WO2017085862A1

WO2017085862A1 - Measurement device, measurement method, and computer program

Info

Publication number: WO2017085862A1
Application number: PCT/JP2015/082690
Authority: WO
Inventors: 義行奧田
Original assignee: パイオニア株式会社
Priority date: 2015-11-20
Filing date: 2015-11-20
Publication date: 2017-05-26
Also published as: JPWO2017085862A1

Abstract

A measurement device 100 is equipped with an acquisition means 1521 which, for each of a plurality of terahertz wave irradiation positions, the locations of which relative to a specimen 10 differ, acquires: first time periods t_a1, t_a2 that are required for a terahertz wave THz to reach a prescribed position after being emitted toward the surface 10a of the specimen 10 and being reflected by said surface; and second time periods t_a1, t_a2 that are required for a terahertz wave to reach the prescribed position after being emitted toward the surface and reflected by the rear surface of the specimen. The measurement device 100 is further equipped with a calculation means 1522 for calculating the refractive index n of the specimen, on the basis of the first and second time periods.

Description

Measuring device, measuring method, and computer program

The present invention relates to a technical field of a measuring apparatus, a measuring method, and a computer program for measuring a refractive index of a sample using, for example, terahertz waves.

A measuring device using a terahertz wave is known as a measuring device for measuring the refractive index of a sample. For example, in Patent Document 1, a sample is irradiated with a terahertz wave through a transmission member that is in contact with the sample, and based on the time waveform of the terahertz wave reflected by the transmission member and the time waveform of the terahertz wave reflected by the sample. An information acquisition device for acquiring the refractive index of a sample is described. For example, Patent Document 2 discloses that a terahertz wave is irradiated on a specimen disposed between a reflecting member and a plate-like member through the plate-like member and reflected at the interface between the plate-like member and the specimen. An information acquisition device is described that acquires the refractive index of a specimen based on the time waveform of the wave and the time waveform of the terahertz wave reflected at the interface between the specimen and the reflecting member.

JP 2014-209094 A Japanese Patent Laying-Open No. 2015-83964

In the information acquisition apparatuses described in Patent Documents 1 and 2, in order to measure the refractive index, a special member (specifically, a transmission member or a plate-like member) with respect to a sample (in other words, a specimen) And the reflective member) need to be in close contact with each other. However, for some reason, there is a possibility that a special member cannot be brought into close contact with the sample. In this case, the technical problem that the information acquisition apparatus described in patent documents 1 and 2 cannot measure the refractive index of a sample arises.

Examples of problems to be solved by the present invention include the above. It is an object of the present invention to provide a measuring apparatus, a measuring method, and a computer program that do not require any special member to be brought into contact with the sample in order to measure the refractive index of the sample.

The first example of the measuring device according to the present invention includes a first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected on the surface, and the surface irradiated on the surface. The second time required for the terahertz wave to reach the predetermined position after being reflected by the back surface of the sample located on the opposite side of the front surface is determined by a plurality of irradiation positions of the terahertz waves having different positions with respect to the sample. An acquisition means for acquiring each and a calculation means for calculating the refractive index of the sample based on the first and second times.

The first example of the measurement method of the present invention includes a first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected on the surface, and the surface irradiated on the surface. The second time required for the terahertz wave to reach the predetermined position after being reflected by the back surface of the sample located on the opposite side of the front surface is determined by a plurality of irradiation positions of the terahertz waves having different positions with respect to the sample. An acquisition step for each acquisition, and a calculation step for calculating the refractive index of the sample based on the first and second times.

The first example of the computer program of the present invention causes a computer to execute the first example of the measurement method of the present invention described above.

FIG. 1 is a block diagram illustrating a configuration of the terahertz wave measuring apparatus according to the present embodiment. FIG. 2 is a flowchart illustrating an example of a flow of a first measurement operation for measuring a refractive index and a thickness performed by the terahertz wave measuring apparatus. FIG. 3 is a cross-sectional view of the sample showing the optical path of the terahertz wave irradiated to the sample and the optical path of the terahertz wave reflected by the sample. FIG. 4 is a graph showing a waveform signal of the terahertz wave detected by the terahertz wave detecting element. FIG. 5 is a cross-sectional view of the sample showing the optical path of the terahertz wave irradiated to the first position and the optical path of the terahertz wave irradiated to the second position. FIG. 6 is a flowchart illustrating an example of a flow of a second measurement operation for measuring the refractive index and the thickness performed by the terahertz wave measuring apparatus. FIG. 7 is a cross-sectional view of the sample showing the optical path of the terahertz wave irradiated to the first position, the optical path of the terahertz wave irradiated to the second position, and the optical path of the terahertz wave irradiated to the third position.

Hereinafter, embodiments of the measurement apparatus, the measurement method, and the computer program will be described.

(Embodiment of measuring device)
<1>
In the measurement apparatus of the present embodiment, the first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected on the surface, and the terahertz wave irradiated on the surface is The second time required to reach the predetermined position after being reflected by the back surface of the sample located on the opposite side of the front surface is acquired for each of the plurality of terahertz wave irradiation positions having different positions with respect to the sample. And obtaining means for calculating the refractive index of the sample based on the first and second times.

According to the measurement apparatus of the present embodiment, as will be described in detail later using specific mathematical formulas, a plurality of first times and a plurality of times corresponding to a plurality of irradiation positions without contacting any special member with the sample. Based on the second time, the refractive index of the sample can be suitably measured (that is, calculated).

<2>
In another aspect of the measurement apparatus of the present embodiment, the thickness of the sample, which is a physical distance between the front surface and the back surface, differs for each irradiation position.

According to this aspect, the terahertz wave is irradiated to a plurality of irradiation positions having different thicknesses of the sample, so that the measuring device can suitably measure (that is, calculate) the refractive index of the sample.

<3>
In another aspect of the measurement apparatus of the present embodiment, the measurement apparatus further includes an irradiation unit that irradiates the terahertz wave toward the surface, and a detection unit that detects the terahertz wave reflected by the sample, and the predetermined position is , The position where the detection means is installed, and the first time is required for the terahertz wave reflected from the surface to reach the detection means after the irradiation means irradiates the terahertz wave The second time is a time required for the terahertz wave reflected from the back surface to reach the detection unit after the irradiation unit irradiates the terahertz wave.

According to this aspect, the measuring apparatus can suitably measure the refractive index of the sample using the irradiation unit and the detection unit.

<4>
In another aspect of the measurement apparatus of the present embodiment, the measurement apparatus further includes changing means for changing the irradiation position by moving a moving object including the sample along a predetermined movement direction.

According to this aspect, the measuring apparatus can suitably acquire the first and second times for each of a plurality of irradiation positions having different positions.

<5>
In another aspect of the measurement apparatus of the present embodiment, the irradiation position is determined by moving a moving object including at least one of the sample, the irradiation unit, and the detection unit along a predetermined movement direction. It further comprises changing means for changing.

<6>
In another aspect of the measuring apparatus for moving the moving object as described above, when the moving direction is parallel to the back surface, the acquisition unit is configured to perform the first operation when the irradiation position is the first position. And the second time and the first and second times when the irradiation position is a second position different from the first position.

According to this aspect, when the moving direction is parallel to the back surface of the sample, even if the irradiation position is changed, the predetermined position (or the terahertz wave irradiation position and the terahertz wave detection position) The distance between at least one of the above and the back surface of the sample does not change. In this case, if the measurement apparatus acquires two first times and two second times respectively corresponding to two different irradiation positions, it can suitably measure the refractive index of the sample. That is, in order to measure the refractive index of the sample, the measuring device does not have to acquire three or more first times and three or more second times respectively corresponding to three or more irradiation positions.

<7>
As described above, in another aspect of the measuring apparatus that acquires the first and second times when the irradiation position is the first position and the first and second times when the irradiation position is the second position, the irradiation position _Are defined as t _a1 and t _{b1, respectively,} and when the irradiation position is the second position, t _a2 is defined as the first time and the second time when the irradiation position is the second position, respectively. And t _b2 , the variable Δt ₁ is defined by Equation 1, the variable Δt ₂ is defined by Equation 2, and the refractive index is defined as n, when the moving direction is parallel to the back surface, The calculating means calculates the refractive index based on Equation 3.

According to this aspect, the measurement apparatus can appropriately measure the refractive index of the sample based on the first and second times by performing the calculation based on the mathematical formulas 1 to 3.

<8>
In another aspect of the measuring apparatus for moving the moving object as described above, when the moving direction is not parallel to the back surface and the back surface is a plane, the moving means keeps the moving direction fixed. By moving the moving object, the irradiation position is sequentially changed to a first position, a second position, and a third position that are different from each other, the moving direction is not parallel to the back surface, and the back surface is flat. In some cases, the acquisition means includes the first and second times when the irradiation position is the first position, the first and second times when the irradiation position is the second position, In addition, when the irradiation position is the third position, the first and second times are acquired, and when the moving direction is not parallel to the back surface and the back surface is a plane, the acquisition unit includes: The first and second times, and The amount of movement of the moving object when the irradiation position is changed from the first position to the second position, and the movement when the irradiation position is changed from the second position to the third position. The refractive index is calculated based on the amount of movement of the object.

According to this aspect, when the moving direction is not parallel to the back surface of the sample, when the irradiation position is changed, the predetermined position (or at least one of the terahertz wave irradiation position and the terahertz wave detection position) is set. The distance between the back of the sample also changes. In this case, if the measurement apparatus acquires three first times and three second times respectively corresponding to three different irradiation positions, the refractive index of the sample can be suitably measured. That is, in order to measure the refractive index of the sample, the measuring device does not need to acquire four or more first times and four or more second times respectively corresponding to four or more irradiation positions.

<9>
As described above, the first and second times when the irradiation position is the first position, the first and second times when the irradiation position is the second position, and the first and second times when the irradiation position is the third position. In another aspect of the measuring apparatus for acquiring the second time, the first and second times when the irradiation position is the first position are defined as t _a1 and t _{b1, respectively,} and the irradiation position is the first position. The first and second times when the two positions are defined are defined as t _a2 and t _{b2, respectively,} and the first and second times when the irradiation position is the third position are defined as t _a3 and t _{b3, respectively.} The variable Δt ₁ is defined by Equation 4, the variable Δt ₂ is defined by Equation 5, the variable Δt ₃ is defined by Equation 6, and the irradiation position is changed from the first position to the second position. The amount of movement of the moving object is defined as P1, and the irradiation position is the first position When the movement amount of the moving object when changing from the position to the third position is defined as P2 and the refractive index is defined as n, the movement direction is not parallel to the back surface and the back surface is a plane. In this case, the calculation unit calculates the refractive index based on Equation 7.

This state

According to the above, the measurement apparatus can appropriately measure the refractive index of the sample based on the first and second times by performing the calculation based on Expression 4 to Expression 7.

<10>
In another aspect of the measuring apparatus for moving the moving object as described above, when the moving direction is not parallel to the back surface and the back surface is a plane, the moving means includes (i) the irradiation position. And (ii) the amount of movement of the moving object when changing from the first position to the second position so as to change sequentially from the first position, the second position, and the third position, which are different from each other. Moving the moving object while fixing the moving direction so as to be the same as the moving amount of the moving object when the irradiation position is changed from the second position to the third position, When the movement direction is not parallel to the back surface and the back surface is a plane, the acquisition means is configured to perform the first and second times when the irradiation position is the first position, and the irradiation position is the first position. The first and second in the second position During, as well as to acquire the first and second time when the irradiation position becomes the third position.

According to this aspect, as described above, when the moving direction is not parallel to the back surface of the sample, the measuring device acquires three first times and three second times respectively corresponding to the three irradiation positions. For example, the refractive index of the sample can be suitably measured.

<11>
As described above, the first and second times when the irradiation position is the first position, the first and second times when the irradiation position is the second position, and the first and second times when the irradiation position is the third position. In another aspect of the measuring apparatus for acquiring the second time, the first and second times when the irradiation position is the first position are defined as t _a1 and t _{b1, respectively,} and the irradiation position is the first position. The first and second times when the two positions are defined are defined as t _a2 and t _{b2, respectively,} and the first and second times when the irradiation position is the third position are defined as t _a3 and t _{b3, respectively.} If the variable Δt ₁ is defined by Equation 8, the variable Δt ₂ is defined by Equation 9, the variable Δt ₃ is defined by Equation 10, and the refractive index is defined as n, the movement direction is parallel to the back surface. If the back surface is a flat surface, the calculation means Based on, it calculates the refractive index.

According to this aspect, the measurement apparatus can appropriately measure the refractive index of the sample based on the first and second times by performing the calculation based on Expression 8 to Expression 11.

<12>
In another aspect of the measurement apparatus of the present embodiment, the calculation unit further calculates the thickness of the sample, which is a physical distance between the front surface and the back surface, based on the calculated refractive index. .

According to this aspect, the measuring apparatus can measure (that is, calculate) the thickness of the sample in addition to the refractive index.

(Embodiment of measurement method)
<13>
In the measurement method of the present embodiment, the first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected on the surface, and the terahertz wave irradiated on the surface is The second time required to reach the predetermined position after being reflected by the back surface of the sample located on the opposite side of the front surface is acquired for each of the plurality of terahertz wave irradiation positions having different positions with respect to the sample. And a calculation step of calculating a refractive index of the sample based on the first and second times.

According to the measurement device of the present embodiment, it is possible to suitably enjoy the same effects as those that can be enjoyed by the measurement device of the present embodiment described above.

Incidentally, in response to various aspects adopted by the measurement apparatus of this embodiment, the measurement method of this embodiment may adopt various aspects.

(Embodiment of computer program)
<14>
The computer program of this embodiment causes a computer to execute the measurement method of this embodiment described above.

According to the computer program of the present embodiment, it is possible to suitably enjoy the same effects as those enjoyed by the measurement apparatus of the present embodiment described above.

Incidentally, in response to various aspects adopted by the measurement apparatus of the present embodiment, the computer program of the present embodiment may adopt various aspects. The computer program may be recorded on a computer-readable recording medium.

The operation and other gains of the measurement apparatus, measurement method, and computer program of the present embodiment will be described in more detail in the following examples.

As described above, the measurement apparatus according to the present embodiment includes an acquisition unit and a calculation unit. The measurement method of this embodiment includes an acquisition process and a calculation process. The computer program of this embodiment causes a computer to execute the measurement method of this embodiment described above. Therefore, the refractive index of the sample is measured even when no special member is brought into contact with the sample.

Hereinafter, embodiments of the measurement device, the measurement method, and the computer program will be described with reference to the drawings. In particular, in the following, the measurement apparatus, the measurement method, and the computer program are described using an example in which the measurement apparatus, the measurement method, and the computer program are applied to the terahertz wave measurement apparatus 100 that measures the refractive index n of the sample 10 by irradiating the sample 10 with the terahertz wave THz. To proceed.

(1) Configuration of Terahertz Wave Measuring Device 100 First, the configuration of the terahertz wave measuring device 100 of the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram illustrating a configuration of a terahertz wave measuring apparatus 100 according to the present embodiment.

As shown in FIG. 1, the terahertz wave measuring apparatus 100 irradiates the sample 10 with the terahertz wave THz, and detects the terahertz wave THz reflected by the sample 10 (that is, the terahertz wave THz irradiated on the sample 10).

The terahertz wave THz is an electromagnetic wave including an electromagnetic wave component belonging to a frequency region (that is, a terahertz region) around 1 terahertz (1 THz = 10 ¹² Hz). The terahertz region is a frequency region that combines light straightness and electromagnetic wave transparency. The terahertz region is a frequency region in which various substances have unique absorption spectra. Therefore, the terahertz wave measuring apparatus 100 can measure the characteristics of the sample 10 by analyzing the terahertz wave THz irradiated on the sample 10. In the present embodiment, the terahertz wave measuring apparatus 100 can measure the refractive index n of the sample 10 which is an example of the characteristics of the sample 10 by analyzing the terahertz wave THz irradiated on the sample 10.

Here, since the period of the terahertz wave THz is a period of the order of sub-picoseconds, it is technically difficult to directly detect the waveform of the terahertz wave THz. Therefore, the terahertz wave measuring apparatus 100 indirectly detects the waveform of the terahertz wave THz by employing a pump-probe method based on time delay scanning. Hereinafter, the terahertz wave measuring apparatus 100 that employs such a pump-probe method will be described more specifically.

As shown in FIG. 1, the terahertz wave measuring apparatus 100 includes a pulse laser apparatus 101, a terahertz wave generating element 110 which is a specific example of “irradiation means”, a beam splitter 161, a reflecting mirror 162, and a reflecting mirror 163. A half mirror 164, an optical delay mechanism 120, a terahertz wave detecting element 130 as a specific example of “detecting means”, a bias voltage generating unit 141, an IV (current-voltage) converting unit 142, A control unit 150 and a stage 170 are provided.

The pulse laser device 101 generates sub-picosecond order or femtosecond order pulse laser light LB having a light intensity corresponding to the drive current input to the pulse laser device 101. The pulse laser beam LB generated by the pulse laser device 101 is incident on the beam splitter 161 via a light guide (not shown) (for example, an optical fiber).

The beam splitter 161 branches the pulsed laser light LB into pump light LB1 and probe light LB2. The pump light LB1 is incident on the terahertz wave generating element 110 through a light guide path (not shown). On the other hand, the probe light LB2 enters the optical delay mechanism 120 via a light guide path and a reflecting mirror 162 (not shown). Thereafter, the probe light LB2 emitted from the optical delay mechanism 120 is incident on the terahertz wave detection element 130 via the reflecting mirror 163 and a light guide path (not shown).

The terahertz wave generating element 110 emits a terahertz wave THz. Specifically, the terahertz wave generating element 110 includes a pair of electrode layers facing each other through a gap. A bias voltage generated by the bias voltage generation unit 141 is applied to the gap via a pair of electrode layers. When the pump light LB1 is irradiated to the gap while an effective bias voltage (for example, a bias voltage other than 0 V) is applied to the gap, the pump light LB1 is also applied to the photoconductive layer formed below the gap. Is irradiated. In this case, carriers are generated in the photoconductive layer irradiated with the pump light LB1 by light excitation by the pump light LB1. As a result, the terahertz wave generating element 110 generates a pulse-shaped current signal in the order of subpicoseconds or in the order of femtoseconds corresponding to the generated carrier. The generated current signal flows through the pair of electrode layers. As a result, the terahertz wave generating element 110 emits the terahertz wave THz resulting from the pulsed current signal.

The terahertz wave THz emitted from the terahertz wave generating element 110 passes through the half mirror 164. As a result, the terahertz wave THz transmitted through the half mirror 164 is irradiated to the sample 10 (particularly, the surface 10a of the sample 10). The terahertz wave THz irradiated on the sample 10 is reflected by the sample 10 (particularly, by the front surface 10a and the back surface 10b of the sample). The terahertz wave THz reflected by the sample 10 is reflected by the half mirror 164. The terahertz wave THz reflected by the half mirror 164 enters the terahertz wave detection element 130.

The terahertz wave detecting element 130 detects the terahertz wave THz incident on the terahertz wave detecting element 130. Specifically, the terahertz wave detection element 130 includes a pair of electrode layers facing each other with a gap interposed therebetween. When the probe light LB2 is irradiated to the gap, the probe light LB2 is also irradiated to the photoconductive layer formed below the gap. In this case, carriers are generated in the photoconductive layer irradiated with the probe light LB2 by light excitation by the probe light LB2. As a result, a current signal corresponding to the carrier flows through the pair of electrode layers included in the terahertz wave detection element 130. When the terahertz wave detection element 130 is irradiated with the terahertz wave THz while the probe light LB2 is irradiated on the gap, the signal intensity of the current signal flowing through the pair of electrode layers changes according to the light intensity of the terahertz wave THz. To do. A current signal whose signal intensity changes according to the light intensity of the terahertz wave THz is output to the IV conversion unit 142 via the pair of electrode layers.

The optical delay mechanism 120 adjusts the difference (that is, the optical path length difference) between the optical path length of the pump light LB1 and the optical path length of the probe light LB2. Specifically, the optical delay mechanism 120 adjusts the optical path length difference by adjusting the optical path length of the probe light LB2. When the optical path length difference is adjusted, the timing at which the pump light LB1 enters the terahertz wave generation element 110 (or the timing at which the terahertz wave generation element 110 emits the terahertz wave THz) and the probe light LB2 at the terahertz wave detection element 130 The time difference from the timing at which the light enters (or the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz) is adjusted. The terahertz wave measuring apparatus 100 indirectly detects the waveform of the terahertz wave THz by adjusting the time difference. For example, when the optical path of the probe light LB2 is increased by 0.3 millimeters (however, the optical path length in the air) by the optical delay mechanism 120, the timing at which the probe light LB2 enters the terahertz wave detection element 130 is delayed by 1 picosecond. Become. In this case, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is delayed by 1 picosecond. Considering that the terahertz wave THz having the same waveform repeatedly enters the terahertz wave detecting element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detecting element 130 detects the terahertz wave THz is gradually shifted. Thus, the terahertz wave detection element 130 can indirectly detect the waveform of the terahertz wave THz. That is, the lock-in detection unit 151 described later can detect the waveform of the terahertz wave THz based on the detection result of the terahertz wave detection element 130.

The current signal output from the terahertz wave detection element 130 is converted into a voltage signal by the IV conversion unit 142.

The control unit 150 performs a control operation for controlling the entire operation of the terahertz wave measuring apparatus 100. The control unit 150 includes a CPU (Central Processing Unit) and a memory. The memory stores a computer program for causing the control unit 150 to perform a control operation. When the computer program is executed by the CPU, a logical processing block for performing a control operation is formed inside the CPU. However, the computer program may not be recorded in the memory. In this case, the CPU may execute a computer program downloaded via a network.

As an example of the control operation, the control unit 150 performs a measurement operation for measuring the characteristics of the sample 10 based on the detection result of the terahertz wave detection element 130 (that is, the voltage signal output from the IV conversion unit 142). In order to perform the measurement operation, the control unit 150 includes a lock-in detection unit 151 and a signal processing unit 152 as logical processing blocks formed in the CPU.

The lock-in detection unit 151 performs synchronous detection on the voltage signal output from the IV conversion unit 142 using the bias voltage generated by the bias voltage generation unit 141 as a reference signal. As a result, the lock-in detection unit 151 detects a sample value of the terahertz wave THz. Thereafter, the same operation is repeated while appropriately adjusting the difference between the optical path length of the pump light LB1 and the optical path length of the probe light LB2 (that is, the optical path length difference). The waveform (time waveform) of the terahertz wave THz detected by the detection element 130 can be detected. The lock-in detection unit 151 outputs a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 to the signal processing unit 152. That is, the lock-in detection unit 151 removes a noise component having a frequency different from that of the reference signal from the voltage signal output from the IV conversion unit 142 (that is, the detection signal of the terahertz wave THz). That is, the lock mark detection unit 151 detects the time waveform signal with relatively high sensitivity and relatively high accuracy by performing synchronous detection using the detection signal and the reference signal. If the terahertz wave measuring apparatus 100 does not use lock-in detection, a DC voltage may be applied to the terahertz wave generating element 110 as a bias voltage.

The signal processing unit 152 measures the characteristics of the sample 10 based on the waveform signal output from the lock-in detection unit 151. For example, the signal processing unit 152 acquires the frequency spectrum of the terahertz wave THz using terahertz time domain spectroscopy, and measures the characteristics of the sample 10 based on the frequency spectrum.

Particularly in this embodiment, the signal processing unit 152 performs a measurement operation of measuring the refractive index n of the sample 10 based on the waveform signal output from the lock-in detection unit 151 as an example of the control operation. Further, as an example of the control operation, the signal processing unit 152 is based on the waveform signal output from the lock-in detection unit 151, and the thickness d of the sample 10 (that is, the direction in which the terahertz wave THz is incident on the sample 10). A measurement operation for measuring the thickness d) along the line is performed. Here, the thickness d means “physical distance between the front surface 10a and the back surface 10b”. In order to perform the measurement operation, the signal processing unit 152 includes a detection time acquisition unit 1521 that is a specific example of the “acquisition unit” and a “calculation unit” as logical processing blocks formed inside the CPU. A refractive index calculation unit 1522 as a specific example and a thickness calculation unit 1523 as a specific example of “calculation means” are provided. Note that specific examples of operations of the detection time acquisition unit 1521, the refractive index calculation unit 1522, and the thickness calculation unit 1523 will be described in detail later and will not be described here.

Stage 170 holds sample 10. In the example shown in FIG. 1, the stage 170 holds the sample 10 so that the back surface 10b of the sample 10 faces the stage 170 side. The stage 170 is movable along a predetermined movement direction while holding the sample 10. When the stage 170 moves, the irradiation position on the sample 10 of the terahertz wave THz changes.

The movement of the stage 170 is controlled by the control unit 150. Specifically, the control unit 150 includes an irradiation position changing unit 153 as a logical processing block formed inside the CPU. The irradiation position changing unit 153 controls the movement of the stage 170 so that the irradiation position of the terahertz wave THz is adjusted (for example, changed to a desired position).

The irradiation position changing unit 153 moves the irradiation position of the terahertz wave THz by moving at least one of the terahertz wave generating element 110 and the terahertz wave detecting element 130 in addition to or instead of moving the stage 170. May be adjusted.

(2) Measuring operation for measuring refractive index n and thickness d performed by terahertz wave measuring apparatus 100 Subsequently, referring to FIGS. 2 to 7, the refractive index n and thickness d performed by the terahertz wave measuring apparatus 100 are determined. A measurement operation to be measured will be described. In the present embodiment, the terahertz wave measuring apparatus 100 performs at least one of two types of measurement operations (first measurement operation and second measurement operation) as a measurement operation for measuring the refractive index n and the thickness d. Hereinafter, the first measurement operation for measuring the refractive index n and the thickness d and the second measurement operation for measuring the refractive index n and the thickness d will be described in order.

(2-1) First Measurement Operation for Measuring Refractive Index n and Thickness d First, a first measurement operation for measuring refractive index n and thickness d performed by the terahertz wave measuring apparatus 100 with reference to FIG. explain. FIG. 2 is a flowchart illustrating an example of a flow of a first measurement operation for measuring the refractive index n and the thickness d performed by the terahertz wave measuring apparatus 100.

As shown in FIG. 2, the irradiation position changing unit 153 controls the stage 170 so that the irradiation position of the terahertz wave THz is the first position on the surface 10a of the sample 10 (step S101).

Thereafter, the terahertz wave generating element 110 emits the terahertz wave THz toward the surface 10a of the sample 10 (step S102). That is, the terahertz wave generating element 110 irradiates the first position on the surface 10a of the sample 10 with the terahertz wave THz (step S102).

The terahertz wave THz irradiated on the sample 10a is reflected by the sample 10. Here, the reflection of the terahertz wave THz by the sample 10 will be described with reference to FIG. FIG. 3 is a cross-sectional view of the sample 10 showing the optical path of the terahertz wave THz irradiated on the sample 10 and the optical path of the terahertz wave THz reflected by the sample 10.

As shown in FIG. 3, a part of the terahertz wave THz irradiated on the sample 10 is reflected by the surface 10 a of the sample 10. The terahertz wave THz reflected by the surface 10a propagates from the sample 10 to the terahertz wave detecting element 130.

On the other hand, a part of the terahertz wave THz irradiated on the sample 10 passes through the inside of the sample 10 without being reflected by the surface 10a. Thereafter, the terahertz wave THz transmitted through the sample 10 reaches the back surface 10 b of the sample 10. As a result, a part of the terahertz wave THz transmitted through the sample 10 is reflected by the back surface 10 b of the sample 10. The terahertz wave THz reflected by the back surface 10b passes through the sample 10 again. Thereafter, the terahertz wave THz transmitted through the sample 10 reaches the surface 10 a of the sample 10. As a result, a part of the terahertz wave THz reflected by the back surface 10 b propagates from the sample 10 to the terahertz wave detecting element 130.

In this embodiment, the front surface 10a and the back surface 10b are the two outer surfaces of the sample 10 facing each other along the propagation direction of the terahertz wave THz in the sample 10 (the horizontal direction in FIGS. 1 and 3). Means. In this case, the surface 10a corresponds to one outer surface close to the terahertz wave generating element 110 and the terahertz wave detecting element 130 among the two outer surfaces. On the other hand, the back surface 10b corresponds to the other outer surface far from the terahertz wave generating element 110 and the terahertz wave detecting element 130 out of the two outer surfaces.

Further, in order to promote the reflection of the terahertz wave THz by the back surface 10b of the sample 10, a reflecting member may be arranged so as to be in contact with or in close contact with the back surface 10b of the sample 10.

2 again, the terahertz wave THz reflected by the sample 10 is detected by the terahertz wave detecting element 130 (step S102). As a result, a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detecting element 130 is input to the signal processing unit 152.

Thereafter, the detection time acquisition unit 1521 acquires the first detection time t _a1 and the second detection time t _b1 based on the waveform signal input to the signal processing unit 152 (step S103). That is, the terahertz wave measuring apparatus 100 acquires the first detection time t _a1 and the second detection time t _b1 based on the detection result of the terahertz wave THz irradiated to the first position. The detection time acquisition unit 1521 outputs the first detection time t _a1 and the second detection time t _b1 acquired when the first position is irradiated with the terahertz wave THz to the refractive index calculation unit 1522. The first detection time t _a1 and the second detection time t _b1 are specific examples of “first time” and “second time”, respectively.

Here, with reference to FIG. 4, the acquisition operation of the first detection time t _a1 and the second detection time t _b1 will be described. FIG. 4 is a graph showing a waveform signal of the terahertz wave THz detected by the terahertz wave detecting element 130.

As shown in FIG. 4, the waveform signal includes a waveform signal corresponding to the terahertz wave THz reflected by the front surface 10a and a waveform signal corresponding to the terahertz wave THz reflected by the back surface 10b. The terahertz wave THz reflected by the back surface 10b reaches the terahertz wave detecting element 130 after passing through the inside of the sample 10, while the terahertz wave THz reflected by the front surface 10a does not pass through the inside of the sample 10 and does not pass through the terahertz wave. The wave detection element 130 is reached. For this reason, the terahertz wave THz reflected by the back surface 10b reaches the terahertz wave detecting element 130 later in time than the terahertz wave THz reflected by the front surface 10a. Therefore, also on the waveform signal, the waveform signal corresponding to the terahertz wave THz reflected by the back surface 10b is delayed in time from the waveform signal corresponding to the terahertz wave THz reflected by the front surface 10a.

The first detection time _ta1 is a time required for the terahertz wave THz reflected from the surface 10a of the sample 10 to reach the terahertz wave detecting element 130 after the terahertz wave generating element 110 starts irradiation with the terahertz wave THz. is there. On the other hand, the second detection time t _b1 is from when the terahertz wave generating element 110 starts irradiation of the terahertz wave THz until the terahertz wave THz reflected by the back surface 10b of the sample 10 reaches the terahertz wave detecting element 130. It takes time. The detection time acquisition unit 1521 can easily acquire (in other words, calculate or specify) the first detection time t _a1 and the second detection time t _b1 by analyzing the waveform signal.

In FIG. 2 again, after that, the terahertz wave measuring apparatus 100 performs the above-described operation (that is, the operation for obtaining the first detection time t _a2 and the second detection time t _b2 ) again after changing the irradiation position. Specifically, the irradiation position changing unit 153 sets the irradiation position of the terahertz wave THz to the second position on the surface 10a of the sample 10 (however, the second position is different from the first position). The stage 170 is controlled (step S101). As a result, the stage 170 moves by a predetermined movement amount along a predetermined movement direction.

Here, the first position and the second position where the terahertz wave THz is irradiated will be described with reference to FIG. FIG. 5 is a cross-sectional view of the sample 10 showing the optical path of the terahertz wave THz irradiated to the first position and the optical path of the terahertz wave THz irradiated to the second position.

As shown in FIG. 5, in the first operation example, the first and second positions are the distances between the terahertz wave generating element 110 and the back surface 10b under the situation where the first position is irradiated with the terahertz wave THz. The first condition is satisfied that L11 and the distance L21 between the terahertz wave generating element 110 and the back surface 10b under the condition where the second position is irradiated with the terahertz wave THz are the same. Further, the first and second positions are a distance L13 between the terahertz wave detecting element 130 and the back surface 10b in a situation where the first position is irradiated with the terahertz wave THz, and the second position is the terahertz wave THz. The second condition that the distance L23 between the terahertz wave detecting element 130 and the back surface 10b under the irradiation condition is the same is satisfied. That is, the irradiation position changing unit 153 controls the stage 170 so as to satisfy the first and second conditions. In other words, the irradiation position changing unit 153 controls the stage 170 so that the terahertz wave THz is irradiated to each of the first position and the second position that satisfy the first and second conditions.

In order to control the stage 170 so as to satisfy the first and second conditions, the irradiation position changing unit 153 controls the stage 170 so that the moving direction of the stage 170 is parallel to the back surface 10b of the sample 10. In other words, in order to control the stage 170 so as to satisfy the first and second conditions, the irradiation position changing unit 153 moves the stage 170 so that the stage 170 moves along a direction parallel to the back surface 10 b of the sample 10. To control. As a result, even when the irradiation position of the terahertz wave THz is changed, the distance between the terahertz wave generating element 110 and the back surface 10b does not change. Similarly, even when the irradiation position of the terahertz wave THz is changed, the distance between the terahertz wave detecting element 130 and the back surface 10b does not change.

Here, the state “the stage 170 moves along a direction parallel to the back surface 10b” means “the stage 170 in a state where the terahertz wave THz is applied to the first position and the second position. This means a state where the stage 170 moves so that the stage 170 under the condition where the terahertz wave THz is irradiated is aligned along a direction parallel to the back surface 10b. Such a state is realized by the stage 170 moving only along the first direction parallel to the back surface 10b. Alternatively, in such a state, even when the stage 170 moves along the first direction parallel to the back surface 10b and the second direction intersecting the back surface 10b, the amount of movement of the stage 170 along the second direction is small. As long as the total is zero (ie offset), it will be realized.

The irradiation position changing unit 153 moves at least one of the terahertz wave generation element 110 and the terahertz wave detection element 130 in addition to or instead of moving the stage 170, so that the irradiation position of the terahertz wave THz is reached. As described above, may be adjusted. Even in this case, the irradiation position changing unit 153 moves at least one of the terahertz wave generating element 110 and the terahertz wave detecting element 130 so as to satisfy the first and second conditions.

In addition, as shown in FIG. 5, in the first operation example, the thickness d1 of the sample 10 at the first position is different from the thickness d2 of the sample 10 at the second position in the first and second positions. Satisfies the third condition. That is, the irradiation position changing unit 153 controls the stage 170 so as to satisfy the third condition. In other words, the irradiation position changing unit 153 controls the stage 170 so that the first position and the second position that satisfy the third condition are irradiated with the terahertz wave THz.

In order to satisfy the third condition, it is preferable that the sample 10 satisfies the condition that the thickness d of the sample 10 varies. The variation in the thickness d may include a variation in the thickness d caused by unevenness (for example, a step or a curved surface) intentionally formed on the surface 10a of the sample 10. Alternatively, the variation in the thickness d may include a variation in the thickness d due to the roughness of the surface 10a of the sample 10 depending on the accuracy of the finishing process.

In addition, when the back surface 10b of the sample 10 is a plane, the first and second positions can easily satisfy the first and second conditions described above. For this reason, in the first measurement operation, the back surface 10b of the sample 10 is preferably a flat surface.

Thereafter, the terahertz wave generating element 110 irradiates the second position on the surface 10a of the sample 10 with the terahertz wave THz (step S112). Thereafter, the terahertz wave detecting element 130 detects the terahertz wave THz reflected by the sample 10 (step S112). As a result, a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detecting element 130 is input to the signal processing unit 152. Thereafter, the detection time acquisition unit 1521 acquires the first detection time t _a2 and the second detection time t _b2 based on the waveform signal input to the signal processing unit 152 (step S113). That is, the terahertz wave measuring apparatus 100 acquires the first detection time t _a2 and the second detection time t _b2 based on the detection result of the terahertz wave THz irradiated to the second position. Detection time acquisition unit 1521, a first detection time _{t a2} and the second detection time _{t b2} obtained when irradiated with a terahertz wave THz in the second position, and outputs a refractive index calculation unit 1522. The first detection time t _a2 and the second detection time t _b2 are specific examples of “first time” and “second time”, respectively.

Thereafter, the refractive index calculator 1522 calculates the refractive index n of the sample 10 based on the first detection time t _a1 and the second detection time t _b1 , and the first detection time t _a2 and the second detection time t _b2. (Step S121). Specifically, the refractive index calculation unit 1522 calculates the refractive index n using Equation 12. Note that Δt _{1 in} Equation 12 corresponds to the time required for the terahertz wave THz to pass through the inside of the sample 10 when the first position is irradiated with the terahertz wave THz. That is, Δt _{1 in} Equation 12 corresponds to the time required for the terahertz wave THz to reach the surface 10a again from the front surface 10a of the sample 10 via the back surface 10b when the first position is irradiated with the terahertz wave THz. To do. Therefore, Δt ₁ can be calculated from an equation: Δt ₁ = t _b1 −t _a1 . Δt _{2 in} Expression 12 corresponds to the time required for the terahertz wave THz to pass through the inside of the sample 10 when the second position is irradiated with the terahertz wave THz. That is, Δt _{2 in} Equation 12 corresponds to the time required for the terahertz wave THz to reach the surface 10a again from the front surface 10a of the sample 10 via the back surface 10b when the second position is irradiated with the terahertz wave THz. To do. For this reason, Δt ₂ can be calculated from an equation: Δt ₂ = t _b2 −t _a2 .

Here, the reason why the refractive index n can be calculated using Equation 12 will be described with reference to FIG. 5 described above. In the following description, for convenience of description, the distance L11 between the terahertz wave generating element 110 and the back surface 10b in a situation where the first position is irradiated with the terahertz wave THz, and the terahertz wave THz at the second position. The distance L21 between the terahertz wave generating element 110 and the back surface 10b under the condition where the terahertz wave is irradiated, and the terahertz wave detecting element 130 and the back surface 10b under the condition where the terahertz wave THz is irradiated at the first position And the distance L23 between the terahertz wave detecting element 130 and the back surface 10b under the condition where the second position is irradiated with the terahertz wave THz are the same (for convenience, L ) That is, L11 = L13 = L21 = L23 = L. However, even when L11 = L21 ≠ L13 = L23, if “L” in the description to be described later is replaced with “(L11 + L13) / 2” or “(L21 + L23) / 2”, Expression 12 is used. It can be seen that there is no change in the reason why the refractive index n can be calculated.

First, the time required for the terahertz wave THz to reach the back surface 10b from the terahertz wave generating element 110 under the condition where the first position is irradiated with the terahertz wave THz is half of the second detection time _tb1 . The optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the back surface 10b under the condition where the terahertz wave THz is irradiated to the first position is (L−d1) + n × d1. (However, for convenience of explanation, the sample 10 is located in the air and the refractive index of the air is approximated to 1). Therefore, when the velocity of the terahertz wave THz in the air is defined as c, Equation 13 is established. For similar reasons, Equation 14 associated with the second position also holds.

On the other hand, the time required for the terahertz wave THz to reach the surface 10a from the terahertz wave generating element 110 under the condition where the first position is irradiated with the terahertz wave THz is half of the first detection time _ta1 . The optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the surface 10a under the condition where the terahertz wave THz is irradiated to the first position is Ld1. Therefore, Formula 15 is established. For similar reasons, Equation 16 associated with the second position also holds.

The variable d1 can be deleted from the equation 13 by substituting the equation 15 into the equation 13. When Equation 13 with the variable d1 deleted is solved for n, Equation 17 is obtained. By substituting Equation 16 into Equation 14, the variable d2 can be deleted from Equation 14. When Formula 14 in which the variable d2 is deleted is solved for n, Formula 18 is obtained.

The variable n can be deleted from the equation 17 by substituting the equation 18 into the equation 17. When Formula 17 in which the variable n is deleted is solved for L, Formula 19 is obtained.

By substituting Equation 19 into Equation 17, the variable L can be deleted from Equation 17. When Equation 17 with the variable L deleted is solved for n, Equation 12 described above is obtained.

In FIG. 2 again, after that, the thickness calculation unit 1523 performs the first detection time t _a1 and the second detection time t _b1 , the first detection time t _a2 and the second detection time t _b2 , and the refraction calculated in step S121. Based on the rate n, the thickness d of the sample 10 is calculated (step S122). In the first operation example, as described above, the thickness d1 of the sample 10 at the first position is different from the thickness d2 of the sample 10 at the second position. Therefore, the thickness calculation unit 1523 calculates each of the thicknesses d1 and d2. Specifically, the thickness calculation unit 1523 calculates the thickness d1 using a mathematical formula of d1 = (c / n) × Δt _1/2 . The thickness calculation unit 1523, using the formula that d2 = (c / n) × Δt 2/2, and calculates the thickness d2.

As described above, the terahertz measurement apparatus 100 according to the present embodiment can suitably measure (that is, calculate) the refractive index n of the sample 10 by executing the first measurement operation. In particular, the terahertz measuring apparatus 100 according to the present embodiment irradiates a plurality of irradiation positions with different thicknesses d of the sample 10 with the terahertz wave THz, so that the refractive index n does not contact the sample 10 with any special member. Can be suitably measured. Furthermore, since the terahertz measuring apparatus 100 of the present embodiment can suitably measure the refractive index n, the thickness d of the sample 10 can also be favorably measured.

Here, as an example of a terahertz wave measuring apparatus of a comparative example that measures the thickness d of the sample 10 without measuring the refractive index n, the thickness d is measured by irradiating the single irradiation position with the terahertz wave THz. A terahertz wave measuring device is assumed. In this case, the terahertz wave measuring apparatus of the comparative example, to obtain a first detection time t _a and the second detection time t _b. Further, the terahertz wave measuring apparatus of the comparative example measures the thickness d of the sample 10 using a mathematical formula of thickness d = c × (t _b −t _a ) / 2. However, as described above, the speed c ′ of the terahertz wave THz inside the sample 10 varies according to the refractive index n. Therefore, the thickness d measured by the terahertz wave measuring apparatus of the comparative example is larger than the original thickness d = (c / n) × (t _b −t _a ) / 2 of the sample 10. End up.

For this reason, the terahertz wave measuring apparatus 100 of the comparative example needs to measure the refractive index n in order to measure the original thickness d. However, as described in Patent Documents 1 and 2, the measurement of the refractive index n is generally troublesome. However, the terahertz wave measuring apparatus 100 of the present embodiment has a great advantage that the refractive index n can be measured relatively easily.

The above-described equation 12 is an equation obtained by solving n simultaneous equations (that is, four equations having L, d1, d2, and n as unknowns) composed of equations 13 to 16. It can be said that. For this reason, the terahertz wave measuring apparatus 100 may calculate the refractive index n by solving simultaneous equations composed of Expressions 13 to 16 for n instead of using Expression 12. For example, the terahertz wave measuring apparatus 100 determines whether the simultaneous equations are satisfied by substituting the assumed values of n into the simultaneous equations, and adjusts the assumed values of n that are substituted into the simultaneous equations until the simultaneous equations are satisfied. The operation may be repeated. In this case, an assumed value of n that satisfies the simultaneous equations corresponds to the refractive index n of the sample 10.

(2-2) Second Measurement Operation for Measuring Refractive Index n and Thickness d Next, a second measurement operation for measuring refractive index n and thickness d performed by the terahertz wave measuring apparatus 100 with reference to FIG. Will be described. FIG. 6 is a flowchart showing an example of the flow of the second measurement operation for measuring the refractive index n and the thickness d performed by the terahertz wave measuring apparatus 100.

In the first measurement operation described above, the stage 170 moves along a direction parallel to the back surface 10b of the sample 10. That is, even when the irradiation position of the terahertz wave THz is changed, the distance between the terahertz wave generating element 110 and the back surface 10b and the distance between the terahertz wave detecting element 130 and the back surface 10b do not change. However, depending on the movement conditions of the stage 170 and the state of the sample 10 (particularly, the state of the back surface 10b), the stage 170 may not be able to move along a direction parallel to the back surface 10b of the sample 10. That is, when the irradiation position of the terahertz wave THz is changed, at least one of the distance between the terahertz wave generating element 110 and the back surface 10b and the distance between the terahertz wave detecting element 130 and the back surface 10b is changed. In some cases.

In this case, even if the terahertz wave measuring apparatus 100 performs the first measurement operation, it is difficult to measure the refractive index n. For this reason, when the stage 170 cannot move along the direction parallel to the back surface 10b of the sample 10, the terahertz wave measuring apparatus 100 measures the refractive index n by performing the second measurement operation. However, the second measurement operation is performed on the sample 10 whose back surface 10b is flat (in other words, the back surface 10b is not intentionally uneven).

Specifically, as illustrated in FIG. 6, the irradiation position changing unit 153 controls the stage 170 so that the irradiation position of the terahertz wave THz is the first position on the surface 10a of the sample 10 (step S201). ). The terahertz wave generating element 110 irradiates the first position with the terahertz wave THz (step S202). Thereafter, the terahertz wave detection element 130 detects the terahertz wave THz reflected by the sample 10 (step S202). As a result, a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detecting element 130 is input to the signal processing unit 152. Thereafter, the detection time acquisition unit 1521 acquires the first detection time t _a1 and the second detection time t _b1 based on the waveform signal input to the signal processing unit 152 (step S203). Note that the operations of step S201, step S202, and step S203 may be the same as the operations of step S101, step S102, and step S103 of the first measurement operation, respectively, unless otherwise specified.

Thereafter, the irradiation position changing unit 153 controls the stage 170 so as to be the second position on the surface 10a of the sample 10 (however, the second position is different from the first position) (step S211). As a result, the stage 170 moves along a predetermined movement direction by a predetermined first movement amount P1 in order to change the irradiation position from the first position to the second position.

However, the second measurement operation is an operation performed mainly when the stage 170 cannot move along a direction parallel to the back surface 10 b of the sample 10. For this reason, when the irradiation position changing unit 153 changes the irradiation position to the second position, even when the irradiation position of the terahertz wave THz is changed, the irradiation position changing unit 153 is not provided between the terahertz wave generating element 110 and the back surface 10b. The stage 170 may not be controlled so as to satisfy the above-described first condition that the distance does not change. Similarly, when changing the irradiation position to the second position, the irradiation position changing unit 153 changes the position between the terahertz wave detection element 130 and the back surface 10b even when the irradiation position of the terahertz wave THz is changed. The stage 170 may not be controlled so as to satisfy the above-described second condition that the distance does not change.

Thereafter, the terahertz wave generating element 110 irradiates the second position with the terahertz wave THz (step S212). Thereafter, the terahertz wave detecting element 130 detects the terahertz wave THz reflected by the sample 10 (step S212). As a result, a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detecting element 130 is input to the signal processing unit 152. Thereafter, the detection time acquisition unit 1521 acquires the first detection time t _a2 and the second detection time t _b2 based on the waveform signal input to the signal processing unit 152 (step S213). Note that the operations of step S211, step S212, and step S213 may be the same as the operations of step S101, step S102, and step S103 of the first measurement operation, respectively, unless otherwise specified.

After that, the irradiation position changing unit 153 controls the stage 170 so as to be the third position on the surface 10a of the sample 10 (however, the third position is different from the first position and the second position) (step). S221). As a result, the stage 170 moves along a predetermined movement direction by a predetermined second movement amount P2 in order to change the irradiation position from the second position to the third position.

Particularly in the second measurement operation, the irradiation position changing unit 153 moves the stage 170 when changing the irradiation position from the second position to the third position when the irradiation position is changed from the first position to the second position. The stage 170 is controlled to be the same as the moving direction of the stage 170. That is, the irradiation position changing unit 153 controls the stage 170 so that the moving direction of the stage 170 when the irradiation position is changed from the first position to the third position via the second position is fixed.

Further, the second measurement operation is an operation performed mainly when the stage 170 cannot move along the direction parallel to the back surface 10b of the sample 10. For this reason, when changing the irradiation position to the third position, the irradiation position changing unit 153 does not have to control the stage 170 so as to satisfy the first condition described above. Similarly, when changing the irradiation position to the third position, the irradiation position changing unit 153 may not control the stage 170 so as to satisfy the second condition described above.

Thereafter, the terahertz wave generating element 110 irradiates the third position with the terahertz wave THz (step S222). Thereafter, the terahertz wave detection element 130 detects the terahertz wave THz reflected by the sample 10 (step S222). As a result, a waveform signal indicating the waveform of the terahertz wave THz detected by the terahertz wave detecting element 130 is input to the signal processing unit 152. Thereafter, the detection time acquisition unit 1521 acquires the first detection time t _a3 and the second detection time t _b3 based on the waveform signal input to the signal processing unit 152 (step S223). Note that the operations of step S221, step S222, and step S223 may be the same as the operations of step S101, step S102, and step S103 of the first measurement operation, respectively, unless otherwise specified.

Thereafter, the refractive index calculation unit 1522 includes the first detection time t _a1 and the second detection time t _b1 , the first detection time t _a2 and the second detection time t _b2 , and the first detection time t _a3 and the second detection time. Based on _tb3 , the refractive index n of the sample 10 is calculated (step S231). Specifically, the refractive index calculation unit 1522 calculates the refractive index n using Equation 20. Note that Δt ₁ and Δt ₂ in Equation 20 have already been described when the first measurement operation is described. Δt _{3 in} Expression 20 corresponds to the time required for the terahertz wave THz to pass through the inside of the sample 10 when the third position is irradiated with the terahertz wave THz. That is, Δt _{3 in} Equation 20 corresponds to the time required for the terahertz wave THz to reach the surface 10a again from the front surface 10a of the sample 10 via the back surface 10b when the third position is irradiated with the terahertz wave THz. To do. Therefore, Δt ₃ can be calculated from an equation: Δt ₃ = t _b3 −t _a3 .

here

The reason why the refractive index n can be calculated using Equation 20 will be described with reference to FIG. FIG. 7 is a cross-sectional view of a sample showing the optical path of the terahertz wave THz irradiated to the first position, the optical path of the terahertz wave THz irradiated to the second position, and the optical path of the terahertz wave THz irradiated to the third position. .

In the following description, for convenience of description, the distance L11 between the terahertz wave generating element 110 and the back surface 10b in a situation where the first position is irradiated with the terahertz wave THz, and the terahertz wave THz at the first position. It is assumed that the distance L13 between the terahertz wave detection element 130 and the back surface 10b under the condition where the light is irradiated is the same (for convenience, it is L1). A distance L21 between the terahertz wave generating element 110 and the back surface 10b in a situation where the second position is irradiated with the terahertz wave THz, and a terahertz wave in a situation where the second position is irradiated with the terahertz wave THz. The distance L23 between the detection element 130 and the back surface 10b is assumed to be the same (for convenience, L2). A distance L31 between the terahertz wave generating element 110 and the back surface 10b in a situation where the third position is irradiated with the terahertz wave THz, and a terahertz wave in a situation where the third position is irradiated with the terahertz wave THz. The distance L33 between the detection element 130 and the back surface 10b is assumed to be the same (for convenience, L3). However, even if L11 ≠ L13, if “L1” in the description to be described later is replaced with “(L11 + L13) / 2”, the reason why the refractive index n can be calculated using Equation 20 remains the same. I understand that. Even when L21 ≠ L23, if “L2” in the description to be described later is replaced with “(L21 + L23) / 2”, the reason why the refractive index n can be calculated using Equation 20 does not change. I understand. Even when L31 ≠ L33, if “L3” in the description to be described later is replaced with “(L31 + L33) / 2”, the reason why the refractive index n can be calculated using Equation 20 does not change. I understand.

In the following description, it is assumed that the thickness d of the sample 10 at the first position is d1. The thickness d of the sample 10 at the second position is assumed to be d2. It is assumed that the thickness d of the sample 10 at the third position is d3.

First, the time required for the terahertz wave THz to reach the back surface 10b from the terahertz wave generating element 110 under the condition where the first position is irradiated with the terahertz wave THz is half of the second detection time _tb1 . The optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the back surface 10b under the situation where the first position is irradiated with the terahertz wave THz is (L1−d1) + n × d1. (However, for convenience of explanation, the sample 10 is located in the air and the refractive index of the air is approximated to 1). Therefore, when the velocity of the terahertz wave THz in the air is defined as c, Equation 21 is established. For the same reason, Equation 22 related to the second position and Equation 23 related to the third position also hold.

On the other hand, the time required for the terahertz wave THz to reach the surface 10a from the terahertz wave generating element 110 under the condition where the first position is irradiated with the terahertz wave THz is half of the first detection time _ta1 . The optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the surface 10a under the condition where the terahertz wave THz is irradiated to the first position is L1-d1. Therefore, Formula 24 is established. For similar reasons, Equation 25 associated with the second position and Equation 26 associated with the third position also hold.

When the formula obtained by substituting “c × t _a1 / 2” of Formula 24 into “L1−d1” in Formula 21 is solved for d1, Formula 27 is obtained. When the formula obtained by substituting “c × t _a2 / 2” of Formula 25 into “L2-d2” in Formula 22 is solved for d2, Formula 28 is obtained. When the formula obtained by substituting “c × t _a3 / 2” of Formula 26 into “L3-d3” in Formula 23 is solved for d3, Formula 28 is obtained.

On the other hand, since the back surface 10b is flat as described above, the inclination of the back surface 10b with respect to the moving direction of the stage 170 is constant. Therefore, Expression 30 is established.

When the mathematical formulas obtained by substituting the mathematical formulas 24, 25 and 26 into the mathematical formula 30 are arranged, the mathematical formula 31 is obtained.

When the mathematical formulas obtained by substituting the mathematical formulas 27, 28, and 29 into the mathematical formula 31 are arranged, the mathematical formula 20 described above is obtained.

In FIG. 2 again, thereafter, the thickness calculation unit 1523 calculates the thickness d of the sample 10 (that is, the thicknesses d1, d2, and d3) (step S232). Specifically, the thickness calculation unit 1523 calculates the thickness d1 using a mathematical formula of d1 = (c / n) × Δt _1/2 . The thickness calculation unit 1523, using the formula that d2 = (c / n) × Δt 2/2, and calculates the thickness d1. The thickness calculation unit 1523, using the formula that d3 = (c / n) × Δt 3/2, and calculates the thickness d1.

As described above, the terahertz measurement apparatus 100 according to the present embodiment can enjoy the same effect as the effect that can be enjoyed when the first measurement operation is performed by executing the second measurement operation. In particular, the terahertz wave measuring apparatus 100 includes a distance between the terahertz wave generating element 110 and the back surface 10b and a distance between the terahertz wave detecting element 130 and the back surface 10b by changing the irradiation position of the terahertz wave THz. Even when at least one of the above changes, the refractive index n of the sample 10 can be suitably measured (that is, calculated).

Note that the movement amount P1 of the stage 170 when the irradiation position is changed from the first position to the second position is the same as the movement amount P2 of the stage 170 when the irradiation position is changed from the second position to the third position. In this case, Equation 20 described above becomes Equation 31. Therefore, when the irradiation position changing unit 153 controls the stage 170 so that the movement amount P1 and the movement amount P2 are the same, the refractive index calculation unit 1522 uses Equation 32 instead of Equation 20. The refractive index n may be calculated.

In addition, the above-described Expression 20 is a simultaneous equation composed of Expression 21 to Expression 26 and Expression 30 (that is, simultaneous equations composed of seven equations with L1, L2, L3, d1, d2, d3, and n as unknowns). It can be said that this is a mathematical expression obtained by solving for n. For this reason, the terahertz wave measuring apparatus 100 may calculate the refractive index n by solving simultaneous equations composed of Expressions 21 to 26 and Expression 30 for n instead of using Expression 20.

The present invention is not limited to the above-described embodiments, and can be appropriately changed without departing from the gist or concept of the invention that can be read from the claims and the entire specification. A measurement method and a computer program are also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Sample

10a Front surface

10b Back surface 100 Terahertz wave measurement apparatus 101 Pulse laser apparatus 110 Terahertz wave generation element 120 Optical delay mechanism 130 Terahertz wave detection element 150 Control part 151 Lock-in detection part 152 Signal processing part 1521 Detection time acquisition part 1522 Refractive index calculation Unit 1523 thickness calculation unit 153 irradiation position changing unit 170 stage LB1 pump light LB2 probe light THz terahertz wave

Claims

The first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected on the surface, and the terahertz wave irradiated on the surface is located on the opposite side of the surface An acquisition means for acquiring a second time required to reach the predetermined position after being reflected by the back surface of the sample for each of a plurality of irradiation positions of the terahertz waves having different positions with respect to the sample;
A measuring device comprising: calculating means for calculating a refractive index of the sample based on the first and second times.
The measurement apparatus according to claim 1, wherein the thickness of the sample, which is a physical distance between the front surface and the back surface, is different for each irradiation position.
Irradiating means for irradiating the terahertz wave toward the surface;
Detecting means for detecting the terahertz wave reflected by the sample; and
The predetermined position is a position where the detection means is installed,
The first time is a time required for the terahertz wave reflected from the surface to reach the detection unit after the irradiation unit irradiates the terahertz wave,
3. The second time is a time required for the terahertz wave reflected from the back surface to reach the detection unit after the irradiation unit irradiates the terahertz wave. 4. The measuring device described in 1.
The measuring apparatus according to claim 1, further comprising changing means for changing the irradiation position by moving a moving object including the sample along a predetermined moving direction.
The apparatus further comprises changing means for changing the irradiation position by moving a moving object including at least one of the sample, the irradiation means, and the detection means along a predetermined movement direction. The measuring device according to claim 3.
When the moving direction is parallel to the back surface, the acquisition unit is configured to perform the first and second times when the irradiation position is the first position, and the irradiation position is the first position. The measurement apparatus according to claim 4 or 5, wherein the first and second times when the second positions are different are acquired.
The first and second times when the irradiation position becomes the first position are defined as t a1 and t b1, respectively, and the first and second times when the irradiation position becomes the second position, respectively. When the variable Δt 1 is defined by Equation 1, the variable Δt 2 is defined by Equation 2, and the refractive index is defined as n, respectively, when t a2 and t b2 are defined, The measurement unit according to claim 6, wherein the calculation unit calculates the refractive index based on Equation 3.
When the moving direction is not parallel to the back surface and the back surface is a flat surface, the moving means moves the moving object while fixing the moving direction so that the irradiation positions are different from each other. Change in order to the first position, the second position and the third position,
When the moving direction is not parallel to the back surface and the back surface is a flat surface, the acquisition unit is configured to perform the first and second times when the irradiation position is the first position, and the irradiation position is Obtaining the first and second times when the second position is reached, and the first and second times when the irradiation position is the third position;
When the moving direction is not parallel to the back surface and the back surface is a flat surface, the acquisition unit moves the irradiation position from the first position to the second position, and the irradiation time. The refractive index is calculated based on the amount of movement of the moving object when changing and the amount of movement of the moving object when changing the irradiation position from the second position to the third position. The measuring device according to claim 4 or 5, wherein:
The first and second times when the irradiation position becomes the first position are defined as t a1 and t b1, respectively, and the first and second times when the irradiation position becomes the second position, respectively. Define t a2 and t b2, respectively , define the first and second times when the irradiation position is the third position as ta 3 and t b3, respectively, and define the variable Δt 1 with Equation 4. The variable Δt 2 is defined by Equation 5, the variable Δt 3 is defined by Equation 6, and the amount of movement of the moving object when the irradiation position is changed from the first position to the second position is defined as P1. When the irradiation position is changed from the second position to the third position, the moving amount of the moving object is defined as P2, and the refractive index is defined as n, the moving direction is parallel to the back surface. If the back surface is a plane, the calculation means Based on the measurement apparatus according to claim 8, characterized in that to calculate the refractive index.
When the moving direction is not parallel to the back surface and the back surface is a plane, the moving means (i) sequentially changes the irradiation position to different first, second, and third positions. And (ii) the amount of movement of the moving object when changing from the first position to the second position changes the irradiation position from the second position to the third position. Moving the moving object while fixing the moving direction so that the moving amount of the moving object is the same as
When the moving direction is not parallel to the back surface and the back surface is a flat surface, the acquisition unit is configured to perform the first and second times when the irradiation position is the first position, and the irradiation position is 6. The first and second times when the second position is reached, and the first and second times when the irradiation position is the third position are acquired. The measuring device described in 1.
The first and second times when the irradiation position becomes the first position are defined as t a1 and t b1, respectively, and the first and second times when the irradiation position becomes the second position, respectively. Define t a2 and t b2, respectively , define the first and second times when the irradiation position is the third position as ta 3 and t b3, respectively, and define the variable Δt 1 with Equation 8. When the variable Δt 2 is defined by Equation 9, the variable Δt 3 is defined by Equation 10, and the refractive index is defined as n, when the movement direction is not parallel to the back surface and the back surface is a plane, The measuring device according to claim 10, wherein the calculating unit calculates the refractive index based on Formula 11.
The said calculating means further calculates the thickness of the said sample which is a physical distance between the said surface and the said back surface based on the calculated said refractive index. Any one of Claim 1 to 11 characterized by the above-mentioned. The measuring device according to claim 1.
The first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected on the surface, and the terahertz wave irradiated on the surface is located on the opposite side of the surface An acquisition step of acquiring a second time required to reach the predetermined position after being reflected on the back surface of the sample for each of the plurality of irradiation positions of the terahertz waves whose positions with respect to the sample are different from each other;
And a calculation step of calculating a refractive index of the sample based on the first and second times.
A computer program for causing a computer to execute the measurement method according to claim 13.