JP6913261B2 - Measuring device, measuring method and computer program - Google Patents

Description

The present invention relates to the technical fields of a measuring device, a measuring method and a computer program for measuring the refractive index of a sample using, for example, a terahertz wave.

As a measuring device for measuring the refractive index of a sample, a measuring device using a terahertz wave is known. For example, Patent Document 1 irradiates a sample with a terahertz wave through a transmission member 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, in Patent Document 2, a sample arranged between a reflective member and a plate-shaped member is irradiated with a terahertz wave through the plate-shaped member, and the terahertz reflected at the interface between the plate-shaped member and the sample is reflected. An information acquisition device that acquires the refractive index of a sample based on the time waveform of the wave and the time waveform of the terahertz wave reflected at the interface between the sample and the reflective member is described.

Japanese Unexamined Patent Publication No. 2014-20909 Japanese Unexamined Patent Publication No. 2015-83964

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

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

The first example of the measuring apparatus of the present invention includes the first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected by the surface, and the surface irradiated with the terahertz wave. 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 the second time required for the plurality of irradiation positions of the terahertz wave having different positions with respect to the sample. An acquisition means for each acquisition and a calculation means for calculating the refractive index of the sample based on the first and second hours are provided.

The first example of the measurement method of the present invention is the first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected by the surface, and the surface irradiated with the terahertz wave. 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 the second time required for the plurality of irradiation positions of the terahertz wave having different positions with respect to the sample. Each includes an acquisition step of acquiring the sample and a calculation step of calculating the refractive index of the sample based on the first and second hours.

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 showing a configuration of a terahertz wave measuring device of this embodiment. FIG. 2 is a flowchart showing an example of the flow of the first measurement operation for measuring the refractive index and the thickness performed by the terahertz wave measuring device. FIG. 3 is a cross-sectional view of a 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 the waveform signal of the terahertz wave detected by the terahertz wave detection element. FIG. 5 is a cross-sectional view of a 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 showing an example of the flow of the second measurement operation for measuring the refractive index and the thickness performed by the terahertz wave measuring device. FIG. 7 is a cross-sectional view of a 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, the measuring device, the measuring method, and the embodiment of the computer program will be described.

(Embodiment of measuring device)
<1>
In the measuring device 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 by the surface, and the terahertz wave irradiated on the surface are said to be the same. 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 a plurality of irradiation positions of the terahertz waves having different positions with respect to the sample. It is provided with an acquisition means for calculating the refractive index of the sample based on the first and second hours.

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

<2>
In another aspect of the measuring device of the present embodiment, the thickness of the sample, which is the 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 sample thicknesses, so that the measuring device can suitably measure (that is, calculate) the refractive index of the sample.

<3>
In another aspect of the measuring device of the present embodiment, the irradiation means for irradiating the terahertz wave toward the surface and the detection means for detecting the terahertz wave reflected by the sample are further provided, and the predetermined position is located. , The position where the detection means is installed, and the first time is required from the irradiation of the terahertz wave by the irradiation means until the terahertz wave reflected on the surface reaches the detection means. The second time is the time required for the terahertz wave reflected on the back surface to reach the detection means after the irradiation means irradiates the terahertz wave.

According to this aspect, the measuring device can suitably measure the refractive index of the sample by using the irradiation means and the detecting means.

<4>
In another aspect of the measuring device of the present embodiment, the changing means for changing the irradiation position is further provided by moving the moving object including the sample along a predetermined moving direction.

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

<5>
In another aspect of the measuring device of the present embodiment, the irradiation position is moved by moving a moving object including at least one of the sample, the irradiation means, and the detection means along a predetermined movement direction. Further provided with a changing means for changing.

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

<6>
In another aspect of the measuring device for moving the moving object as described above, when the moving direction is parallel to the back surface, the acquisition means obtains the first position when the irradiation position is the first position. And the second time, and the first and second hours when the irradiation position is a second position different from the first position are acquired.

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) and the back surface of the sample does not change. In this case, the measuring device can suitably measure the refractive index of the sample by acquiring the two first time and the two second time corresponding to the two different irradiation positions. That is, the measuring device does not have to acquire three or more first hours and three or more second hours corresponding to each of the three or more irradiation positions in order to measure the refractive index of the sample.

<7>
In another aspect of the measuring device that acquires the first and second hours when the irradiation position is the first position and the first and second hours when the irradiation position is the second position as described above, the irradiation position. The first and second hours when is the first _{position are defined as ta1} and _{tb1, respectively,} and the first and second hours when the irradiation position is the second position are _{ta2, respectively.} And t _b2 , the variable Δt ₁ is defined by the mathematical formula 1, the variable Δt ₂ is defined by the mathematical formula 2, and the refractive index is defined as n. The calculation means calculates the refractive index based on the mathematical formula 3.

According to this aspect, the measuring device can suitably measure the refractive index of the sample based on the first and second hours by performing the calculation based on the mathematical formulas 1 to 3.

<8>
In another aspect of the measuring device for moving the moving object as described above, when the moving direction is not parallel to the back surface and the back surface is flat, the moving means keeps the moving direction fixed. By moving the moving object, the irradiation positions are changed in order to different first positions, second positions, and third positions, and the moving direction is not parallel to the back surface and the back surface is a flat surface. In some cases, the acquisition means has the first and second hours when the irradiation position is the first position, and the first and second hours when the irradiation position is the second position. Further, when the first and second hours when the irradiation position is the third position are acquired and the moving direction is not parallel to the back surface and the back surface is flat, the acquisition means , The first and second hours, 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 irradiation position is changed from the second position to the second position. The refractive index is calculated based on the amount of movement of the moving object when changing to the third position.

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 to the back of the sample also changes. In this case, the measuring device can suitably measure the refractive index of the sample by acquiring the three first hours and the three second hours corresponding to the three different irradiation positions. That is, the measuring device does not have to acquire four or more first hours and four or more second hours corresponding to each of the four or more irradiation positions in order to measure the refractive index of the sample.

<9>
As described above, the first and second hours when the irradiation position is the first position, the first and second hours 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 device for acquiring the second time, the first and second hours when the irradiation position is the first position _{are defined as ta1} and _{tb1, respectively,} and the irradiation position is the first position. The first and second hours when the two _{positions are set are defined as ta2} and t _{b2, respectively,} and the first and second hours when the irradiation position is the third position are defined as _ta3 and t _{b3, respectively.} The variable Δt ₁ is defined by the formula 4, the variable Δt ₂ is defined by the formula 5, the variable Δt ₃ is defined by the formula 6, and the irradiation position is changed from the first position to the second position. The moving amount of the moving object in the case of changing the irradiation position from the second position to the third position is defined as P2, and the refractive index is defined as P2. Is defined as n, and when the moving direction is not parallel to the back surface and the back surface is flat, the calculation means calculates the refractive index based on the mathematical formula 7.

According to this aspect, the measuring device can suitably measure the refractive index of the sample based on the first and second hours by performing the calculation based on the formulas 4 to 7.

<10>
In another aspect of the measuring device for moving the moving object as described above, when the moving direction is not parallel to the back surface and the back surface is flat, the moving means (i) sets the irradiation position. The amount of movement of the moving object when the first position, the second position, and the third position, which are different from each other, are changed in order, and (ii) the first position is changed to the second position. The moving object is moved while the moving direction is fixed 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 moving direction is not parallel to the back surface and the back surface is flat, the acquisition means uses the first and second hours when the irradiation position is the first position, and the irradiation position is the first position. The first and second hours when the second position is set, and the first and second hours when the irradiation position is the third position are acquired.

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

<11>
As described above, the first and second hours when the irradiation position is the first position, the first and second hours 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 device that acquires the second time, the first and second hours when the irradiation position is the first position _{are defined as ta1} and _{tb1, respectively,} and the irradiation position is the first position. The first and second hours when the two _{positions are set are defined as ta2} and t _{b2, respectively,} and the first and second hours when the irradiation position is the third position are defined as _ta3 and t _{b3, respectively.} If the variable Δt ₁ is defined by the mathematical formula 8, the variable Δt ₂ is defined by the mathematical formula 9, the variable Δt ₃ is defined by the mathematical formula 10, and the refractive index is defined as n, the moving direction is parallel to the back surface. If the back surface is flat, the calculation means calculates the refractive index based on Equation 11.

According to this aspect, the measuring device can suitably measure the refractive index of the sample based on the first and second hours by performing the calculation based on the mathematical formulas 8 to 11.

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

According to this aspect, the measuring device can measure (ie, 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 by the surface, and the terahertz wave irradiated on the surface are said to be the same. 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 a plurality of irradiation positions of the terahertz waves having different positions with respect to the sample. The acquisition step is provided with a calculation step of calculating the refractive index of the sample based on the first and second hours.

According to the measuring device of the present embodiment, it is possible to preferably enjoy the same effect as the effect that can be enjoyed by the measuring device of the present embodiment described above.

In addition, various aspects may be adopted as the measurement method of this embodiment corresponding to various aspects adopted by the measuring apparatus of this embodiment.

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

According to the computer program of the present embodiment, it is possible to preferably enjoy the same effect as that of the measuring device of the present embodiment described above.

The computer program of the present embodiment may also adopt various aspects corresponding to the various aspects adopted by the measuring device of the present embodiment. Further, the computer program may be recorded on a computer-readable recording medium.

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

As described above, the measuring device of the present embodiment includes an acquisition means and a calculation means. The measurement method of the present embodiment includes an acquisition step and a calculation step. The computer program of the present embodiment causes a computer to execute the measurement method of the present embodiment described above. Therefore, the refractive index of the sample is measured even when the sample is not brought into contact with any special member.

Hereinafter, examples of the measuring device, the measuring method, and the computer program will be described with reference to the drawings. In particular, in the following, the measuring device, the measuring method and the computer program will be described with reference to an example applied to the terahertz wave measuring device 100 which 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 this embodiment will be described with reference to FIG. FIG. 1 is a block diagram showing a configuration of the terahertz wave measuring device 100 of this embodiment.

As shown in FIG. 1, the terahertz wave measuring device 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 has both the straightness of light and the transmission of electromagnetic waves. The terahertz region is the frequency domain in which various substances have their own absorption spectra. Therefore, the terahertz wave measuring device 100 can measure the characteristics of the sample 10 by analyzing the terahertz wave THz applied to the sample 10. In this embodiment, the terahertz wave measuring device 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 applied to the sample 10.

Here, since the period of the terahertz wave THz is a period on the order of subpicoseconds, it is technically difficult to directly detect the waveform of the terahertz wave THz. Therefore, the terahertz wave measuring device 100 indirectly detects the waveform of the terahertz wave THz by adopting the pump-probe method based on the time-delayed scanning. Hereinafter, the terahertz wave measuring device 100 that employs such a pump-probe method will be described in more detail.

As shown in FIG. 1, the terahertz wave measuring device 100 includes a pulse laser device 101, a terahertz wave generating element 110 which is a specific example of the “irradiation means”, a beam splitter 161 and a reflecting mirror 162, and a reflecting mirror 163. , The half mirror 164, the optical delay mechanism 120, the terahertz wave detection element 130 which is a specific example of the "detection means", the bias voltage generation unit 141, the IV (current-voltage) conversion unit 142, and the like. It includes a control unit 150 and a stage 170.

The pulse laser device 101 generates a subpicosecond 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 light LB generated by the pulse laser device 101 is incident on the beam splitter 161 via a light guide path (for example, an optical fiber or the like) (not shown).

The beam splitter 161 splits the pulsed laser beam LB into a pump beam LB1 and a probe beam LB2. The pump light LB1 is incident on the terahertz wave generating element 110 via a light guide path (not shown). On the other hand, the probe light LB2 is incident on the optical delay mechanism 120 via a light guide path and a reflector 162 (not shown). After that, the probe light LB2 emitted from the optical delay mechanism 120 enters the terahertz wave detection element 130 via the reflector 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 applied to the gap while an effective bias voltage (for example, a bias voltage other than 0V) is applied to the gap, the pump light LB1 is also applied to the photoconducting layer formed under the gap. Is irradiated. In this case, carriers are generated in the photoconducting layer irradiated with the pump light LB1 by photoexcitation by the pump light LB1. As a result, the terahertz wave generating element 110 generates a pulsed current signal on the order of subpicoseconds or femtoseconds according to the generated carrier. The generated current signal flows through a pair of electrode layers. As a result, the terahertz wave generating element 110 emits the terahertz wave THz caused by 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 applied to the sample 10 (particularly, the surface 10a of the sample 10). The terahertz wave THz applied to the sample 10 is reflected by the sample 10 (in particular, by the front surface 10a and the back surface 10b of the sample, respectively). 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 is incident on the terahertz wave detection element 130.

The terahertz wave detection element 130 detects the terahertz wave THz incident on the terahertz wave detection element 130. Specifically, the terahertz wave detection element 130 includes a pair of electrode layers facing each other via a gap. When the gap is irradiated with the probe light LB2, the photoconducting layer formed under the gap is also irradiated with the probe light LB2. In this case, carriers are generated in the photoconducting layer irradiated with the probe light LB2 by photoexcitation 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 THz is irradiated to the terahertz wave detection element 130 while the probe light LB2 is irradiated to 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. do. The 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 optical LB2. When the optical path length difference is adjusted, the timing at which the pump light LB1 enters the terahertz wave generating element 110 (or the timing at which the terahertz wave generating element 110 emits the terahertz wave THz) and the timing at which the probe light LB2 emits the terahertz wave THz and the probe light LB2 are the terahertz wave detecting element 130. The time difference from the timing of incident on the terahertz wave (or the timing at which the terahertz wave detection element 130 detects the terahertz wave THz) is adjusted. The terahertz wave measuring device 100 indirectly detects the waveform of the terahertz wave THz by adjusting this time difference. For example, when the optical path of the probe light LB2 is lengthened by 0.3 mm (however, the optical path length in air) by the optical delay mechanism 120, the timing at which the probe light LB2 is incident on the terahertz wave detection element 130 is delayed by 1 picosecond. Become. In this case, the timing at which the terahertz wave detection element 130 detects the terahertz wave THz is delayed by one picosecond. Considering that terahertz wave THz having the same waveform is repeatedly incident on the terahertz wave detection element 130 at intervals of about several tens of MHz, the timing at which the terahertz wave detection element 130 detects the terahertz wave THz is gradually shifted. As a result, the terahertz wave detection element 130 can indirectly detect the waveform of the terahertz wave THz. That is, the lock-in detection unit 151, which will be described later, can detect the terahertz wave THz waveform 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 device 100. The control unit 150 includes a CPU (Central Processing Unit) and a memory. A computer program for causing the control unit 150 to perform a control operation is recorded in the memory. 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 the computer program downloaded via the 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 by 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 inside 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 the sample value of the terahertz wave THz. After that, 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), so that the lock-in detection unit 151 performs the terahertz wave. The terahertz wave THz waveform (time waveform) detected by the detection element 130 can be detected. The lock-in detection unit 151 outputs a waveform signal indicating the terahertz wave THz waveform 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 (that is, the detection signal of the terahertz wave THz) output from the IV conversion unit 142. 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. When the terahertz wave measuring device 100 does not use the 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 by using the terahertz time region spectroscopy, and measures the characteristics of the sample 10 based on the frequency spectrum.

In this embodiment, in particular, the signal processing unit 152 performs a measurement operation for 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 has a thickness d of the sample 10 (that is, a direction in which the terahertz wave THz is incident on the sample 10) based on the waveform signal output from the lock-in detection unit 151. A measurement operation is performed to measure the thickness d) along the line. The thickness d here means "the physical distance between the front surface 10a and the back surface 10b". In order to perform the measurement operation, the signal processing unit 152 is one of the detection time acquisition unit 1521, which is a specific example of the "acquisition means", and one of the "calculation means", as logical processing blocks formed inside the CPU. A refractive index calculation unit 1522, which is a specific example, and a thickness calculation unit 1523, which is a specific example of the “calculation means”, are provided. A specific example of the operation 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 the description thereof will be omitted here.

The stage 170 holds the 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 can move along a predetermined moving direction while holding the sample 10. When the stage 170 moves, the irradiation position of the terahertz wave THz on the sample 10 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 as to adjust (for example, change to a desired position) the irradiation position of the terahertz wave THz.

The irradiation position changing unit 153 moves the terahertz wave THz irradiation position 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) Measurement operation for measuring the refractive index n and the thickness d performed by the terahertz wave measuring device 100 Subsequently, referring to FIGS. 2 to 7, the refractive index n and the thickness d performed by the terahertz wave measuring device 100 are measured. The measurement operation to be measured will be described. In this embodiment, the terahertz wave measuring device 100 performs at least one of two types of measurement operations (first measurement operation and second measurement operation) as measurement operations 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 the refractive index n and the thickness d First , with reference to FIG. 2, the first measurement operation for measuring the refractive index n and the thickness d performed by the terahertz wave measuring device 100. explain. FIG. 2 is a flowchart showing an example of the flow of the first measurement operation for measuring the refractive index n and the thickness d performed by the terahertz wave measuring device 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).

After that, 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 terahertz wave THz to the first position on the surface 10a of the sample 10 (step S102).

The terahertz wave THz applied to 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 to 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 to the sample 10 is reflected by the surface 10a of the sample 10. The terahertz wave THz reflected by the surface 10a propagates from the sample 10 to the terahertz wave detection element 130.

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

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

Further, in order to promote the reflection of the terahertz wave THz by the back surface 10b of the sample 10, the 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.

Again, in FIG. 2, 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 showing the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 is input to the signal processing unit 152.

After that, the detection time acquisition unit 1521 acquires the first detection time _ta1 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 device 100 acquires _{the first detection time ta1} 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 ta1} and the second detection time t _b1 acquired when the terahertz wave THz is applied to the first position to the refractive index calculation unit 1522. The first detection time _ta1 and the second detection time t _b1 are specific examples of the "first time" and the "second time", respectively.

Here, the acquisition operation of the first detection time _ta1 and the second detection time t _b1 will be described with reference to FIG. FIG. 4 is a graph showing a waveform signal of the terahertz wave THz detected by the terahertz wave detection element 130.

As shown in FIG. 4, the waveform signal includes a waveform signal corresponding to the terahertz wave THz reflected on the front surface 10a and a waveform signal corresponding to the terahertz wave THz reflected on the back surface 10b. The terahertz wave THz reflected on the back surface 10b reaches the terahertz wave detection element 130 after passing through the inside of the sample 10, while the terahertz wave THz reflected on the front surface 10a does not pass through the inside of the sample 10 and reaches the terahertz. It reaches the wave detection element 130. Therefore, the terahertz wave THz reflected on the back surface 10b reaches the terahertz wave detection element 130 with a time delay from the terahertz wave THz reflected on the front surface 10a. Therefore, even on the waveform signal, the waveform signal corresponding to the terahertz wave THz reflected on the back surface 10b is delayed in time from the waveform signal corresponding to the terahertz wave THz reflected on the front surface 10a.

The first detection time _ta1 is the time required from when the terahertz wave generating element 110 starts irradiating the terahertz wave THz to when the terahertz wave THz reflected on the surface 10a of the sample 10 reaches the terahertz wave detecting element 130. be. On the other hand, the second detection time t _b1 is from the time when the terahertz wave generating element 110 starts irradiating the terahertz wave THz to the time when the terahertz wave THz reflected on the back surface 10b of the sample 10 reaches the terahertz wave detecting element 130. It is the time required. The detection time acquisition unit 1521 can easily acquire (in other words, calculate or specify) _{the first detection time ta1} and the second detection time t _{b1 by analyzing the waveform signal.}

In FIG. 2 again, after that, the terahertz wave measuring device 100 performs the above-described operation (that is, the operation of acquiring _{the first detection time ta2} 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 be 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 amount of movement 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 a 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 condition that 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 that the terahertz wave THz is irradiated to the second position are the same. Further, in the first and second positions, the distance L13 between the terahertz wave detection element 130 and the back surface 10b under the condition that the terahertz wave THz is irradiated in the first position, and the terahertz wave THz in the second position. The second condition that the distance L23 between the terahertz wave detection element 130 and the back surface 10b under the irradiated 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 satisfying 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 along the direction parallel to the back surface 10b 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 detection element 130 and the back surface 10b does not change.

The state in which the stage 170 moves along the direction parallel to the back surface 10b is defined as the stage 170 under the condition that the terahertz wave THz is irradiated to the first position and the second position. It means a state in which the stage 170 moves so that the stage 170 and the stage 170 under the condition of being irradiated with the terahertz wave THz are lined up in a direction parallel to the back surface 10b. Such a state is realized by moving the stage 170 only in 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 large. As long as the total is zero (that is, offset), it will be realized.

The irradiation position changing unit 153 moves 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 to move the terahertz wave THz irradiation position. May be adjusted as described above. Also 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. The third condition is satisfied. 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 terahertz wave THz is irradiated to each of the first position and the second position satisfying the third condition.

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 the variation in the thickness d due to the unevenness (for example, a step, a curved surface, etc.) intentionally formed on the surface 10a of the sample 10. Alternatively, the variation in the thickness d may include the 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.

When the back surface 10b of the sample 10 is flat, the first and second positions are likely to satisfy the above-mentioned first and second conditions. Therefore, in the first measurement operation, it is preferable that the back surface 10b of the sample 10 is flat.

After that, the terahertz wave generating element 110 irradiates the terahertz wave THz to the second position on the surface 10a of the sample 10 (step S112). After that, the terahertz wave detection element 130 detects the terahertz wave THz reflected by the sample 10 (step S112). As a result, a waveform signal showing the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 is input to the signal processing unit 152. After that, the detection time acquisition unit 1521 acquires the first detection time _ta2 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 device 100 acquires _{the first detection time ta2} and the second detection time t _b2 based on the detection result of the terahertz wave THz irradiated to the second position. _{The detection time acquisition unit 1521 outputs the first detection time ta2} and the second detection time t _b2 acquired when the terahertz wave THz is applied to the second position to the refractive index calculation unit 1522. The first detection time _ta2 and the second detection time t _b2 are specific examples of the "first time" and the "second time", respectively.

After that, the refractive index calculation unit 1522 calculates the refractive index n of the sample 10 based on _{the first detection time ta1} and the second detection time t _b1 , and the first detection time _ta2 and the second detection time t _b2. (Step S121). Specifically, the refractive index calculation unit 1522 calculates the refractive index n using the mathematical formula 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. do. Therefore, Δt ₁ can be calculated from the mathematical formula Δt ₁ = t _b1- t _{a1. Δt 2 in} Equation 12 corresponds to the time required for the terahertz wave THz to pass through the inside of the sample 10 when the terahertz wave THz is irradiated to the second position. 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 terahertz wave THz is irradiated to the second position. do. Therefore, Δt ₂ can be calculated from the mathematical formula Δt ₂ = t _b2- t _a2.

Here, the reason why the refractive index n can be calculated using the mathematical formula 12 will be described with reference to FIG. 5 described above. In the following description, for convenience of explanation, the distance L11 between the terahertz wave generating element 110 and the back surface 10b under the condition that the terahertz wave THz is irradiated to the first position, 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 that the terahertz wave is irradiated, and the terahertz wave detecting element 130 and the back surface 10b under the condition that the terahertz wave THz is irradiated at the first position. The distance L13 between the terahertz waves and the distance L23 between the terahertz wave detection element 130 and the back surface 10b under the condition that the second position is irradiated with the terahertz wave THz are the same (for convenience, L). There is). That is, it is assumed that L11 = L13 = L21 = L23 = L. However, even when L11 = L21 ≠ L13 = L23, if "L" in the explanation described later is replaced with "(L11 + L13) / 2" or "(L21 + L23) / 2", the mathematical formula 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 that the first position is irradiated with the terahertz wave THz is half of _{the second detection time t b1.} Under the condition that the first position is irradiated with the terahertz wave THz, the optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the back surface 10b of the terahertz wave THz 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, if the velocity of the terahertz wave THz in the air is defined as c, the mathematical formula 13 holds. For the same reason, the formula 14 related to 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 that the terahertz wave THz is irradiated to the first position is half of _{the first detection time ta1.} Under the condition that the first position is irradiated with the terahertz wave THz, the optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the surface 10a of the terahertz wave THz is L−d1. Therefore, the mathematical formula 15 holds. For the same reason, the formula 16 related to the second position also holds.

By substituting the equation 15 for the equation 13, the variable d1 can be deleted from the equation 13. When the formula 13 in which the variable d1 is deleted is solved for n, the formula 17 is obtained. By substituting the equation 16 for the equation 14, the variable d2 can be deleted from the equation 14. Solving the formula 14 with the variable d2 eliminated for n gives the formula 18.

By substituting the equation 18 for the equation 17, the variable n can be deleted from the equation 17. When the formula 17 in which the variable n is eliminated is solved for L, the formula 19 is obtained.

By substituting Equation 19 into Equation 17, the variable L can be eliminated from Equation 17. When the formula 17 in which the variable L is eliminated is solved for n, the above-mentioned formula 12 is obtained.

Again in FIG. 2, after that, the thickness calculation unit 1523 determines the first detection time _ta1 and the second detection time t _b1 , the first detection time _ta2 and the second detection time t _b2 , and the refraction calculated in step S121. The thickness d of the sample 10 is calculated based on the rate n (step S122). In the first operation example, as described above, the thickness d1 of the sample 10 at the first position and the thickness d2 of the sample 10 at the second position are different. Therefore, the thickness calculation unit 1523 calculates the thicknesses d1 and d2, respectively. Specifically, the thickness calculation unit 1523 calculates the thickness d1 by using the mathematical formula _{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 measuring device 100 of 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 device 100 of the present embodiment irradiates the terahertz wave THz to a plurality of irradiation positions having different thicknesses d of the sample 10 so that the sample 10 does not come into contact with any special member and has a refractive index n. Can be suitably measured. Further, since the terahertz measuring device 100 of this embodiment can preferably measure the refractive index n, the thickness d of the sample 10 can also be preferably measured.

Here, as an example of a terahertz wave measuring device of a comparative example in which the thickness d of the sample 10 is measured without measuring the refractive index n, the thickness d is measured by irradiating a 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, using equation of thickness _{d = c × (t b -t} a) / 2, for measuring the thickness d of the sample 10. However, as described above, the velocity c'of the terahertz wave THz inside the sample 10 varies depending on the refractive index n. Therefore, the thickness d measured by the terahertz wave measuring device of the comparative example becomes a value larger than _{the original thickness d = (c / n) × (t b} −t _{a) / 2 of the sample 10.} It ends up.

Therefore, the terahertz wave measuring device 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, it is generally time-consuming to measure the refractive index n. However, the terahertz wave measuring device 100 of this embodiment has a great advantage that the refractive index n can be measured relatively easily.

The above-mentioned mathematical formula 12 is a mathematical formula obtained by solving a simultaneous equation composed of the mathematical formulas 13 to 16 (that is, a simultaneous equation consisting of four equations having L, d1, d2 and n as unknown variables) for n. It can be said that. Therefore, the terahertz wave measuring device 100 may calculate the refractive index n by solving the simultaneous equations composed of the equations 13 to 16 for n instead of using the equation 12. For example, the terahertz wave measuring device 100 determines whether or not the simultaneous equations are established by substituting the assumed values of n into the simultaneous equations, and adjusts the assumed values of n to be substituted into the simultaneous equations until the simultaneous equations are satisfied. You may repeat the operation of In this case, the assumed value of n for which the simultaneous equations hold corresponds to the refractive index n of the sample 10.

(2-2) Second measurement operation for measuring the refractive index n and the thickness d Next, referring to FIG. 6, the second measurement operation for measuring the refractive index n and the thickness d performed by the terahertz wave measuring device 100. 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 device 100.

In the first measurement operation described above, the stage 170 moves along the 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 moving 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 the 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 changes. In some cases.

In this case, it is difficult for the terahertz wave measuring device 100 to measure the refractive index n even if the first measurement operation is performed. Therefore, when the stage 170 cannot move along the direction parallel to the back surface 10b of the sample 10, the terahertz wave measuring device 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 formed with irregularities).

Specifically, as shown 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). After that, the terahertz wave detection element 130 detects the terahertz wave THz reflected by the sample 10 (step S202). As a result, a waveform signal showing the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 is input to the signal processing unit 152. After that, the detection time acquisition unit 1521 acquires the first detection time _ta1 and the second detection time t _b1 based on the waveform signal input to the signal processing unit 152 (step S203). Unless otherwise specified, the operations of steps S201, S202, and S203 may be the same as the operations of steps S101, S102, and S103 of the first measurement operation, respectively.

After that, the irradiation position changing unit 153 controls the stage 170 so as to be at 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 mainly performed when the stage 170 cannot move along the direction parallel to the back surface 10b of the sample 10. Therefore, when the irradiation position changing unit 153 changes the irradiation position to the second position, even if the irradiation position of the terahertz wave THz is changed, the irradiation position changing unit 153 is located between the terahertz wave generating element 110 and the back surface 10b. It is not necessary to control the stage 170 so as to satisfy the above-mentioned first condition that the distance does not change. Similarly, when the irradiation position changing unit 153 changes the irradiation position to the second position, the terahertz wave detection element 130 and the back surface 10b are between the terahertz wave detection element 130 and the back surface 10b even when the irradiation position of the terahertz wave THz is changed. It is not necessary to control the stage 170 so as to satisfy the above-mentioned second condition that the distance does not change.

After that, the terahertz wave generating element 110 irradiates the terahertz wave THz to the second position (step S212). After that, the terahertz wave detection element 130 detects the terahertz wave THz reflected by the sample 10 (step S212). As a result, a waveform signal showing the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 is input to the signal processing unit 152. After that, the detection time acquisition unit 1521 acquires the first detection time _ta2 and the second detection time t _b2 based on the waveform signal input to the signal processing unit 152 (step S213). Unless otherwise specified, the operations of steps S211, S212, and S213 may be the same as the operations of steps S101, S102, and S103 of the first measurement operation, respectively.

After that, the irradiation position changing unit 153 controls the stage 170 so as to be at 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.

In the second measurement operation, particularly when the irradiation position changing unit 153 changes the irradiation position from the first position to the second position in the moving direction of the stage 170 when the irradiation position is changed from the second position to the third position. The stage 170 is controlled so as to be in the same direction 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.

The second measurement operation is mainly performed when the stage 170 cannot move along the direction parallel to the back surface 10b of the sample 10. Therefore, 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 does not have to control the stage 170 so as to satisfy the second condition described above.

After that, the terahertz wave generating element 110 irradiates the terahertz wave THz to the third position (step S222). After that, the terahertz wave detection element 130 detects the terahertz wave THz reflected by the sample 10 (step S222). As a result, a waveform signal showing the waveform of the terahertz wave THz detected by the terahertz wave detection element 130 is input to the signal processing unit 152. After that, the detection time acquisition unit 1521 acquires the first detection time _ta3 and the second detection time t _b3 based on the waveform signal input to the signal processing unit 152 (step S223). Unless otherwise specified, the operations of steps S221, S222, and S223 may be the same as the operations of steps S101, S102, and S103 of the first measurement operation, respectively.

Thereafter, the refractive index calculation unit 1522, a first detection time _{t a1} and the second detection time _{t b1,} first detection time _{t a2} and the second detection time _{t b2,} and the first detection time _{t a3} and the second detection time The refractive index n of the sample 10 is calculated based on t _{b3 (step S231).} Specifically, the refractive index calculation unit 1522 calculates the refractive index n using the mathematical formula 20. It should be noted that Δt ₁ and Δt ₂ in the mathematical formula 20 have already been explained at the time of explaining the first measurement operation. _{Δt 3} in the equation 20 corresponds to the time required for the terahertz wave THz to pass through the inside of the sample 10 when the terahertz wave THz is irradiated to the third position. That is, Δt ₃ in the 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 terahertz wave THz is irradiated to the third position. do. Therefore, Δt ₃ can be calculated from the mathematical formula Δt ₃ = t _b3- t _a3.

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

In the following description, for convenience of explanation, the distance L11 between the terahertz wave generating element 110 and the back surface 10b under the condition that the terahertz wave THz is irradiated to the first position, 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 of being irradiated is the same (for convenience, it is L1). The distance L21 between the terahertz wave generating element 110 and the back surface 10b under the condition that the terahertz wave THz is irradiated at the second position, and the terahertz wave under the condition that the terahertz wave THz is irradiated at the second position. It is assumed that the distance L23 between the detection element 130 and the back surface 10b is the same (for convenience, it is L2). The distance L31 between the terahertz wave generating element 110 and the back surface 10b under the condition that the terahertz wave THz is irradiated at the third position, and the terahertz wave under the condition that the terahertz wave THz is irradiated at the third position. It is assumed that the distance L33 between the detection element 130 and the back surface 10b is the same (for convenience, it is L3). However, even when L11 ≠ L13, if "L1" in the explanation described later is replaced with "(L11 + L13) / 2", there is no change in the reason why the refractive index n can be calculated using the mathematical formula 20. You can see that. Even when L21 ≠ L23, if "L2" in the explanation described later is replaced with "(L21 + L23) / 2", there is no change in the reason why the refractive index n can be calculated using the mathematical formula 20. I understand. Even when L31 ≠ L33, if "L3" in the explanation described later is replaced with "(L31 + L33) / 2", there is no change in the reason why the refractive index n can be calculated using the mathematical formula 20. I understand.

Further, in the following description, it is assumed that the thickness d of the sample 10 at the first position is d1. It is assumed that the thickness d of the sample 10 at the second position is 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 that the first position is irradiated with the terahertz wave THz is half of _{the second detection time t b1.} Under the condition that the first position is irradiated with the terahertz wave THz, the optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the back surface 10b of 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, if the velocity of the terahertz wave THz in the air is defined as c, the mathematical formula 21 holds. For the same reason, the formula 22 related to the second position and the formula 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 that the terahertz wave THz is irradiated to the first position is half of _{the first detection time ta1.} Under the condition that the first position is irradiated with the terahertz wave THz, the optical path length (that is, the optical distance) from the terahertz wave generating element 110 to the surface 10a of the terahertz wave THz is L1-d1. Therefore, the mathematical formula 24 holds. For the same reason, the formula 25 related to the second position and the formula 26 related to the third position also hold.

_{When the mathematical formula obtained by substituting "c × ta1} / 2" of the mathematical formula 24 into "L1-d1" in the mathematical formula 21 is solved for d1, the mathematical formula 27 is obtained. _{When the mathematical formula obtained by substituting "c × ta2} / 2" of the mathematical formula 25 into "L2-d2" in the mathematical formula 22 is solved for d2, the mathematical formula 28 is obtained. _{When the mathematical formula obtained by substituting "c × ta3} / 2" of the mathematical formula 26 into "L3-d3" in the mathematical formula 23 is solved for d3, the mathematical 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, the mathematical formula 30 holds.

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.

By rearranging the mathematical formulas obtained by substituting the mathematical formulas 27, 28 and 29 with respect to the mathematical formula 31, the above-mentioned mathematical formula 20 can be obtained.

Again in FIG. 2, the thickness calculation unit 1523 then calculates the thickness d (that is, the thicknesses d1, d2, and d3) of the sample 10 (step S232). Specifically, the thickness calculation unit 1523 calculates the thickness d1 by using the mathematical formula _{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 measuring device 100 of the present embodiment can enjoy the same effect as the effect that can be enjoyed when the first measurement operation is executed by executing the second measurement operation. In particular, the terahertz wave measuring device 100 has 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).

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

Further, the above-mentioned formula 20 is a simultaneous equation composed of the formulas 21 to 26 and 30 (that is, a simultaneous equation consisting of seven equations having L1, L2, L3, d1, d2, d3 and n as unknowns). It can be said that it is a mathematical formula obtained by solving for n. Therefore, instead of using the equation 20, the terahertz wave measuring device 100 may calculate the refractive index n by solving a simultaneous equation composed of the equations 21 to 26 and 30 for n.

The present invention is not limited to the above-described embodiment, and can be appropriately modified within the scope of claims and within a range not contrary to the gist or idea of the invention that can be read from the entire specification. Measuring methods and computer programs are also included in the technical scope of the present invention.

10 Sample 10a Front surface 10b Back surface 100 Terahertz wave measuring device 101 Pulse laser device 110 Terahertz wave generating element 120 Optical delay mechanism 130 Terahertz wave detecting element 150 Control unit 151 Lock-in detection unit 152 Signal processing unit 1521 Detection time acquisition unit 1522 Refraction rate calculation Part 1523 Thickness calculation part 153 Irradiation position change part 170 Stage LB1 Pump light LB2 Probe light THz terahertz wave

Claims (8)

It ’s a measuring device,
The first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected by the surface, and the terahertz wave irradiated on the surface are located on the opposite side of the surface. An acquisition means for acquiring the 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.
By moving the relative position of the sample with respect to the measuring device along a predetermined moving direction, the irradiation position is changed in order to the first position, the second position, and the third position, which are different from each other.
The first and second hours when the irradiation position is the first position, the first and second hours when the irradiation position is the second position, and the first and second hours acquired by the acquisition means. The first and second hours when the irradiation position is the third position, and the first movement amount of the relative position when the irradiation position is changed from the first position to the second position. Further, it is provided with a calculation means for calculating the refractive index of the sample based on the second movement amount of the relative position when the irradiation position is changed from the second position to the third position. Characteristic measuring device. The first and second hours when the irradiation position is the first position are _{defined as ta1} and _{tb1, respectively,} and the first and second hours when the irradiation position is the second position are defined as ta1 and tb1, respectively. defined as respectively _{t a2} and _{t b2,} the first and second time when the irradiation position becomes the third position is defined as, respectively _{t a3} and _{t b3,} define the variable Delta] t ₁ in the formula 1, The variable Δt ₂ is defined by the mathematical formula 2, the variable Δt ₃ is defined by the mathematical formula 3, the first movement amount is defined as P1, the second movement amount is defined as P2, and the refractive index is defined as n. The measuring device according to claim 1, wherein the calculation means calculates the refractive index based on the mathematical formula 4.

It ’s a measuring device,
The first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected by the surface, and the terahertz wave irradiated on the surface are located on the opposite side of the surface. An acquisition means for acquiring the 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.
By moving the relative position of the sample with respect to the measuring device along a predetermined moving direction, the irradiation position is moved to the first position, the second position separated from the first position by the first distance along the moving direction. And the changing means for sequentially changing from the second position to the third position separated by the first distance along the moving direction.
The first and second hours when the irradiation position is the first position, the first and second hours when the irradiation position is the second position, and the first and second hours acquired by the acquisition means. A measuring device including a calculation means for calculating the refractive index of the sample based on the first and second times when the irradiation position is the third position. The first and second hours when the irradiation position is the first position are _{defined as ta1} and _{tb1, respectively,} and the first and second hours when the irradiation position is the second position are defined as ta1 and tb1, respectively. defined as respectively _{t a2} and _{t b2,} the first and second time when the irradiation position becomes the third position is defined as, respectively _{t a3} and _{t b3,} define the variable Delta] t ₁ in equation 5, If the variable Δt ₂ is defined by the mathematical formula 6, the variable Δt ₃ is defined by the mathematical formula 7, and the refractive index is defined as n, the calculation means calculates the refractive index based on the mathematical formula 8. The measuring device according to claim 3.

The measuring device according to claim 1 or 2, wherein the changing means moves the relative position along the moving direction that is not parallel to the back surface when the back surface of the sample is flat. It is a measurement method using a measuring device.
The first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected by the surface, and the terahertz wave irradiated on the surface are 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 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 change step of changing the irradiation position to a first position, a second position, and a third position, which are different from each other, by moving the relative position of the sample with respect to the measuring device along a predetermined moving direction.
The first and second hours when the irradiation position is the first position, the first and second hours when the irradiation position is the second position, and the first and second hours acquired in the acquisition step. The first and second hours when the irradiation position is the third position, and the first movement amount of the relative position when the irradiation position is changed from the first position to the second position. It also includes a calculation step of calculating the refractive index of the sample based on the second movement amount of the relative position when the irradiation position is changed from the second position to the third position. Characteristic measurement method. It is a measurement method using a measuring device.
The first time required for the terahertz wave irradiated on the surface of the sample to reach a predetermined position after being reflected by the surface, and the terahertz wave irradiated on the surface are 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 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.
By moving the relative position of the sample with respect to the measuring device along a predetermined moving direction, the irradiation position is moved to the first position, the second position separated from the first position by the first distance along the moving direction. And the changing step of sequentially changing from the second position to the third position separated by the first distance along the moving direction.
The first and second hours when the irradiation position is the first position, the first and second hours when the irradiation position is the second position, and the first and second hours acquired in the acquisition step. A measurement method comprising a calculation step of calculating the refractive index of the sample based on the first and second times when the irradiation position is the third position. A computer program comprising causing a computer to execute the measurement method according to claim 6 or 7.

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