JP2013061219A - Inspection method and inspection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique with which, when inspecting a photo device by irradiating the photo device with pulse light, a light intensity of the pulse light can be set appropriately.SOLUTION: An inspection method is provided for inspecting a photo device. The inspection method includes the steps of: (a) detecting an electric field strength of an electromagnetic wave generated from the photo device through a detector by irradiating a photo-detection plane of the photo device with pulse light emitted from a femto-second laser while changing a light intensity of the pulse light; (b) acquiring a maximum light intensity of the pulse light at the time when the electric field strength of the electromagnetic wave detected in the step (a) becomes maximum; and (c) detecting the electric field strength of the electromagnetic wave pulse generated in the photo device through the detector by irradiating the photo device with pulse light of which the light intensity is determined based on the maximum light intensity which has been acquired in the step (b).

Description

  The present invention relates to a technique for inspecting a photo device using pulsed light.

  In a manufacturing process of a solar cell which is one type of photo device, an inspection for measuring electric characteristics of the solar cell is performed using a so-called four-terminal measurement method (for example, Patent Document 1). Specifically, a current measuring probe pin and a voltage measuring probe pin are applied to the collecting electrodes provided on the light receiving surface and the back surface of the solar cell. In this state, the voltage applied to the solar cell is changed while the simulated sunlight is irradiated, and the relationship between the current and voltage is measured. Thereby, the IV characteristic of a solar cell is measured.

JP 2010-182969 A

  However, in the case of a conventional solar cell inspection device, it is necessary to bring a probe pin for current measurement or voltage measurement into contact with the current collecting electrode. For this reason, there is a problem that the probe pin is rubbed off due to peeling of the plating of the probe pin. Moreover, since the probe pin is brought into contact with the solar cell, the solar cell element may be damaged during the inspection.

  Therefore, the applicants have proposed an inspection apparatus for inspecting a photo device in a non-contact manner (Japanese Patent Application No. 2011-155665). This inspection apparatus utilizes the fact that an electromagnetic wave mainly in the terahertz region is generated when light of a specific wavelength is irradiated to a photo device. In this inspection apparatus, the performance of a photo device can be evaluated by detecting generated electromagnetic waves. According to this inspection apparatus, since the photo device can be inspected in a substantially non-contact state, it is possible to suppress destruction of the photo device.

  By the way, in the inspection apparatus, a laser apparatus (specifically, a femtosecond laser) that emits pulsed light is used. The light intensity of the pulsed light emitted from the laser device greatly affects the life of the laser device. Therefore, it is desirable that the light intensity be as weak as possible in order to extend the life (continuous operation time) of the laser device or reduce maintenance costs. However, in order to increase the intensity of the electromagnetic wave generated in the photo device, it is necessary to emit pulsed light having a required light intensity. Therefore, it is desired to optimize the light intensity of the pulsed light in order to appropriately inspect the photo device while suppressing the cost of the laser apparatus. However, few techniques for optimizing light intensity are known.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a technique for appropriately setting the light intensity of pulsed light when the photo device is irradiated with pulsed light for inspection.

  In order to solve the above-mentioned problem, a first aspect is an inspection method for inspecting a photo device, wherein (a) the light intensity of pulsed light emitted from a femtosecond laser is changed and the light receiving surface of the photo device is The step of detecting the electric field strength of the electromagnetic wave generated from the photo device by irradiating the pulsed light with a detector, and (b) when the electric field strength of the electromagnetic wave detected in the step (a) is maximized. Detecting the maximum light intensity of the pulsed light; and (c) irradiating the photo device with pulsed light having a light intensity determined based on the maximum light intensity detected in the step (b). And detecting the electric field intensity of the electromagnetic wave pulse generated by the photo device with the detector.

  The second aspect is the inspection method according to the first aspect, wherein the step (c) is a step of irradiating the photo device with pulsed light having a light intensity not exceeding the maximum light intensity.

  Further, the third aspect is the inspection method according to the first or second aspect, further comprising: (e) applying a reverse bias voltage to the photo device when performing the step (a). Including.

  The fourth aspect is an inspection method according to any one of the first to third aspects, wherein the step (a) includes (a-1) pulsed light from the femtosecond laser, Branching into pump light directed to the photo device and probe light directed to the detector; (a-2) an optical path length of either the first optical path of the pump light or the second optical path of the probe light; Changing the process.

  According to a fifth aspect, in the inspection method according to the fourth aspect, in the step (a), the optical path length of the first optical path or the second optical path in the step (a-3) (a-2) A step of obtaining a maximum optical path length when the electric field intensity detected by the detector is substantially maximum when the optical path length of the first optical path or the second optical path is the maximum. The light intensity of the pulsed light is changed while being fixed at the hour optical path length.

  A sixth aspect is an inspection method according to the first or second aspect, wherein, in the step (a), the detector is composed of a Schottky barrier diode.

  According to a seventh aspect, in an inspection apparatus for inspecting a photo device, an irradiation unit that irradiates a light receiving surface of a photo device with pulsed light emitted from a femtosecond laser; and A detection unit for detecting an electric field intensity of an electromagnetic wave generated from the device, a control unit for controlling the irradiation unit so that the light intensity of the pulsed light is changed, and the electromagnetic wave when the light intensity is changed by the control unit. A light intensity setting unit that sets a non-light intensity of the pulsed light emitted from the femtosecond laser based on the maximum light intensity of the pulsed light when the electric field intensity of the pulsed light becomes maximum.

  According to the inspection method according to the first aspect, it is possible to appropriately set the light intensity of the pulsed light for inspection irradiated to the photo device.

  Further, according to the inspection method according to the second aspect, it is possible to extend the life of the femtosecond laser and reduce the maintenance cost while increasing the electric field intensity of the detected electromagnetic wave pulse as much as possible.

  Further, according to the inspection method according to the third aspect, the electric field strength of the terahertz wave can be amplified by applying a reverse bias voltage.

  Moreover, according to the inspection method according to the fourth aspect, the time waveform of the electromagnetic wave pulse can be restored, and therefore the timing for measuring the electric field strength of the electromagnetic wave pulse can be determined satisfactorily.

  According to the inspection method according to the fifth aspect, the signal-to-noise ratio can be improved because the electric field intensity of the electromagnetic wave pulse detected by the detector is substantially maximized. Therefore, since the electric field strength can be detected satisfactorily, the light intensity can be set appropriately.

  According to the inspection method according to the sixth aspect, by using the Schottky barrier diode as a detector, it is possible to detect the magnitude of the averaged electric field intensity of the electromagnetic wave pulse generated in the photo device. Therefore, since the electric field intensity is acquired without restoring the time waveform, the light intensity can be set quickly.

  According to the inspection apparatus according to the seventh aspect, it is possible to appropriately set the light intensity of the pulse light for inspection irradiated to the photo device.

1 is a schematic configuration diagram of an inspection apparatus according to a first embodiment. It is a schematic block diagram of the irradiation part and detection part which were shown in FIG. It is a schematic sectional drawing of a solar cell panel. It is the top view which looked at the solar cell panel from the light-receiving surface side. It is the top view which looked at the solar cell panel from the back side. It is a flowchart when test | inspecting the solar cell panel which is a photo device. It is a figure which shows the time waveform of the terahertz wave pulse decompress | restored by the time waveform structure part. FIG. 4 is a diagram showing correlation data CD1 and a graph of the correlation data CD1. FIG. 4 is a diagram showing correlation data CD2 and a graph of the correlation data CD2. FIG. 4 is a diagram showing correlation data CD3 and a graph of the correlation data CD3. It is a detailed flowchart of a test | inspection (1). It is a figure which shows the spectrum distribution of a terahertz wave pulse. It is a detailed flowchart of a test | inspection (2). It is an example of the electric field strength distribution image displayed on a monitor. It is a schematic block diagram of the irradiation part and detection part of the inspection apparatus which concern on 2nd Embodiment. It is a schematic block diagram of the irradiation part and detection part of the inspection apparatus which concern on 3rd Embodiment.

  Hereinafter, embodiments will be described in detail with reference to the drawings. However, the constituent elements described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

<1. First Embodiment>
FIG. 1 is a schematic configuration diagram of an inspection apparatus 100 according to the first embodiment. 2 is a schematic configuration diagram of the irradiation unit 12 and the detection unit 13 shown in FIG. The inspection apparatus 100 has a configuration suitable for inspecting the characteristics of a depletion layer of a solar cell panel 90 that is a kind of substrate on which a photo device is formed.

  In the inspection apparatus 100, the substrate to be inspected is not limited to the solar cell panel 90. Any substrate including a photo device that converts light including visible light into current can be an inspection object of the inspection apparatus 100. Specifically, an image sensor such as a CMOS sensor or a CCD sensor is assumed as a photo device other than the solar battery panel. Some image sensors are known in which a light receiving element is formed on the back side of a substrate on which a photo device is formed in use. Even with such a substrate, the terahertz wave pulse LT1 can be detected satisfactorily if it is installed in the inspection apparatus 100 with the main surface on the light receiving side in use as the light receiving surface.

  Photo devices such as solar cells have a pn junction part in which p-type and n-type semiconductors are joined. In the vicinity of the pn junction, a depletion layer with few electrons and holes is formed in the vicinity of the pn junction by generating a diffusion current in which electrons and holes are diffused and combined with each other. In this region, a force is generated to pull electrons and holes back to the n-type and p-type regions, respectively, so that an electric field is generated inside the photo device. When light having a certain amount of energy (energy exceeding the forbidden band width) is irradiated to the pn junction, the photoelectrons move to the n-type semiconductor side by the internal electric field at the pn junction, and the remaining holes are p-type Move to semiconductor. In the photo device, this current is extracted to the outside through electrodes attached to the n-type semiconductor and the p-type semiconductor, respectively. As described above, in the photo device, the movement of free electrons and free holes generated when the depletion layer of the pn junction is irradiated with light is used as DC power.

  The inventors have found that when a photo device is irradiated with pulsed light having a predetermined wavelength, an electromagnetic wave pulse having a specific wavelength is generated. This is considered that electromagnetic waves are generated when photoexcited carriers move by irradiating light to a photoexcited carrier generation region such as a depletion layer. That is, the generated electromagnetic wave pulse reflects the characteristics of the photoexcited carrier generation region such as a depletion layer. Therefore, the characteristics of the depletion layer of the pn junction can be inspected by analyzing the detected electromagnetic wave pulse. Based on this principle, the inspection apparatus 100 is configured to detect an electromagnetic wave pulse generated when pulsed light having a predetermined wavelength is irradiated toward the solar cell panel 90.

  As shown in FIG. 1, the inspection apparatus 100 includes a stage 11, an irradiation unit 12, a detection unit 13, a visible camera 14, a motor 15, a control unit 16, a monitor 17, and an operation input unit 18.

  The stage 11 fixes the solar cell panel 90 on the stage 11 by fixing means (not shown). As the fixing means, one using a holding tool for holding the substrate, an adhesive sheet, or an adsorption hole formed on the surface of the stage 11 is assumed. However, any fixing means may be applied as long as the solar cell panel 90 can be fixed. In the present embodiment, the stage 11 holds the solar cell panel 90 such that the irradiation unit 12 and the detection unit 13 are disposed on the light receiving surface 91 </ b> S side of the solar cell panel 90.

  As shown in FIG. 2, the irradiation unit 12 includes a femtosecond laser 121. The femtosecond laser 121 emits pulsed light (pulsed light LP1) having a wavelength including a visible light region of, for example, 360 nm (nanometer) or more and 1 μm (micrometer) or less. In the present embodiment, linearly polarized pulsed light 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 is emitted. Note that pulse light in other wavelength regions (for example, visible light wavelengths such as blue wavelength (450 to 495 nm) and green wavelength (495 to 570 nm)) may be emitted.

  The pulsed light LP1 emitted from the femtosecond laser 121 is divided into two by the beam splitter B1. One of the divided pulse lights (pump light LP11) is applied to the solar cell panel 90. At this time, the irradiation unit 12 performs irradiation of the pump light LP11 from the light receiving surface 91S side. In addition, the pump light LP11 is applied to the solar cell panel 90 so that the optical axis of the pump light LP11 is obliquely incident on the light receiving surface 91S of the solar cell panel 90. In the present embodiment, the irradiation angle is set so that the incident angle is 45 degrees. However, the incident angle is not limited to such an angle, and can be appropriately changed within a range of 0 to 90 degrees.

  FIG. 3 is a schematic cross-sectional view of the solar cell panel 90. FIG. 4 is a plan view of the solar cell panel 90 as viewed from the light receiving surface 91S side. FIG. 5 is a plan view of the solar cell panel 90 viewed from the back side. The solar cell panel 90 is configured as a solar cell panel that is a thin film crystalline silicon system. The solar cell panel 90 includes a flat plate-like back electrode 92 formed of aluminum or the like in order from the bottom, a p-type silicon layer 93, an n-type silicon layer 94, an antireflection film 95, and a lattice-shaped light receiving surface electrode 96. It is comprised as a crystalline silicon type solar cell which has the laminated structure comprised by these. The antireflection film 95 is made of silicon oxide, silicon nitride, titanium oxide, or the like. Of the main surfaces of the solar cell panel 90, the main surface on the side where the light-receiving surface electrode 96 is provided is a light-receiving surface 91S. That is, the solar cell panel 90 is designed to generate electricity by receiving light from the light receiving surface 91S side. A transparent electrode may be used for the light receiving surface electrode 96. The inspection apparatus 100 may be applied to inspection of solar cells other than crystalline silicon (such as amorphous silicon). In the case of an amorphous silicon solar cell, the energy gap is generally larger than the energy gap of 1.2 eV of a crystalline silicon solar cell, such as 1.75 eV to 1.8 eV. In such a case, by setting the wavelength of the femtosecond laser 121 to, for example, 700 μm or less, terahertz waves can be favorably generated in the amorphous silicon solar cell.

  The light receiving surface 91S of the solar cell panel 90 has a required texture structure in order to suppress light reflection loss. Specifically, unevenness of several μm to several tens of μm formed by anisotropic etching or the like, or a V-shaped groove by a mechanical method is formed. As described above, the light receiving surface 91S of the solar cell panel 90 is generally formed so that the light can be collected as efficiently as possible. Therefore, when pulsed light with a predetermined wavelength is irradiated, the pulsed light easily reaches the pn junction 97. For example, in the case of a solar cell panel, light having a wavelength of 1 μm or less mainly having a visible light wavelength region can easily reach the pn junction 97.

  The junction between the p-type silicon layer 93 and the n-type silicon layer 94 is a pn junction 97 where a depletion layer is formed. When this portion is irradiated with the pump light LP11, an electromagnetic wave pulse is generated and emitted to the outside. In the present embodiment, the electromagnetic wave pulse detected by the detection unit 13 is an electromagnetic wave pulse having a frequency of 0.01 THz to 10 THz (hereinafter referred to as a terahertz wave pulse LT1).

  Returning to FIG. 2, the other pulse light split by the beam splitter B1 enters the detector 132 as the probe light LP12 via the delay unit 131 and the mirror. Further, the terahertz wave pulse LT1 generated in response to the irradiation of the pump light LP11 is collected by the parabolic mirrors M1 and M2 and enters the detector 132.

  The detector 132 is composed of a photoconductive switch. When the probe light LP12 is irradiated to the detector 132 in a state where the terahertz wave is incident on the detector 132, a current corresponding to the electric field strength of the terahertz wave pulse LT1 is instantaneously generated in the detector 132. The current corresponding to the electric field strength is converted into a digital quantity via an I / V conversion circuit, an A / D conversion circuit, or the like. In this way, the detection unit 13 detects the electric field intensity of the terahertz wave that has passed through the solar cell panel 90 in response to the irradiation with the probe light. Although a photoconductive switch is used as the detector 132, other elements such as a nonlinear optical crystal may be used. Further, the electric field strength of the terahertz wave pulse LT1 may be detected using a Schottky barrier diode.

  The delay unit 131 is an optical element for continuously changing the arrival time of the probe light LP12 from the beam splitter B1 to the detector 132. The delay unit 131 is fixed to a moving stage (not shown) that moves in the incident direction of the probe light LP12. The delay unit 131 includes a folding mirror 10M that folds the probe light LP12 in the incident direction. The delay unit 131 precisely changes the optical path length of the probe light LP12 by driving the moving stage and moving the folding mirror 10M based on the control of the control unit 16. Thereby, the delay unit 131 changes the time difference between the time when the terahertz wave pulse LT1 reaches the detection unit 13 and the time when the probe light LP12 reaches the detection unit 13. Therefore, the delay unit 131 detects the electric field strength of the terahertz wave pulse LT1 in the detection unit 13 (detector 132) by changing the optical distance (optical path length) of the optical path (second optical path) of the probe light LP12. Timing (detection timing or sampling timing) can be delayed.

  Note that the delay unit 131 may change the arrival time of the terahertz wave pulse LT1 and the probe light to the detection unit 13 in other manners. For example, the electro-optic effect may be used. That is, an electro-optic element whose refractive index changes by changing the applied voltage may be used as the delay element. Specifically, an electro-optic element disclosed in Japanese Patent Application Laid-Open No. 2009-175127 can be used. Further, the optical path length of the optical path (first optical path) of the pump light LP11 may be changed. Also in this case, the time for the terahertz wave pulse LT1 to reach the detector 132 and the time for the probe light LP12 to reach the detector 132 can be relatively shifted. Therefore, the detection timing of the electric field strength of the terahertz wave pulse LT1 in the detector 132 can be delayed.

  In addition, a reverse bias voltage application circuit 99 that applies a reverse bias voltage between the back electrode 92 and the light receiving surface electrode 96 at the time of inspection is connected to the solar cell panel 90. By applying a reverse bias voltage between the voltages, the depletion layer of the pn junction 97 can be enlarged. Thereby, since the electric field strength of the terahertz wave pulse LT1 detected by the detector 132 can be increased, the detection sensitivity of the terahertz wave pulse LT1 in the detection unit 13 can be improved. However, the reverse bias voltage application circuit 99 can be omitted.

  Returning to FIG. 1, the visible camera 14 is composed of a CCD camera, and includes an LED and a laser as a light source. The visible camera 14 is used for photographing the entire solar cell panel 90 or photographing a position where the pump light LP11 is irradiated. The image data acquired by the visible camera 14 is transmitted to the control unit 16.

  The motor 15 drives an XY table (not shown) that moves the stage in a two-dimensional plane. The motor 15 drives the XY table to move the solar cell panel 90 held on the stage 11 relative to the irradiation unit 12. The inspection apparatus 100 can move the solar cell panel 90 to an arbitrary position within the two-dimensional plane by the motor 15. The inspection device 100 can inspect the wide range (inspection target region) of the solar cell panel 90 by irradiating the pump light LP11 with the motor 15. Instead of moving the solar cell panel 90, or while moving the solar cell panel 90, a moving means for moving the irradiation unit 12 and the detection unit 13 in a two-dimensional plane may be provided. Also in these cases, the terahertz wave pulse LT1 can be detected for each region of the solar cell panel 90. Note that the motor 15 may be omitted, and the stage 11 may be manually moved by an operator.

  The control unit 16 has a general computer configuration including a CPU, a RAM, an auxiliary storage unit (hard disk), etc. (not shown). The control unit 16 is connected to the femtosecond laser 121 of the irradiation unit 12, the delay unit 131 and the detector of the detection unit 13, and the motor 15, and controls these operations and receives data from them. Specifically, the control unit 16 receives data related to the electric field strength of the terahertz wave pulse LT1 from the detector 132. Further, the control unit 16 controls the movement of a moving stage (not shown) that moves the delay unit 131, or the delay unit 131 such as the moving distance of the folding mirror 10M from a linear scale or the like provided on the moving stage. Or receive data related to the location.

  The control unit 16 is connected to a time waveform constructing unit 21, a spectrum analyzing unit 23, an image generating unit 25, and a light intensity setting unit 27 configured by a dedicated arithmetic circuit. These units are realized by the CPU operating according to the program. Note that some or all of these functions may be realized in software by the CPU included in the control unit 16 operating according to a predetermined program.

  The time waveform constructing unit 21 constructs a terahertz wave time waveform for the terahertz wave pulse LT1 generated in the solar cell panel 90 based on the electric field strength detected by the detector 13 (detector 132). Specifically, the time for the probe light to reach the detector 132 is changed by changing the optical path length of the probe light (the optical path length of the first optical path) by moving the folding mirror 10M of the delay unit 131. . As a result, the timing at which the detector 132 detects the electric field strength of the terahertz wave pulse LT1 is changed. Thus, the time waveform of the terahertz wave pulse LT1 is constructed by detecting the electric field strength of the terahertz wave pulse LT1 at a plurality of mutually different detection timings.

  The spectrum analysis unit 23 performs spectrum analysis on the solar cell panel 90 that is the inspection target, based on the time waveform of the terahertz wave pulse LT1. Specifically, the spectrum analysis unit 23 acquires an amplitude intensity spectrum related to the frequency by performing Fourier transform on the time waveform of the terahertz wave pulse LT1 generated in response to the irradiation of the pump light LP11.

  The image generation unit 25 visualizes the electric field intensity distribution of the terahertz wave pulse LT1 generated when the pulsed light LP1 is irradiated with respect to the inspection target region (a part or the whole of the solar cell panel 90) of the solar cell panel 90. Generate an image. Specifically, the electric field intensity distribution image is obtained by superimposing a color or a pattern according to the electric field intensity at each measurement position on the visible light image of the light receiving surface 91S of the solar battery panel 90 acquired through the visible camera 14. Is generated.

  The light intensity setting unit 27 is a setting unit that sets the light intensity emitted from the laser light source. The control unit 16 causes the femtosecond laser 121 (laser device) to emit laser light (pulse light) having the light intensity set by the light intensity setting unit 27.

  A monitor 17 and an operation input unit 18 are connected to the control unit 16. The monitor 17 is a display device such as a liquid crystal display, and displays various image information to the operator. On the monitor 17, an image of the light receiving surface 91 </ b> S of the solar battery panel 90 photographed by the visible camera 14, a time waveform of the terahertz wave pulse LT <b> 1 constructed by the time waveform construction unit 21, an analysis result by the spectrum analysis unit 23, or an image An electric field intensity distribution image generated by the generation unit 25 is displayed. Further, the monitor 17 displays a GUI (Graphical User Interface) screen necessary for setting inspection conditions.

  The operation input unit 18 includes various input devices such as a mouse and a keyboard. The operator can perform a predetermined operation input via the operation input unit 18. Note that the monitor 17 may function as the operation input unit 18 by configuring the monitor 17 as a touch panel.

  The above is the description of the configuration of the inspection apparatus 100. Next, a photo device inspection method using the inspection apparatus 100 will be described in detail.

<1.2. Photo device inspection>
FIG. 6 is a flowchart when inspecting the solar cell panel 90 which is a photo device. Note that the operation of the inspection apparatus 100 described below is controlled by the control unit 16 unless otherwise specified. Moreover, the flowchart shown in FIG. 6 is an example. Therefore, depending on the process contents, a plurality of processes may be executed in parallel, or the execution order of each process may be changed as appropriate. In the inspection apparatus 100, when inspecting the solar cell panel 90 that is a photo device, first, the light intensity of the pulsed light emitted from the femtosecond laser 121 is optimized (steps S11 to S19). After that, the solar cell panel 90 is inspected by irradiating the solar cell panel 90 with pulsed light having an optimal light intensity (step S20).

  First, a photo device (solar cell panel 90) to be inspected is installed on the stage 11 (step S11). In this step S11, the operator may install the solar cell panel 90 on the stage 11, or the solar cell panel 90 may be installed on the stage 11 using a transport device (not shown). At this time, as described above, the solar cell panel 90 is installed on the stage 11 so that the pulsed light (pump light LP11) is irradiated toward the light receiving surface 91S of the solar cell panel 90.

  When the solar cell panel 90 is fixed to the stage 11, the inspection apparatus 100 moves the solar cell panel 90 by driving the motor 15 so that pulse light is irradiated to an arbitrary position of the solar cell panel 90. . The position to be irradiated with the pulsed light may be defined in preset coordinate data, or may be designated as appropriate by an operator input via the operation input unit 18. Further, the operator may move the stage 11 manually so that the predetermined position of the solar cell panel 90 is irradiated with the pulsed light.

  Next, the inspection apparatus 100 performs terahertz time domain spectroscopy (THz-TDS), thereby generating a time waveform of the terahertz wave generated when the predetermined position of the solar cell panel 90 is irradiated with pulsed light (pump light LP11). Is restored (step S12). More specifically, the inspection apparatus 100 controls the delay unit 131 while irradiating the solar cell panel 90 with pulsed light, thereby changing the detection timing of the electric field strength in the detector 132 and changing the electric field of the terahertz wave pulse. Intensity is detected. At this time, a reverse bias voltage may be applied to the solar cell panel 90 by driving the reverse bias voltage application circuit 99.

  FIG. 7 is a diagram illustrating a time waveform of the terahertz wave pulse restored by the time waveform constructing unit 21. In FIG. 7, the horizontal axis indicates time, and the vertical axis indicates electric field strength. In the lower stage, a plurality of probe lights LP12 having different timings (detection timings t1 to t8) reaching the detector 132 by the delay unit 131 are conceptually shown. In FIG. 7, a time waveform 41 indicated by a solid line is a time waveform of the terahertz wave pulse restored in step S12 shown in FIG.

  The terahertz wave pulse having the time waveform 41 shown in FIG. 7 repeatedly arrives at the detector 132 at a predetermined cycle. Here, when the delay unit 131 is adjusted so that the probe light reaches the detector 132 at the detection timing t1, the electric field strength of the value E1 is detected by the detector. When the detection timing is delayed by t2 to t8 by adjusting the delay unit 131, the electric field strengths of values E2 to E8 are detected by the detection unit 13, respectively. In this way, by measuring the electric field strength of the terahertz wave pulse terahertz wave pulse while finely changing the detection timing, and plotting the obtained electric field strength value on a two-dimensional graph along the time axis, The time waveform 41 of the pulse can be restored.

  Returning to FIG. 6, the inspection apparatus 100 specifies the position of the folding mirror 10 </ b> M corresponding to the detection timing at which the electric field strength of the terahertz wave pulse is substantially maximum based on the time waveform 41 illustrated in FIG. 7. Then, the folding mirror 10M is moved and fixed to the specified position (step S13). In the time waveform 41, the electric field intensity is maximum (E3) at the detection timing t3. Accordingly, the position of the folding mirror 10M is set at a position corresponding to the detection timing t3. As a result, the optical path length of the probe light LP12 is set to the optical path length when it becomes the substantially maximum value of the terahertz wave pulse.

By setting the position of the folding mirror 10M in this way, the electric field strength can be detected at the timing when the electric field strength of the terahertz wave pulse becomes maximum. Therefore, the signal-to-noise ratio can be increased when acquiring correlation data indicating the correlation between the light intensity of pulsed light and the electric field intensity of the terahertz wave pulse, which will be described later.

  When a Schottky barrier diode is employed as the detector 132, the detector 132 detects the magnitude of the electric field intensity of the time-averaged terahertz wave pulse. In this case, the reconstruction of the terahertz wave pulse (step S12) and the acquisition of the maximum value (step S13) can be skipped, so that the light intensity can be set quickly.

  Next, the inspection apparatus 100 determines whether to apply a reverse bias voltage (step S14). Whether to apply the reverse bias voltage may be determined in advance, or a screen for confirming whether the reverse bias voltage needs to be applied is displayed on the monitor 17 or the like so that the operator can appropriately input the setting. May be.

  When applying the reverse bias voltage (YES in step S14), the inspection apparatus 100 drives the reverse bias voltage application circuit 99 to apply a voltage having a predetermined magnitude to the solar cell panel 90 (step S15). Then, the inspection apparatus 100 proceeds to the next step S16. If no reverse bias voltage application is required (NO in step S14), inspection apparatus 100 skips step S15 and proceeds to step S16.

  In step S16, the inspection apparatus 100 acquires correlation data indicating the correlation between the light intensity of the pulsed light and the electric field intensity of the terahertz wave pulse. In this step, specifically, the light intensity of the pulsed light LP1 emitted from the femtosecond laser 121 is gradually increased from zero to a required intensity, and the electric field intensity detected at that time by the detector 132 is sequentially recorded. A specific example of the correlation data will be described later. When the correlation data is acquired, the inspection apparatus 100 detects the light intensity when the electric field intensity reaches the maximum value based on the correlation data (step S17).

  Further, the inspection apparatus 100 determines whether to increase the reverse bias voltage applied to the solar cell panel 90 (step S18). This determination is performed based on, for example, whether or not the reverse bias voltage exceeds a predetermined voltage. If the applied reverse bias voltage does not exceed the specified voltage amount (YES in step S18), inspection apparatus 100 returns to step S15 and applies a voltage obtained by adding the required amount of voltage to solar cell panel 90. To do. Then, subsequent steps S16 and S17 are executed again. When the reverse bias voltage applied in step S18 exceeds the specified voltage (NO in step S18), the inspection apparatus 100 proceeds to the next step S19. Note that step S14 and step S18 may be omitted. In this case, the reverse bias voltage applied between the electrodes may be a fixed value (including the case where no reverse bias voltage is applied).

  8 to 10 are diagrams showing correlation data CD1 to CD3 and graphs of the correlation data CD1 to CD3. The correlation data CD1 to CD3 are acquired by repeatedly performing Steps S14 to S18 with respect to mutually different positions of the solar cell panel 90 (specifically, positions P1 to P3 shown in FIG. 4). It is data.

  Referring to the correlation data CD1, when the reverse bias voltage is zero, even if the light intensity is increased from zero to 70 mW, the detected electric field intensity is always a noise (background) level electric field intensity (= 0.5). There is no increase or decrease. However, when the reverse bias voltage is increased from 0V to 10V, the magnitude of the detected electric field intensity gradually increases. This is because the electric field strength of the terahertz wave pulse generated by the reverse bias voltage is amplified.

  Here, when the light intensity of the pulsed light applied to the solar cell panel 90 is increased, the generation amount of the terahertz wave pulse is also increased, so that the electric field intensity detected by the detector is also increased. However, as shown in the correlation data CD1, the electric field intensity of the terahertz wave pulse is saturated at a certain level of light intensity, and the electric field intensity starts to decrease even if it is further increased. For example, when the reverse bias voltage is 1 V, the electric field strength gradually increases when the light intensity is increased from 0 mW to 15 mW or 20 mW, and the electric field intensity is maximum when the light intensity is 15 mW or 20 mW. That is, the maximum light intensity is 15 mW or 20 mW. However, when the light intensity is increased from 20 mW to 30 mW, the electric field intensity starts to decrease. Similarly, when the reverse vise voltage is 2 V or 4 V, the electric field strength becomes maximum when it is 20 mW or 40 mW, and thereafter, the electric field intensity starts to decrease.

  Such a phenomenon that the electric field intensity is saturated without being proportional to the magnitude of the light intensity is considered to be due to the following reason. That is, when a photo device such as the solar cell panel 90 is irradiated with pulsed light from the femtosecond laser 121, photoexcited carriers are generated. The generated photoexcited carriers are attracted to the current collecting electrode (light receiving surface electrode 96, etc.) under the influence of reverse bias voltage, internal electric field, or diffusion. When the light intensity of the pulsed light is relatively low, the photoexcited carriers are sufficiently attracted to the electrode. However, when the light intensity is increased, the photoexcited carriers are not sufficiently attracted. As a result, the photoexcited carriers are filled in the irradiated portion of the pulsed light. Then, since the amount of photoexcited carriers generated by pulsed light irradiation decreases, it is considered that the electric field strength of the terahertz wave pulse also decreases. Therefore, it is considered that the following equation (1) is established when the electric field strength becomes maximum.

(Amount of photo-excited carriers) = (Amount of photo-excited carriers absorbed by reverse bias, internal electric field or diffusion) (1)

  In the correlation data CD1 to CD3 shown in FIGS. 8 to 10, the light intensity is changed and the bias voltage is applied under substantially the same conditions. However, the detected electric field strengths are different from each other. ing. Specifically, the electric field strength is highest overall in the correlation data CD2, and then the electric field strength decreases in the order of the correlation data CD2 and the correlation data CD1. Here, the closer to the light receiving surface electrode 96, the more easily the photoexcited carriers are absorbed when the pulsed light is irradiated. For this reason, it is considered that the electric field intensity of the generated terahertz wave pulse also increases. Therefore, as shown in FIG. 4, since the distance from the light receiving surface electrode 96 is increased in the order of the positions P2, P3, and P1, the magnitude of the detected electric field intensity is considered to decrease in this order. Further, in the correlation data CD2 and CD3, a terahertz wave pulse having a certain level of intensity can be detected at a light intensity of about 5 to 10 mW even when no reverse bias voltage is applied (0 V). In other words, the present invention can be applied in principle to inspection of a photo device that does not have an electrode for applying a reverse bias voltage.

  Returning to FIG. 6, when the correlation data is acquired, the inspection apparatus 100 sets the light intensity for inspection based on the correlation data (step S <b> 19). Specifically, the light intensity setting unit 27 sets the light intensity (maximum light intensity) when the electric field intensity is maximum to the light intensity for inspection. As is clear from the correlation data CD1 to CD3, when the intensity of the irradiated pulsed light is too strong, the electric field intensity of the terahertz wave pulse generated from the photo device is decreased. Therefore, by specifying the boundary where the electric field strength starts to decrease from the correlation data, the electric field strength of the terahertz wave pulse detected by the detector 132 can be maximized without unnecessarily increasing the light intensity. it can. Therefore, it is possible to improve the signal nozzle ratio, extend the life of the lamp of the femtosecond laser 121, and reduce the maintenance cost.

  Note that, as indicated by the correlation data CD <b> 1 to CD <b> 3 in FIGS. 8 to 10, the maximum light intensity may vary depending on the magnitude of the reverse bias voltage applied to the solar cell panel 90. In step S19, a specific reverse bias voltage is appropriately selected from several reverse bias voltages, and the maximum light intensity determined under the reverse bias voltage is used for inspection. Is set to the light intensity. The selection of the reverse bias voltage can be performed based on an arbitrary criterion. For example, the reverse bias voltage may be selected based on whether or not the magnitude of the electric field intensity recorded in the correlation data exceeds a threshold value.

  In step S19, the measurement light intensity is set in accordance with the maximum light intensity, but may be set to a light intensity of a size other than this. The light intensity for measurement is preferably set to a light intensity that does not exceed the maximum light intensity in consideration of extending the life of the femtosecond laser 121 and the like. However, a size slightly exceeding the maximum light intensity is sufficiently acceptable.

  Next, the inspection apparatus 100 inspects the solar cell panel 90 by emitting the pulse light having the light intensity set in step S19 from the femtosecond laser 121 (step S20). In step S20, various portions of the solar cell panel 90 are irradiated with pulsed light (pump light LP11), and the electric field strength of the generated terahertz wave pulse is detected by the detector 132.

  The inspection apparatus 100 according to the present embodiment is configured to be able to perform two types of inspections roughly. First, the first inspection is (1) an inspection based on a time waveform of a terahertz wave pulse (hereinafter referred to as inspection (1)). In this inspection (1), a time waveform of a terahertz wave pulse generated when the pump light LP11 is irradiated to a specific region (inspection position) is constructed. Further, spectrum analysis based on the constructed time waveform is performed. By these analyses, it is possible to perform an inspection relating to depletion layer formation in a specific region of the solar cell panel 90 and an inspection relating to impurities.

  The second inspection is (2) inspection based on the electric field intensity distribution of the terahertz wave pulse for the entire solar cell panel 90 (hereinafter referred to as inspection (2)). In this inspection (2), the electric field intensity of the terahertz wave pulse generated when the pump light LP11 is irradiated is measured for each region on the solar cell panel 90. Thereby, the formation defect part of a depletion layer in the inspection object area | region of the solar cell panel 90, or the lattice defect of a polycrystalline silicon can be specified. In the following, the inspection (1) will be described first, and then the inspection (2) will be described.

  FIG. 11 is a detailed flowchart of the inspection (1). When the inspection (1) is started, the inspection apparatus 100 determines whether to apply a reverse bias voltage (step S21). When a reverse bias voltage is applied (YES in step S21), a voltage having the same magnitude as the reverse bias voltage when the light intensity set in step S19 is determined is applied between the electrodes of the solar cell panel 90. (Step S22). For example, in the correlation data CD1, when the reverse bias voltage is 2 V, the maximum light intensity is 20 mW. Based on this correlation data, when the light intensity is set to 20 mW in step S19, a reverse bias voltage of 2 V is applied in step S22. If no reverse bias voltage is applied, the inspection apparatus 100 skips step S22 and proceeds to step S23.

  In the next step S23, the inspection apparatus 100 moves the solar cell panel 90 according to the inspection position. This inspection position is designated in advance by the operator via the operation input unit 18 as data (coordinate data) regarding the position on the solar cell panel 90 to be inspected. Based on the coordinate data, the control unit 16 drives the motor 15 to move the stage 11 so that the inspection position is irradiated with pulsed light. The operator himself / herself may move the solar cell panel 90 according to the inspection position by manually moving the stage 11.

  When the movement of the solar cell panel 90 is completed, the inspection apparatus 100 restores the time waveform of the terahertz wave pulse generated according to the irradiation with the pump light LP11 based on THz-TDS (step S24). Specifically, it is almost the same as step S12 shown in FIG. However, in this step S24, the solar cell panel 90 is irradiated with the pulsed light having the light intensity set in step S19. By this step S24, similarly to the time waveform 41 shown in FIG. 7, the time waveform of the terahertz wave pulse generated at the inspection position is restored.

  Thus, by restoring the time waveform, the characteristics of the depletion layer of the pn junction 97 at the inspection position can be inspected. For example, a formation defect of a depletion layer can be detected by inspecting the presence / absence of detection of a terahertz wave pulse or by comparing the amplitude of the electric field strength of the constructed time waveform with standard data. Moreover, formation failure of various photoexcited carrier generation regions of the solar cell can be detected by the same process.

  Next, the inspection apparatus 100 performs spectrum analysis based on the restored time waveform (step S25). In this step, the spectrum distribution of the terahertz wave pulse is acquired by the spectrum analysis unit 23 performing Fourier transform on the time waveform.

  FIG. 12 is a diagram illustrating a spectrum distribution of a terahertz wave pulse. In FIG. 12, the vertical axis indicates the spectral intensity, and the horizontal axis indicates the frequency. In the spectrum distribution 51 acquired in step S25, the spectrum intensity is relatively strong at a frequency in the range of 0.1 THz to 1 THz. By acquiring such a spectral distribution 51, the characteristics of the depletion layer of the pn junction 97 formed at each inspection position can be inspected. For example, in the spectrum distribution 51, when the spectrum intensity of a specific frequency indicated by an arrow is significantly lower than a reference value (not shown) serving as a reference, impurities that absorb the specific frequency are depleted. It can be detected that it is contained in a layer or the like. It is also possible to estimate the type and concentration of impurities from the absorbed frequency. Note that the spectrum analysis in step S26 can be omitted.

  Returning to FIG. 11, when the spectrum analysis is completed, the inspection apparatus 100 displays an image indicating the inspection result on the monitor 17 (step S26). Specifically, the time waveform of the terahertz wave pulse acquired in step S25, the spectrum distribution (see FIG. 12) acquired in step S26, and the like are displayed on the monitor 17 as an analysis result. The above is the description of the inspection (1). Next, inspection (2) will be described.

<Inspection (2)>
FIG. 13 is a detailed flowchart of the inspection (2). In the inspection (1), the time waveform and spectrum analysis of the terahertz wave pulse generated in response to the irradiation with the pump light LP11 are performed for a specific region on the solar cell panel 90. On the other hand, in inspection (2), the state of the photoexcited carrier generation region is inspected for the entire surface of the solar cell panel 90.

  When the inspection (2) is started, the inspection apparatus 100 determines whether to apply a reverse bias voltage to the solar cell panel 90 (step S20), and if necessary, applies a reverse bias voltage between the electrodes (step S20). S21). This flow is the same as steps S20 and S21 in the inspection (1).

  Next, in the inspection apparatus 100, the delay unit 131 is adjusted so that the electric field strength of the terahertz wave pulse detected by the detector 132 is maximized (step S23a). In this step, the folding mirror 10M is disposed at the position of the folding mirror 10M set in step S13. By detecting the maximum value of the electric field intensity of the terahertz wave pulse in this way, the electric field intensity can be easily detected, so that the detection sensitivity of the terahertz wave pulse can be improved. However, the folding mirror 10M may be arranged at other positions so that the electric field strength of the terahertz wave pulse is detected at other detection timings.

  Next, the inspection apparatus 100 moves the solar cell panel 90 in the two-dimensional plane by driving the motor 15 (step S24a). At this time, the pulsed light having the light intensity set in step S19 is applied to the solar cell panel 90, and the electric field intensity of the terahertz wave pulse generated thereby is detected by the detector 132. The electric field strength distribution for the inspection target region on the solar cell panel 90 is acquired. For example, the solar cell panel 90 is moved in the positive direction along the main scanning direction and then moved (shifted) by a required distance in the sub-scanning direction orthogonal to the main scanning direction. Is moved in the direction opposite to the positive direction. By repeating this, the electric field strength of the terahertz wave pulse can be efficiently obtained for the entire region of the solar cell panel 90.

  When the electric field strength of the terahertz wave pulse is acquired, the inspection apparatus 100 generates an image showing the electric field strength distribution (electric field strength distribution image) and displays it on the monitor 17 (step S25a).

  FIG. 14 is an example of an electric field intensity distribution image I1 displayed on the monitor 17. The electric field intensity distribution image I1 is an image showing the solar cell panel 90 photographed by the visible camera 14, and is colored according to the magnitude of the electric field intensity detected at each inspection position. In FIG. 14, for convenience of explanation, the distribution of the magnitude of the electric field strength is expressed by using different types of hatching. Specifically, a portion having an electric field strength of 10 or more, a portion of 8 or more and less than 10, and a portion of 4 or more and less than 8 can be identified. Of course, this expression method is an example, and can be appropriately changed. For example, the range of the electric field strength may be further finely divided, or the electric field strength distribution may be expressed by other methods.

  As shown in FIG. 14, in the solar cell panel 90, the electric field strength is the strongest around the light receiving surface electrode 96, and the electric field strength decreases as the distance from the light receiving surface electrode 96 increases. By generating and displaying such an electric field intensity distribution image I1, the formation state of the photoexcited carrier generation region can be grasped at once for the inspection target region of the solar cell panel 90. Furthermore, a lattice defect of polycrystalline silicon can be estimated from an abnormality in the detected electric field strength.

  In this embodiment, the distribution of the maximum electric field intensity is imaged. For example, the distribution of the electric field intensity detected when each of the femtosecond lasers 121 is irradiated with pulsed light in a plurality of wavelength regions is imaged. You may make it do. At this time, it is also possible to color-code each wavelength region so that the electric field intensity distribution for each wavelength region can be visually recognized in the same image.

  In the inspection (2) of the present embodiment, the electric field strength of the terahertz wave pulse is detected only at one detection timing by fixing the folding mirror 10M. However, for example, as described in the inspection (1), the time waveform of the generated terahertz wave pulse may be restored for each inspection position in the inspection target region by controlling the delay unit 131. An electric field intensity distribution for each specific frequency space can be obtained by Fourier-transforming the acquired time waveform to acquire a spectral distribution. You may make it produce | generate the image which visualized this electric field strength distribution by color-coding etc. according to a predetermined rule.

  Further, when there are a plurality of solar cell panels 90 to be inspected, it is not necessary to perform the above steps S11 to S19 every time. In particular, when a plurality of solar cell panels 90 are manufactured in the same manner, the light intensity is set once using one solar cell panel 90 and the other solar cell panels 90 are inspected. What is necessary is just to carry out by this light intensity.

  As described above, according to the inspection apparatus 100 according to the present embodiment, by irradiating the photoexcited carrier generation region formed in the solar cell panel 90 with the pulsed light and detecting the terahertz wave pulse generated accordingly, The characteristics of a photocarrier generation region such as a depletion layer can be inspected. Therefore, since it is possible to perform inspection in a non-contact state, it is possible to improve the efficiency of failure and defect determination of the solar cell panel 90. Moreover, damage to the solar cell panel 90 can be prevented by eliminating the contact of the probe used in the conventional inspection.

<2. Second Embodiment>
In the above embodiment, the optical axis of the pulsed light (pump light LP11) is incident obliquely (incident angle 45 °) on the light receiving surface 91S of the solar cell panel 90. The incident angle is such as this. It is not limited to things.

  FIG. 15 is a schematic configuration diagram of the irradiation unit 12A and the detection unit 13A of the inspection apparatus 100A according to the second embodiment. In the following description, elements having the same functions as those of the components of the inspection apparatus 100 according to the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  Also in the inspection apparatus 100A, the pulsed light LP1 emitted from the femtosecond laser 121 is split into the pump light LP11 and the probe light LP12 by the beam splitter B1. However, in this embodiment, the divided pump light LP11 passes through the transparent conductive film substrate (ITO) 19 and enters the pump light LP11 perpendicular to the light receiving surface 91S of the solar cell panel 90. Of the terahertz wave pulse LT1 generated in response to the irradiation of the pump light LP11, the terahertz wave pulse LT1 emitted toward the light receiving surface 91S is reflected from the transparent conductive substrate 19 and is detected via a lens or the like. Incident 132.

  Even in the inspection apparatus 100A including the irradiation unit 12A and the detection unit 13A, the terahertz wave pulse LT1 generated in response to the irradiation of the pump light LP11 can be detected. Therefore, similarly to the inspection apparatus 100 according to the first embodiment, according to the inspection apparatus 100A, the light intensity of the pulsed light applied to the solar cell panel 90 can be appropriately set, and light excitation such as a depletion layer of the solar cell panel 90 can be performed. The characteristics of the carrier generation region can be inspected in a non-contact state.

<3. Third Embodiment>
In the second embodiment, the terahertz wave pulse LT1 emitted to the light receiving surface 91S side is detected, but the terahertz wave pulse LT1 transmitted to the back surface side of the solar cell panel 90 may be detected.

  FIG. 16 is a schematic configuration diagram of the irradiation unit 12B and the detection unit 13B of the inspection apparatus 100B according to the third embodiment. Also in the inspection apparatus 100B, the pulsed light LP1 emitted from the femtosecond laser 121 is split into the pump light LP11 and the probe light LP12 by the beam splitter B1. In the present embodiment, the divided pump light LP11 is perpendicularly incident on the light receiving surface 91S of the solar cell panel 90. Of the terahertz wave pulse LT1 generated in response to the irradiation of the pump light LP11, the terahertz wave pulse LT1 emitted (transmitted) to the back surface side of the solar cell panel 90 is passed through the parabolic mirrors M1, M2, and the like. The detection unit 13B is configured to enter the detector 132.

  Even in the inspection apparatus 100B including the irradiation unit 12B and the detection unit 13B, the terahertz wave pulse LT1 generated in response to the irradiation with the pump light LP11 can be detected. Therefore, according to the inspection apparatus 100B, similarly to the inspection apparatus 100 according to the first embodiment, the light intensity of the pulsed light applied to the solar cell panel 90 can be appropriately set, and the photoexcited carrier generation region of the solar cell panel 90 can be set. Characteristics can be inspected in a non-contact state. In addition, the structure and material which can permeate | transmit a terahertz wave are limited to some extent. Therefore, as shown in FIG. 5, in the case of the solar cell panel 90 in which the back electrode 92 is provided on the entire surface, it is preferable to inspect with the inspection devices 100 and 100A rather than the inspection device 100B.

<4. Modification>
Although the embodiment has been described above, the present invention is not limited to the above, and various modifications are possible.

  For example, in the above embodiment, the solar cell panel 90 is inspected using pulsed light having a wavelength near 800 nm. However, you may make it test | inspect the board | substrate with which the solar cell panel 90 or another photo device was formed using the pulsed light of a 1.5-micrometer and 1.0-micrometer second high-ultrasonic wave. For example, a photo device formed on a wafer may be inspected.

  The light intensity may be measured by the femtosecond laser 121, or the pulsed light emitted from the femtosecond laser 121 may be measured. As a measuring method of the pulsed light, a part of the pulsed light may be extracted to measure the intensity, and the remaining light intensity may be calculated, or all the pulsed light may be blocked and measured. .

  Moreover, when acquiring correlation data, you may make it change the light intensity of the pulsed light (pump light LP11) irradiated to the solar cell panel 90, making the pulsed light radiate | emitted from the femtosecond laser 121 constant. Of course, the light intensity of the pulsed light LP1 emitted from the femtosecond laser 121 may be changed.

  Moreover, each structure demonstrated by said each embodiment and each modification can be suitably combined or abbreviate | omitted unless it mutually contradicts.

100, 100A, 100B Inspection device 10M Folding mirror 12, 12A, 12B Irradiation unit 121 Femtosecond laser 13, 13A, 13B Detection unit 131 Delay unit 132 Detector 14 Visible camera 15 Motor 16 Control unit 17 Monitor 18 Operation input unit 21 hours Waveform construction unit 23 Spectrum analysis unit 25 Image generation unit 27 Light intensity setting unit 41 Time waveform 51 Spectrum distribution 90 Solar cell panel 97 Junction 99 Reverse bias voltage application circuit B1 Beam splitter CD1 to CD3 Correlation data I1 Electric field intensity distribution image LP1 Pulse Light LP11 Pump light LP12 Probe light LT1 Terahertz wave pulse t1 to t8 Detection timing

Claims (7)

In an inspection method for inspecting a photo device,
(a) By changing the light intensity of the pulsed light emitted from the femtosecond laser and irradiating the light receiving surface of the photo device with the pulsed light, the electric field intensity of the electromagnetic wave generated from the photo device is detected by the detector. Detecting step;
(b) obtaining the maximum light intensity of the pulsed light when the electric field intensity of the electromagnetic wave detected in the step (a) is maximized;
(c) by irradiating the photo device with pulsed light having a light intensity determined based on the maximum light intensity acquired in the step (b), the electric field intensity of the electromagnetic wave pulse generated in the photo device is Detecting with the detector;
Including inspection methods. The inspection method according to claim 1,
The step (c) is an inspection method in which the photo device is irradiated with pulsed light having a light intensity not exceeding the maximum light intensity. The inspection method according to claim 1 or 2,
(e) a step of applying a reverse bias voltage to the photo device when performing the step (a),
An inspection method further comprising: The inspection method according to any one of claims 1 to 3, wherein
The step (a)
(a-1) branching the pulsed light from the femtosecond laser into pump light directed to the photo device and probe light directed to the detector;
(a-2) changing the optical path length of either the first optical path of the pump light or the second optical path of the probe light;
Including inspection methods. The inspection method according to claim 4,
The step (a)
(a-3) Maximum optical path when the electric field intensity detected by the detector is substantially maximum when the optical path length of the first optical path or the second optical path is changed in the step (a-2). The process of obtaining the length,
Further including
An inspection method in which the light intensity of the pulsed light is changed in a state where the optical path length of the first optical path or the second optical path is fixed to the maximum optical path length. The inspection method according to claim 1 or 2,
In the step (a),
An inspection method in which the detector comprises a Schottky barrier diode. In an inspection apparatus for inspecting a photo device,
An irradiation unit that irradiates the light receiving surface of a photo device with pulsed light emitted from a femtosecond laser;
A detection unit for detecting electric field strength of electromagnetic waves generated from the photo device in response to the irradiation of the pulsed light;
A control unit that controls the irradiation unit such that the light intensity of the pulsed light is changed;
Light that sets the non-light intensity of the pulsed light emitted from the femtosecond laser based on the maximum light intensity of the pulsed light when the electric field intensity of the electromagnetic wave becomes maximum when the light intensity is changed by the control unit An intensity setting unit;
An inspection apparatus comprising:

Images