KR20180040636A - Film thickness measuring apparatus and film thickness measuring method - Google Patents

Abstract

There is provided a technique for performing a film thickness inspection of a film containing an active material formed on a current collector in a noncontact manner in a manufacturing process of a lithium ion battery. The film thickness measuring apparatus 1 includes a terahertz wave irradiator 10 for irradiating a sample 9 with a terahertz wave LT1 and a reflected wave LT3 of the terahertz wave LT1 reflected from the sample 9, And a photoconductive switch 34A for detecting the reflected light from the photoconductive element. The film thickness measuring apparatus 1 includes a surface reflected wave LT31 reflected from the surface of the active material film 91 in the sample 9 among the reflected waves LT3 detected by the reflected wave detecting unit 30A, A time difference acquiring module 509 for acquiring a time difference? T reaching the photoconductive switch 34A of the interface reflected wave LT32 reflected at the interface between the active material film 91 and the current collector 93 in the liquid crystal cell 9 And a film thickness calculating section 511 for calculating the film thickness d of the active material film 91 based on the time difference DELTA t and the refractive index n _s of the active material film 91. [

Description

Film thickness measuring apparatus and film thickness measuring method

The present invention relates to a technique for measuring a film thickness of a film of an active material formed on a current collector.

The lithium ion secondary battery (LiB) is composed of a positive electrode, a negative electrode, and a separator arranged to separate them from each other to prevent electrical short-circuiting between the positive electrode and the negative electrode. The positive electrode is formed by applying a metal active material such as lithium cobalt oxide, conductive graphite (carbon black, etc.) and a binder resin onto a collector such as an aluminum foil. The negative electrode is formed by applying graphite (natural graphite, artificial graphite or the like) and a binder resin as active materials onto a current collector such as an aluminum foil. The separator is made of a polyolefin-based insulating film or the like. The positive electrode, the negative electrode and the separator are porous and exist in a state in which the organic electrolyte permeates. As the organic electrolyte, for example, an organic solvent such as ethylene carbonate or diethyl carbonate containing a lithium salt such as lithium hexafluorophosphate (LiPF ₆ ) is used.

The positive and negative electrodes constitute a battery by using a positive electrode and a negative electrode with active materials having different potentials at the time of discharge and blowing, when lithium ions are released and taken into the active material when a potential is applied thereto. The following are examples of reactions in the positive and negative electrodes of the emission display.

Positive _{electrode: LiCoO 2 ⇔ Li 1-x} CoO 2 + xLi + + xe -

Negative electrode: xLi ⁺ + xe ^- 6C ⇔ Li _x C ₆

Patent Document 1 discloses that if there is a bias in the film thickness uniformity of the binder resin, problems such as peeling of the active material layer occur. Patent Document 2 discloses that it is important to level the slurry for electrode formation, that is, to make the film thickness uniform when the electrode layer is thickened in order to cope with high capacity of the capacitor.

In Patent Documents 3 and 4, both the positive electrode and the negative electrode are adjusted to the weight per unit area as the apparent weight with respect to the amount of the active material, but the film thickness after the coating process is not inspected. Then, defective products are detected by a cycle test of charging and discharging in LiB which is the final product.

Japanese Patent Application Laid-Open No. 2004-71472 International Publication No. 2011/024789 pamphlet Japanese Laid-Open Patent Publication No. 2014-116317 Japanese Laid-Open Patent Publication No. 2014-96386 Japanese Patent Publication No. 2006-526774

However, as described in Patent Document 3 or Patent Document 4, when only the apparent weight of the active material is adjusted and the defective product is inspected with the final product without performing the film thickness inspection, the economical There was a problem that the loss was large.

Since the apparent weight of the active material is constant in the coating liquid for the positive electrode material and the negative electrode material, the amount of the active material can be calculated from the film thickness. Therefore, when the film thickness is measured, the amount of the active material can be specified. However, as described above, the film thickness inspection immediately after coating and drying is not carried out.

As a nondestructive inspection method, for example, Patent Document 5 discloses that electromagnetic waves having a frequency in the range of 25 GHz to 100 GHz are used. However, the technique of Patent Document 5 can not examine the film thickness by analyzing the component concentration of the sample from the spectral characteristics. Particularly, it is impossible to measure a thin film containing carbon and which does not transmit visible light, like the positive electrode and the negative electrode of a lithium ion battery.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a technique for performing a film thickness inspection of a film containing an active material formed on a current collector in a noncontact manner in a manufacturing process of a lithium ion battery.

A first aspect of the present invention is a film thickness measuring apparatus for measuring a film thickness of an active material film formed on a current collector. The film thickness measuring apparatus includes a terahertz wave irradiating a sample with a terahertz wave in a frequency band of 0.01 to 10 kHz, And a detector for detecting a reflected wave of the terahertz wave reflected from the sample, wherein the surface wave reflected from the surface of the active material film in the sample, among the reflected waves detected by the reflected wave detecting unit, A time difference acquiring section for acquiring a time difference of reaching the detector of the interface reflection wave reflected at the interface between the active material film and the current collector in the sample; And a film thickness calculating section for calculating the film thickness.

The second aspect is the film thickness measurement device according to the first aspect, wherein the time difference acquisition section acquires the time difference based on a peak time in the time waveform of the reflected wave.

The third aspect is the film thickness measuring apparatus according to the second aspect, wherein the time difference acquisition section subtracts the time waveform of the reflected wave obtained from the surface reflection sample from the time waveform of the reflected wave obtained from the sample, And the surface reflection sample is formed on the surface of the current collector such that the active material film absorbs all of the interface reflection waves when the terahertz wave is irradiated.

The fourth aspect is the film thickness measuring apparatus according to the third aspect, wherein the time difference acquiring section obtains the time waveform of the reflected wave obtained from the sample and the time waveform of the reflected wave obtained from the surface reflected sample, And then subtract the peak time.

The fifth aspect is the film thickness measuring device according to any one of the first to fourth aspects, wherein in the sample, the position at which the terahertz wave is irradiated is set in a biaxial direction parallel to the surface of the sample And an image generating unit for generating a film thickness distribution image showing a film thickness distribution of a plurality of points on the sample calculated by the film thickness calculating unit.

A sixth aspect is the film thickness measuring apparatus according to any one of the first to fifth aspects, wherein the terahertz wave irradiating unit irradiates the sample with a terahertz wave in the frequency band of 0.01 to 1 kHz.

The seventh aspect is the film thickness measuring apparatus according to any one of the first to sixth aspects, further comprising a filter processing section for performing low-pass filtering of the reflected wave.

The eighth aspect is the film thickness measuring device according to the seventh aspect, wherein the low-pass filter process is a process of transmitting a terahertz wave of 1 kV or less.

The ninth aspect is a film thickness measuring method for measuring a film thickness of an active material film formed on a current collector, the method comprising the steps of: (a) irradiating a sample with a terahertz wave in a frequency band of 0.01 to 10 kHz, (B) a surface wave reflected from a surface of the active material film in the sample, of the reflected wave detected by the detector, and a surface wave reflected from the surface of the active material film in the sample, (C) calculating a film thickness of the active material film based on the time difference and the refractive index of the active material film; and (c) calculating a thickness of the active material film based on the time difference and the refractive index of the active material film And a film thickness calculating step.

According to the film thickness measuring apparatus according to the first aspect, since the film thickness is measured using the reflected wave of the terahertz wave, the film thickness can be measured in a noncontact manner when the active material film is formed on the current collector. As a result, defects such as excess and deficiency of the active material can be detected early, and the economic loss due to the generation of defective products can be reduced.

According to the film thickness measuring apparatus relating to the second aspect, it is possible to easily acquire the film thickness by obtaining the time difference between the surface reflected wave and the interface reflected wave based on the peak time relatively easy to specify.

According to the film thickness measuring apparatus according to the third aspect, by removing the reflected wave obtained from the surface reflected sample from the reflected wave obtained from the sample, the component of the surface reflected wave can be removed. As a result, have.

Further, according to the film thickness measuring apparatus according to the fourth aspect, it is possible to satisfactorily remove the component of the surface reflection from the time waveform of the reflected wave obtained from the sample by adjusting the time.

According to the film thickness measuring apparatus according to the fifth aspect, the film thickness distribution can be grasped easily by generating the film thickness distribution image.

According to the film thickness measuring apparatus relating to the sixth aspect, unnecessary frequency components can be removed from the reflected wave by setting the frequency band of the irradiated terahertz wave to 0.01 ㎔ to 1 높은, which has high permeability of the active material film. This makes it possible to increase the measurement accuracy of the film thickness of the active material film.

According to the film thickness measuring apparatus related to the seventh aspect, by limiting the components of the reflected wave to low frequencies, the correlation between the time difference obtained by the time difference acquiring section and the film thickness becomes higher. As a result, the film thickness of the active material film can be obtained with higher accuracy.

According to the film thickness measuring device related to the eighth aspect, the component of the reflected wave is set to 1 kV or less, whereby the correlation between the time difference obtained by the time difference acquiring part and the film thickness becomes higher. As a result, the film thickness of the active material film can be obtained with higher accuracy.

According to the film thickness measuring method according to the ninth aspect, since the film thickness is measured using the reflected wave of the terahertz wave, the film thickness can be measured in a noncontact manner when the active material film is formed on the current collector. As a result, defects such as excess and deficiency of the active material can be detected early, and the economic loss due to the generation of defective products can be reduced.

1 is a schematic configuration diagram showing a film thickness measuring apparatus according to the first embodiment.
2 is a schematic perspective view showing a sample stage for measuring a transmission wave in a decomposed state.
3 is a schematic perspective view showing a sample stage for measuring a transmission wave.
4 is a schematic side view showing a sample stage for measuring reflected waves.
5 is a view showing another supporting state of the sample.
6 is a block diagram showing the configuration of the control unit according to the first embodiment.
Fig. 7 is a flowchart showing a refractive index acquiring process according to the first embodiment.
Fig. 8 is a diagram showing a time waveform of a transmission wave restored for obtaining a refractive index.
9 is a flow chart showing the film thickness measurement process according to the first embodiment.
10 is a graph showing a time waveform of a measured reflected wave using a positive electrode (film thickness of 88 mu m) of a lithium ion battery as a sample.
11 is a diagram showing a time waveform of a reflected wave when a negative electrode of a lithium ion battery is used as a sample.
12 is a diagram showing a time waveform after subtracting the time waveform of the surface reflection in the time waveform of the film thickness measurement object.
13 is a graph showing a calibration curve of actual film thickness and peak time difference.
14 is a diagram showing a time waveform processed by a low-pass filter with respect to the time waveform shown in Fig.
Fig. 15 is a diagram showing a calibration curve of an actual film thickness and a time difference when subjected to low-pass filter processing.
16 is a diagram showing an example of a film thickness distribution image in which an image generation module is generated.
17 is a view showing a frequency spectrum of a transmission wave transmitted through a film of a negative electrode active material (graphite) of a lithium ion battery.
18 is a schematic side view showing the active material film forming system 100 equipped with the film thickness measuring device 1A according to the second embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. Note that the constituent elements described in this embodiment are merely examples, and the scope of the present invention is not limited to them. In the drawings, for the sake of easy understanding, the dimensions and the numbers of the respective parts may be exaggerated or simplified in accordance with necessity.

<1. First Embodiment>

&Lt; Configuration of Film Thickness Measuring Apparatus &gt;

1 is a schematic configuration diagram showing a film thickness measuring apparatus 1 according to the first embodiment. 1, the film thickness measuring apparatus 1 includes a terahertz wave irradiating unit 10, a sample stage 20, a transmitted wave detecting unit 30, a reflected wave detecting unit 30A, delay units 40 and 40A, , And a control unit 50. [ The transmission wave detecting unit 30 and the delay unit 40 constitute a refractive index acquisition system configured to acquire a refractive index of a film containing an active material (hereinafter referred to as an &quot; active material film &quot;). The reflected wave detecting section 30A and the delay section 40A constitute a film thickness measuring system for measuring the film thickness of the active material film.

<Terahertz wave investigation department (10)>

The terahertz wave irradiator 10 is configured to irradiate the sample 9 supported on the sample stage 20 with the terahertz wave LT1.

The terahertz wave irradiation unit 10 includes a femtosecond pulse laser 11.

The femtosecond pulse laser 11 oscillates laser pulse light (pulse light LP10) having a wavelength including a visible light region of, for example, 360 nm (nanometer) or more and 1.5 m (micrometer) or less. As an example, the femtosecond pulse laser 11 is configured to oscillate a linearly polarized pulse light LP10 having a center wavelength of 800 nm, a period of several kHz to several hundred MHz, and a pulse width of about 10 to 150 femtoseconds . Of course, the femtosecond pulse laser 11 oscillates the pulse light LP10 in other wavelength regions (for example, a visible light wavelength such as a blue wavelength (450 to 495 nm) and a green wavelength (495 to 570 nm)) .

The pulse light LP10 oscillated from the femtosecond pulse laser 11 is split by the beam splitter B1 into two pulses, one of which is a pump light LP1 (first pulse light) and the other of which is a probe light LP2 2-pulse light). The pump light LP1 is incident on the photoconductive switch 14 on the emitter side through the chopper 12 and the plane mirror 13 controlled by the high frequency signal oscillator 300. [ A bias voltage is applied to the photoconductive switch 14 by the amplifier 15 and a pulse-like terahertz wave LT1 is generated as the pulse-like pump LP1 is incident. The photoconductive switch 14 is an example of a terahertz wave generator for generating a terahertz wave.

The terahertz wave generated in the photoconductive switch 14 is preferably in the frequency band included in 0.01 to 10 kHz, more preferably in the range of 0.01 to 1 kHz. In addition, the frequency of the terahertz wave generated in the photoconductive switch 14 is approximately determined according to the shape of the photoconductive switch 14 concerned. For example, in the case of a diaphragm type, a terahertz wave in a range of 0.1 to 4 kV can be favorably generated, and in the case of a bow tie type, a terahertz wave in a range of 0.03 kV to 2 kV can be favorably generated.

The terahertz wave LT1 generated in the photoconductive switch 14 is diffused through the early-stage silicon lens 16. Then, the terahertz wave LT1 is collimated by the parabolic mirror 17 and is condensed on the parabolic mirror 18. Then, the terahertz wave LT1 is irradiated to the sample 9 placed at the focal position.

The terahertz wave irradiator 10 may be configured so as to irradiate the sample 9 with the terahertz wave LT1. For example, the pump light LP1 emitted from the femtosecond pulse laser 11 may be incident on the photoconductive switch 14 by an optical fiber cable. It is also possible to omit the objective lens 18 and shorten the distance between the photoconductive switch 14 and the objective lens 17 so that the focal point where the terahertz wave LT1 reflected by the objective lens 17 is condensed The sample 9 may be placed at the position. One or both of the barrier rings 17 and 18 may be replaced with a terahertz lens.

&Lt; Transmitted-wave detection unit 30 &gt;

The transmitted wave detecting section 30 detects the electric field strength of the transmitted wave LT2 which is the terahertz wave LT1 transmitted through the sample 9. The transmitted wave detecting section 30 is implemented to obtain the refractive index of the active material film composed of the active material as described later. In the case of obtaining the refractive index, an active material film is formed on the surface of the transparent substrate made of a material (for example, PET) having a high transmittance of terahertz wave and the surface of the transparent substrate as the sample 9. In the case of forming a thin film on a transparent substrate, for example, it is preferable that the slurry of the active material is evenly coated on one major surface (the widest surface) of the plate-shaped transparent substrate and dried.

Here, the configuration of the sample stage 20 for measuring the transmission wave LT2 will be described. 2 is a schematic perspective view showing a sample stage 20 for measuring the transmission wave LT2 in an exploded manner. 3 is a schematic perspective view showing the sample stage 20 for measuring the transmission wave LT2.

When the transmission wave LT2 is measured, the sample stage 20 moves the sample 9 in a direction perpendicular to the traveling direction of the terahertz wave LT1 and in a direction perpendicular to the direction of travel of the barrier face 18 and the barrier face 31 Grasp at the focus position. More specifically, the sample stage 20 is provided with supporting means for supporting the sample 9 in accordance with the shape thereof. As an example, in the case of holding the transparent base material as the sample 9, the sample stage 20 is constituted by the sample pressing frames 21 and 22 as shown in Figs. The sample pressing frames 21 and 22 are connected to each other with screws or the like in a state in which the peripheral edge of the sample 9 is held by the sample pressing frames 21 and 22. The sample pressing frames 21 and 22 connected to the sample stage 20 are fixed to the pedestal 23 of the sample stage 20 in a standing posture with screws or the like.

As shown in Fig. 1, the transmission wave LT2 transmitted through the sample 9 becomes parallel light by the parabolic mirror 31 disposed at the position of the focal distance from the sample 9. Then, the transmission wave LT2, which has become parallel light, is condensed on the anti-reflection mirror 32. Then, the light is incident on the photoconductive switch 34 through the first-stage silicon lens 33. The photoconductive switch 34 is disposed at the position of the focal length of the barrier mirror 32.

The other probe light beam LP2 (second pulse light), which is emitted from the femtosecond pulse laser 11 and divided into two by the beam splitter B1, passes through the plane mirror 35 and the delay unit 40 And is incident on the photoconductive switch 34. [ When the photoconductive switch 34 receives the probe light LP2, a current corresponding to the electric field intensity of the transmission wave LT2 incident on the photoconductive switch 34 flows. The voltage change at this time is amplified by the lock-in amplifier 36 and is received by the control unit 50 through the predetermined interface at the frequency according to the high-frequency signal oscillator 300. [ The photoconductive switch 34 is an example of a transmission wave detector that detects the electric field intensity of the transmission wave LT2.

In addition, either or both of the parabolic mirrors 31 and 32 may be replaced with a terahertz lens. The distance between the specimen 9 and the parabolic mirror 31 may be shorter than the focal distance of the parabolic mirror 31 by omitting the parabolic mirror 32. [ The transmission wave LT2 may be incident on the photoconductive switch 34 by disposing the photoconductive switch 34 at the focus position of the anti-reflection mirror 31. [

<Delay unit 40>

The delay unit 40 detects the time at which the probe light LP2 is incident on the photoconductive switch 34 as the transmission wave detector with respect to the time when the pump light LP1 is incident on the photoconductive switch 14 as a terahertz wave oscillator Relative delay.

More specifically, the delay unit 40 includes plane mirrors 41 and 42, a delay stage 43, and a delay stage moving mechanism 44. The probe light LP2 is reflected by the plane mirror 35 and then reflected by the plane mirror 41 in the direction toward the retardation stage 43. [ The retardation stage 43 has a return mirror for returning the incident probe light LP2 in a direction opposite to the incident direction. The probe light LP2 returned by the retardation stage 43 is reflected by the plane mirror 42 and is incident on the photoconductive switch 34. [

The delay stage 43 is moved by the delay stage moving mechanism 44 in parallel with the direction in which the probe light LP2 is incident. As an example of the configuration of the delay stage moving mechanism 44, a linear motor or an electric slider mechanism for rotationally driving a screw shaft to which a nut member on the slider side is screwed is driven by a servo motor to drive the delay stage 43 in the axial direction And the amount of movement of the retardation stage 43 is measured by a linear gauge or the like.

The optical path length of the probe light LP2 from the femtosecond pulse laser 11 to the photoconductive switch 34 can be changed by linearly moving the delay stage 43 in parallel with the probe light LP2. Thus, the timing of the probe light (LP2) incident on the photoconductive switch (34) can be changed. That is, the photoconductive switch 34 can change the timing (phase) for detecting the electric field intensity of the transmission wave LT2.

Further, the delay section 40 may be formed on the optical path of the pump light LP1 (first pulse light). That is, by changing the optical path length of the pump light LP1, the timing at which the pump light LP1 reaches the photoconductive switch 34 can be delayed. This makes it possible to change the timing at which the electric field intensity of the transmission wave LT2 is detected by the photoconductive switch 34 because the timing at which the terahertz wave LT1 in the pulse phase is generated can be changed.

&Lt; Reflected wave detector 30A &gt;

 The reflected wave detecting section 30A is configured to detect the electric field intensity of the reflected wave LT3 which is the terahertz wave LT1 reflected by the sample 9. [ The detection of the reflected wave LT3 is performed to measure the film thickness of the active material film formed on the current collector such as an aluminum foil, as described later. Therefore, the specimen 9 for measuring the reflected wave LT3 becomes a current collector on which the active material film for measuring the film thickness is formed.

4 is a schematic side view showing a sample stage 20 for measuring the reflected wave LT3. When the reflected wave LT3 is measured, as shown in Fig. 4, the sample stage 20 uses the support base 20A for supporting the sample 9 (the current collector 93 on which the active material film 91 is formed) do. As shown in Fig. 1, a sample stage moving mechanism 24 is connected to the support table 20A. The sample stage moving mechanism 24 moves the support table 20A in a uniaxial direction or in two mutually orthogonal directions in a plane parallel to the main surface of the sample 9. Thus, in the sample 9, the position where the terahertz wave LT1 is irradiated can be displaced in the biaxial direction parallel to the surface of the sample 9. That is, the sample stage moving mechanism 24 is an example of the irradiation position changing unit. It is also possible to use a moving mechanism for moving the terahertz wave irradiator 10 and the reflected wave detector 30A in the biaxial direction parallel to the surface of the sample 9 instead of moving the sample 9 together with the support table 20A The irradiation position of the terahertz wave LT1 may be changed.

As an example of the configuration of the sample stage moving mechanism 24, the support base 20A is moved in the axial direction by an electric slider mechanism or the like that rotationally drives the screw shaft to which the nut member on the side of the linear motor or the slider is screw- As shown in FIG. The movement amount of the support table 20A may be measured by a linear gauge or the like.

4, the side of the current collector 93 opposite to the side of the active material film 91 to which the terahertz wave LT1 is irradiated is supported on the surface of the supporting table 20A. However, . Fig. 5 is a view showing another supporting state of the sample 9. Fig. In the example shown in Fig. 5, on the surface of the support table 20B, the side of the active material film 91 to which the terahertz wave LT1 is irradiated is supported. In this case, the terahertz wave LT1 is transmitted through the support table 20B and irradiated to the sample 9. [ Therefore, it is preferable that the support table 20B is made of a material (for example, quartz, resin (polyethylene terephthalate (PET)), rubber) having high permeability of the terahertz wave LT1. In addition, a through hole for passing the terahertz wave may be formed on the support table 20B.

In the reflected wave detecting section 30A, wire grids 81 and 82 are formed on the optical path of the terahertz wave LT1 from the parabolic mirror 18 to the sample 9. The wire grids 81 and 82 are arranged with their polarization angles changed. 14, the wire grid 81 is arranged at an angle of 90 degrees with respect to the angle of incidence of the terahertz wave LT1, and the wire grid 82 is arranged at an angle of 45 degrees with respect to the wire grid 81, As shown in Fig. Thus, by setting the angle of polarization between the wire grid 81 and the wire grid 82 to be 45 degrees, the attenuation of the electric field intensity of the reflected wave LT3 can be minimized.

The terahertz wave LT1 transmitted through the wire grids 81 and 82 is incident on the sample stage 20 and partially reflected by the sample 9. The reflected terahertz reflex reflected wave LT3 is reflected by the wire grid 82 and is incident on the barrier mirror 83. [ The reflected wave LT3 reflected by the parabolic mirror 83 is condensed by the parabolic mirror 84 and is incident on the photoconductive switch 34A (detector).

When the photoconductive switch 34A receives the probe light LP3 received through the delay unit 40A, a current corresponding to the electric field intensity of the reflected wave LT3 incident on the photoconductive switch 34A flows . The probe light LP3 is a beam of light generated by branching the probe light LP2 by the beam splitter B2. The voltage change caused by the current flowing in the photoconductive switch 34A is amplified by the lock-in amplifier 36A and is received by the control unit 50. [

&Lt; Delay unit 40A &gt;

The delay unit 40A includes the plane mirrors 41A and 42A, the delay stage 43A and the delay stage moving mechanism 44A and has substantially the same configuration as the delay unit 40. [ The delay stage 43A is moved by the delay stage moving mechanism 44A in parallel with the direction in which the probe light LP3 is incident. The optical path length of the probe light LP3 from the femtosecond pulse laser 11 to the photoconductive switch 34A is changed by linearly moving the delay stage 43 in parallel with the probe light LP3. Thus, the timing of the probe light LP3 incident on the photoconductive switch 34A is changed. That is, the delay unit 40A changes the timing (phase) at which the photoconductive switch 34A detects the electric field intensity of the reflected wave LT3.

<Control unit 50>

6 is a block diagram showing the configuration of the control unit 50 according to the first embodiment. Although not shown, the control unit 50 is constituted by a general computer having a CPU, a ROM, a RAM and the like.

The CPU of the control section 50 operates as a sample stage control module 501, a delay stage control module 503, a transmitted wave intensity acquisition module 505 and a refractive index acquisition module 507 Function. The CPU functions as a delay stage control module 503A, a reflected wave intensity acquisition module 505A, a time difference acquisition module 509, a film thickness calculation module 511 and an image generation module 513. In addition, some or all of these functions may be realized in hardware by a dedicated circuit or the like.

The sample stage control module 501 is configured to control the sample stage moving mechanism 24. The delay stage control module 503 is configured to control the delay stage moving mechanism 44.

The transmission wave intensity acquisition module 505 reads the voltage value generated by the photoconductive switch 34 through the lock-in amplifier 36 to acquire the electric field intensity of the transmission wave LT2. The transmission wave intensity acquisition module 505 restores the time waveform of the transmission wave TL2 by performing the terahertz time domain spectroscopy (THz-TDS). That is, the delay stage control module 503 moves the delay stage 43 of the delay section 40 so that the transmission wave intensity acquisition module 505 acquires the electric field intensity of the transmission wave LT2 at a different timing (phase) do. As a result, the time waveform of the transmission wave LT2 is restored.

The refractive index acquisition module 507 acquires the refractive index of the sample from the time waveform based on the field intensity of the transmission wave LT2 acquired by the transmission wave intensity acquisition module 505. [ Details of obtaining the refractive index will be described later. The refractive index of the film acquired by the refractive index acquiring module 507 may be temporarily stored as the refractive index information C1 in the storage section 60 (temporary storage such as RAM or the like in addition to nonvolatile storage such as a hard disk, Quot ;, and &quot; remember &quot;). The refractive index information C1 is readable by the film thickness calculating module 511 described later.

The delay stage control module 503A is configured to control the delay stage moving mechanism 44A.

The reflected wave intensity acquisition module 505A reads the voltage value generated by the photoconductive switch 34A through the lock-in amplifier 36A to obtain the electric field intensity of the reflected wave LT3. The reflected wave intensity acquisition module 505A restores the time waveform of the reflected wave TL3 by performing the terahertz time domain spectroscopy (THz-TDS). That is, the delay stage control module 503A moves the delay stage 43A of the delay section 40A so that the reflected wave intensity acquisition module 505A acquires the electric field intensity of the reflected wave LT3 at a different timing (phase). As a result, the time waveform of the reflected wave LT3 is restored.

The time difference acquisition module 509 calculates the time difference from the reflected wave LT3 restored by the reflected wave intensity acquisition module 505A on the surface of the active material film in the sample 9 with respect to the sample (here, the current collector on which the active material film is formed) And obtains the time difference of reaching the detector (light conductive switch 34A) of the surface reflected wave and the interface reflected wave reflected from the interface between the active material film and the current collector in the sample. The details of the time difference acquisition will be described later.

The film thickness calculating module 511 calculates the film thickness of the active material film based on the time difference acquired by the time difference acquiring module 509, the refractive index of the active material film formed on the current collector, and the incident angle of the terahertz wave LT1 . The refractive index of the active material film is stored in the storage section 60 as the refractive index information C1.

The image generation module 513 is configured to generate an image (film thickness distribution image) showing a film thickness distribution obtained by performing film thickness measurement at a plurality of points on the surface of the sample 9 and display the image have. The image generation module 513 may be configured to generate a two-dimensional image in which the difference in film thickness at each point of the sample 9 is expressed by a color tone or a shape (dotted pattern), or a three- Or the like.

To the control unit 50, a display unit 61 and an operation input unit 62 are connected. The display section 61 is constituted by a liquid crystal display or the like and displays a time waveform of the transmitted wave LT2 and a time waveform of the reflected wave LT3 in addition to the image produced by the various measurement results And the like). The operation input unit 62 is an input device configured by, for example, a keyboard and a mouse, and accepts various operations (operations for inputting commands and various data) from the operator. Specifically, the operation of selecting the operation mode (including the correlation information acquisition mode or the catalyst loading amount measurement mode) of the film thickness measuring apparatus 1 or the operation of specifying the measurement point (or measurement range) in the sample 9 And so on. The operation input section 62 may be constituted by various switches, a touch panel, and the like.

<Refractive Index Acquisition Processing>

7 is a flowchart showing the refractive index acquiring process according to the first embodiment. When the film thickness of the active material film formed on the current collector is calculated, the refractive index of the active material film is required. In the case where the refractive index of the active material film is already known, this refractive-index acquisition processing can be omitted. The configuration (transmission wave detecting unit 30, delay unit 40, etc.) for obtaining the refractive index may also be omitted in the film thickness measuring apparatus 1. [

First, the peak time of the terahertz wave LT1 having passed through the space in which the sample 9 and the sample stage 20 are not disposed is measured (step S11). More specifically, THz-TDS for detecting the terahertz wave LT1 that has passed through the space in the transmission wave detector 30 is executed, and the time waveform is restored. Then, in the restored time waveform, the peak time (T _R ), that is, the time at which the electric field intensity reaches the maximum (peak) is specified.

Subsequently, the peak time of the transmission wave LT2 transmitted through only the transmission substrate is measured (step S12). More specifically, the sample 9 composed of only the transmissive substrate is placed on the sample stage 20, and the terahertz wave LT1 is irradiated. Then, the THz-TDS for detecting the transmission wave LT2 transmitted only through the transmissive substrate is executed, and the time waveform is restored. Then, in the restored time waveform, the peak time T _B is specified.

Subsequently, the peak time of the transmission wave LT2 transmitted through the transmissive substrate (the transmissive substrate with the active material film) on the surface thereof is measured (step S13). Specifically, a sample 9 composed of a transmissive base material with an active material film attached thereto is fixed to the sample stage 20, and the terahertz wave LT1 is irradiated to the sample 9. Here, the transmissive substrate constituting the transmissive substrate to which the active material film is attached is the same as the transmissive substrate measured in Step S12, or has the same material and thickness as those of the transmissive substrate. Then, THz-TDS for detecting the transmission wave LT2 transmitted through the transmissive substrate with the active material film is executed, and the time waveform is restored. In the restored time waveform, the peak time T _SB is specified. Fig. 8 shows the restored time waveforms WR, WB and WSB. The time waveform WR is a time waveform of the terahertz wave LT1 that has passed through the space. The time waveform WB is a time waveform of a transmission wave transmitted through the transmission substrate. The time waveform WSB is a time waveform of a transmission wave transmitted through a transparent base material having an active material film attached thereto.

Subsequently, the refractive index of the active material film is calculated based on the peak times acquired in steps S11 to S13 (step S14). Hereinafter, the principle of calculating the refractive index will be described.

First, the refractive index of the active material film is n _S , the speed of light under vacuum is c, and the light speed of the active material film is v _S. Then, the refractive index n _S is expressed by the following equation (1).

[Equation 1]

Next, by subtracting the peak time (T _R ) of the terahertz wave (LT1) passing through the space at the peak time (T _B ) of the transmission wave transmitted through only the transmission substrate, the peak time difference (? T _B ) can be obtained. Here, when the thickness (L _B ) of the transparent base material and the velocity (v _B ) of the terahertz wave in the transparent base material are used, this peak time difference? T _B is expressed by the following formula (2).

&Quot; (2) &quot;

Based on the above equation (2), the velocity v _B is expressed by the following equation (3).

&Quot; (3) &quot;

Further, based on (3) above, the refractive index (n _B ) of the transparent base material is expressed by the following formula (4).

&Quot; (4) &quot;

Peak time difference to continue, the terahertz wave by the time (Δt _SB) transmitted through the transmissive substrate with active material film is attached, subtracting the time (Δt _B) of the terahertz wave is transmitted through the transmissive substrate, corresponding to the active material layer transmission time (? T _S ) can be acquired. This is expressed by the following equation (5).

&Quot; (5) &quot;

In addition, the peak time difference (Δt _S) is the active material film of a thickness (L _S), the terahertz wave is pray speed (v _S) naahgan time, the difference in time at a rate naahgan (c) in the air to. That is, the peak time difference? T _S is expressed by the following equation (6).

&Quot; (6) &quot;

Then, the following equation (7) is obtained based on the equations (5) and (6).

&Quot; (7) &quot;

From equation (7), the velocity v _s of the terahertz wave passing through the active material film is expressed by the following equation (8).

&Quot; (8) &quot;

In addition, the time (Δt _SB) is a film peak time (T _SB) in, the peak time (T _R) of the terahertz wave through the space of the light transmitted through the affixed transmitting substrate terahertz wave can be calculated by subtracting. In addition, the time (Δt _B) is a peak time (T _R) at the peak time (T _B) of the wave a THz transmitted through the transmissive substrate, the terahertz wave that has passed through the space can be determined by subtracting (formula (2 ) Reference).

From the equation (8), the refractive index n _{S of the} active material film is expressed by the following equation (9).

&Quot; (9) &quot;

Here, the film thickness (L _S ) of the active material film in the transmissive substrate to which the active material film is attached can be measured using a known film thickness meter. Therefore, by substituting this film thickness L _S and the peak times (T _R , T _B , T _SB ) of the respective terahertz waves obtained in steps S11 to S13 into equation (9), the refractive index n _S ) can be acquired.

This is the description of the flow of the refractive index acquisition processing. Next, the film thickness measurement will be described.

9 is a flow chart showing the film thickness measurement process according to the first embodiment.

First, a sample 9 to be measured is placed on the sample stage 20 (step S21). Here, as shown in Fig. 4, the sample 9 is an active material film formed on the surface of a current collector (for example, aluminum foil or copper foil) constituting a lithium ion battery.

Next, a THz-TDS is applied to the sample 9 to detect the reflected wave LT3 reflected therefrom and the sample 9 is irradiated with the THz wave. Then, the reflected wave intensity acquisition module 505A restores the time waveform of the reflected wave LT3 (step S22).

Subsequently, the film thickness calculating module 511 calculates a THz wave reflected on the surface of the active material film based on the reflected wave LT3 restored in step S22 and a THz wave reflected on the interface between the active material film and the collector, The time difference? T reaching the photoconductive switch 34A (step S23). Then, the film thickness is calculated based on the time difference? T (step S24). Details of the steps S23 and S24 will be described with reference to Fig.

As shown in Fig. 4, the terahertz wave LT1 irradiated on the sample 9 is reflected by the sample 9, and the reflected wave LT3 is reflected by the sample 9 on the side of the active material film 91 of the sample 9 A surface reflection wave LT31 reflected from the surface and a boundary reflection wave LT32 further reflected in the active material film 91 and reflected at the interface between the active material film 91 and the current collector 93.

The time for reaching the detector (the photoconductive switch 34A) is delayed relative to the surface reflected wave LT31 as the interface reflected wave LT32 passes through the active material film 91. [ Here, the delay time (time difference) is set at? T. The absolute refractive index in the air is 1, the light velocity is c, the velocity of the terahertz wave moving in the active material film 91 is v, the incident angle is θ ₀ , and the refraction angle is θ ₁ . The refractive index of the active material film 91 obtained by the refractive index acquisition processing or the like shown in Fig. 6 is set to n. Then, the following equation (10) is established by Snell's law.

&Quot; (10) &quot;

(10), the film thickness d of the active material film 91 can be obtained by the following equation (11).

&Quot; (11) &quot;

Based on the above principle, the film thickness calculating module 511 substitutes the time difference? T, the refractive index n and the incident angle? ₀ of the terahertz wave LT1 into the equation (11) d.

10 is a diagram showing the time waveform W1 of the measured reflected wave LT3 using the positive electrode (film thickness of 88 mu m) of the lithium ion battery as a sample. 10, the horizontal axis represents the time axis and the vertical axis represents the electric field intensity. In this example, the photoconductive switch 14 for generating the terahertz wave LT1 is of Bowtie type and the photoconductive switch 34A for detecting the reflected wave LT3 is of the diaphragm type.

In the time waveform W1 shown in Fig. 10, the first peak point P1 appears in the peak time T1, and the next peak point P2 appears in the subsequent peak time T2. Among them, the peak point P1 corresponds to the peak of the surface reflected wave LT31, and the peak point P2 corresponds to the peak of the interface reflected wave LT32. That is to say that the arrival time difference of the surface reflected wave LT31 and the interface reflected wave LT32 to the photoconductive switch 34A is a time difference t between the peak points P1 and P2 (= T2 - T1 = 1.5 ps) . The refractive index of the active material film obtained by the refractive index acquisition treatment was 2.5. Applying these values to Expression (11), the film thickness d of the active material film becomes 89.75 占 퐉, and a value close to the actual film thickness (88 占 퐉) can be obtained by measuring the reflected wave LT3.

11 is a diagram showing the time waveform of the reflected wave LT3 when the negative electrode of the lithium ion battery is used as a sample. In Fig. 11, the time waveforms measured in the respective samples having the film thicknesses of the active material film of 48 mu m, 49 mu m, 53 mu m, 56 mu m, 63 mu m and 71 mu m are shown.

As shown in Fig. 11, when the negative electrode of the lithium ion battery is used as a sample, the first peak point corresponding to the peak of the surface reflected wave LT31 can easily be specified in each time waveform. However, the next peak point corresponding to the peak of the interface reflected wave LT32 is thought to be near the point indicated by the arrow, but it is slightly buried in the upward convex waveform, making it difficult to specify accurately. This is because the interfacial reflection wave LT32 reflected at the interface between the active material film and the current collector is reflected (reflected) from the surface of the active material film because the active material of the active material (negative electrode active material, for example, graphite) formed on the current collector has low transmittance and high absorbance Is reflected in the surface reflection wave LT31. Thus, in the time waveform of the reflected wave LT3, the component of the surface reflected wave LT31 is removed by extracting the component of the surface reflected wave LT31.

Specifically, first, a terahertz wave LT1 is irradiated on a sample (front surface reflection sample) on which an active material film having a sufficient thickness is formed on the current collector, and the reflected wave LT3 is restored. Here, the sufficient thickness refers to the thickness of the active material film 91 to such an extent that substantially all of the interface reflected wave LT32 reflected from the interface between the active material film 91 and the current collector 93 is absorbed. The reflected wave LT3 recovered from the surface reflection sample is a surface reflection wave LT31 reflected mostly from the surface of the active material film 91 of the surface reflection sample and is reflected at the interface between the active material film 91 and the current collector 93 Lt; RTI ID = 0.0 &gt; LT32. &Lt; / RTI &gt; Hereinafter, the time waveform reconstructed using the surface reflection sample is referred to as &quot; time reflection waveform of surface reflection &quot;.

Subsequently, the time waveform of the surface reflection is subtracted from the time waveform of the film thickness measurement object. Thus, it is possible to extract a peak point corresponding to the peak of the interface reflection wave LT32 from the time waveform of the film thickness measurement object. The time waveform W2 shown in Fig. 10 is a time waveform of surface reflection.

Here, it is difficult to completely match the height position of the surface of the active material film 91 on the surface of the film thickness measurement object and the height position of the surface of the active material film of the surface reflection sample, and to measure the reflected wave LT3 from each. Therefore, a time difference is likely to occur between the surface reflected wave LT31 of the film thickness measurement object and the surface reflected wave LT31 from the surface reflection sample. Therefore, since the component of the surface reflection wave LT31 reflected from the surface of the active material film is removed with high accuracy from the time waveform of the film thickness measurement object, the time waveform of the film measurement object and the time (phase) It is advisable to subtract from it. Concretely, the position of the first peak of the time waveform of the film thickness measuring object and the time of the first peak of the time waveform of the surface reflection match each other. However, the time alignment may be omitted, not essential processing.

5, the height position of the surface of the active material film 91 in the film thickness measurement object and the height position of the surface of the active material film of the surface reflection sample can be matched with each other. Therefore, the time difference of the surface reflected wave LT31 reflected on the surfaces of both active material films 91 is hard to occur. Therefore, the time alignment can be omitted.

12 is a diagram showing a time waveform after subtracting the time waveform of the surface reflection from the time waveform of the film thickness measurement object. The time waveforms of the film thicknesses shown in Fig. 12 include peaks in the vicinity of the arrows, and these peaks correspond to the peaks of the interface reflected waves LT32. Therefore, the time (T1) at which the first peak specified in Fig. 11 appears and the peak time difference? T at the peak time (T2) specified in Fig. 12 can be obtained. Then, the film thickness of each sample can be calculated by substituting the peak time difference? T into the above-described equation (11).

Fig. 13 is a diagram showing a calibration curve L1 of an actual film thickness and a peak time difference? T. 13, the horizontal axis indicates the film thickness and the vertical axis indicates the peak time difference? T. In this example, since the correlation coefficient is 0.73, it can be seen that the peak time difference? T has a relatively high correlation with the actual film thickness.

Fig. 14 is a diagram showing a time waveform when the time waveform shown in Fig. 12 is processed by a low-pass filter. Fig. Here, the threshold value of the low-pass filter is 1.0 ㎔ or less. 15 is a graph showing the actual film thickness and the calibration line L2 of the time difference? T when subjected to the low-pass filter processing. The correlation coefficient when the low-pass filter process is performed is 0.95, which is closer to "1" than the correlation coefficient (= 0.73) when the low-pass filter process is not performed. In other words, by specifying the time difference? T between the surface reflected wave LT31 and the interface reflected wave LT32 based on the time waveform recovered at a frequency of 1.0 kHz or less, the film thickness can be more accurately calculated.

The low-pass filter processing may be realized, for example, by forming a low-pass filter on the optical path of the reflected wave LT3, or may be realized by arithmetic processing such as Fourier transform.

In addition, the terahertz wave LT1 irradiated on the sample 9 may have a frequency band of 0.01 to 1 kHz. For example, a low-pass filter may be disposed on the optical path of the terahertz wave LT1, or a terahertz wave LT1 generated by the terahertz wave irradiating unit 10 may enter the frequency band.

Returning to Fig. 9, when the film thickness calculation in step S24 is completed, the control unit 50 determines whether or not the change of the measurement position is unnecessary. That is, when the film thickness measurement is set to be performed at a plurality of points in advance, the presence or absence of the other points to be measured is determined in step S24. In the case where the film thickness measurement is set to be performed only at one point, step S24 is omitted.

If it is determined in step S24 that there is a point at which film thickness measurement should be performed, the measurement position is changed (step S25). Concretely, the sample stage moving mechanism 24 moves the support table 20A of the sample stage 20 so that the terahertz wave LT1 is irradiated to the position where the film thickness measurement is performed.

If it is determined in step S24 that there is no point where film thickness measurement should be performed, the image generation module 513 generates an image (film thickness distribution image) showing the film thickness distribution and displays it on the display section 61 (Step S27).

16 is a diagram showing an example of the film thickness distribution image I20 in which the image generation module 513 is generated. The film thickness distribution image I20 shown in Fig. 16 is a three-dimensional graph showing the film thickness distribution. The X axis and Y axis represent biaxial directions parallel to the surface of the sample 9, and the Z axis represents the film thickness . Thus, according to the film thickness distribution image I20, the change in the film thickness between the measurement points can be visually recognized easily.

As described above, according to the film thickness measuring apparatus 1, the film thickness can be measured when the active material film 91 of the active material is formed on the current collector 93. This makes it possible to detect defects such as excess and deficiency of the amount of active material at an early stage, and to suppress an increase in economic loss.

17 is a diagram showing a frequency spectrum of a transmission wave transmitted through a film of a negative electrode active material (graphite) of a lithium ion battery. The frequency spectrum is obtained by Fourier transforming the time waveform. In Fig. 17, transmission waves are detected by changing the combination of the types of the photoconductive switches 14 and 34. Fig. "B" indicates Bowtie type, and "d" indicates diaphragm type. As is apparent from Fig. 17, the negative electrode active material of the lithium ion battery has a high transmittance of 1 kPa or less. Therefore, by making the terahertz wave to be irradiated to be 1 ㎔ or less, an extra frequency component can be removed from the reflected wave LT3, and the film thickness can be obtained with high accuracy.

<2. Second Embodiment>

18 is a schematic side view showing the active material film forming system 100 equipped with the film thickness measuring device 1A according to the second embodiment. The active material film forming system 100 is a system for forming an active material film 91 on one side of a sheet-like current collector 93 that is transported in a roll-to-roll manner. The active material film forming system 100 is provided with a film thickness measuring device 1A for measuring the film thickness of the active material film during the conveying path of the current collector 93. [

In the active material film forming system 100, the current collector 93 wound up from the take-up roller 701 is conveyed to the coating portion 71 via the conveying rollers 702 and 703.

The coating portion 71 includes a slit die 711, a coating liquid supply portion 713, and a supporting roller 715. The slit die 711 has a slit-shaped discharge port extending in the width direction of the current collector 93. The coating liquid supply portion 713 supplies a coating liquid (slurry) containing an active material to the slit die 711 through a pipe. The support roller 715 is disposed at a position opposite to the discharge port of the slit die 711 to support the back surface of the current collector 93.

The current collector 93 coated with the coating liquid in the coating portion 71 is conveyed to the drying portion 72. [ The drying section 72 performs drying treatment of the coating film of the coating solution formed on one side of the current collector 93 by the slit die 711 of the coating section 71. [ The drying section 72, as an example, heats the current collector 93 by supplying hot air toward the current collector 93 to evaporate moisture or a solvent of the coating liquid.

The current collector 93 dried in the drying section 72 is wound by the winding roller 706 via the conveying rollers 704 and 705.

The film thickness measuring device 1A is disposed at a position between the conveying rollers 704 and 705 and is configured to measure the film thickness of the active material film 91 formed on the dry current collector 93 . The arrangement position of the film thickness measuring device 1A is not limited to this. For example, it may be disposed at a position between the drying section 72 and the conveying roller 704, or at a position between the conveying roller 705 and the winding roller 706. The film thickness measuring device 1A irradiates a terahertz wave LT1 to the active material film 91 formed on one surface of the current collector 93 by the drying process to detect the reflected reflected wave LT3.

The film thickness measuring device 1 is a sheet member that is a sample to be measured and is conveyed by roll rollers and is supported by conveying rollers 704 and 705. The film thickness measuring device 1 is a film thickness measuring device having a sample stage 20, Is different from the device (1). Other configurations of the film thickness measuring apparatus 1A are substantially the same as those of the film thickness measuring apparatus 1 except that the terahertz wave irradiating unit 10, the reflected wave detecting unit 30A, the delay unit 40A, .

The active material film forming system 100 may be modified to form the active material film 91 on both sides of the current collector 93. [ In this case, the active material film forming system includes a film thickness measuring device 1A for measuring the film thickness of the active material film 91 on one side, a film thickness measuring device 91 for measuring the film thickness of the active material film 91 on the other side, (1A).

The thickness of the active material film 91 formed on the surface of the current collector 93 can be specified by measuring the reflected wave LT3 according to the film thickness measuring device 1A according to the present embodiment. That is, at the time when the active material film 91 is formed on the current collector 93, it is possible to monitor the film thickness. Therefore, defects such as excess and deficiency of the active material can be detected at an early stage and the economic loss can be reduced.

Further, according to the film thickness measuring device 1A, the film thickness of the active material film can be inspected in a non-contact or non-destructive manner. Therefore, since the film thickness can be measured without destroying or destroying the sample, the occurrence of waste due to sampling can be reduced.

Although the present invention has been described in detail, the above description is by way of example and not limitation in all aspects. Numerous modifications that are not illustrated are deemed to be possible without departing from the scope of the invention. The configurations described in each of the above-described embodiments and modified examples may be appropriately combined or omitted as long as they do not contradict each other.

1, 1A: Film thickness measuring device
10: terahertz wave investigation unit
20: Sample stage
20A: Support
30: Transmission wave detector
30A:
34: Photoelectric conversion switch (transmission wave detector)
34A: Photoelectric switch (Reflected wave detector)
40, 40A:
50:
501: sample stage control module
505: Transmission wave intensity acquisition module
505A: Reflected wave intensity acquisition module
507: refractive index acquisition module
509: time difference acquisition module
511: Film thickness calculating module
513: Image generation module
60:
9: Sample
91: active material film
93: The whole house
100: Active material film forming system
C1: refractive index information
Im1: film thickness distribution image
LP1: Pump
LT1: Terahertz wave
LT2: Transmission wave
LT3: Reflected wave
LT31: surface reflection wave
LT32: interface reflection wave
T1, T2: Peak time
Δt: Peak time difference
d: film thickness
n _S : Refractive index of active material film

Claims (9)

1. A film thickness measuring device for measuring a film thickness of an active material film formed on a current collector,
A terahertz wave irradiator for irradiating a sample with a terahertz wave in a frequency band included in 0.01 to 10 kHz,
A reflected wave detecting unit having a detector for detecting a reflected wave of the terahertz wave reflected from the sample;
Wherein the surface wave reflected from the surface of the active material film in the sample and the interface reflection wave reflected from the interface between the active material film and the current collector in the sample, A time difference acquiring section for acquiring a time difference that reaches the time point at which the vehicle is traveling,
And a film thickness calculating section for calculating a film thickness of the active material film based on the time difference and the refractive index of the active material film. The method according to claim 1,
And the time difference acquiring section acquires the time difference based on a peak time in the time waveform of the reflected wave. 3. The method of claim 2,
Wherein the time difference acquisition unit specifies a peak time of the interface reflection wave by subtracting the time waveform of the reflected wave obtained from the surface reflection sample from the time waveform of the reflected wave obtained from the sample,
Wherein the surface reflection sample is formed on the surface of the current collector so that the active material film has a thickness that absorbs all of the interface reflection waves when the terahertz wave is irradiated. The method of claim 3,
Wherein the time difference acquisition unit subtracts the peak time of each reflected wave from the time waveform of the reflected wave obtained from the sample and the time waveform of the reflected wave obtained from the surface reflected sample. 5. The method according to any one of claims 1 to 4,
An irradiating position displacing unit for displacing the irradiated terahertz wave in a biaxial direction parallel to the surface of the sample;
And a film thickness distribution image representing a film thickness distribution of a plurality of points on the sample calculated by the film thickness calculating section. 6. The method according to any one of claims 1 to 5,
Wherein the terahertz wave irradiating unit irradiates the sample with a terahertz wave in the frequency band of 0.01 to 1 kHz. 7. The method according to any one of claims 1 to 6,
Further comprising a filter processing section for performing low-pass filtering of the reflected wave. 8. The method of claim 7,
Wherein the low-pass filter process is a process of transmitting a terahertz wave of 1 kHz or less. A film thickness measuring method for measuring a film thickness of an active material film formed on a current collector,
(a) a detecting step of irradiating a sample with a terahertz wave in a frequency band of 0.01 to 10 kHz and detecting a reflected wave of the terahertz wave reflected from the sample with a detector;
(b) a surface reflection wave reflected from a surface of the active material film in the sample among the reflected waves detected by the detector, and a surface reflection wave reflected from an interface between the active material film and the current collector in the sample, A time difference acquiring step of acquiring a time difference reaching the detector,
(c) a film thickness calculating step of calculating a film thickness of the active material film based on the time difference and the refractive index of the active material film.

Images