JP6589239B2 - Film thickness measuring apparatus and film thickness measuring method - Google Patents

Description

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

A lithium ion secondary battery (LiB) is composed of a positive electrode, a negative electrode, and a separator arranged so as to separate them in order to prevent an electrical short circuit between the positive electrode and the negative electrode. The positive electrode is configured by applying a metal active material such as lithium cobaltate, conductive graphite (such as carbon black), and a binder resin on a current collector such as an aluminum foil. Moreover, the negative electrode is comprised by apply | coating graphite (natural graphite, artificial graphite, etc.) and binder resin which are active materials on collectors, such as aluminum foil. Further, 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 where the organic electrolyte is impregnated. 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.

  When a potential is applied to the positive electrode and the negative electrode, release and incorporation of lithium ions into the active material occur, and an active material having different potentials at the time of release and incorporation is used for the positive electrode and the negative electrode to form a battery. . The following are examples of reactions in the positive electrode and the negative electrode during discharge electricity.

Positive electrode: LiCoO ₂ ＬｉLi _1-x CoO ₂ + xLi ⁺ + xe ^{−
Negative: xLi + + xe - 6C ⇔} Li x C 6

  Patent Document 1 describes that problems such as peeling of the active material layer occur if the thickness uniformity of the binder resin is biased. Further, in Patent Document 2, it is important to achieve leveling properties of the electrode forming slurry, that is, to make the film thickness uniform when the electrode layer is thickened in order to cope with the increase in the capacity of the capacitor. Points are listed.

  Moreover, in patent document 3 and patent document 4, although the amount of active materials is adjusted with the weight per unit area as a basis weight about both the positive electrode and the negative electrode, the film thickness inspection after a coating process, etc. are performed. Absent. A defective product is detected by a charge / discharge cycle test in LiB, which is the final product.

JP 2004-71472 A International Publication No. 2011/024789 Pamphlet JP, 2014-116317, A JP 2014-96386 A JP-T-2006-526774

  However, as described in Patent Document 3 or Patent Document 4, when only the adjustment of the basis weight of the active material amount is performed and the defective product inspection is performed on the final product without performing the film thickness inspection, There was a problem that the economic loss was large when this occurred.

  Further, since the basis 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, if the film thickness is measured, the amount of active material can be specified, but as described above, the film thickness inspection immediately after coating and drying is not performed.

  As a nondestructive inspection method, for example, Patent Document 5 describes using an electromagnetic wave having a frequency in the range of 25 GHz to 100 GHz. However, the technique of Patent Document 5 analyzes the component concentration of the sample from the spectral characteristics, and cannot inspect the film thickness. In particular, it is not possible to measure a thin film that contains carbon and does not transmit visible light, such as a positive electrode and a negative electrode of a lithium ion battery.

  Therefore, an object of the present invention is to provide a technique for performing non-contact film thickness inspection of a film containing an active material formed on a current collector in a manufacturing process of a lithium ion battery.

In order to solve the above-described problem, a first aspect is a film thickness measuring apparatus for measuring the film thickness of an active material film formed on a current collector, and includes a terahertz in a frequency band included in 0.01 THz to 10 THz. A terahertz wave irradiating unit that irradiates the sample with a wave; a reflected wave detecting unit that includes a detector that detects a reflected wave of the terahertz wave reflected by the sample; and the reflected wave detected by the reflected wave detecting unit Of these, the time difference between the surface reflected wave reflected at the surface of the active material film in the sample and the interface reflected wave reflected at the interface between the active material film and the current collector in the sample reaching the detector A time difference acquisition unit that acquires the thickness of the active material film based on the time difference and the refractive index of the active material film, and the time difference acquisition unit includes: Pi in the time waveform The time difference acquisition unit acquires the time difference based on the time of the reflection, and the time difference acquisition unit 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. The peak time of the wave is specified, and the surface reflection sample is formed by forming the active material film on the surface of the current collector with a thickness that completely absorbs the interface reflected wave when the terahertz wave is irradiated. There is .

Moreover, a 2nd aspect is a film thickness measuring apparatus which concerns on a 1st aspect, Comprising: The said time difference acquisition part is the time waveform of the said reflected wave obtained with the said sample, The said obtained with the said surface reflection sample The time waveform of the reflected wave is subtracted after matching the peak time of each reflected wave.

A third aspect is a film thickness measuring apparatus according to the first or second aspect , wherein a position of the sample irradiated with the terahertz wave is set in a biaxial direction parallel to the surface of the sample. An irradiation position displacement unit to be displaced, and an image generation unit that generates a film thickness distribution image indicating the film thickness distribution at a plurality of points on the sample calculated by the film thickness calculation unit are further provided.

A fourth aspect is a film thickness measuring apparatus according to any one of the first to third aspects , wherein the terahertz wave irradiating unit emits a terahertz wave in a frequency band from 0.01 THz to 1 THz. Irradiate the sample.

Moreover, a 5th aspect is a film thickness measuring apparatus which concerns on any one of the 1st to 4th aspect, Comprising: The filter process part which carries out the low-pass filter process of the said reflected wave is further provided.

A sixth aspect is the film thickness measuring apparatus according to the fifth aspect , wherein the low-pass filter process is a process of transmitting a terahertz wave of 1 THz or less.

A seventh aspect is a film thickness measurement method for measuring the film thickness of an active material film formed on a current collector, and (a) a sample of a terahertz wave in a frequency band included between 0.01 THz and 10 THz. A detection step of detecting a reflected wave of the terahertz wave reflected by the sample with a detector; and (b) a surface of the active material film in the sample among the reflected waves detected by the detector. A time difference acquisition step of acquiring a time difference of reaching the detector between the surface reflected wave reflected at the interface and the interface reflected wave reflected at the interface between the active material film and the current collector in the sample; and (c) based on the refractive index of the time difference and the active material layer, the saw including a film thickness calculation step of calculating the film thickness of the active material layer, wherein the step (b), the peak time in the time waveform of the reflected wave Based on the time difference, By subtracting the time waveform of the reflected wave obtained from the surface reflected sample from the time waveform of the reflected wave obtained from the material, the peak time of the interface reflected wave is specified, and the surface reflected sample is irradiated with the terahertz wave The active material film having a thickness that completely absorbs the interface reflected wave is formed on the surface of the current collector .

  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 non-contact manner when the active material film is formed on the current collector. . This makes it possible to detect defects such as excess or deficiency in the amount of active material at an early stage, and reduce economic loss due to the occurrence of defective products.

In addition , the film thickness can be easily acquired by acquiring the time difference between the surface reflected wave and the interface reflected wave based on the peak time that is relatively easy to identify.

In addition , by subtracting 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, whereby the interface reflected wave can be extracted well.

Moreover, according to the film thickness measuring apparatus which concerns on a 2nd aspect, the component of a surface reflection can be favorably removed from the time waveform of the reflected wave obtained by the sample by carrying out time adjustment and subtracting.

Moreover, according to the film thickness measuring apparatus which concerns on a 3rd aspect, a film thickness distribution can be grasped | ascertained easily by producing | generating a film thickness distribution image.

According to the film thickness measuring apparatus according to the fourth aspect, by setting the frequency band of the terahertz wave to be irradiated to 0.01 THz to 1 THz where the active material film has high transparency, an unnecessary frequency component is removed from the reflected wave. Can do. Thereby, the measurement accuracy of the thickness of the active material film can be increased.

According to the film thickness measurement apparatus according to the fifth aspect, by limiting the component of the reflected wave to the low frequency band, the correlation between the time difference obtained by the time difference acquisition unit and the film thickness becomes higher. Thereby, the thickness of the active material film can be obtained with higher accuracy.

According to the film thickness measurement apparatus according to the sixth aspect, the correlation between the time difference obtained by the time difference acquisition unit and the film thickness is further increased by setting the reflected wave component to 1 THz or less. Thereby, the thickness of the active material film can be obtained with higher accuracy.

According to the film thickness measuring method according to the seventh aspect, since the film thickness is measured using the reflected wave of the terahertz wave, the film thickness can be measured in a non-contact manner when the active material film is formed on the current collector. . This makes it possible to detect defects such as excess and deficiency of the substance at an early stage, and reduce economic loss due to the generation of defective products.

It is a schematic block diagram which shows the film thickness measuring apparatus which concerns on 1st Embodiment. It is a schematic perspective view which decomposes | disassembles and shows the sample stage for measuring a transmitted wave. It is a schematic perspective view which shows the sample stage for measuring a transmitted wave. It is a schematic side view which shows the sample stage for measuring a reflected wave. It is a figure which shows the other support aspect of a sample. It is a block diagram which shows the structure of the control part which concerns on 1st Embodiment. It is a flowchart which shows the refractive index acquisition process which concerns on 1st Embodiment. It is a figure which shows the time waveform of the transmitted wave decompress | restored for refractive index acquisition. It is a flowchart which shows the film thickness measurement process which concerns on 1st Embodiment. It is a figure which shows the time waveform of the reflected wave measured using the positive electrode (film thickness of 88 micrometers) of a lithium ion battery as a sample. It is a figure which shows the time waveform of a reflected wave when the negative electrode of a lithium ion battery is made into a sample. It is a figure which shows the time waveform after subtracting the time waveform of surface reflection from the time waveform of the film thickness measurement object. It is a figure which shows the calibration curve of an actual film thickness and a peak time difference. It is a figure which shows the time waveform processed with the low-pass filter about the time waveform shown in FIG. It is a figure which shows the calibration curve of an actual film thickness and time difference when low-pass filter processing is carried out. It is a figure which shows an example of the film thickness distribution image which the image generation module produced | generated. It is a figure which shows the frequency spectrum of the transmitted wave which permeate | transmitted the film | membrane of the negative electrode active material (graphite) of a lithium ion battery. It is a schematic side view which shows the active material film formation system 100 incorporating the film thickness measuring apparatus 1A which concerns on 2nd Embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, the component described in this embodiment is an illustration to the last, and is not a thing of the meaning which limits the scope of the present invention only to them. In the drawings, the size and number of each part may be exaggerated or simplified as necessary for easy understanding.

<1. First Embodiment>
<Configuration of film thickness measuring device>
FIG. 1 is a schematic configuration diagram showing a film thickness measuring apparatus 1 according to the first embodiment. As shown in FIG. 1, the film thickness measurement apparatus 1 includes a terahertz wave irradiation unit 10, a sample stage 20, a transmitted wave detection unit 30, a reflected wave detection unit 30 </ b> A, delay units 40 and 40 </ b> A, and a control unit 50. Yes. The transmitted wave detection unit 30 and the delay unit 40 constitute a refractive index acquisition system provided for acquiring the refractive index of a film containing an active material (hereinafter referred to as “active material film”). The reflected wave detection unit 30A and the delay unit 40A constitute a film thickness measurement system provided for measuring the film thickness of the active material film.

<Terahertz wave irradiation unit 10>
The terahertz wave irradiation unit 10 is configured to irradiate the sample 9 supported by 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 μm (micrometer) or less. As an example, the femtosecond pulse laser 11 is configured to oscillate linearly polarized pulsed light LP10 having a center wavelength of about 800 nm, a period of several kHz to several hundred MHz, and a pulse width of about 10 to 150 femtoseconds. The Of course, the femtosecond pulse laser 11 is configured to oscillate pulsed light LP10 in other wavelength regions (for example, visible light wavelengths such as blue wavelength (450 to 495 nm), green wavelength (495 to 570 nm)). Also good.

  The pulsed light LP10 oscillated from the femtosecond pulse laser 11 is split into two by the beam splitter B1, and one becomes pump light LP1 (first pulsed light) and the other becomes probe light LP2 (second pulsed light). . The pump light LP1 enters the photoconductive switch 14 on the emitter side via the chopper 12 and the flat mirror 13 controlled by the high-frequency signal oscillator 300. A bias voltage is applied to the photoconductive switch 14 by an amplifier 15, and a pulsed terahertz wave LT1 is generated in response to incidence of the pulsed pump light LP1. The photoconductive switch 14 is an example of a terahertz wave generator that generates a terahertz wave.

  The terahertz wave generated in the photoconductive switch 14 is preferably in a frequency band included in 0.01 THz to 10 THz, and more preferably in a frequency band within a range of 0.01 THz to 1 THz. Note that the frequency of the terahertz wave generated in the photoconductive switch 14 is largely determined by the shape of the photoconductive switch 14. For example, terahertz waves in the range of 0.1 THz to 4 THz can be generated satisfactorily in the case of the dipole type, and terahertz waves in the range of 0.03 THz to 2 THz can be generated in the case of the bowtie type.

  The terahertz wave LT1 generated by the photoconductive switch 14 is diffused through the super hemispherical silicon lens 16. The terahertz wave LT1 is converted into parallel light by the parabolic mirror 17 and further collected by the parabolic mirror 18. Then, the sample 9 arranged at the focal position is irradiated with the terahertz wave LT1.

  The terahertz wave irradiation unit 10 may be configured in any manner as long as the sample 9 can be irradiated with the terahertz wave LT1. For example, the pump light LP1 oscillated from the femtosecond pulse laser 11 may be incident on the photoconductive switch 14 by an optical fiber cable. Further, the parabolic mirror 18 is omitted, the distance between the photoconductive switch 14 and the parabolic mirror 17 is shortened, and the sample is placed at the focal position where the terahertz wave LT1 reflected by the parabolic mirror 17 is condensed. 9 may be arranged. One or both of the parabolic mirrors 17 and 18 may be replaced with a terahertz lens.

<Transmission wave detector 30>
The transmitted wave detection unit 30 detects the electric field intensity of the transmitted wave LT2 that is the terahertz wave LT1 that has passed through the sample 9. As will be described later, the transmitted wave detection unit 30 is performed in order to acquire the refractive index of an active material film made of an active material. When obtaining the refractive index, the sample 9 is assumed to have a transmissive substrate made of a material having high terahertz wave permeability (for example, PET), and an active material film formed on the surface of the transmissive substrate. The When forming a thin film on a transmissive substrate, for example, a slurry obtained by uniformly applying a slurry of an active material material to one main surface (widest surface) of a plate-shaped transmissive substrate is preferable.

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

  When measuring the transmitted wave LT2, the sample stage 20 holds the sample 9 at the focal position of the parabolic mirror 18 and a parabolic mirror 31 described later, which is perpendicular to the traveling direction of the terahertz wave LT1. More specifically, the sample stage 20 includes a support unit that supports the sample stage 20 according to the shape of the sample 9. As an example, when holding a transmissive substrate which is the sample 9, the sample stage 20 is composed of sample holding frames 21 and 22, as shown in FIGS. In a state where the periphery of the sample 9 is gripped by the sample holding frames 21 and 22, the sample holding frames 21 and 22 are connected to each other with screws or the like. The connected sample holding frames 21 and 22 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 transmitted wave LT2 that has passed through the sample 9 is converted into parallel light by a parabolic mirror 31 disposed at a focal distance from the sample 9. Then, the transmitted wave LT2 that has become parallel light is collected by the parabolic mirror 32. Then, the light enters the photoconductive switch 34 through the super hemispherical silicon lens 33. The photoconductive switch 34 is arranged at the position of the focal length of the parabolic mirror 32.

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

  One or both of the parabolic mirrors 31 and 32 may be replaced with a terahertz lens. Further, the parabolic mirror 32 may be omitted, and the distance between the sample 9 and the parabolic mirror 31 may be shorter than the focal length of the parabolic mirror 31. Then, by arranging the photoconductive switch 34 at the focal position of the parabolic mirror 31, the transmitted wave LT2 may be incident on the photoconductive switch 34.

<Delay unit 40>
The delay unit 40 relatively delays the time during which the probe light LP2 enters the photoconductive switch 34, which is a transmitted wave detector, with respect to the time when the pump light LP1 enters the photoconductive switch 14, which is a terahertz wave oscillator. .

  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 delay stage 43. The delay stage 43 includes a folding mirror that folds the incident probe light LP2 in a direction opposite to the incident direction. The probe light LP2 turned back by the delay stage 43 is reflected by the plane mirror 42 and then enters the photoconductive switch 34.

  The delay stage 43 is moved in parallel with the direction in which the probe light LP2 is incident by the delay stage moving mechanism 44. As a configuration example of the delay stage moving mechanism 44, the delay stage 43 is moved in the axial direction by an electric slider mechanism or the like that rotates a screw shaft to which a nut member on a linear motor or a slider is screwed by driving a servo motor. It may be configured to measure the amount of movement of the delay stage 43 with 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. Thereby, the timing of the probe light LP2 incident on the photoconductive switch 34 can be changed. That is, the timing (phase) at which the photoconductive switch 34 detects the electric field intensity of the transmitted wave LT2 can be changed.

  The delay unit 40 may be provided on the optical path of the pump light LP1 (first pulse light). That is, the timing at which the pump light LP1 reaches the photoconductive switch 34 can be delayed by changing the optical path length of the pump light LP1. Thereby, since the timing at which the pulsed terahertz wave LT1 is generated can be changed, the timing (phase) at which the photoconductive switch 34 detects the electric field intensity of the transmitted wave LT2 can be changed.

<Reflected wave detection unit 30A>
The reflected wave detection unit 30A is configured to detect the electric field intensity of the reflected wave LT3 that 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 an active material film formed on a current collector such as an aluminum foil, as will be described later. Therefore, the sample 9 for measuring the reflected wave LT3 is a current collector on which an active material film for film thickness measurement is formed.

  FIG. 4 is a schematic side view showing the sample stage 20 for measuring the reflected wave LT3. When measuring the reflected wave LT3, as shown in FIG. 4, the sample stage 20 uses a support 20A that supports the sample 9 (the current collector 93 on which the active material film 91 is formed). As shown in FIG. 1, a sample stage moving mechanism 24 is connected to the support base 20A. The sample stage moving mechanism 24 moves the support base 20A in one axial direction or two axial directions orthogonal to each other in a plane parallel to the main surface of the sample 9. Thereby, in the sample 9, the position irradiated with the terahertz wave LT1 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 an irradiation position changing unit. Note that the terahertz wave LT1 is not moved by moving the sample 9 together with the support 20A but by moving a terahertz wave irradiation unit 10 and the reflected wave detection unit 30A in two axial directions parallel to the surface of the sample 9. The irradiation position 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 in which a screw shaft to which a linear motor or a nut member on the slider side is screwed is rotated by driving a servo motor. It is conceivable to configure. Further, the movement amount of the support base 20A may be measured with a linear gauge or the like.

  In the example shown in FIG. 4, the current collector 93 side opposite to the active material film 91 irradiated with the terahertz wave LT1 is supported on the surface of the support base 20A. It is not limited. FIG. 5 is a view showing another support mode of the sample 9. The example shown in FIG. 5 supports the active material film 91 side irradiated with the terahertz wave LT1 on the surface of the support base 20B. In this case, the terahertz wave LT1 is transmitted through the support base 20B and irradiated onto the sample 9. For this reason, it is preferable that the support base 20B is made of a material (for example, quartz, resin (polyethylene terephthalate (PET)), rubber, or the like) that has high transmittance of the terahertz wave LT1. Note that a through hole for allowing terahertz waves to pass therethrough may be formed in the support base 20B.

  In the reflected wave detection unit 30A, wire grids 81 and 82 are provided 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 different polarization angles. As an example, the wire grid 81 is arranged to form 90 degrees with respect to the incident angle of the terahertz wave LT1, and the wire grid 82 forms an angle of 45 degrees with respect to the wire grid 81 as shown in FIG. Are arranged as follows. Thus, by setting the polarization angles of the wire grid 81 and the wire grid 82 so that the angle difference between them is 45 degrees, the attenuation of the electric field strength 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 a part of the sample 9 is reflected. The reflected wave LT3 which is the reflected terahertz wave is reflected by the wire grid 82 and enters the parabolic mirror 83. The reflected wave LT3 reflected by the parabolic mirror 83 is collected by the parabolic mirror 84 and enters the photoconductive switch 34A (detector).

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

<Delay unit 40A>
The delay unit 40A includes plane mirrors 41A and 42A, a delay stage 43A, and a delay stage moving mechanism 44A, and has substantially the same configuration as the delay unit 40. The delay stage 43A is moved in parallel with the direction in which the probe light LP3 is incident by the delay stage moving mechanism 44A. 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. As a result, 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 strength of the reflected wave LT3.

<Control unit 50>
FIG. 6 is a block diagram illustrating a configuration of the control unit 50 according to the first embodiment. Although not shown, the control unit 50 is configured as a general computer including a CPU, a ROM, a RAM, and the like.

  The CPU of the control unit 50 functions 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 by operating according to a program (not shown). 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. Note that 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 transmitted wave intensity acquisition module 505 acquires the electric field intensity of the transmitted wave LT2 by reading the voltage value generated by the photoconductive switch 34 via the lock-in amplifier 36. The transmitted wave intensity acquisition module 505 restores the time waveform of the transmitted wave TL2 by performing terahertz time domain spectroscopy (THz-TDS). That is, when the delay stage control module 503 moves the delay stage 43 of the delay unit 40, the transmitted wave intensity acquisition module 505 acquires the electric field intensity of the transmitted wave LT2 at different timings (phases). As a result, the time waveform of the transmitted wave LT2 is restored.

  The refractive index acquisition module 507 acquires the refractive index of the sample from the time waveform based on the electric field intensity of the transmitted wave LT2 acquired by the transmitted wave intensity acquisition module 505. Details of the refractive index acquisition will be described later. The refractive index of the film acquired by the refractive index acquisition module 507 is temporarily stored in the storage unit 60 (nonvolatile storage such as a hard disk, an optical disk or a magneto-optical disk as well as information such as a RAM as refractive index information C1. Stored in memory). The refractive index information C1 can be read by a film thickness calculation 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 acquires the electric field intensity of the reflected wave LT3 by reading the voltage value generated by the photoconductive switch 34A via the lock-in amplifier 36A. The reflected wave intensity acquisition module 505A restores the time waveform of the reflected wave TL3 by performing terahertz time domain spectroscopy (THz-TDS). That is, when the delay stage control module 503A moves the delay stage 43A of the delay unit 40A, the reflected wave intensity acquisition module 505A acquires the electric field intensity of the reflected wave LT3 at different timings (phases). Thereby, the time waveform of the reflected wave LT3 is restored.

  The time difference acquisition module 509 is a surface reflected from the surface of the active material film in the sample 9 from the reflected wave LT3 restored by the reflected wave intensity acquisition module 505A for the sample (here, the current collector on which the active material film is formed). A time difference between the reflected wave and the interface reflected wave reflected at the interface between the active material film and the current collector in the sample and reaching the detector (the photoconductive switch 34A) is acquired. Details of the time difference acquisition will be described later.

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

  The image generation module 513 is configured to generate an image (film thickness distribution image) indicating the film thickness distribution obtained by measuring the film thickness at a plurality of points on the surface of the sample 9 and display the image on the display unit 61. ing. The image generation module 513 may be configured to generate a two-dimensional image in which a difference in film thickness at each point of the sample 9 is expressed by a color tone or a pattern (such as a halftone dot pattern), or a three-dimensional image It may be configured to generate a three-dimensional image expressed in

  A display unit 61 and an operation input unit 62 are connected to the control unit 50. The display unit 61 is configured by a liquid crystal display or the like, and includes various measurement results (for example, including the time waveform of the transmitted wave LT2, the time waveform of the reflected wave LT3, in addition to the image generated by the image generation module 513). indicate. The operation input unit 62 is an input device configured by a keyboard and a mouse, for example, and accepts various operations (operations for inputting commands and various data) from the operator. Specifically, an operation for selecting an operation mode (including a correlation information acquisition mode or a catalyst loading amount measurement mode) of the film thickness measuring apparatus 1 or an operation for specifying a measurement location (or measurement range) in the sample 9 or the like. Accept. The operation input unit 62 may be configured by various switches, a touch panel, and the like.

<Refractive index acquisition processing>
FIG. 7 is a flowchart showing refractive index acquisition processing according to the first embodiment. When calculating the film thickness of the active material film formed on the current collector, the refractive index of the active material film is required, and thus a refractive index acquisition process is executed. When the refractive index of the active material film is known, this refractive index acquisition process can be omitted. Further, the configuration for acquiring the refractive index (the transmitted wave detection unit 30, the delay unit 40, etc.) may be omitted from the film thickness measurement device 1.

First, the peak time of the terahertz wave LT1 that has passed through a space where no sample 9 or sample stage 20 is arranged is measured (step S11). Specifically, THz-TDS for detecting the terahertz wave LT1 that has passed through the space is executed by the transmitted wave detection unit 30, and the time waveform is restored. Then, in the restored time waveform, the peak time T _R , that is, the time when the electric field strength is maximum (peak) is specified.

Subsequently, the peak time of the transmitted wave LT2 that has passed through only the transmissive substrate is measured (step S12). Specifically, a sample 9 composed of only a transmissive substrate is placed on the sample stage 20 and irradiated with the terahertz wave LT1. And THz-TDS which detects the transmitted wave LT2 which permeate | transmitted only the permeable base material is performed, and the time waveform is decompress | restored. Then, the restored time waveform, peak time T _B is identified.

Subsequently, the peak time of the transmitted wave LT2 that has passed through the transmission base material (transmission base material with an active material film) having an active material film formed on the surface is measured (step S13). Specifically, a sample 9 composed of a transmissive substrate with an active material film is fixed to the sample stage 20, and the sample 9 is irradiated with the terahertz wave LT1. Here, the transmissive substrate constituting the transmissive substrate with the active material film is the same as the transmissive substrate measured in step S12, or has the same material and thickness as the transmissive substrate. . And THz-TDS which detects the transmitted wave LT2 which permeate | transmitted the permeation | transmission base material with an active material film is performed, and the time waveform is decompress | 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 the transmitted wave that has passed through the transmissive substrate. The time waveform WSB is a time waveform of a transmitted wave that has passed through the transmissive substrate with an active material film.

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

First, let n _{S be} the refractive index of the active material film, c be the speed of light in vacuum, and v _S be the speed of light in the active material film. Then, the refractive index n _S is expressed by the following formula (1).

Then, from the peak time of the transmitted wave transmitted through only transparent substrate T _B, by subtracting the peak time T _R of the terahertz wave LT1 which has passed through the space, the peak time difference Delta] t _B corresponding to the transmission time of the transmission base Can be sought. Here, when the thickness L _{B of} the transmissive substrate and the velocity v _B of the terahertz wave in the transmissive substrate are set, this peak time difference Δt _B is expressed by the following equation (2).

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

Furthermore, based on the above (3), the refractive index n _B of the transmissive substrate is expressed by the following formula (4).

Then, from the time Delta] t _SB terahertz wave is transmitted through the active material layer with transparent substrates, by subtracting the time Delta] t _B to the terahertz wave transmitted through the transmission substrate, the peak time difference Delta] t corresponding to the transmission time of the active material layer _S can be acquired. This is expressed by the following equation (5).

The peak time difference Δt _S is also the difference between the time when the terahertz wave traveled at the speed v _S and the time traveled at the speed c in the air through the active material film having the film thickness L _S. That is, the peak time difference Δt _S is expressed by the following equation (6).

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

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

The time Delta] t _SB from peak time T _SB of terahertz waves transmitted through the film-transmissive substrate can be determined by subtracting the peak time T _R of the terahertz wave that has passed through the space. The time Delta] t _B is a transparent substrate from the peak time T _B of the terahertz waves transmitted through, can be determined by subtracting the peak time T _R of the terahertz wave which has passed through the space (formula (2) refer).

From Expression (8), the refractive index n _S of the active material film is expressed by the following Expression (9).

Here, the film thickness L _S of the active material film in the permeable substrate with the active material film 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 the equation (9), the refraction of the active material film The rate n _S can be obtained.

  The above is the description of the flow of the refractive index acquisition process. Next, the film thickness measurement will be described.

  FIG. 9 is a flowchart showing a film thickness measurement process according to the first embodiment.

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

  Subsequently, THz-TDS is performed in which the terahertz wave LT1 is irradiated toward the sample 9 and the reflected wave LT3 reflected by the sample 9 is detected. Then, the reflected wave intensity acquisition module 505A restores the time waveform of the reflected wave LT3 (step S22).

  Subsequently, based on the reflected wave LT3 restored in step S22, the film thickness calculation module 511 generates a terahertz wave reflected from the active material film surface and a terahertz wave reflected from the interface between the active material film and the current collector. A time difference Δt that reaches the photoconductive switch 34A that is a detector is specified (step S23). Based on this time difference Δt, the film thickness is calculated (step S24). Details of steps S23 and S24 will be described with reference to FIG.

  As shown in FIG. 4, the terahertz wave LT1 irradiated to the sample 9 is reflected by the sample 9, and the reflected wave LT3 reflected is a surface reflected wave LT31 reflected by the surface of the active material film 91 of the sample 9. And an interface reflected wave LT32 that further travels through the active material film 91 and is reflected at the interface between the active material film 91 and the current collector 93.

Since the interface reflected wave LT32 passes through the active material film 91, the time to reach the detector (photoconductive switch 34A) is delayed compared to the surface reflected wave LT31. Here, the delay time (time difference) is set to Δt. Then, the absolute refractive index in the air is 1, the speed of light is c, the speed of the terahertz wave traveling through the active material film 91 is v, the incident angle is θ ₀ , and the refractive angle is θ ₁ . Further, the refractive index of the active material film 91 acquired by the refractive index acquisition process shown in FIG. Then, the following equation (10) is established according to Snell's law.

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

Based on the above principle, the film thickness calculation module 511 calculates the film thickness d by substituting the time difference Δt, the refractive index n, and the incident angle θ ₀ of the terahertz wave LT1 into Expression (11).

  FIG. 10 is a diagram showing a time waveform W1 of a reflected wave LT3 measured using a positive electrode (film thickness: 88 μm) of a lithium ion battery as a sample. In FIG. 10, the horizontal axis represents the time axis, and the vertical axis represents the electric field strength. In this example, the photoconductive switch 14 that generates the terahertz wave LT1 is a bow-tie type, and the photoconductive switch 34A that detects the reflected wave LT3 is a dipole type.

  In the time waveform W1 shown in FIG. 10, the first peak point P1 appears at the peak time T1, and the next peak point P2 appears at the subsequent peak time T2. Among these, 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, it is understood that the arrival time difference between the surface reflected wave LT31 and the interface reflected wave LT32 to the photoconductive switch 34A is the time difference Δt (= T2−T1 = 1.5 ps) between the peak points P1 and P2. Moreover, the refractive index of the active material film obtained by the refractive index acquisition process was 2.5. When these values are applied to the formula (11), the film thickness d of the active material film becomes 89.75 μm, and therefore a value close to the actual film thickness (88 μm) is obtained by measuring the reflected wave LT3. Can do.

  FIG. 11 is a diagram showing a 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 waveform measured by each sample whose film thickness of an active material film | membrane is 48 micrometers, 49 micrometers, 53 micrometers, 56 micrometers, 63 micrometers, and 71 micrometers is shown.

  As shown in FIG. 11, when a negative electrode of a lithium ion battery is used as a sample, the first peak point corresponding to the peak of the surface reflected wave LT31 can be easily specified in each time waveform. However, although the next peak point corresponding to the peak of the interface reflected wave LT32 is considered to be in the vicinity indicated by the arrow, it is slightly buried in the upward convex waveform, making it difficult to specify accurately. ing. This is because the active material film formed on the current collector (negative electrode active material, for example, graphite) has low transmittance and high absorbance, so that the interface reflection is reflected at the interface between the active material film and the current collector. This is probably because the wave LT32 is buried in the surface reflected wave LT31 reflected on the active material film surface. Therefore, the component of the interface reflected wave LT32 is extracted by removing the component of the surface reflected wave LT31 from the time waveform of the reflected wave LT3.

  Specifically, first, a terahertz wave LT1 is irradiated to a sample (surface reflection sample) in 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 means the thickness of the active material film 91 to such an extent that the interface reflected wave LT32 reflected at the interface between the active material film 91 and the current collector 93 is almost completely absorbed. The reflected wave LT3 restored by the surface reflection sample is almost the surface reflection wave LT31 reflected by the surface of the active material film 91 of the surface reflection sample, and the interface reflected by the interface between the active material film 91 and the current collector 93. The reflected wave LT32 is hardly included. Hereinafter, the time waveform restored using the surface reflection sample is referred to as a “surface waveform of the surface reflection”.

  Subsequently, the time waveform of the surface reflection is subtracted from the time waveform of the film thickness measurement target. Thereby, a peak point corresponding to the peak of the interface reflected wave LT32 can be extracted from the time waveform of the film thickness measurement target. In addition, the time waveform W2 shown in FIG. 10 is a time waveform of surface reflection.

  Here, the height position of the surface of the active material film 91 in the film thickness measurement target and the height position of the active material film surface of the surface reflection sample are completely matched, and the reflected wave LT3 from each is measured. It is difficult. For this reason, the surface reflected wave LT31 to be measured for film thickness and the surface reflected wave LT31 from the surface reflected sample are likely to be shifted in time. Therefore, in order to remove the component of the surface reflected wave LT31 reflected from the active material film surface with high accuracy from the time waveform of the film thickness measurement target, the time (phase) between the time waveform of the film measurement target and the time waveform of the surface reflection. It is desirable to subtract after adjusting. Specifically, the position may be aligned so that the time of the first peak of the time waveform of the film thickness measurement target and the time of the first peak of the time waveform of surface reflection coincide. However, the time adjustment is not an essential process and can be omitted.

  When the support mode shown in FIG. 5 is adopted, the height position of the surface of the active material film 91 in the film thickness measurement target can be matched with the height position of the surface of the active material film of the surface reflection sample. For this reason, the time shift of the surface reflected wave LT31 reflected on the surfaces of both the active material films 91 hardly occurs. For this reason, the time adjustment can be omitted.

  FIG. 12 is a diagram illustrating a time waveform after the surface reflection time waveform is subtracted from the time waveform of the film thickness measurement target. The time waveform of each film thickness shown in FIG. 12 includes peaks in the vicinity indicated by the arrows, and these peaks correspond to the peak of the interface reflected wave LT32. Therefore, the peak time difference Δt between the time T1 at which the first peak specified in FIG. 11 appears and the peak time T2 specified in FIG. 12 can be obtained. The film thickness of each sample can be calculated by substituting this peak time difference Δt into the above equation (11).

  FIG. 13 is a diagram showing a calibration curve L1 between the actual film thickness and the peak time difference Δt. In FIG. 13, the horizontal axis indicates the film thickness, and the vertical axis indicates the peak time difference Δt. In this example, since the correlation coefficient is 0.73, it can be seen that the peak time difference Δt 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. Here, the threshold value of the low-pass filter is 1.0 THz or less. FIG. 15 is a diagram showing a calibration curve L2 between the actual film thickness and the time difference Δt when low-pass filter processing is performed. 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. That is, by specifying the time difference Δt between the surface reflected wave LT31 and the interface reflected wave LT32 based on the time waveform restored at a frequency of 1.0 THz or less, the film thickness can be calculated more accurately.

  The low-pass filter process may be realized by providing a low-pass filter on the optical path of the reflected wave LT3, or may be realized by an arithmetic process such as Fourier transform.

  Further, the terahertz wave LT1 irradiated on the sample 9 may be in a frequency band of 0.01 to 1 THz. For example, a low-pass filter may be disposed on the optical path of the terahertz wave LT1, or the terahertz wave LT1 generated by the terahertz wave irradiation unit 10 may be included in the frequency band.

  Returning to FIG. 9, when the film thickness calculation in step S <b> 24 is completed, the control unit 50 determines whether or not the measurement position needs to be changed. That is, if it is set in advance to perform film thickness measurement at a plurality of points, in step S24, it is determined whether or not there are other points at which measurement is performed. Note that if the film thickness is set to be measured only at one point, step S24 is omitted.

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

  If it is determined in step S24 that there is no point at which film thickness measurement is to be performed, the image generation module 513 generates an image indicating the film thickness distribution (film thickness distribution image) and displays it on the display unit 61 (step S27). ).

  FIG. 16 is a diagram illustrating an example of the film thickness distribution image I20 generated by the image generation module 513. A film thickness distribution image I20 shown in FIG. 16 is an image representing the film thickness distribution in a three-dimensional graph, and the X axis and the Y axis indicate two axial directions parallel to the surface of the sample 9, and the Z axis Indicates the film thickness. Thus, according to the film thickness distribution image I20, a change in film thickness between measurement points can be easily visually recognized.

  As described above, according to the film thickness measuring device 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 or deficiency in the amount of active material at an early stage and suppress an increase in economic loss.

  FIG. 17 is a diagram illustrating a frequency spectrum of a transmitted wave that has passed through a negative electrode active material (graphite) film 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. In the graph G1, the photoconductive switches 14 and 34 are both bow-tie type (b). In the graph G2, the photoconductive switch 14 is a bow tie type, and the photoconductive switch 34 is a dipole type. In the graph G3, the photoconductive hydrotreaters 14 and 34 are both dipole type. As is apparent from FIG. 17, the negative electrode active material of the lithium ion battery has high transmission intensity at 1 THz or less. For this reason, by setting the terahertz wave to be irradiated to 1 THz 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>
FIG. 18 is a schematic side view showing an active material film forming system 100 in which a film thickness measuring apparatus 1A according to the second embodiment is incorporated. The active material film forming system 100 is a system that forms an active material film 91 on one surface of a sheet-like current collector 93 that is conveyed by a roll-to-roll method. The active material film forming system 100 includes a film thickness measuring device 1 </ b> A that measures the film thickness of the active material film in the middle of the conveyance path of the current collector 93.

  In the active material film forming system 100, the current collector 93 unwound from the unwinding roller 701 is conveyed to the coating unit 71 via the conveying rollers 702 and 703.

  The coating unit 71 includes a slit die 711, a coating liquid supply unit 713, and a support roller 715. The slit die 711 includes a slit-like discharge port extending in the width direction of the current collector 93. The coating liquid supply unit 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 facing the discharge port of the slit die 711 and supports the back surface of the current collector 93.

  The current collector 93 to which the coating liquid is applied by the coating unit 71 is conveyed to the drying unit 72. The drying unit 72 performs a drying process on the coating film of the coating liquid formed on one surface of the current collector 93 by the slit die 711 of the coating unit 71. For example, the drying unit 72 heats the current collector 93 by supplying hot air toward the current collector 93 to evaporate the moisture or the solvent of the coating liquid.

  The current collector 93 dried by the drying unit 72 is taken up by the take-up roller 706 via the transport rollers 704 and 705.

  The film thickness measuring device 1A is disposed at a position between the transport rollers 704 and 705, and measures the film thickness of the active material film 91 formed on the current collector 93 (measurement object) in a dry state. It is configured. The arrangement position of the film thickness measuring device 1A is not limited to this. For example, it may be arranged at a position between the drying unit 72 and the conveyance roller 704 or at a position between the conveyance roller 705 and the take-up roller 706. The film thickness measuring apparatus 1A irradiates the active material film 91 formed on one side of the current collector 93 with the terahertz wave LT1 and detects the reflected wave LT3 reflected.

  The film thickness measuring apparatus 1 is a sheet member on which a sample as a measurement object is conveyed by a roll-to-roll, and is supported by conveying rollers 704 and 705, and is provided with a sample stage 20. 1 is different. About the other structure of the film thickness measuring apparatus 1A, it is comprised by the terahertz wave irradiation part 10, the reflected wave detection part 30A, the delay part 40A, and the control part 50 similarly to the film thickness measuring apparatus 1. FIG.

  The active material film forming system 100 may be modified so that the active material film 91 is formed on both surfaces of the current collector 93. In this case, the active material film forming system includes a film thickness measuring device 1A that measures the film thickness of the active material film 91 on one side and a film thickness measuring device 1A that measures the film thickness of the active material film 91 on the other side. It may be.

  According to the film thickness measuring apparatus 1A according to the present embodiment, the film 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. That is, when the active material film 91 is formed on the current collector 93, the film thickness can be monitored. For this reason, it becomes possible to discover defects, such as excess and deficiency of an active material material, at an early stage, and economic loss can be reduced.

  Further, according to the film thickness measuring apparatus 1A, the film thickness of the active material film can be inspected in a non-contact / non-destructive manner. For this reason, since the film thickness can be measured without destroying or damaging the sample, generation of waste due to sampling can be reduced.

  Although the present invention has been described in detail, the above description is illustrative in all aspects, and the present invention is not limited thereto. It is understood that countless variations that are not illustrated can be envisaged without departing from the scope of the present invention. Moreover, each structure demonstrated by said each embodiment and each modification can be suitably combined or abbreviate | omitted unless it mutually contradicts.

DESCRIPTION OF SYMBOLS 1,1A Film thickness measurement apparatus 10 Terahertz wave irradiation part 20 Sample stage 20A Support stand 30 Transmission wave detection part 30A Reflection wave detection part 34 Photoconductive switch (transmission wave detector)
34A photoconductive switch (reflected wave detector)
40, 40A Delay unit 50 Control unit 501 Sample stage control module 505 Transmitted wave intensity acquisition module 505A Reflected wave intensity acquisition module 507 Refractive index acquisition module 509 Time difference acquisition module 511 Film thickness calculation module 513 Image generation module 60 Storage unit 9 Sample 91 Activity Material film 93 Current collector 100 Active material film forming system C1 Refractive index information Im1 Film thickness distribution image LP1 Pump light LT1 Terahertz wave LT2 Transmitted wave LT3 Reflected wave LT31 Surface reflected wave LT32 Interface reflected wave T1, T2 Peak time Δt Peak time difference d Thickness n Refractive index of _S active material film

Claims (7)

A film thickness measuring device for measuring a film thickness of an active material film formed on a current collector,
A terahertz wave irradiation unit that irradiates the sample with terahertz waves in a frequency band included in 0.01 THz to 10 THz;
A reflected wave detector comprising a detector for detecting the reflected wave of the terahertz wave reflected by the sample;
Of the reflected waves detected by the reflected wave detection unit, the reflected surface wave reflected by the surface of the active material film in the sample and reflected by the interface between the active material film and the current collector in the sample A time difference acquisition unit for acquiring a time difference of reaching the detector with the interface reflected wave;
Based on the time difference and the refractive index of the active material film, a film thickness calculation unit that calculates the film thickness of the active material film,
Equipped with a,
The time difference acquisition unit acquires the time difference based on a peak time in the time waveform of the reflected wave,
The time difference acquisition unit identifies the peak time of the interface reflected 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,
The surface reflection sample is a film thickness measuring device in which the active material film having a thickness that completely absorbs the interface reflection wave when the terahertz wave is irradiated is formed on the surface of the current collector. The film thickness measuring device according to claim 1 ,
The time difference acquisition unit subtracts the time waveform of the reflected wave obtained from the sample and the time waveform of the reflected wave obtained from the surface reflection sample after matching the peak time of each reflected wave. Thickness measuring device. The film thickness measuring device according to claim 1 or 2 ,
In the sample, an irradiation position displacement unit that displaces the position irradiated with the terahertz wave in a biaxial direction parallel to the surface of the sample;
An image generation unit that generates a film thickness distribution image indicating a film thickness distribution at a plurality of points on the sample, calculated by the film thickness calculation unit;
A film thickness measuring device further comprising: The film thickness measuring apparatus according to any one of claims 1 to 3 ,
The terahertz wave irradiating unit irradiates the sample with a terahertz wave having a frequency band of 0.01 THz to 1 THz. The film thickness measuring device according to any one of claims 1 to 4 ,
A film thickness measuring apparatus, further comprising: a filter processing unit that performs low-pass filtering of the reflected wave. The film thickness measuring device according to claim 5 ,
A film thickness measuring apparatus, wherein the low-pass filter process is a process of transmitting a terahertz wave of 1 THz or less. A film thickness measuring method for measuring a film thickness of an active material film formed on a current collector,
(A) a detection step of irradiating a sample with a terahertz wave in a frequency band included between 0.01 THz and 10 THz and detecting the reflected wave of the terahertz wave reflected by the sample with a detector;
(B) Of the reflected waves detected by the detector, a surface reflected wave reflected by the surface of the active material film in the sample and a reflection at the interface between the active material film and the current collector in the sample A time difference acquisition step of acquiring a time difference to reach the detector with the interface reflected wave;
(C) a film thickness calculating step for calculating a film thickness of the active material film based on the time difference and the refractive index of the active material film;
Only including,
The step (b) acquires the time difference based on the peak time in the time waveform of the reflected 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, the peak time of the interface reflected wave is specified,
The surface reflection sample is a film thickness measurement method in which the active material film having a thickness that completely absorbs the interface reflected wave when the terahertz wave is irradiated is formed on the surface of the current collector .

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