JP2014181975A - Photo device detection device and photo device inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technology that allows a signal indicated by an electromagnetic wave radiated from a photo device to be analyzed in more detail than before.SOLUTION: A photo device inspection device 100 is the device that measures a solar battery 9, and comprises: an irradiation part 12 that irradiates the solar battery 9 with inspection pulse light LP11; a polarization element 41 that polarizes an electromagnetic wave LT1 radiated from the solar battery 9 in accordance with irradiation of detection pulse light LP12; and a detection part 13 that detects the electromagnetic wave LT1 polarized by the polarization element 41. The polarization element 41 is, for example, a wire grid polarization element composed of a plurality of parallely extending wire parts, and is provided with a polarization element drive mechanism 411 that rotates and drives the polarization element 41 around an axis orthogonal to a direction where the wire part extends.

Description

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

  Photosensors such as photodiodes, CMOS sensors or CCD sensors, photocells such as solar cells or LEDs, free electrons and holes (photoexcited carriers) generated by irradiating light to a depletion layer generated at a pn junction or the like As an element that outputs to the outside via an electrode. For this reason, in photo devices, it is an important technique to allow photoexcited carriers generated in the depletion layer to reach the electrode without recombination.

  The photoexcited carriers generated in the depletion layer are majority carriers. For this reason, the photo device has a structure that is difficult to recombine originally. However, there are the following problems in the development or manufacturing process of photo devices.

  First, an electrode of a photo device is provided on the surface of a semiconductor, and silver or a transparent electrode is used as an electrode material. In the contact portion between the electrode and the semiconductor, defects in the manufacturing process often occur. For example, when an electrode is formed by applying an electrode material, there may be a portion where the adhesion of the electrode is weak. In this case, there is a possibility that the movement of the photoexcited carrier to the electrode is hindered.

  Further, the surface of the photo device may be oxidized or mixed with impurities when exposed to air. These may cause recombination of photoexcited carriers.

  Furthermore, for example, in a solar cell which is a kind of photo device, polycrystalline Si may be used in order to reduce manufacturing costs. However, since it is polycrystalline, carriers on the Si surface may be trapped at the boundaries of the polycrystal. Therefore, research and development of a technique for avoiding carrier trapping at the boundary portion of the polycrystal is demanded.

  The present applicants have already proposed a technique for inspecting a photo device by detecting an electromagnetic wave radiated from the photo device by irradiation with pulsed light (Patent Document 1). Electromagnetic waves generated in response to pulsed light are radiated depending on the generation, movement, and annihilation of photoexcited carriers. Therefore, by analyzing the radiated electromagnetic wave, the characteristics and defects of the photo device can be inspected.

  In addition, in a semiconductor device such as an LSI, which is different from a photo device, a technique for radiating electromagnetic waves by irradiating pulsed laser light has been proposed (Patent Document 2). Patent Document 2 describes that the polarization direction of an electromagnetic wave is detected using a polarizing element. Since the polarization direction of the electromagnetic wave is parallel to the internal electric field, the direction of the internal electric field can be analyzed by detecting the polarization direction of the electromagnetic wave.

JP2013-19861A JP 2006-24774 A

  The electromagnetic wave radiated from the photo device mainly includes information on acceleration and movement of photoexcited carriers depending on an internal electric field such as a pn junction or a Schottky junction or an external electric field applied to the photo device. ing. The emitted electromagnetic wave also includes information on the surface recombination of photoexcited carriers due to the above-described poor contact between the electrode and the semiconductor. However, techniques for analyzing these various information from electromagnetic waves radiated from photo devices are not always sufficient, and there is room for improvement. In Patent Document 2, no consideration is given to the inspection of the photo device. For this reason, it is not easy to apply the technique to inspection of a photo device.

  Accordingly, an object of the present invention is to provide a technique that makes it possible to analyze a signal indicated by an electromagnetic wave radiated from a photo device in more detail.

  In order to solve the above-described problem, a first aspect is a photo device inspection apparatus that inspects a photo device, wherein an irradiation unit that irradiates the photo device with pulse light for inspection, and according to irradiation of the pulse light for inspection A polarizing element that polarizes the electromagnetic wave emitted from the photo device, and a detection unit that detects the electromagnetic wave polarized by the polarizing element.

  The second aspect is a photo grid inspection device according to the first aspect, wherein the polarizing element is a wire grid polarizing element composed of a plurality of wire parts extending in parallel, and the polarizing element is the wire part. And a polarizing element driving mechanism for polarizing the direction in which the polarizing element polarizes the electromagnetic wave by rotating around an axis perpendicular to the direction in which the electromagnetic wave extends.

  The third aspect is the photo device inspection apparatus according to the second aspect, wherein an axis extending in a direction intersecting the surface of the photo device irradiated with the inspection pulse light is used as a rotation axis. And a support mechanism for rotatably supporting the device.

  According to a fourth aspect, in the photo device inspection apparatus according to any one of the first to third aspects, the photo device further includes a scanning mechanism that scans the photo device with the pulse light for inspection. .

  According to a fifth aspect, in the photo device inspection apparatus according to any one of the first to fourth aspects, the detection unit has the same pulse period as that of the inspection pulse light. A detector for detecting the electric field intensity of the electromagnetic wave by receiving the light, and the photo device inspection apparatus is configured to make a relative time for the detection pulsed light to reach the detector relative to the electromagnetic wave. Is further provided with a delay unit that delays the delay time.

  According to a sixth aspect, in the photo device inspection apparatus according to any one of the first to fifth aspects, a reverse bias voltage application unit that applies a reverse bias voltage to the photo device is further provided. .

  Further, the seventh aspect is a photo device inspection method for inspecting a photo device, wherein (a) irradiating the photo device with pulse light for inspection and emitting electromagnetic waves from the photo device; ) A step of polarizing the electromagnetic wave radiated in the step (a), and a step of (c) detecting the electromagnetic wave polarized in the step (b).

  According to the photo device inspection apparatus according to the first aspect, a component in a specific direction of an electromagnetic wave can be detected by polarizing the electromagnetic wave using a polarizing element. Thereby, electromagnetic waves can be separated for each component in each polarization direction. Therefore, various information can be analyzed from the signal indicated by the electromagnetic wave.

  According to the photo device inspection apparatus according to the second aspect, it is possible to detect electromagnetic waves in a direction parallel to the surface of the photo device and a direction perpendicular thereto.

  In addition, according to the photo device inspection apparatus according to the third aspect, by rotating the photo device, the component in the direction parallel to the surface of the photo device can be separated from the electromagnetic wave by the one polarizing element.

  In addition, according to the photo device inspection apparatus according to the fourth aspect, the inspection can be efficiently performed by scanning the range to be inspected with the inspection pulse light.

  Moreover, according to the photo device inspection apparatus according to the fifth aspect, the time waveform of the electromagnetic wave can be restored.

  Further, according to the photo device inspection apparatus according to the sixth aspect, the intensity of the radiated electromagnetic wave can be increased by applying the reverse bias voltage. Thereby, the S / N ratio of electromagnetic wave detection can be improved.

1 is a schematic configuration diagram of a photo device inspection apparatus according to an embodiment. It is a block diagram which shows the connection of a control part and another element. It is a schematic sectional drawing of a solar cell. It is a figure for demonstrating the direction to which a photoexcited carrier moves. It is a figure which shows a mode that the electromagnetic wave polarized in a Z direction is detected with a polarizing element. It is a figure which shows a mode that the electromagnetic wave polarized in a Y direction is detected with a polarizing element. It is a flowchart which shows an example of the test | inspection of the solar cell by a photo device test | inspection apparatus. It is a figure which shows the time waveform of the electromagnetic waves decompress | restored by the time waveform decompression | restoration part. It is a figure which shows the electric field intensity distribution image obtained using the polarizing element. It is a figure which shows the electric field intensity distribution image obtained without using a polarizing element. It is a schematic block diagram of the irradiation part and detection part with which the photo device inspection apparatus which concerns on a modification is provided. It is a schematic block diagram of the irradiation part and detection part with which the photo device inspection apparatus which concerns on a modification is provided.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the drawings, the size and number of each part may be exaggerated or simplified as needed for easy understanding. Moreover, the components described in this embodiment are merely examples, and are not intended to limit the scope of the present invention only to them.

<1. Embodiment>
<1.1. Configuration and Function>
FIG. 1 is a schematic configuration diagram of a photo device inspection apparatus 100 according to the embodiment. FIG. 2 is a block diagram showing the connection between the control unit 16 and other elements. The photo device inspection apparatus 100 irradiates a photo device with pulsed light, and detects an electromagnetic wave (for example, a terahertz wave having a frequency of 0.1 THz to 30 THz) radiated from the photo device in response to the irradiation of the pulsed light. By doing so, inspection regarding the characteristics or defects of the photo device is performed.

  In the present application, a photo device refers to an electronic device that utilizes the photoelectric effect of a semiconductor, such as a photodiode, an image sensor such as a CMOS sensor or a CCD sensor, a solar cell, or an LED. In the present embodiment, a case where the solar cell 9 is inspected as a photo device will be described, but other photo devices can be similarly inspected.

  The surface 9S of the solar cell 9 shown in FIG. 1 is formed in a substantially planar shape, but may be formed in a curved surface shape or the like. In the following description, two directions that are parallel to the surface 9S and orthogonal to each other are defined as an X direction and a Y direction (see FIG. 1). A direction perpendicular to the X direction and the Y direction (that is, a direction perpendicular to the surface 9S) is defined as a Z direction. The XYZ coordinates shown in FIG. 1 are a coordinate system effective only for the solar cell 9 in FIG. That is, FIG. 1 schematically shows the components of the photo device inspection apparatus 100, and the XYZ coordinates do not define the positional relationship between the components in FIG.

  As shown in FIG. 1, the photo device inspection apparatus 100 includes a stage 11, an irradiation unit 12, a detection unit 13, a delay unit 14, a stage drive mechanism 15, and a control unit 16.

  The stage 11 holds the solar cell 9 fixed on the stage 11 by fixing means (not shown). Examples of the fixing means include those using a sandwiching tool for sandwiching the solar cell 9, an adhesive sheet, or an adsorption hole formed on the surface of the stage 11. However, other fixing means may be employed as long as the solar cell 9 can be held.

  The irradiation unit 12 includes a femtosecond laser 121 as a light source that emits pulsed light. For example, the femtosecond laser 121 emits pulsed light (pulsed light) having a wavelength including a visible light region of 360 nm (nanometer) or more and 1.5 μm (micrometer) or less. As a specific example, linearly polarized pulsed light having a center wavelength of around 800 nm, a period of several kHz to several hundred MHz, and a pulse width of about 10 to 150 femtoseconds is emitted from the femtosecond laser. Of course, 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 emitted from the femtosecond laser 121 is split into two by the beam splitter BS1. One of the divided pulse lights (inspection pulse light LP11) is guided to the solar cell 9. The other pulsed light (detection pulsed light LP12) is guided to the detector 131 of the detection unit 13 that detects electromagnetic waves.

  In the present embodiment, the light sources of the inspection pulse light LP11 and the detection pulse light LP12 are a single femtosecond laser 121. Therefore, the pulse periods of the inspection pulse light LP11 and the detection pulse light LP12 are the same. Note that the inspection pulse light LP11 and the detection pulse light LP12 may be emitted from each of two femtosecond lasers having the same pulse period.

  The inspection pulse light LP11 is modulated by several kHz by the optical chopper 123. An AOM (Acousto-Optic Modulator) or the like may be used as the modulation element. The inspection pulse light LP11 modulated by the optical chopper 123 is guided to the solar cell 9.

  When the portion of the solar cell 9 where the internal electric field exists is irradiated with the inspection pulse light LP11 having energy exceeding the forbidden band width, free electrons and free holes are generated and accelerated by the internal electric field. As a result, a pulsed current is generated, and an electromagnetic wave is generated accordingly. It is known that the internal electric field is generated at, for example, a pn junction or a Schottky junction.

  FIG. 3 is a schematic cross-sectional view of the solar cell 9. The solar cell 9 has a structure in which a flat plate-like back electrode 92 made of aluminum or the like, a p-type silicon layer 93, an n-type silicon layer 94, an antireflection film 95, and a light-receiving surface electrode 96 are laminated in this order. Have.

  The antireflection film 95 is made of silicon oxide, silicon nitride, titanium oxide, or the like. Of the main surface of the solar cell 9, the surface 9S on the side where the light-receiving surface electrode 96 is provided is the light-receiving surface. That is, the solar cell 9 is designed to generate power by receiving light from the light receiving surface side. A transparent electrode may be used for the light receiving surface electrode 96. Note that the photo device inspection apparatus 100 may be applied to inspection of solar cells other than single crystal or polycrystalline 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, electromagnetic waves (mainly terahertz waves) can be favorably generated in the amorphous silicon solar cell.

  The light receiving surface (surface 9S) of the solar cell 9 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 of the solar cell 9 is generally formed so as to be able to collect light as efficiently as possible. Therefore, when the inspection pulse light LP11 having a predetermined wavelength is irradiated, the inspection pulse light LP11 is likely to reach a pn junction 97 described later. For example, in the case of the solar cell 9, the light having a wavelength of 1 μm or less mainly having a visible light wavelength region can easily reach the pn junction 97. That is, the photo device such as the solar cell 9 is inspected using the inspection pulse light LP11 as compared with a semiconductor device (an electronic device including a transistor, an integrated circuit (IC or LSI), a resistor, a capacitor, or the like using a semiconductor). It is suitable for.

  A depletion layer is formed in the junction part (pn junction part 97) of the p-type silicon layer 93 and the n-type silicon layer 94 by generating a diffusion potential which is an internal electric field. When this portion is irradiated with the inspection pulse light LP11, photoexcited carriers (free electrons and free holes) are generated. Then, the photoexcited carrier is accelerated by an internal electric field or the like, and a pulsed current is generated. Then, the electromagnetic wave LT1 depending on the time change of the current is generated and radiated to the outside.

  The electromagnetic wave LT1 is generated depending on the state (strength, direction, etc.) of the electric field. Specifically, the electric field strength (amplitude) of the electromagnetic wave LT1 is proportional to the strength of the internal electric field, and the polarization direction (the direction of the electric field vector) of the electromagnetic wave LT1 is parallel to the direction of the internal electric field. That is, the electromagnetic wave LT1 is generated depending on the pn junction or the wiring state connected to the pn junction. For this reason, by detecting the electromagnetic wave LT1, it is possible to examine the characteristics of the solar cell 9 and to perform inspections such as defect determination.

  As shown in FIG. 1, the electromagnetic wave LT1 radiated from the solar cell 9 is collected by parabolic mirrors M1 and M2. More specifically, the parabolic mirrors M1 and M2 collect the electromagnetic wave LT1 radiated to the same side as the surface 9S irradiated with the inspection pulse light LP11. Then, the collected electromagnetic wave LT1 is incident on the detector 131. A polarizing element 41 is provided on the optical path of the electromagnetic wave LT1 from the solar cell 9 to the detector 131. The emitted electromagnetic wave LT1 is polarized in a specific direction by the polarizing element 41 and then detected by the detector 131. The polarizing element 41 is configured to be rotatable by a polarizing element driving mechanism 411 as will be described later.

  The detector 131 is configured by a photoconductive switch (photoconductive antenna) on which the detection pulsed light LP12 is incident. As the photoconductive switch, a dipole type, a bow tie type, a spiral type, and the like are known. In the present embodiment, a spiral photoconductive switch having a small polarization dependency is suitable as the detector 131. When the detection pulsed light LP12 is applied to the detector 131 in a state where the electromagnetic wave LT1 is incident on the detector 131, a current corresponding to the electric field strength of the electromagnetic wave LT1 is instantaneously generated in the photoconductive switch. The current corresponding to the electric field strength is converted into a digital quantity via a lock-in amplifier (not shown), an I / V conversion circuit, an A / D conversion circuit, and the like. Thus, the detection unit 13 detects the electric field intensity of the electromagnetic wave LT1 radiated from the solar cell 9 in response to the irradiation with the detection pulsed light LP12.

  Note that other elements such as a Schottky barrier diode may be used for the detector 131. The Schottky barrier diode has a small polarization dependency and is suitable as the detector 131. It is also conceivable to use a nonlinear optical crystal as the detector 131.

  A delay unit 14 is provided on the optical path of the detection pulsed light LP12 from the beam splitter BS1 to the detector 131. The delay unit 14 is an optical element for continuously changing the arrival time for the detection pulsed light LP12 to reach the detector 131. The delay unit 14 includes a delay stage 141 and a delay stage moving mechanism 143. The delay stage 141 includes a folding mirror 10M that folds the detection pulsed light LP12 in the incident direction. The delay stage moving mechanism 143 translates the delay stage 141 along the incident direction of the detection pulsed light LP12 based on the control of the control unit 16. As the delay stage 141 moves in parallel, the optical path length of the detection pulse light LP12 from the beam splitter BS1 to the detector 131 is continuously changed.

  The delay stage 141 changes the time difference between the time for the electromagnetic wave LT1 to reach the detector 131 and the time for the detection pulsed light LP12 to reach the detector 131. By changing the optical path length of the detection pulsed light LP12 by the delay stage 141, the timing (detection timing or sampling timing) at which the detector 131 detects the electric field strength of the electromagnetic wave LT1 is delayed.

  Note that the arrival time of the detection pulsed light LP12 to the detector 131 can be changed by another configuration different from the delay stage 141. Specifically, it can be considered to use the electro-optic effect. That is, an electro-optic element whose refractive index changes by changing the applied voltage may be used as the delay element. For example, an electro-optic element disclosed in Japanese Patent Application Laid-Open No. 2009-175127, which is a patent document, can be used.

  Further, the optical path length of the inspection pulse light LP11 (pump light) or the optical path length of the electromagnetic wave LT1 radiated from the solar cell 9 may be changed. Even in this case, the time for the electromagnetic wave LT1 to reach the detector 131 can be shifted relative to the time for the detection pulsed light LP12 to reach the detector 131. That is, the detection timing of the electric field intensity of the electromagnetic wave LT1 in the detector 131 can be delayed.

  The photo device inspection apparatus 100 includes a reverse bias voltage application circuit 99 that applies a reverse bias voltage to the solar cell 9 during inspection. For example, when the solar cell 9 is a solar cell, a reverse bias voltage application circuit 99 is connected to electrodes formed on the light receiving surface and the opposite surface of the solar cell, and a reverse bias voltage is applied. By applying the reverse bias voltage, the depletion layer of the pn junction can be enlarged. Thereby, since the electric field strength of the electromagnetic wave LT1 detected by the detector 131 can be increased, the detection sensitivity of the electromagnetic wave LT1 in the detection unit 13 can be improved. However, the reverse bias voltage application circuit 99 can be omitted.

  The stage drive mechanism 15 is a device that moves the stage 11 in a two-dimensional plane, and is configured by, for example, an XY table. The stage drive mechanism 15 moves the solar cell 9 held on the stage 11 relative to the irradiation unit 12. The photo device inspection apparatus 100 can move the solar cell 9 to an arbitrary position in the two-dimensional plane by the stage driving mechanism 15.

  In the present embodiment, the stage 11 is moved in the X and Y directions by the stage driving mechanism 15 so that a required inspection range on the solar cell 9 can be scanned with the inspection pulse light LP11. That is, the stage drive mechanism 15 constitutes a scanning mechanism. However, it is also conceivable to realize scanning of the inspection range by changing the optical path of the inspection pulse light LP11 instead of moving the stage 11 by the stage driving mechanism 15. Specifically, a galvanometer mirror (not shown) is provided, and the inspection pulse light is irradiated on the surface 9S of the solar cell 9 in two directions (X direction and Y direction) perpendicular to the optical axis of the inspection pulse light LP11. It is conceivable to scan LP11. It is also conceivable to use a polygon mirror, a piezo mirror, an acoustooptic device, or the like instead of the galvanometer mirror.

  Further, the stage drive mechanism 15 rotates about the axis Q1 extending in the direction intersecting the surface 9S of the solar cell 9 irradiated with the detection pulsed light LP12 (here, the orthogonal Z direction) with the stage 11 as the rotation axis. Let That is, the stage 11 is also a support mechanism that rotatably supports the solar cell 9. For example, when the stage drive mechanism 15 is composed of an XY table, a motor installed on the XY table is driven, and the rotational driving force is transmitted to the stage 11 so that the stage 11 is Rotate. Of course, the stage 11 may be rotated by other configurations. In addition, the rotation axis (axis Q1) of the stage 11 does not necessarily need to be orthogonal to the surface 9S, and may be at least crossed.

  The control unit 16 is configured by a general computer including a CPU, a ROM, a RAM, and the like (not shown). As shown in FIG. 2, the control unit 16 is connected to the femtosecond laser 121, the detector 131, the delay stage moving mechanism 143, the stage driving mechanism 15, the polarizing element driving mechanism 411, and the reverse bias voltage applying circuit 99. , Control the operation of each of these elements, or receive data from each of these elements.

  The control unit 16 is connected to the image generation unit 21 and the time waveform restoration unit 23. The image generation unit 21 and the time waveform restoration unit 23 may be functions realized by the CPU included in the control unit 16 operating according to a program (not shown), or may be realized in hardware by a dedicated circuit. Also good.

  The image generation unit 21 visualizes the electric field intensity distribution of the electromagnetic wave LT1 emitted by irradiating the inspection pulse light LP11 in the inspection target range of the solar cell 9 (part or all of the solar cell 9). Generate an image. In the electric field intensity distribution image, the difference in electric field intensity is visually expressed in different colors or different patterns.

  The time waveform restoration unit 23 restores the time waveform of the electromagnetic wave LT1 radiated from the solar cell 9 based on the electric field strength detected by the detector 131. Specifically, by moving the delay stage 141, the time for the detection pulsed light LP12 to reach the detector 131 is changed, and the electric field intensity of the electromagnetic wave LT1 detected at each phase is acquired. And the time waveform of electromagnetic wave LT1 is decompress | restored by plotting this acquired electric field strength on a time-axis.

  The control unit 16 is connected to a storage unit 31 that stores various data. The storage unit 31 may be configured by a portable medium (for example, a magnetic medium, an optical disk medium, or a semiconductor memory) in addition to a fixed disk such as a hard disk. The control unit 16 and the storage unit 31 may be connected via a network line.

  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 surface 9S of the solar cell 9 taken by a camera (not shown), an electric field intensity distribution image generated by the image generation unit 21, or a time waveform of the electromagnetic wave LT1 restored by the time waveform restoration unit 23 is displayed. Etc. are displayed. The monitor 17 also displays a GUI (Graphical User Interface) screen necessary for setting inspection conditions (inspection range, etc.).

  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.

<Polarizing element 41>
Next, details of the polarizing element 41 will be described with reference to FIGS.

  FIG. 4 is a diagram for explaining the movement of photoexcited carriers. In FIG. 4, the solar cell 9 is schematically shown for convenience of explanation. The photoexcited carrier is generated by an internal electric field of a depletion layer formed at the pn junction 97, an internal electric field generated at a Schottky junction between an electrode and a semiconductor, or an electric field (external electric field) applied by a reverse bias voltage application circuit 99. Travel, accelerated and diffused.

  Photoexcited carriers usually move greatly in this direction because a large force acts in a direction perpendicular to the pn junction 97 (Z direction). However, as shown in FIG. 4, it also moves in the direction toward the electrode. That is, the movement in the X and Y directions is caused by diffusion of photoexcited carriers or an external electric field applied by the reverse bias voltage application circuit 99. The movement and annihilation of photoexcited carriers in the X and Y directions greatly affect the performance of the solar cell 9 that is a photo device. For example, in a polycrystalline silicon solar cell, it is desired to reduce carrier recombination due to grain boundaries, and an analysis device is required. In the present embodiment, by providing the polarizing element 41, it is possible to separate components in the X and Y directions from the electromagnetic wave LT1.

  FIG. 5 is a diagram showing how the electromagnetic wave LT1 polarized in the Z direction is detected by the polarizing element 41. FIG. FIG. 6 is a diagram illustrating a state in which the polarizing element 41 detects the electromagnetic wave LT1 polarized in the Y direction. As shown in FIGS. 5 and 6, the polarizing element 41 is a wire grid polarizing element provided with a plurality of metal wire portions 43 extending in parallel. The wire part 43 is regularly arrange | positioned according to the wavelength of electromagnetic wave LT1. By arranging the wire portion 43 in accordance with the polarization direction of the electromagnetic wave LT1 to be detected, the electromagnetic wave polarized in a specific direction can be transmitted among the electromagnetic wave LT1. In the detector 131, the electric field strength of the electromagnetic wave that has been transmitted through the polarizing element 41 is detected.

  For example, in the case of the solar cell 9, the pn junction direction (Z direction) is a direction in which photoexcited carriers are mainly accelerated. For this reason, it is thought that the component polarized in parallel to the pn junction direction in the electromagnetic wave LT1 radiated from the solar cell 9 includes information on the generation efficiency of photoexcited carriers. Accordingly, the polarizing element 41 is rotationally driven so that the plurality of wire portions 43 extend in the vertical direction perpendicular to the pn junction direction (see FIG. 5). Thereby, the detection sensitivity of the electromagnetic wave component polarized in the Z direction in the electromagnetic wave LT1 can be improved.

  As shown in FIG. 6, the component in the direction parallel to the pn junction 97 also includes information on generation, movement, and annihilation of photoexcited carriers in the direction. FIG. 6 shows a case where an electromagnetic wave component polarized in the Y direction is detected, and the polarizing element 41 is rotationally driven so that the plurality of wire portions 43 are perpendicular to the polarization direction (Y direction) desired to be detected. Specifically, the polarizing element driving mechanism 411 rotates the polarizing element 41 by 90 degrees around the axis Q2 perpendicular to the direction in which the wire portion 43 extends from the state shown in FIG. Thereby, the component polarized in the Y direction in the electromagnetic wave LT1 can be detected.

  In addition, it is the structure which cannot detect the component of a X direction among electromagnetic waves LT1 only by rotationally driving the polarizing element 41 which concerns on this character embodiment. However, in the present embodiment, the stage drive mechanism 15 can rotate the solar cell 9 by 90 ° around the axis Q1 parallel to the Z direction. For this reason, it is possible to detect a component polarized in the X direction of the electromagnetic wave LT1.

  In this embodiment, the polarizing element 41 is mechanically rotated by the polarizing element driving mechanism 411. However, the polarizing element 41 may be manually rotated. Further, a support unit that detachably supports the polarization element 41 may be provided, and the polarization element 41 may be reattached so as to change the direction of the wire portion 43 with respect to the support unit.

<1.2. Inspection>
FIG. 7 is a flowchart showing an example of the inspection of the solar cell 9 by the photo device inspection apparatus 100. In the following description, each operation of the photo device inspection apparatus 100 is controlled by the control unit 16 unless otherwise specified. Further, depending on the content of the process, a plurality of processes may be executed in parallel, or the execution order of each process may be changed as appropriate.

  A solar cell 9 as a sample is fixed to the stage 11 (FIG. 7: Step S1). At this time, the stage 11 is moved by the stage drive mechanism 15 so that the inspection pulse light LP11 is irradiated to a required inspection range on the stage 11. The operator may move the stage 11 manually.

  When the movement of the stage 11 is completed, the reverse bias voltage application circuit 99 is connected to the back surface electrode 92 and the light receiving surface electrode 96 of the solar cell 9, and the reverse bias voltage is applied to the solar cell 9 (FIG. 7: Step S2). Note that step S2 can be omitted.

  When a reverse bias voltage is applied to the solar cell 9, the detection timing at which the detector 131 detects the electromagnetic wave LT1 emitted from the solar cell 9 is set (FIG. 7: Step S3). Specifically, when the control unit 16 drives the delay stage driving mechanism 143, the position of the folding mirror 10M is fixed so that the timing at which the detection pulsed light LP12 reaches the detector 131 is fixed at a required detection timing. Is adjusted. An example of determining the detection timing will be specifically described with reference to FIG.

  FIG. 8 is a diagram showing a time waveform 51 of the electromagnetic wave LT1 restored by the time waveform restoration unit 23. As shown in FIG. In FIG. 8, the horizontal axis indicates time, and the vertical axis indicates electric field strength. In the lower part, a plurality of detection pulse lights LP12 whose timings (detection timings t1 to t8) reaching the detector 131 are changed by the delay unit 14 are conceptually shown.

  For example, when the inspection pulse light LP11 is irradiated to a specific position of the solar cell 9, the electromagnetic wave LT1 indicated by the time waveform 51 repeatedly arrives at the detector 131 at a predetermined cycle. Here, when the delay unit 14 is adjusted so that the probe light reaches the detector 131 at the detection timing t1, the electric field intensity of the value ES1 is detected by the detector 131. Further, when the detection timing is delayed by t2 to t8 by adjusting the delay unit 14, the electric field strengths of the values ES2 to ES8 are detected by the detection unit 13, respectively. In this manner, the electric field strength of the electromagnetic wave LT1 is measured while finely changing the detection timing, and the obtained electric field strength value is plotted on a graph along the time axis, whereby the time waveform 51 of the electromagnetic wave LT1 is obtained. Restored.

  Here, in the electromagnetic wave LT1, the electric field strength larger than the electric field strength (reference electric field strength) in the normal state is defined as a positive electric field strength, and the electric field strength smaller than the reference electric field strength is defined as a negative electric field strength. Then, in the time waveform 51, the electric field strength becomes maximum on the positive side at the detection timing t3. In other words, the large electromagnetic wave LT1 can be detected by fixing the delay stage 141 at a position corresponding to the detection timing t3. Therefore, the S / N ratio of detection can be increased. Further, at the detection timing t4, the electric field intensity of the electromagnetic wave LT1 is maximum on the negative side. It may be possible to fix the delay stage 141 at a position corresponding to the detection timing t4.

  Returning to FIG. 7, when the detection timing is set, the polarization direction of the electromagnetic wave LT1 detected by the detector 131 is set (FIG. 7: Step S4). The polarization direction of the electromagnetic wave LT1 (the direction of the electric field vector of the electromagnetic wave LT1) is parallel to the electric field inside the solar cell 9, that is, the moving direction of the photoexcited carriers. For this reason, the arrangement of the wire portion 43 of the polarizing element 41 is set so as to transmit the electromagnetic wave LT1 polarized in parallel with the moving direction of the photoexcited carrier that the operator wants to detect. Note that, as described above, the polarizing element 41 starts from the radiated electromagnetic wave LT1 (having components in the X, Y, and Z directions) and is one of the X direction and the Y direction (Y direction in the description of FIG. 6). ) And the component in the Z direction can be separated. For this reason, the solar cell 9 may be rotated 90 degrees by the stage drive mechanism 15 for the component polarized in the other direction (X direction in the description of FIG. 6) of the X direction and the Y direction. Thereby, since a polarization direction can be rotated 90 degree | times with respect to the solar cell 9, the component of the other direction of electromagnetic waves LT1 can be isolate | separated.

  When the polarization direction to be detected is set, the required inspection range set on the solar cell 9 is scanned with the inspection pulse light LP11 (FIG. 7: Step S5). Specifically, the stage 11 is moved in the X and Y directions by the stage driving mechanism 15 to move the solar cell 9 relative to the inspection pulse light LP11. Thus, the inspection pulse light LP11 is irradiated to the inspection range. As described above, it is also conceivable to realize scanning of the inspection range by providing a galvanometer mirror or the like so that the optical path of the inspection pulse light LP11 can be changed. During scanning, the electric field intensity of the radiated electromagnetic wave LT1 is detected by the detector 131, and the intensity information and the radiated position information are associated with each other and stored in the storage unit 31.

  When the scanning is completed, an image indicating the electric field intensity distribution of the electromagnetic wave LT1 is generated and displayed on the monitor 17 (FIG. 7: Step S6).

  FIG. 9 is a diagram illustrating an electric field intensity distribution image 61 obtained using the polarizing element 41. FIG. 10 is a diagram showing an electric field intensity distribution image 63 obtained without using the polarizing element 41. In the electric field intensity distribution images 61 and 63 shown in FIGS. 9 and 10, the position of the light receiving surface electrode 96 is indicated by a broken line. Further, in the electric field intensity distribution images 61 and 63, the scales attached in the horizontal direction and the vertical direction indicate the distances in the X direction and the Y direction from predetermined origin positions on the solar cell 9, respectively. In the electric field intensity distribution image 61, the component in the Y direction of the electromagnetic wave LT1 is detected by adjusting the polarizing element 41.

  Compared with the electric field intensity distribution image 63, the electric field intensity distribution image 61 can grasp the crystal grain outline 71 more clearly, and the light receiving surface electrode 96 can also be grasped clearly. ing.

  As described above, by polarizing the electromagnetic wave LT1 with the polarizing element 41, the electromagnetic wave LT1 can be detected separately in the X direction, the Y direction, and the Z direction. The electromagnetic wave LT1 includes information on acceleration and movement of electrons depending on an internal electric field such as a pn junction or a Schottky junction, or an external electric field applied to the photo device. The emitted electromagnetic wave also includes information on the surface recombination of photoexcited carriers due to the above-described poor contact between the electrode and the semiconductor. By separating the components in each direction from the electromagnetic wave LT1, it is possible to analyze these various information in more detail.

  In addition, the inspection method of the solar cell 9 is not limited to what is shown by FIG. For example, it is conceivable to inspect the solar cell 9 by restoring the time waveform 51 as shown in FIG. That is, in the time waveform 51, the signal of the electric field strength that changes mainly to the positive side (the portion surrounded by the alternate long and short dash line) includes information when photoexcited carriers are generated by the irradiation of the measurement probe light LP11. it is conceivable that. In addition, in the time waveform 51, the electric field intensity signal (part surrounded by a two-dot chain line) mainly changing to the negative side has information on movement and recombination of photoexcited carriers generated by the irradiation of the measurement probe light LP11. It is thought that it is included. For this reason, restoring the time waveform of the electromagnetic wave LT1 detected using the polarizing element 41, and inspecting the solar cell 9 based on the restored time waveform is to analyze the dynamics of the photoexcited carrier, It is extremely effective. Further, spectrum analysis may be performed by Fourier transforming the restored time waveform.

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

  FIG. 11 is a schematic configuration diagram of an irradiation unit 12A and a detection unit 13A included in the photo device inspection apparatus 100A according to the modification. In the following description, elements having functions similar to those of the constituent elements of the photo device inspection apparatus 100 are denoted by the same reference numerals and description thereof is omitted.

  Also in the photo device inspection apparatus 100A, the pulse light emitted from the femtosecond laser 121 is split into the inspection pulse light LP11 and the detection pulse light LP12 by the beam splitter BS1. However, in the present embodiment, the inspection pulse light LP11 passes through the transparent electrode substrate 19 and enters the inspection pulse light LP11 perpendicular to the surface 9S of the solar cell 9. The electromagnetic wave LT1 radiated to the surface 9S side reflects the transparent conductive substrate 19 and enters the detector 131 via the lens, the polarizing element 41, and the like. That is, the photo device inspection apparatus 100A is configured as a coaxial incident type inspection apparatus.

  FIG. 12 is a schematic configuration diagram of an irradiation unit 12B and a detection unit 13B included in the photo device inspection apparatus 100B according to the modification. Also in the photo device inspection apparatus 100B, the pulse light emitted from the femtosecond laser 121 is split into the inspection pulse light LP11 and the detection pulse light LP12 by the beam splitter BS1. The inspection pulse light LP11 is perpendicularly incident on the surface 9S of the solar cell 9. Then, the electromagnetic wave LT1 radiated (transmitted) to the back surface side of the solar cell 9 enters the detector 131 via the parabolic mirrors M1 and M2 and the polarizing element 41. That is, the photo device inspection apparatus 100B is configured as a transmission type inspection apparatus.

  In such photo device inspection apparatuses 100 </ b> A and 100 </ b> B, the solar cell 9 can be inspected as in the photo device inspection apparatus 100.

  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.

100, 100A, 100B Photo device inspection apparatus 11 Stage 12, 12A, 12B Irradiation unit 121 Femtosecond laser 13, 13A, 13B Detection unit 131 Detector 14 Delay unit 141 Delay stage 15 Stage drive mechanism 16 Control unit 21 Image generation unit 23 Time waveform restoration unit 41 Polarizing element 411 Polarizing element driving mechanism 43 Wire part 9 Solar cell (photo device)
99 Reverse bias voltage application circuit 9S Surface LP11 Inspection pulse light LP12 Detection pulse light LT1 Electromagnetic wave Q1, Q2 axis

Claims (7)

A photo device inspection apparatus for inspecting a photo device,
An irradiation unit for irradiating the photo device with pulse light for inspection;
A polarizing element that polarizes the electromagnetic wave radiated from the photo device in response to irradiation of the inspection pulse light;
A detection unit for detecting the electromagnetic wave polarized by the polarizing element;
A photo device inspection apparatus. The photo device inspection apparatus according to claim 1,
The polarizing element is a wire grid polarizing element composed of a plurality of wire portions extending in parallel, and the polarizing element is rotated by driving the polarizing element around an axis perpendicular to a direction in which the wire portion extends. A polarizing element drive mechanism for polarizing the direction of polarizing electromagnetic waves,
A photo device inspection apparatus further comprising: The photo device inspection apparatus according to claim 2,
A photo device inspection apparatus, further comprising: a support mechanism that rotatably supports the photo device with an axis extending in a direction intersecting the surface of the photo device irradiated with the inspection pulse light as a rotation axis. . In the photo device inspection apparatus according to any one of claims 1 to 3,
A scanning mechanism for scanning the photo device with the pulsed light for inspection;
A photo device inspection apparatus further comprising: In the photo device inspection apparatus according to any one of claims 1 to 4,
The detection unit includes a detector that detects the electric field strength of the electromagnetic wave by receiving the pulse light for detection having the same pulse period as the pulse light for inspection,
The photo device inspection apparatus comprises:
A photo device inspection apparatus, further comprising a delay unit that relatively delays a time for the detection pulsed light to reach the detector with respect to the electromagnetic wave. In the photo device inspection apparatus according to any one of claims 1 to 5,
A photo device inspection apparatus, further comprising: a reverse bias voltage application unit that applies a reverse bias voltage to the photo device. A photo device inspection method for inspecting a photo device,
(a) irradiating the photo device with pulsed light for inspection to emit electromagnetic waves from the photo device;
(b) polarizing the electromagnetic wave radiated in the step (a),
(c) detecting the electromagnetic wave polarized in the step (b),
A photo device inspection method.