Interferometry method and interferometry apparatus

Abstract

The present invention provides an interference measurement method and apparatus that can appropriately measure the physical properties of a sample in a non-contact manner. [Solution] The interference measurement method using the interference measurement device 1 includes: a first step of obtaining a first interference waveform W1 for each optical path length difference in the first state by performing measurements while changing the optical path length difference between the first optical path P1 and the second optical path P2 in a first state in which no sample S is placed in the second optical path P2; a second step of converting the first interference waveform W1 into a first electric field amplitude waveform WE1; a third step of obtaining a second interference waveform W2 for each optical path length difference in the second state by performing measurements while changing the optical path length difference in a second state in which a sample S is placed in the second optical path P2; a fourth step of converting the second interference waveform W2 into a second electric field amplitude waveform WE2; and a fifth step of obtaining measured values ​​regarding the physical properties of the sample S based on the electric field amplitudes corresponding to the peaks of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2, respectively.

Description

[Technical Field]

[0001] This disclosure relates to an interference measurement method and an interference measurement apparatus. [Background technology]

[0002] Conventionally, contact-type measurement methods such as the two-probe method and the four-probe method, which measure the resistance of a sample by applying probes to its surface, have been used as methods for measuring the physical properties of a sample (for example, the impurity concentration of a semiconductor) (for example, Patent Document 1). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-238646 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the contact-type measurement methods described above, it is necessary to accurately apply the probe to a predetermined position on the sample, and if the probe is not applied to the correct position, there is a risk of damaging the sample. To avoid such problems, there is a need for non-contact (non-destructive) methods for measuring the physical properties of a sample.

[0005] Therefore, the purpose of this disclosure is to provide an interference measurement method and an interference measurement apparatus that can appropriately measure the physical properties of a sample in a non-contact manner. [Means for solving the problem]

[0006] [1] A light source that outputs measurement light having a frequency in the range of 0.1 THz to 50 THz, An interference optical system comprising: a beam splitter that splits the measurement light into a first branched beam and a second branched beam; a first optical path from the time the first branched beam is output from the beam splitter until it is re-incident to the beam splitter; and a second optical path, which is different from the first optical path from the time the second branched beam is output from the beam splitter until it is re-incident to the beam splitter, and is configured to switch between a first state in which no sample is placed and a second state in which the sample is placed, wherein the first branched beam and the second branched beam re-incident to the beam splitter are combined, and the difference in optical path length between the first optical path and the second optical path is variable, 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 branched light and the second branched light in the beam splitter, An interference intensity measuring unit measures the intensity of the interference light based on the electrical signal value output from the photomultiplier tube, An interference measurement method using an interference measuring device comprising: an electric field amplitude calculation unit that calculates the electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement unit, 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, The first step is to obtain a first interference waveform showing the intensity of the interference light for each optical path length difference in the first state by performing measurements using the interference intensity measuring unit while changing the optical path length difference in the first state, The second step involves the electric field amplitude calculation unit converting the first interference waveform into a first electric field amplitude waveform, which is a waveform of the electric field amplitude. A third step involves performing measurements using the interference intensity measuring unit while changing the optical path length difference in the second state, thereby obtaining a second interference waveform that shows the intensity of the interference light for each optical path length difference in the second state, The fourth step involves the electric field amplitude calculation unit converting the second interference waveform into a second electric field amplitude waveform, which is a waveform of the electric field amplitude. An interference measurement method comprising: a fifth step of obtaining measured values ​​relating to the physical properties of the sample based on the electric field amplitudes corresponding to the peaks of the first electric field amplitude waveform and the second electric field amplitude waveform, respectively.

[0007] In the interference measurement method described in [1] above, by measuring the interference light while changing the optical path length difference for both a first state in which no sample is placed in one of the optical paths (second optical path) of the interference optical system and a second state in which a sample is placed, a first interference waveform and a second interference waveform showing the intensity of the interference light for each optical path length difference are obtained. Furthermore, by converting the intensity of the interference light from each of the first and second interference waveforms into an electric field amplitude, a first electric field amplitude waveform and a second electric field amplitude waveform are obtained. Based on the electric field amplitudes corresponding to the peaks of each of these waveforms, measurement values ​​regarding the physical properties of the sample can be obtained. In other words, according to the above interference measurement method, the physical properties of the sample can be determined based on measurement values ​​obtained by irradiating the sample with light (second branch light) without contacting the sample with a measuring instrument (probe), etc. Therefore, according to the above interference measurement method, the physical properties of the sample can be appropriately measured in a non-contact manner.

[0008] [2] The sample is a semiconductor material, and the interference measurement method of [1].

[0009] According to the configuration described in [2] above, the physical properties of a semiconductor material sample, such as carrier density, can be easily measured using a non-contact measurement method.

[0010] [3] The resistivity of the semiconductor material is 4 Ωcm or less, the interference measurement method of [2].

[0011] According to the configuration described in [3] above, by using a semiconductor material as a sample in which the change in amplitude reflectance of the measured light (peak value of the second electric field amplitude waveform / peak value of the first electric field amplitude waveform) is relatively large in response to changes in carrier density, the physical properties of the sample can be easily measured based on the amplitude reflectance.

[0012] [4] The frequency of the measurement light is included in the range of 0.1 THz to 30 THz, and any of the interference measurement methods of [1] to [3].

[0013] According to the configuration of [4] above, since the change in the amplitude reflectance with respect to the change in the physical properties of the sample (for example, carrier density) can be made relatively large, the physical properties of the sample can be measured more accurately based on the amplitude reflectance.

[0014] [5] The frequency of the measurement light is included in the range of 0.1 THz to 10 THz, and the interference measurement method of [4].

[0015] According to the configuration of [5] above, the effect of [4] above can be obtained more preferably.

[0016] [6] In the fifth step, based on the electric field amplitude corresponding to the maximum peak of the first electric field amplitude waveform and the electric field amplitude corresponding to the maximum peak of the second electric field amplitude waveform, a measurement value regarding the physical properties of the sample is obtained, and any of the interference measurement methods of [1] to [4].

[0017] According to the configuration of [6] above, by focusing on the electric field amplitudes of the maximum peaks of each of the first electric field amplitude waveform and the second electric field amplitude waveform, a measurement with a high signal-to-noise ratio can be performed.

[0018] [7] The interference measurement device further includes an excitation optical system that irradiates the sample disposed in the second optical path in the second state with excitation light, The third step changes the combination of the delay time and the optical path length difference by controlling the delay time, which is the time difference between the timing when the second branched light is incident on the sample and the timing when the excitation light is irradiated on the sample by the excitation optical system, and performs measurement by the interference intensity measurement unit for each combination to obtain the second interference waveform for each delay time, The fourth step obtains the second electric field amplitude waveform for each delay time, The fifth step is an interference measurement method, one of [1] to [6], which obtains a measurement of the time response of the sample based on the electric field amplitude corresponding to the peaks of the first electric field amplitude waveform and the second electric field amplitude waveform for each delay time.

[0019] According to the configuration described in [7] above, it becomes possible to evaluate the time response of the physical properties of a sample irradiated with excitation light.

[0020] [8] The sample is a semiconductor material, The interference measurement method according to [7], wherein the excitation light is visible light or near-infrared light.

[0021] According to the configuration described in [8] above, the carriers in the semiconductor sample can be efficiently excited by the excitation light, making it possible to suitably evaluate the physical properties of the semiconductor sample.

[0022] [9] The measurement light is generated by directing a portion of the light generated by the light source onto an optical crystal, and the other portion of the light generated by the light source is input to the excitation optical system as the excitation light. An interference measurement method according to [7] or [8], wherein the delay time is controlled by changing the optical path length of the excitation light in the excitation optical system.

[0023] According to the configuration described in [9] above, measurement light and excitation light can be generated from a single light source, and the delay time can be easily controlled by changing the optical path length of the excitation optical system.

[0024]

[10] An interference measurement method according to any of [2] to [9], wherein the processing of the third step, the fourth step, and the fifth step is repeatedly performed while changing the impurity concentration of the sample.

[0025] According to the configuration described in

[10] above, by performing a process that changes the impurity concentration of the sample while understanding the physical property information of the sample at each state, it is possible to easily and efficiently adjust the impurity concentration of the sample to a desired range.

[0026]

[11] An interference optical system comprising: a beam splitter that splits measurement light having a frequency in the range of 0.1 THz to 50 THz into a first branched beam and a second branched beam; a first optical path from the time the first branched beam is output from the beam splitter until it is re-incident to the beam splitter; and a second optical path different from the first optical path from the time the second branched beam is output from the beam splitter until it is re-incident to the beam splitter, configured to switch between a first state in which no sample is placed and a second state in which the sample is placed, wherein the first branched beam and the second branched beam re-incident to the beam splitter are combined, and the difference in optical path length between the first optical path and the second optical path is variable, An excitation optical system that irradiates the sample placed in the second optical path with excitation light when in the second state, A light source that generates light, causes a portion of the light to incident on an optical crystal to generate the measurement light, and inputs the other portion of the light as the excitation light to the excitation optical system, 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 branched light and the second branched light in the beam splitter, An interference intensity measuring unit measures the intensity of the interference light based on the electrical signal value output from the photomultiplier tube, The system includes an electric field amplitude calculation unit that calculates the electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement unit, 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, An interferometry device in which the optical path length of the excitation light in the excitation optical system is configured to be variable.

[0027] The above-described interferometry device enables the implementation of the interferometry method described above, allowing for appropriate non-contact measurement of the physical properties of a sample. Furthermore, by incorporating both an interference optical system and an excitation optical system, the device can evaluate the time response of the physical properties of a sample irradiated with excitation light. Additionally, since both the measurement light and the excitation light can be generated from a single light source, the device configuration can be simplified and miniaturized compared to cases where the measurement light and excitation light are output from separate light sources. Moreover, by changing the optical path length of the excitation optical system, the delay time between the timing of the incident measurement light (second branch light) on the sample and the timing of the irradiation with excitation light can be easily set, making it easy to obtain measurement values ​​related to the time response. [Effects of the Invention]

[0028] According to this disclosure, it is possible to provide an interference measurement method and an interference measurement apparatus that can appropriately measure the physical properties of a sample in a non-contact manner. [Brief explanation of the drawing]

[0029] [Figure 1] This figure shows an example of the configuration of the interference measuring device 1 according to the first embodiment. [Figure 2] This figure shows an example configuration of the photomultiplier tube 30. [Figure 3] This is an example of a graph showing the time dependence of the voltage signal V output from the photomultiplier tube 30. [Figure 4] This is an example of a graph showing the relationship (FN formula) between the output value of the photomultiplier tube 30, obtained by fitting, and the electric field amplitude of the incident light. [Figure 5] This table shows an example of the correspondence between the electric field amplitude of incident light calculated using the FN formula and the output value of the photomultiplier tube 30. [Figure 6] This is a flowchart showing an example of an interference measurement method (first measurement example) using the interference measurement device 1. [Figure 7] This figure shows examples of the first interference waveform W1 and the second interference waveform W2. [Figure 8]This figure shows examples of the first electric field amplitude waveform WE1 and the second electric field amplitude waveform WE2. [Figure 9] This graph shows the relationship between the amplitude reflectance R of the measured light at different frequencies for each of several Si semiconductor substrates with different resistivity ρ. [Figure 10] This graph shows the relationship between the amplitude reflectance R of the measured light at different frequencies for each of several GaN semiconductor substrates with different resistivity ρ. [Figure 11] This figure shows an example configuration of the interference measurement device 1A according to the second embodiment. [Figure 12] This is a flowchart showing an example of an interference measurement method using the interference measurement device 1A (second measurement example). [Figure 13] This figure shows an example of a first interference waveform W1 and a second interference waveform W2(t) corresponding to a certain delay time t. [Figure 14] This figure shows an example of a first electric field amplitude waveform WE1 and a second interference waveform W3 corresponding to a certain delay time t. [Figure 15] This figure shows an example of amplitude reflectance R(t) for each delay time. [Modes for carrying out the invention]

[0030] One embodiment of the present disclosure will be described in detail with reference to the drawings. In the following description, the same or equivalent elements will be denoted by the same reference numerals, and redundant descriptions will be omitted. [First Embodiment]

[0031] Referring to Figures 1 to 9, the interference measurement device 1 of the first embodiment will be described, along with an interference measurement method (first measurement example) using the interference measurement device 1. As shown in Figure 1, the interference measurement device 1 comprises a light source 10, an interference optical system 20, a photomultiplier tube 30, an interference intensity measurement unit 40, an electric field amplitude calculation unit 50, and an analysis unit 60. The interference intensity measurement unit 40, the electric field amplitude calculation unit 50, and the analysis unit 60 may be configured by a computer system including, for example, a processor, memory, storage, and communication devices. That is, the functions of the interference intensity measurement unit 40, the electric field amplitude calculation unit 50, and the analysis unit 60 are performed, for example, by the operation of the above-mentioned hardware elements by a predetermined program.

[0032] The light source 10 outputs measurement light L having a frequency in the range of 0.1 THz to 50 THz. In this embodiment, as an example, the light source 10 includes an output unit 11 that outputs visible light or near-infrared light L0, and an optical crystal 12 that converts said light L0 into measurement light L.

[0033] The output unit 11 is, for example, an ultrashort pulse laser. As an example, the output unit 11 is a femtosecond laser light source. Examples of the output unit 11 include a Ti sapphire pulse laser (wavelength 800 nm), an Er pulse fiber laser (wavelength 1550 nm), a Yb pulse fiber laser (wavelength 1030 nm), a Tm pulse fiber laser (wavelength 1900 nm), and an Nd pulse solid-state laser (wavelength 1030 nm).

[0034] The optical crystal 12 is formed from a material capable of generating measurement light L (e.g., terahertz waves) within the frequency range described above. Examples of optical crystals 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 photoconductive antennas (excitation wavelength 800 nm), and InGaAs photoconductive antennas (excitation wavelength 1.5 μm). The optical crystal 12 is located downstream of the output unit 11. The light L0 output from the output unit 11 is converted into measurement light L within the frequency range described above by passing through the optical crystal 12.

[0035] However, the form of the light source 10 is not limited to the above. For example, the light source 10 may be configured as an injection-seeded terahertz-wave parametric oscillator (is-TPG) using an Nd microchip laser (wavelength 1030 nm) as the excitation laser. The light source 10 may also be a light source capable of outputting continuous light. For example, the light source 10 may be a resonant tunneling diode (RTD), an impact avalanche and transit time diode (IMPATT), a quantum cascade laser light source, a THz gas laser light source, etc.

[0036] 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 measurement light L is a terahertz wave with a frequency of 0.5 THz.

[0037] The interference optical system 20 includes a beam splitter 21, a first mirror 22, a second mirror 23, and lenses 24 and 25. The beam splitter 21 may be made of, for example, silicon or an ITO mirror. The interference optical system 20 has a first optical path P1, which is a round-trip path between the beam splitter 21 and the first mirror 22, and a second optical path P2, which is a round-trip path between the beam splitter 21 and the second mirror 23. The first optical path P1 is the optical path from when one of the first branched beams L1, which is split by the beam splitter 21, is output from the beam splitter 21 until it is re-incident to the beam splitter 21. The second optical path P2 is the optical path from when the other second branched beam L2, which is split by the beam splitter 21, is output from the beam splitter 21 until it is re-incident to the beam splitter 21.

[0038] The beam splitter 21 splits the measurement light L output from the light source 10 into a first branched beam L1 and a second branched beam L2. In this embodiment, the beam splitter 21 is positioned between the light source 10 (optical crystal 12 in this embodiment) and the first mirror 22. The first branched beam L1 is the component of the measurement light L that passes through (travels in a straight line) the beam splitter 21. The first branched beam L1 is reflected by the mirror surface 22a of the first mirror 22 and enters the beam splitter 21 again (on the side opposite to the incident surface of the measurement light L). The second branched beam L2 is the component that is reflected by the beam splitter 21 and travels in a direction perpendicular to the direction of propagation of the measurement light L. The second branched beam L2 is reflected by the mirror surface 23a of the second mirror 23 or by the sample S placed on the mirror surface 23a and enters the beam splitter 21 again (on the same side as the incident surface of the measurement light L).

[0039] In the interference optical system 20, the second optical path P2 is configured to switch between a first state in which no predetermined sample S is placed and a second state in which a sample S is placed. Figure 1 shows the second state. As an example, the second state is a state in which the sample S is placed on the mirror surface 23a of the second mirror 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.

[0040] In the interference optical system 20, the difference in optical path length between the first optical path P1 and the second optical path P2 is configured to be variable. For example, the first mirror 22 that forms the first optical path P1 is configured to be movable in a direction D1 parallel to the direction of propagation of the first branched light L1 (a direction perpendicular to the mirror surface 22a). The position of the first mirror 22 in direction D1 is set, for example, in the initial state, such that the difference in optical path length Δd between the first optical path P1 and the second optical path P2 is near zero. That is, in the example in Figure 1, in the initial state, the distance from the beam splitter 21 to the mirror surface 22a of the first mirror 22 and the distance from the beam splitter 21 to the mirror surface 23a of the second mirror 23 are set to be approximately the same.

[0041] Furthermore, the mechanism for changing the optical path length difference Δd is not limited to the mechanism of this embodiment (a mechanism that makes the first mirror 22 movable in direction D1). Instead of the first mirror 22 (or in addition to the first mirror 22), the second mirror 23 may be configured to be movable in a direction parallel to the direction of propagation of the second branched light L2 (a direction perpendicular to the mirror surface 23a). Alternatively, a mechanism that can change the optical path length difference Δd at high speed may be provided by interposing a rotating mirror that can swing (rotate) within a predetermined angular range in at least one of the first optical path P1 and the second optical path P2.

[0042] The beam splitter 21 combines the first branched light L1 that is re-incident to the beam splitter 21 through the first optical path P1 and the second branched light L2 that is re-incident to the beam splitter 21 through the second optical path P2, thereby generating interference light IL. In this embodiment, the component of the first branched light L1 that is re-incident to the beam splitter 21 (on the side opposite to the incident surface of the measurement light L) that is reflected by the beam splitter 21 and the component of the second branched light L2 that is re-incident to the beam splitter 21 (on the same side as the incident surface of the measurement light L) that is transmitted through the beam splitter 21 are combined, causing interference light IL to be emitted toward the side of the beam splitter 21 opposite to the side where the second mirror 23 is located.

[0043] Lens 24 is positioned between the beam splitter 21 and the second mirror 23 in the second optical path P2. In the second state, lens 24 is a lens that focuses the second branched light L2 to increase the incidence efficiency of the second branched light L2 onto the sample S placed on the mirror surface 23a. Lens 24 is, for example, a terahertz wave band focusing lens with a focal length of 50 mm (e.g., Tsurupica®).

[0044] Lens 25 is positioned downstream of the beam splitter 21 in the optical path of the interferential light IL (i.e., between the beam splitter 21 and the photomultiplier tube 30). Lens 25 is a lens that focuses the interferential light IL to increase the incidence efficiency of the interferential light IL to the photomultiplier tube 30. Lens 25 is, for example, a focusing lens for the terahertz wave band, similar to lens 24.

[0045] The photomultiplier tube 30 is positioned downstream of the beam splitter 21, where the interference light IL output from the beam splitter 21 is directed. The photomultiplier tube 30 is sensitive to the wavelength range of the measurement light L (in this embodiment, the light band including terahertz waves) and outputs an electrical signal value corresponding to the incident light intensity of the interference light IL.

[0046] Figure 2 is a block diagram showing an example configuration of a photomultiplier tube 30. The photomultiplier tube 30 has an electron emission section 31, an electron multiplication section 32, and a signal output section 33 arranged inside a housing 34 whose interior is kept under vacuum. The housing 34 is provided with a window section 35.

[0047] The electron emission unit 31 emits electrons e upon incidence of light ν that has passed through the window 35. The electron emission unit 31 is a photoelectric conversion unit designed to be sensitive to the bandwidth of the measurement light L to be detected. The electron emission unit 31 has a configuration in which, for example, a metamaterial structure (metasurface) is formed on the main surface of the substrate, and emits electrons e upon incidence of light on the metasurface.

[0048] The electron multiplication unit 32 multiplies the electrons e emitted from the electron emission unit 31. The electron multiplication unit 32 includes multiple stages of dynodes or microchannel plates. The electron multiplication factor in the electron multiplication unit 32 corresponds to the voltage applied to the multiple stages of dynodes or microchannel plates. The signal output unit 33 collects the electrons e multiplied by the electron multiplication unit 32 and outputs them as a current signal J. The interference intensity measurement unit 40, described later, may receive either the current signal J output from the signal output unit 33 or the voltage signal obtained after the current signal J has been converted by the IV conversion circuit. In this embodiment, the voltage signal is input to the interference intensity measurement unit 40 as an electrical signal value output from the photomultiplier tube 30.

[0049] The interference intensity measurement 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 is a graph showing the time dependence of the voltage signal V output from the photomultiplier tube 30. The interference intensity measurement unit 40 reads the time change of the voltage signal V output from the photomultiplier tube 30 when the optical path length difference Δd is set to a certain value. The interference intensity measurement 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 length difference Δd.

[0050] The electric field amplitude calculation unit 50 determines the electric field amplitude of the interference light IL from the intensity of the interference light IL (Vp-p in this embodiment) measured by the interference intensity measurement unit 40, based on the relationship between the electric field amplitude value of the light incident on the photomultiplier tube 30 and the value of the electrical signal (voltage signal) output from the photomultiplier tube 30.

[0051] The value of the electrical signal output from the photomultiplier tube 30 may be described by a polynomial with the electric field amplitude E of the light incident on the photomultiplier tube 30 as a variable, but it may also be described using the following equation (1) which represents the efficiency of electron emission in the metasurface. This equation is expressed by the current J emitted from the metasurface. FN This represents the relationship between the field amplitude E of the incident light (interference light IL) and is called the Fowler-Nordheim relationship (hereinafter referred to as the "FN equation"). The FN equation is an example of information that shows the relationship between the above-mentioned field amplitude and the value of the electrical signal output from the photomultiplier tube 30.

[0052]

number

[0053] In this FN formula, a FN and b FN is called the FN constant and is a certain constant value. β is the field enhancement factor, which is approximately 400 as an example. Φ is the work function of the material of the metasurface of the electron emission section 31, which is 3.5 eV for gold. F and ν F is a constant. When the electric field amplitude of the incident light is not large, t F and ν F Each of these values ​​may be set to 1. In that case, the FN expression is expressed by the following equation (2).

[0054]

number

[0055] The FN formula represents the relationship between the current J emitted from the electron emission part 31 of the photomultiplier tube 30 FN and the electric field amplitude E of the incident light. Similarly, the relationship between the output value of the photomultiplier tube 30 and the electric field amplitude E of the incident light can also be represented

[0056] The a FN and b FN in the FN formula need to be determined respectively. For this purpose, the electric field amplitude E of the incident light is set to each value, and the output value (amplitude Vp - p) of the photomultiplier tube 30 is measured. By performing fitting processing using these measured values, the values of a FN and b FN can be obtained respectively. Fig. 4 is a graph showing the relationship (FN formula) between the output value of the photomultiplier tube 30 obtained by fitting processing and the electric field amplitude E of the incident light. Five measured values are shown as circles in this figure <于

[0057] <于 The electric field amplitude calculation part 50 can, for example, obtain the electric field amplitude of the interference light IL from the intensity of the interference light IL measured by the interference intensity measurement part 40 based on the above-mentioned FN formula. To obtain the electric field amplitude E of the incident light from the output value of the photomultiplier tube 30 using the FN formula, for example, the following method can be used. By calculating using the FN formula, the output value of the photomultiplier tube 30 is obtained for each value of the electric field amplitude E of the incident light. Fig. 5 is a table showing an example of the correspondence between the electric field amplitude E of the incident light and the output value of the photomultiplier tube 30 by calculation using the FN formula. The electric field amplitude calculation part 50 obtains the electric field amplitude E of the incident light that is closest to the fitting value from the actual output value of the photomultiplier tube 30 (the intensity of the interference light IL obtained by the interference intensity measurement part 40). Alternatively, the electric field amplitude E of the incident light may be obtained by interpolation calculation <于

[0058] <于 Based on the calculation result (electric field amplitude E for each optical path length difference Δd) by the electric field amplitude calculation part 50, the analysis part 60 executes various operations for obtaining measurement values regarding the physical properties of the sample S. Examples of the processing of the analysis part 60 will be described together with the flowchart described later <于

[0059] <于 Referring to the flowchart in Figure 6 and the examples of measurement results in Figures 7 and 8, an example of an interference measurement method using the interference measurement device 1 (first measurement example) will be explained. As an example, the first measurement example is used to estimate the carrier density of the sample S (wafer surface) at each stage and to change the impurity concentration (doping concentration) of the sample S until the carrier density reaches a desired value.

[0060] In step S1 (first step), the interference intensity measurement unit 40 is used to measure the interference intensity while changing the optical path length difference Δd in the first state (a state in which no sample S is placed), thereby obtaining a first interference waveform W1 (Figure 7) that shows the intensity of the interference light IL for each optical path length difference Δd in the first state.

[0061] More specifically, by setting the second optical path P2 without a sample S (i.e., without sample S in Figure 1) and setting the optical path length difference Δd to a certain value, and outputting measurement light L from the light source 10, the interference intensity measurement unit 40 measures the intensity (Vp-p) of the interference light IL corresponding to the optical path length difference Δd. By performing the above measurement for each value of the optical path length difference Δd while changing the optical path length difference Δd (in this embodiment, while scanning the first mirror 22 in direction D1), the first interference waveform W1 can be obtained. The horizontal axis of the graph in Figure 7 shows the time difference Δt (=Δd / c) corresponding to the optical path length difference Δd. Here, c is the speed of light in a vacuum. The vertical axis of the graph in Figure 7 shows the intensity (Vp-p) of the interference light IL.

[0062] In step S2 (second step), the electric field amplitude calculation unit 50 converts the first interference waveform W1 into a first electric field amplitude waveform WE1 (Figure 8), which is the waveform of the electric field amplitude. The electric field amplitude calculation unit 50 can obtain the first electric field amplitude waveform WE1 by converting the value (Vp-p) of the first interference waveform W1 into an electric field amplitude using the relationship based on the FN formula described above (for example, the correspondence table obtained from the FN formula (Figure 5)). The horizontal axis of the graph in Figure 8 shows the time difference Δt, similar to the graph in Figure 7. On the other hand, the vertical axis of the graph in Figure 8 shows the electric field amplitude (kV / cm) of the interference light IL.

[0063] Next, the sample S is placed in the second optical path P2 (on the mirror surface 23a of the second mirror 23), and measurements are performed in the same manner as in steps S1 and S2 described above.

[0064] In step S3 (third step), the interference intensity measurement unit 40 is used to measure the intensity of the interference light IL for each optical path length difference in the second state (the state in which the sample S is placed), thereby obtaining a second interference waveform W2 (Figure 7) that shows the intensity of the interference light IL for each optical path length difference in the second state. The process in step S3 differs from that in step S1 only in that the sample S is placed; otherwise, it is the same as the process in step S1.

[0065] In step S4 (the fourth step), the electric field amplitude calculation unit 50 converts the second interference waveform W2 into a second electric field amplitude waveform WE2 (Figure 8), which is the waveform of the electric field amplitude. The processing in step S4 differs from that in step S2 only in that the sample S is placed therein; otherwise, it is the same as the processing in step S2.

[0066] Next, the analysis unit 60 obtains measured values ​​regarding the physical properties of the sample S from 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), the amplitude reflectance R is first calculated as a measured value regarding the physical properties of the sample S, and then the carrier density of the sample S is calculated from the amplitude reflectance R.

[0067] 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, a measured value (amplitude reflectance R) relating to the physical properties of the sample S is obtained. For example, by assuming that the reflectance when the sample is not placed (i.e., the reflectance of the second branched light L2 at the mirror surface 23a) is 100%, the analysis unit 60 can calculate the amplitude reflectance R as the value obtained by dividing the electric field amplitude E2 of the peak p2 in the second state by the electric field amplitude E1 of the peak p1 in the first state (E2 / E1).

[0068] In the example shown in Figure 8, the electric field amplitudes E1 and E2 corresponding to the maximum peaks p1 and p2 of each electric field amplitude waveform WE1 and WE2 were used. However, for the calculation of the amplitude reflectance R, the electric field amplitudes corresponding to the second and subsequent peaks of each electric field amplitude waveform WE1 and WE2 may also be used. However, as shown in Figure 8, the maximum peaks p1 and p2 of each electric field amplitude waveform WE1 and WE2 are more prominent than the second and subsequent peaks. 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, measurements with a high signal-to-noise ratio can be performed.

[0069] In step S6, the analysis unit 60 calculates (estimates) the carrier density of the sample S from the amplitude reflectance R. An example of the process for calculating the carrier density is described below.

[0070] The amplitude reflectance R(ω) (THz spectral reflectance) at a certain angular frequency ω from a semiconductor sample S is expressed by the following equation (3). Note that the angular frequency ω can be determined by first evaluating the spectral sensitivity of the photomultiplier tube 30 and determining its center frequency.

[0071]

number

[0072] 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. By rearranging equation (3) above and moving only the dielectric constant ε(ω) to the left side, we obtain equation (4) below.

[0073]

number

[0074] On the other hand, the dielectric constant ε(ω) can also be expressed by the following equations (5) and (6).

[0075]

number

[0076] Here, ε ∞ This shows the dielectric constant at the high-frequency limit (=11.7), and ω p γ represents the plasma frequency, γ represents the damping ratio, and n c This indicates the carrier density, m * ε₀ represents the specific effective mass, e represents the elementary charge, and ε₀ represents the permittivity of vacuum.

[0077] For example, the analysis unit 60 calculates the dielectric constant ε(ω) based on the amplitude reflectance R(ω) (=E2 / E1) calculated in step S5 and the above equation (4), and performs fitting using the above equation (5), thereby ω p And γ can be determined. Subsequently, the analysis unit 60 calculates the carrier density n based on the above formula (5). c Alternatively, a known damping ratio for sample S can be applied to γ, and the carrier density n can be calculated. c The dielectric constant for each element may be calculated in advance based on the above equations (5) and (6). In this case, the analysis unit 60 calculates the amplitude reflectance R(ω), the dielectric constant ε obtained from the above equation (4), and the carrier density n obtained as described above. c By comparing it with the dielectric constant of each sample, the carrier density corresponding to the amplitude reflectance R(ω) can be estimated. For example, the analysis unit 60 can obtain the carrier density as physical property information of the sample S from the amplitude reflectance R(ω) by performing the above calculation.

[0078] In step S7, if the carrier density calculated by the analysis unit 60 falls within a predetermined desired range (step S7: YES), the measurement is terminated. On the other hand, if the carrier density does not fall within the desired range (step S7: NO), a process is performed to change the impurity concentration (doping amount) of the sample S (step S8). After that, the process from step S3 is repeated. Through the above process, the impurity concentration of the sample S can be adjusted so that the carrier concentration (estimated value) of the sample S falls within the desired range.

[0079] In the interference measurement method using the interference measurement device 1 described above, by measuring the interference light IL while changing the optical path length difference Δd for both a first state in which the sample S is not placed in one of the optical paths (second optical path P2) of the interference optical system 20 and a second state in which the sample S is placed, a first interference waveform W1 and a second interference waveform W2 showing the intensity of the interference light IL for each optical path length difference Δd are obtained (see Figure 7). Furthermore, by converting the intensity of the interference light IL for each of the first interference waveform W1 and the second interference waveform W2 into an electric field amplitude, a first electric field amplitude waveform WE1 and a second electric field amplitude waveform WE2 are obtained (see Figure 8). Then, 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, measurement values ​​regarding the physical properties of the sample S can be obtained. In this embodiment, the amplitude reflectance R of the sample S and the carrier density estimated based on the amplitude reflectance R were obtained as the above measurement values. According to the above interference measurement method, the physical properties of sample S can be determined based on measurements obtained by irradiating the sample S with light (second branched light L2) without bringing a measuring instrument (probe) or the like into contact with the sample S. Therefore, according to the above interference measurement method, the physical properties of sample S can be appropriately measured (evaluated) in a non-contact manner.

[0080] In the above interference measurement method, sample S is a semiconductor material. With the above configuration, the physical properties of sample S, which is a semiconductor material, such as carrier density, can be easily measured using a non-contact measurement method. In other words, since it is not necessary to bring the probes into contact with sample S as in conventional two-probe and four-probe methods, damage to sample S (for example, damage caused by the probes coming into contact with unintended areas) can be avoided.

[0081] Furthermore, the resistivity of the semiconductor material of sample S is preferably 4 Ωcm or less. In other words, sample S is preferably a so-called low-resistivity substrate. With the above configuration, by using a semiconductor material as sample S in which the change in amplitude reflectance R(E2 / E1) with respect to changes in carrier density is relatively large, the physical properties of sample S can be measured with greater accuracy based on the amplitude reflectance R.

[0082] Figure 9 shows the relationship between the amplitude reflectance R at each frequency of the measurement light L for each of several Si semiconductor substrates with different resistivity ρ (an example of sample S). Figure 10 shows the relationship between the amplitude reflectance R at each frequency of the measurement light L for each of several GaN semiconductor substrates with different resistivity ρ (an example of sample S). Here, carrier density and resistivity ρ are closely related. That is, when the carrier density changes, the resistivity ρ of sample S changes accordingly, and the amplitude reflectance R changes as a result. From Figures 9 and 10, it can be seen that, although it depends on the material of sample S, the difference in amplitude reflectance R due to 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. For the above reasons, it is preferable that the frequency of the measurement light L is within the range of 0.1 THz to 30 THz. With the above configuration, the change in amplitude reflectance R in response to changes in the physical properties of sample S (e.g., carrier density) can be made relatively large, so that the physical properties of sample S can be measured with greater accuracy based on the amplitude reflectance R. Furthermore, from the viewpoint of further improving the above effects, the frequency of the measurement light L is preferably in the range of 0.1 THz to 10 THz, more preferably in the range of 0.1 THz to 1 THz, and even more preferably in the range of 0.2 THz to 0.5 THz.

[0083] In the above interference measurement method (first measurement example), the processes in 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 falls within a desired range. With the above configuration, by performing a process to change the impurity concentration of sample S and understanding the physical property information of sample S (for example, carrier density) at each state, the process of adjusting the impurity concentration of sample S to a desired range (i.e., the impurity concentration corresponding to the desired carrier density) can be performed easily and efficiently. [Second Embodiment]

[0084] Referring to Figures 11 to 15, the interference measurement device 1A of the second embodiment will be described, along with an interference measurement method (second measurement example) using the interference measurement device 1A. In the second embodiment, as a measurement value related to the physical properties of the sample S, a measurement value related to the time response of the sample S is obtained. As shown in Figure 11, the interference measurement device 1A differs from the interference measurement device 1 in that it further comprises a half-wave plate 71, a polarizing beam splitter 72, a mirror 73, and an excitation optical system 80. The half-wave plate 71, the polarizing beam splitter 72, and the mirror 73 are arranged between the output unit 11 and the optical crystal 12. The half-wave plate 71 is arranged between the output unit 11 and the polarizing beam splitter 72 and adjusts the polarization direction of the light output from the output unit 11. The polarizing beam splitter 72 splits the light output from the output unit 11 into light L0 that passes through the polarizing beam splitter 72 and heads toward the interference optical system 20 via the mirror 73, and excitation light Le that is reflected by the polarizing beam splitter 72 and heads toward the excitation optical system 80, according to a splitting ratio corresponding to the polarization direction of the light. In this embodiment, the splitting ratio between light L0 and excitation light Le in the polarizing beam splitter 72 can be adjusted to any ratio by changing the polarization direction of the light output from the output unit 11 by rotating the half-wave plate 71. This makes it possible to appropriately and easily adjust the intensity ratio of excitation light Le and light L0 according to the type of sample S, etc. Note that if it is not necessary to adjust the splitting ratio between light L0 and excitation light Le as described above, the half-wave plate 71 may be omitted, and the polarizing beam splitter 72 may be a beam splitter whose splitting ratio does not change according to the polarization direction. The light L0 reflected by the mirror 73 is converted into measurement light L by passing through the optical crystal 12 and is directed to the interference optical system 20 (beam splitter 21), similar to the first embodiment. The optical crystal 12 may be placed in front of the mirror 73 (between the polarizing beam splitter 72 and the mirror 73).

[0085] The excitation optical system 80 includes mirrors 81-84, a moving mechanism 85 for moving mirrors 81 and 82, a lens 86, and a damper 87. Mirrors 81-84 are arranged in such order that the excitation light Le is reflected. That is, the excitation light Le reflected by mirror 81 goes to mirror 82, the excitation light Le reflected by mirror 82 goes to mirror 83, and the excitation light Le reflected by mirror 83 goes to mirror 84. The excitation light Le reflected by mirror 84 is irradiated onto the sample S placed on the mirror surface 23a of the second mirror 23.

[0086] The movement mechanism 85 moves mirrors 81 and 82 in parallel in direction D2 as a whole, such that the distance between mirrors 81 and 82 remains constant, while the distance from the polarizing beam splitter 72 to mirror 81 and the distance between mirrors 82 and 83 vary. The movement of mirrors 81 and 82 by the movement mechanism 85 changes the optical path length of the excitation light Le from the polarizing beam splitter 72 to the sample S. In other words, by adjusting the position of mirrors 81 and 82 with the movement mechanism 85, it is possible to control the delay time, which is the time difference between the first timing when the measurement light L (second branched light L2) is incident on the sample S and the second timing when the excitation light Le is irradiated onto the sample S by the excitation optical system 80.

[0087] Lens 86 is positioned between mirrors 83 and 84. Lens 86 is a lens for focusing the excitation light Le onto the irradiation position (target position) of the sample S. If the distance from mirror 84 to sample S is long, lens 86 may be positioned between mirror 84 and sample S.

[0088] The damper 87 is positioned where the excitation light Le reflected from the sample S is directed. The damper 87 plays a role in preventing the excitation light Le from entering other optical elements by shielding it.

[0089] Referring to the flowchart in Figure 12 and the examples of measurement results in Figures 13 to 15, an example of an interference measurement method using the interference measurement device 1A (second measurement example) will be explained. As an example, in the second measurement example, by measuring while changing the delay time described above, the carrier density of the sample S in each state for each delay time is estimated and used to evaluate the time response characteristics of the photoexcited sample S.

[0090] Steps S11 and S12 (the first and second steps) are the same as steps S1 and S2 in the first measurement example (Figure 6). That is, steps S11 and S12 acquire the first interference waveform W1 and the first electric field amplitude waveform WE1 of the first state (a state in which there is no sample S to be irradiated with excitation light Le, and therefore no excitation light Le is irradiated). In the interference measurement device 1A, in order to perform steps S11 and S12, for example, a damper (a member similar to damper 87) that shields the excitation light Le can be placed at any point in the excitation optical system 80 so that the excitation light Le does not irradiate the mirror surface 23a.

[0091] Step S13 (the third step) is a modified version of the process in step S3 of the first measurement example (Figure 6), performed for each combination of the delay time t and the optical path length difference Δd described above. Specifically, step S13 controls the delay time t, which is the time difference (t2-t1) between the timing t1 when the second branched light L2 is incident on the sample S and the timing t2 when the excitation light Le is irradiated onto the sample S by the excitation optical system 80. By changing the combination of delay time t and the optical path length difference Δd, the interference intensity measurement unit 40 measures each combination, thereby obtaining the second interference waveform W2(t) for each delay time t. A delay time of "t=0" indicates a state where the second branched light L2 and the excitation light Le are incident on and irradiated onto the sample S simultaneously. A delay time of "t>0" indicates a state where the excitation light Le is irradiated onto the sample S before the second branched light L2. A delay time of "t<0" indicates a state where the second branched light L2 is incident on the sample S before the excitation light Le.

[0092] Figure 13 is a graph with the same horizontal and vertical axes as Figure 7, showing the second interference waveform W2(t) corresponding to a certain delay time t (t>0). In the example in Figure 13, the carrier density of sample S temporarily changes (increases) when the sample S is irradiated with excitation light Le, and as a result, the reflectivity of the measurement light L in sample S is improved compared to the state without photoexcitation. As a result, the intensity of the interference light IL incident on the photomultiplier tube 30 increases, and the peak value of the second interference waveform W2(t) is larger than the peak value of the second interference waveform W2 (see Figure 7).

[0093] The process in step S13 can be performed, for example, as follows. First, the delay time t is set to a certain value by adjusting the optical path length of the excitation light Le in the excitation optical system 80 using the moving mechanism 85. Next, similar to step S3 in the first measurement example (Figure 6), measurements corresponding to each optical path length difference Δd are performed while changing the optical path length difference Δd. This yields a second interference waveform W2(t) for a certain delay time t. By performing the above process while changing the delay time t, a second interference waveform W2(t) corresponding to each of multiple delay times t can be obtained.

[0094] Step S14 (the fourth step) is a modified version of the process in step S4 of the first measurement example (Figure 6), performed for each combination of delay time t and optical path length difference Δd. That is, step S14 obtains the second electric field amplitude waveform WE2(t) for each delay time t by performing the same conversion process as in step S4 on the second interference waveform W2(t) for each delay time t.

[0095] Figure 14 is a graph with the same horizontal and vertical axes as Figure 8, showing the second electric field amplitude waveform WE2(t) corresponding to a certain delay time t (the same as the delay time t in Figure 13). Figure 14 also shows the second electric field amplitude waveform WE2 when no photoexcitation occurs (the waveform obtained from the first measurement example). In the example in Figure 14, as described above, the peak value of the second interference waveform W2(t) is larger than the peak value of the second interference waveform W2, resulting in the peak value E2(t) of the second electric field amplitude waveform WE2(t) being larger than the peak value E2 of the second electric field amplitude waveform WE2.

[0096] Step S15 (the fifth step) is a modified version of the process in step S5 of the first measurement example (Figure 6), performed for each combination of delay time t and optical path length difference Δd. In other words, step S15 is the process of calculating the amplitude reflectance R(t) (=E2(t) / E1) for each delay time t.

[0097] Figure 15 shows an example of amplitude reflectance R(t) for each delay time. The graph in Figure 15 has delay time on the horizontal axis and amplitude reflectance on the vertical axis, plotting amplitude reflectance R(t) corresponding to several delay times t. As shown in Figure 15, the second measurement example allows us to understand the time response characteristics of sample S to photoexcitation (the magnitude of amplitude reflectance R(t) with respect to delay time t) for each delay time t. That is, step S15 is an example of a process to obtain measured values ​​(here, amplitude reflectance R(t)) related to the time response of sample S based on the electric field amplitudes E1 and E2(t) corresponding to the respective 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.

[0098] Step S16 (the fifth step) is a modified version of the process in step S6 of the first measurement example (Figure 6), performed for each combination of delay time t and optical path length difference Δd. In other words, step S16 is a process that calculates (estimates) the carrier density corresponding to the amplitude reflectance R(t) for each delay time t. Step S16 is an example of a process that obtains measured values ​​(in this case, carrier density for each delay time t) regarding the time response of sample S based on the electric field amplitudes E1 and E2(t) corresponding to the respective 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.

[0099] As described above, the interferometric measurement device 1A is equipped with an excitation optical system 80 that irradiates the sample S, which is placed in the second optical path P2, with excitation light Le when it is in the second state. Furthermore, the interference measurement method using the interference measurement device 1A includes the steps of: changing the combination of delay time t and optical path length difference Δd by controlling the delay time t, which is the time difference (t2-t1) between the timing t1 when the second branched light L2 is incident on the sample S and the timing t2 when the excitation light Le is irradiated onto the sample S by the excitation optical system 80, and performing measurements for each combination using the interference intensity measurement unit 40 to obtain a second interference waveform W2(t) for each delay time t (for example, step S13 in Figure 12); obtaining a second electric field amplitude waveform WE2(t) for each delay time t (for example, step S14 in Figure 12); and obtaining measured values ​​regarding the time response of the sample S based on the electric field amplitudes E1 and E2(t) corresponding to the respective 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 (for example, steps S15 and S16 in Figure 12). In step S15, the amplitude reflectance R(t) at each delay time t is obtained as a measured value related to the time response of sample S. In step S16, the carrier density at each delay time t is obtained as a measured value related to the time response of sample S. With the above configuration, it is possible to evaluate the time response of the physical properties of sample S irradiated with excitation light Le. For example, from the carrier density at each delay time t, it is possible to perform dynamic evaluations such as the relaxation time of photoexcited carriers in sample S.

[0100] Sample S is a semiconductor material, and the excitation light Le (in this embodiment, light L0 output from the output unit 11) is visible light or near-infrared light. With the above configuration, the carriers of the semiconductor sample (sample S) can be efficiently excited by the excitation light Le, so that the physical properties of the semiconductor sample can be suitably evaluated.

[0101] Furthermore, in the interference measurement method using the interference measurement device 1A, measurement light L is generated by directing a portion of the light L0 generated in the light source 10 (output unit 11) onto the optical crystal 12, and the other portion of the light L0 generated in the light source 10 (output unit 11) is input to the excitation optical system 80 as excitation light Le. The delay time t is controlled by changing the optical path length of the excitation light Le in the excitation optical system 80. In this embodiment, the optical path length of the excitation light Le changes by scanning the moving mechanism 85, and as a result, the delay time t changes. With the above configuration, measurement light L and excitation light Le can be generated from a single light source 10 (output unit 11), and the delay time t can be easily controlled (set) by changing the optical path length of the excitation optical system 80.

[0102] Furthermore, the interferometry device 1A includes an excitation optical system 80 that irradiates the sample S, which is positioned in the second optical path P2, with excitation light Le when it is in the second state, and a light source 10 that generates light L0, generates measurement light L by causing a portion of the light L0 to be incident on the optical crystal 12, and inputs the other portion of the light L0 as excitation light Le to the excitation optical system 80. The optical path length of the excitation light Le in the excitation optical system 80 is configured to be variable. Because the above-described interferometry method can be implemented in the interferometry device 1A, the physical properties of the sample S can be appropriately measured in a non-contact manner. In addition, by including the excitation optical system 80 together with the interference optical system 20, the interferometry device 1A can evaluate the time response of the physical properties (in this embodiment, amplitude reflectance, carrier density, etc.) of the sample S irradiated with 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 device configuration can be simplified and miniaturized compared to the case where the measurement light L and the excitation light Le are output from separate light sources. Furthermore, by changing the optical path length of the excitation optical system 80, the delay time t between the timing of the incident of measurement light L (second branch light L2) on the sample S and the timing of the irradiation of excitation light Le can be easily set, thus making it easy to obtain measurement values ​​related to the time response. [Differentiation]

[0103] Although several embodiments of this disclosure have been described above, this disclosure is not limited to the configurations shown in each of the embodiments described above. The materials and shapes of each configuration are not limited to the specific materials and shapes described above, but a variety of other materials and shapes can be used. Furthermore, some of the configurations included in each of the embodiments described above may be omitted or modified as appropriate, or they can be combined as desired.

[0104] For example, the processing flow of the interference measurement method described above is not limited to those shown in Figures 6 and 12. For example, in the first measurement example shown in Figure 6, steps S3 and S4 may be performed before steps S1 and S2. Also, steps S2 and S4 may be performed after steps S1 and S3. Furthermore, when evaluating the physical properties of the completed sample S, steps S7 and S8 may be omitted. Also, for example, when only the amplitude reflectance R is to be obtained as physical property information of the sample S (for example, when carrier density is not used for evaluating the physical properties of the sample S), the measurement may be completed after obtaining the amplitude reflectance R in step S5.

[0105] Furthermore, the first and second measurement examples described above may be combined. For example, in a semiconductor process that increases the carrier density of sample S, the carrier density of sample S may be monitored using the first measurement example (measurement without photoexcitation), while the time response of carriers in sample S may be evaluated using the second measurement example (measurement with photoexcitation). For example, using an interference measurement device 1A equipped with an excitation optical system 80 in addition to the interference optical system 20, S1 to S6 of the first measurement example may be performed while photoexcitation to sample S is blocked, and S13 to S16 of the second measurement example may be performed. In this case, by evaluating the time response of carriers in addition to the carrier density in the first measurement example, it is possible to evaluate whether or not 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, resulting in a different time response than when uniformly doped.

[0106] Furthermore, the delay time in the interference measurement device 1A (i.e., a configuration that includes an excitation optical system 80 in addition to the interference optical system 20) may be controlled by using different light sources for the measurement light L and the excitation light Le, and by controlling the timing of outputting the excitation light Le from the excitation light Le light source. However, in this case, it becomes necessary to control the timing of the pulse outputs of the two different light sources with high precision. Therefore, by making the light sources (output unit 11) for the excitation light Le and the measurement light L common, as in the above embodiment, and configuring the optical path length of the excitation optical system 80 to be variable, the delay time can be easily adjusted.

[0107] Furthermore, the photomultiplier tube 30 may be capable of imaging the incident light intensity distribution. If the electron multiplication unit 32 includes a microchannel plate (for example, an image intensifier), imaging of the incident light intensity distribution is possible. By using such a photomultiplier tube 30, analytical imaging of the sample S becomes possible.

[0108] Furthermore, sample S only needs to be one whose physical properties can be evaluated by measurements (e.g., amplitude reflectance) obtained by the interferometric measurement method described above, and may be composed of materials other than semiconductor materials. For example, sample S may be a substance other than a semiconductor that has properties that respond to light. For example, sample S may be a nonlinear optical crystal (e.g., ZnTe, LiTiO3, etc.). In nonlinear optical crystals, the response time to light, the complex refractive index, etc., are important physical property parameters. The interferometric measurement method described above is useful because it can measure the above-mentioned physical property parameters nondestructively even for sample S made of materials other than semiconductor materials. [Explanation of Symbols]

[0109] 1,1A...Interference measurement device, 10...Light source, 12...Optical crystal, 20...Interference optical system, 21...Beam splitter, 30...Photomultiplier tube, 40...Interference intensity measurement unit, 50...Electric field amplitude calculation unit, 80...Excitation optical system, IL...Interference light, L...Measurement light, L1...First branched light, L2...Second branched light, Le...Excitation light, P1...First optical path, P2...Second optical path, S...Sample, W1...First interference waveform, W2...Second interference waveform, WE1...First electric field amplitude waveform, WE2...Second electric field amplitude waveform.

Claims

1. A light source that outputs measurement light having a frequency in the range of 0.1 THz to 50 THz, An interference optical system comprising: a beam splitter that splits the measurement light into a first branched beam and a second branched beam; a first optical path from the time the first branched beam is output from the beam splitter until it is re-incident to the beam splitter; and a second optical path, which is different from the first optical path from the time the second branched beam is output from the beam splitter until it is re-incident to the beam splitter, and is configured to switch between a first state in which no sample is placed and a second state in which the sample is placed, wherein the first branched beam and the second branched beam re-incident to the beam splitter are combined, and the difference in optical path length between the first optical path and the second optical path is variable, 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 branched light and the second branched light in the beam splitter, An interference intensity measuring unit measures the intensity of the interference light based on the electrical signal value output from the photomultiplier tube, An interference measurement method using an interference measuring device comprising: an electric field amplitude calculation unit that calculates the electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement unit, 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, The first step is to obtain a first interference waveform showing the intensity of the interference light for each optical path length difference in the first state by performing measurements with the interference intensity measuring unit while changing the optical path length difference in the first state, The second step involves the electric field amplitude calculation unit converting the first interference waveform into a first electric field amplitude waveform, which is a waveform of the electric field amplitude. A third step involves performing measurements by the interference intensity measuring unit while changing the optical path length difference in the second state, thereby obtaining a second interference waveform that shows the intensity of the interference light for each optical path length difference in the second state, The fourth step involves the electric field amplitude calculation unit converting the second interference waveform into a second electric field amplitude waveform, which is a waveform of the electric field amplitude. An interference measurement method comprising: a fifth step of obtaining measured values ​​relating to the physical properties of the sample based on the electric field amplitudes corresponding to the peaks of the first electric field amplitude waveform and the second electric field amplitude waveform, respectively.

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

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

4. The interference measurement method according to claim 1, wherein the frequency of the measurement light is included in the range of 0.1 THz to 30 THz.

5. The interference measurement method according to claim 4, wherein the frequency of the measurement light is included in the range of 0.1 THz to 10 THz.

6. The interference measurement method according to claim 1, wherein in the fifth step, a measurement value relating to the physical properties of the sample is obtained based on the electric field amplitude corresponding to the maximum peak of the first electric field amplitude waveform and the electric field amplitude corresponding to the maximum peak of the second electric field amplitude waveform.

7. The interference measurement device further comprises an excitation optical system that irradiates the sample placed in the second optical path with excitation light when in the second state, The third step involves controlling the delay time, which is the time difference between the timing at which the second branched light is incident on the sample and the timing at which the excitation light is irradiated onto the sample by the excitation optical system, thereby changing the combination of the delay time and the optical path length difference, and obtaining the second interference waveform for each delay time by performing measurements with the interference intensity measuring unit for each combination. The fourth step involves acquiring the second electric field amplitude waveform for each delay time, The interference measurement method according to claim 1, wherein the fifth step is to obtain a measurement value relating to the time response of the sample based on the electric field amplitude corresponding to each peak of the first electric field amplitude waveform and the second electric field amplitude waveform for each delay time.

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

9. The measurement light is generated by directing a portion of the light generated by the light source onto an optical crystal, and the remaining portion of the light generated by the light source is input to the excitation optical system as the excitation light. The interference measurement method according to claim 7 or 8, wherein the delay time is controlled by changing the optical path length of the excitation light in the excitation optical system.

10. The interference measurement method according to claim 2, wherein the processing of the third step, the fourth step, and the fifth step is repeatedly performed while changing the impurity concentration of the sample.

11. An interference optical system comprising: a beam splitter that splits measurement light having a frequency in the range of 0.1 THz to 50 THz into a first branched beam and a second branched beam; a first optical path from the time the first branched beam is output from the beam splitter until it is re-incident to the beam splitter; and a second optical path, which is different from the first optical path from the time the second branched beam is output from the beam splitter until it is re-incident to the beam splitter, and is configured to switch between a first state in which no sample is placed and a second state in which the sample is placed; wherein the first branched beam and the second branched beam re-incident to the beam splitter are combined, and the difference in optical path length between the first optical path and the second optical path is variable; An excitation optical system that irradiates the sample placed in the second optical path with excitation light when in the second state, A light source that generates light, causes a portion of the light to incident on an optical crystal to generate the measurement light, and inputs the other portion of the light as the excitation light to the excitation optical system, 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 branched light and the second branched light in the beam splitter, An interference intensity measuring unit measures the intensity of the interference light based on the electrical signal value output from the photomultiplier tube, The system includes an electric field amplitude calculation unit that calculates the electric field amplitude of the interference light from the intensity of the interference light measured by the interference intensity measurement unit, 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, An interferometry device in which the optical path length of the excitation light in the excitation optical system is configured to be variable.

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