Interferometry method and interferometry device

Abstract

An interference measurement method using an interference measurement device according to the present invention comprises: a first step for acquiring a first interference waveform in a first state by changing an optical path length difference between a first optical path and a second optical path in the first state in which a sample is not disposed in the second optical path; a second step of converting the first interference waveform into a first electric field amplitude waveform; a third step for acquiring a second interference waveform in a second state by changing the optical path length difference in the second state in which the sample is disposed in the second optical path; a fourth step of converting the second interference waveform into a second electric field amplitude waveform; and a fifth step for acquiring a measured value relating to the physical properties of the sample on the basis of the electric field amplitudes corresponding to the respective peaks of the first electric field amplitude waveform and the second electric field amplitude waveform.

Description

Technical Field

[0001] This disclosure relates to an interferometric measurement method and an interferometric measurement device.

[0002] Cross-reference of related applications

[0003] This application claims the benefit of priority to Japanese Patent Application No. 2024-152350, filed on September 4, 2024, the entire disclosure of which is incorporated herein by reference. Background Technology

[0004] Conventionally, as a method for determining the physical properties of a sample (e.g., the impurity concentration of a semiconductor), contact-type measurement methods such as the 2-probe method and the 4-probe method are used to measure the resistance of the sample by bringing a probe into contact with the surface of the sample (e.g., Patent Document 1: Japanese Patent Application Publication No. 2-238646). Summary of the Invention

[0005] In contact-based measurement methods like those described above, the probe needs to contact the sample at a specified location with high precision. If the probe's position deviates, the sample may be damaged. To avoid such problems, non-contact (non-destructive) methods for measuring sample properties are required.

[0006] Therefore, the purpose of this disclosure is to provide an interferometric measurement method and apparatus capable of appropriately determining the physical properties of a sample in a non-contact manner.

[0007] This disclosure includes the following interferometric measurement methods [1] to

[10] and the interferometric measurement apparatus

[11] .

[0008] [1] An interferometric measurement method using an interferometric measuring device, wherein,

[0009] The interferometric measuring device includes:

[0010] A light source that outputs measurement light with frequencies ranging from 0.1 THz to 50 THz;

[0011] An interferometric optical system comprising: a beam splitter that branches the measurement light into a first branch and a second branch; a first optical path that is the path from which the first branch light is output from the beam splitter to a point where it is incident on the beam splitter again; and a second optical path that is a path different from the first optical path that is from which the second branch light is output from the beam splitter to a point where it is incident on the beam splitter again, and configured to change between a first state without a sample and a second state with the sample, wherein the interferometric optical system combines the first branch light and the second branch light incident on the beam splitter again, and the optical path difference between the first optical path and the second optical path is variable;

[0012] A photomultiplier tube that outputs an electrical signal value corresponding to the incident light intensity of the interference light of the measurement light generated by the combination of the first branch light and the second branch light in the beam splitter;

[0013] An interference intensity measuring unit measures the intensity of the interference light based on the electrical signal value output from the photomultiplier tube; and

[0014] The electric field amplitude calculation unit calculates the electric field amplitude of the interference light based on the relationship between the value of the electric field amplitude of the light incident on the photomultiplier tube and the value of the electrical signal output from the photomultiplier tube, and according to the intensity of the interference light measured by the interference intensity measurement unit.

[0015] The interferometric measurement method includes:

[0016] The first step is to change the optical path difference in the first state and measure it using the interference intensity measuring unit, thereby obtaining a first interference waveform representing the intensity of the interference light for each optical path difference in the first state.

[0017] The second step is to convert the first interference waveform into a first electric field amplitude waveform, which is the waveform of the electric field amplitude, through the electric field amplitude calculation unit.

[0018] The third step is to change the optical path difference in the second state and measure it using the interference intensity measuring unit, thereby obtaining a second interference waveform representing the intensity of the interference light for each optical path difference in the second state.

[0019] The fourth step involves converting the second interference waveform into a second electric field amplitude waveform, which is the waveform of the electric field amplitude, using the electric field amplitude calculation unit; and

[0020] The fifth step involves obtaining measurement values ​​related to the physical properties of the sample based on the electric field amplitudes corresponding to the peaks of the first and second electric field amplitude waveforms, respectively.

[0021] In the interferometric measurement method described above [1], for both the first state where no sample is placed in one optical path (second optical path) of the interferometric optical system and the second state where a sample is placed, the intensity of the interferometric light representing each optical path difference is obtained by measuring the interferometric light while changing the optical path difference. Furthermore, for each of the first and second interferometric waveforms, the intensity of the interferometric light is converted into an electric field amplitude to obtain a first electric field amplitude waveform and a second electric field amplitude waveform. Moreover, based on the electric field amplitude corresponding to the peaks of these waveforms, a measured value related to the physical properties of the sample can be obtained. That is, according to the above interferometric measurement method, the physical properties of the sample can be determined based on the measured value obtained by irradiating light (second branch light) without contacting the sample with the measuring instrument (probe) or the like. Therefore, according to the above interferometric measurement method, the physical properties of the sample can be appropriately measured in a non-contact manner.

[0022] [2] According to the interferometric measurement method of [1], where,

[0023] The sample is a semiconductor material.

[0024] Based on the structure described above [2], the physical properties of a sample as a semiconductor material, such as carrier density, can be easily measured in a non-contact manner.

[0025] [3] According to the interferometric measurement method of [2], the resistivity of the semiconductor material is less than 4 Ωcm.

[0026] Based on the structure described above [3], by using a semiconductor material whose change in amplitude reflectivity (peak value of the second electric field amplitude waveform / peak value of the first electric field amplitude waveform) is large relative to the change in carrier density as a sample, the physical properties of the sample can be easily determined based on the amplitude reflectivity.

[0027] [4] According to any one of [1] to [3], the interferometric measurement method, where,

[0028] The frequency of the measured light is in the range of 0.1 THz to 30 THz.

[0029] Based on the structure described above [4], the amplitude reflectivity can be made to change more significantly with respect to the changes in the physical properties of the sample (e.g., carrier density), thus enabling the determination of the physical properties of the sample with higher accuracy based on the amplitude reflectivity.

[0030] [5] According to the interferometric measurement method of [4], where,

[0031] The frequency of the measured light is in the range of 0.1 THz to 10 THz.

[0032] Based on the structure described above [5], the effects described above [4] can be obtained more appropriately.

[0033] [6] According to any one of [1] to [5], the interferometric measurement method, where,

[0034] In the fifth step, measurements related to the physical properties of the sample are obtained based on the electric field amplitude corresponding to the largest peak of the first electric field amplitude waveform and the electric field amplitude corresponding to the largest peak of the second electric field amplitude waveform.

[0035] Based on the structure described above [6], the SN ratio can be measured by focusing on the electric field amplitude of the maximum peak of the first electric field amplitude waveform and the second electric field amplitude waveform.

[0036] [7] According to any one of [1] to [6], the interferometric measurement method, where,

[0037] The interferometric measuring device further comprises: an excitation optical system, which, in the second state, irradiates excitation light onto the sample disposed in the second optical path.

[0038] In the third step, the combination of the delay time and the optical path difference is varied by controlling the delay time, and the interference intensity measuring unit measures each combination to obtain the second interference waveform for each delay time. The delay time is the time difference between the moment the second branch light is incident on the sample and the moment the excitation light illuminates the sample through the excitation optical system.

[0039] The fourth step involves obtaining the second electric field amplitude waveform for each of the aforementioned delay times.

[0040] The fifth step obtains a measurement value related to the time response of the sample based on the electric field amplitude corresponding to the peak of the first electric field amplitude waveform and the second electric field amplitude waveform for each of the delay times.

[0041] Based on the structure described above [7], the time response of the physical properties of a sample irradiated with excitation light can be evaluated.

[0042] [8] According to the interferometric measurement method of [7], where,

[0043] The sample is a semiconductor material.

[0044] The excitation light is visible light or near-infrared light.

[0045] Based on the structure described above [8], the carriers of the semiconductor sample can be efficiently excited by excitation light, thus enabling appropriate evaluation of the physical properties of the semiconductor sample.

[0046] [9] According to the interferometric measurement method of [7] or [8], where,

[0047] The measurement light is generated by incidenting a portion of the light generated in the light source onto an optical crystal, and the other portion of the light generated in the light source is input as the excitation light into the excitation optical system.

[0048] The delay time is controlled by changing the optical path length of the excitation light in the excitation optical system.

[0049] According to the structure described above [9], measurement light and excitation light can be generated from a light source, and the delay time can be easily controlled by changing the optical path of the excitation optical system.

[0050]

[10] According to any one of [2] to [9], the interferometric measurement method, wherein,

[0051] While changing the impurity concentration of the sample, the third, fourth, and fifth steps are repeatedly performed.

[0052] Based on the structure described above

[10] , by simultaneously changing the impurity concentration of the sample and obtaining information on the physical properties of the sample under each state, it is possible to easily and efficiently adjust the impurity concentration of the sample to the desired range.

[0053]

[11] An interferometric measuring device, wherein,

[0054] have:

[0055] An interferometric optical system comprising: a beam splitter that branches a measurement beam having a frequency in the range of 0.1 THz to 50 THz into a first branch beam and a second branch beam; a first optical path that is the optical path from which the first branch beam is output from the beam splitter to where it is re-incidentally incident on the beam splitter; and a second optical path that is the optical path from which the second branch beam is output from the beam splitter to where it is re-incidentally incident on the beam splitter, and is configured to change between a first state without a sample and a second state with the sample, wherein the interferometric optical system performs wave combining of the first branch beam and the second branch beam re-incidentally incident on the beam splitter, and the optical path difference between the first optical path and the second optical path is variable;

[0056] An excitation optical system, in the second state, irradiates the sample disposed in the second optical path with excitation light;

[0057] A light source that generates light, produces the measurement light by incidenting a portion of the light onto an optical crystal, and inputs another portion of the light as the excitation light into the excitation optical system;

[0058] A photomultiplier tube that outputs an electrical signal value corresponding to the incident light intensity of the interference light of the measurement light generated by the combination of the first branch light and the second branch light in the beam splitter;

[0059] An interference intensity measuring unit measures the intensity of the interference light based on the electrical signal value output from the photomultiplier tube; and

[0060] The electric field amplitude calculation unit calculates the electric field amplitude of the interference light based on the relationship between the value of the electric field amplitude of the light incident on the photomultiplier tube and the value of the electrical signal output from the photomultiplier tube, and according to the intensity of the interference light measured by the interference intensity measurement unit.

[0061] The optical path of the excitation light in the excitation optical system is variable.

[0062] The aforementioned interferometric measuring apparatus enables the implementation of the interferometric measurement method described above, thereby allowing for the appropriate non-contact determination of sample properties. Furthermore, the apparatus includes an interferometric optical system and an excitation optical system, enabling the evaluation of the time response of the properties of a sample irradiated with excitation light. Additionally, since both the measurement light and excitation light can be generated from a single light source, the apparatus structure can be simplified and miniaturized compared to the case where the measurement light and excitation light are output from different light sources. Moreover, by varying the optical path of the excitation optical system, the delay time between the moment the measurement light (second branch light) incident on the sample and the moment the excitation light irradiates can be easily set, thus allowing for easy acquisition of measurements related to the time response.

[0063] The effects of the invention

[0064] According to this disclosure, an interferometric measurement method and interferometric measurement apparatus are available that can appropriately determine the physical properties of a sample in a non-contact manner. Attached Figure Description

[0065] Figure 1 This is a diagram showing the structure of the interferometric measuring device 1 according to the first embodiment.

[0066] Figure 2 This is a diagram showing a structural example of a photomultiplier tube 30.

[0067] Figure 3 This is an example of a graph showing the time dependence of the voltage signal V output from the photomultiplier tube 30.

[0068] Figure 4 This is an example of a graph showing the relationship (FN equation) between the output value of the photomultiplier tube 30 obtained through fitting and the electric field amplitude of the incident light.

[0069] Figure 5 This is a table showing an example of the correspondence between the electric field amplitude of the incident light calculated using the FN formula and the output value of the photomultiplier tube 30.

[0070] Figure 6 This is a flowchart illustrating an example (first measurement example) of an interferometric measurement method using interferometric measuring device 1.

[0071] Figure 7 This is a diagram showing an example of the first interference waveform W1 and the second interference waveform W2.

[0072] Figure 8 This is a diagram showing an example of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2.

[0073] Figure 9 It is a graph showing the relationship between the amplitude and reflectivity R of each frequency of measured light for multiple Si semiconductor substrates with different resistivity ρ.

[0074] Figure 10 This is a graph showing the relationship between the amplitude and reflectivity R of each frequency of measured light for multiple GaN semiconductor substrates with different resistivities ρ.

[0075] Figure 11 This is a diagram showing a structural example of the interferometric measuring device 1A according to the second embodiment.

[0076] Figure 12 This is a flowchart illustrating an example (second measurement example) of an interferometric measurement method using interferometric measuring device 1A.

[0077] Figure 13 This is a diagram representing an example of the first interference waveform W1 and the second interference waveform W2(t) corresponding to a certain delay time t.

[0078] Figure 14 This is a diagram showing an example of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2(t) corresponding to a certain delay time t.

[0079] Figure 15 This is a graph representing an example of the amplitude reflectivity R(t) for each delay time. Detailed Implementation

[0080] Hereinafter, an embodiment of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same or equivalent elements will be referred to by the same reference numerals, and repeated descriptions will be omitted.

[0081] [First Implementation Method]

[0082] Reference Figures 1-9The interferometric measuring apparatus 1 of the first embodiment will be described, and the interferometric measuring method (first measurement example) using the interferometric measuring apparatus 1 will also be described. Figure 1 As shown, the interferometric measuring device 1 includes a light source 10, an interferometric optical system 20, a photomultiplier tube 30, an interferometric intensity measuring unit 40, an electric field amplitude calculation unit 50, and an analysis unit 60. The interferometric intensity measuring unit 40, the electric field amplitude calculation unit 50, and the analysis unit 60 are, for example, configured as a computer system including a processor, memory, storage, and communication equipment. That is, the functions of the interferometric intensity measuring unit 40, the electric field amplitude calculation unit 50, and the analysis unit 60 are executed according to a predetermined program via the aforementioned hardware elements.

[0083] The light source 10 outputs measurement light L with a frequency ranging from 0.1 THz to 50 THz. In this embodiment, as an example, the light source 10 has an output section 11 that outputs visible light or near-infrared light L0 and an optical crystal 12 that converts the light L0 into measurement light L.

[0084] The output unit 11 is, for example, an ultrashort pulse laser. As an example, the output unit 11 is a femtosecond laser source. Examples of output units 11 include Ti sapphire pulsed lasers (wavelength 800nm), Er pulsed fiber lasers (wavelength 1550nm), Yb pulsed fiber lasers (wavelength 1030nm), Tm pulsed fiber lasers (wavelength 1900nm), and Nd pulsed solid-state lasers (wavelength 1030nm).

[0085] The optical crystal 12 is formed of a material capable of generating measurement light L (e.g., terahertz waves) within the aforementioned frequency range. Examples of the optical crystal 12 include nonlinear optical crystals such as ZnTe crystals (excitation wavelength 800 nm), GaSe crystals (excitation wavelength 800 nm), DAST crystals (excitation wavelength 1.5 μm), GaAs optical guide antennas (excitation wavelength 800 nm), and InGaAs optical guide antennas (excitation wavelength 1.5 μm). The optical crystal 12 is disposed at the rear end of the output section 11. The light L0 output from the output section 11 passes through the optical crystal 12, thereby being converted into measurement light L within the aforementioned frequency range.

[0086] However, the form of the light source 10 is not limited to the above. For example, the light source 10 can be composed of an injection-seeded terahertz parametric oscillator (is-TPG) using an Nd microchip laser (wavelength: 1030 nm) as the excitation laser. Alternatively, the light source 10 can also be a light source capable of outputting continuous light. For example, the light source 10 can also be a resonant tunneling diode (RTD), an IMPAT diode (impact-ionization avalanche transit-time diode), a quantum cascade laser source, a THz gas laser source, etc.

[0087] In this embodiment, the output unit 11 is a Ti sapphire pulsed laser, and the light L0 is visible to near-infrared light with a wavelength of 800 nm. The optical crystal 12 is a ZnTe crystal, and the frequency of the measured light L is a terahertz wave of 0.5 THz.

[0088] The interferometric optical system 20 includes a beam splitter 21, a first reflecting mirror 22, a second reflecting mirror 23, and lenses 24 and 25. The beam splitter 21 can be constructed, for example, from a silicon or ITO mirror. The interferometric optical system 20 has a first optical path P1 serving as a round-trip path between the beam splitter 21 and the first reflecting mirror 22, and a second optical path P2 serving as a round-trip path between the beam splitter 21 and the second reflecting mirror 23. The first optical path P1 is the path from which a first branch light L1, branched from one side of the beam splitter 21, exits from the beam splitter 21 and is re-incidentally incident on the beam splitter 21. The second optical path P2 is the path from which a second branch light L2, branched from the other side of the beam splitter 21, exits from the beam splitter 21 and is re-incidentally incident on the beam splitter 21.

[0089] Beam splitter 21 branches the measurement light L output from light source 10 into a first branch light L1 and a second branch light L2. In this embodiment, beam splitter 21 is disposed between light source 10 (optical crystal 12 in this embodiment) and first reflector 22. The first branch light L1 is the component of measurement light L that passes through (straight-through) beam splitter 21. The first branch light L1 is reflected by the reflective surface 22a of the first reflector 22 and re-enters beam splitter 21 (the surface opposite to the incident surface of measurement light L). The second branch light L2 is the component reflected by beam splitter 21 and directed in a direction orthogonal to the travel direction of measurement light L. The second branch light L2 is reflected by the reflective surface 23a of the second reflector 23 or by the sample S disposed on the reflective surface 23a and re-enters beam splitter 21 (the surface with the same incident surface as measurement light L).

[0090] In the interference optical system 20, the second optical path P2 is configured to change the first state of the sample S not being configured and the second state of the sample S being configured. Figure 1This indicates the second state. As an example, the second state is when the sample S is disposed on the reflective surface 23a of the second reflector 23. The sample S is, for example, a semiconductor material. In this embodiment, the sample S is a plate-shaped semiconductor substrate (semiconductor wafer). Specific examples of such a sample S include silicon substrates, GaN substrates, SiC substrates, GaAs substrates, etc.

[0091] In the interferometric optical system 20, the optical path difference between the first optical path P1 and the second optical path P2 is variable. As an example, the first reflecting mirror 22 forming the first optical path P1 is configured to move parallel to the direction D1 (perpendicular to the reflecting mirror surface 22a) parallel to the travel direction of the first branch light L1. The position of the first reflecting mirror 22 in direction D1 is set, for example, as an initial state, such that the optical path difference Δd between the first optical path P1 and the second optical path P2 is close to zero. That is, in Figure 1 In the example, as an initial state, the distance from beam splitter 21 to the reflecting surface 22a of the first reflecting mirror 22 is approximately the same as the distance from beam splitter 21 to the reflecting surface 23a of the second mirror 23.

[0092] Furthermore, the mechanism for changing the optical path difference Δd is not limited to the mechanism of this embodiment (the mechanism that enables the first reflector 22 to move in direction D1). It may also be configured such that, instead of the first reflector 22 (or in addition to the first reflector 22), the second reflector 23 can move in a direction parallel to the travel direction of the second branch light L2 (a direction perpendicular to the reflector surface 23a). Alternatively, a mechanism may be provided that enables high-speed changing of the optical path difference Δd by having a rotating mirror capable of oscillating (rotating) within a predetermined angular range in at least one of the first optical path P1 and the second optical path P2.

[0093] Beam splitter 21 combines the first branch light L1, which is incident again on the beam splitter 21 via the first optical path P1, and the second branch light L2, which is incident again on the beam splitter 21 via the second optical path P2, to generate interference light IL. In this embodiment, by combining the component of the first branch light L1, which is incident again on the beam splitter 21 (the side opposite to the incident surface of the measurement light L), which is reflected by the beam splitter 21, and the component of the second branch light L2, which is incident again on the beam splitter 21 (the side with the same incident surface as the measurement light L), which is transmitted through the beam splitter 21, the interference light IL is emitted toward the side opposite to the side where the beam splitter 21 and the second mirror 23 are located.

[0094] Lens 24 is positioned between beam splitter 21 and second reflector 23 in the second optical path P2. Lens 24 is a lens that focuses the second branch light L2 to improve the incident efficiency of the second branch light L2 onto the sample S disposed on the reflector surface 23a in the second state. Lens 24 is, for example, a focusing lens for terahertz bands with a focal length of 50 mm (e.g., Tsurupica (registered trademark) etc.).

[0095] Lens 25 is positioned after beam splitter 21 in the optical path of the interference light IL (i.e., between beam splitter 21 and photomultiplier tube 30). Lens 25 is a lens that focuses the interference light IL to improve the incident efficiency of the interference light IL onto the photomultiplier tube 30. Lens 25 is, for example, a focusing lens for terahertz bands, similar to lens 24.

[0096] The photomultiplier tube 30 is positioned at the rear end of the beam splitter 21, facing the direction of the interference light IL output from the beam splitter 21. The photomultiplier tube 30 is sensitive to the wavelength range of the measurement light L (in this embodiment, the frequency band of light including terahertz waves) and outputs an electrical signal value corresponding to the intensity of the incident light IL.

[0097] Figure 2 This is a block diagram illustrating a structural example of a photomultiplier tube 30. The photomultiplier tube 30 has an electron emission section 31, an electron multiplier section 32, and a signal output section 33 disposed inside a housing 34 that maintains a vacuum. A window 35 is provided in the housing 34.

[0098] When light ν is incident through the window 35, the electron emission unit 31 emits electrons e through the incident light. The electron emission unit 31 is a photoelectric conversion unit designed to be sensitive to the frequency band of the measurement light L of the object being detected. For example, the electron emission unit 31 has a structure in which a metamaterial structure (metasurface) is formed on the main surface of the substrate, and emits electrons e by incident light onto the metasurface.

[0099] The electron multiplier 32 multiplies the electrons e emitted from the electron emission unit 31. The electron multiplier 32 includes a multi-stage multiplication electrode or a microchannel plate. The electron multiplication rate in the electron multiplier 32 corresponds to the voltage applied to the multi-stage multiplication electrode or microchannel plate. The signal output unit 33 collects the electrons e multiplied by the electron multiplier 32 and outputs them as a current signal J. In the interference intensity measuring unit 40 (described later), the current signal J output from the signal output unit 33 can be input, or a voltage signal converted from the current signal J by the IV conversion circuit can be input. In this embodiment, this voltage signal is input to the interference intensity measuring unit 40 as an electrical signal value output from the photomultiplier tube 30.

[0100] The interference intensity measuring unit 40 measures the intensity of the interference light IL incident on the photomultiplier tube 30 based on the electrical signal (voltage signal in this embodiment) output from the photomultiplier tube 30. Figure 3 This is a graph showing the time dependence of the voltage signal V output from the photomultiplier tube 30. The interference intensity measuring unit 40 reads the time change of the voltage signal V output from the photomultiplier tube 30 when the optical path difference Δd is set to a certain value. The interference intensity measuring unit 40 can determine the magnitude Vp-p of the amplitude of the voltage signal V at this time as the intensity of the interference light IL corresponding to the optical path difference Δd.

[0101] The electric field amplitude calculation unit 50 calculates the electric field amplitude of the interference light IL based on the relationship between the value of the electric field amplitude of the light incident on the photomultiplier tube 30 and the value of the electrical signal (voltage signal) output from the photomultiplier tube 30, and according to the intensity of the interference light IL (Vp-p in this embodiment) measured by the interference intensity measurement unit 40.

[0102] The value of the electrical signal output from the photomultiplier tube 30 can be described by a polynomial with the electric field amplitude E of the light incident on the photomultiplier tube 30 as the variable, but it can also be described by the following equation (1) which represents the efficiency of electron emission from the metasurface. This equation represents the current J emitted from the metasurface. FN The relationship between the electric field amplitude E of the incident light (interference light IL) and the tunneling principle (Fowler-Nordheim relations) (hereinafter referred to as "FN equation"). The FN equation is an example of information representing the relationship between the above electric field amplitude and the value of the electrical signal output from the photomultiplier tube 30.

[0103]

[0104] In this FN formula, a FN and b FN The constant FN is called the FN constant and is a fixed value. β is the field enhancement factor, which is approximately 400 as an example. Φ is the work function of the metasurface material of the electron emission section 31, which is 3.5 eV if it is gold. F and ν F It is a constant. When the electric field amplitude of the incident light is small, t can be considered a constant. F and ν F Each of them is set to 1. In this case, the FN formula is represented by the following formula (2).

[0105]

[0106] FN represents the current J emitted from the electron emission section 31 of the photomultiplier tube 30. FNThe relationship between the electric field amplitude E of the incident light and the output value of the photomultiplier tube 30 can be expressed in the same way as that between the electric field amplitude E of the incident light and the electric field amplitude E of the incident light.

[0107] We need to find a in the FN formula. FN and b FN Each of these values ​​was determined. Therefore, the electric field amplitude E of the incident light was set to various values ​​to measure the output value (amplitude Vp-p) of the photomultiplier tube 30. A fitting process was then performed using these measured values ​​to determine a. FN and b FN Their respective values. Figure 4 This is a graph showing the relationship (FN equation) between the output value of the photomultiplier tube 30 obtained through fitting and the electric field amplitude E of the incident light. In this graph, five measured values ​​are represented by circles.

[0108] As an example, the electric field amplitude calculation unit 50 can calculate the electric field amplitude of the interference light IL based on the intensity of the interference light IL measured by the interference intensity measurement unit 40, according to the FN formula described above. To calculate the electric field amplitude E of the incident light from the output value of the photomultiplier tube 30 using the FN formula, the following method can be used, for example. By using the FN formula, the output value of the photomultiplier tube 30 is calculated for each value of the electric field amplitude E of the incident light. Figure 5 This table shows examples of the correspondence between the electric field amplitude E of the incident light calculated using the FN formula and the output value of the photomultiplier tube 30. The electric field amplitude calculation unit 50 calculates the electric field amplitude E of the incident light that is closest to the fitted value based on the actual output value of the photomultiplier tube 30 (the intensity of the interference light IL obtained by the interference intensity measurement unit 40). Alternatively, the electric field amplitude E of the incident light can also be calculated by interpolation.

[0109] The analysis unit 60 performs various calculations to obtain measurement values ​​related to the physical properties of the sample S based on the calculation results (electric field amplitude E for each optical path difference Δd) from the electric field amplitude calculation unit 50. An example of the processing by the analysis unit 60 is described in the following flow diagram. Figure 1 Let me explain.

[0110] Reference Figure 6 Flowchart and Figure 7 and Figure 8 An example of the measurement results will be given to an example (first measurement example) of the interferometric measurement method of the interferometric measuring apparatus 1. As an example, in the first measurement example, the purpose is to estimate the carrier density of the sample S (wafer surface) in each stage by changing the impurity concentration (doping concentration) of the sample S until the carrier density becomes the desired value.

[0111] In step S1 (first step), the optical path difference Δd is changed in the first state (the state where the sample S is not configured) and measured using the interference intensity measuring unit 40, thereby obtaining a first interference waveform W1 representing the intensity of the interference light IL for each optical path difference Δd in the first state. Figure 7 ).

[0112] More specifically, let's assume that the sample S is not configured in the second optical path P2 (i.e., in...). Figure 1 In a state where sample S is absent, with the optical path difference Δd set to a certain value, measurement light L is output from the light source 10, and the intensity (Vp-p) of the interference light IL corresponding to that optical path difference Δd is measured by the interference intensity measuring unit 40. By performing the above measurement on each value of the optical path difference Δd while changing it (in this embodiment, the first reflecting mirror 22 is scanned in direction D1), the first interference waveform W1 can be obtained. Furthermore, Figure 7 The horizontal axis of the graph represents the time difference Δt (=Δd / c) corresponding to the optical path difference Δd. Here, c is the speed of light in a vacuum. Additionally, Figure 7 The vertical axis of the curve represents the intensity (Vp-p) of the interference light IL.

[0113] In step S2 (second step), the electric field amplitude calculation unit 50 converts the first interference waveform W1 into a waveform of electric field amplitude, namely the first electric field amplitude waveform WE1. Figure 8 The electric field amplitude calculation unit 50 uses the relationship based on the FN formula as described above (for example, the correspondence table obtained from the FN formula). Figure 5 The value (Vp-p) of the first interference waveform W1 is converted into the electric field amplitude, thus yielding the first electric field amplitude waveform WE1. Additionally, Figure 8 The horizontal axis of the curve represents the curve with Figure 7 The curves show the same time difference Δt. On the other hand, Figure 8 The vertical axis of the curve represents the electric field amplitude (kV / cm) of the interference light IL.

[0114] Next, sample S is placed on the second optical path P2 (on the reflective surface 23a of the second reflector 23), and the same measurements as steps S1 and S2 described above are performed.

[0115] In step S3 (third step), the optical path difference Δd is changed in the second state (the state in which sample S is disposed) and measured using the interference intensity measuring unit 40, thereby obtaining a second interference waveform W2 representing the intensity of the interference light IL for each optical path difference in the second state. Figure 7 The process in step S3 differs from that in step S1 only in that sample S is configured; otherwise, it is the same as that in step S1.

[0116] In step S4 (fourth step), the electric field amplitude calculation unit 50 converts the second interference waveform W2 into a waveform of electric field amplitude, namely the second electric field amplitude waveform WE2. Figure 8 The process in step S4 differs from that in step S2 only in that sample S is configured; otherwise, it is the same as that in step S2.

[0117] Next, the analysis unit 60 obtains measurement values ​​related to the physical properties of sample S based on the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2 obtained in steps S2 and S4 (steps S5 and S6) (fifth step). In this example (first measurement example), as the measurement values ​​related to the physical properties of sample S, the amplitude reflectivity R is first calculated, and then the carrier density of sample S is calculated based on the amplitude reflectivity R.

[0118] In step S5, based on the electric field amplitudes E1 and E2 corresponding to the peaks p1 and p2 of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2, respectively, a measured value (amplitude reflectivity R) related to the physical properties of the sample S is obtained. For example, by assuming the reflectivity of the unsampled state (i.e., the reflectivity of the second branch light L2 on the reflecting mirror 23a) to be 100%, the analysis unit 60 can calculate the amplitude reflectivity R by dividing the value of the electric field amplitude E2 of the peak p2 of the second state by the value of the electric field amplitude E1 of the peak p1 of the first state.

[0119] Here, in Figure 8 In the example, the electric field amplitudes E1 and E2 corresponding to the largest peaks p1 and p2 of the electric field amplitude waveforms WE1 and WE2 were used. However, in the calculation of the amplitude reflectivity R, the electric field amplitudes corresponding to the second and subsequent peaks of the electric field amplitude waveforms WE1 and WE2 can also be used. However, as... Figure 8 As shown, the maximum peaks p1 and p2 of each electric field amplitude waveform WE1 and WE2 are significantly more pronounced than the peaks after the second peak. Therefore, by focusing on the electric field amplitudes E1 and E2 of the maximum peaks p1 and p2 of each electric field amplitude waveform WE1 and WE2, the SN ratio can be measured.

[0120] In step S6, the analysis unit 60 calculates (estimates) the carrier density of sample S from the amplitude reflectivity R. An example of the process used to calculate the carrier density will be described below.

[0121] The amplitude reflectance R(ω) (THz spectral reflectance) of a sample S from a semiconductor at a certain angular frequency ω is represented by the following equation (3). In addition, regarding the angular frequency ω, by evaluating the spectral sensitivity of the photomultiplier tube 30 in advance, the center frequency of the photomultiplier tube 30 can be determined, and the angular frequency ω corresponding to that center frequency can be determined.

[0122]

[0123] Here, ω represents the angular frequency, n represents the complex refractive index of sample S, i represents the imaginary number, d represents the penetration depth (~13.5 μm), and ε(ω) represents the dielectric constant of sample S. If the above equation (3) is transformed and only the dielectric constant ε(ω) is moved to the left, the following equation (4) is obtained.

[0124]

[0125] On the other hand, the dielectric constant ε(ω) can also be represented by the following equations (5) and (6).

[0126]

[0127] Here, ε ∞ The dielectric constant ω represents the dielectric constant at the high-frequency limit (=11.7). p The plasma frequency is represented by γ, the damping ratio by n. c Denotes carrier density, m * ε represents the effective mass, e represents the elementary charge, and ε0 represents the dielectric constant of vacuum.

[0128] For example, the analysis unit 60 calculates the dielectric constant ε(ω) based on the amplitude reflectivity R(ω) (=E2 / E1) calculated in step S5 and the above equation (4), and performs a fitting using the above equation (5), thereby obtaining ω. p And γ. Next, the analysis unit 60 can calculate the carrier density n based on the above equation (5). c Alternatively, a known damping ratio can be applied to γ ​​for sample S, and the carrier density n can be pre-calculated based on equations (5) and (6) above. c The dielectric constant. In this case, the analysis unit 60 calculates the amplitude reflectivity R(ω) and the dielectric constant ε obtained according to the above equation (4) and the carrier density n obtained as described above. c By comparing the dielectric constants, the carrier density corresponding to the amplitude reflectivity R(ω) can be estimated. As an example, the analysis unit 60 can obtain the carrier density, which is the physical property information of the sample S, from the amplitude reflectivity R(ω) by performing the calculations described above.

[0129] In step S7, if the carrier density calculated by the analysis unit 60 is within a predetermined desired range (step S7: Yes), the measurement ends. On the other hand, if the carrier density is not within the desired range (step S7: No), a process is performed to change the impurity concentration (doping amount) of sample S (step S8). Then, the process from step S3 onwards is performed again. Based on the above processes, the impurity concentration of sample S can be adjusted so that the carrier concentration (estimated value) of sample S is within the desired range.

[0130] In the interferometric measurement method using the interferometric measuring device 1 described above, for each of the first state where the sample S is not arranged in one optical path (second optical path P2) of the interferometric optical system 20 and the second state where the sample S is arranged, the interferometric light IL is measured while the optical path difference Δd is changed, thereby obtaining a first interference waveform W1 and a second interference waveform W2 representing the intensity of the interferometric light IL for each optical path difference Δd (refer to...). Figure 7 Furthermore, for each of the first interference waveform W1 and the second interference waveform W2, by converting the intensity of the interference light IL into electric field amplitude, the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2 are obtained (refer to...). Figure 8 Furthermore, based on the electric field amplitudes E1 and E2 corresponding to the peaks p1 and p2 of these electric field amplitude waveforms WE1 and WE2, measurements related to the physical properties of sample S can be obtained. In this embodiment, the measured values ​​are obtained based on the amplitude reflectivity R of sample S and the carrier density estimated from the amplitude reflectivity R. According to the above-described interferometric measurement method, the physical properties of sample S can be determined based on the measured values ​​obtained by irradiating light (second branch light L2) without contacting the measuring instrument (probe) or the like with sample S. Therefore, according to the above-described interferometric measurement method, the physical properties of sample S can be appropriately measured (evaluated) in a non-contact manner.

[0131] In the above-described interferometric measurement method, the sample S is a semiconductor material. Based on this structure, the physical properties of the sample S, which is a semiconductor material, such as carrier density, can be easily measured in a non-contact manner. That is, unlike conventional two-probe and four-probe methods, it is not necessary to bring the probe into contact with the sample S, thus avoiding damage to the sample S (e.g., damage caused by the probe contacting undesirable areas).

[0132] Furthermore, the resistivity of the semiconductor material in sample S is preferably below 4 Ωcm. That is, sample S is preferably a so-called low-resistivity substrate. Based on the above structure, by using a semiconductor material in which the change in amplitude reflectivity R (E2 / E1) is large relative to the change in carrier density as sample S, the physical properties of sample S can be determined with higher accuracy based on this amplitude reflectivity R.

[0133] Figure 9 This represents the relationship between the amplitude reflectivity R of each frequency of the measured light L for multiple Si semiconductor substrates (an example of sample S) with different resistivity ρ. Figure 10 This represents the relationship between the amplitude reflectivity R of the measured light L at each frequency for multiple GaN semiconductor substrates (an example of sample S) with different resistivities ρ. Here, carrier density is closely related to resistivity ρ. That is, when the carrier density changes, the resistivity ρ of sample S changes accordingly, and thus the amplitude reflectivity R changes. Figure 9 and Figure 10 It is known that, although it depends on the material of the sample S, the difference in amplitude reflectivity R caused by the difference in resistivity ρ (i.e., the difference in carrier density) is relatively large in the frequency range of 0.1 THz to 30 THz. Based on the above, the frequency of the measurement light L preferably falls within the range of 0.1 THz to 30 THz. According to the above structure, the change in amplitude reflectivity R relative to the changes in the physical properties of the sample S (e.g., carrier density) is relatively large, and therefore the physical properties of the sample S can be determined with higher accuracy based on the amplitude reflectivity R. Furthermore, from the viewpoint of further improving the above effect, the frequency of the measurement light L is preferably within the range of 0.1 THz to 10 THz, more preferably within the range of 0.1 THz to 1 THz, and even more preferably within the range of 0.2 THz to 0.5 THz.

[0134] In the above-described interferometric measurement method (first measurement example), steps S3 to S6 are repeatedly performed while changing the impurity concentration of sample S. In this embodiment, the impurity concentration of sample S is adjusted until the carrier density of sample S enters the desired range. Based on the above structure, by performing the process of changing the impurity concentration of sample S while obtaining the physical property information of sample S in each state (for example, carrier density), it is possible to easily and efficiently adjust the impurity concentration of sample S to the desired range (i.e., the impurity concentration corresponding to the desired carrier density).

[0135] [Second Implementation]

[0136] Reference Figures 11-15 The interferometric measuring apparatus 1A of the second embodiment will be described, and the interferometric measuring method (second measurement example) using the interferometric measuring apparatus 1A will also be described. In the second embodiment, as measured values ​​related to the physical properties of the sample S, measured values ​​related to the time response of the sample S are acquired. Figure 11As shown, the interferometric measuring device 1A differs from the interferometric measuring device 1 in that it also includes a half-wavelength plate 71, a polarizing beam splitter 72, a reflector 73, and an excitation optical system 80. The half-wavelength plate 71, polarizing beam splitter 72, and reflector 73 are disposed between the output section 11 and the optical crystal 12. The half-wavelength plate 71, disposed between the output section 11 and the polarizing beam splitter 72, adjusts the polarization direction of the light output from the output section 11. The polarizing beam splitter 72 causes the light output from the output section 11 to branch at a ratio corresponding to its polarization direction, resulting in light L0 passing through the polarizing beam splitter 72 and heading towards the interferometric optical system 20 via the reflector 73, and excitation light Le reflected by the polarizing beam splitter 72 and heading towards the excitation optical system 80. In this embodiment, by rotating the half-wavelength plate 71, the polarization direction of the light output from the output section 11 is changed, thereby allowing the branching ratio of light L0 and excitation light Le in the polarizing beam splitter 72 to be adjusted to an arbitrary ratio. Therefore, the intensity ratio of excitation light Le to light L0 can be adjusted appropriately and easily according to the type of sample S, etc. Furthermore, if it is not necessary to adjust the branching ratio of light L0 to excitation light Le as described above, the half-wavelength plate 71 can be omitted, and the polarization beam splitter 72 can also be a beam splitter whose branching ratio does not change according to the polarization direction. The light L0 reflected by the mirror 73 is converted into measurement light L by the optical crystal 12 and faces the interference optical system 20 (beam splitter 21) in the same manner as in the first embodiment. Additionally, the optical crystal 12 can also be positioned at the front end of the mirror 73 (between the polarization beam splitter 72 and the mirror 73).

[0137] The excitation optical system 80 includes mirrors 81-84, a moving mechanism 85 for moving mirrors 81 and 82, a lens 86, and a vibration damper 87. Mirrors 81-84 are arranged such that the excitation light Le is reflected sequentially. That is, the excitation light Le reflected by mirror 81 is directed towards mirror 82, the excitation light Le reflected by mirror 82 is directed towards mirror 83, and the excitation light Le reflected by mirror 83 is directed towards mirror 84. The excitation light Le reflected by mirror 84 illuminates the sample S disposed on the mirror surface 23a of the second mirror 23.

[0138] The moving mechanism 85 moves mirrors 81 and 82 together in parallel along direction D2, so that while the distance between mirrors 81 and 82 remains constant, the distance from the polarizing beam splitter 72 to mirror 81 and the distance between mirrors 82 and 83 change. The movement of mirrors 81 and 82 by the moving mechanism 85 changes the optical path length of the excitation light Le from the polarizing beam splitter 72 to the sample S. That is, by adjusting the positions of mirrors 81 and 82 by the moving mechanism 85, the time difference, i.e., the delay time, between the first moment when the measurement light L (second branch light L2) is incident on the sample S and the second moment when the excitation light Le illuminates the sample S through the excitation optical system 80 can be controlled.

[0139] Lens 86 is disposed between mirrors 83 and 84. Lens 86 is used to focus the excitation light Le onto the irradiation position (target position) of sample S. In addition, when the distance from mirror 84 to sample S is long, lens 86 can also be disposed between mirror 84 and sample S.

[0140] The vibration damper 87 is positioned in the direction towards which the excitation light Le reflected by the sample S is directed. By blocking the excitation light Le, the vibration damper 87 prevents the excitation light Le from incident on other optical elements.

[0141] Reference Figure 12 Flowchart and Figures 13-15 An example of the measurement results will be given to an example (second measurement example) of the interferometric measurement method of the interferometric measuring device 1A. As an example, in the second measurement example, it is used to evaluate the time response characteristics of the photoexcited sample S by estimating the carrier density of the sample S in each state at each delay time by performing the measurement while changing the above-mentioned delay time.

[0142] Steps S11 and S12 (first step and second step) and the first measurement example ( Figure 6 Steps S1 and S2 are the same. That is, through steps S11 and S12, the first interference waveform W1 and the first electric field amplitude waveform WE1 of the first state (the state in which the excitation light Le is not irradiated because there is no sample S as the object of irradiation of the sample S) are obtained. In addition, in the interferometric measurement device 1A, in order to perform steps S11 and S12, for example, a damper (the same component as the damper 87) that blocks the excitation light Le can be placed at any part of the excitation optical system 80 so that the excitation light Le does not irradiate the reflecting mirror surface 23a.

[0143] Step S13 (third step) is to perform the first measurement example for each combination of the above-mentioned delay time t and optical path difference Δd. Figure 6This is a modified step of step S3. Specifically, in step S13, by controlling the time difference (t2-t1), i.e., the delay time t, between the moment t1 when the second branch light L2 is incident on the sample S and the moment t2 when the excitation optical system 80 irradiates the sample S with the excitation light Le, the combination of delay time t and optical path difference Δd is varied. Measurements are performed based on the interference intensity measurement unit 40 for each combination, thereby obtaining the second interference waveform W2(t) for each delay time t. Furthermore, a delay time “t=0” indicates that the sample S is simultaneously incident with and irradiated by both the second branch light L2 and the excitation light Le; a delay time “t>0” indicates that the sample S is irradiated with the excitation light Le before the second branch light L2; and a delay time “t<0” indicates that the sample S is incident with the second branch light L2 before the excitation light Le.

[0144] Figure 13 It has the same Figure 7 The same graph on the horizontal and vertical axes represents the second interference waveform W2(t) corresponding to a certain delay time t (t>0). Figure 13 In the example, by irradiating sample S with excitation light Le, the carrier density of sample S temporarily changes (increases), resulting in an increase in the reflectivity of the measurement light L in sample S compared to the state without photoexcitation. Consequently, the intensity of the interference light IL incident on photomultiplier tube 30 increases, thus the peak value of the second interference waveform W2(t) is greater than the peak value of the second interference waveform W2 (refer to...). Figure 7 ).

[0145] The processing in step S13 can be performed, for example, as follows. First, the optical path of the excitation light Le in the excitation optical system 80 is adjusted using the moving mechanism 85, and the delay time t is set to a certain value. Next, it is compared with the first measurement example ( Figure 6 Similarly, in step S3, while changing the optical path difference Δd, measurements corresponding to each optical path difference Δd are performed. This yields a second interference waveform W2(t) for a given delay time t. By changing the delay time t and performing the above processing, second interference waveforms W2(t) corresponding to multiple delay times t are obtained.

[0146] Step S14 (fourth step) is to perform the first measurement example for each combination of delay time t and optical path difference Δd. Figure 6 The processing method of step S4 is modified. That is, step S14 obtains the second electric field amplitude waveform WE2(t) for each delay time t by performing the same transformation process as step S4 on the second interference waveform W2(t) for each delay time t.

[0147] Figure 14 It has the same Figure 8 The same graph with the same horizontal and vertical axes represents a curve with respect to a certain delay time t (and) Figure 13 The second electric field amplitude waveform WE2(t) corresponds to the same delay time t. Furthermore, in Figure 14 The diagram also illustrates the second electric field amplitude waveform WE2 (the waveform obtained from the first measurement example) without photoexcitation. Figure 14 In the example, as mentioned above, the peak value of the second interference waveform W2(t) is greater than the peak value of the second interference waveform W2. As a result, the peak value of the second electric field amplitude waveform WE2(t), i.e., E2(t), is greater than the peak value of the second electric field amplitude waveform WE2, i.e., E2.

[0148] Step S15 (the fifth step) involves performing the first measurement example for each combination of delay time t and optical path difference Δd. Figure 6 The processing method of step S5 is a modified step. That is, step S15 is the process of calculating the amplitude reflectivity R(t) (=E2(t) / E1) for each delay time t.

[0149] Figure 15 This is a graph representing an example of the amplitude reflectivity R(t) for each delay time. Figure 15 The graph is a curve with the delay time on the horizontal axis and the amplitude reflectivity on the vertical axis, depicting the amplitude reflectivity R(t) corresponding to several delay times t. For example... Figure 15 As shown, according to the second measurement example, the time response characteristics of photoexcitation of sample S for each delay time t (the magnitude of amplitude reflectivity R(t) relative to delay time t) can be determined. That is, step S15 is an example of a process that obtains a measured value (here, amplitude reflectivity R(t)) related to the time response of sample S based on the electric field amplitudes E1 and E2(t) corresponding to the peaks p1 and p2 of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2(t) for each delay time t.

[0150] Step S16 (the fifth step) involves performing the first measurement example for each combination of delay time t and optical path difference Δd. Figure 6 Step S6 is a modified version of the previous step. Specifically, step S16 is the process of calculating (estimating) the carrier density corresponding to the amplitude reflectivity R(t) for each delay time t. Step S16 is an example of a process that obtains measured values ​​(here, the carrier density for each delay time t) related to the time response of the sample S based on the electric field amplitudes E1 and E2(t) corresponding to the peaks p1 and p2 of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2(t) for each delay time t.

[0151] As described above, the interferometric measuring device 1A includes an excitation optical system 80 that illuminates the excitation light Le onto the sample S disposed in the second optical path P2 in the second state. Furthermore, the interferometric measurement method using the interferometric measuring device 1A includes the following steps: by controlling the time difference (t2-t1) between the moment when the second branch light L2 is incident on the sample S and the moment when the excitation light Le is illuminated onto the sample S by the excitation optical system 80, i.e., the delay time t, the combination of the delay time t and the optical path difference Δd is varied; for each combination, a measurement is performed based on the interference intensity measuring unit 40, thereby obtaining the second interference waveform W2(t) for each delay time t (as an example). Figure 12 Step S13); the step of obtaining the second electric field amplitude waveform WE2(t) for each delay time t (as an example, Figure 12 Step S14); and the step of obtaining the measured values ​​related to the time response of sample S based on the electric field amplitudes E1 and E2(t) corresponding to the peaks p1 and p2 of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2(t) for each delay time t (as an example, Figure 12 Steps S15 and S16). In addition, step S15, as a measurement related to the time response of sample S, obtains the amplitude reflectivity R(t) for each delay time t. Step S16, as a measurement related to the time response of sample S, obtains the carrier density for each delay time t. Based on the above structure, the time response of the physical properties of sample S irradiated by excitation light Le can be evaluated. For example, dynamic evaluation of the relaxation time, etc., of photoexcited carriers within sample S can be performed based on the carrier density for each delay time t.

[0152] The sample S is a semiconductor material, and the excitation light Le (in this embodiment, the light L0 emitted from the output unit 11) is visible light or near-infrared light. According to the above structure, the charge carriers of the semiconductor sample (sample S) can be efficiently excited by the excitation light Le, and thus the physical properties of the semiconductor sample can be appropriately evaluated.

[0153] Furthermore, in the interferometric measurement method using the interferometric measuring device 1A, a portion of the light L0 generated in the light source 10 (output unit 11) is incident onto the optical crystal 12 to generate the measurement light L, and another portion of the light L0 generated in the light source 10 (output unit 11) is input as the excitation light Le to the excitation optical system 80. The delay time t is controlled by changing the optical path of the excitation light Le in the excitation optical system 80. In this embodiment, the optical path of the excitation light Le changes by the scanning movement mechanism 85, and as a result, the delay time t changes. According to the above structure, the measurement light L and the excitation light Le can be generated from a light source 10 (output unit 11), and the delay time t can be easily controlled (set) by changing the optical path of the excitation optical system 80.

[0154] Furthermore, the interferometric measuring apparatus 1A includes: an excitation optical system 80, which, in a second state, irradiates an excitation light Le onto a sample S disposed in a second optical path P2; and a light source 10, which generates light L0, generates a measurement light L by incidenting a portion of the light L0 onto an optical crystal 12, and inputs another portion of the light L0 as the excitation light Le into the excitation optical system 80. The optical path length of the excitation light Le in the excitation optical system 80 is variable. In the interferometric measuring apparatus 1A, the above-described interferometric measurement method can be implemented, thereby enabling the appropriate non-contact determination of the physical properties of the sample S. In addition, the interferometric measuring apparatus 1A includes an interferometric optical system 20 and an excitation optical system 80, thereby enabling the evaluation of the time response of the physical properties (amplitude reflectivity, carrier density, etc.) of the sample S irradiated with the excitation light Le. Furthermore, since the measurement light L and the excitation light Le can be generated from a single light source 10 (output unit 11), the apparatus structure can be simplified and miniaturized compared to the case where the measurement light L and the excitation light Le are output from different light sources. Furthermore, by changing the optical path of the excitation optical system 80, the delay time t between the moment when the measurement light L (second branch light L2) is incident on the sample S and the moment when the excitation light Le is irradiated can be easily set, thus making it easy to obtain the measurement value related to the time response.

[0155] [Variation Example]

[0156] The above describes several embodiments of this disclosure, but this disclosure is not necessarily limited to the structures shown in the above embodiments. The materials and shapes of each structure are not limited to the specific materials and shapes described above, and a wide variety of materials and shapes other than those described can be used. In addition, some of the structures included in the above embodiments may be appropriately omitted or modified, or may be arbitrarily combined.

[0157] For example, the processing flow of the above interferometric measurement method is not limited to Figure 6 and Figure 12 The process is shown. For example, in Figure 6 In the first measurement example shown, steps S3 and S4 can also be performed before steps S1 and S2. Alternatively, steps S2 and S4 can be performed after steps S1 and S3. Furthermore, when evaluating the physical properties of the completed sample S, steps S7 and S8 can be omitted. Additionally, for example, if only the amplitude reflectivity R is obtained as physical property information of sample S (e.g., when carrier density is not used for physical property evaluation of sample S), the measurement can be completed after obtaining the amplitude reflectivity R in step S5.

[0158] Alternatively, the first measurement example and the second measurement example described above can be combined. For example, in a semiconductor process that increases the carrier density of sample S, the carrier density of sample S can be monitored using the first measurement example (measurement without photoexcitation), while the time response of carriers in sample S can be evaluated using the second measurement example (measurement with photoexcitation). For example, an interferometric measurement apparatus 1A equipped with an excitation optical system 80 in addition to the interferometric optical system 20 can be used to perform S1 to S6 of the first measurement example and S13 to S16 of the second measurement example in a state where photoexcitation of sample S is blocked. In this case, in addition to the carrier density in the first measurement example, the time response of carriers is also evaluated, thereby enabling evaluation of whether carriers are uniformly doped on the surface (wafer surface) of sample S. For example, if carriers are not uniformly doped on the surface of sample S, the carrier mobility changes, thus exhibiting a different time response than in the case of uniform doping.

[0159] Furthermore, the delay time in the interferometric measuring device 1A (i.e., a structure in which an excitation optical system 80 is provided in addition to the interferometric optical system 20) can also be controlled by making the light source of the measurement light L different from the light source of the excitation light Le, thereby controlling the timing of the output of the excitation light Le from the light source of the excitation light Le. However, in this case, it is necessary to control the timing of the pulse output of the two different light sources with high precision. Therefore, by sharing the light sources (output section 11) of the excitation light Le and the measurement light L as described in the above embodiment, and by configuring the optical path of the excitation optical system 80 to be variable, the delay time can be easily adjusted.

[0160] Alternatively, the photomultiplier tube 30 can also be a photomultiplier tube capable of imaging the intensity distribution of incident light. When the electron multiplier section 32 includes a microchannel plate (e.g., an image intensifier), imaging of the intensity distribution of incident light is possible. By using such a photomultiplier tube 30, analytical imaging of the sample S is possible.

[0161] Furthermore, sample S can be made of materials other than semiconductors, as long as its properties can be evaluated based on measurements obtained using the interferometry method described above (e.g., amplitude reflectivity). For example, sample S can also be a material other than a semiconductor that has the property of responding to light. For example, sample S can be a nonlinear optical crystal (e.g., ZnTe, LiTiO3, etc.). In nonlinear optical crystals, the response time to light and complex refractive index are important physical property parameters. The interferometry method described above is useful because it can nondestructively measure such physical property parameters for samples S other than semiconductor materials.

Claims

1. An interferometric measurement method using an interferometric measurement apparatus, wherein the interferometric measurement apparatus includes: a light source that outputs measurement light having a frequency included in a range of 0.1 THz to 50 THz; an interference optical system that has a beam splitter that branches the measurement light into first branch light and second branch light, a first optical path that is an optical path of the first branch light from the beam splitter to re-entry into the beam splitter, and a second optical path that is an optical path of the second branch light from the beam splitter to re-entry into the beam splitter different from the first optical path, and is configured to be able to change between a first state in which no sample is disposed and a second state in which the sample is disposed, the interference optical system combining the first branch light and the second branch light re-entering into the beam splitter, an optical path difference between the first optical path and the second optical path being variable; a photomultiplier tube that outputs an electric signal value corresponding to an incident light intensity of interference light of the measurement light generated by the combining of the first branch light and the second branch light in the beam splitter; an interference intensity measurement section that measures an intensity of the interference light based on the electric signal value output from the photomultiplier tube; and an electric field amplitude calculation section that, based on a relationship between a value of an electric field amplitude of light incident on the photomultiplier tube and a value of an electric signal output from the photomultiplier tube, calculates an electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement section, the interferometric measurement method including: a first step of changing the optical path difference in the first state and measuring by the interference intensity measurement section, thereby acquiring a first interference waveform representing the intensity of the interference light for each of the optical path differences in the first state; a second step of converting, by the electric field amplitude calculation section, the first interference waveform into a first electric field amplitude waveform that is a waveform of an electric field amplitude; a third step of changing the optical path difference in the second state and measuring by the interference intensity measurement section, thereby acquiring a second interference waveform representing the intensity of the interference light for each of the optical path differences in the second state; a fourth step of converting, by the electric field amplitude calculation section, the second interference waveform into a second electric field amplitude waveform that is a waveform of an electric field amplitude; and a fifth step of acquiring a measurement value related to a physical property of the sample based on electric field amplitudes corresponding to peaks of the first electric field amplitude waveform and the second electric field amplitude waveform, respectively.

2. The interferometric measurement method according to claim 1, wherein the sample is a semiconductor material.

3. The interferometric measurement method according to claim 2, wherein the semiconductor material has a resistivity of 4 Ωcm or less.

4. The interferometric measurement method according to any one of claims 1 to 3, wherein the frequency of the measurement light is included in a range of 0.1 THz to 30 THz.

5. The interferometric measurement method according to claim 4, wherein the frequency of the measurement light is included in a range of 0.1 THz to 10 THz. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ 6. The interferometry method according to any one of claims 1 to 5, wherein in the fifth step, a measured value relating to a physical property of the sample is obtained based on an electric field amplitude corresponding to a largest peak of the first electric field amplitude waveform and an electric field amplitude corresponding to a largest peak of the second electric field amplitude waveform.

7. The interferometry method according to any one of claims 1 to 6, wherein the interferometry apparatus further comprises an excitation optical system configured to irradiate excitation light to the sample disposed in the second optical path in the second state, in the third step, the second interference waveform for each of the delay times is obtained by controlling the delay time so as to vary a combination of the delay time and the optical path difference, and measuring the interference intensity by the interference intensity measuring section for each combination, the delay time being a time difference between a time at which the second branch light is incident on the sample and a time at which the excitation light is irradiated on the sample by the excitation optical system, the fourth step obtains the second electric field amplitude waveform for each of the delay times, the fifth step obtains a measured value relating to a temporal response of the sample based on electric field amplitudes corresponding to peaks of the first electric field amplitude waveform and the second electric field amplitude waveform for each of the delay times.

8. The interferometry method according to claim 7, wherein the sample is a semiconductor material, the excitation light is visible light or near-infrared light.

9. The interferometry method according to claim 7 or 8, wherein the measurement light is generated by causing a part of light generated in the light source to be incident on an optical crystal, and another part of the light generated in the light source is input to the excitation optical system as the excitation light, the delay time is controlled by varying an optical path of the excitation light in the excitation optical system.

10. The interferometry method according to claim 2, wherein the third step, the fourth step, and the fifth step are repeatedly performed while varying an impurity concentration of the sample.

11. An interferometry apparatus, comprising: an interference optical system having: a beam splitter configured to branch measurement light having a frequency included in a range of 0.1 THz to 50 THz into first branch light and second branch light; a first optical path which is an optical path of the first branch light from output from the beam splitter to re-entry into the beam splitter; and a second optical path which is an optical path of the second branch light from output from the beam splitter to re-entry into the beam splitter different from the first optical path, and configured to be able to change a first state in which no sample is disposed and a second state in which the sample is disposed, the interference optical system being configured to combine the first branch light and the second branch light re-entering into the beam splitter, an optical path difference between the first optical path and the second optical path being variable; an excitation optical system configured to irradiate excitation light to the sample disposed in the second optical path in the second state. ​ a light source that generates light, generates the measurement light by causing a portion of the light to be incident to an optical crystal, and inputs another portion of the light to the excitation optical system as the excitation light; a photomultiplier that outputs an electric signal value corresponding to an incident light intensity of the interference light generated by the interference of the measurement light that is generated by the combination of the first branched light and the second branched light in the beam splitter; an interference intensity measurement section that measures the intensity of the interference light based on the electric signal value output from the photomultiplier; and an electric field amplitude calculation section that calculates the electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement section based on a relationship between the value of the electric field amplitude of the light incident to the photomultiplier and the value of the electric signal output from the photomultiplier, the optical path of the excitation light in the excitation optical system is variable.

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