarization separation angle, and calcite may have a large wavelength dependence of the polarization separation angle. A stripe pitch of an interference fringe may have the same value at a plurality of wavelengths of illumination light. 
       FIG.  27    is conceptual diagram of the polarizing optical element unit  37  in the ellipsometer  4  of  FIG.  24   .  FIG.  27    will be described with reference to  FIG.  24   . 
     Referring to  FIG.  27   , when the upper Nomarski prism  132  is configured of calcite and the lower Nomarski prism  131  is configured of magnesium fluoride, a polarization separation angle immediately before the image detector  42  may be relatively large on a long wavelength side and relatively small on a short wavelength side. By designing as described above, the wavelength dependence of a space between the interference fringes may be reduced. Other configurations and effects are the same as those described with respect to the ellipsometer  1  of  FIG.  4   , the apparatus  1 A for inspecting the semiconductor device of  FIG.  13   , the ellipsometers  2  and  3  of  FIGS.  14  and  17   , and/or the modification examples of  FIGS.  20  to  23   . 
     The technical spirits of the inventive concepts are not limited to the above-described example embodiments, and it is possible to appropriately change the scope without departing from the spirits. For example, the configurations of the example embodiments of  FIGS.  4 ,  13 ,  14 ,  17 , and  20  to  23    may be combined with each other. Also, an apparatus for inspecting a semiconductor device including the ellipsometers of the example embodiments of  FIGS.  14 ,  17 ,  20  to  23 , and  24    may be included in the technical spirits of the inventive concepts. 
     In one example embodiment of the inventive concepts, light of linear polarization is transmitted through an objective lens to illuminate a measurement sample simultaneously from a plurality of angles of incidence and azimuth of incidence, reflected light reflected from the measurement sample is incident on the objective lens, is transmitted through a relay lens and a polarizing optical clement unit, and then light is received by an image detector disposed at a pupil conjugation location of the objective lens. 
     In an example embodiment of the inventive Concepts, the polarizing optical clement unit includes at least two uniaxial birefringent crystals and a linear polarizer, the two uniaxial birefringent crystals having crystal optical axes perpendicular to each other and perpendicular to the optical axis are combined, and are separated in the radial direction on the optical axis with respect to light that had two polarization components upon reflection from a sample. 
     In one example embodiment of the inventive concepts, the uniaxial birefringent crystal has a spherical surface in which at least one surface is a convex surface or a concave surface, and does not have refractive power when the two uniaxial birefringent crystals are combined. The two polarization components separated in the uniaxial birefringent crystal interfere with each other on an image detector by a linear polarizer provided immediately before the image detector to form an interference fringe in the form of a concentric circle. Contrast and phase information of an obtained image of the interference fringe are processed to obtain ψ and Δ of ellipsometry measurement results. 
     While the inventive concepts have been particularly shown and described with reference to sonic example embodiments thereof, it will be understood that various changes in form and details may be made therein without departing from the spirit and scope of the following claims.