JP6489421B2 - Light intensity setting method, inspection method, and inspection apparatus - Google Patents

Description

  The present invention relates to a technique for inspecting a semiconductor sample, and more particularly to a technique for optimizing the intensity of light applied to a semiconductor sample.

  For example, terahertz waves can be generated by irradiating a solar cell, which is a kind of photo device, with pulsed light having a predetermined wavelength (Patent Document 1). Patent Document 1 discloses a technique for performing inspections such as performance measurement and defect detection of the solar cell by detecting the electric field strength of the generated terahertz wave.

  In general, the electric field strength of the terahertz wave emitted from the photo device can be increased by increasing the light intensity (light quantity) of the pulsed light applied to the photo device (Patent Document 2). However, if the light intensity is increased excessively, the photo device may be damaged. Therefore, Patent Document 2 discloses a technique for suitably setting the light intensity of pulsed light applied to a photo device that is a semiconductor sample. Specifically, by measuring the electric field intensity while changing the light intensity of the pulsed light, the light intensity (maximum light intensity) when the electric field intensity becomes maximum is determined. Based on the maximum light intensity, the light intensity of the pulsed light for inspection is determined.

JP2013-19861A JP 2013-61219 A

  However, a technique for optimizing the light intensity of light applied to a semiconductor sample including a photo device is not known except by the technique described in Patent Document 2, and it is more reliable to damage the semiconductor sample. In order to prevent this, a new criterion for setting the light intensity more appropriately is desired.

  Therefore, an object of the present invention is to provide a technique for setting the light intensity with which a semiconductor sample is irradiated based on a suitable determination criterion.

In order to solve the above-mentioned problem, a first aspect is a light intensity setting method for setting the intensity of light irradiated on a semiconductor sample. (A) From a semiconductor sample according to irradiation with light having a first light intensity. A first acquisition step of acquiring a first time waveform of the radiated terahertz wave; and (b) a terahertz wave radiated from the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity. A second acquisition step of acquiring the second time waveform, and (c) vibration for detecting occurrence of electric field intensity vibration in the second time waveform based on a comparison between the first time waveform and the second time waveform. And (d) in the step (c), when the occurrence of the vibration of the electric field intensity is detected, the light intensity of the light applied to the semiconductor sample is smaller than the second light intensity. 3 including the light intensity setting step of setting the light intensity The step (c) includes (c-1) a step of counting inflection points included in the first time waveform and the second time waveform, and (c-2) counting by the step (c-1). Detecting the occurrence of the vibration by determining whether or not a change in the quantity of the inflection points included in the first time waveform and the second time waveform exceeds a specified quantity; The step (c-1) includes a step of excluding the two inflection points from the count when the change amount of the electric field strength at the two inflection points that are continuous in time is smaller than a predetermined value. It is .

The second aspect is the light intensity setting method according to the first aspect. (E) The step of smoothing the first time waveform and the second time waveform prior to the step (c), Further, the step (c-1) is a step of counting the number of the inflection points in the first time waveform and the second time waveform smoothed in the step (e) .

  The third aspect is the light intensity setting method according to the first or second aspect, wherein the step (c) is included in one or more phase sections in the first time waveform and the second time waveform. A step of detecting the occurrence of the vibration based on a change in the number of inflection points to be generated, and each of the one or more phase sections is a section including a phase of the inflection point in the first time waveform.

  According to a fourth aspect, in the light intensity setting method according to the third aspect, the step (c) generates the vibration based on a change in the number of inflection points included in the plurality of phase sections. Detecting.

A fifth aspect is a light intensity setting method for setting the intensity of light irradiated on a semiconductor sample, and (a) a terahertz wave radiated from a semiconductor sample in response to irradiation with light having a first light intensity. A first acquisition step of acquiring a first time waveform; and (b) a second time waveform of a terahertz wave emitted from the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity. A second acquisition step of acquiring, and (c) a vibration generation detecting step of detecting occurrence of a vibration of an electric field strength in the second time waveform based on a comparison between the first time waveform and the second time waveform; d) In the step (c), when the occurrence of the vibration of the electric field intensity is detected, the light intensity of the light applied to the semiconductor sample is set to a third light intensity that is smaller than the second light intensity. A light intensity setting step, and the step (c) , Smoothing the intensity of the frequency spectrum obtained by Fourier transforming the first time waveform and the second time waveform, and determining whether the difference value of the smoothed intensity exceeds a predetermined criterion A step of detecting the occurrence of the vibration .

  Further, a sixth aspect is the light intensity setting method according to the fifth aspect, wherein the step (c) is a step of detecting the occurrence of the vibration based on a frequency region of 0.5 THz or more in the frequency spectrum. including.

According to a seventh aspect, there is provided an inspection method for inspecting a semiconductor sample, wherein (a) a first time waveform of a terahertz wave emitted from a semiconductor sample in response to irradiation with light having a first light intensity is acquired. 1 acquisition step, and (b) a second acquisition step of acquiring a second time waveform of a terahertz wave irradiated from the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity; (C) a vibration generation detecting step of detecting occurrence of vibration of an electric field intensity in the second time waveform by comparing the first time waveform and the second time waveform; and (d) in the step (c). A light intensity setting step of setting the light intensity of the light applied to the semiconductor sample to a third light intensity smaller than the second light intensity when occurrence of vibration of the electric field intensity is detected; ) Third light set in step (d) In accordance with the irradiation of the degree of light, seen including a terahertz wave detecting step of detecting the terahertz wave radiated from the semiconductor sample, wherein step (c), (c-1) the first time waveform and the second A step of counting inflection points included in the 2-hour waveform; and (c-2) the inflection points included in the first time waveform and the second time waveform counted in the step (c-1). Detecting the occurrence of the vibration by determining whether or not the change in quantity exceeds a specified quantity, and the step (c-1) includes two inflections that are continuous in time. This is a step of excluding the two inflection points from the count when the change amount of the electric field intensity at the point is smaller than a predetermined value .
The eighth aspect further includes the step (f) of smoothing the first time waveform and the second time waveform prior to the step (c) in the inspection method according to the seventh aspect. The step (c-1) is a step of counting the number of inflection points in the first time waveform and the second time waveform smoothed in the step (f).

According to a ninth aspect, there is provided an inspection apparatus for inspecting a semiconductor sample, wherein an irradiation unit for irradiating the semiconductor sample with light, and detecting a terahertz wave emitted from the semiconductor sample in response to the light irradiation. A time waveform acquisition unit that acquires a time waveform of the terahertz wave based on the intensity of the terahertz wave detected by the detection unit, and the intensity of the light that the irradiation unit irradiates the semiconductor sample A light intensity setting unit that sets a first time waveform of a terahertz wave radiated from the semiconductor sample in response to irradiation with light having a first light intensity, and the first light. A time waveform acquisition unit for acquiring a second time waveform of a terahertz wave emitted from the semiconductor sample in response to irradiation with light having a second light intensity greater than the intensity; and the first time waveform and the second time waveform Comparison By Rukoto, and a vibration generation detection unit that detects the occurrence of oscillation of the electric field intensity in the second time waveform, the vibration generating detection unit, the inflection point in the first hour waveform and the second time waveform The occurrence of the vibration is detected by determining whether or not the change in the quantity exceeds a predetermined quantity, and the quantity of the inflection points is the electric field strength between two inflection points that are continuous in time. If the amount of change is smaller than a predetermined value Ru obtained by excluding the two inflection points from the count.
According to a tenth aspect, in the inspection apparatus according to the ninth aspect, the vibration occurrence detection unit counts the number of inflection points in the smoothed first time waveform and second time waveform. To do.

  According to the first aspect, the light intensity for inspection of the inspection light can be suitably set based on the occurrence of the electric field intensity vibration in the time waveform of the terahertz wave. Thereby, it is possible to set the light intensity that can generate a high-intensity terahertz wave while suppressing damage to the semiconductor sample.

Further , the occurrence of vibration can be directly detected by measuring the change in the number of inflection points in the time waveform.

  According to the third aspect, the occurrence of vibration can be easily detected by measuring the number of inflection points in the phase interval including the phase at which the inflection point is taken in the first time waveform.

  According to the 4th aspect, the detection accuracy of a vibration generation can be improved by measuring the change of the number of inflection points in a plurality of phase sections.

  According to the fifth aspect, it is possible to improve the detection accuracy of the occurrence of vibration by detecting the occurrence of vibration based on the change of the frequency spectrum.

  According to the sixth aspect, the detection accuracy of vibration generation can be improved by detecting vibration generation based on a frequency region of 0.5 THz or more that is related to vibration.

1 is a schematic configuration diagram of a terahertz wave measurement system according to an embodiment. It is a schematic sectional drawing of a solar cell. It is a figure which shows the time waveform of a terahertz wave. It is a block diagram which shows the electrical connection of the control part and other element in a test | inspection apparatus. It is a figure which shows the flow of operation | movement of an inspection apparatus. It is a figure which shows the correlation of light intensity and electric field strength. It is a figure which shows the time waveform of the terahertz wave radiated | emitted by irradiation of the test | inspection light of limit light intensity and excess light intensity. It is the elements on larger scale which show the part of the 1st phase area in a time waveform. It is the elements on larger scale which show the part of the 2nd phase area in a time waveform. It is the elements on larger scale which show the part of the 3rd phase area in a time waveform. It is the elements on larger scale which show the part of the 4th phase area in a time waveform. It is a figure which shows a frequency spectrum. It is a figure which expands and shows the frequency spectrum of a low frequency area | region (0.5 THz or less).

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

<Embodiment>
<Configuration of inspection device>
FIG. 1 is a schematic configuration diagram of an inspection apparatus 100 according to the embodiment. The inspection apparatus 100 includes an inspection light irradiation unit 22, a terahertz wave detection unit 23 and a delay unit 24, a moving stage 3, a sample stage 4, a camera 6, and a control unit 7.

  The inspection apparatus 100 irradiates a semiconductor sample with inspection light (inspection light LP11 described later), and detects a terahertz wave generated in response to the irradiation of the inspection light. Moreover, the inspection apparatus 100 images the intensity of the detected terahertz wave (electromagnetic wave of 0.1 THz to 30 THz).

  Here, the semiconductor sample is an electronic device (semiconductor device) composed of a transistor, an integrated circuit (IC or LSI), a resistor or a capacitor, an image sensor such as a photodiode, a CMOS sensor, or a CCD sensor, a solar cell Alternatively, an electronic device (photo device) that utilizes the photoelectric effect of a semiconductor, such as an LED, is included. The surface of the semiconductor sample is assumed to be flat, but may be formed to be curved.

  Below, although the case where the solar cell 9 is test | inspected as a semiconductor sample is demonstrated, it can test | inspect similarly about another semiconductor sample.

  The inspection light irradiation unit 22 includes a femtosecond laser 221. The femtosecond laser 221 emits pulsed light (pulsed light LP1) having a wavelength including a visible light region of, for example, 360 nm (nanometers) or more and 1.5 μm (micrometers) 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 221. 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 LP1 emitted from the femtosecond laser 221 is divided into two by the beam splitter BE1. One of the divided pulse lights is irradiated to the solar cell 9 as the inspection light LP11. At this time, the inspection light irradiation unit 22 irradiates the inspection light LP11 from the light receiving surface 91 side. Further, the inspection light LP11 is applied to the solar cell 9 so that the optical axis of the inspection light LP11 is obliquely incident on the light receiving surface 91 of the solar cell 9. 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 the range of 0 to 90 degrees.

  In this example, the terahertz wave LT1 radiated to the light receiving surface 91 side is detected. However, the light receiving surface 91 of the solar cell 9 may be irradiated with the inspection light LP11 and the terahertz wave LT1 radiated to the back surface of the solar cell 9 may be detected. In this case, the holding unit that holds the solar cells 9 such as the voltage application table 41 and the moving stage 3 may be formed of a shape or material that allows the terahertz wave LT1 to pass. Further, the inspection light LP11 is irradiated perpendicularly to the light receiving surface 91 of the solar cell 9 (that is, at an incident angle of 90 degrees), and radiates coaxially with the inspection light LP11 on the light receiving surface 91 side of the solar cell 9. The terahertz wave to be detected may be detected. In this case, it is conceivable to dispose a transparent conductive film substrate (ITO) on the optical paths of the inspection light LP11 and the terahertz wave LT1. The transparent conductive film substrate has a property of transmitting the inspection light LP11 and reflecting the terahertz wave LT1. For this reason, it is conceivable to detect by taking out the terahertz wave LT1 coaxial with the inspection light LP11 to the outside by the transparent conductive film substrate.

  As shown in FIG. 1, a neutral density filter ND1 is disposed on the optical path of the inspection light LP11 from the beam splitter BE1 to the solar cell 9. The neutral density filter ND1 is a device that reduces the amount of light (light intensity) of the inspection light LP11. In the inspection apparatus 100, the neutral density filter ND1 constitutes means for adjusting the light intensity of the inspection light LP11.

  On the optical path of the inspection light LP11 to the neutral density filter ND1 and the solar cell 9, a beam diameter changing mechanism including a plurality of lenses (not shown) and a power meter PM1 are provided. The power meter PM1 measures the light amount (light intensity) of the inspection light LP11 whose light amount has been adjusted by the neutral density filter ND1.

  FIG. 2 is a schematic cross-sectional view of the solar cell 9. The solar cell 9 is configured as a solar cell that is based on crystalline silicon, for example. The solar cell 9 includes, in order from the bottom, a flat plate-like back side electrode 92 made of aluminum, a p-type semiconductor layer 93, an n-type semiconductor layer 94, an antireflection film 95, and a lattice-like front side electrode 96. And a pn junction 97. The antireflection film 95 is made of silicon oxide, silicon nitride, titanium oxide, or the like.

  Of the main surfaces on both sides of the solar cell 9, the main surface on the side where the surface-side electrode 96 is provided is a light receiving surface. That is, the solar cell 9 is designed so as to suitably generate power by receiving light from the light receiving surface side. A transparent electrode may be used for the surface side 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 221 to, for example, 700 μm or less, terahertz waves can be generated satisfactorily in an amorphous silicon solar cell. The same concept can be applied to other semiconductor solar cells (CIGS type, GaAS type, etc.).

  When the portion of the solar cell 9 where the internal electric field exists is irradiated with the inspection light LP11 having energy exceeding the forbidden band width, photocarriers (free electrons and 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, the pn junction 97 or the Schottky junction.

  According to Maxwell's equation, when a change occurs in the current, an electromagnetic wave having an intensity proportional to the time derivative of the current is generated. That is, when a photoexcited carrier generation region such as a depletion layer is irradiated with pulsed light, generation and extinction of a photocurrent occurs instantaneously. An electromagnetic wave pulse (terahertz wave LT1) is generated in proportion to the temporal differentiation of the instantaneously generated photocurrent.

  As shown in FIG. 1, the other pulse light split by the beam splitter BE1 enters the terahertz wave detector 231 of the terahertz wave detection unit 23 via the delay unit 24 as the detection light LP12. Further, the terahertz wave LT1 generated in response to the irradiation of the inspection light LP11 is appropriately condensed by a parabolic mirror or the like, and enters the terahertz wave detector 231.

  The terahertz wave detector 231 includes, for example, a photoconductive switch (photoconductive antenna) as an electromagnetic wave detecting element. When the terahertz wave LT1 is incident on the terahertz wave detector 231 and the detection light LP12 is applied to the terahertz wave detector 231, a current corresponding to the electric field strength of the terahertz 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. In this manner, the terahertz wave detection unit 23 detects the electric field intensity of the terahertz wave LT1 that has passed through the solar cell 9 in accordance with the irradiation of the detection light LP12. Note that another element different from the photoconductive switch, such as a Schottky barrier diode or a nonlinear optical crystal, may be employed as the detection element.

  The delay unit 24 is an optical device that continuously changes the arrival time of the detection light LP12 to the terahertz wave detector 231. The delay unit 24 includes a delay stage 241 that moves linearly along the incident direction of the detection light LP12 and a delay stage drive mechanism 242 that moves the delay stage 241. The delay stage 241 includes a folding mirror 10M that folds the detection light LP12 in the incident direction. The delay stage driving mechanism 242 translates the delay stage 241 along the incident direction of the detection light LP12 based on the control of the control unit 7. As the delay stage 241 moves in parallel, the optical path length of the detection light LP12 from the beam splitter BE1 to the terahertz wave detector 231 is continuously changed.

  The delay stage 241 changes the difference (phase difference) between the time when the terahertz wave LT1 reaches the terahertz wave detector 231 and the time when the detection light LP12 reaches the terahertz wave detector 231. Specifically, by changing the optical path length of the detection light LP12 by the delay stage 241, the timing (detection timing or sampling timing) at which the terahertz wave detector 231 detects the electric field strength of the terahertz wave LT1 is delayed.

  Note that the arrival time of the detection light LP12 at the terahertz wave detector 231 can be changed by a configuration different from that of the delay stage 241. 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.

  Further, instead of changing the optical path length of the detection light LP12, the optical path length of the inspection light LP11 directed to the solar cell 9 or the optical path length of the terahertz wave LT1 emitted from the solar cell 9 may be changed. In any case, the time for the terahertz wave LT1 to reach the terahertz wave detector 231 can be shifted with respect to the time for the detection light LP12 to reach the terahertz wave detector 231. That is, the detection timing of the terahertz wave LT1 in the terahertz wave detector 231 can be delayed.

  The moving stage 3 is moved in the horizontal direction (X-axis direction, Y-axis direction) and the vertical direction (Z-axis direction) by the stage drive mechanism 31. The stage drive mechanism 31 includes an X-axis direction moving mechanism that moves the moving stage 3 in the X-axis direction, a Y-axis direction moving mechanism that moves the moving stage 3 in the Y-axis direction, and an elevating mechanism that moves the moving stage 3 up and down in the Z-axis direction. It has. Furthermore, the stage drive mechanism 31 is appropriately provided with a rotation mechanism that moves in the rotation direction around the Z axis (θ axis direction).

  The stage drive mechanism 31 moves the solar cell 9 held on the sample stage 4 attached to the moving stage 3 relative to the inspection light irradiation unit 22 in the XY plane. That is, the inspection apparatus 100 is configured to be able to scan the light receiving surface 91 of the solar cell 9 with the inspection light LP11. Accordingly, in the present embodiment, the stage drive mechanism 31 constitutes a scanning mechanism. However, instead of moving the solar cell 9 or moving the solar cell 9, a moving unit that moves the inspection light irradiation unit 22 and the terahertz wave detection unit 23 in the XY plane may be provided.

  Further, a scanning mechanism that changes the optical path of the inspection light LP11 itself may be employed. Specifically, it is conceivable to change the optical path of the inspection light LP11 along the XY plane parallel to the light receiving surface 91 of the solar cell 9 by a galvano mirror that reciprocally swings. Further, instead of the galvanometer mirror, a polygon mirror, a piezo mirror, or an acoustooptic device may be employed.

  The sample stage 4 is attached to the upper surface of the moving stage 3. The sample stage 4 includes a voltage application table 41 and an electrode pin unit 43.

  The voltage application table 41 is made of a material having high electrical conductivity such as copper, and the surface thereof is gold-plated. A plurality of suction holes are formed on the surface of the voltage application table 41. The suction hole is connected to a suction pump, and the back surface of the solar cell 9 is sucked to the voltage application table 41 by driving the suction pump. As a result, the solar cell 9 is fixed to the sample stage 4. A plurality of suction grooves may be provided on the surface of the voltage application table 41, and the plurality of suction holes may be formed in the suction grooves. In this case, the solar cell 9 is adsorbed along the plurality of adsorbing grooves, thereby being firmly fixed. The voltage application table 41 of the sample stage 4 is an example of a holding unit.

  As the moving stage 3 moves in the X-axis direction, Y-axis direction, and Z-axis direction, the solar cell 9 held on the sample stage 4 on the moving stage 3 moves in the X-axis direction, Y-axis direction, and Z-axis direction. Move to each.

  When terahertz wave measurement is performed on the solar cell 9, a reverse bias voltage may be applied to the solar cell 9 via the voltage application table 41 and the electrode pin unit 43 of the sample table 4. Thereby, the intensity of the terahertz wave LT1 radiated from the solar cell 9 can be increased. It is also conceivable that the voltage application table 41 and the electrode pin unit 43 are short-circuited to short-circuit the front surface side electrode and the back surface side electrode 92 of the solar cell 9. Even in this case, the intensity of the terahertz wave LT1 radiated from the solar cell 9 can be increased.

  Next, a method for restoring the time waveform of the terahertz wave LT1 will be described. FIG. 3 is a diagram illustrating a time waveform 80 of the terahertz wave LT1. In FIG. 3, the horizontal axis indicates time (phase), and the vertical axis indicates the electric field strength. Also, in FIG. 3, below the graph showing the time waveform 80, a plurality of detection lights LP <b> 12 having different timings (time t <b> 1 to t <b> 8) reaching the terahertz wave detector 231 by the delay stage 241 are conceptual. Has been shown.

  For example, when the delay stage 241 is adjusted so that the detection light LP12 reaches the terahertz wave detector 231 at time t1, the terahertz wave detector 231 detects the electric field intensity of the value E1. That is, the time t1 corresponds to the phase at which the terahertz wave LT1 becomes E1. Similarly, when the detection timing is delayed from time t2 to time t8, the electric field strengths (values E2 to E8) corresponding to the phases are detected.

  By controlling the delay stage 241 and finely changing the detection timing, the electric field strength of each phase of the terahertz wave LT1 is acquired. By plotting the acquired electric field intensity on the graph along the time axis, the time waveform 80 of the terahertz wave LT1 is restored.

  Further, by restoring the time waveform of the terahertz wave LT1, for example, the detection timing at which the electric field strength of the terahertz wave LT1 is maximized can be specified. For example, in the case of the time waveform 80 shown in FIG. 3, it can be seen that the terahertz wave having the maximum electric field intensity can be detected at time t3. Therefore, when the terahertz wave LT1 is detected with the detection timing fixed without restoring the time waveform, the delay stage 241 is controlled in accordance with the detection timing at which the electric field strength becomes maximum in the time waveform restored in advance. Good. This facilitates detection of terahertz waves.

  Note that the arrival time of the detection light LP12 to the terahertz wave detector 231 can be changed by another configuration different from the delay stage 241. 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 light LP11 or the optical path length of the terahertz wave LT1 radiated from the solar cell 9 may be changed. Even in this case, the time for the terahertz wave LT1 to reach the terahertz wave detector 231 can be shifted relative to the time for the detection light LP12 to reach the terahertz wave detector 231. That is, the detection timing of the electric field strength of the terahertz wave LT1 in the terahertz wave detector 231 can be delayed.

  The control unit 7 is electrically connected to each unit included in the inspection apparatus 100, and controls the operation of each unit of the inspection apparatus 100 while executing various arithmetic processes.

  FIG. 4 is a block diagram illustrating an electrical connection between the control unit 7 and other elements in the inspection apparatus 100. The control unit 7 includes a CPU 71 as an arithmetic device, a read-only ROM 72, a RAM 73 mainly used as a working area of the CPU 71, and a storage unit 74 that is a non-volatile recording medium. As described above, the control unit 7 includes the CPU 71, the ROM 72, the RAM 73, and the storage unit 74, and is configured as a general computer.

  The ROM 72 stores basic programs and the like. The RAM 73 is used as a work area when the CPU 71 performs a predetermined process. The storage unit 74 is configured by a non-volatile storage device such as a flash memory or a hard disk device. A program PG1 is installed in the storage unit 74. Various functions (for example, a light intensity setting unit 711, a time waveform acquisition unit 712, a vibration generation detection unit 713, etc.) are realized by the CPU 71 as the main control unit performing arithmetic processing according to the procedure described in the program PG1. Is done.

  The light intensity setting unit 711 sets the light intensity of the light (inspection light LP11) applied to the solar cell 9. The light intensity setting unit 711 includes a time waveform acquisition unit 712 and a vibration generation detection unit 713. The procedure by which the light intensity setting unit 711 sets the light intensity will be described in detail later.

  The time waveform acquisition unit 712 acquires the time waveform of the terahertz wave emitted from the solar cell 9. The acquisition of the time waveform is performed as described in FIG.

  The vibration generation detection unit 713 detects the occurrence of minute vibrations in the time waveform. Details of this will be described later.

  The program PG1 is normally used by being previously stored in a memory such as the storage unit 74, but is recorded in a recording medium such as a CD-ROM or DVD-ROM or an external flash memory (program product). (Or provided by downloading from an external server via a network), and may be additionally or exchanged stored in a memory such as the storage unit 74. Note that some or all of the functions realized in the control unit 7 may be realized in hardware by a dedicated logic circuit or the like.

  The control unit 7 is connected to each element of the inspection apparatus 100 such as the display unit 61, the operation unit 62, the stage driving mechanism 31, the delay stage driving mechanism 242, and the camera 6 through a bus wiring, a network line, or a serial communication line. Has been. The control unit 7 controls the operation of these elements and receives data from these elements.

  The display unit 61 is a display device that displays an image such as a liquid crystal display, and displays various kinds of information such as a time waveform of a terahertz wave and a frequency spectrum.

  The operation unit 62 is an input device configured by, for example, a keyboard and a mouse, and receives various operations (operations such as inputting commands and various data) from the operator. The operation unit 62 may be configured with various switches, a touch panel, and the like.

<Operation of inspection device>
Next, the operation of the inspection apparatus will be described. FIG. 5 is a diagram illustrating a flow of operation of the inspection apparatus 100. The flowchart shown in FIG. 5 is for inspecting the solar cell 9 which is a semiconductor sample based on the terahertz wave measurement in the inspection apparatus 100.

  In the flowchart shown in FIG. 5, the processes from step S <b> 11 to step S <b> 14 are light intensity setting processes for setting the light intensity of the inspection light LP <b> 11 irradiated on the solar cell 9. The process of step S15 is an inspection process for inspecting the solar cell 9 using the inspection light LP11 having the light intensity set by the light intensity setting process.

  First, the reason for setting the light intensity for inspection will be described. FIG. 6 is a diagram showing a correlation between light intensity and electric field intensity. In FIG. 6, the horizontal axis indicates the light intensity, and the vertical axis indicates the electric field intensity.

  The data shown in FIG. 6 is obtained by measuring the electric field intensity of the generated terahertz wave by fixing the detection timing (phase) of the electric field intensity, irradiating the solar cell 9 with the inspection light LP11 having different light intensity. As shown in FIG. 6, the electric field strength increases as the light intensity increases. However, when a certain light intensity is exceeded, the electric field strength starts to decrease. The point where the electric field intensity starts to decrease is referred to as a limit point P1, and the light intensity at this time is referred to as a limit light intensity LE1. Moreover, the point which turned to decrease is called excess point P2, and let the light intensity at this time be excess light intensity LE2.

  As shown in FIG. 6, in order to increase the detection sensitivity of the terahertz wave, it is only necessary to increase the light intensity of the inspection light LP11 to be irradiated. However, if the light intensity exceeds the limit point P1, the detection sensitivity decreases. Further, when the light intensity of the inspection light LP11 increases, the solar cell 9 may be damaged. Therefore, a suitable setting of the light intensity of the inspection light LP11 that can satisfactorily inspect the solar cell 9 is executed in steps S11 to S14 shown in FIG. And the test | inspection of the solar cell 9 using this suitable test | inspection light LP11 is performed by step S15.

  Returning to FIG. 5, each step S11 to step S15 will be described.

  In step S11, the solar cell 9 is irradiated with the inspection light LP11 having a predetermined light intensity (first light intensity), and thereby the time waveform (first time waveform) of the terahertz wave LT1 radiated from the solar cell 9 is acquired. It is a 1st acquisition process.

  Step S12 irradiates the solar cell 9 with the inspection light LP11 having a second light intensity larger than the first light intensity, and thereby the time waveform (second time waveform) of the terahertz wave LT1 radiated from the solar cell 9 It is the 2nd acquisition process which acquires.

  The acquisition of the time waveform in step S11 and step S12 is performed under the control of the time waveform acquisition unit 712.

  Step S13 is a vibration occurrence detection step of detecting the occurrence of minute vibrations of the electric field strength in the second time waveform based on the comparison between the first time waveform and the second time waveform. Here, the minute vibration means a vibration having a sufficiently small electric field strength as compared with the vertical vibration of the electric field strength of a typical terahertz wave LT1 as shown in FIG. If vibration is detected in step S13 (YES in step S13), the process proceeds to the next step S14. If no vibration is detected (NO in step S13), step S12 is executed again. That is, the light intensity is further increased and the second time waveform is acquired again.

  In the case of the flowchart shown in FIG. 5, in step S13, the first time waveform and the second time waveform are compared. If no vibration is detected, the second time waveform (“new”) obtained by executing step S12 again. This will be referred to as a “2-hour waveform”) and the first time waveform. However, the previously acquired second time waveform may be replaced with the first time waveform (“new first time waveform”) so that the new first time waveform and the new second time waveform are compared. Good.

  Here, as a technique for detecting the occurrence of vibration in step S13, two detection methods will be exemplarily described.

<First detection method>
First, the first detection method is a method of detecting the occurrence of vibration based on the increase of the inflection point included in the time waveform. That is, the occurrence of vibration is directly detected by measuring the number of inflection points. This will be specifically described with reference to FIGS.

  FIG. 7 is a diagram showing time waveforms 81 and 82 of terahertz waves emitted by irradiation with the inspection light LP11 having the limiting light intensity LE1 and the excess light intensity LE2. The time waveform 81 corresponds to the limit light intensity LE1, and the time waveform 82 corresponds to the excess light intensity LE2 that is larger than the limit light intensity LE1. That is, the time waveform 81 corresponds to the first time waveform, and the time waveform 82 corresponds to the second time waveform.

  The time waveform 81 has four main inflection points IP1, IP2, IP3 and IP4 (hereinafter referred to as “IP1 to IP4”) in order from the earliest in time. The inflection points IP1 and IP3 are the peaks of peaks that are convex downward (that is, the electric field strength turns from decreasing to increasing). The inflection points IP2 and IP4 are the peaks of peaks that are convex upward (that is, the electric field strength turns from increasing to decreasing). The electric field strengths at the inflection points IP1 to IP4 are E11, E12, E13, and E14, respectively. E11 and E13 are negative electric field strengths, and E12 and E14 are positive electric field strengths. Inflection point IP1 is the first negative peak, and inflection point IP2 is the first positive peak. The inflection point IP3 is a second negative peak, and the inflection point IP3 is a second negative peak.

  On the other hand, in the time waveform 82, in each of the first phase section PS1 to the fourth phase section PS4 including the main inflection points IP1 to IP4, vibrations in which the electric field strength swings up and down are generated. The vibration of the electric field strength is considered to be caused by the vibration of a coherent photon (coherent vibration phenomenon).

  FIG. 8 is a partially enlarged view showing a portion of the first phase section PS1 in the time waveforms 81 and 82. FIG. FIG. 9 is a partial enlarged view showing a portion of the second phase section PS2 in the time waveforms 81 and 82. As shown in FIG. FIG. 10 is a partially enlarged view showing a portion of the third phase section PS3 in the time waveforms 81 and 82. FIG. FIG. 11 is a partially enlarged view showing a portion of the fourth phase section PS4 in the time waveforms 81 and 82. As shown in FIG.

  In the first phase section PS1, the time waveform 81 has one inflection point (inflection point IP1), whereas the time waveform 82 has five (see FIG. 8). In the second phase section PS2, the time waveform 81 has one inflection point (inflection point IP2), whereas the time waveform 82 has three (see FIG. 9). Further, in the third phase section PS3, the time waveform 81 has one inflection point (inflection point IP3), whereas the time waveform 82 has nine inflection points (see FIG. 10). . In the fourth phase section PS4, there are five inflection points (including the inflection point IP4) in the time waveform 81, whereas there are fifteen inflection points in the time waveform 82 (FIG. 11).

  Thus, the number of inflection points existing in the time waveform increases by increasing the light intensity of the inspection light LP11 from the limit light intensity LE1 to the excess light intensity LE2. By detecting the increase in the inflection point, it can be determined whether or not the limit point at which the radiated electric field intensity reaches the maximum is exceeded.

  In particular, the increase of the inflection point in the time waveform 82 occurs remarkably in the first phase section PS1 to the fourth phase section PS4 in which each of the main inflection points IP1 to IP4 of the time waveform 81 is included. For this reason, if the number of inflection points in at least one phase section among the first phase section PS1 to the fourth phase section PS4 is acquired, the occurrence of vibration of the electric field strength can be easily detected.

  Specifically, the light intensity setting unit 711 specifies one or more inflection points for the first time waveform acquired in step S11, and one or more phases including the phases of the one or more inflection points. Determine the interval. Here, the specified one or more inflection points are the first negative peak (for example, the inflection point IP1), the first positive peak (for example, the inflection point IP2), the second in the first time waveform. It is desirable to be either a negative peak (for example, the inflection point IP3) or an inflection point that becomes the second positive peak (for example, the inflection point IP4). Moreover, although the time length of one phase area may be set arbitrarily, it is desirable not to mutually overlap. In step S13, the number of inflection points in only one or more phase sections is measured for the second time waveform acquired in step S12. Thereby, generation | occurrence | production of a vibration can be detected efficiently.

  By measuring the number of inflection points in two or more phase sections, the detection accuracy of vibration generation can be increased. For example, it may be determined that vibration has occurred when the number of inflection points increases in any one of two or more phase sections. Alternatively, it may be determined that vibration has occurred when inflection points increase in all of two or more phase intervals among two or more phase intervals.

  In step S12, the time waveform of only the one or more phase sections may be restored. In this case, the measurement time of the terahertz wave LT1 necessary for restoring the second time waveform can be shortened.

  When determining whether or not vibration has occurred, for example, it may be determined whether or not the increase in the inflection point exceeds a predetermined quantity. Moreover, in order to suppress that noise is detected as an inflection point, the time waveform may be smoothed by a moving average. Alternatively, when the amount of change between two inflection points that are continuous in time is extremely small, the two inflection points may be excluded from the count. Whether the amount of change is large or small can be determined, for example, by determining whether the amount of change exceeds a predetermined ratio with respect to the electric field strength of one of the two inflection points. That is, when the amount of change exceeds a predetermined ratio, the two inflection points are counted, and when the amount of change does not exceed a predetermined ratio, the two inflection points are excluded from the count. You can do it.

<Second detection method>
The second detection method is a method of detecting vibration generation based on frequency analysis. That is, each acquired frequency spectrum is obtained by performing Fourier transform on the acquired first time waveform and second time waveform (terahertz time spectroscopy). And vibration generation | occurrence | production is detected by comparing the frequency spectrum of a 1st time waveform and a 2nd time waveform.

  FIG. 12 is a diagram showing a frequency spectrum. In FIG. 12, the horizontal axis indicates the frequency, and the vertical axis indicates the spectrum intensity (electric field intensity). The spectrum waveform F81 and the spectrum waveform F82 are frequency spectra of the time waveform 81 and the time waveform 82. Each of the spectrum waveform F83 and the spectrum waveform F84 is a frequency spectrum of a terahertz wave radiated from the solar cell 9 when the inspection light LP11 has light intensities LE3 and LE4. The light intensities LE3 and LE4 are light intensities smaller than the limit light intensity LE1, and LE3 is light intensities smaller than LE4 (see FIG. 6).

  As shown in FIG. 12, in the spectrum waveform F82 corresponding to the time waveform 82 in which the vibration is generated, the spectrum intensity is higher in the high frequency region of 0.5 THz or more than the other spectrum waveforms F81, F83, and F84. Remarkably stronger.

  In addition, FIG. 13 is a figure which shows the frequency spectrum of a low frequency area | region (0.5 THz or less). As shown in FIG. 13, when the light intensity of the inspection light LP11 is increased in order, such as LE1, LE2, LE3, and LE4, the spectrum intensity in the low frequency region reaches a peak at LE3.

  From the above, it is considered that the spectrum intensity in the high frequency region of 0.5 THz or higher in the frequency spectrum of the first time waveform and the second time waveform is related to the minute vibration of the electric field strength. Therefore, the occurrence of vibration can be detected with high accuracy by comparing the high frequency regions. At that time, the spectral intensities can be easily compared by removing the noise by moving each frequency waveform along the frequency axis direction and smoothing it. Further, in order to determine whether or not vibration has occurred, a determination criterion is set in advance. For example, this criterion may be set as a ratio to the spectrum intensity of the first time waveform as a comparison source. That is, for example, when the difference value of the spectrum intensity between the first time waveform and the second time waveform exceeds a predetermined ratio with respect to the spectrum intensity of the first time waveform, it is determined that the spectrum intensity has increased.

  Returning to FIG. 5, step S <b> 14 is a light intensity setting step for setting the light intensity for measurement of the inspection light LP <b> 11. Specifically, the light intensity for inspection of the inspection light LP11 is set to a light intensity (third light intensity) smaller than the light intensity (second light intensity) at which occurrence of vibration is detected in step S13. The third light intensity is, for example, the light intensity of the inspection light LP11 irradiated in step S11 and the light of the inspection light LP11 irradiated when obtaining the second time waveform in which no vibration is generated in step S13. It is considered to be the largest of the strengths. Alternatively, in step S13, the light intensity may be set to 80% to 90% of the light intensity (second light intensity) at which occurrence of vibration is detected. By making the light intensity for inspection smaller than the second light intensity, the possibility of damaging the solar cell 9 can be reduced, and a relatively high-intensity terahertz wave can be detected.

  Step S15 is an inspection process for inspecting the solar cell 9 using the inspection light LP11 having the third light intensity determined in Step S14. Specifically, the solar cell 9 is inspected for characteristics of the solar cell 9 by irradiating the solar cell 9 with the inspection light LP11 and detecting a radiated terahertz wave. Note that by restoring the time waveform of the radiated terahertz wave, an inspection based on the shape of the terahertz wave waveform or the magnitude of the electric field strength can be performed. It is also possible to perform a Fourier transform on the time waveform to obtain a frequency spectrum and perform an inspection based on the frequency spectrum. Further, it is possible to perform an inspection by scanning a predetermined area of the solar cell 9 with the inspection light LP11 and imaging the intensity distribution of the radiated terahertz wave.

  In the flowchart shown in FIG. 5, in steps S12 and S13, the light intensity of the inspection light LP11 is increased to detect whether vibration has occurred. However, the light intensity of the inspection light LP11 may be weakened so as to detect whether the vibration has disappeared. Specifically, the light intensity of the inspection light LP11 is weakened in stages, and the light intensity when the decrease in the number of inflection points reaches its peak is detected. Alternatively, the light intensity is detected when the increase in the high frequency region of the spectrum intensity reaches its peak. In the light intensity setting in step S14, the light intensity for inspection is set to a light intensity that is equal to or smaller than the light intensity that has reached the peak. Thereby, it is possible to determine the light intensity of the inspection light LP11 capable of generating a high-intensity terahertz wave while suppressing damage to the solar cell 9. Therefore, the inspection process of the solar cell 9 can be performed satisfactorily.

  In the above embodiment, pulsed light is emitted from the femtosecond laser 221, and pulsed terahertz waves are emitted from the solar cell 9. However, instead of the femtosecond laser 221, it is also possible to use two light sources that emit two continuous lights having slightly different oscillation frequencies (see JP 2013-170864 A). Specifically, an optical beat signal corresponding to the difference frequency is generated by superimposing two continuous lights by a coupler formed by an optical fiber or the like that is an optical waveguide. Then, by irradiating the solar cell 9 with this optical beat signal, an electromagnetic wave (terahertz wave) corresponding to the frequency of the optical beat signal can be emitted. The present invention can also be applied when setting the light intensity of the optical beat signal at that time.

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

DESCRIPTION OF SYMBOLS 100 Inspection apparatus 22 Inspection light irradiation part 23 Terahertz wave detection part 24 Delay part 3 Moving stage 4 Sample stage 61 Display part 62 Operation part 7 Control part 71 CPU
711 Light intensity setting unit 712 Time waveform acquisition unit 713 Vibration generation detection unit 74 Storage unit 80 to 82 Time waveform 9 Solar cell F81 to F84 Spectrum waveform IP1 to IP4 Inflection point LE1 Limiting light intensity LE2 Excess light intensity LE3, LE4 Light intensity LP1 pulse light LP11 inspection light LP12 detection light LT1 terahertz wave ND1 neutral density filter P1 limit point P2 excess point PM1 power meter PS1 first phase section PS2 second phase section PS3 third phase section PS4 fourth phase section

Claims (10)

A light intensity setting method for setting the intensity of light irradiated on a semiconductor sample,
(A) a first acquisition step of acquiring a first time waveform of a terahertz wave emitted from a semiconductor sample in response to irradiation with light of a first light intensity;
(B) a second acquisition step of acquiring a second time waveform of the terahertz wave emitted from the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity;
(C) a vibration generation detecting step for detecting occurrence of a vibration of an electric field strength in the second time waveform based on a comparison between the first time waveform and the second time waveform;
(D) In the step (c), when the occurrence of the vibration of the electric field intensity is detected, the light intensity of the light applied to the semiconductor sample is set to a third light intensity smaller than the second light intensity. A light intensity setting process,
Only including,
The step (c)
(C-1) counting inflection points included in the first time waveform and the second time waveform;
(C-2) It is determined whether or not the amount of change in the number of inflection points included in the first time waveform and the second time waveform counted in the step (c-1) exceeds a specified number. A step of detecting the occurrence of the vibration,
Including
The step (c-1) is a step of excluding the two inflection points from the count when the amount of change in electric field strength at two inflection points that are continuous in time is smaller than a predetermined value . Light intensity setting method. The light intensity setting method according to claim 1,
(E) smoothing the first time waveform and the second time waveform prior to the step (c);
Further including
The step (c-1) is a light intensity setting method, which is a step of counting the number of inflection points in the first time waveform and the second time waveform smoothed in the step (e) . The light intensity setting method according to claim 1 or 2,
The step (c)
Detecting the occurrence of the vibration based on a change in the number of inflection points included in one or more phase sections in the first time waveform and the second time waveform,
The light intensity setting method, wherein each of the one or more phase sections is a section including a phase of an inflection point in the first time waveform. In the light intensity setting method according to claim 3,
The step (c)
A light intensity setting method including a step of detecting occurrence of the vibration based on a change in the number of inflection points included in a plurality of the phase sections. A light intensity setting method for setting the intensity of light irradiated on a semiconductor sample ,
(A) a first acquisition step of acquiring a first time waveform of a terahertz wave emitted from a semiconductor sample in response to irradiation with light of a first light intensity;
(B) a second acquisition step of acquiring a second time waveform of the terahertz wave emitted from the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity;
(C) a vibration generation detecting step for detecting occurrence of a vibration of an electric field strength in the second time waveform based on a comparison between the first time waveform and the second time waveform;
(D) In the step (c), when the occurrence of the vibration of the electric field intensity is detected, the light intensity of the light applied to the semiconductor sample is set to a third light intensity smaller than the second light intensity. A light intensity setting process,
Including
The step (c)
Smoothing the intensity of the frequency spectrum obtained by Fourier transforming the first time waveform and the second time waveform, and determining whether the difference value of the smoothed intensity exceeds a predetermined criterion. A light intensity setting method including the step of detecting the occurrence of the vibration. In the light intensity setting method according to claim 5,
The step (c)
A light intensity setting method including a step of detecting occurrence of the vibration based on a frequency region of 0.5 THz or more in the frequency spectrum. An inspection method for inspecting a semiconductor sample,
(A) a first acquisition step of acquiring a first time waveform of a terahertz wave emitted from a semiconductor sample in response to irradiation with light of a first light intensity;
(B) a second acquisition step of acquiring a second time waveform of the terahertz wave irradiated from the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity;
(C) a vibration generation detecting step of detecting occurrence of vibration of electric field strength in the second time waveform by comparing the first time waveform and the second time waveform;
(D) In the step (c), when the occurrence of the vibration of the electric field intensity is detected, the light intensity of the light applied to the semiconductor sample is set to a third light intensity smaller than the second light intensity. A light intensity setting process,
(E) a terahertz wave detecting step of detecting a terahertz wave radiated from the semiconductor sample in response to irradiation with light having the third light intensity set in the step (d);
Only including,
The step (c)
(C-1) counting inflection points included in the first time waveform and the second time waveform;
(C-2) It is determined whether or not the amount of change in the number of inflection points included in the first time waveform and the second time waveform counted in the step (c-1) exceeds a specified number. A step of detecting the occurrence of the vibration,
Including
The step (c-1) is a step of excluding the two inflection points from the count when the amount of change in electric field strength at two inflection points that are continuous in time is smaller than a predetermined value . Inspection method. The inspection method according to claim 7,
(F) smoothing the first time waveform and the second time waveform prior to the step (c);
Further including
  The step (c-1) is an inspection method in which the number of the inflection points is counted in the first time waveform and the second time waveform smoothed in the step (f). An inspection apparatus for inspecting a semiconductor sample,
An irradiation unit for irradiating the semiconductor sample with light;
A detection unit for detecting a terahertz wave emitted from the semiconductor sample in response to the light irradiation;
Based on the intensity of the terahertz wave detected by the detection unit, a time waveform acquisition unit that acquires a time waveform of the terahertz wave;
A light intensity setting unit that sets the intensity of the light that the irradiation unit irradiates the semiconductor sample; and
Including
The light intensity setting unit is
A first time waveform of a terahertz wave radiated from the semiconductor sample in response to irradiation with light having a first light intensity, and the semiconductor sample in response to irradiation with light having a second light intensity greater than the first light intensity. A time waveform acquisition unit for acquiring a second time waveform of the terahertz wave radiated from,
A vibration generation detector that detects the occurrence of vibration of the electric field strength in the second time waveform by comparing the first time waveform and the second time waveform;
Equipped with a,
The vibration generation detection unit detects the occurrence of the vibration by determining whether or not the amount of change in the number of inflection points in the first time waveform and the second time waveform exceeds a predetermined number,
The quantity of the inflection points is obtained by excluding the two inflection points from the count when the change amount of the electric field strength between the two inflection points that are continuous in time is smaller than a predetermined value. Inspection equipment. The inspection apparatus according to claim 9, wherein
  The vibration generation detection unit counts the number of inflection points in the smoothed first time waveform and second time waveform.

Images