Ellipsometry

Abstract

To improve accuracy of film thickness measurement by ellipsometry.SOLUTION: A device includes: a holder for holding an object to be measured; a light-projecting unit for causing a first light to which a first polarization is performed to incident on the object at a prescribed angle of incidence; and a light-receiving unit for receiving a second light created by reflecting the first light by the object and measuring light intensity of a third light created by performing second polarization to the second light. The light-projecting unit has an aperture stop that adjusts a numerical aperture of the light-projecting unit to 0.1 or less, and further adjusts a numerical aperture of the light-receiving unit to 0.7 times or less, a polarizing unit for performing the first polarization, and an objective lens for focusing the first light onto the object to a major axis of 100 μm or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to ellipsometers. [Background technology]

[0002] As a method for measuring the thickness of a thin film formed on a substrate, a film thickness measurement by ellipsometry is known. An apparatus for performing ellipsometry is commonly called an ellipsometer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-068937 A [Patent Document 2] JP 2009-103598 A [Patent Document 3] JP 2010-223822 A [Patent Document 4] Patent No. 4260683 [Patent Document 5] Patent No. 4950813 [Patent Document 6] Patent No. 6857186 Summary of the Invention [Problem to be solved by the invention]

[0004] In film thickness measurement by ellipsometry, the reflection angle between the light reflected from the thin film and the surface of the thin film has a large effect on the measurement accuracy, so it is desirable for the distribution of the reflection angle to be narrow.

[0005] The field stop used in Patent Document 6 prevents light outside the field of view from being detected, but the field stop does not necessarily narrow the distribution of the reflection angles of light within the field of view.

[0006] The present disclosure has been made in consideration of the above-mentioned problems, and has an object to narrow the distribution of reflection angles, thereby improving the accuracy of film thickness measurement by ellipsometry. [Means for solving the problem]

[0007] A first aspect of an ellipsometer according to the present disclosure includes a holding unit that holds an object to be measured, a light-projecting unit that directs a first light having a first polarization to be incident on the object at a predetermined angle of incidence, and a light-receiving unit that receives a second light that is the first light reflected by the object and measures the light intensity of a third light that is the second light that has been polarized in a second way.

[0008] The light-projecting unit includes an aperture stop that adjusts the numerical aperture of the light-projecting unit to 0.1 or less and to 0.7 times or less the numerical aperture of the light-receiving unit, a polarization unit that performs the first polarization, and an objective lens that focuses the first light onto the target to a major axis of 100 μm or less.

[0009] A second aspect of the ellipsometer according to the present disclosure is the first aspect, wherein the light at the light receiving portion passes through an area within 0.7 times the outer diameter of a lens of the light receiving portion when viewed from the central axis of the lens.

[0010] A third aspect of the ellipsometer according to the present disclosure is the first or second aspect, in which the first polarized light is elliptically polarized light, the polarizing unit includes a first polarizing plate that linearly polarizes light and a wave plate that imparts a phase difference between two orthogonal polarized components, and the second polarized light is linearly polarized light whose polarization direction is variable, and the light receiving unit has a second polarizing plate that polarizes the second polarized light.

[0011] A fourth aspect of the ellipsometer according to the present disclosure is the third aspect, in which the light receiving unit further includes a collimator lens for obtaining a fourth light, which is a parallel light, from the second light, a beam splitter provided between the collimator lens and the second polarizing plate for splitting the fourth light into a fifth light and a sixth light, and a light receiving element for measuring the light intensity of the fifth light by the beam splitter. The second polarizing plate performs the second polarization on the sixth light to emit the third light.

[0012] A fifth aspect of the ellipsometer according to the present disclosure is any one of the first to fourth aspects, in which a filter or a mask is used for the aperture stop.

[0013] A sixth aspect of the ellipsometer according to the present disclosure is any one of the first to fifth aspects, in which the light receiving section has a field stop into which the second light is incident. The second polarization is performed on the light exiting the field stop.

[0014] A seventh aspect of the ellipsometer according to the present disclosure is any one of the first to fifth aspects, in which the light receiving unit has a reflector that receives the second light and selectively reflects the second light, and the light reflected from the reflector is subjected to the second polarization.

[0015] An eighth aspect of the ellipsometer according to the present disclosure is any one of the first to fifth aspects, wherein the light projecting section further has an optical aperture, and the light emitted from the polarizing section passes through the optical aperture and enters the objective lens. Effect of the Invention

[0016] The ellipsometer according to the first aspect narrows the distribution of incidence angles, thereby narrowing the distribution of exit angles, and thus improving the accuracy of film thickness measurements by ellipsometry.

[0017] The ellipsometer according to the second aspect eliminates undesired refraction in the light receiving section, thereby improving the accuracy of film thickness measurement by ellipsometry.

[0018] The ellipsometer according to the third aspect is useful for realizing a first polarization and a second polarization.

[0019] The ellipsometer according to the fourth aspect contributes to normalizing the light intensity of the third light by the light intensity of the fifth light, and contributes to making the light intensity of the third light used in calculations in film thickness measurement by ellipsometry substantially equal to or higher than a predetermined level, thereby contributing to improving the accuracy of film thickness measurement by ellipsometry.

[0020] According to the ellipsometer of the fifth aspect, the aperture of the light projecting unit can be easily adjusted for various characteristics.

[0021] According to the ellipsometer of the sixth aspect and the ellipsometer of the seventh aspect, the influence of things other than the object of measurement on the film thickness measurement by ellipsometry is reduced, improving the accuracy of the film thickness measurement.

[0022] According to the ellipsometer of the eighth aspect, the field stop in the light receiving section can be omitted. [Brief description of the drawings]

[0023] [Figure 1] 1 is a schematic diagram illustrating a configuration of a film thickness measurement device according to the present disclosure. [Diagram 2] FIG. 4 is a block diagram illustrating a configuration of a control unit. [Diagram 3] FIG. 2 is a cross-sectional view illustrating a thin film and its surroundings. [Figure 4] 2 is a cross-sectional view showing a schematic configuration of a light projecting unit according to the first embodiment. FIG. [Diagram 5] FIG. 2 is a cross-sectional view illustrating a schematic configuration of a light receiving section according to the first embodiment. [Figure 6] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 7] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 8] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 9] FIG. 11 is a cross-sectional view illustrating a schematic configuration of a light receiving section according to a second embodiment. [Figure 10]FIG. 11 is a cross-sectional view illustrating a schematic configuration of a light receiving section according to a third embodiment. [Figure 11] 4 is a cross-sectional view illustrating a configuration of a reflector. FIG. [Figure 12] 11A and 11B are cross-sectional views illustrating other configurations of the reflector. [Figure 13] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 14] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 15] FIG. 13 is a cross-sectional view illustrating a schematic configuration of a light projecting unit according to a fourth embodiment. [Figure 16] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 17] 1 is a graph illustrating the relative distribution of light intensity with respect to position. [Figure 18] FIG. 13 is a cross-sectional view illustrating a schematic configuration of a light receiving section according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0024] Hereinafter, each embodiment of the present disclosure will be described with reference to the attached drawings. The components described in each embodiment are merely examples, and the scope of the present disclosure is not intended to be limited to only the examples. The drawings are merely schematic. In the drawings, the dimensions and numbers of each part may be exaggerated or simplified as necessary to facilitate understanding. In the drawings, parts having similar configurations and functions are given the same reference numerals, and duplicated descriptions are appropriately omitted.

[0025] In this specification, expressions indicating a relative or absolute positional relationship (e.g., "parallel," "orthogonal," "center") not only indicate the exact positional relationship, but also indicate a state including tolerances and a state in which the same degree of functionality is obtained. Expressions indicating that two or more things are in an equal state (e.g., "same," "equal," "homogeneous") not only indicate a state in which they are strictly equal quantitatively, but also indicate a state in which there is a difference that allows for tolerances or similar functions, unless otherwise specified.

[0026] Unless otherwise specified, expressions indicating a shape (such as "rectangular" or "cylindrical") not only represent a strict geometrical shape, but also represent a shape having, for example, irregularities or chamfers, within the scope of obtaining the same degree of effect.

[0027] The expressions "comprise," "include," "have," "includes," or "have" of one element are not exclusive expressions excluding the presence of other elements.

[0028] Unless otherwise specified, the expression "connected" includes a state in which two elements are in contact with each other, as well as a state in which two elements are separated by another element.

[0029] 1 is a schematic diagram illustrating the configuration of a film thickness measurement apparatus 10 according to the present disclosure. The film thickness measurement apparatus 10 measures the thickness of a thin film (which will be described later as a thin film 92 with reference to FIG. 3) formed on a substrate 9. For example, a semiconductor substrate is used as the substrate 9.

[0030] Film thickness measuring device 10 includes ellipsometer 1 and film thickness calculation unit 7. Ellipsometer 1 includes a stage 2, a stage moving mechanism 21, a light projecting unit 3, a light receiving unit 4, a substrate observing unit 5, a control unit 6, and a polarization state acquiring unit 8. The broken line between film thickness calculation unit 7 and ellipsometer 1 in Fig. 1 illustrates that film thickness calculation unit 7 is not included in ellipsometer 1. However, film thickness calculation unit 7 may be included in ellipsometer 1, and film thickness measuring device 10 may be the same as ellipsometer 1.

[0031] FIG. 2 is a block diagram illustrating the configuration of the control unit 6. The control unit 6 has, for example, a calculation unit, a memory, and a storage unit. The calculation unit is realized, for example, by one or more central processing units (CPUs) 61. The memory is realized, for example, by a volatile storage medium such as a random access memory (RAM) 62, or a non-volatile storage medium such as a read only memory (ROM) 63. The storage unit is realized, for example, by a fixed disk 64 such as a hard disk drive (HDD) or a solid state drive (SSD). The storage unit can store, for example, programs and various information. The calculation unit can realize various functions by, for example, reading and executing a program stored in the storage unit. At this time, the RAM 62 is used, for example, as a workspace, and stores information that is temporarily generated or acquired. The ROM 63 stores, for example, a basic program executed by the control unit 6. FIG. 2 illustrates a case in which the control unit 6 has a display 65 and an input unit 66. A display 65 displays various information to the operator. An input unit 66 employs, for example, a keyboard and a mouse, and is used by the operator to input data and commands.

[0032] The components of the control unit 6, such as the CPU 61, RAM 62, ROM 63, fixed disk 64, display 65, and input unit 66, are connected to one another via a bus 60. At least a part of the functional configuration realized by the control unit 6 may be realized by hardware such as a dedicated electronic circuit.

[0033] The stage 2 holds, for example places, the substrate 9. The stage movement mechanism 21 moves the stage 2. The light projecting unit 3 emits light L1 having a first polarization, for example, elliptically polarized light (including circularly polarized light: the same applies below), to a main surface on one side of the substrate 9 (this will be described later as surface 91 with reference to FIG. 3). The light receiving unit 4 receives light L2 from the substrate 9. The light L2 is reflected light that is produced by reflecting the light L1 off the substrate 9.

[0034] FIG. 3 is a cross-sectional view illustrating a thin film 92, the object of which film thickness is to be measured, and its periphery. Substrate 9 has a surface 91. Surface 91 is located at the end of substrate 9 on the first direction side. For example, the first direction is vertically upward. For convenience, the following description will be given assuming that the first direction is the Z direction in a right-handed Cartesian coordinate system XYZ. A direction other than the Z direction that is parallel to the plane of incidence of light L1, L2 is adopted as the X direction. The Y direction is depicted as the direction into the paper in FIG. 1 and FIG. 3.

[0035] A thin film 92 is formed on a surface 91. The technology in this disclosure is useful for measuring the film thickness of the thin film 92. For example, the thin film 92 has a width of about 50 μm to 100 μm in an XY plane perpendicular to the Z direction. For example, when the substrate 9 is a semiconductor substrate, the thin film 92 is used as a test pattern for a semiconductor element formed on the semiconductor substrate.

[0036] Light L1 is incident on a surface 92a on the first direction side of the thin film 92 from the light projecting unit 3. Light L2 is obtained when the light L1 is reflected by the surface 92a and is received by the light receiving unit 4. In Fig. 3, the optical axis J1 of the light L1 and the optical axis J2 of the light L2 are depicted, along with the reflection angle θ2 at the reflection. A virtual line T is parallel to the Z direction and is assumed to be in the incident plane, and the angle between the virtual line T and the optical axis J1 is depicted as the incident angle θ1 (which is equal to the reflection angle θ2).

[0037] The light projector 3 projects light L1 onto the surface 92a at a predetermined angle of incidence θ1, and the light receiver 4 receives light L2 and acquires the light intensity used for polarization analysis of the surface 92a. The polarization state acquirer 8 generates information W required for polarization analysis based on the light intensity, the reflection angle θ2, and the polarization direction at the light receiver 4. The information W is provided from the polarization state acquirer 8 to the film thickness calculator 7. The film thickness calculator 7 is connected to the bus 60, and under the control of the controller 6, performs polarization analysis using the information W to determine the film thickness of the thin film 92.

[0038] A thin film 92, the object of which the film thickness is to be measured, is provided on a substrate 9, and the stage 2 holds the substrate 9. Therefore, the stage 2 can be said to be a holder that holds the object of measurement.

[0039] The stage movement mechanism 21 has a Y-direction movement mechanism 22 and an X-direction movement mechanism 23. The Y-direction movement mechanism 22 moves the stage 2 in the Y direction. The X-direction movement mechanism 23 moves the stage 2 in the X direction. In the Y-direction movement mechanism 22, a ball screw (not shown) is connected to a motor 221. When the motor 221 rotates, the X-direction movement mechanism 23 moves along the guide rail 222 in the Y direction in FIG. 1 or the opposite direction.

[0040] The X-direction moving mechanism 23 is configured similarly to the Y-direction moving mechanism 22. When the motor 231 rotates, the stage 2 moves in the X direction or the opposite direction along the guide rail 232 by a ball screw (not shown).

[0041] The stage moving mechanism 21 has a lifting mechanism 24. The lifting mechanism 24 moves the substrate 9 together with the stage 2 in the Z direction and the opposite direction.

[0042] The position of the stage 2 is adjusted so that the surface 92a is located at the position where the light L1 is most converged. The substrate observation unit 5 includes an observation light source 51, a camera 52, a half mirror 53, and an objective lens 54. The observation light source 51 emits light, for example, white light. The light emitted from the observation light source 51 is incident perpendicularly on the surface 91 via the half mirror 53 and the objective lens 54. The reflected light from the substrate 9 is received by the camera 52 via the objective lens 54, the half mirror 53, and the lens 55.

[0043] For example, a mark for adjusting position (so-called alignment mark) is provided on surface 91, and the mark is imaged by camera 52. Based on the image of the mark, control unit 6 controls X-direction moving mechanism 23 and Y-direction moving mechanism 22 to adjust the position of surface 91 in the X and Y directions, and controls lifting mechanism 24 to adjust the position of surface 91 in the Z direction. Stage moving mechanism 21, observation light source 51, and camera 52 are connected to bus 60 (see FIG. 2), and control unit 6 performs the above-mentioned controls.

[0044] <First embodiment> 4 is a cross-sectional view showing a schematic configuration of light projecting unit 3A. In the first embodiment, light projecting unit 3A is employed as light projecting unit 3 (see FIG. 1). Light projecting unit 3A has light source 31, collimator lens 320, aperture stop 33, polarizing plate 321, wave plate 322, and objective lens 323. In light projecting unit 3A, light source 31, collimator lens 320, aperture stop 33, polarizing plate 321, wave plate 322, and objective lens 323 are arranged in this order.

[0045] The light source 31 emits light L0. The light L0 enters a collimator lens 320, and parallel light parallel to the optical axis J0 of the light L0 enters an aperture stop 33, for example, perpendicularly. The optical axis J0 passes through an aperture 33a of the aperture stop 33. The parallel light incident on the aperture stop 33 is narrowed down, linearly polarized by a polarizing plate 321, a phase difference is given between two mutually orthogonal polarized components by a wave plate 322, the light is collected by an objective lens 323, and is emitted as light L1. The polarizing plate 321 and the wave plate 322 can be collectively seen as a polarizing unit 32 that performs elliptically polarizing (first polarization) on the parallel light.

[0046] For example, the light source 31 is a semiconductor laser and the light L0 is laser light. Because the light L2 that is the subject of polarization analysis in the ellipsometer 1 is obtained by reflection of the light L1, the polarization analysis is significantly affected by the wavelength of the light L2, and the light L1 is obtained from the light L0, it is desirable for the light L0 to have a narrow wavelength band.

[0047] A mechanical diaphragm may be used as the aperture diaphragm 33, or a filter or mask, which will be described later, may be used. Components used in general ellipsometers are used as the polarizing plate 321 and the wave plate 322. The light source 31 is connected to a bus 60 (see FIG. 2), and is turned on and off and the amount of light is adjusted by the control unit 6.

[0048] 4 illustrates a cross section including the optical axis J1 in the case where the optical axis J0 of the light L0 and the optical axis J1 of the light L1 coincide with each other. In the light projecting unit 3A, it is not essential that the optical axes J0 and J1 coincide with each other, and a reflecting element may be provided so that the optical axis J0 and the optical axis J1 are not parallel to each other.

[0049] The thickness of the thin film 92 is calculated based on information obtained by observing the light L2, which is reflected light from the surface 92a. Therefore, it is desirable that the focal point F of the objective lens 323 is located on the surface 92a so that the surface 92a is located at the position where the light L1 is most converged.

[0050] In order to improve the measurement accuracy of the ellipsometer 1, it is desirable to narrow the distribution of the incidence angle θ1. This is because the narrower the distribution of the incidence angle θ1, the narrower the distribution of the reflection angle θ2, and the narrower the distribution of the reflection angle θ2, the more the accuracy of the polarization analysis using the reflection angle θ2 is improved. From this viewpoint, it is desirable to have a small angle φ at which the light L1 narrows from the objective lens 323 to the optical axis J1 (hereinafter tentatively referred to as the "constriction angle"). Since the aperture stop 33 narrows the light L0, the numerical aperture of the light projecting unit 3A (hereinafter tentatively referred to as the "light projection system numerical aperture") decreases, and the constriction angle φ also decreases. Therefore, the reduction in the light projection system numerical aperture contributes to the improvement of the measurement accuracy of the ellipsometer 1.

[0051] For example, the light L1 is condensed on a region on the surface 92a whose major axis is 100 μm or less. The incident angle θ1 is, for example, 60 to 70 degrees, and the numerical aperture of the projection system is, for example, 0.1 or less.

[0052] 5 is a cross-sectional view showing a schematic configuration of the light receiving section 4A. In the first embodiment, the light receiving section 4A is employed as the light receiving section 4 (see FIG. 1). The light receiving section 4A has a condenser lens 452, a field stop 454, a collimator lens 453, a polarizing plate 41, a rotation mechanism 411, and a light receiving element 422. In the light receiving section 4A, the condenser lens 452, the field stop 454, the collimator lens 453, the polarizing plate 41, the rotation mechanism 411, and the light receiving element 422 are arranged in this order.

[0053] In FIG. 5, the broken line between the light receiving section 4A and the polarization state obtaining section 8 illustrates that the polarization state obtaining section 8 is not included in the light receiving section 4A.

[0054] The light L2 is collected by the collecting lens 452, enters the field stop 454, passes through the field stop 454 and enters the collimator lens 453, and the light L3, which is a parallel light, is obtained. The optical axis J2 and the optical axis J3 of the light L3 pass through an opening 454a of the field stop 454. The field stop 454 is disposed so that the opening 454a is located at a position optically conjugate with the surface 92a, preferably at a position optically conjugate with the region where the light L1 is collected. For example, the opening 454a is a square of 100 μm×100 μm when viewed along the optical axes J2 and J3.

[0055] Light L3 passes through polarizing plate 41 and is subjected to a second polarization, for example, linear polarization, and becomes light L8, which reaches light receiving element 422. Light emerging from field stop 454 passes through collimator lens 453 to obtain light L3. Therefore, it can be said that the second polarization of the light emerging from field stop 454 is performed by polarizing plate 41.

[0056] The light receiving element 422 measures the light intensity Q1 of the light L8. For example, a Glan-Thompson prism or a polarizing sheet is used as the polarizing plate 41. For example, a photodiode array or a single photodiode is used as the light receiving element 422.

[0057] The rotation mechanism 411 rotates the polarizing plate 41 around an axis parallel to the optical axis J3. The rotation mechanism 411 is connected to the bus 60, and its operation is controlled by the control unit 6. For example, the rotation mechanism 411 is realized using a stepping motor. The method of measuring the film thickness of the thin film 92 using the relationship between the light L1 elliptically polarized (first polarization) by the polarizing plate 321 and the wave plate 322 and the light L8 linearly polarized (second polarization) in a variable direction by the rotation of the polarizing plate 41 (film thickness measurement by ellipsometry) itself is well known, so a detailed description will be omitted.

[0058] 5 illustrates a cross section including the optical axis J3 in a case where both the optical axis J3 and the optical axis J8 of the light L8 coincide with the optical axis J2. It is not essential that the optical axis J8 coincides with the optical axes J2 and J3 in the light receiving unit 4A, and a reflecting element may be provided so that the optical axis J8 is not parallel to the optical axes J2 and J3.

[0059] 6, 7, and 8 are graphs illustrating the relative distribution of light intensity with respect to position, with the horizontal axis representing position and the vertical axis representing relative light intensity.

[0060] 6 shows the light intensity of light L1 on surface 92a as curve G1. The horizontal axis shows position P1 of the intersection of optical axis J1 and surface 92a, and region R1 on surface 92a where light L1 is focused. By employing aperture stop 33, it is possible to reduce the constriction angle φ in region R1.

[0061] 7 shows as a curve G2 the light intensity of light L2 incident on field stop 454. The horizontal axis shows the position P2 of the optical axis J2 in field stop 454 and the area R2 occupied by aperture 454a.

[0062] 8 shows the light intensity of light L3 emerging from field stop 454 as curve G3. The horizontal axis shows position P3 of optical axis J3 and region R2 in field stop 454. Since optical axes J2 and J3 coincide in field stop 454, positions P2 and P3 also coincide.

[0063] Even if the light L1 is condensed on the surface 92a, the light L1 actually reaches a range wider than the region R1. For example, the light L1 is diffracted at the edge of the thin film 92, and as a result, the light L1 is also irradiated onto the surface 91. In this case, as shown in FIG. 6, the light L1 also reaches the outside of the region R1, although the light intensity is smaller than that inside the region R1.

[0064] Light L2 reflects the light intensity distribution of light L1, and as shown in Fig. 7, light L2 also reaches the outside of region R2, although the light intensity is smaller than inside region R2. The light intensity distribution of the region outside region R2 reflects the light intensity distribution of the region outside region R1. Light L2 in the region outside region R2 may be obtained by being reflected from surface 91, not from surface 92a.

[0065] From this viewpoint, the light L2 in the region outside the region R2 is blocked by the field stop 454, and the light L3 is obtained from the light L2 in the region R2. As can be seen from a comparison between Fig. 8 and Fig. 7, the difference in light intensity inside and outside the region R2 is increased by the field stop 454. The field stop 454 reduces the degree to which the light L8 transmitted through the polarizing plate 41 and measured by the light receiving element 422 is affected by factors other than the surface 92a, for example the surface 91, and thus improves the accuracy of the film thickness measurement by ellipsometry.

[0066] The light intensity Q1 of the light L8 acquired by the light receiving element 422 is output to the polarization state acquisition unit 8 together with the polarization direction α of the polarizing plate 41. In Fig. 5, the polarization direction α is diagrammatically drawn as being obtained from the rotation mechanism 411. This is because the polarization direction α depends on the angle of the polarizing plate 41 rotated by the rotation mechanism 411 (for example, the polarization direction α is shifted by a certain angle from that angle) and can be obtained.

[0067] The polarization state acquisition unit 8 acquires the phase difference Δ between the p-polarized component and the s-polarized component and the reflection amplitude ratio angle Ψ using the light intensity Q1, the polarization direction α, the incident angle θ1, etc., and outputs these as information W. As described above, the information W is used by the film thickness calculation unit 7 for polarization analysis to obtain the film thickness of the thin film 92.

[0068] The polarization state acquisition unit 8 is connected to the bus 60, and obtains information W under the control of the control unit 6. The incident angle θ1 is input to the control unit 6, for example, from an input unit 66, and is realized by the control unit 6 controlling the positional relationship between the light projector 3, the light receiver 4, and the stage 2. The incident angle θ1 is input to the polarization state acquisition unit 8, for example, from the control unit 6 via the bus 60.

[0069] The light-projecting unit 3A exemplified in the first embodiment as the light-projecting unit 3 has the aperture stop 33 as described above, thereby reducing the numerical aperture of the light-projecting system of the light-projecting unit 3A (for example, 0.1 or less), narrowing the distribution of the incident angle θ1, and thereby improving the accuracy of the film thickness measurement by ellipsometry.

[0070] The light receiving unit 4A exemplified in the first embodiment as the light receiving unit 4 has the field stop 454 as described above, thereby suppressing reflected light from other than the thin film 92, which is the subject of film thickness measurement, and thus improving the accuracy of the film thickness measurement by ellipsometry.

[0071] The employment of light-receiving unit 4A is not essential to the employment of light-projecting unit 3A, and the employment of light-receiving unit 4A is not essential to the employment of light-projecting unit 3A. For example, even if condenser lens 452 and field stop 454 are eliminated in light-receiving unit 4A and light L2 is directly incident on collimator lens 453, the effect of aperture stop 33 itself is not impaired. For example, even if aperture stop 33 is eliminated in light-projecting unit 3A and the entire light emitted from collimator lens 320 is elliptically polarized by polarizing plate 321 and wave plate 322 to obtain light L1, the effect of field stop 454 itself is not impaired.

[0072] Generally, the polishing accuracy is low at the outer edge portion of a lens that is farther away from the central axis than 7 / 10 (=0.7) times the outer diameter of the lens, making it difficult to obtain the desired refraction. Not obtaining the desired refraction reduces the accuracy of film thickness measurement by ellipsometry. Eliminating undesired refraction improves the accuracy of film thickness measurement by ellipsometry. Therefore, it is desirable for the light at the light receiving unit 4 to pass through an area within 0.7 times the outer diameter of the lens when viewed from the central axis of the lens that the light receiving unit 4 has.

[0073] It is desirable that light L2 passes through a region within 0.7 times the outer diameter of condenser lens 452 when viewed from the central axis of condenser lens 452. It is desirable that light L3 passes through a region within 0.7 times the outer diameter of collimator lens 453 when viewed from the central axis of collimator lens 453.

[0074] From the same viewpoint, it is desirable that the numerical aperture of the light receiving unit 4 (hereinafter tentatively referred to as the "light receiving system numerical aperture") is 10 / 7 (≒1.4) times or more the numerical aperture of the light projecting system. It is desirable that the numerical aperture of the light projecting system is 7 / 10 (=0.7) times or less the numerical aperture of the light receiving system. For example, it is desirable that the numerical aperture of the condenser lens 452 is 10 / 7 (≒1.4) times or more the numerical aperture of the light projecting unit 3.

[0075] <Second embodiment> 9 is a cross-sectional view showing a schematic configuration of the light receiving section 4B. In the second embodiment, the light receiving section 4B is adopted as the light receiving section 4 (see FIG. 1). The light receiving section 4B has a configuration in which a light receiving element 423 and a beam splitter 424 are added to the light receiving section 4A (see FIG. 5).

[0076] In FIG. 9, the broken line between the light receiving section 4B and the polarization state obtaining section 8 illustrates that the polarization state obtaining section 8 is not included in the light receiving section 4B.

[0077] For example, a photodiode array or a single photodiode is used as the light receiving element 423. Although a plate type is used as the beam splitter 424 in the example shown in Fig. 9, a cube type may also be used.

[0078] The beam splitter 424 is provided between the collimator lens 453 and the polarizing plate 41. The beam splitter 424 splits the light L3 emitted from the collimator lens 453 into light L7 and L9. For example, the beam splitter 424 transmits the light L9 and reflects the light L7. Unlike the polarizing plate 41 in the light receiving unit 4A, the light L9 is incident on the polarizing plate 41 in the light receiving unit 4B, instead of the light L3. The polarizing plate 41 performs a second polarization on the light L9 and emits light L8.

[0079] 9 illustrates a cross section including the optical axis J3 in the case where the optical axis J8 coincides with all of the optical axes J2, J3 and the optical axis J9 of the light L9. It is not essential that the optical axis J8 coincides with the optical axes J2, J3, and J9 in the light receiving unit 4B, and a reflecting element may be provided so that the optical axis J8 is not parallel to the optical axes J2, J3, and J9.

[0080] Due to the characteristics of the beam splitter 424, the light intensity Q2 of the light L7 obtained by the light receiving element 423 is proportional to the light intensity of the light L9. Normalizing the light intensity Q1 using the light intensity Q2, specifically, dividing the light intensity Q1 by the value of the light intensity Q2 (the dimension of the division result is the dimension of the light intensity), improves the accuracy of film thickness measurement by ellipsometry for the following reasons.

[0081] The positional relationship between stage 2 and light projector 3 may fluctuate due to, for example, vibration of the respective components. In this case, if opening 454a is wide, light L1 reflected by surface 91 is likely to be included in light L2. To improve the accuracy of film thickness measurement by ellipsometry, it is desirable to reduce such reflected light. To reduce such reflected light, it is desirable to narrow opening 454a.

[0082] Narrowing the opening 454a reduces the light intensity Q1. The light intensity Q2 is proportional to the light intensity of the light L9 before it is linearly polarized by the polarizing plate 41. Therefore, normalizing the light intensity Q1 with the light intensity Q2 makes it possible to make the light intensity Q1 in the calculation of the phase difference Δ and the reflection amplitude ratio angle Ψ substantially equal to or higher than a predetermined level, regardless of the direction of polarization by the polarizing plate 41. Making the light intensity Q1 used in the calculation substantially equal to or higher than a predetermined level improves the accuracy of film thickness measurement by ellipsometry.

[0083] The light intensities Q1, Q2, together with the polarization direction α, are provided to the polarization state acquisition unit 8, which uses these together with the incident angle θ1, etc. to acquire the phase difference Δ and the reflection amplitude ratio angle Ψ, which are output from the polarization state acquisition unit 8 as information W. As described above, the information W is used by the film thickness calculation unit 7 for polarization analysis to determine the film thickness of the thin film 92.

[0084] The light receiving unit 4B exemplified in the second embodiment as the light receiving unit 4 has, in comparison with the light receiving unit 4A, the above-mentioned beam splitter 424 and light receiving element 423. With this configuration, while suppressing reflected light from other than the thin film 92 that is the subject of film thickness measurement, the light intensity Q1 obtained by the light receiving element 422 is substantially at or above a predetermined level, thereby improving the accuracy of the film thickness measurement by ellipsometry.

[0085] As in the first embodiment, the use of light-projecting unit 3A does not necessarily require the use of light-receiving unit 4B, and the use of light-receiving unit 4B does not necessarily require the use of light-projecting unit 3A.

[0086] <Third embodiment> 10 is a cross-sectional view showing a schematic configuration of the light receiving section 4C. In the third embodiment, the light receiving section 4C is used as the light receiving section 4 (see FIG. 1). The light receiving section 4C has a configuration in which the field stop 454 of the light receiving section 4A (see FIG. 5) is replaced with a reflector 455.

[0087] Light L2 is collected by collecting lens 452 and enters reflector 455. Light reflected from reflector 455 enters collimator lens 453, and light L3 is emitted from collimator lens 453 to polarizer 41. In Fig. 10, a cross section including optical axes J2 and J3 is illustrated.

[0088] In FIG. 10, the broken line between the light receiving section 4C and the polarization state obtaining section 8 illustrates that the polarization state obtaining section 8 is not included in the light receiving section 4C.

[0089] FIG. 11 is a cross-sectional view illustrating the configuration of the reflector 455. In the cross-sectional view, the optical axes J2 and J3 are also shown. The reflector 455 has a light-transmitting material 45b, a reflective film 45c, and an anti-reflective film 45g. The reflective film 45c is selectively provided on the main surface 45a of the light-transmitting material 45b. The reflective film 45c is formed, for example, by a reflective coating on the light-transmitting material 45b. The anti-reflective film 45g is provided on the main surface 45a exclusively with the reflective film 45c. The anti-reflective film 45g is formed, for example, by an anti-reflective coating on the main surface 45a.

[0090] 12 is a cross-sectional view illustrating another configuration of the reflector 455. The cross-sectional view also shows the optical axes J2 and J3. The reflector 455 has a substrate 45d, a reflective film 45c, and a light absorbing material 45e. The reflective film 45c is selectively provided on the main surface 45f of the substrate 45d. The light absorbing material 45e is provided on the main surface 45f exclusively with the reflective film 45c. The light absorbing material 45e is formed by, for example, coating the main surface 45f.

[0091] The intersection H of the optical axes J2 and J3 is on the reflective film 45c. The reflector 455 is disposed so that the reflective film 45c is located at a position optically conjugate with the surface 92a, preferably at a position optically conjugate with the area where the light L1 is condensed. For example, the reflective film 45c has a square shape of 100 μm×100 μm.

[0092] In the configuration shown in Fig. 11, the light L2 that does not reach the reflective film 45c passes through the non-reflective film 45g and the light-transmitting material 45b and does not reach the collimator lens 453. In the configuration shown in Fig. 12, the light L2 that does not reach the reflective film 45c is absorbed by the light absorbing material 45e and does not reach the collimator lens 453. In either of the configurations shown in Fig. 11 and Fig. 12, the reflector 455 selectively reflects the light L2.

[0093] 13 and 14 are graphs illustrating the relative distribution of light intensity with respect to position. In both of Fig. 13 and Fig. 14, the horizontal axis represents position, and the vertical axis represents relative light intensity.

[0094] 13 shows, as a curve G4, the light intensity of light L2 incident on the reflector 455. The horizontal axis shows the position P4 of the optical axis J2 on the reflector 455 (which can also be called the position of the intersection H) and the region R4 where the reflective film 45c is provided.

[0095] 14 shows the light intensity of light L3 emitted from reflector 455 as curve G5. The horizontal axis shows position P5 (which can also be called the position of intersection H) of optical axis J3 on reflector 455 and region R4. Positions P4 and P5 coincide with each other.

[0096] Light L2 reflects the light intensity distribution of light L1 (see FIG. 6), and as shown in FIG. 13, light L2 also reaches the outside of region R4, although the light intensity is smaller than inside region R4. However, such a light intensity distribution in the region outside region R4 reflects the light intensity distribution in the region outside region R1. Therefore, light L2 in the region outside region R4 may be obtained by being reflected from surface 91, not from surface 92a.

[0097] From this viewpoint, the light L2 in the region outside the region R4 is not reflected by the reflector 455, and the light L3 is obtained from the light L2 in the region R4. As can be seen from a comparison between Fig. 13 and Fig. 14, the reflector 455 increases the difference in the light intensity of the light L2 inside and outside the region R4. The reflector 455 reduces the degree to which the light L3 transmitted through the polarizing plate 41 and measured by the light receiving element 422 is affected by factors other than the surface 92a, for example the surface 91, and thus improves the accuracy of the film thickness measurement by ellipsometry.

[0098] The film thickness measurement may be affected by the physical properties of the reflective film 45c, but such effects are reduced by using a calibration value previously obtained by ellipsometry using the reflective film 45c.

[0099] <Fourth embodiment> 15 is a cross-sectional view showing a schematic configuration of light projector 3B. In the fourth embodiment, light projector 3B is employed as light projector 3 (see FIG. 1). Light projector 3B has a configuration in which objective lens 323 of light projector 3A (see FIG. 4) is replaced with condenser lens 324, optical aperture 34, and objective lens 325.

[0100] In light projecting section 3B, light source 31, collimator lens 320, aperture stop 33, polarizing plate 321, wave plate 322, condenser lens 324, optical stop 34, and objective lens 325 are arranged in this order.

[0101] The light is collimated by the collimator lens 320 and passes through the aperture stop 33, and is elliptically polarized by the polarizing unit 32. The light emitted from the polarizing unit 32 passes through the optical stop 34 and enters the objective lens 325. More specifically, the elliptically polarized light becomes light L6 that is collected at the aperture 34a of the optical stop 34 by the collecting lens 324. The light L6 that has passed through the optical stop 34 enters the objective lens 325, becomes light L1, and is output from the objective lens 325 to the thin film 92, where it is collected on the surface 92a.

[0102] The optical diaphragm 34 is disposed such that an opening 34a is located at a position optically conjugate with the region where the light L1 is collected on the surface 92a. The optical diaphragm 34 reduces the light L1 from being irradiated onto any surface other than the surface 92a.

[0103] 16 and 17 are graphs illustrating the relative distribution of light intensity with respect to position. In both of these graphs, the horizontal axis represents position, and the vertical axis represents relative light intensity.

[0104] Fig. 16 shows the light intensity of light L6 entering the optical aperture 34 as a curve G6. The horizontal axis shows the position P6 of the optical axis J6 of light L6 in the optical aperture 34 and the area R6 occupied by the opening 34a. Fig. 17 shows the light intensity of light L6 exiting the optical aperture 34 as a curve G7. The horizontal axis shows the position P6 and the area R6.

[0105] 16 and 17, the difference in the light intensity of light L6 inside and outside region R6 increases due to the optical diaphragm 34. The optical diaphragm 34 reduces the extent to which light L1 is irradiated onto surfaces other than surface 92a, thereby improving the accuracy of film thickness measurement by ellipsometry.

[0106] In the fourth embodiment, the field stop 454 used in the light receiving units 4A and 4B (see FIGS. 5 and 9, respectively) and the reflector 455 used in the light receiving unit 4C (see FIG. 10) can be omitted. This is because the functions performed by the field stop 454 and the reflector 455 can be achieved by the optical stop 34.

[0107] 18 is a cross-sectional view showing a schematic configuration of the light receiving section 4D. In the fourth embodiment, the light receiving section 4D is employed as the light receiving section 4 (see FIG. 1). The light receiving section 4D has a collimator lens 453, a polarizing plate 41, a rotating mechanism 411, and a light receiving element 422. In the light receiving section 4D, the collimator lens 453, the polarizing plate 41, the rotating mechanism 411, and the light receiving element 422 are arranged in this order.

[0108] In FIG. 18, the broken line between the light receiving section 4D and the polarization state obtaining section 8 illustrates that the polarization state obtaining section 8 is not included in the light receiving section 4D.

[0109] The light L2 enters the collimator lens 453, and a parallel light beam L3 is obtained. The light L3 passes through the polarizing plate 41, as in the light receiving section 4A, and becomes light L8, and reaches the light receiving element 422. The light receiving element 422 measures the light intensity Q1 of the light L8.

[0110] The numerical aperture of the light receiving system is preferably 10 / 7 (≒1.4) times or more the numerical aperture of the light projecting system. The numerical aperture of the light projecting system is preferably 7 / 10 (=0.7) times or less the numerical aperture of the light receiving system. For example, the numerical aperture of collimator lens 453 is preferably 10 / 7 (≒1.4) times or more the numerical aperture of the light projecting system of light projector 3B.

[0111] By using light projector 3B as light projector 3, the constriction angle φ in region R1 is reduced, suppressing reflected light from other than thin film 92, which is the target of film thickness measurement, thereby improving the accuracy of film thickness measurement by ellipsometry.

[0112] <Transformation> In the above embodiment, the following modifications may be adopted.

[0113] <Modification of light source 31> When a semiconductor laser is used for the light source 31, the use of a semiconductor laser having an optical fiber on the emission side narrows the region R1, and improves the measurement accuracy of the film thickness distribution of the thin film 92.

[0114] A super luminescent diode (SLED) may be used as the light source 31. In this case, it is also desirable to provide an optical fiber on the output side. In general, the spectrum of light emitted from a super luminescent diode is wide. When a super luminescent diode is used as the light source 31, the light emitted from the super luminescent diode is passed through a narrow band filter and then used as light L0, which improves the accuracy of film thickness measurement by ellipsometry. This is because the wavelength of light L2 is used in calculations by ellipsometry, and this wavelength is the same as or depends on the wavelength of light L0.

[0115] <Modification of field stop 454> In addition to a configuration in which a mechanical opening 454a is provided, a filter or a mask may be used for the field stop 454. By using a filter or a mask, it is easy to adjust the opening of the light receiving unit 4 with various characteristics.

[0116] For example, a filter having a distribution of transmittance, with high transmittance in a region corresponding to the opening 454a and low transmittance in other regions, may be used for the field stop 454. Specific examples of such filters include an apodizing filter, a top hat filter, and an elliptical filter, whose transmittance varies sharply, and a Gaussian distribution filter, whose transmittance varies gently.

[0117] For example, using a phase-shifting mask for field stop 454 improves the contrast of the resulting image, thus reducing the effect of surface 91 on the ellipsometric calculations and improving the accuracy of the calculations.

[0118] <Deformation of aperture stop 33> The aperture stop 33 may be provided with a mechanical aperture 33a, or may be a filter or a mask. The filter is preferably one that has a high transmittance in the area corresponding to the aperture 33a, a low transmittance in the other area, and a steep change in transmittance at the edge of the aperture 33a. An example of the filter is an apodizing filter.

[0119] When an optical fiber is utilized in the light source 31 , a small numerical aperture optical fiber may be used as the aperture stop 33 .

[0120] <Deformation of Collimator Lens 453> The light L8 received by the light receiving element 422 does not necessarily have to be parallel light. Therefore, when the polarizing plate 41 has a function of polarizing light other than parallel light, the light L3 does not necessarily have to be parallel light. From this viewpoint, a lens other than a collimator lens may be used instead of the collimator lens 453. For example, the beam width of the light L3 may decrease as it approaches the polarizing plate 41. Alternatively, the collimator lens 453 may be omitted.

[0121] <Deformation of Reflector 455> When the reflectance of the light L2 on the main surface 45a (see FIG. 11) is small, the anti-reflection film 45g may be omitted. When the reflectance of the light L2 on the main surface 45f (see FIG. 12) is small, the light absorbing material 45e may be omitted.

[0122] It goes without saying that all or part of the components constituting each of the above-mentioned embodiments and various modified examples can be appropriately combined within a range that does not contradict each other. For example, the beam splitter 424 used in the light receiving unit 4B can be disposed between the polarizing plate 41 and the collimator lens 453 in the light receiving units 4C and 4D, and the light intensity Q2 of the light L7 can be obtained using the light receiving element 423. [Explanation of symbols]

[0123] 1 Ellipsometer 2 Stage 3,3A,3B Emitter 4,4A,4B,4C,4D Light receiving part 41,321 Polarizing plate 32 Polarizing section 322 Wave plate 323,325 Objective Lens 33 Aperture Diaphragm 34 Optical aperture 92 Thin Film 320,453 Collimator lens 454 Field of view aperture 455 Reflector 422,423 Photodetector 424 Beam Splitter J0, J1, J2, J3, J6, J8, J9 Optical axis L0, L1, L2, L3, L6, L7, L8, L9 Light Q1,Q2 Light intensity α Polarization direction θ1 Incident angle

Claims

1. A holder for holding an object to be measured; a light projecting unit that projects a first polarized light onto the target at a predetermined angle of incidence; a light receiving unit that receives second light resulting from the first light being reflected by the object and measures the light intensity of third light resulting from the second light being polarized in a second manner; Equipped with The light projecting unit includes: an aperture stop that adjusts the numerical aperture of the light projecting unit to 0.1 or less and to 0.7 times or less of the numerical aperture of the light receiving unit; A polarizing unit that performs the first polarization; an objective lens that focuses the first light onto the target so that the major axis of the light is 100 μm or less; An ellipsometer having

2. 2. The ellipsometer of claim 1, An ellipsometer, wherein the light at the light receiving unit passes through an area within 0.7 times the outer diameter of a lens included in the light receiving unit when viewed from a central axis of the lens.

3. 3. An ellipsometer according to claim 1 or 2, the first polarization is elliptical polarization, The polarizing unit A first polarizing plate that performs linear polarization; A wave plate that gives a phase difference between two orthogonal polarized components. Including, The second polarized light is a linear polarized light having a variable polarization direction, The light receiving unit A second polarizing plate for performing the second polarization An ellipsometer having

4. 4. The ellipsometer of claim 3, The light receiving unit a collimator lens for obtaining a fourth light, which is a parallel light, from the second light; a beam splitter provided between the collimator lens and the second polarizing plate, the beam splitter splitting the fourth light into a fifth light and a sixth light; a light receiving element for measuring the light intensity of the fifth light by the beam splitter; Further comprising: the second polarizing plate polarizes the sixth light in the second direction and emits the third light.

5. 3. An ellipsometer according to claim 1 or 2, An ellipsometer, wherein the aperture stop is a filter or a mask.

6. 3. An ellipsometer according to claim 1 or 2, the light receiving unit has a field stop onto which the second light is incident, The light exiting the field stop is polarized in the second direction.

7. 3. An ellipsometer according to claim 1 or 2, the light receiving unit has a reflector that receives the second light and selectively reflects the second light, The light reflected from the reflector is polarized in the second direction.

8. 3. An ellipsometer according to claim 1 or 2, The light projecting unit further includes an optical aperture, and the light emitted from the polarizing unit passes through the optical aperture and enters the objective lens.

Images