JP2012208098A - Physical property measuring device and physical property measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a physical property measuring device and a physical property measuring method for nondestructively and precisely measuring physical properties of a thin film.SOLUTION: A device for measuring physical properties of a thin film comprises: a laser generation source; excitation means for exciting a thin film; control means for controlling a polarization direction of a laser generated by the laser generation source; irradiation means that generates p-polarized and s-polarized terahertz waves by receiving the laser controlled by the control means and irradiates the thin film excited by the excitation means with the terahertz waves; detection means for detecting the p-polarized and s-polarized terahertz waves reflected off the thin film irradiated with the terahertz waves by the irradiation means; measurement means for measuring an amplitude and a phase spectrum of each of the p-polarized and s-polarized terahertz waves detected by the detection means; and means for measuring an amplitude ratio and a phase difference between the p-polarized and s-polarized terahertz waves detected by the detection means based on the amplitudes and the phase spectra measured by the measurement means.

Description

  The present invention relates to a physical property measuring apparatus and a physical property measuring method for nondestructively measuring physical properties of a thin film material.

  With the progress of semiconductor element development, new thin film materials are being developed. In evaluating such a thin film material, it is necessary to evaluate the electrical characteristics of the thin film material. However, since many thin film materials are difficult to obtain and expensive, measurement of electrical characteristics performed by destroying the thin film material is avoided. Therefore, Patent Document 1 discloses a terahertz spectroscopic analysis technique that measures the electrical characteristics of a thin film material in a nondestructive manner.

JP 2002-98634 A

  However, when measuring the electrical characteristics of a thin film material with high reliability by terahertz spectroscopy analysis, it is necessary to increase the S / N ratio of the measurement value, and for that purpose, a sufficient carrier concentration is required. However, since organic field effect transistors (OFETs) such as P3HT have a low carrier concentration, it is difficult to measure their electrical characteristics with high reliability.

  The present invention has been made in view of such circumstances, and an object thereof is to provide a physical property measuring apparatus and a physical property measuring method capable of measuring the physical properties of a thin film nondestructively and with high reliability. It is in.

  The physical property measuring apparatus of the present invention is a device for measuring physical properties of a thin film, a light source that generates a light pulse, an excitation unit that excites the thin film, and a control unit that controls the polarization direction of the light pulse generated by the light source Receiving a light pulse controlled by the control means to generate p-polarized and s-polarized terahertz waves, and irradiating the thin film excited by the excitation means with the terahertz waves; and the irradiation means Detection means for detecting p-polarized light and s-polarized terahertz wave reflected by the thin film irradiated with the terahertz wave, and amplitude and phase spectrum of each of the p-polarized light and s-polarized terahertz wave detected by the detection means are calculated. Based on the first calculating means and the amplitude and phase spectrum calculated by the first calculating means, the p-polarized light and the s-polarized terahertz detected by the detecting means are obtained. Second calculation means for calculating the amplitude ratio and phase difference of the two waves, and third calculation means for calculating the complex refractive index spectrum of the thin film based on the amplitude ratio and phase difference calculated by the second calculation means; It is characterized by providing.

  The physical property measuring apparatus according to the present invention further includes fourth calculation means for calculating a complex conductivity spectrum of the thin film based on the complex refractive index spectrum calculated by the third calculation means.

  The physical property measuring apparatus of the present invention further includes means for calculating a carrier concentration of the thin film based on the complex conductivity spectrum calculated by the fourth calculating means.

  The physical property measuring apparatus according to the present invention is characterized in that the light source generates a femtosecond light pulse.

  In the physical property measuring apparatus of the present invention, the light source is a laser light source.

  The physical property measurement method of the present invention is a method for measuring the physical properties of a thin film, wherein the thin film is irradiated with a p-polarized terahertz wave and the characteristics of the p-polarized terahertz wave reflected by the thin film are obtained. The second step of irradiating the thin film with the terahertz wave and obtaining the characteristics of the s-polarized terahertz wave reflected by the thin film, and the p-polarized and s-polarized terahertz waves obtained by the first and second steps A first step of setting a light pulse generated by the light source in a first polarization direction, and a third step of calculating the physical properties of the thin film based on the characteristics of Receiving a light pulse in the first polarization direction set by the setting step to generate a p-polarized terahertz wave and irradiating the thin film; and an excitation step for exciting the thin film; A first detection step for detecting p-polarized terahertz waves reflected by the thin film excited by the excitation step, and a first calculation for calculating the amplitude and phase spectrum of the p-polarized terahertz waves detected by the first detection step A second setting step for setting a light pulse generated by the light source in a second polarization direction, and a light pulse in the second polarization direction set by the second setting step. Generating an s-polarized terahertz wave by receiving the light and irradiating the thin film; a second detecting step of detecting the s-polarized terahertz wave reflected by the thin film excited by the excitation step; A second calculation step of calculating an amplitude and a phase spectrum of the s-polarized terahertz wave detected by the two detection steps, The p-polarized and s-polarized terahertz waves detected by the first and second detecting steps based on the amplitude and phase spectrum of the p-polarized and s-polarized terahertz waves calculated by the first and second calculating steps. A third calculation step for calculating the amplitude ratio and the phase difference of the wave, and a fourth calculation step for calculating the complex refractive index spectrum of the thin film based on the amplitude ratio and the phase difference calculated by the third calculation step. It is characterized by including.

  The physical property measurement method of the present invention further includes a fifth calculation step of calculating a complex electric conductivity spectrum of the thin film based on the complex refractive index spectrum calculated in the fourth calculation step.

  The physical property measurement method of the present invention further includes a step of calculating a carrier concentration of the thin film based on the complex conductivity spectrum calculated in the fifth calculation step.

  According to the present invention, the electrical characteristics of the thin film formed on the substrate surface can be measured with high reliability and non-destructiveness.

It is a block diagram of the physical property measuring apparatus which concerns on embodiment. 1 is a block diagram of a terahertz spectrometer according to an embodiment. It is explanatory drawing which shows the time waveform of the electric field strength containing the terahertz wave which carried out multiple reflection within the board | substrate, a Fourier-transform spectrum, and a reflectance. It is explanatory drawing which shows the time waveform, Fourier-transform spectrum, and reflectance of an electric field strength at the time of deleting the terahertz wave which carried out multiple reflection within the board | substrate. It is a block diagram of the spectroscopic ellipsometer in an embodiment. It is a block diagram of a computer in an embodiment. It is a flowchart which shows the procedure which calculates | requires the electric field strength of the time domain of reflected p polarization. It is a flowchart which shows the procedure which calculates | requires the electric field strength of the time domain of reflected s-polarized light. It is a flowchart which shows the procedure which calculates | requires the electric field strength of the frequency domain which excluded the multiple reflection in a board | substrate. It is a flowchart which shows the procedure which calculates | requires the electrical property value of a thin film sample.

Hereinafter, it will be specifically described with reference to the drawings showing embodiments.
In the embodiment, the frequency domain spectrum of the terahertz wave reflected from the thin film sample is obtained using terahertz time domain spectroscopy. The time domain spectroscopy is a spectroscopy that obtains a frequency domain spectrum and a phase difference spectrum of an electromagnetic wave by time-series Fourier transform of a time waveform of the electric field strength of the electromagnetic wave.

<Physical property measuring device>
FIG. 1 is a block diagram of a physical property measuring apparatus 1 according to an embodiment.
The physical property measuring device 1 includes a terahertz spectroscopic device 2, a film thickness measuring device 3, and a computer 4. A film thickness measuring device 3 may be provided separately from the physical property measuring device 1. The computer 4 may be mounted inside the terahertz spectrometer 2.
The terahertz spectrometer 2 and the film thickness measuring device 3 are electrically connected to a computer 4, and the computer 4 transmits / receives measurement data and calculation data to / from the terahertz spectrometer 2 and the thick film measuring device 3.

FIG. 2 is a block diagram of the terahertz spectrometer 2 according to the embodiment.
The terahertz spectrometer 2 includes a laser 21, a beam splitter 22, a terahertz wave generator 23, a sample holding unit 24, a terahertz wave detector 25, a time delay mechanism 26, and a polarization rotator 29 such as a Pockels cell.
The laser 21 emits femtosecond light pulses to the beam splitter 22. The laser 21 also emits femtosecond light pulses to the thin film sample H attached to the sample holder 24. When the thin film sample H is irradiated with femtosecond light pulses, carriers are excited in the thin film sample H and the complex refractive index of the thin film sample changes, so that the reflectivity of the terahertz wave changes according to the carrier concentration.
The beam splitter 22 divides the laser pulse emitted from the laser 21 into two, pump light and probe light.

  The polarization rotator 29 receives the pump light and controls the polarization direction thereof. The terahertz wave generator 23 emits terahertz waves when pump light is irradiated from the polarization rotator 29. The frequency of the terahertz wave emitted from the terahertz wave generator 23 is, for example, 0.1 to 5 THz (terahertz). The terahertz wave generator 23 is, for example, a nonlinear optical crystal (such as zinc telluride or LiNb03). When the terahertz wave generator 23 is a nonlinear optical crystal, the polarization direction of the terahertz wave generated by the terahertz wave generator 23 depends on the polarization direction of the pump light. Therefore, the polarization direction of the terahertz wave radiated from the terahertz wave generator 23 is changed by rotating the polarization direction of the pump light by the polarization rotator 29. The terahertz wave generator 23 has two types of terahertz waves, p-polarized light and s-polarized light. Radiate waves.

  The p-polarized or s-polarized terahertz wave radiated from the terahertz wave generator 23 is reflected by the mirror 27 and applied to the thin film sample H formed on the surface of the substrate H attached to the sample holder 24.

  The probe light is incident on the time delay mechanism 26. The probe light is a reference wave having a time delay with respect to the pump light in order to measure the time waveform of the electric field intensity of the reflected p-polarized light and reflected s-polarized terahertz wave reflected from the thin film sample H.

  The reflected p-polarized light and reflected s-polarized terahertz wave reflected from the thin film sample H are reflected by the mirror 28 and applied to the terahertz wave detector 25. The terahertz wave detector 25 is, for example, a semiconductor element, a nonlinear optical crystal, or the like.

  The time delay mechanism 26 changes the optical path length of the probe light divided by the beam splitter 22 and gives a time delay to the probe light with respect to the pump light. The time delay mechanism 26 is provided with a movable mirror that reflects and returns the probe light. The optical path length of the probe light changes by moving this mirror little by little with respect to the reflection direction. Since the optical path length of the pump light is constant, the probe light given the time delay by the time delay mechanism 26 reaches the terahertz wave detector 25 later than the pump light. Thus, by giving an arbitrary time delay to the probe light by the time delay mechanism 26, a time waveform of the electric field intensity of the terahertz wave of the reflected p-polarized light and the reflected s-polarized light is obtained.

  When the reflected p-polarized and reflected s-polarized terahertz waves reflected by the thin film sample H enter the terahertz wave detector 25, a current proportional to the electric field strength of the incident reflected p-polarized light and reflected s-polarized terahertz waves is detected. To 25. This current value is converted into a signal and transmitted from the terahertz wave detector 25 to the computer 4.

  In the present embodiment, the laser 21 irradiates the thin film sample H with femtosecond light pulses in synchronization with the timing at which the terahertz wave generator 23 irradiates the thin film sample H with p-polarized and s-polarized terahertz waves. Thereby, since the thin film sample H is excited to be in a state where the carrier concentration is increased, the electrical characteristics can be analyzed with high reliability even for a thin film sample having a low carrier concentration. In order to increase the carrier concentration, it is preferable to use a femtosecond light pulse after wavelength conversion as necessary.

<Substrate K>
The substrate K is devised as follows in order to reduce the measurement error of the transmitted wave.
The substrate K is a quartz crystal. By using a quartz crystal for the substrate K, it is possible to measure transmitted light with high accuracy in a wide frequency range. The terahertz wave radiated from the terahertz wave generator 23 has a high intensity near the center frequency (0.3 to 1 THz) and can be measured even with a thin film sample H having a low transmittance. However, in the vicinity of 50 GHz (gigahertz) or 5 THz, it is difficult to measure the thin film sample H with low intensity and low transmittance. Therefore, by using, for example, a quartz crystal having a high transmittance instead of a quartz glass having a low transmittance for the substrate K, the frequency range of transmitted waves that can be measured can be expanded. The wider the frequency range of the transmitted wave, the higher the reliability of the analysis of the electrical characteristics of the thin film sample H that is performed based on the measured transmitted wave.

The front and back surfaces of the substrate K have a parallelism corresponding to an error of 1 μm or less with respect to 0.001 degree or less or a thickness of 1 mm.
Further, the thickness of the substrate K is as thick as 1.0 mm. This is related to the deletion of the time waveform of the terahertz wave that is multiply reflected in the substrate K. Therefore, the influence of multiple reflection on the analysis when terahertz waves are multiple reflected in the substrate K will be described below.

  As a result of multiple reflections in the substrate K, when the time waveform of the delayed terahertz wave is Fourier transformed to obtain a frequency domain spectrum, intense interference fringes appear, making data analysis difficult. Therefore, the waveform after the time when the reflected wave reflected multiple times in the substrate K appears in the time waveform is deleted, and the time waveform of the terahertz wave is Fourier-transformed with a time width in which the time waveform of the reflected wave does not appear. Obtain a spectrum.

  FIG. 3 is an explanatory diagram showing a time waveform, a Fourier transform spectrum, and a reflectance of an electric field intensity including a terahertz wave that is multiple-reflected in the substrate K. FIG. 3A is an explanatory diagram showing a time waveform of an electric field strength including a terahertz wave that is multiple-reflected in the substrate K. FIG. The vertical axis represents the terahertz wave amplitude, and the horizontal axis represents time (unit: ps: picoseconds). The electric field strength is proportional to the terahertz wave amplitude. FIG. 3B is an explanatory diagram showing a Fourier transform spectrum obtained by Fourier transforming the time waveform of FIG. 3A. The vertical axis represents the terahertz wave amplitude, and the horizontal axis represents the frequency (unit: terahertz). FIG. 3C is an explanatory diagram showing the reflectance of the thin film sample H obtained from the Fourier transform spectrum of FIG. 3B. The vertical axis represents reflectance, and the horizontal axis represents frequency (unit: terahertz).

  FIG. 4 is an explanatory diagram showing a time waveform, a Fourier transform spectrum, and a reflectance of an electric field intensity when a terahertz wave that has been multiple-reflected in the substrate K is deleted. FIG. 4A is an explanatory diagram showing a time waveform of the electric field intensity obtained by deleting the terahertz wave that is multiple-reflected in the substrate K from FIG. 3A. The vertical axis represents the terahertz wave amplitude, and the horizontal axis represents time (unit: ps). FIG. 4B is an explanatory diagram showing a Fourier transform spectrum obtained by Fourier transforming the time waveform of FIG. 4A. The vertical axis represents the terahertz wave amplitude, and the horizontal axis represents the frequency (unit: terahertz). The thick line shows the Fourier transform spectrum of the reflected wave reflected from the thin film sample H. FIG. 4C is an explanatory diagram showing the reflectance of the thin film sample H obtained from the Fourier transform spectrum of FIG. 4B. The vertical axis represents reflectance, and the horizontal axis represents frequency (unit: terahertz).

  In FIG. 3, when Fourier transform is performed without deleting the time waveform of the electric field intensity due to multiple reflection, intense interference fringes appear in the Fourier transform spectrum, and the accuracy of the reflectivity of the thin film sample H obtained from this Fourier transform spectrum. Is low. On the other hand, in the case of FIG. 4, the time waveform of the electric field strength due to multiple reflection appearing after 25 ps is deleted. Therefore, no interference fringes appear in the Fourier transform spectrum, and the accuracy of the reflectance of the thin film sample H obtained from the Fourier transform spectrum is higher than when the time waveform of the electric field strength due to multiple reflection is not deleted.

When the first multiple reflected wave appears after Δt from the first main pulse, Δt can be obtained from Equation (1).
Δt = 2nd / c (1)
Here, n is the refractive index of the terahertz band of the substrate K, d is the thickness of the substrate K, and c is the speed of light.

  In order to suppress the absorption of the terahertz wave and increase the transmittance of the terahertz wave, the thinner the substrate K is, the better. For example, when the thickness of the substrate K is about 0.2 mm, it has mechanical strength that does not hinder the carrying of the thin film sample H, and can improve the reflectivity of terahertz waves. However, from Equation (1), as the thickness d of the substrate K is thinner, Δt becomes shorter and it becomes difficult to separate the multiple reflected waves from the first main pulse.

  In the example of FIG. 3, the slow vibration component of the main pulse of 13.5 ps continues to around 23 ps, and Δt of 10 ps or more is necessary to separate the multiple reflected wave from the main pulse. For example, when the thickness d of the substrate K is 1.0 mm, the refractive index n of the terahertz band of the quartz crystal is n = 2.1, so Δt = 14.0 ps. If Δt is 14 ps, the main pulse and the multiple reflected wave can be sufficiently separated. However, when the thickness of the substrate K is greater than 1.0 mm, the reflectance is lowered and the S / N ratio of the reflectance is lowered.

In the embodiment, the thickness of the quartz crystal substrate K is set to a value of 1.0 mm with a margin in order to increase the degree of freedom in separating the main pulse and the multiple reflected waves.
The thickness of the substrate K may be 0.7 mm corresponding to Δt = 10 ps, for example.
Incidentally, even in the example of FIG. 3, the reflected wave reflected once in the substrate K appears as the first multiple reflected wave in the vicinity of about 27.5 ps after 14 ps with respect to 13.5 ps where the main pulse appears.

  In the embodiment, the reflected waveform is measured in the time domain. In the acquired time waveform data, multiple reflected waves appear at time intervals according to the thickness of the substrate, so the time width of the time waveform data used for analysis, that is, Fourier transform including the multiple reflected pulses up to the main pulse. By selecting whether or not to perform the analysis, it is possible to analyze the data by controlling the number of reflections.

<Spectroscopic ellipsometer>
The film thickness measuring device 3 in the embodiment is, for example, a spectroscopic ellipsometer 30. The spectroscopic ellipsometer 30 is an apparatus that measures a reflection amplitude ratio angle Ψ and a phase difference Δ between p-polarized light and s-polarized light while irradiating a thin film sample H with linearly polarized waves and changing the wavelength of the irradiated light.

FIG. 5 is a block diagram of the spectroscopic ellipsometer 30 in the embodiment.
The Xe lamp 31 is a so-called white light source including a large number of wavelength components. The light emitted from the Xe lamp 31 is guided to the polarizer 33 through the optical fiber 32. The light polarized by the polarizer 33 enters the surface of the thin film sample H to be measured at a specific incident angle. The reflection from the thin film sample H is guided to an analyzer 35 through a photoelastic modulator (PEM) 34. The position of the PEM 34 can be either behind the polarizer 33 or in front of the analyzer 35.

  By the photoelastic modulator (PEM) 34, the reflected light is phase-modulated to a frequency of 50 kHz to produce linear to elliptically polarized light. Therefore, Ψ and Δ are determined with a resolution of several milliseconds. The output of the analyzer 35 is input to the spectroscope 37 via the optical fiber 36. The spectroscope 37 performs measurement for each wavelength, and transmits the measurement result to the data acquisition unit 38 as an analog signal. The data fetcher 38 converts the analog signal into a digital signal and transmits it to the computer 4.

  In the spectroscopic ellipsometry, an optical model using the thickness, optical constant, etc. of the thin film sample H as analysis variables is constructed in advance and recorded in the spectroscopic ellipsometer. The spectroscopic ellipsometer simulates the optical model and generates reference data for Ψ and Δ. The spectroscopic ellipsometer fits measurement data and reference data, and outputs an analysis variable of an optical model that gives reference data that most closely matches the measurement data as a measurement result. The fitting of the measurement data and the reference data may be a simple difference comparison or a comparison by the least square method. Also, linear regression analysis may be used to minimize the fitting error.

  Although the spectroscopic ellipsometer 30 may include a computer that performs the above-described fitting, in the embodiment, the computer 4 performs the above-described fitting based on the received output data.

<Computer>
FIG. 6 is a block diagram of the computer 4 in the embodiment. The computer 4 includes a control unit 41, a ROM (Read Only Memory) 42, a RAM (Random Access Memory) 43, a communication unit 44, an operation unit 45, a display unit 46, and an external interface 47.
A program is recorded in the ROM 42. The control unit 41 reads a program from the ROM 42 and executes various processes. The RAM 43 temporarily records work variables, measurement data, and the like. For example, the communication unit 44 receives signals of Ψ and Δ related to the film thickness transmitted from the film thickness measuring device 3. The control unit 41 performs fitting of the measurement data and the reference data, and obtains the thickness of the thin film sample H. The control unit 41 records the obtained thickness of the thin film sample H in the RAM 43.

  The operation unit 45 includes input devices such as a keyboard and a mouse, and the user operates the computer 4 via the operation unit 45 and the communication unit 44. Further, the user can operate the terahertz spectrometer 2 and the film thickness measuring device 3 via the operation unit 45. The display unit 46 displays data input via the communication unit 44 and the operation unit 45, calculation results executed by the control unit 41, and the like. The external interface 47 is an interface for exchanging information with an external recording medium (not shown). The external interface 47 is also an interface that can be connected to the Internet.

<Operation of physical property measuring device>
Next, the operation of the physical property measuring apparatus 1 according to the embodiment will be described.
The user records the complex refractive index of the terahertz band of the substrate K, the thickness of the substrate K, the dielectric constant of the vacuum, the dielectric constant other than free carriers and the elementary charge amount for the thin film sample H in the RAM 43 via the operation unit 45. To do. Alternatively, these numerical values may be recorded in the ROM 42 in advance.

  The user installs the thin film sample H on the spectroscopic ellipsometer 30 and makes polarized light incident on the thin film sample H from the polarizer 33 via the operation unit 45 of the computer 4. The control unit 41 acquires measurement data of Ψ and Δ from the data fetcher 38 via the communication unit 44. The control unit 41 performs fitting of the measurement data and the reference data, and obtains the thickness of the thin film sample H. The control unit 41 records the obtained thickness of the thin film sample H in the RAM 43 of the computer 4.

  Note that the user may record the thickness of the thin film sample H in the RAM 43 by manual input from the operation unit 45. In that case, the spectroscopic ellipsometer 30 is incorporated with a computer for performing fitting. The user reads the thickness of the thin film sample H from the display unit of the computer integrated with the spectroscopic ellipsometer 30 and records the read thickness of the thin film sample H in the RAM 43 by manual input via the operation unit 45.

  The user forms the thin film sample H on the surface of the substrate K. The control unit 41 of the computer 4 causes the laser 21 to emit femtosecond light pulses toward the beam splitter 22. The laser pulse is divided into pump light and probe light by the beam splitter 22. The polarization direction of the pump light divided by the beam splitter 22 is controlled by a polarization rotator 29, and the terahertz wave generator 23 is irradiated to the terahertz wave generator 23. The terahertz wave generator 23 emits p-polarized light or s-polarized light.

First, the user adjusts the polarization rotator 29 so that the polarization direction of the terahertz wave emitted from the terahertz wave generator 23 becomes p-polarized light.
The terahertz wave generator 23 emits p-polarized light. The p-polarized light radiated from the terahertz wave generator 23 is reflected by the mirror 27 and irradiated to the thin film sample H formed on the surface of the substrate K for several seconds. The reflected p-polarized light reflected by the thin film sample H is reflected by the mirror 28 and detected by the terahertz wave detector 25. When the reflected p-polarized light reflected by the thin film sample H enters the terahertz wave detector 25, a current proportional to the electric field intensity of the incident reflected p-polarized light flows through the terahertz wave detector 25. On the other hand, the probe light is given a time delay by the time delay mechanism 26 and is detected by the terahertz wave detector 25.

  The control unit 41 moves the reflection mirror of the time delay mechanism 26 to the rear opposite to the reflection direction by a predetermined amount, and repeats the above processing using the probe light given a predetermined time delay. Thereby, the temporal change in the electric field intensity of the reflected p-polarized light reflected from the thin film sample H is recorded in the RAM 43. Thus, the terahertz wave detector 25 transmits a signal indicating the electric field strength of the reflected p-polarized light to the computer 4. The control unit 41 receives this signal via the communication unit 44 and records this signal value in the RAM 43 as the electric field intensity time waveform of the reflected p-polarized light.

Next, the user adjusts the polarization rotator 29 so that the polarization direction of the terahertz wave emitted from the terahertz wave generator 23 becomes s-polarized light.
The terahertz wave generator 23 emits s-polarized light. The s-polarized light emitted from the terahertz wave generator 23 is reflected by the mirror 27 and irradiated to the thin film sample H formed on the surface of the substrate K for several seconds. The s-polarized light reflected by the thin film sample H is reflected by the mirror 28 and detected by the terahertz wave detector 25. When the reflected s-polarized light reflected by the thin film sample H enters the terahertz wave detector 25, a current proportional to the electric field strength of the incident reflected s-polarized light flows through the terahertz wave detector 25. On the other hand, the probe light is given a time delay by the time delay mechanism 26 and is detected by the terahertz wave detector 25.

  The control unit 41 moves the reflection mirror of the time delay mechanism 26 to the rear opposite to the reflection direction by a predetermined amount, and repeats the above processing using the probe light given a predetermined time delay. Thereby, the temporal change in the electric field intensity of the reflected s-polarized light reflected from the thin film sample H is recorded in the RAM 43. As described above, the terahertz wave detector 25 transmits a signal indicating the electric field strength of the reflected s-polarized light to the computer 4. The control unit 41 receives this signal via the communication unit 44 and records this signal value in the RAM 43 as an electric field strength time waveform of reflected s-polarized light.

FIG. 7 is a flowchart showing a procedure for obtaining the electric field intensity in the time domain of reflected p-polarized light, and FIG. 8 is a flowchart showing a procedure for obtaining the electric field intensity in the time domain of reflected s-polarized light.
First, the electric field strength in the time domain of reflected p-polarized light is obtained, and then the electric field strength in the time domain of reflected s-polarized light is obtained.

  The laser 21 emits a femtosecond light pulse to the thin film sample H (step S101). Thereby, the thin film sample H will be in an excited state and the carrier concentration of the thin film sample H will increase. The terahertz wave generator 23 irradiates the thin film sample H with p-polarized light in synchronization with the timing at which the laser 21 emits a laser pulse to the thin film sample H (step S102). The control unit 41 receives a signal indicating the electric field intensity of the reflected p-polarized light reflected from the thin film sample H from the terahertz wave detector 25 and records it in the RAM 43 (step S103).

  The control unit 41 determines whether or not the measurement of the electric field intensity of the reflected p-polarized light has been performed a predetermined number of times (step S104). Note that the predetermined number of times in step S104 is, for example, 50 times. If the control unit 41 determines that the measurement has not been performed a predetermined number of times (step S104: NO), the process returns to step S103. When it is determined that the measurement has been performed a predetermined number of times (step S104: YES), the control unit 41 accumulates the electric field intensity of the reflected p-polarized light, and records the accumulated value in the RAM 43 (step S105).

  The control unit 41 determines whether or not the reflection mirror of the time delay mechanism 26 is at the measurement end position (step S106). When the control unit 41 determines that the reflection mirror of the time delay mechanism 26 is not at the measurement end position (step S106: NO), the control unit 41 moves the reflection mirror of the time delay mechanism 26 backward by a predetermined amount (step S107). Return processing to. When the control unit 41 determines that the reflection mirror of the time delay mechanism 26 is at the measurement end position (step S106: YES), the control unit 41 proceeds to processing using s-polarized light.

  The terahertz wave generator 23 irradiates the thin film sample H with s-polarized light in synchronization with the timing at which the laser 21 emits a laser pulse to the thin film sample H (step S108). The control unit 41 receives a signal indicating the electric field intensity of the reflected s-polarized light reflected from the thin film sample H from the terahertz wave detector 25 and records it in the RAM 43 (step S109).

  The control unit 41 determines whether or not the measurement of the electric field intensity of the reflected s-polarized light has been performed a predetermined number of times (step S110). Note that the predetermined number of times in step S110 is, for example, 50 times. When it is determined that the control unit 41 has not measured the predetermined number of times (step S110: NO), the process returns to step S109. When it is determined that the measurement has been performed a predetermined number of times (step S110: YES), the control unit 41 accumulates the electric field intensity of the reflected s-polarized light, and records the accumulated value in the RAM 43 (step S111).

  The control unit 41 determines whether or not the reflection mirror of the time delay mechanism 26 is at the measurement end position (step S112). When the control unit 41 determines that the reflection mirror of the time delay mechanism 26 is not at the measurement end position (step S112: NO), the control unit 41 moves the reflection mirror of the time delay mechanism 26 backward by a predetermined amount (step S113), and step S108. Return processing to. When it is determined that the reflection mirror of the time delay mechanism 26 is at the measurement end position (step S112: YES), the control unit 41 ends the process.

  The control unit 41 reads the electric field intensity in the time domain of the reflected p-polarized light from the RAM 43, converts the read electric field intensity into an electric field intensity in the frequency domain by Fourier transform, and records it in the RAM 43. That is, the control unit 41 converts the electric field intensity in the time domain of the reflected p-polarized light into the amplitude spectrum of the reflected p-polarized light and the phase spectrum of the reflected p-polarized light, and records it in the RAM 43. In addition, the control unit 41 reads the electric field intensity in the time domain of the reflected s-polarized light from the RAM 43, converts the read electric field intensity into an electric field intensity in the frequency domain by Fourier transform, and records the electric field intensity in the RAM 43. That is, the control unit 41 converts the electric field intensity in the time domain of the reflected s-polarized light into an amplitude spectrum of the reflected s-polarized light and a phase spectrum of the reflected s-polarized light, and records the converted in the RAM 43.

  Here, when executing the Fourier transform, the control unit 41 obtains a time Δt at which the first multiple reflected wave appears from the first main pulse by using the equation (1). Therefore, the control unit 41 reads the real part of the complex refractive index of the terahertz band of the substrate K and the thickness of the substrate K from the RAM 43, and calculates Δt. The control unit 41 reads the time waveform of the electric field strength on the substrate K and the thin film H from the RAM 43. The control unit 41 converts each electric field intensity in the time domain into an electric field intensity in the frequency domain by Fourier transform with a time width up to Δt. The control unit 41 records the electric field strength in the frequency domain on the substrate K and the thin film H in the RAM 43.

FIG. 9 is a flowchart showing a procedure for obtaining the electric field strength in the frequency domain excluding the multiple reflection in the substrate K.
The control unit 41 reads the refractive index of the substrate K and the thickness of the substrate K from the RAM 43 (step S201). The control unit 41 calculates the time at which multiple reflected waves first appear after the main pulse from the refractive index and thickness of the substrate K (step S202). The control unit 41 reads the time waveform of the electric field strength in the thin film sample H from the RAM 43 (step S203). The control unit 41 performs a Fourier transform on the time waveform of the electric field strength of the transmitted wave that has passed through the substrate K and the thin film sample H with the time width obtained in step S202 (step S204). The control unit 41 records the electric field strength in the frequency domain of the transmitted wave transmitted through the substrate K and the thin film H obtained by Fourier transform in the RAM 43 (step S205), and ends the process.

  Next, based on the amplitude spectrum and phase spectrum of the reflected p-polarized light and the amplitude spectrum and phase spectrum of the reflected s-polarized light, the reflection amplitude ratio angle Ψ and the phase difference Δ of the reflected p-polarized light and the reflected s-polarized light are obtained.

The control unit 41 reads the amplitude spectrum of the reflected p-polarized light and the amplitude spectrum of the reflected s-polarized light from the RAM 43, and obtains Ψ from the ratio (reflected s-polarized light / reflected p-polarized light). Where | Ψ | ² is the ellipsometry signal spectrum. Further, the control unit 41 reads the phase spectrum of the reflected p-polarized light and the phase spectrum of the reflected s-polarized light from the RAM 43, and obtains Δ from the ratio (reflected s-polarized light / reflected p-polarized light). The control unit 41 uses the absolute value of the difference between the measured value of Ψexp (−iΔ) and the calculated value obtained from the optical model of the sample as an error function, and the complex refractive index spectrum N = n−ik that minimizes the error function. Is obtained by fitting. At this time, the film thickness of the thin film sample H recorded in the RAM 43 is used. By using the fitting to determine the complex refractive index spectrum N _S of the thin film sample H in an excited state from the value of Ψ and delta.

  In addition, the rotational speed of the polarization rotator 29 is increased, the polarization direction of the terahertz wave is modulated at a high speed, and a signal synchronized with the frequency is detected by a lock-in amplifier (not shown). External noise can be removed and sensitivity to carriers can be improved. In the case of normal transmission and reflection measurement, sample measurement and reference measurement are required, and it is difficult to accurately measure the phase shift as the sample moves. On the other hand, according to the present method using the reflected p-polarized light and the reflected s-polarized light, the reference measurement accompanied by the movement of the sample becomes unnecessary, so that such a problem does not occur.

Next, the control unit 41 calculates a complex conductivity spectrum based on the complex refractive index spectrum by the following procedure.
The control unit 41 reads the complex refractive index spectrum of the thin film sample H from the RAM 43. The control unit 41 calculates the complex dielectric constant of the thin film sample H and the complex conductivity spectrum of the thin film sample H using the complex refractive index spectrum of the thin film sample H read from the RAM 43. Here, the control unit 41 includes equations (2) to (4) indicating the relationship between the complex dielectric constant and the complex refractive index spectrum, and equations (5) to (4) indicating the relationship between the complex dielectric constant and the complex electric conductivity spectrum. From (7), the complex dielectric constant of the thin film sample H and the complex electric conductivity spectrum of the thin film sample H are calculated.

ε = N ² (2)
ε ₁ = n ² −κ ² (3)
ε ₂ = 2nκ (4)
Here, ε is a complex dielectric constant, and ε = ε ₁ −iε ₂ .

However, ε ₀ is a dielectric constant of vacuum, and ε _∞ is a dielectric constant other than free carriers. Further, σ is a complex conductivity spectrum, and σ = σ ₁ −iσ ₂ .

The control unit 41 reads the vacuum dielectric constant and the dielectric constant other than the free carrier from the RAM 43, and uses the read vacuum dielectric constant and the dielectric constant other than the free carrier for the above calculation.
The control unit 41 records the calculated complex dielectric constant of the thin film sample H and the complex conductivity spectrum of the thin film sample H in the RAM 43.

  The control unit 41 determines the carrier mobility of the thin film sample H. The determination method is to calculate the carrier mobility of the thin film sample H so that the difference between the complex conductivity spectrum of the thin film sample H obtained from the measurement and the complex conductivity spectrum calculated by the electrical conduction model is minimized. Determine the parameters to be used. The electrical conduction models that can be used here include the drude model, the extended drude model, the localized drude model, and the drude-smith model.

  The Drude model, which is a classic electron gas model, is effective for silicon, GaAs, general semiconductor materials, and the like. The extended Drude model is effective for materials with high electron correlation (such as high-temperature superconductors). A localized drude model that takes into account carrier localization is effective for organic conductive materials and the like. The Drude-Smith model is effective for silicon nanocrystals and the like. Below, the example which determines carrier mobility using a Drude model is demonstrated.

  The complex electric conductivity spectrum σ (ω) given by the Drude model is expressed by Equation (8).

Where N _c is the carrier concentration, e is the elementary charge amount, τ is the carrier scattering time, m ^* is the effective mass, and Γ (= 1 / τ) is the scattering probability. Further, ω _p ² is a plasma frequency and is represented by Expression (9).
Here, the carrier concentration N _c is estimated from the absorption coefficient of the thin film sample and the wavelength of the femtosecond light pulse that is an excitation laser.

  Equation (10) is an error function G () consisting of the difference between the complex conductivity spectrum σ (ω) of the thin film sample H obtained from the measurement and the complex conductivity spectrum of the thin film sample H given by Equation (8). ω).

  The control unit 41 reads out the complex conductivity spectrum calculated above from the RAM 43 and substitutes it into σ (ω) in Expression (9). Further, the control unit 41 reads the vacuum dielectric constant and the elementary charge amount from the RAM 43 and substitutes them into the equation (10).

  The control unit 41 calculates the error function G (ω) while changing the carrier concentration, effective mass, and carrier scattering time or scattering probability of the thin film sample H, and gives the minimum value of the error function G (ω). The carrier concentration, effective mass, and carrier scattering time or scattering probability of the thin film sample H are determined.

  In determining the minimum value of the error function G (ω) and the above parameters, the calculation speed may be increased by a simplex method of linear programming or the like. Further, when the calculated value of the error function G (ω) becomes smaller than a predetermined value, or when the number of calculation of the error function G (ω) exceeds the predetermined number, the calculation is terminated to speed up the calculation. You may plan.

The above is the determination of parameters when the Drude model is applied to the electrical conduction model. The control unit 41 executes the same parameter determination for the extended Drude model, the localized Drude model, and the Drude-Smith model, and determines the electric conduction model and parameter that minimizes the error function G (ω).
When the thin film is an organic semiconductor, only the localized drude model may be applied.
The control unit 41 records the determined electrical conduction model, the carrier concentration of the thin film sample H, the effective mass, and the carrier scattering time or scattering probability in the RAM 43.

  The control unit 41 reads the elementary charge amount, effective mass, and carrier scattering time or scattering probability from the RAM 43, calculates the carrier mobility from Expression (11), and records the calculated carrier mobility in the RAM 43.

  Where μ is the carrier mobility.

FIG. 10 is a flowchart showing a procedure for obtaining the electrical characteristic value of the thin film sample H.
The control unit 41 reads the complex refractive index spectrum of the thin film sample H from the RAM 43 (step S301). The control unit 41 reads the dielectric constant other than the vacuum dielectric constant and the free carrier from the RAM 43 (step S302). The control unit 41 calculates the complex dielectric constant and complex electrical conductivity spectrum of the thin film sample H based on the read complex refractive index spectrum of the thin film sample H, vacuum dielectric constant, and dielectric constant other than free carriers (step S303). ).

  The control unit 41 selects one of the unselected electrical conduction models from the drude model, the extended drude model, the localized drude model, and the drude-smith model (step S304). The control unit 41 calculates an error function G (ω) including a difference between the calculated complex electric conductivity spectrum from the complex electric conductivity spectrum measured from the terahertz wave and the complex electric conductivity spectrum calculated from the selected electric conductivity model. (Step S305). The control unit 41 reads a parameter to be substituted for the error function G (ω) from the RAM 43 (step S306). The control unit 41 substitutes the read parameter for the error function G (ω) (step S307). The control unit 41 calculates the error function G (ω) while changing parameters other than the read parameters (step S308).

  The control unit 41 determines whether or not the error function G (ω) has been calculated for all the electrical conduction models (step S309). When the control unit 41 determines that the error function G (ω) is not calculated for all the electrical conduction models (step S309: NO), the controller 41 calculates the error function G (ω) for another electrical conduction model. The process returns to step S304. When it is determined that the error function G (ω) has been calculated for all the electrical conduction models (step S309: YES), the control unit 41 determines an electrical conduction model that minimizes the error function G (ω) and its parameters. (Step S310). The control unit 41 calculates the carrier mobility of the thin film sample H based on the determined parameter of the electrical conduction model (step S311), and ends the process.

  It should be understood that the embodiment disclosed this time is illustrative in all respects and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the meanings described above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Physical property measurement apparatus 2 Terahertz spectroscopy apparatus 3 Film thickness measurement apparatus 4 Computer 21 Laser 22 Beam splitter 23 Terahertz wave generator 24 Sample holding part 25 Terahertz wave detector 26 Time delay mechanism 27 Mirror 28 Mirror 29 Polarization rotator

Claims (8)

In an apparatus for measuring physical properties of thin films,
A light source that generates a light pulse;
An excitation means for exciting the thin film;
Control means for controlling the polarization direction of a light pulse generated by the light source;
Irradiating means for generating p-polarized and s-polarized terahertz waves by receiving the light pulse controlled by the control means, and irradiating the thin film excited by the excitation means with the terahertz waves;
Detecting means for detecting p-polarized and s-polarized terahertz waves reflected by the thin film irradiated with the terahertz waves by the irradiating means;
First calculation means for calculating the amplitude and phase spectrum of each of the p-polarized light and the s-polarized terahertz wave detected by the detecting means;
Second calculation means for calculating the amplitude ratio and phase difference of the p-polarized light and the s-polarized terahertz wave detected by the detection means based on the amplitude and phase spectrum calculated by the first calculation means;
A physical property measurement apparatus comprising: third calculation means for calculating a complex refractive index spectrum of the thin film based on the amplitude ratio and the phase difference calculated by the second calculation means.   The physical property measuring apparatus according to claim 1, further comprising fourth calculation means for calculating a complex conductivity spectrum of the thin film based on the complex refractive index spectrum calculated by the third calculation means.   The physical property measuring apparatus according to claim 2, further comprising means for calculating a carrier concentration of the thin film based on the complex conductivity spectrum calculated by the fourth calculating means.   The physical property measuring apparatus according to claim 1, wherein the light source generates a femtosecond light pulse.   The physical property measuring apparatus according to claim 1, wherein the light source is a laser light source. In a method for measuring physical properties of a thin film,
irradiating the thin film with p-polarized terahertz waves, and determining the characteristics of the p-polarized terahertz waves reflected by the thin film;
irradiating the thin film with s-polarized terahertz waves, and determining the characteristics of the s-polarized terahertz waves reflected by the thin film;
A third step of calculating physical properties of the thin film based on the p-polarized and s-polarized terahertz wave characteristics obtained by the first and second steps,
The first step includes
A first setting step of setting a light pulse generated by the light source in a first polarization direction;
An irradiation step of generating a p-polarized terahertz wave by receiving a light pulse in the first polarization direction set in the first setting step and irradiating the thin film;
An excitation step for exciting the thin film;
A first detection step of detecting p-polarized terahertz waves reflected by the thin film excited by the excitation step;
A first calculation step of calculating the amplitude and phase spectrum of the p-polarized terahertz wave detected by the first detection step;
The second step includes
A second setting step of setting a light pulse generated by the light source in a second polarization direction;
An irradiation step of generating an s-polarized terahertz wave by receiving a light pulse in the second polarization direction set in the second setting step and irradiating the thin film;
A second detection step of detecting s-polarized terahertz waves reflected by the thin film excited by the excitation step;
A second calculation step of calculating the amplitude and phase spectrum of the s-polarized terahertz wave detected by the second detection step;
The third step is
Based on the amplitude and phase spectrum of the p-polarized and s-polarized terahertz waves calculated by the first and second calculating steps, the amplitude of the p-polarized and s-polarized terahertz waves detected by the first and second detecting steps. A third calculation step for calculating the ratio and the phase difference;
And a fourth calculation step of calculating a complex refractive index spectrum of the thin film based on the amplitude ratio and the phase difference calculated in the third calculation step.   The physical property measurement method according to claim 6, further comprising a fifth calculation step of calculating a complex conductivity spectrum of the thin film based on the complex refractive index spectrum calculated in the fourth calculation step.   The physical property measurement method according to claim 7, further comprising a step of calculating a carrier concentration of the thin film based on the complex conductivity spectrum calculated in the fifth calculation step.

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