Method and apparatus for measuring film properties

Abstract

This improves the reliability and throughput of characteristic measurement of films formed on substrates. [Solution] Polarization components consisting of p-polarized and s-polarized terahertz waves with mutually orthogonal vibration planes are incident on a substrate, the time waveforms of the electric field strengths of the p-polarized and s-polarized waves are obtained from the time waveform of the electric field strength of the polarization components reflected from the substrate, the spectra of the measured amplitude ratio of the p-polarized and s-polarized waves and the spectra of the measured phase difference of the p-polarized and s-polarized waves are obtained, the spectra of the calculated amplitude ratio of the p-polarized and s-polarized waves and the spectra of the calculated phase difference of the p-polarized and s-polarized waves are obtained by simulation using an optical model of the substrate, the properties of the film formed on the substrate are measured by fitting which at least matches the spectra of the calculated amplitude ratio to the spectra of the measured amplitude ratio, and the most reliable measurement value is used from among the multiple measurement values ​​used when measuring the properties of the film.

Description

[Technical Field]

[0001] This disclosure relates to a film property measurement method and a film property measurement apparatus. [Background technology]

[0002] In recent years, ellipsometry using terahertz waves has become known as a technique that can non-destructively measure the electrical properties of films formed on substrates, such as epitaxial films. Ellipsometry is an analytical method that measures the polarization state of reflected light produced when incident terahertz waves incident on a substrate are reflected at the substrate interface (for example, the boundary between films or the boundary between a film and a substrate) (see, for example, Patent Document 1).

[0003] Of the incident light, the polarization component that vibrates parallel to the plane of incidence perpendicular to the substrate surface is p-polarized light, and the polarization component that vibrates perpendicular to the plane of incidence is s-polarized light. The p-polarized and s-polarized light incident on the substrate are linearly polarized such that their phase and amplitude are the same. When these p-polarized and s-polarized lights are reflected at the substrate interface, their respective phases and amplitudes change depending on the optical constants of the film (refractive index and extinction coefficient for each wavelength) and the film thickness.

[0004] Then, p-polarized and s-polarized light with changed phase and amplitude are detected, and these p-polarized and s-polarized light with changed phase and amplitude constitute elliptic polarization. Furthermore, the change in the polarization state of the reflected light is expressed as the spectrum of the amplitude ratio Ψ of the detected p-polarized and s-polarized light (hereinafter referred to as "measured amplitude ratio Ψ") and the spectrum of the phase difference Δ of the measured p-polarized and s-polarized light (hereinafter referred to as "measured phase difference Δ").

[0005] On the other hand, an optical model is constructed that assumes the film thickness and optical constants of each film to match the substrate on which the film properties are measured, and the spectrum of the amplitude ratio Ψ and the spectrum of the phase difference Δ are calculated from the optical model through simulation. In the simulation, changing the film thickness and optical constants of each film changes the calculated spectrum of the amplitude ratio Ψ (hereinafter referred to as "calculated amplitude ratio Ψ") and the calculated spectrum of the phase difference Δ (hereinafter referred to as "calculated phase difference Δ").

[0006] In ellipsometry, the simulation is fitted by changing the film thickness and optical constants of each film until the spectrum of the measured amplitude ratio Ψ and the spectrum of the calculated amplitude ratio Ψ, and the spectrum of the measured phase difference Δ and the spectrum of the calculated phase difference Δ, nearly match. Then, the film thickness of each film in the simulation when the spectra nearly match is considered to be the actual film thickness, and the optical constants of each film in the simulation are considered to be the actual optical constants of each film. Furthermore, since the electrical properties of each film can be determined by the optical constants, the electrical properties of each film can be determined based on the optical constants that have been considered to be the actual optical constants of each film through fitting. This makes it possible to measure the electrical properties of each film formed on the substrate, such as carrier concentration. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2012-208098 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The technology disclosed herein improves the reliability and throughput of characteristic measurement of films formed on a substrate. [Means for solving the problem]

[0009] One aspect of the technology described herein is a substrate film characteristic measurement method for measuring the characteristics of a film formed on a substrate, comprising: injecting a terahertz wave incident light into the substrate, comprising a polarization component consisting of p-polarized light vibrating parallel to an incident plane perpendicular to the surface of the substrate and s-polarized light vibrating perpendicular to the incident plane; detecting the time waveform of the electric field intensity of the polarization component reflected from the substrate; obtaining the time waveforms of the electric field intensity of p-polarized and s-polarized light from the time waveform of the detected polarization component; and performing a Fourier transform on the obtained time waveforms of the electric field intensity of p-polarized and s-polarized light to obtain a spectrum of the measured amplitude ratio, which is the spectrum of the amplitude ratio of the electric field intensity of p-polarized and s-polarized light, and the phase difference spectrum of p-polarized and s-polarized light. The spectral values ​​of the measured phase difference, which is a parameter, are obtained, an optical model of the substrate is constructed, and a calculated amplitude ratio spectrum, which is the spectral values ​​of the amplitude ratio of the electric field intensities of the p-polarized and s-polarized light, and a calculated phase difference spectrum, which is the spectral values ​​of the phase difference between the p-polarized and s-polarized light, are obtained by simulation using the optical model, the properties of the film formed on the substrate are measured by fitting, which involves matching the spectral values ​​of the calculated amplitude ratio to the spectral values ​​of the measured amplitude ratio, and matching the spectral values ​​of the calculated phase difference to the spectral values ​​of the measured phase difference, and a highly reliable measured value is used from among a plurality of measured values ​​used when measuring the properties of the film. [Effects of the Invention]

[0010] The technology described herein can improve the reliability and throughput of characteristic measurement of films formed on a substrate. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing the configuration of a film property measurement device according to one embodiment of the technology described herein. [Figure 2] This is a diagram illustrating the fitting performed by the ellipsometer's control unit. [Figure 3] This graph shows the variation in carrier concentrations measured by fitting in an ellipsometer. [Figure 4] This graph plots the measured amplitude ratio tangent tanΨ at specific frequencies when the tanΨ stability index g falls below the threshold α. [Figure 5] This is a flowchart showing the carrier concentration measurement process as a membrane characteristic measurement method according to the first embodiment. [Figure 6] This figure shows the time waveform of the electric field intensity of the polarization component detected for each rotation angle of the rotating polarizer. [Figure 7] This graph shows the fluctuations in electric field intensity in the time waveform of the raw (polarized) electric field intensity during the preliminary, main observation period, and subsequent stages. [Figure 8] This graph shows the fluctuations in the pre-observation, main observation period, and post-observation period for 128 carrier concentration measurements. [Figure 9] This graph shows the relationship between the average value of the electric field intensity fluctuations during each period and the carrier concentration in 128 carrier concentration measurements. [Figure 10] This graph compares the change in the tanΨ stability index g with the change in the preceding fluctuations in the time waveform of the electric field intensity of the polarization component EC. [Figure 11] This is a diagram illustrating how to set the fluctuation generation threshold. [Figure 12] This flowchart shows the time waveform detection process as a film characteristic measurement method according to the second embodiment. [Figure 13] This graph shows the carrier concentrations in epitaxial membranes measured using mercury probe CV method and ellipsometry, respectively. [Figure 14] This graph shows the relationship between brightness and frequency for measured p-polarized and measured s-polarized signals. [Figure 15] This graph shows the relationship between the sensitivity of the calculated amplitude ratio tangent tangent tanΨ and frequency in response to changes in carrier concentration in an optical model. [Figure 16] This graph shows the changes in brightness of measured p-polarized and measured s-polarized signals when the detection of the polarization component EC is repeated. [Figure 17]This figure shows an optical model consisting of an epitaxial film, a buffer layer, and a substrate. [Figure 18] This graph shows the variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when each parameter is changed by approximately ±10% from its median value. [Figure 19] This graph shows the relationship between carrier concentration and mobility. [Figure 20] This graph shows the variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when each parameter other than the epitaxial film thickness, substrate carrier concentration, and mobility is changed by approximately ±10% from the median value. [Figure 21] This graph shows the variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when each parameter other than the epitaxial film thickness, substrate carrier concentration and mobility, and buffer layer thickness is changed by approximately ±10% from the median value. [Figure 22] This is a flowchart showing the parameter measurement process as a film characteristic measurement method according to the third embodiment. [Figure 23] This figure shows the time waveform of the signal intensity of a measurement signal at a certain rotation angle of a rotating polarizer. [Figure 24] This graph shows the standard deviation of the signal intensity of the measured signal in the preceding stage at each rotation angle of the rotating polarizer. [Figure 25] This graph shows the relationship between the noise characteristic values ​​of the measurement signal in the preceding stage of a certain rotation angle of the rotating polarizer, and the dose amount of the epitaxial film obtained by fitting, when the dose amount of the epitaxial film on the substrate was measured 128 times. [Figure 26] This graph shows the relationship between the noise characteristic values ​​of the measurement signal during the main observation period for a certain rotation angle of the rotating polarizer, when the dose amount of the epitaxial film on the substrate was measured 128 times, and the dose amount of the epitaxial film obtained by fitting. [Figure 27]This graph shows the relationship between the maximum signal intensity of the measurement signal in the preceding stage of a certain rotation angle of the rotating polarizer and the maximum signal intensity of the measurement signal in the main observation period, for the same measurement run. [Figure 28] This figure compares the distribution range of the maximum signal intensity of the measured signal in the preceding stage and the distribution range of the maximum signal intensity of the measured signal in the main observation period at a certain rotation angle of the rotating polarizer. [Figure 29] This is a flowchart illustrating the process for acquiring a stable time waveform as a film characteristic measurement method according to the fourth embodiment. [Modes for carrying out the invention]

[0012] Figure 1 is a schematic diagram showing the configuration of a film property measurement device according to one embodiment of the technology described herein. In Figure 1, the ellipsometer 10, which is a film property measurement device that performs ellipsometry, comprises a femtosecond laser oscillator 11, a beam splitter 12, a terahertz wave generator 13, an incident light elliptical mirror 14, and an incident light polarizer 15 as its components. The ellipsometer 10 also comprises a rotating polarizer 16, a reflected light polarizer 17, a reflected light elliptical mirror 18, a terahertz wave detector 19, an optical delay mechanism 20, and a control unit 21 as other components.

[0013] The femtosecond laser oscillator 11 emits femtosecond light pulses to the beam splitter 12. The beam splitter 12 splits the laser pulses emitted from the femtosecond laser oscillator 11 into two beams: a pump beam and a probe beam. The pump beam is directed to the terahertz wave generator 13, which generates terahertz light from the pump beam and radiates the terahertz waves toward the incident light elliptical mirror 14. The frequency of the terahertz waves radiated by the terahertz wave generator 13 is, for example, 0.1 to 5 THz. The incident light elliptical mirror 14 focuses the terahertz waves radiated from the terahertz wave generator 13 toward the substrate S.

[0014] An incident light polarizer 15 is interposed between the incident light elliptical mirror 14 and the substrate S. The incident light polarizer 15 transmits the linearly polarized component of the terahertz waves emitted from the terahertz wave generator 13, which includes p-polarized light, a polarization component that vibrates parallel to the incident plane perpendicular to the surface of the substrate S, and s-polarized light, a polarization component that vibrates perpendicular to the incident plane. The incident light polarizer 15 is configured such that the phase and amplitude of the transmitted p-polarized and s-polarized light are the same.

[0015] When p-polarized and s-polarized light is incident on a substrate S, it is reflected at the interface of the substrate S. The substrate S has, for example, a buffer layer formed on its surface and an epitaxial film made of SiC (silicon carbide) formed on the buffer layer. Therefore, the interface of the substrate S corresponds to the surface of the epitaxial film, the boundary between the epitaxial film and the buffer layer, and the boundary between the buffer layer and the substrate surface. At this time, the reflected light from each boundary and surface interferes, changing the amplitude of the p-polarized and s-polarized light. Also, since the speed of light passing through the buffer layer and epitaxial film changes according to the refractive index of the buffer layer and epitaxial film, the phase of the p-polarized and s-polarized light also changes. That is, the reflected p-polarized and s-polarized light have different phases and amplitudes, so the reflected p-polarized and s-polarized light constitutes elliptic polarization.

[0016] The rotating polarizer 16 rotates around the optical axis of the reflected light from the substrate S, for example in increments of 15°, and transmits the polarization component from the reflected light according to the rotation angle. The reflected light polarizer 17 stabilizes the detection accuracy of the polarization component transmitted through the rotating polarizer 16.

[0017] Here, the reflected p-polarized light is E p And the reflected s-polarized light is E s Let the rotation angle of the rotating polarizer 16 be θ. B Therefore, the polarization component E transmitted through the rotating polarizer 16 B It is expressed by the following formula.

[0018]

number

[0019] Also, let the transmission angle of the reflected light polarizer 17 be θ C Then, among the polarization components E B the polarization component E C that passes through the reflected light polarizer 17 is expressed by the following formula. And the reflected light ellipse mirror 18 condenses the polarization component E C towards the terahertz wave detector 19, and the terahertz wave detector 19 detects the electric field strength of the polarization component E C C in the following formula is a stray light component that does not depend on the rotating polarizer 16.

[0020]

Equation

[0021] In the present embodiment, the transmission angle θ C of the reflected light polarizer 17 is set to -π / 4. Therefore, in the formula of the polarization component E C cosθ c becomes 1 / √2, sinθ c becomes -1 / √2, and the polarization component E C is expressed by the following formula. A, B, and C' in the following formula are coefficients.

[0022]

Equation

[0023] In the polarization component E C of the above formula, when θ B is 0, it indicates the p-polarization that passes through the reflected light polarizer 17, and when θ B is π / 2, it indicates the s-polarization that passes through the reflected light polarizer 17. Therefore, if the coefficients A and B are calculated, the p-polarization and s-polarization that pass through the reflected light polarizer 17 can be obtained from the above formula. That is, the stray light component that does not depend on the angle of the rotating polarizer 16 included in the observation data can be removed from the polarization component E C and appropriate p-polarization and s-polarization can be obtained.

[0024] Furthermore, the probe light split by the beam splitter 12 is incident on the optical delay mechanism 20. The optical delay mechanism 20 has a mirror (retro reflector) 22 that reflects and folds back the probe light, and by moving the mirror 22 parallel to the probe light, the optical path length of the probe light is changed. Meanwhile, the polarization component E transmitted through the reflected light polarizer 17, which is terahertz light generated from the pump light... C Since the optical path length does not change, the optical delay mechanism 20 directs the polarization component E to the probe light. C A time delay is added to it.

[0025] Then, the probe light with time delay added has polarization component E C It arrives at the terahertz wave detector 19 later than the probe light. The terahertz wave detector 19 uses the probe light with an arbitrary time delay as a reference wave and the polarization component E C The time waveform of the electric field intensity can be detected. In addition, the terahertz wave detector 19 can detect the polarization component E C A current proportional to the electric field strength flows, and the terahertz wave detector 19 transmits a signal converted from these currents to the control unit 21. The control unit 21 obtains the time waveforms of the p-polarized and s-polarized electric field strengths from the received signal. Subsequently, the polarization component E detected by the terahertz wave detector 19 is used. C The p-polarized and s-polarized signals obtained from these sources are referred to as "measured p-polarized signals" and "measured s-polarized signals," respectively.

[0026] In ellipsometer 10, probe light and pump light (polarization component E C Multiple mirrors are placed along the optical path of the probe light and pump light, and by changing the direction of propagation of the probe light and pump light with each mirror, the ellipsometer 10 is prevented from becoming unnecessarily large.

[0027] The control unit 21 obtains the spectrum of the tangent tanΨ of the amplitude ratio of the electric field intensities of the measured p-polarized and measured s-polarized fields (hereinafter referred to as "measured amplitude ratio tangent tanΨ") by performing a Fourier transform on the time waveforms of the measured p-polarized and measured s-polarized fields. The control unit 21 also obtains the spectrum of the phase difference Δ between the measured p-polarized and measured s-polarized fields (hereinafter referred to as "measured phase difference Δ") by performing a Fourier transform on the time waveforms of the electric field intensities of the measured p-polarized and measured s-polarized fields.

[0028] In addition, in ellipsometer 10, the polarization component E C Since the detection of the time waveforms of the electric field intensity (measured p-polarization and measured s-polarization) is repeated, multiple time-continuous spectra of the measured amplitude ratio tangent tanΨ are obtained, and multiple time-continuous spectra of the measured phase difference Δ are obtained.

[0029] The measured amplitude ratio tangent tanΨ and measured phase difference Δ are indicators of the change in polarization state. The measured amplitude ratio tangent tanΨ and measured phase difference Δ are defined by the following equations. Note that in the following equations, r p is the Fresnel amplitude reflection coefficient for p-polarized light, and r s is the Fresnel amplitude reflection coefficient for s-polarized light. Also, δ rp is the phase of the measured p-polarization, and δ rs This represents the phase of the measured s-polarization.

[0030]

number

[0031] Furthermore, the control unit 21 constructs an optical model of the substrate S. At this time, the control unit 21 assumes the thickness of the buffer layer and epitaxial film, as well as optical constants (refractive index and extinction coefficient for each wavelength), as fitting variables. Then, using the assumed fitting variables, the control unit 21 calculates the spectrum of the amplitude ratio tangent tanΨ and the spectrum of the phase difference Δ by simulation using the optical model. Hereafter, the amplitude ratio tangent tanΨ calculated from the optical model will be referred to as "calculated amplitude ratio tangent tanΨ," and the phase difference Δ calculated from the optical model will be referred to as "calculated phase difference Δ." Subsequently, the control unit 21 performs fitting by changing the fitting variables until the spectrum of the measured amplitude ratio tangent tanΨ and the spectrum of the calculated amplitude ratio tangent tanΨ, and the spectrum of the measured phase difference Δ and the spectrum of the calculated phase difference Δ, are in close agreement.

[0032] Figure 2 is a diagram illustrating the fitting performed by the control unit 21. In Figure 2, solid lines represent the measured amplitude ratio tangent tanΨ and measured phase difference Δ, while dashed lines represent the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ. The upper spectral curve represents the phase difference Δ, and the lower spectral curve represents the amplitude ratio tangent tanΨ.

[0033] First, the control unit 21 compares the spectrum of the calculated amplitude ratio tangent tanΨ, calculated using the assumed fitting variables, with the spectrum of the measured amplitude ratio tangent tanΨ, and also compares the spectrum of the calculated phase difference Δ with the spectrum of the measured phase difference Δ.

[0034] If the spectrum of the calculated amplitude ratio tangent tanΨ does not match the spectrum of the measured amplitude ratio tangent tanΨ, and furthermore, the spectrum of the calculated phase difference Δ does not match the spectrum of the measured phase difference Δ (Figure 2(A)), the fitting variables are changed. Then, the spectrum of the calculated amplitude ratio tangent tanΨ calculated using the changed fitting variables is compared with the spectrum of the measured amplitude ratio tangent tanΨ, and the spectrum of the calculated phase difference Δ is compared with the spectrum of the measured phase difference Δ. The control unit 21 repeats changing the fitting variables until the spectrum of the calculated amplitude ratio tangent tanΨ closely matches the spectrum of the measured amplitude ratio tangent tanΨ, and furthermore, the spectrum of the calculated phase difference Δ closely matches the spectrum of the measured phase difference Δ. The degree of agreement between the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the measured amplitude ratio tangent tanΨ, and the degree of agreement between the spectrum of the calculated phase difference Δ and the spectrum of the measured phase difference Δ are determined, for example, by the least squares method.

[0035] Then, when the spectrum of the calculated amplitude ratio Ψ closely matches the spectrum of the measured amplitude ratio tangent tanΨ, and the spectrum of the calculated phase difference Δ closely matches the spectrum of the measured phase difference Δ, the control unit 21 outputs the fitting variables at that time as the fitting result. The control unit 21 also identifies the film thickness and optical constants of the buffer layer and epitaxial film as the actual film thickness and optical constants of the buffer layer and epitaxial film, based on the fitting result. Since the optical constants change according to the electrical characteristics of each film, the electrical characteristics (dielectric constant and carrier concentration) of the buffer layer and epitaxial film can be calculated inversely from the identified optical constants. As a result, the control unit 21 can measure parameters such as the film thickness and carrier concentration of the buffer layer and epitaxial film.

[0036] The fitting described above is performed by the terahertz wave detector 19, which detects the polarization component E C The time waveform of the electric field intensity is detected, and this process is executed each time the spectrum of the measured amplitude ratio tangent tanΨ or the measured phase difference Δ is obtained.

[0037] Next, a first embodiment of the technology relating to this disclosure will be described. However, p-polarized and s-polarized light in the ellipsometer 10 are susceptible to disturbances, and for example, even slight rattle in the rotation mechanism of the rotating polarizer 16 can cause variations in the amount of light (electric field intensity) transmitted through the rotating polarizer 16. As a result, the spectra of the measured amplitude ratio tangent tanΨ and measured phase difference Δ obtained from the time waveforms of the measured p-polarized and measured s-polarized electric field intensity will vary, and consequently, the carrier concentration measured by fitting will also vary, as has been confirmed by the applicant.

[0038] Figure 3 is a graph showing the variation in carrier concentration measured by fitting in the ellipsometer 10. The graph in Figure 3 plots the carrier concentration when the carrier concentration was measured 128 times by fitting. As shown in the graph in Figure 3, even when using the same substrate S, the minimum measured carrier concentration was approximately 3.7 × E 15 (cm -3 ) whereas the maximum carrier concentration measured was approximately 8.2 × E 15 (cm -3 As a result, the measured carrier concentrations vary considerably.

[0039] Conventionally, the ellipsometer 10 was used to measure numerous carrier concentrations by repeatedly performing fittings, and the average value of all measured carrier concentrations was obtained as the carrier concentration measurement result. This method is expected to reduce the influence of disturbances on carrier concentrations through averaging, thereby improving the reliability of the carrier concentration measurement results.

[0040] However, this method has the drawback of reducing throughput because it involves numerous fittings. On the other hand, simply reducing the number of carrier concentration measurements by fitting in order to suppress the decrease in throughput also presents a problem: the reliability of the carrier concentration measurement results obtained by averaging decreases.

[0041] In response to this, the film characteristic measurement method according to the first embodiment selects the measured amplitude ratio tangent tanΨ (measured value) at a specific frequency that is not significantly affected by external disturbances.

[0042] In ellipsometer 10, when fitting is repeated, the polarization component E C The time waveform of the electric field intensity is repeatedly detected, and the spectra of the measured amplitude ratio tangent tanΨ and the measured phase difference Δ are also repeatedly obtained. At this time, for example, a certain polarization component E C If the system is significantly affected by external disturbances, it is thought that the spectra of multiple measured amplitude ratio tangents tanΨ and measured phase difference Δ, which are acquired continuously over time, will vary. Therefore, the applicant considered using the spectrum of measured amplitude ratio tangents tanΨ with less variation among the multiple spectra of measured amplitude ratio tangents tanΨ acquired continuously over time, that is, the spectrum of measured amplitude ratio tangents tanΨ that is not significantly affected by external disturbances.

[0043] Specifically, the applicant focused on the measured amplitude ratio tangent tanΨ at a specific frequency in the spectrum of the measured amplitude ratio tangent tanΨ, and considered fitting using the measured amplitude ratio tangent tanΨ at the median specific frequency when the change in the measured amplitude ratio tangent tanΨ of three temporally consecutive specific frequencies is below a threshold. In this case, the change in the measured amplitude ratio tangent tanΨ of three temporally consecutive specific frequencies used in the study (hereinafter referred to as the "tanΨ stability index") g(m) is the sum of the absolute values ​​of the differences between the measured amplitude ratio tangent tanΨ of the median specific frequency and the measured amplitude ratio tangent tanΨ of the preceding and succeeding specific frequencies, and corresponds to the variability of the measured amplitude ratio tangent tanΨ of the median specific frequency, and is expressed by the following formula. Here, m is the number of measurements, ABS indicates the absolute value, and tanΨ(m) is the measured amplitude ratio tangent tanΨ of a specific frequency in the spectrum of the measured amplitude ratio tangent tanΨ at measurement m.

[0044]

number

[0045] Then, the measured amplitude ratio tangent tanΨ(m) at specific frequencies was selected when the tanΨ stability index g(m) became smaller than the threshold α. Because the tanΨ stability index g(m) for these selected specific frequencies is small, it is considered that they are not significantly affected by disturbances.

[0046] Figure 4 is a graph plotting selected measured amplitude ratio tangent tanΨ at specific frequencies when the tanΨ stability index g is smaller than the threshold α. Figure 4(A) shows the case where the threshold α is set to 0.002, and Figure 4(B) shows the case where the threshold α is set to 0.001. As shown in Figure 4, the premise for selecting measured amplitude ratio tangent tanΨ at specific frequencies is that the polarization component E C The time waveform of the electric field intensity was detected 128 times, and the spectrum of the measured amplitude ratio tangent tanΨ was also acquired 128 times.

[0047] As shown in Figure 4(A), when the threshold α was set to 0.002, the variation (difference between maximum and minimum values) of the measured amplitude ratio tangent tanΨ for the selected specific frequencies was 0.0047. At this time, the variation (difference between maximum and minimum values) of the carrier concentration measured by fitting using the spectrum corresponding to the measured amplitude ratio tangent tanΨ for the selected specific frequencies was ±0.15 × E 15 (cm -3 ) was.

[0048] Furthermore, as shown in Figure 4(B), when the threshold α was set to 0.001, the variation (difference between maximum and minimum values) of the measured amplitude ratio tangent tanΨ for the selected specific frequencies was 0.0023. At this time, the variation (difference between maximum and minimum values) of the carrier concentration measured by fitting using the spectrum corresponding to the measured amplitude ratio tangent tanΨ for the selected specific frequencies was ±0.07 × E 15 (cm -3 ) was.

[0049] On the other hand, the polarization component E CThe variation (difference between maximum and minimum values) of the measured amplitude ratio tangent tanΨ at a specific frequency in the spectrum of all measured amplitude ratio tangent tanΨ obtained by repeating the detection of the time waveform of the electric field intensity 128 times was 0.009. At this time, the variation (difference between maximum and minimum values) of the carrier concentration measured by fitting using the spectrum of all measured amplitude ratio tangent tanΨ was ±0.28 × E 15 (cm -3 ) was.

[0050] From the above, it was confirmed that the variation in the measured amplitude ratio tangent tanΨ of a specific frequency selected based on the tanΨ stability index g was smaller than the variation in the measured amplitude ratio tangent tanΨ of all specific frequencies obtained. Furthermore, it was confirmed that the carrier concentration measured using the spectrum corresponding to the measured amplitude ratio tangent tanΨ of a specific frequency selected based on the tanΨ stability index g was smaller than the carrier concentration measured using the spectrum of all measured amplitude ratio tangent tanΨ. In other words, it was found that by selecting the measured amplitude ratio tangent tanΨ of a specific frequency that is not significantly affected by disturbances based on the tanΨ stability index g, the variation in the measured carrier concentration can be suppressed and the reliability of the carrier concentration measurement results can be improved.

[0051] Furthermore, the reliability of the measured amplitude ratio tangent tanΨ at a specific frequency that falls within the variation of the measured amplitude ratio tangent tanΨ at multiple specific frequencies selected based on the tanΨ stability index g described above is considered high. Therefore, once the variation of the measured amplitude ratio tangent tanΨ at a selected specific frequency is obtained, it is considered that the reliability of the measured carrier concentration can be improved by performing fitting using the spectrum corresponding to the measured amplitude ratio tangent tanΨ at a specific frequency that falls within that variation in subsequent measurements.

[0052] Figure 5 is a flowchart showing the carrier concentration measurement process as a film characteristic measurement method according to the first embodiment. The carrier concentration measurement process in Figure 5 is performed in the ellipsometer 10 by the control unit 21 executing a program. In addition, before executing the carrier concentration measurement process in Figure 5, the control unit 21 measures the polarization component E C The time waveform of the electric field intensity is detected many times to obtain many spectra of the measured amplitude ratio tangent tanΨ, and the variation of the measured amplitude ratio tangent tanΨ at a specific frequency that is not significantly affected by disturbances, selected based on the tanΨ stability index g, is obtained (hereinafter referred to as the "reference variation of tanΨ"). The threshold α of the tanΨ stability index g used to select the measured amplitude ratio tangent tanΨ at a specific frequency for obtaining the reference variation of tanΨ is not particularly limited, but for example, 0.001 or 0.002 as described above can be used.

[0053] In the process shown in Figure 5, first, the femtosecond laser oscillator 11 emits a femtosecond light pulse, and the polarization component E generated at this time C The time waveform of the electric field intensity is detected, and the time waveforms of the electric field intensity in p-polarization and s-polarization are then obtained (step S51). Next, a new spectrum of the measured amplitude ratio tangent tanΨ is obtained from the time waveforms of the electric field intensity in p-polarization and s-polarization, and the measured amplitude ratio tangent tanΨ at a specific frequency is obtained from the obtained spectrum of the measured amplitude ratio tangent tanΨ (step S52), and it is determined whether the obtained measured amplitude ratio tangent tanΨ at the specific frequency falls within the reference variation of tanΨ (step S53).

[0054] In step S53, if it is determined that the measured amplitude ratio tangent tanΨ at a specific frequency obtained does not fall within the reference variation of tanΨ, the measurement cycle is increased by one and the process returns to step S51 (step S54). Steps S51 and S52 are repeated to obtain the measured amplitude ratio tangent tanΨ at a specific frequency from the spectrum of the new measured amplitude ratio tangent tanΨ.

[0055] In step S53, if it is determined that the measured amplitude ratio tangent tanΨ at a specific frequency obtained falls within the reference variation of tanΨ, fitting is performed using the spectrum corresponding to the measured amplitude ratio tangent tanΨ at the specific frequency obtained, and the carrier concentration is measured (step S55). After that, this process is terminated.

[0056] According to the carrier concentration measurement process shown in Figure 5, fitting is performed using the spectrum corresponding to the measured amplitude ratio tangent tanΨ at a specific frequency that falls within the variation of the measured amplitude ratio tangent tanΨ at that specific frequency, which is not significantly affected by disturbances. In other words, fitting is performed using a spectrum of a highly reliable measured amplitude ratio tangent tanΨ. This improves the reliability of carrier concentration measurements.

[0057] Furthermore, according to the carrier concentration measurement process shown in Figure 5, if an actual amplitude ratio tangent tanΨ that falls within the reference variation of tanΨ is obtained, subsequent acquisition of the actual amplitude ratio tangent tanΨ is not performed, thus improving throughput.

[0058] Incidentally, as mentioned above, since the spectrum of the measured amplitude ratio tangent tanΨ is obtained from the time waveforms of the electric field intensity of measured p-polarized and measured s-polarized signals, the applicant also confirmed the relationship between the stability of the signal values ​​(luminance) of measured p-polarized and measured s-polarized signals and the reliability of the measured amplitude ratio tangent tanΨ at a specific frequency. Specifically, the stability indices of measured p-polarized and measured s-polarized signals corresponding to the measured amplitude ratio tangent tanΨ at a specific frequency where the tanΨ stability index g is smallest were confirmed. The stability index of measured p-polarized signals is the change in luminance of three measured p-polarized signals acquired consecutively in time, and, similar to the tanΨ stability index g, is expressed as the sum of the absolute values ​​of the differences between the luminance of the median measured p-polarized signal and the luminances of the preceding and succeeding measured p-polarized signals. Similarly, the stability index of measured s-polarized signals is the change in luminance of three measured s-polarized signals acquired consecutively in time, and, similar to the stability index of measured s-polarized signals, is expressed as the sum of the absolute values ​​of the differences between the luminance of the median measured s-polarized signal and the luminances of the preceding and succeeding measured s-polarized signals.

[0059] At this time, the applicant confirmed that the stability indices of the measured p-polarized and measured s-polarized light corresponding to the measured amplitude ratio tangent tanΨ with the smallest tanΨ stability index g were the smallest. In other words, it was confirmed that there is a correlation between the luminance stability of the measured p-polarized and measured s-polarized light and the reliability of the measured amplitude ratio tangent tanΨ at a specific frequency. Therefore, in the film characteristic measurement method according to this embodiment, it was considered that a highly reliable carrier concentration can be measured by selecting measured p-polarized and measured s-polarized light with high luminance stability and fitting the spectra of the measured amplitude ratio tangent tanΨ corresponding to these measured p-polarized and measured s-polarized light.

[0060] Furthermore, in this embodiment, a highly reliable spectrum of the measured amplitude ratio tangent tanΨ was obtained based on the variation of the measured amplitude ratio tangent tanΨ at specific frequencies that are not significantly affected by disturbances, selected based on the tanΨ stability index g, and fitting was performed using this spectrum of the measured amplitude ratio tangent tanΨ.

[0061] However, fitting for measuring carrier concentration can also be performed using the spectrum of the measured phase difference Δ. Therefore, first, measured phase difference Δ at specific frequencies that are not significantly affected by disturbances is selected based on the stability index of the measured phase difference Δ. Then, based on the variability of the selected measured phase difference Δ, a highly reliable spectrum of the measured phase difference Δ is obtained, and by performing fitting using the obtained highly reliable spectrum of the measured phase difference Δ, it was thought that a reliable carrier concentration could be measured.

[0062] Next, a second embodiment of the technology relating to this disclosure will be described. In the ellipsometer 10, in one measurement of the carrier concentration in the terahertz wave detector 19, the rotating polarizer 16 rotates once in increments of 15°, for example. At this time, the mirror 22 of the optical delay mechanism 20 is moved for each rotation angle of the rotating polarizer 16, thereby polarizing the polarization component E CThe time waveform of the electric field intensity (raw electric field intensity) is detected. Therefore, when the rotating polarizer 16 rotates once during one carrier concentration measurement, 25 polarization components E are detected, as shown in Figure 6. C The time waveform of the electric field intensity is detected. Then, if the carrier concentration is measured 128 times in the ellipsometer 10, a total of 3200 polarization components E are detected. C The time waveform of the electric field intensity is detected.

[0063] Polarization component E C The time waveform of the electric field intensity is composed of a preliminary stage detected before the incident light enters the substrate S, a main observation period stage detected when the incident light enters the substrate S, and a post-stage stage detected after the incident light enters the substrate S, in accordance with the movement of the mirror 22 of the optical delay mechanism 20 (Figure 6). Here, detection of the preliminary stage requires 8 ps (picoseconds), detection of the main observation period stage requires 10 ps, ​​and detection of the post-stage stage requires 10 ps.

[0064] Incidentally, since the object to which the incident light is irradiated does not change in the preceding stage, the main observation period, and the subsequent stage, the electric field strength (measured value) is theoretically constant in each of these stages. However, due to minute rattles in the rotation mechanism of the rotating polarizer 16, the polarization component E C Large fluctuations in electric field strength can occur in the preceding, main observation period, and subsequent parts of the time waveform of the electric field strength. C Large fluctuations in electric field intensity that occur in the time waveform of the electric field intensity contribute to variations in the brightness of p-polarized and s-polarized light, the spectra of the measured amplitude ratio tangent tanΨ, the spectra of the measured phase difference Δ, and the carrier concentration obtained afterward.

[0065] Therefore, in a single carrier concentration measurement, after rotating the rotating polarizer 16 once (360° rotation), the polarization component E detected at any rotation angle is... CIf it is found that there are large fluctuations in the electric field strength in the time waveform of the electric field strength, the rotation angle of the rotating polarizer 16 is initialized, and the rotating polarizer 16 is rotated again to determine the polarization component E at each rotation angle. C It was necessary to re-detect the time waveform of the electric field intensity. As a result, there was a problem of reduced throughput.

[0066] In response to this, the film characteristic measurement method according to the second embodiment uses the polarization component E C Based on the preceding portion of the time waveform of the electric field strength, it is determined whether or not large fluctuations in the electric field strength occur during the main observation period.

[0067] By the way, in the previous stage, the incident light does not enter the substrate S, so the polarization component E C The time waveform of the electric field intensity reflects the elementary state of the ellipsometer 10 excluding the substrate S. Therefore, the polarization component E C If a large fluctuation in electric field strength occurs in the preceding stage of the time waveform of the electric field strength, it is considered that there is some kind of abnormality in the ellipsometer 10, for example, an abnormality in the rotation mechanism of the rotating polarizer 16. Furthermore, in such a case, it is considered that the abnormality in the rotation mechanism of the rotating polarizer 16 will continue in the subsequent stages, and therefore the detected polarization component E C It is also thought that large fluctuations in electric field strength are likely to occur in the time waveform of the electric field strength. Therefore, the applicant has proposed that the polarization component E C We investigated whether it is possible to predict the occurrence of fluctuations in electric field strength during the main observation period using the preceding portion of the time waveform of the electric field strength.

[0068] First, the polarization component E of the preceding stage, the main observation period, and the subsequent stage. C The change in the fluctuation of electric field intensity in the time waveform was confirmed. Figure 7 shows the raw (polarization component E) of the preceding stage, the main observation period, and the subsequent stage. C This graph shows the fluctuations in electric field intensity in the time waveform of the electric field intensity of ). In Figure 7, the data number on the horizontal axis corresponds to the polarization component E for each rotation angle of the rotating polarizer 16. CThis corresponds to the detection of the time waveform of the electric field intensity. The fluctuation of the electric field intensity on the vertical axis is the standard deviation of the electric field intensity during the preceding stage, the main observation period, and the subsequent stage. Since the 25 data numbers correspond to the number of detections in one rotation of the rotating polarizer 16, the graph in Figure 7 shows data for four consecutive rotations of the rotating polarizer 16. Figure 7(A) shows the fluctuation of the electric field intensity during the main observation period (hereinafter abbreviated as "fluctuation of the main observation period"). Figure 7(B) shows the fluctuation of the electric field intensity during the preceding and subsequent stages (hereinafter abbreviated as "fluctuation of the preceding stage" and "fluctuation of the subsequent stage," respectively).

[0069] As shown in Figures 7(A) and 7(B), it was confirmed that the patterns of change in fluctuations during the main observation period, the preceding fluctuations, and the subsequent fluctuations were similar.

[0070] Furthermore, the applicant plotted and compared all the fluctuations detected in the preceding stage, the main observation period, and the subsequent stage during 128 carrier concentration measurements. Figure 8 is a graph showing the fluctuations in the preceding stage, the main observation period, and the subsequent stage during 128 carrier concentration measurements. As described above, 25 polarization components E were detected in one carrier concentration measurement. C Since the time waveform of the electric field intensity is detected, 3200 fluctuations of electric field intensity are plotted in the graph of Figure 8. Furthermore, Figure 8(A) shows the fluctuations in the preceding stage, Figure 8(B) shows the fluctuations during the main observation period, and Figure 8(C) shows the fluctuations in the subsequent stage.

[0071] As shown in Figures 8(A) to 8(C), it was confirmed that fluctuations in the electric field intensity for data numbers 200 to 275 and 700 to 750 were consistently reduced in each graph, for example, in the fluctuations during the main observation period, the preceding stage, and the subsequent stage (see the white arrows in each figure). Therefore, it was confirmed from each graph in Figure 8 that the patterns of change in the fluctuations during the main observation period, the preceding stage, and the subsequent stage are similar.

[0072] Furthermore, the applicant confirmed the relationship between the average value of the electric field intensity fluctuations for each period in 128 carrier concentration measurements and the measured carrier concentration. Figure 9 is a graph showing the relationship between the average value of the electric field intensity fluctuations for each period in 128 carrier concentration measurements and the carrier concentration. Figure 9(A) shows the relationship between the average value of the fluctuations in the preceding stage and the carrier concentration, Figure 9(B) shows the relationship between the average value of the fluctuations in the main observation period and the carrier concentration, and Figure 9(C) shows the relationship between the average value of the fluctuations in the subsequent stage and the carrier concentration.

[0073] As shown in Figures 9(A) to 9(C), it was confirmed that a common trend was observed in each graph: a smaller average value of electric field intensity fluctuations correlated with smaller carrier concentration variability. Considering the similar distribution patterns of carrier concentrations in each graph, it was concluded that the fluctuation patterns in the main observation period, the preceding fluctuations, and the subsequent fluctuations were similar.

[0074] Based on the results of the analysis of the graphs in Figures 7 to 9 above, the applicant has determined that the polarization component E C We have found that if a large fluctuation in electric field strength occurs in the preceding part of the time waveform of the electric field strength, there is a high probability that a large fluctuation in electric field strength will also occur in the main observation period. In other words, the applicant has found that the polarization component E C We obtained the insight that the occurrence of fluctuations in electric field strength during the main observation period can be predicted based on the preceding portion of the time waveform of the electric field strength.

[0075] Furthermore, the applicant uses the stability index g of the measured amplitude ratio tangent tanΨ at a specific frequency obtained in 128 carrier concentration measurements, and the polarization component E detected in 128 carrier concentration measurements. C The relationship between the time waveform of the electric field intensity and the preceding fluctuations was also confirmed. Figure 10 shows the change in the stability index g of tanΨ and the polarization component E CThis graph compares the change in the fluctuation pattern of the preceding stage in the time waveform of the electric field intensity. Figure 10(A) shows the change in the tanΨ stability index g, and Figure 10(B) shows the change in the fluctuation pattern of the preceding stage. The horizontal axis of Figure 10(A) represents the number of times the carrier concentration was measured, and the horizontal axis of Figure 10(B) represents the polarization component E for each rotation angle of the rotating polarizer 16. C The data number corresponds to the detection of the time waveform of the electric field strength, and the data number corresponds to 25 times the measurement count in Figure 10(A). As shown in Figures 10(A) and 10(B), it was confirmed that when the tanΨ stability index g decreases, the fluctuations in the preceding stage also decrease. Therefore, it was thought that when the fluctuation of the electric field strength is small, the tanΨ stability index g decreases, and the reliability of the measured amplitude ratio tangent tanΨ obtained at that time increases, and thus the reliability of the measured carrier concentration also improves.

[0076] Furthermore, based on the above findings, the applicant has determined that when the rotating polarizer 16 is rotated, the polarization component E detected at a certain rotation angle... C If a large fluctuation in electric field strength occurs in the preceding part of the time waveform of the electric field strength, the polarization component E C Before detecting the portion of the time waveform of the electric field intensity during the main observation period, the polarization component E at the rotation angle is detected. C We devised a method to re-detect the time waveform of the electric field intensity.

[0077] In this case, it is necessary to set a threshold (hereinafter referred to as the "fluctuation generation threshold") to determine whether or not a large fluctuation in electric field strength occurred in the preceding stage, and the applicant set this threshold based on the carrier concentration.

[0078] Figure 11 is a diagram illustrating the method for setting the fluctuation generation threshold. Figure 11 shows the relationship between the average value of the preliminary fluctuations in 128 carrier concentration measurements and the amount of shift of each carrier concentration from the average value of the 128 measured carrier concentrations.

[0079] As shown in Figure 11, the allowable shift amount is set as the shift amount from the average carrier concentration to the acceptable carrier concentration as a measurement result. In addition, a regression line is obtained between the average value of the fluctuations in the previous stage and the shift amount of each carrier concentration, and the average value of the fluctuations in the previous stage corresponding to the allowable shift amount is obtained from this regression line. Then, the average value of the fluctuations in the previous stage corresponding to the allowable shift amount is set as the fluctuation generation threshold. Note that the method of setting the fluctuation generation threshold shown in Figure 11 is just one example, and the fluctuation generation threshold may be set by other methods.

[0080] Figure 12 is a flowchart showing the time waveform detection process as a film characteristic measurement method according to the second embodiment. The time waveform detection process in Figure 12 is performed when the carrier concentration is measured once in the ellipsometer 10, by the control unit 21 executing a program.

[0081] First, the rotation angle of the rotating polarizer 16 is initialized to 0° (step S121). Then, the polarization component E is detected by the terahertz wave detector 19. C The preceding portion of the time waveform of the electric field intensity is detected (step S122).

[0082] Next, it is determined whether the detected fluctuation in the preceding stage is smaller than the fluctuation generation threshold (step S123). If the fluctuation in the preceding stage in the detected time waveform is greater than or equal to the fluctuation generation threshold, the process returns to step S122, and the polarization component E C The detection of the time waveform of the electric field intensity is restarted from the previous step.

[0083] In step S123, if the preceding fluctuation in the detected time waveform is smaller than the fluctuation generation threshold, then the polarization component E C The portion of the time waveform of the electric field intensity during the main observation period is detected (step S124), and further, the polarization component E CThe later stages of the time waveform of the electric field intensity are detected. If the time required to detect the main observation period portion is short, the detection of the main observation period portion may be performed without waiting for the judgment result of step S123 (step S123 may be skipped). In this case, if the fluctuation of the main observation period portion in the detected time waveform is greater than or equal to the fluctuation generation threshold, the detected time waveform may be discarded and the process may return to step S122.

[0084] Next, it is determined whether the rotation angle of the rotating polarizer 16 has reached 360° (step S125). If the rotation angle of the rotating polarizer 16 has not reached 360°, the rotation angle of the rotating polarizer 16 is changed so that it increases by 15° (step S126). Then, the process returns to step S122, and the polarization component E is determined at the changed rotation angle. C The preceding portion of the time waveform of the electric field intensity is detected. In step S124, if the rotation angle of the rotating polarizer 16 reaches 360°, this process is terminated.

[0085] According to the time waveform detection process in Figure 12, if the detected fluctuation in the preceding stage is above the fluctuation generation threshold, the subsequent polarization component E C Without detecting the main observation period portion or subsequent stages of the time waveform, the polarization component E C The detection of the time waveform of the electric field intensity is restarted from the previous step. If a large fluctuation occurs in the detected time waveform, the polarization component E is checked once. C After waiting for the detection of the later part of the time waveform to be completed, the polarization component E C This eliminates the need to recalculate the time waveform. Therefore, throughput can be improved.

[0086] Furthermore, as a result of performing the time waveform detection process shown in Figure 12, time waveforms containing large fluctuations in electric field strength are no longer detected. This improves the reliability of the measured amplitude ratio tangent tanΨ and measured phase difference Δ obtained by the Fourier transform of the electric field strength time waveform. Moreover, it improves the reliability of the carrier concentration measurement results.

[0087] In the time waveform detection process shown in Figure 12, a fluctuation threshold was set to determine whether a large fluctuation in electric field strength occurred in the preceding stage. However, it is also possible to use a trained model to have artificial intelligence determine whether a large fluctuation in electric field strength occurred in the preceding stage. In this case, for example, a trained model configured as a convolutional neural network is generated by machine learning using training data. The training data here includes fluctuations in the preceding stage of numerous detected time waveforms of electric field strength, and each of these preceding stage fluctuations is associated with the result of whether or not each preceding stage fluctuation is acceptable from a reliability standpoint. When a preceding stage fluctuation is input to the generated trained model, it outputs a result indicating whether or not that preceding stage fluctuation is acceptable from a reliability standpoint.

[0088] Next, a third embodiment of the technology relating to this disclosure will be described. Conventionally, the carrier concentration of an epitaxial film made of SiC on a substrate S is measured by the mercury probe CV method or the non-contact CV method. For example, in the mercury probe CV method, a mercury probe electrode is brought into direct contact with the epitaxial film on the substrate S to form a Schottky junction, and the capacitance (C)-reverse voltage (V) characteristics are measured across this Schottky junction. The carrier concentration is then calculated from the measurement results of the CV characteristics. In the non-contact CV method, the change in depletion capacitance of a PN junction is measured non-contact using a pseudo-electrode created by corona discharge.

[0089] On the other hand, as mentioned above, in recent years, the carrier concentration of epitaxial films is measured by ellipsometry using terahertz waves. In ellipsometry, the carrier concentration is measured by fitting the measured amplitude ratio tangent tanΨ and measured phase difference Δ spectra with the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ spectra calculated from the optical model of the substrate S.

[0090] The applicant measured the carrier concentration of an epitaxial film on the same substrate S using both mercury probe CV method and ellipsometry. Figure 13 is a graph showing the carrier concentrations of the epitaxial film measured using mercury probe CV method and ellipsometry, respectively. In this case, as shown in Figure 13, the carrier concentration measured using ellipsometry varied with respect to the X direction of the substrate S, and there was a large difference (up to approximately 1.2 × E) between it and the carrier concentration measured using mercury probe CV method. 16 (cm -3 )) occurred partially.

[0091] In ellipsometry, the reflection of incident p-polarized and s-polarized light at multiple interfaces of the substrate S was considered to be the cause of the difference shown in Figure 13. Therefore, the applicant first performed ellipsometry using only substrate S without a buffer layer or epitaxial film. Furthermore, ellipsometry was performed using substrate S with only a buffer layer formed on it. Then, taking into account the parameters (carrier concentration, etc.) (characteristics) of the substrate S and buffer layer obtained at this time, ellipsometry was performed using substrate S with an epitaxial film formed on it, and it was confirmed that the large difference described above no longer occurred.

[0092] However, this method requires ellipsometry not only using the substrate S on which the epitaxial film is formed, but also using the substrate S alone or the substrate S on which only the buffer layer is formed. This results in a very time-consuming measurement of carrier concentration and a decrease in throughput.

[0093] In response to this, the film characteristic measurement method according to the third embodiment allows for the determination of the carrier concentration of the epitaxial film with suppressed variation simply by performing ellipsometry using a substrate S on which a buffer layer or epitaxial film is formed.

[0094] By the way, the applicant first considers the polarization component E CThe relationship between the signal values ​​(luminance) and frequency of the measured p-polarized and s-polarized signals obtained was examined. Figure 14 is a graph showing the relationship between the luminance and frequency of the measured p-polarized and s-polarized signals, with Figure 14(A) showing the measured p-polarized signal and Figure 14(B) showing the measured s-polarized signal. As shown in Figure 14, the luminance of the measured p-polarized and s-polarized signals changes as the frequency changes, but the luminance values ​​of the measured p-polarized and s-polarized signals are much larger near 1 THz than near 2 THz. Therefore, it appears preferable to measure the buffer concentration using the measured p-polarized and s-polarized signals near 1 THz.

[0095] On the other hand, the applicant used an optical model of the substrate S and performed simulations by changing the fitting variables to confirm the relationship between the sensitivity of the calculated amplitude ratio tangent tanΨ to changes in carrier concentration (calculated amplitude ratio tangent tanΨ divided by carrier concentration) and frequency. Figure 15 is a graph showing the relationship between the sensitivity of the calculated amplitude ratio tangent tanΨ to changes in carrier concentration and frequency in the optical model. As shown in Figure 15, the sensitivity of the calculated amplitude ratio tangent tanΨ to changes in carrier concentration is much greater near 2 THz than near 1 THz.

[0096] In fitting using an optical model, the fitting variable is changed to match the spectrum of the calculated amplitude ratio tangent tanΨ to the spectrum of the measured amplitude ratio tangent tanΨ. Here, in fitting that matches spectra across all frequencies (0.5 THz to 3 THz), the fitting is performed not only in the frequency range where the calculated amplitude ratio tangent tanΨ is highly sensitive to changes in carrier concentration, but also in the frequency range where it is less sensitive to changes in carrier concentration. Therefore, when the fitting variable is changed in minute increments, the spectrum of the calculated amplitude ratio tangent tanΨ does not change dynamically, and a fine-tuning of the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the measured amplitude ratio tangent tanΨ is not possible. As a result, the reliability of the fitting variable when the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the measured amplitude ratio tangent tanΨ are nearly identical cannot be said to be very high.

[0097] On the other hand, in fitting the spectra of the calculated amplitude ratio tangent tanΨ in the frequency range where it is highly sensitive to changes in carrier concentration, even a small change in the fitting variable causes the spectrum of the calculated amplitude ratio tangent tanΨ to change dynamically. This allows for fine-tuning of the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the measured amplitude ratio tangent tanΨ. As a result, the reliability of the fitting variable is considered to be high when the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the measured amplitude ratio tangent tanΨ are in near agreement.

[0098] Therefore, based on the example in the graph of Figure 15, it is considered preferable to perform fitting in the frequency range near 2 THz from the standpoint of obtaining highly reliable fitting variables, and consequently, from the standpoint of reliable carrier concentration measurement.

[0099] Furthermore, the applicant states that the polarization component E C The frequency-dependent changes in the measured p-polarized and s-polarized signal values ​​(luminance) were examined when detection was repeated. Figure 16 shows the polarization component E C These graphs show the changes in brightness of measured p-polarized and measured s-polarized signals when detection is repeated. Figure 16(A) shows the change in brightness of measured p-polarized signals at 1 THz, Figure 16(B) shows the change in brightness of measured s-polarized signals at 1 THz, Figure 16(C) shows the change in brightness of measured p-polarized signals at 2 THz, and Figure 16(D) shows the change in brightness of measured s-polarized signals at 2 THz. For example, comparing the graph in Figure 16(A) with the graph in Figure 16(C), the variation in brightness of measured p-polarized signals is smaller at 2 THz than at 1 THz. Also, comparing the graph in Figure 16(B) with the graph in Figure 16(D), the variation in brightness of measured s-polarized signals is also smaller at 2 THz than at 1 THz. From these findings, it was confirmed that measured s-polarized and measured p-polarized signals in the frequency range near 2 THz are more reliable than measured s-polarized and measured p-polarized signals in the frequency range near 1 THz.

[0100] Incidentally, the spectra corresponding to the measured amplitude ratio tangent tanΨ obtained from the time waveforms of the electric field intensity of highly reliable measured s-polarized and measured p-polarized fields are also considered to be highly reliable, and it is expected that a highly reliable carrier concentration can be measured by fitting using the obtained spectra corresponding to the measured amplitude ratio tangent tanΨ. Therefore, in order to measure a highly reliable carrier concentration, it is considered preferable to perform fitting in the frequency range near 2 THz, even from the viewpoint of the variability in the brightness of measured s-polarized and measured p-polarized fields.

[0101] From the above, it was found that the spectrum of the calculated amplitude ratio tangent tanΨ has a frequency region that is highly sensitive to changes in parameters such as carrier concentration. Similarly, it is thought that the spectrum of the calculated phase difference Δ also has a frequency region that is highly sensitive to changes in parameters such as carrier concentration.

[0102] Here, if the spectra (measured values) of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ can be divided into frequency regions that are highly sensitive to changes in each parameter, then it is thought that each parameter can be measured accurately by fitting using each divided frequency region.

[0103] Furthermore, in ellipsometry using a substrate S on which a buffer layer or epitaxial film is formed, if the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ can be separated for each parameter into frequency regions that are highly sensitive to changes in each parameter, it is conceivable that it would be possible to eliminate the need to perform ellipsometry using only a substrate S on which no buffer layer or epitaxial film is formed, or using a substrate S on which only a buffer layer is formed.

[0104] Therefore, the applicant used an optical model to simulate and confirm whether there are frequency regions that are highly sensitive to changes in each parameter in the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the calculated phase difference Δ, and whether these frequency regions can be distinguished. Specifically, the applicant first constructed an optical model consisting of an epitaxial film, a buffer layer, and a substrate, as shown in Figure 17, and used this optical model to simulate and calculate the amount of change in the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ when each parameter was changed.

[0105] The parameters used to be varied were the carrier concentration, mobility, and scattering time of the substrate; the carrier concentration, mobility, scattering time, and film thickness of the buffer layer; and the carrier concentration, mobility, scattering time, and film thickness of the epitaxial film. In the simulation, as shown in Table 1 below, a median value (reference value) was set for each parameter, and the amount of variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ was calculated when each parameter was changed by approximately ±10% from the median value.

[0106] [Table 1]

[0107] The variation in the calculated amplitude ratio tangent tanΨ is expressed as the increase or decrease in the calculated amplitude ratio tangent tanΨ at the upper and lower limits of the range of change for each parameter, with respect to the calculated amplitude ratio tangent tanΨ at the median value of each parameter, where tanΨ at the median value of each parameter is set to 1. Similarly, the variation in the calculated phase difference Δ is expressed as the increase or decrease in the calculated phase difference Δ at the upper and lower limits of the range of change for each parameter, with respect to the calculated phase difference Δ at the median value of each parameter, where Δ at the median value of each parameter is set to 1. Therefore, the variation in the calculated amplitude ratio tangent tanΨ and the variation in the calculated phase difference Δ correspond to the sensitivity of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ when the changes in each parameter are varied.

[0108] Figure 18 is a graph showing the variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when each parameter is changed by approximately ±10% from the median value for all parameters. Figure 18(A) shows the variation in the calculated amplitude ratio tangent tanΨ, and Figure 18(B) shows the variation in the calculated phase difference Δ. Note that scattering time is proportional to mobility and shows the same trend, so it is omitted from Figures 18, 20, and 21 below.

[0109] As shown in Figure 18(A), it was confirmed that in the frequency range below 1 THz, the amount of variation in the calculated amplitude ratio tangent tanΨ was large when the carrier concentration and mobility of the substrate were changed, while the amount of variation in the calculated amplitude ratio tangent tanΨ was almost zero when other parameters were changed. Furthermore, as shown in Figure 18(B), it was confirmed that the amount of variation in the calculated phase difference Δ was large in the entire frequency range when the thickness of the epitaxial film was changed.

[0110] This suggests that the thickness of the epitaxial film can be accurately measured by fitting the calculated phase difference Δ spectrum across the entire frequency range. However, when the thickness of the epitaxial film is changed, the variation in the calculated phase difference Δ shows a peak between 1.4 THz and 2.4 THz. Near this peak, the calculated phase difference Δ is thought to fluctuate extremely in response to changes in the thickness of the epitaxial film, i.e., it fluctuates nonlinearly, making fitting somewhat difficult. Furthermore, the formation of the peak may be strongly influenced by changes in other parameters. Therefore, it was considered that the thickness of the epitaxial film could be accurately measured by fitting the calculated phase difference Δ spectrum using frequencies between 1.0 THz and 1.3 THz and above 2.5 THz, excluding the frequency range between 1.4 THz and 2.4 THz.

[0111] Furthermore, it was considered that the carrier concentration and mobility of the substrate could be accurately measured by fitting the spectrum of the calculated amplitude ratio tangent tanΨ in the frequency range below 1 THz, for example, in the frequency range between 0.8 THz and 1.0 THz.

[0112] Incidentally, as shown in Figure 19, the relationship between carrier concentration and mobility is publicly known from literature, etc., so for example, after measuring the carrier concentration of the substrate by fitting, the mobility of the substrate can also be determined from the measured carrier concentration of the substrate based on the relationship between carrier concentration and mobility shown in Figure 19.

[0113] In this manner, after measuring the thickness of the epitaxial film and the carrier concentration and mobility of the substrate by fitting using the spectra of the divided calculated amplitude ratio tangent tanΨ and calculated phase difference Δ, the applicant focused on the amount of variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when the remaining parameters, excluding the thickness of the epitaxial film and the carrier concentration and mobility of the substrate, were changed.

[0114] Figure 20 is a graph showing the variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when each parameter other than the epitaxial film thickness, substrate carrier concentration, and mobility is changed by approximately ±10% from the median value.

[0115] As shown in Figure 20(B), it was confirmed that the amount of variation in the calculated phase difference Δ when the thickness of the buffer layer is changed is large across the entire frequency range. Therefore, it was thought that the thickness of the buffer layer could be accurately measured by fitting the spectrum of the calculated phase difference Δ across the entire frequency range. However, the amount of variation in the calculated phase difference Δ when the thickness of the buffer layer is changed also has a peak between 1.4 THz and 2.4 THz. Therefore, it was thought that the thickness of the buffer layer could be accurately measured by fitting the spectrum of the calculated phase difference Δ in the frequency range between 1.0 THz and 1.3 THz and above 2.5 THz, excluding the frequency range between 1.4 THz and 2.4 THz.

[0116] Incidentally, using the calculated phase difference Δ spectrum in the frequency range between 1.0 THz and 1.3 THz or above 2.5 THz is common to the measurement of epitaxial film thickness described above. Therefore, it is also possible that it is difficult to distinguish between the measurement of buffer layer thickness and the measurement of epitaxial film thickness using only fitting with the calculated phase difference Δ spectrum in the frequency range between 1.0 THz and 1.3 THz or above 2.5 THz.

[0117] On the other hand, comparing Figure 18(A) and Figure 20(A), in the frequency range of 2.4 THz and above, the pattern of change in the calculated amplitude ratio tangent tanΨ when the thickness of the epitaxial film is changed is different from the pattern of change in the calculated amplitude ratio tangent tanΨ when the thickness of the buffer layer is changed.

[0118] Therefore, in order to distinguish it from the measurement of the epitaxial film thickness, the measurement of the buffer layer thickness involves not only fitting using the spectrum of the calculated phase difference Δ in the frequency range between 1.0 THz and 1.3 THz and above 2.5 THz, but also fitting using the spectrum of the calculated amplitude ratio tangent tanΨ in the frequency range above 2.4 THz.

[0119] In this manner, after measuring the thickness of the buffer layer by fitting using the spectra of the divided calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ, the applicant focused on the amount of variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when the remaining parameters, excluding the thickness of the buffer layer, were changed.

[0120] Figure 21 is a graph showing the variation in the calculated amplitude ratio tangent tanΨ and calculated phase difference Δ when each parameter other than the epitaxial film thickness, substrate carrier concentration and mobility, and buffer layer thickness is changed by approximately ±10% from the median value.

[0121] As shown in Figure 21(A), it was confirmed that the amount of variation in the calculated amplitude ratio tangent tanΨ when the carrier concentration of the epitaxial film is changed is large in the frequency range between 1 THz and 1.8 THz. Also, as shown in Figure 21(B), it was confirmed that the amount of variation in the calculated phase difference Δ when the carrier concentration of the epitaxial film is changed is also large in this frequency range between 1 THz and 1.8 THz.

[0122] This suggests that the carrier concentration of the epitaxial film can be accurately measured by fitting the spectrum of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ in the frequency range between 1 THz and 1.8 THz.

[0123] From the above, we found that in the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ obtained using an optical model consisting of an epitaxial film, a buffer layer, and a substrate, there exists a frequency region that is highly sensitive to changes in each parameter. Therefore, it was found that the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ obtained by ellipsometry using a substrate S on which a buffer layer and an epitaxial film are formed can be divided into frequency regions that are highly sensitive to changes in each parameter.

[0124] Figure 22 is a flowchart showing the parameter measurement process as a film characteristic measurement method according to the third embodiment. The parameter measurement process in Figure 22 is based on the finding that, in the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ described above, there exists a frequency range for each parameter that is highly sensitive to changes in each parameter. Furthermore, the parameter measurement process in Figure 22 is executed in the ellipsometer 10 by the control unit 21 executing a program. Note that the execution of the parameter measurement process in Figure 22 is performed in the ellipsometer 10 by measuring the polarization component E of the reflected light from the substrate S on which the buffer layer and epitaxial film are formed. C It is assumed that the function has been detected and that the spectra of the measured amplitude ratio tangent tanΨ and measured phase difference Δ have been obtained.

[0125] First, the thickness of the epitaxial film is measured by fitting using the spectrum of the calculated phase difference Δ in the frequency range between 1.0 THz and 1.3 THz and above 2.5 THz (step S221).

[0126] Next, fitting is performed using the spectrum of the calculated amplitude ratio tangent tanΨ in the frequency domain between 0.8 THz and 1.0 THz to measure the carrier concentration of the substrate. At this time, the mobility of the substrate is calculated from the carrier concentration of the substrate based on the relationship between carrier concentration and mobility shown in Figure 19 (Step S222).

[0127] Next, fitting is performed using the spectrum of the calculated phase difference Δ in the frequency range between 1.0 THz and 1.3 THz and above 2.5 THz, and fitting is also performed using the spectrum of the calculated amplitude ratio tangent tanΨ in the frequency range above 2.4 THz, and the thickness of the buffer layer is measured (step S223). In addition, when fitting using the spectrum of the calculated phase difference Δ in the frequency range between 1.0 THz and 1.3 THz and above 2.5 THz in order to measure the thickness of the buffer layer, the thickness of the epitaxial film is also measured again (step S223). The reason why the thickness of the epitaxial film is measured again in step S223, even though the thickness of the epitaxial film has been measured once in step S221, is that the thickness of the epitaxial film is affected by the thickness of the buffer layer, and also because, taking into account the other parameters measured up to step S222, the thickness of the epitaxial film measured by fitting using the spectrum of the calculated phase difference Δ may change.

[0128] Next, the carrier concentration of the epitaxial film is measured by fitting the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the calculated phase difference Δ in the frequency domain between 1 THz and 1.8 THz (step S224), and this process is completed.

[0129] According to this embodiment, the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ in ellipsometry using a substrate S on which a buffer layer and an epitaxial film are formed are divided into frequency regions that are highly sensitive to changes in each parameter. By performing fitting using the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ in the divided frequency regions, the parameters of the substrate, buffer layer, and epitaxial film can be measured. Therefore, when measuring the parameters of the substrate, buffer layer, and epitaxial film, it is not necessary to perform ellipsometry using the substrate S alone or a substrate S on which only a buffer layer is formed, thereby improving throughput.

[0130] Furthermore, according to this embodiment, the spectra of the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ are divided into frequency regions that are highly sensitive to changes in each parameter and fitted accordingly. This allows for fine-tuning of the spectra of the calculated amplitude ratio tangent tanΨ and the measured amplitude ratio tangent tanΨ, as well as fine-tuning of the spectra of the calculated phase difference Δ and the measured phase difference Δ, during the fitting process for measuring each parameter. As a result, the reliability of the parameters as measurement results can be improved.

[0131] Note that the parameter measurement process in Figure 22 is merely an example. When the thickness of the epitaxial film or the buffer layer changes, the shape of the fluctuations in the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ when each parameter is changed from its median value changes, so the parameter measurement process in Figure 22 cannot be used as is. When the thickness of the epitaxial film or the buffer layer changes, it is necessary to recalculate the fluctuations in the calculated amplitude ratio tangent tanΨ and the calculated phase difference Δ when each parameter is changed from its median value using an optical model, and to find a new frequency range that is highly sensitive to changes in each parameter.

[0132] However, the essence of the technology according to this embodiment is to divide the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the calculated phase difference Δ into frequency regions that are highly sensitive to changes in each parameter and then perform fitting. Therefore, even if the frequency region that is highly sensitive to changes in each parameter changes in the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the calculated phase difference Δ, as long as the spectrum of the calculated amplitude ratio tangent tanΨ and the spectrum of the calculated phase difference Δ are divided into frequency regions that are highly sensitive to changes in each parameter, the technology does not deviate from the essence of the technology according to this embodiment.

[0133] Furthermore, in this embodiment, for example, when performing the parameter measurement process shown in Figure 22, the ellipsometric measurement results of the substrate S on which the epitaxial film to be measured is formed can be substituted with the ellipsometric measurement results of the back surface of a SiC wafer. Also, when performing the parameter measurement process shown in Figure 22, a trained model generated by machine learning using the measurement results of each parameter of the substrate S measured by existing mercury probe CV methods or non-contact CV methods as training data may be used in combination. This can improve the reliability of the measurement results of each parameter. However, it should be noted that analysis of multilayer films is difficult with known mercury probe CV methods.

[0134] Next, a fourth embodiment of the technology relating to this disclosure will be described. However, in the first embodiment described above, the spectra of the measured amplitude ratio tangent tanΨ and the measured phase difference Δ vary due to minute rotational rattle of the rotation mechanism of the rotating polarizer 16. For example, until the acquired measured amplitude ratio tangent tanΨ falls within the reference variation of tanΨ, the polarization component E C The detection of the time waveform of the electric field intensity is repeated.

[0135] Furthermore, as described above, in the measurement of parameters of each layer of the substrate S in a single terahertz wave detector 19, the polarization component E changes each time the rotating polarizer 16 rotates by 15°. Cdetects the time waveform of the electric field strength. However, due to the slight rattling of the rotation mechanism of the rotating polarizer 16, etc., fluctuations may occur in the time waveform of the electric field strength of the polarization component E C In the second embodiment, until the fluctuation in the time waveform of the electric field strength of the polarization component E C becomes smaller than the fluctuation generation threshold value, the detection of the time waveform of the electric field strength of the polarization component E C is repeated.

[0136] Thus, in the first embodiment and the second embodiment, the detection of the time waveform of the electric field strength of the stable polarization component E C is repeated until the time waveform of the electric field strength of the polarization component E C is obtained. In this embodiment, correspondingly, without repeating the detection of the time waveform of the electric field strength of the polarization component E C a stable time waveform of the electric field strength of the polarization component E C is obtained.

[0137] Note that since the terahertz wave detector 19 detects the time waveform of the electric field strength of the polarization component E C as a signal, in this embodiment, hereinafter, the "electric field strength of the polarization component E C is referred to as the "signal strength of the measurement signal E C ".

[0138] Here, the applicant believes that the factors causing fluctuations in the spectrum of the measured amplitude ratio tangent tanΨ and the measured phase difference Δ and the fluctuations in the time waveform of the signal strength of the measurement signal E C are that noise derived from the measurement system of the ellipsometer 10 such as the slight rattling of the rotation mechanism of the rotating polarizer 16 is included in the measurement signal E C Therefore, the applicant confirmed whether noise is included in the measurement signal E

[0139] FIG. 23 shows the measurement signal E at a certain rotation angle of the rotating polarizer 16 C In CThis figure shows the time waveform of the signal intensity. Figure 23 shows 128 measured signals E of a certain rotation angle of the rotating polarizer 16, detected when the parameter was measured 128 times in the ellipsometer 10. C The time waveform of the signal intensity is superimposed, and in part A of the figure, the measured signal E from the previous stage is shown. C The time waveform of the signal intensity is partially magnified and shown, with the measured signal E in portion B of the figure representing the main observation period. C The time waveform of the signal intensity is shown partially magnified.

[0140] As shown in section A, the measurement signal E from the previous stage C The signal intensity is not constant and changes, but as mentioned above, the preceding stage is the part detected before the incident light enters the substrate S, so ideally, the measured signal E of the preceding stage C The signal strength is 0. Therefore, the measured signal E from the previous stage is 0. C The change in signal intensity is measured by the E C This is thought to be noise (noise originating from the measurement system of ellipsometer 10).

[0141] Figure 24 shows the measured signal E of the preceding stage at each rotation angle of the rotating polarizer 16. C This is a graph showing the standard deviation of the signal intensity. Figure 24 shows the 128 preceding stage measurement signals E detected when the parameter was measured 128 times. C The standard deviation of the signal intensity is displayed. As shown in Figure 24, even if the number of parameter measurements changes, the measured signal E is different at each rotation angle of the rotating polarizer 16. C The standard deviation of the signal intensity remains almost unchanged. Here, the measured signal E from the previous stage C The standard deviation of the signal intensity is the measured signal E from the previous stage. C Since these are characteristic noise values, Figure 24 shows the measurement signal E from the previous stage at each rotation angle of the rotating polarizer 16, even if the number of parameter measurements changes. C This indicates that the noise remains almost unchanged. In other words, the measured signal E from the previous stage CThis means that the noise is highly reproducible, but since the 128 parameter measurements were performed on the same ellipsometer 10, the measurement signal E from the preceding stage C The noise is thought to originate from the measurement system of ellipsometer 10.

[0142] Furthermore, as shown in section B of Figure 23, the measurement signal E of the main observation period. C Since the signal intensity does not change smoothly, the measured signal E in the main observation period portion is also not smooth. C It is thought that this includes some noise in addition to the signal corresponding to the reflected light from the substrate S (elliptical polarization composed of p-polarized and s-polarized light). And the measurement signal E from the previous stage C The time waveform of the signal intensity and the measured signal E during the main observation period. C The time waveform of the signal intensity is detected by the terahertz wave detector 19 of the same ellipsometer 10, so the measured signal E of the preceding stage C Noise similar to that in the measured signal E during the main observation period C It is also thought to be included in this.

[0143] Therefore, the applicant uses the measurement signal E of the preceding stage. C The noise generation pattern and the measured signal E during the main observation period. C We attempted to compare the noise generation patterns. Specifically, we measured the dose amount of the epitaxial film on the substrate S 128 times using the ellipsometer 10, and compared the measurement signal E of the rotating polarizer 16 in the preceding stage of a certain rotation angle. C The relationship between the noise characteristic values ​​and the dose amount of the epitaxial film obtained (measured) by fitting (hereinafter abbreviated as "relationship in the previous stage"), and the measured signal E for the main observation period portion of the same rotation angle of the rotating polarizer 16. C We obtained the relationship between the noise characteristics and the dose amount of the epitaxial film acquired (measured) by fitting (hereinafter abbreviated as "relationship during the main observation period"), and attempted to compare the relationship in the preceding stage with the relationship during the observation period.

[0144] Figure 25 is a graph showing the relationship in the preceding stage, and Figure 26 is a graph showing the relationship during the main observation period. Here, the measured signal E C The noise characteristics are the measured signal E for each period (preliminary stage, main observation period). C The maximum, minimum, or standard deviation of the signal intensity was used. Figure 25(A) shows the measured signal E C The noise characteristic value of the measured signal E C Figure 25(B) shows the relationship in the preceding stage when the maximum signal intensity of is used. C The noise characteristic value of the measured signal E C Figure 25(C) shows the relationship in the preceding stage when the minimum signal intensity of is used. C The noise characteristic value of the measured signal E C The relationship in the preceding stage is shown using the standard deviation of the signal intensity. Also, Figure 26(A) shows the measured signal E C The noise characteristic value of the measured signal E C Figure 26(B) shows the relationship during the main observation period when the maximum signal intensity of is used. C The noise characteristic value of the measured signal E C Figure 26(C) shows the relationship during the main observation period when the minimum signal intensity of is used. C The noise characteristic value of the measured signal E C This graph shows the relationship during the main observation period when using the standard deviation of signal intensity. The vertical dashed lines in each graph represent the average value of the acquired dose.

[0145] From the graph in Figure 25(A), in the preceding stage, the measured signal E C It can be seen that as the maximum value of the signal intensity increases, the deviation from the average value of each dose also increases. On the other hand, from the graph in Figure 26(A), it can be seen that even in the main observation period, the measured signal E C It can be seen that as the maximum value of the signal intensity increases, the deviation from the average value of each dose also increases. That is, the measured signal E CThe relationship between the maximum signal intensity and the deviation from the average value for each dose was found to be similar in the preceding stage and the main observation period.

[0146] Furthermore, from the graph in Figure 25(B), in the preceding stage, the measured signal E C It can be seen that as the minimum value of the signal intensity decreases (the absolute value of the minimum value increases), the deviation from the average value of each dose increases. On the other hand, from the graph in Figure 26(B), it can be seen that even in the main observation period, the measured signal E C It can be seen that as the minimum value of the signal intensity decreases (the absolute value of the minimum value increases), the deviation from the average value of each dose increases. That is, the measured signal E C The relationship between the minimum signal intensity and the deviation from the average value for each dose was found to be similar in the preliminary stage and the main observation period.

[0147] Furthermore, from the graph in Figure 25(C), in the preceding stage, the measured signal E C It can be seen that as the standard deviation of the signal intensity increases, the deviation from the mean value for each dose also increases. On the other hand, from the graph in Figure 26(C), it can be seen that even in the main observation period, the measured signal E C It can be seen that as the standard deviation of the signal intensity increases, the deviation from the average value of each dose also increases. That is, the measured signal E C The relationship between the standard deviation of signal intensity and the deviation from the mean value for each dose was found to be similar in the preceding stage and the main observation period.

[0148] As mentioned above, the measurement signal E C The maximum, minimum, and standard deviation of the signal intensity are all measured from the E C Since this is a characteristic value of the noise, the measurement signal E from the preceding stage is used for the deviation from the average value of each dose. C The noise and the measured signal E from the main observation period. C It was confirmed that the noise behaves similarly. That is, the measured signal E in the main observation period. C This is the measurement signal E from the previous stage. CIt was confirmed that it contains noise similar to that of [another source].

[0149] Furthermore, the applicant measured the dose amount of the epitaxial film on the substrate S 128 times using the ellipsometer 10, and obtained the measurement signal E from the preceding stage. C The characteristic values ​​of the noise and the measured signal E during the main observation period. C We also checked the relationship with the noise characteristic values. Specifically, the measurement signal E of the portion preceding a certain rotation angle of the rotating polarizer 16 in the same measurement run. C The maximum value of the signal intensity (hereinafter abbreviated as "maximum value of the previous stage") and the measured signal E for the portion of the main observation period at the same rotation angle of the rotating polarizer 16. C We examined the relationship with the maximum value of the signal intensity (hereinafter abbreviated as "maximum value during the main observation period").

[0150] Figure 27 is a graph showing the relationship between the maximum value of a certain rotation angle of the rotating polarizer 16 in the preceding stage and the maximum value during the main observation period in the same measurement run. From the graph in Figure 27, it was confirmed that there is a correlation between the maximum value of the preceding stage and the maximum value during the main observation period (see dashed line in the figure).

[0151] Furthermore, although not shown in the figure, the applicant also obtained the measurement signal E of a portion of the rotation angle preceding a certain rotation angle of the rotating polarizer 16 in the same measurement run. C The minimum signal intensity and the measured signal E for the portion of the main observation period at the same rotation angle of the rotating polarizer 16. C We also checked the relationship with the minimum value of the signal intensity. And the measured signal E from the previous stage C The minimum signal intensity and the measured signal E during the main observation period. C We also confirmed that the minimum signal intensity is correlated.

[0152] Furthermore, although not shown in the figure, the measurement signal E of the preceding stage of a certain rotation angle of the rotating polarizer 16 during the same measurement run. C The standard deviation of the signal intensity and the measured signal E for the portion of the main observation period at the same rotation angle of the rotating polarizer 16. C We also checked the relationship with the standard deviation of the signal intensity. And the measured signal E from the previous stage CThe standard deviation of the signal intensity and the measured signal E for the main observation period. C We also confirmed that the standard deviation of the signal intensity of E is correlated. Here, as mentioned above, the measured signal E C The maximum, minimum, and standard deviation of the signal intensity are all measured from the E C Since it is a characteristic value of the noise, the measured signal E from the previous stage C Noise and the measured signal E of the main observation period C It was found that the noise was correlated with the measured signal E during the main observation period. C However, the measurement signal E from the preceding stage C This was considered evidence that it contained noise similar to that of [another source].

[0153] As explained above, the measurement signal E from the previous stage C Noise similar to that in the measured signal E during the main observation period C Since it is also included in the measurement signal E of the main observation period C Measurement signal E from the preceding stage C By removing noise similar to the above noise, the measurement signal E for the main observation period corresponds only to the reflected light from the substrate S. C That is, the measured signal E from the stable main observation period portion (free of noise). C It is thought that the time waveform of the signal intensity can be obtained.

[0154] However, as shown in Figures 23, 25, and 26, the measured signal E of the main observation period. C The signal strength is the measured signal E from the previous stage. C Because it is amplified from the signal intensity, the measured signal E for the main observation period C The noise is also from the measurement signal E in the previous stage. C It is thought to be amplified from the noise.

[0155] Here, the measurement signal E from the previous stage C Noise and the measured signal E of the main observation period C The noise ratio is the same as the measured signal E from the previous stage at the same rotation angle. CThe distribution range (variability) of the noise feature values ​​and the measured signal E during the main observation period. C This is thought to be reflected in the ratio of the distribution range (variability) of the noise's characteristic values.

[0156] Therefore, in this embodiment, for example, the ratio of the distribution range of the maximum value in the previous stage and the distribution range of the maximum value in the main observation period at the same rotation angle (hereinafter referred to as the "correction coefficient") is obtained, and this correction coefficient is used to measure the measurement signal E of the previous stage. C From the noise, the measured signal E for the main observation period C Estimate the noise.

[0157] Figure 28 compares the distribution range of the maximum value in the previous stage and the distribution range of the maximum value during the main observation period at a certain rotation angle of the rotating polarizer 16. In Figure 28, the distribution range of the maximum value in the previous stage is, for example, 0.006 (Figure 28(A)), and the distribution range of the maximum value during the main observation period is, for example, 0.25 (Figure 28(B)). Therefore, a correction coefficient of approximately 41.7 (=0.25 / 0.006) is obtained at this rotation angle.

[0158] Furthermore, when obtaining the correction coefficient, not only the ratio of the distribution range of the maximum value in the previous stage to the distribution range of the maximum value in the main observation period is considered, but also the measurement signal E from the previous stage. C Distribution range of the minimum signal intensity and the measured signal E during the main observation period C The ratio of the minimum signal intensity to the distribution range, and the measured signal E from the preceding stage. C Distribution range of the standard deviation of the signal intensity and the measured signal E for the main observation period. C The ratio of the standard deviation of the signal intensity to the distribution range can be used.

[0159] In this embodiment, the correction coefficient obtained in this way is used in the measurement signal E of the preceding step. C By multiplying by the noise feature value, the measured signal E for the main observation period is obtained. C The noise characteristic values ​​are estimated, and the measured signal E of the main observation period is obtained. C The measured signal E of the main observation period estimated from CThis reduces the noise characteristics. This results in a stable measurement signal E for the main observation period. C The time waveform of the signal intensity is obtained.

[0160] By the way, as shown in the graph in Figure 24, when the rotation angle of the rotating polarizer 16 changes, the measurement signal E of the previous stage changes. C The standard deviation of the signal intensity of the measured signal E fluctuates. As mentioned above, C The standard deviation of the signal intensity is the measured signal E C Since this is a characteristic value of the noise, as can be seen from the graph in Figure 24, when the rotation angle of the rotating polarizer 16 changes, the measured signal E of the previous stage changes. C The noise is thought to change. Therefore, the measurement signal E of the preceding stage C The noise and correction coefficient need to be acquired for each rotation angle of the rotating polarizer 16. Therefore, in this embodiment, the measurement signal E of the stable main observation period is obtained. C Before acquiring the time waveform of the signal intensity, numerous parameter measurements are performed in the ellipsometer 10, and the measurement signal E of the preceding stage acquired at that time C The distribution range of the noise feature values ​​and the measured signal E during the main observation period. C Based on the distribution range of the noise feature values, correction coefficients are obtained in advance for each rotation angle of the rotating polarizer 16.

[0161] Figure 29 is a flowchart showing the process for acquiring a stable time waveform as a film characteristic measurement method according to the fourth embodiment. The time waveform detection process in Figure 29 is performed when the carrier concentration is measured once in the ellipsometer 10, by the control unit 21 executing a program. Note that the measurement signal E in this process C The characteristic value of the noise is the measured signal E C This could be the maximum value, minimum value, or standard deviation of the signal intensity.

[0162] First, the rotation angle of the rotating polarizer 16 is initialized to 0° (step S291). Then, the terahertz wave detector 19 measures the signal E C The time waveform of the signal intensity is detected (step S292).

[0163] Next, the measurement signal E of the preceding stage is obtained from the detected time waveform. C The noise is acquired (step S293), and furthermore, the measurement signal E of the acquired previous stage is obtained. C The noise characteristic value is multiplied by a correction coefficient corresponding to the rotation angle of the current rotating polarizer 16 to obtain the measured signal E for the main observation period. C The characteristic values ​​of the noise are estimated (step S294).

[0164] Next, the measurement signal E for the main observation period. C The measured signal E of the main observation period estimated from C By reducing the noise features, the measured signal E of the main observation period is obtained. C Correction (step S295) is performed on the measurement signal E of the stable main observation period portion. C The time waveform of the signal intensity is obtained.

[0165] Next, it is determined whether the rotation angle of the rotating polarizer 16 has reached 360° (step S296). If the rotation angle of the rotating polarizer 16 has not reached 360°, the rotation angle of the rotating polarizer 16 is changed so that it increases by 15° (step S297). Then, the process returns to step S292, and steps S292 to S295 are executed at the changed rotation angle to obtain the measurement signal E for the stable main observation period. C The time waveform of the signal intensity is obtained. In step S296, if the rotation angle of the rotating polarizer 16 reaches 360°, this process is terminated.

[0166] According to this embodiment, the measurement signal E of the preceding stage is measured for each rotation angle of the rotating polarizer 16. C From the noise characteristic values, the measured signal E of the main observation period C The noise characteristic values ​​are estimated, and the measured signal E of the main observation period is obtained. C The measured signal E of the main observation period estimated from C By reducing the noise features, the measurement signal E of the stable main observation period is obtained. C The time waveform of the signal intensity is obtained. That is, the measured signal E during the stable main observation period.C When acquiring the time waveform of the signal intensity, the polarization component E C Since it is not necessary to repeatedly detect the time waveform of the electric field strength, the throughput of acquiring the time waveform can be improved.

[0167] Furthermore, in this embodiment, the measurement signal E of the acquired main observation period portion C Since noise is no longer included, the measurement signal E for the main observation period is C This can further improve its reliability.

[0168] Furthermore, the measurement signal E C Since the noise originating from the measurement system of the ellipsometer 10, which is included as noise, is thought to include noise caused by the measurement environment, such as temperature, it is thought that noise caused by the environment in which the ellipsometer 10 is placed can also be removed by performing the stable time waveform acquisition process shown in Figure 29. Therefore, for example, even if parameter measurements are performed when the temperature of the environment in which the ellipsometer 10 is placed or the temperature of the ellipsometer 10 itself is unstable, the measurement signal E of the stable main observation period can be removed. C It is thought that the time waveform of the signal intensity can be obtained.

[0169] While preferred embodiments of this disclosure have been described above, this disclosure is not limited to the embodiments described above, and various modifications and changes are possible within the scope of its essence. [Explanation of Symbols]

[0170] S substrate 10 Ellipsometer 16 Rotating polarizers 19 Terahertz wave detector 20 Optical delay mechanism 21 Control Unit

Claims

1. A method for measuring the properties of a film formed on a substrate, Of the incident terahertz light, a polarization component consisting of p-polarized light vibrating parallel to the incident plane perpendicular to the surface of the substrate and s-polarized light vibrating perpendicular to the incident plane is incident on the substrate. The time waveform of the electric field intensity of the polarized component reflected from the substrate is detected. From the time waveform of the electric field intensity of the detected polarization component, the time waveforms of the electric field intensity of p-polarized and s-polarized elements are obtained. By performing a Fourier transform on the time waveforms of the acquired p-polarized and s-polarized electric field intensities, the measured amplitude ratio spectrum, which is the spectrum of the amplitude ratio of the electric field intensities of the p-polarized and s-polarized electric field intensities, and the measured phase difference spectrum, which is the spectrum of the phase difference between the p-polarized and s-polarized electric field intensities, are obtained. An optical model of the aforementioned substrate is constructed, By performing a simulation using the optical model described above, the calculated amplitude ratio spectrum, which is the spectrum of the amplitude ratio of the electric field intensities of the p-polarized and s-polarized light, and the calculated phase difference spectrum, which is the spectrum of the phase difference between the p-polarized and s-polarized light, are obtained. The characteristics of the film formed on the substrate are measured by fitting, which involves at least one of the following: fitting the spectrum of the calculated amplitude ratio to the spectrum of the measured amplitude ratio, and fitting the spectrum of the calculated phase difference to the spectrum of the measured phase difference. A method for measuring the properties of a film, which uses a highly reliable measurement value from among several measurement values ​​used when measuring the properties of the aforementioned film.

2. Multiple spectra of the measured amplitude ratios, which are continuous in time, are obtained. The measured value is the measured amplitude ratio of a specific frequency in each of the spectra of the plurality of measured amplitude ratios. The film characteristic measurement method according to claim 1, comprising selecting the measured amplitude ratio of a specific frequency that is not significantly affected by disturbances from a plurality of measured amplitude ratios of the specific frequency.

3. The film characteristic measurement method according to claim 2, wherein the measured amplitude ratio of the selected specific frequency is the median measured amplitude ratio of the specific frequency when the amount of change in the measured amplitude ratio of three temporally consecutive specific frequencies is less than or equal to a threshold.

4. The film characteristic measurement method according to claim 3, wherein the amount of change in the measured amplitude ratio of three time-consecutive specific frequencies is the sum of the absolute values ​​of the difference between the measured amplitude ratio of the median specific frequency and the measured amplitude ratios of the preceding and succeeding specific frequencies.

5. The film characteristic measurement method according to claim 4, wherein the threshold is 0.002 or 0.

001.

6. Obtain the variation in the measured amplitude ratio of multiple selected specific frequencies. The film characteristic measurement method according to claim 2, wherein in subsequent measurements, a spectrum of the measured amplitude ratio is newly acquired, and if the measured amplitude ratio of the specific frequency of the newly acquired spectrum of the measured amplitude ratio falls within the acquired variation, the fitting is performed using the newly acquired spectrum of the measured amplitude ratio.

7. The film characteristic measurement method according to claim 6, wherein if the measured amplitude ratio of the specific frequency of the newly acquired measured amplitude ratio spectrum falls within the acquired variation, the measured amplitude ratio spectrum is not newly acquired thereafter.

8. The measured value is the electric field intensity of the polarized component reflected from the substrate. The time waveform of the electric field intensity of the polarization component has a preceding stage portion and a portion of the main observation period that follows the preceding stage portion. The film characteristic measurement method according to claim 1, wherein it is determined whether or not large fluctuations in electric field intensity occur in the main observation period portion based on the preceding portion of the time waveform of the electric field intensity of the polarization component.

9. The film characteristic measurement method according to claim 8, wherein if it is determined that a large fluctuation in electric field intensity occurs in the portion of the main observation period, the detection of the time waveform of the electric field intensity of the polarization component is repeated.

10. The film characteristic measurement method according to claim 8, wherein a trained model is used to determine whether or not a large fluctuation in electric field strength occurred in the preceding stage.

11. The measured values ​​are the spectrum of the calculated amplitude ratio and the spectrum of the calculated phase difference. The spectra of the calculated amplitude ratio and the calculated phase difference are divided into frequency regions that are highly sensitive to changes in the characteristics of the substrate and the film, respectively. The film characteristic measurement method according to claim 1, wherein the fitting is performed using the spectrum of the calculated amplitude ratio in the divided frequency domains and the spectrum of the calculated phase difference in the divided frequency domains.

12. The film characteristic measurement method according to claim 1, wherein the film is made of silicon carbide, and the film characteristic to be measured is the carrier concentration.

13. A substrate film characteristic measuring device for measuring the characteristics of a film formed on a substrate, It comprises multiple components and a control unit, The control unit controls the operation of the plurality of components of the substrate film characteristic measuring device, Of the incident terahertz light, a polarization component consisting of p-polarized light vibrating parallel to the incident plane perpendicular to the surface of the substrate and s-polarized light vibrating perpendicular to the incident plane is incident on the substrate. The time waveform of the electric field intensity of the polarized component reflected from the substrate is detected. From the time waveform of the electric field intensity of the detected polarization component, the time waveforms of the electric field intensity of p-polarized and s-polarized elements are obtained. By performing a Fourier transform on the time waveforms of the electric field intensities of the p-polarized and s-polarized fields, the measured amplitude ratio spectrum, which is the spectrum of the amplitude ratio of the electric field intensities of the p-polarized and s-polarized fields, and the measured phase difference spectrum, which is the spectrum of the phase difference between the p-polarized and s-polarized fields, are obtained. An optical model of the aforementioned substrate is constructed, By performing a simulation using the optical model described above, the calculated amplitude ratio spectrum, which is the spectrum of the amplitude ratio of the electric field intensities of the p-polarized and s-polarized light, and the calculated phase difference spectrum, which is the spectrum of the phase difference between the p-polarized and s-polarized light, are obtained. The characteristics of the film formed on the substrate are measured by fitting, which involves at least one of the following: fitting the spectrum of the calculated amplitude ratio to the spectrum of the measured amplitude ratio, and fitting the spectrum of the calculated phase difference to the spectrum of the measured phase difference. The control unit is a film characteristic measuring device that uses a highly reliable measurement value from among a plurality of measurement values ​​used when measuring the characteristics of a film.

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