JP5824284B2 - Electromagnetic pulse measuring device - Google Patents

Electromagnetic pulse measuring device Download PDF

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JP5824284B2
JP5824284B2 JP2011179563A JP2011179563A JP5824284B2 JP 5824284 B2 JP5824284 B2 JP 5824284B2 JP 2011179563 A JP2011179563 A JP 2011179563A JP 2011179563 A JP2011179563 A JP 2011179563A JP 5824284 B2 JP5824284 B2 JP 5824284B2
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path length
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electromagnetic wave
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英俊 中西
英俊 中西
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株式会社Screenホールディングス
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  The present invention relates to a technique for imaging sample information.

  2. Description of the Related Art Conventionally, research on imaging for imaging sample information using a terahertz wave, which is a type of electromagnetic wave, has been performed. Terahertz waves have both the properties of radio waves and light, and industrial applications are expected in terms of high transparency and safety (Non-patent Document 1).

  Several techniques are known for imaging using terahertz waves. One is imaging using terahertz time domain spectroscopy (THz-TDS). In this imaging, a frequency spectrum for each position of the sample is acquired by THz-TDS. Then, an image in which the position information of the sample is associated with the frequency spectrum information corresponding to each position is generated.

  In addition, imaging using a terahertz camera has been proposed. In this imaging, image data is acquired by detecting terahertz waves with imaging elements arranged in a two-dimensional plane (Non-Patent Document 2).

  In the analysis of a sample using a terahertz wave, when high resolution is required, it is necessary to acquire a frequency spectrum by THz-TDS. When the information about the terahertz wave is imaged and displayed on the display, it is necessary to convert the information about the terahertz wave into information that is easy for humans to observe (easy to see). Here, since human eyes are sensitive to visible light, it is effective to convert the data into so-called three primary colors of light. However, the frequency spectrum obtained by THz-TDS is expressed by an N-dimensional multidimensional vector space whose frequency space ranges from several terahertz to several tens of terahertz. Therefore, it is necessary to devise in order to convert the frequency spectrum information into a three-dimensional space represented by three primary colors.

  As one method for converting a frequency spectrum into three-dimensional data, in Non-Patent Document 3, the first principal component axis is in the direction with the largest variance, the second principal component axis is in the direction with the second largest variance, and the third variance is in the direction. The third principal component axis is redefined in the direction in which the value is large, and the image is imaged around a vector having a large variance. In this case, the luminance difference on the image becomes large, and an image that can be easily identified by humans can be acquired.

  As another method, in Non-Patent Document 4, data of 2 to 13 terahertz is divided into three in terms of frequency, and the intensity is averaged for each frequency band to be colored.

Toyouchi Masayoshi, "Current Status and Prospects of Terahertz Wave Technology", Applied Physics, Vol. 75, No. 2 (2006), p. 160 Yuichi Kato, "Protecting Safety with Terahertz Waves", Applied Physics, Vol. 80, No. 1 (2011), p. 11 Hiromichi Hoshina et al., "Terahertz spectral image data analysis using chemometrics and application to liver cancer tissue", [online], [searched on July 20, 2011], Internet <URL: http: //www.riken. jp / ExtremePhotonics / TH_imaging / No.12.pdf> Fukunaga "Non-destructive investigation of cultural properties by terahertz spectroscopy", National Institute of Information and Communications Technology, Vol. 54, No. 1 (2008), p. 57

  However, when imaging by THz-TDS is performed, imaging is performed through restoration of terahertz wave pulses, Fourier transform processing, statistical processing, and the like. For this reason, when THz-TDS is performed on a wide area of the sample, there is a problem that a very long time is required for measurement. For this reason, there is a demand for a technique for efficiently imaging sample information.

  Therefore, an object of the present invention is to provide a technique for efficiently imaging information on a sample acquired using an electromagnetic wave pulse.

In order to solve the above problems, a first aspect is an electromagnetic wave pulse measuring device that measures an electromagnetic wave pulse transmitted or reflected through a sample, receives pulsed light emitted from a laser light source, and irradiates the sample with the electromagnetic wave pulse. An irradiating section, a detecting section for detecting an electromagnetic wave pulse transmitted or reflected by the sample in response to the irradiation of the pulsed light, a first optical path of the pulsed light from the laser light source to the irradiating section, or the An optical path length changing unit that changes an optical path length of the second optical path of the pulsed light from a laser light source to the detection unit, a relative movement mechanism that moves the irradiation unit relative to the sample, and the optical path length A control unit that controls the optical path length changing unit to be set to each of a first measurement optical path length, a second measurement optical path length, and a third measurement optical path length that are different from each other; and the optical path length Wherein when it is set to each of the first to third measuring optical path length, is the pulsed light irradiated on each position of the sample, the electric field intensity detected by the detecting unit for each position, A data conversion unit that converts to gradation data indicating gradation characteristics of three specific colors, and information on the electric field intensity at a portion corresponding to each position of the sample is expressed in a color tone according to the gradation data. An image generation unit for generating an image.

  According to a second aspect, in the electromagnetic wave pulse measurement device according to the first aspect, the three specific colors are red, green, and blue.

  Further, a third aspect is the electromagnetic wave pulse measuring device according to the first or second aspect, wherein the first optical path length for measurement is such that the electromagnetic wave pulse transmitted or reflected from a specific position of the sample has a substantially peak. And the optical path length at the peak time.

  Further, a fourth aspect is the electromagnetic wave pulse measuring apparatus according to the third aspect, wherein a pulse half-value width obtaining unit for obtaining a pulse half-value width when the electric field intensity of the electromagnetic wave pulse is a maximum half value; An optical path difference acquisition unit that acquires an optical path difference of the optical path length corresponding to a value width, wherein the second and third optical path lengths for measurement add the optical path difference to the optical path length at the peak time Or an optical path length obtained by subtracting the optical path difference from the optical path length at the peak time.

According to a fifth aspect, in the electromagnetic wave pulse measurement device according to any one of the first to fourth aspects, the electromagnetic wave pulse wave includes a terahertz wave pulse having a frequency of 0.01 THz to 100 THz.
According to a sixth aspect, in the electromagnetic wave pulse measuring apparatus for measuring the electromagnetic wave pulse transmitted or reflected through the sample, the irradiation unit that receives the pulsed light emitted from the laser light source and irradiates the sample with the electromagnetic wave pulse; A detection unit that detects an electromagnetic wave pulse that has been transmitted or reflected through a sample in response to irradiation of the pulsed light, and a first optical path of the pulsed light from the laser light source to the irradiation unit, or from the laser light source to the detection unit An optical path length changing unit that changes the optical path length of the second optical path of the pulsed light, a relative movement mechanism that moves the irradiation unit relative to the sample, and a first optical path length that is different from each other. A control unit that controls the optical path length changing unit to be set to each of the measurement optical path length, the second measurement optical path length, and the third measurement optical path length; and the optical path lengths from the first to third of A data conversion unit for converting the electric field intensity detected by the detection unit when set to each of the fixed optical path lengths into gradation data indicating gradation characteristics of three specific colors; and the electric field intensity An image generating unit that generates an image in which information relating to the tone data is expressed in a color tone, and a pulse half-value width acquiring unit that acquires a pulse half-value width when the electric field intensity of the electromagnetic wave pulse is a maximum half value; An optical path difference acquisition unit that acquires an optical path difference of the optical path length corresponding to the half width of the pulse, and the first measurement optical path length is obtained by transmitting or reflecting the electromagnetic wave pulse transmitted or reflected from a specific position of the sample. The optical path length at the time of a peak that is substantially a peak, and the second and third optical path lengths for measurement are the optical path length obtained by adding the optical path difference to the optical path length at the peak, or the optical path length at the peak From the optical path length It is the optical path length and obtained by subtracting the Kihikariro difference.

  According to the electromagnetic wave pulse measurement device according to the first aspect, the electric field strength is detected and imaged in a state where the optical path length is set to three measurement optical path lengths. Therefore, since the measurement time required for imaging can be shortened, an image for imaging can be generated efficiently.

  Moreover, according to the electromagnetic wave pulse measuring device which concerns on a 2nd aspect, the detected electric field strength can be expressed with the color which is easy for a person to identify. Therefore, the electric field strength can be properly grasped from the generated image.

  Further, according to the electromagnetic wave pulse measuring apparatus according to the third aspect, when the optical path length is fixed to the first optical path length for measurement and the electromagnetic wave pulse is irradiated to various positions of the sample, the specific position of the sample and other Unless the physical property differs greatly depending on the position, the electric field intensity of the electromagnetic wave pulse itself transmitted or reflected by the sample can be detected effectively.

  In addition, according to the electromagnetic wave pulse measuring device according to the fourth aspect, when the electric field intensity detected when the electromagnetic wave pulse is irradiated to a specific position of the sample becomes substantially peak, and at a timing earlier or later by the pulse half width. The electric field strength will be detected. Therefore, as long as the physical properties do not differ greatly between the specific position of the sample and other positions, the electric field strength of the electromagnetic wave pulse itself that is transmitted or reflected by the sample can be detected effectively.

  Moreover, according to the electromagnetic wave pulse measuring apparatus which concerns on a 5th aspect, the physical-property measurement of a sample can be performed using a terahertz wave pulse.

It is a figure showing composition of a terahertz wave measuring device concerning an embodiment. It is a flowchart when analyzing a reference wave. It is a figure which shows an example of the time waveform of the reference wave decompress | restored by THz-TDS. It is a flowchart when imaging is performed about a sample. It is a flowchart when imaging is performed about a sample. It is a flowchart when imaging is performed about a sample. It is a figure which shows an example of the time waveform of the transmitted wave decompress | restored in step S203 shown in FIG. It is a figure for demonstrating the relationship between the detection timing of a terahertz wave, the optical path length for a measurement, and the position of a reflective mirror.

  Hereinafter, embodiments will be described in detail with reference to the drawings. However, the configuration described in this embodiment is merely an example, and is not intended to limit the scope of the present invention.

<1. Embodiment>
<1.1. Configuration and Function of Terahertz Wave Measuring Device 100>
FIG. 1 is a diagram illustrating a configuration of a terahertz wave measuring apparatus 100 according to the embodiment. The terahertz wave measuring apparatus 100 (electromagnetic wave pulse measuring apparatus) is for imaging the sample W by terahertz time domain spectroscopy (THz-TDS) using terahertz wave pulses (hereinafter also simply referred to as terahertz waves). Device. Here, the terahertz wave refers to an electromagnetic wave having a component in an arbitrary frequency band of 0.01 THz to 100 THz (particularly 0.1 THz to 30 THz). Further, the sample W to be measured is assumed to be various substrates such as a semiconductor wafer, a display device panel, or a solar cell panel. However, various artificial objects or various natural objects other than these may be used as the sample W.

  As shown in FIG. 1, the terahertz wave measuring apparatus 100 includes a laser light source 11, an irradiation unit 12, a detection unit 13, a delay unit 14, a moving mechanism 15, and a control unit 17.

  The laser light source 11 emits pulsed light (pulsed light LP1). As the laser light source 11, for example, a femtosecond pulse laser is used. The pulsed light is, for example, linearly polarized light having a center wavelength of about 780 to 830 nm in the near infrared region, a period of several kHz to several hundred MHz, and a pulse width of several tens to several hundreds fsec (for example, 10 to 150 fsec). Of pulsed light. When a femtosecond fiber laser is used, the wavelength is about 1 to 1.5 μm.

  The pulsed light LP1 is divided into two by the beam splitter B1. One of the divided pulse lights LP1 enters the irradiation unit 12 as pump light (pump light LP11) via the mirror M1. The irradiation unit 12 includes an optical switch element. By irradiating the optical switch element with the pump light LP11, a terahertz wave (terahertz wave LT1) is generated. That is, the irradiation unit 12 functions as a terahertz wave generation unit. The generated terahertz wave is collected by an optical system composed of curved mirrors M2 and M3, and is irradiated onto the sample W. That is, the irradiation unit 12 irradiates the sample W with the terahertz wave in accordance with the irradiation with the pump light LP11. The terahertz wave that has passed through the sample W is collected by an optical system including the curved mirrors M4 and M5 and enters the detection unit 13.

  The other of the pulsed light LP1 divided by the beam splitter B1 enters the detection unit 13 via the delay unit 14 and mirrors M6 and M7 as probe light (probe light LP12). The detection unit 13 includes an optical switch element. If the optical switch element is irradiated with the probe light LP12 in a state where the optical switch element is irradiated with the terahertz wave transmitted through the sample W, a current corresponding to the electric field strength of the terahertz wave is instantaneously generated in the optical switch element. The current corresponding to the electric field strength is converted into a digital quantity via an I / V conversion circuit, an A / D conversion circuit, or the like. In this way, the detection unit 13 detects the electric field intensity of the terahertz wave that has passed through the sample W in response to the irradiation (light reception) of the probe light. In the present embodiment, an optical switch element is used in the irradiation unit 12 or the detection unit 13, but other elements such as a nonlinear optical crystal can also be used.

  The delay unit 14 is an optical element for continuously changing the arrival time of the probe light LP12 from the beam splitter B1 to the detection unit 13. The delay unit 14 includes a reflection mirror 14M that folds the probe light LP12 in the incident direction, and a moving stage 141 that moves the reflection mirror 14M along the incident direction of the probe light LP12. The delay unit 14 drives the moving stage 141 based on the control of the control unit 17 to linearly move the reflection mirror 14M, thereby precisely changing the optical path length of the probe light. Thereby, the delay unit 14 changes the time difference between the time for the terahertz wave to reach the detection unit 13 and the time for the probe light LP12 to reach the detection unit 13. The timing at which the detection unit 13 detects the electric field strength of the terahertz wave by driving the delay unit 14 and changing the optical path length of the probe light LP12 (the optical path length of the second optical path from the laser light source 11 to the detection unit 13) ( Detection timing or sampling timing) can be delayed. As described above, in the present embodiment, the delay unit 14 constitutes an optical path length changing unit.

Specifically, for example, when the reflecting mirror 14M is moved away from the beam splitter B1 by 15 μm, the optical path length of the probe light LP12 is extended by 30 μm, which is a reciprocal amount. When the optical path length is extended by 30 μm, the time for the probe light LP12 to reach the detection unit 13 is delayed by 100 fsec when the light speed c is 3.0 × 10 8 m per second.

  Note that the delay unit 14 may change the arrival time of the terahertz wave and the probe light LP12 to the detection unit 13 by other methods. For example, the electro-optic effect may be used. That is, an electro-optic element whose refractive index changes by changing the applied voltage may be used as the delay element. Specifically, an electro-optical element disclosed in Japanese Patent Application Laid-Open No. 2009-175127 may be used.

  In this embodiment, the optical path length of the probe light LP12 is changed. However, the optical path length of the pump light LP11 (the optical path length of the first optical path from the laser light source 11 to the irradiation unit 12) may be changed. Good. Even in such a case, the timing at which the detection unit 13 detects the terahertz wave emitted from the irradiation unit 12 can be arbitrarily delayed.

  The moving mechanism 15 includes an XY table (not shown). The moving mechanism 15 moves the sample W relative to the irradiation unit 12 while holding the sample W by the XY table. The terahertz wave measuring apparatus 100 moves the sample W to an arbitrary position in the two-dimensional plane by the moving mechanism 15. Thereby, the terahertz wave measuring apparatus 100 can irradiate a wide range of the sample W with the terahertz wave.

  The driving mechanism of the moving mechanism 15 is not limited to the XY table, and may be configured in any way as long as the sample W can be moved on the two-dimensional plane. Further, the moving mechanism 15 may be configured so that the sample W can be moved by an operator's manual operation. Further, instead of moving the sample W, or while moving the sample W, the irradiation unit 12, the curved mirrors M2 to M5, the detection unit 13, and the like may be moved in a two-dimensional plane. Even in these cases, it is possible to irradiate a wide range of the sample W with terahertz waves.

  The control unit 17 is configured as a general computer including a CPU and a RAM. The control unit 17 is connected to the laser light source 11, the irradiation unit 12, the detection unit 13, the delay unit 14, and the moving mechanism 15, and controls the operation of these elements and receives data from these elements. Specifically, the control unit 17 receives data regarding the electric field strength of the terahertz wave from the detection unit 13. Further, the control unit 17 instructs the movement stage of the delay unit 14 to move, or receives data related to the position of the reflection mirror 14M such as the movement distance from a linear scale or the like provided on the movement stage.

  The terahertz wave measuring apparatus 100 includes a pulse restoration unit 21, a pulse half width acquisition unit 22, an optical path difference acquisition unit 23, a mirror position setting unit 24, a data conversion unit 25, and an image generation unit 26. Each of these elements is connected to the control unit 17.

  The pulse restoration unit 21 restores the pulse waveform from the electric field strength detected by the detection unit 13. Specifically, when the control unit 17 controls the delay unit 14 (optical path length changing unit), the electric field strength is detected by the detection unit 13 at a plurality of mutually different detection timings. Then, after the acquired data is sent to the control unit 17, a time waveform is constructed in the pulse restoration unit 21. Details of the time waveform restored by the pulse restoration unit 21 will be described later.

  The pulse half-value width obtaining unit 22 obtains a pulse half-value width when the electric field intensity of the electromagnetic wave pulse becomes the maximum half value. Here, the half width of the pulse means a time difference between two times when a half value of the maximum value of the electric field strength is detected before and after the electric field strength of the terahertz wave pulse becomes maximum. A specific example of the pulse half width will be described later.

The optical path difference acquisition unit 23 acquires an optical path difference corresponding to the pulse half-value width acquired by the pulse half-value width acquisition unit 22. Specifically, the optical path difference acquisition unit 23 acquires an optical path difference corresponding to the pulse half width (delay time) by calculation. For example, when the pulse half-value width is 200 fsec, the pulse half-value width is 60 μm (= 3.0 × 10 8 (m / sec) × 200 (fsec)) assuming that the speed of light is 3.0 × 10 8 m / sec. This corresponds to the optical path difference of the probe light LP12.

  The mirror position setting unit 24 sets a position where the reflection mirror 14M is arranged at the time of measurement. In this embodiment, as will be described later, the sample W is irradiated with the terahertz wave in a state where the optical path length of the probe light is set to three measurement optical path lengths (first to third measurement optical path lengths). The As will be described later, the three optical path lengths for measurement include the peak optical path length when the electric field intensity of the reference terahertz wave reaches the peak (maximum) and the optical path difference calculated by the optical path difference acquisition unit 23. To be determined.

  The data conversion unit 25 converts the electric field intensity detected by the detection unit 13 into multi-gradation data indicating gradation characteristics of a specific color. Specifically, in this embodiment, the terahertz wave is irradiated to each position of the sample W in a state where the optical path length of the probe light LP12 is set to each of the three measurement optical path lengths. For this reason, three electric field strengths are acquired for each position. The data conversion unit 25 converts each of the three electric field strengths into gradation data indicating the shade of red (R), green (G), or blue (B) using the JIS conventional color name. In the gradation data, the respective shades of RGB are expressed by, for example, 256 gradations (= 8 bits). However, the gradation is not limited to 256 gradations, and the intensity of the specific color may be expressed by a plurality of gradations other than that.

  The image generation unit 26 generates an image for imaging in which the electric field strength of the portion corresponding to each position of the sample W is expressed by a color corresponding to the gradation data. In this image for imaging, it is expressed by a composite color in which the tones of three colors (RGB) corresponding to the electric field strength are combined. Each pixel position corresponds to a position on the sample W. Therefore, the image for imaging is an image expressing the position information corresponding to the sample W and the electric field strength detected at the position for each pixel. The image generated by the image generation unit 26 is appropriately displayed on the display unit 33.

  As shown in FIG. 1, a storage unit 31, an input unit 32, and a display unit 33 that displays various images are connected to the control unit 17. The storage unit 31 is configured by a storage medium such as a hard disk, and can store various data. The input unit 32 includes input devices such as a mouse and a keyboard that are operated by an operator to input various data to the terahertz wave measuring apparatus 100. The display unit 33 is composed of a liquid crystal panel or the like. Note that the display unit 33 may include a part or all of the functions of the input unit 32 by configuring the display unit 33 with a touch panel. The above is the description of the configuration of the terahertz wave measuring apparatus 100. Next, imaging using the terahertz wave measuring apparatus 100 will be described.

<1.2. Imaging Using Terahertz Wave Measuring Device 100>
FIG. 2 is a flowchart when the reference wave is analyzed. In the following description, it is assumed that the terahertz wave measuring apparatus 100 operates based on the control of the control unit 17 unless otherwise specified.

  The reference wave is a terahertz wave emitted from the irradiation unit 12. As will be described later, the pulse half-value width is obtained by analyzing this reference wave. If the pulse half width is already known, the analysis of the reference wave can be omitted.

  When the analysis of the reference wave is performed, THz-TDS is performed in a state where the sample W or the like is not installed on the XY table of the moving mechanism 15 (that is, a state where there is nothing) (step S11). Specifically, the electric field intensity of the terahertz wave is acquired by the detection unit 13 while changing the timing at which the probe light LP12 reaches the detection unit 13 by moving the reflection mirror 14M. Based on the acquired electric field strength, the pulse restoration unit 21 restores the waveform (time waveform) of the terahertz wave (reference wave). Then, the pulse half width WHM is obtained from the restored time waveform of the terahertz wave (reference wave) by the pulse half width acquisition unit 22 (step S12). A method of obtaining the pulse half width WHM will be described with reference to FIG.

FIG. 3 is a diagram illustrating an example of the time waveform 41 of the reference wave restored by THz-TDS. In FIG. 3, the horizontal axis indicates time, and the vertical axis indicates electric field strength. The time waveform 41 is restored by plotting the electric field strength detected by the detection unit 13 at each timing along the time axis. Here, it is assumed that the maximum value of the electric field intensity of the reference wave is E 0 and the time at that time is t 10 . Then, the pulse half width WHM is a time before and after the timing t 10 to a maximum value E 0, the time difference between the two timings electric field intensity is half the maximum value E 0 (E 0/2) ( or duration ). Therefore, in the example shown in FIG. 3, the time difference (= t 12 −t 11 ) between the timing t 11 and the timing t 12 is the pulse half width WHM. Next, imaging of the sample W is performed using the pulse half width WHM.

  4, 5, and 6 are flowcharts when imaging is performed on the sample W. FIG. In order to image the sample W, the sample W is fixed to the XY table of the moving mechanism 15 (step S201). Then, the sample mechanism W is moved to a required position by driving the moving mechanism 15 (step S202). The position of the sample W at this time is arbitrarily set. And THz-TDS is performed and the time waveform of the terahertz wave (transmitted wave) which permeate | transmits the sample W is decompress | restored (step S203).

  Next, the mirror position setting unit 24 determines a position for fixing the reflection mirror 14M (step S204). As described above, in this embodiment, the optical path length of the probe light LP12 is. The terahertz wave is detected in a state where the three optical path lengths for measurement are set. In step S204, the three measurement optical path lengths are specifically set. A method for setting the three measurement optical path lengths will be described with reference to FIGS.

  FIG. 7 is a diagram showing an example of the time waveform 43 of the transmitted wave restored in step S203 shown in FIG. In FIG. 7, the horizontal axis indicates time, and the vertical axis indicates electric field strength. FIG. 8 is a diagram for explaining the relationship among the terahertz wave detection timing, the measurement optical path length, and the position of the reflection mirror 14M.

In time waveform 43 of the transmitted wave as shown in FIG. 7, at a timing t 20, the electric field strength are substantially peak (= E20). This peak optical path length L 20 which substantially peak electric field intensity corresponds to the time to be detected is set to three measuring optical path length (the first measuring optical path length) in detecting the terahertz waves. Further, in FIG. 8, as shown in the lower part, the position of the reflection mirror 14M is by being arranged at a position Z 20, the optical path length of the probe light LP12 is set to peak at optical path length L 20.

The remaining two of the three optical path lengths for measurement have a timing t that is earlier by the pulse half-value width WHM than when the electric field intensity of the transmitted wave restored in step S203 has a substantially peak (timing t 20 ). 21 and the optical path length L 21 (second measurement optical path length) and the optical path length L 22 (third measurement optical path length) respectively corresponding to the timing t 22 delayed by the pulse half-value width WHM. The optical path length difference (optical path difference ΔL) corresponding to the pulse half width WHM is acquired by the optical path difference acquisition unit 23. Specifically, the optical path difference ΔL is expressed by the following equation, where c is the speed of light.

  ΔL = c × WHM

A value obtained by subtracting the optical path difference ΔL from the optical path length L 20 is the optical path length L 21 . Further, a value obtained by adding the optical path difference ΔL of the optical path length L 21 is the optical path length L 22. Then, in FIG. 8, as shown in the lower part, a reflection mirror 14M from the position Z 20 when the incident direction of the probe light LP12 disposed at a position Z 21 that moves ΔZ min in the opposite direction, the probe light LP12 optical path length is L 21. Also, when is disposed a reflection mirror 14M at a position Z 22 that moves ΔZ min to the incident direction of the probe light LP12, the optical path length L 22 of the probe light LP12. Note that ΔZ at this time is expressed by the following expression because the reflection mirror 14M is a folded-type optical element.

  ΔZ = ΔL / 2 = c × WHM / 2

As described above, the three arrangement positions (positions Z 20 , Z 21 , Z 22 ) of the reflection mirror 14M during the measurement in step S204 are set.

Returning again to FIG. 4, the positioning of the reflection mirror 14M of step S204 is completed, it moves the reflection mirror 14M at a position Z 20 (step S205). This position Z 20 is when the field strength of the detected terahertz wave in step S202 (transmission wave) is substantially peak, the position of the reflecting mirror 14M.

The terahertz wave measuring apparatus 100, in a state in which the reflection mirror 14M fixed to the position Z 20, by driving the moving mechanism 15 to move the specimen W in a two dimensional plane. Thereby, a terahertz wave is irradiated to each position on the sample W, and the electric field strength of the transmitted wave is detected by the detection unit 13 (step S206). At this time, when irradiating terahertz waves to a continuous region of the sample W, for example, the sample W is repeatedly moved in the main scanning direction and the sub-scanning direction orthogonal to the main scanning direction while irradiating the terahertz waves. By doing so, it is possible to measure efficiently. Of course, the sample W may be moved by other methods to irradiate the terahertz wave.

  The detection data of the electric field intensity acquired in step S206 includes information (position information) regarding the position where the terahertz wave is irradiated on the sample W and information regarding the electric field intensity detected when the position is irradiated with the terahertz wave ( Field strength information). This data is appropriately stored in the storage unit 31.

Next, the terahertz wave measuring apparatus 100, the reflection mirror 14M, moving from the position Z 20 to the position Z 21 (step S207). As described above, at this position Z 21 , the optical path length L 21 (second optical path length of the probe light LP12 is shorter than the optical path length L 20 at the position Z 20 by an optical path difference ΔL corresponding to the pulse half width WHM. (Measurement optical path length).

The terahertz wave measuring apparatus 100 is in a state of fixing the reflection mirror 14M at a position Z 21, to irradiate the terahertz wave (step S208). In step S208, as in step S206, the sample W moves in the horizontal plane, so that each position of the sample W is irradiated with terahertz waves, and the electric field strength is detected by the detection unit 13 (step S208). The electric field strength detection data acquired in step S208 is stored in the storage unit 31.

  The electric field strength data acquired in step S207 is appropriately stored in the storage unit 31. Then, in the next step S209, it is determined whether or not the number of positions where the electric field intensity acquired in step S208 is substantially zero exceeds a predetermined threshold value.

  The timing for measuring the terahertz wave in step S208 is determined based on the transmitted wave restored in step S202. For this reason, when the state of the sample W is different for each position of the sample W (for example, the thickness is different), the time for the terahertz wave to pass through the sample W may be different for each position. Therefore, depending on the position to be inspected, it may be assumed that the measurement in step S208 is performed at a timing at which the transmitted wave is not detected, so that the detected electric field strength is substantially zero.

Therefore, in this embodiment, in step S209, if the number of positions at which the electric field intensity is substantially zero exceeds a predetermined threshold value ( "YES" in step S209), it moves the reflection mirror 14M to the position Z 23 (step S301 FIG. 5). This position Z 23 is, although not shown, from the position Z 21 as shown in the lower part 8, which is further allowed further ΔZ moved direction of incidence of the probe light LP12 position. When the reflecting mirror 14M is disposed at a position Z 23, the optical path length of the probe light LP12 is, 2 · [Delta] L less than their optical path length L 20.

The terahertz wave measuring apparatus 100 is in a state of fixing the reflection mirror 14M at a position Z 23, similarly like step S206, irradiating the terahertz wave to a sample W (step S302). At this time, as the sample W moves in the two-dimensional plane, each position of the sample W is irradiated with the terahertz wave, and the electric field strength is detected by the detection unit 13. The acquired electric field strength detection data is stored in the storage unit 31 as appropriate.

In step S302, the reflection mirror 14M is disposed at a position Z 23, than the detection timing t 20, so that the detected electric field intensity is performed twice minute earlier timing pulse half width WHM. Therefore, the possibility of detection of the electric field strength of the terahertz wave that could not be detected by the measurement in step S208 because it transmits faster than the terahertz wave detected in step S202 can be increased.

When the position that becomes substantially zero in step S209 does not exceed the predetermined threshold (“NO” in step S209) or when the measurement in step S302 is completed, the terahertz wave measuring apparatus 100 moves the reflecting mirror 14M to the position Z 21. The position is moved from (or position Z 23 ) to position Z 22 (step S210). As described above, the position Z 22 is a position where the optical path length of the probe light LP12 becomes an optical path length L 22 longer than the optical path length L 20 at the position Z 20 by an optical path difference ΔL corresponding to the pulse half-value width WHM. It is.

The terahertz wave measuring apparatus 100 is in a state of fixing the reflection mirror 14M at a position Z 22, to irradiate the terahertz wave (step S211). In step S211, similarly to step S206 and the like, the sample W moves in the two-dimensional plane, so that each position of the sample W is irradiated with a terahertz wave, and the electric field strength is detected by the detection unit 13. The electric field strength detection data acquired in step S211 is appropriately stored in the storage unit 31.

The terahertz wave measuring apparatus 100 determines whether or not the number of positions where the electric field intensity is substantially zero exceeds a predetermined threshold in the electric field intensity detection data acquired in step S211 (step S212). If the number of locations where the electric field intensity is substantially zero in step S211 exceeds a predetermined threshold value ( "YES" in step S211), the terahertz wave measuring apparatus 100 moves the reflection mirror 14M to the position Z 24 (step S401, FIG. 6).

Although not shown, the position Z 24 is a position where the reflecting mirror 14M is further moved by ΔZ along the incident direction of the probe light LP12 from the position Z 22 shown in the lower part of FIG. Therefore, when placing the reflective mirror 14M at a position Z 24, the optical path length of the probe light LP12 is, 2 · [Delta] L min longer than the optical path length L 20.

The terahertz wave measuring apparatus 100 is in a state of fixing the reflection mirror 14M at a position Z 24, similarly like step S206, irradiating the terahertz wave to a sample W (step S402). At this time, as the sample W moves in the two-dimensional plane, each position of the sample W is irradiated with the terahertz wave, and the electric field strength is detected by the detection unit 13. The acquired electric field strength detection data is stored in the storage unit 31 as appropriate.

In step S402, the reflection mirror 14M is disposed at a position Z 24, than the detection timing t 20, so that the detected electric field intensity is performed twice minute late timing of the pulse half width WHM. Therefore, it is possible to increase the possibility of detecting the electric field intensity of the terahertz wave that could not be detected in the measurement of step S211 because, for example, the transmission time for transmitting the sample W is longer than the terahertz wave detected in step S202. it can.

  When the position that is substantially zero in step S211 does not exceed the predetermined threshold (“NO” in step S211), or when the measurement in step S402 is completed, the terahertz wave measuring apparatus 100 converts the electric field strength into gradation data. Conversion is performed (step S213). Specifically, the data conversion unit 25 performs step S205, step S208 (however, when step S301 is performed, step S302) and step S209 (however, when step S401 is performed, step S402). ) Is converted into gradation data indicating gradation characteristics of R, G, and B. Each of the three types of electric field strengths acquired in steps S205, S208, and S209 may be converted without overlapping with any of the R, G, and B gradation data. For example, the electric field intensity acquired in step S205 is converted into R gradation data, the electric field intensity acquired in step S208 is converted into B gradation data, and the electric field intensity acquired in step S209 is converted into G gradation data. Alternatively, the electric field intensity acquired in step S205 may be B gradation data, the electric field intensity acquired in step S208 may be G gradation data, and the electric field intensity acquired in step S209 may be R floor. You may make it convert into key data. As described above, the combination of the three types of electric field strengths and the gradation data relating to the converted R, G, and B can be arbitrarily set.

  Note that conversion to gradation data may use a conversion table. For example, the table for conversion is divided into a predetermined number of gradations (for example, 256) between the maximum value and the minimum value of the electric field intensity of the reference wave (see FIG. 3) or the transmitted wave (see FIG. 7). A specific gradation value is defined for each range of the electric field strength. However, the conversion table may be one in which the gradation value is appropriately defined for each electric field strength without depending on the reference wave or the transmitted wave.

  When the terahertz wave measuring apparatus 100 completes the data conversion in step S213, the terahertz wave measuring apparatus 100 generates an image for imaging based on the acquired gradation data and displays the image on the display unit 33 (step S214). In the present embodiment, three field strength values are acquired at each position of the sample W. In an image for imaging, the three electric field strengths are expressed by a composite color obtained by mixing three colors (RGB) having specific gradation characteristics (shading) according to the strength. Note that general image processing (for example, edge enhancement, gradation change, etc.) may be performed on the imaging image.

  This completes the description of imaging using the terahertz wave measuring apparatus 100.

  In the present embodiment, imaging is performed by limiting the optical path length of the probe light LP12 to three measurement optical path lengths. For this reason, since the measurement time required for imaging can be shortened, imaging can be performed efficiently.

  The three measurement optical path lengths are the peak optical path length at which the electric field intensity of the transmitted wave substantially peaks when a specific position on the sample W is irradiated with the terahertz wave, and the pulse half-value width WHM of the transmitted wave. It is determined based on the corresponding optical path difference ΔL. For this reason, when terahertz waves are irradiated to various positions of the sample W, the electric field intensity of the transmitted wave can be effectively detected as long as the physical properties are not greatly different between the specific position of the sample W and other positions.

  In the present embodiment, the electric field strength detected under the three measurement optical path lengths is converted into RGB colors that can be identified by a person. Therefore, in the image for imaging, the degree of the three electric field strengths at each position of the sample W can be effectively grasped by expressing these colors as a combined color.

  Steps S205 to S206 (measurement with the first measurement optical path length), steps S207 to S209 (measurement with the second measurement optical path length), and steps S210 to S212 (third measurement). The measurement with the optical path length for use does not need to be performed in the order shown in FIG. 2, and can be arbitrarily changed.

<2. Modification>
Although the embodiment has been described above, the present invention is not limited to the above, and various modifications are possible.

For example, in the above-described embodiment, the position of the reflection mirror 14M is set based on the pulse half width WHM, but other standards can be used. For example, the pulse width (corresponding to the time difference between the timing t a when the electric field intensity becomes zero) and the timing t b from the time waveform 41 of the reference wave shown in FIG. 3 may be used as an alternative to the pulse half width WHM. .

  In the above embodiment, the pulse half width WHM is obtained from the reference wave (time waveform 41 shown in FIG. 3), but is obtained from the transmitted wave that has passed through the sample W (time waveform 43 shown in FIG. 7). You may make it do. In this case, the analysis of the reference wave shown in FIG. 2 can be omitted.

In the above embodiment, the transmission wave transmitted through the sample W optical path length (optical path length L 20), the first measuring optical path length when the electric field strength is substantially peak of (time waveform 43 shown in FIG. 7) (The optical path length at the time of measurement in step S205). However, the optical path length when the electric field intensity of the reference wave (time waveform 41 shown in FIG. 3) has a substantially peak may be used as the first measurement optical path length. Further, regardless of the optical path length L 20, the required fixed timing may be used as the first measuring optical path length. However, it is desirable that the first measurement optical path length is the optical path length of the probe light LP12 when at least the electric field intensity of the terahertz wave that passes through the sample W can be detected.

  In the above embodiment, the second and third measurement optical path lengths are determined by subtracting or adding the optical path difference ΔL corresponding to the pulse half-value width WHM to the first measurement optical path length. . However, as described in steps S301 and S401, the second and third measurement optical path lengths may be determined by subtracting or adding a value obtained by multiplying the optical path difference ΔL by a required value. Further, the second and third measurement optical path lengths may be determined by adding or subtracting a required value without depending on the pulse half width WHM.

  In the above-described embodiment, the sample W is irradiated with the terahertz wave emitted from the irradiation unit 12, and the transmitted transmitted wave is detected by the detection unit 13. However, the detection unit 13 may detect the terahertz wave reflected on the surface side of the sample W irradiated with the terahertz wave.

  In addition, the pulse restoration unit 21, the pulse half-width acquisition unit 22, the optical path difference acquisition unit 23, the mirror position setting unit 24, the data conversion unit 25, and the image generation unit 26 described in the above embodiment are processed by the CPU according to a predetermined program. Therefore, it may be realized by software by operating, or a part or all of these functions may be realized by hardware using a dedicated logic circuit or the like.

  In addition, the configurations described in the above embodiments and modifications can be appropriately combined or omitted as long as they do not contradict each other.

100 Terahertz wave measuring device (electromagnetic pulse measuring device)
DESCRIPTION OF SYMBOLS 11 Laser light source 12 Irradiation part 13 Detection part 14 Delay part 141 Movement stage 14M Reflection mirror 15 Movement mechanism 17 Control part 21 Pulse reconstruction part 22 Pulse half value width acquisition part 23 Optical path difference acquisition part 24 Mirror position setting part 25 Data conversion part 26 Image Generation unit 31 Storage unit 32 Input unit 33 Display unit 41 Time waveform (reference wave)
43 Time waveform (transmitted wave)
L 20 optical path length (first optical path length for measurement)
L 21 optical path length (second optical path length for measurement)
L 22 optical path length (third optical path length for measurement)
L 23 , L 24 optical path length LP 1 pulse light LP 11 pump light LP 12 probe light LT 1 terahertz wave W sample WHM pulse half width Z 20 , Z 21 , Z 22 , Z 23 , Z 24 position ΔL optical path difference

Claims (6)

  1. In an electromagnetic wave pulse measuring device that measures an electromagnetic wave pulse transmitted or reflected through a sample,
    An irradiation unit that receives pulsed light emitted from a laser light source and irradiates a sample with an electromagnetic wave pulse;
    A detection unit that detects an electromagnetic wave pulse transmitted or reflected by the sample in response to irradiation of the pulsed light;
    A first optical path of the pulsed light from the laser light source to the irradiation unit, or an optical path length changing unit that changes an optical path length of the second optical path of the pulsed light from the laser light source to the detection unit;
    A relative movement mechanism for moving the irradiation unit relative to the sample;
    A control unit that controls the optical path length changing unit so that the optical path length is set to each of the first optical path length for measurement, the second optical path length for measurement, and the third optical path length for measurement;
    When the optical path length is set to each of the first to third measurement optical path lengths, the pulsed light is irradiated to each position of the sample and detected by the detection unit for each position. A data conversion unit that converts electric field strength into gradation data indicating gradation characteristics of three specific colors, and
    An image generating unit that generates an image in which information about the electric field strength of a portion corresponding to each position of the sample is expressed in a color tone according to the gradation data;
    An electromagnetic pulse measuring device comprising:
  2. In the electromagnetic wave pulse measuring device according to claim 1,
    The electromagnetic wave pulse measuring device in which the three specific colors are red, green and blue.
  3. In the electromagnetic wave pulse measuring device according to claim 1 or 2,
    The first optical path length for measurement is an electromagnetic pulse measuring apparatus in which the optical path length at the time of peak when the electromagnetic pulse transmitted or reflected from a specific position of the sample is substantially peaked.
  4. In the electromagnetic wave pulse measuring device according to claim 3,
    A pulse half-value width obtaining unit for obtaining a pulse half-value width when the electric field intensity of the electromagnetic wave pulse is the maximum half value;
    An optical path difference acquisition unit for acquiring an optical path difference of the optical path length corresponding to the pulse half-width,
    Further comprising
    The second and third optical path lengths for measurement are optical path lengths obtained by adding the optical path difference to the optical path length at the peak, or optical path lengths obtained by subtracting the optical path difference from the optical path length at the peak. Electromagnetic pulse measuring device.
  5. In the electromagnetic wave pulse measuring device according to any one of claims 1 to 4,
    The electromagnetic wave pulse measuring apparatus in which the electromagnetic wave pulse wave includes a terahertz wave pulse having a frequency of 0.01 THz to 100 THz.
  6.   In an electromagnetic wave pulse measuring device that measures an electromagnetic wave pulse transmitted or reflected through a sample,
      An irradiation unit that receives pulsed light emitted from a laser light source and irradiates a sample with an electromagnetic wave pulse;
    A detection unit that detects an electromagnetic wave pulse transmitted or reflected by the sample in response to irradiation of the pulsed light;
      A first optical path of the pulsed light from the laser light source to the irradiation unit, or an optical path length changing unit that changes an optical path length of the second optical path of the pulsed light from the laser light source to the detection unit;
      A relative movement mechanism for moving the irradiation unit relative to the sample;
      A control unit that controls the optical path length changing unit so that the optical path length is set to each of the first optical path length for measurement, the second optical path length for measurement, and the third optical path length for measurement;
      When the optical path length is set to each of the first to third measurement optical path lengths, the electric field strength detected by the detection unit is converted into gradation data indicating gradation characteristics of three specific colors. A data conversion unit to convert each;
      An image generating unit that generates an image in which information on the electric field strength is expressed in a color tone according to the gradation data;
      A pulse half-value width obtaining unit for obtaining a pulse half-value width when the electric field intensity of the electromagnetic wave pulse is the maximum half value;
      An optical path difference acquisition unit for acquiring an optical path difference of the optical path length corresponding to the pulse half-width,
    With
      The first optical path length for measurement is the optical path length at the peak when the electromagnetic wave pulse transmitted or reflected from the specific position of the sample is substantially peaked,
      The second and third optical path lengths for measurement are optical path lengths obtained by adding the optical path difference to the optical path length at the peak, or optical path lengths obtained by subtracting the optical path difference from the optical path length at the peak. Electromagnetic pulse measuring device.
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