Testing device

Abstract

To provide a testing device for a substrate with an excellent S / N with a simple configuration.SOLUTION: The testing device includes an electro-optical sensor, a test signal application unit, a light source, and a camera. The electro-optical sensor is arranged near the substrate to test and changes the double-refraction characteristic in response to receipt of an electric field from the substrate. The test signal application unit applies a modulated test signal on the substrate. The light source radiates illumination light on the electro-optical sensor. The camera takes an image of return light of the illumination light emitted from the electro-optical sensor in response to receipt of illumination light from the light source when a test signal is applied to the substrate.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The embodiment relates to a test apparatus. [Background technology]

[0002] An electromagnetic field imaging device utilizing the Pockels effect is known as a device for non-contact detection of the electromagnetic field distribution of a substrate operating at a certain operating frequency. This electromagnetic field imaging device is configured to place an electro-optic element, the birefringence of which changes with an electric field, near the substrate to be observed, apply a signal at the operating frequency of the substrate to the substrate, and irradiate the electro-optic element with laser light modulated at a modulation frequency set according to the operating frequency of the substrate. The imaging device captures, as an image, detection light that includes a difference frequency component between the modulation frequency and the operating frequency generated in the electro-optic element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-20304 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of a configuration in which modulated laser light is irradiated onto an electro-optical element, a configuration for modulating the laser light, such as a Mach-Zehnder Modulator (MZM) or an electro-absorption (EA) modulator, is required. This configuration for modulating the laser light is relatively expensive. Furthermore, since the power of the laser light is reduced by modulation, the S / N ratio of the image obtained by the imaging device tends to be low.

[0005] The present disclosure provides a substrate testing device that has a simple configuration and a good S / N ratio. [Means for solving the problem]

[0006] A test device according to one embodiment includes an electro-optical sensor, a test signal application unit, a light source, and a camera. The electro-optical sensor is disposed near a substrate to be tested and changes birefringence characteristics upon receiving an electric field from the substrate. The test signal application unit applies a modulated test signal to the substrate. The light source irradiates illumination light onto the electro-optical sensor. The camera captures an image of return light of the illumination light emitted from the electro-optical sensor upon receiving the illumination light from the light source when the test signal is applied to the substrate. Effect of the Invention

[0007] According to the embodiment, a substrate testing device with a simple configuration and good S / N ratio is provided. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of a configuration of a test device according to an embodiment. [Diagram 2] FIG. 2 is a diagram illustrating an example of a configuration of the signal processing unit. [Diagram 3] FIG. 3 is a diagram illustrating a configuration of an example of a computer. [Figure 4] FIG. 4 is a flow chart showing an example of a testing method using the testing device. [Diagram 5] FIG. 5 is a diagram showing a test in a state where the substrate is immersed in water. [Figure 6] FIG. 6 is a diagram conceptually showing quadrature demodulation of pixel signals of four frames when the cosine component pixel signals and the sine component pixel signals are out of phase with respect to the phase of the test signal. [Figure 7] FIG. 7 is a diagram conceptually showing orthogonal demodulation of pixel signals of two frames when the phase of a test signal and the phase of a cosine component pixel signal match. [Figure 8] FIG. 8 is a diagram showing an example of a configuration of a test device according to the fourth modification. [Figure 9] FIG. 9 is a diagram showing a configuration of another example of the signal processing unit according to the fourth modification. In FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment will be described with reference to the drawings. FIG. 1 is a diagram showing an example of the configuration of a test device according to an embodiment. The test device according to the embodiment is used for testing a board that does not require application of a signal of a specific operating frequency. A test of a board that does not require application of a signal of a specific operating frequency is, for example, a continuity test of an interposer. However, the test device according to the embodiment can be used for testing various boards other than interposers that do not require application of a signal of a specific operating frequency.

[0010] The test device 1 includes a laser device 101, a collimator lens 102, a quarter-wave plate 103, a half-wave plate 104, a polarizing beam splitter (PBS) 105, a quarter-wave plate 106, a half-wave plate 107, a mirror 108, an electro-optical (EO) sensor 109, an oscillator 110, a frequency divider / phase shifter 111, an amplitude modulator 112, a demultiplexer 113, an imaging lens 114, a camera 115, a signal processing unit 116, a computer 117, and probe electrodes 118, 119, and 120. In FIG. 1, the number of probe electrodes is described as three. The number of probe electrodes is not limited to three, and may be one or two, or may be four or more. The number of probe electrodes may be appropriately set according to, for example, the size of the substrate D and / or the number of connection pads.

[0011] The laser device 101 is a light source that generates a laser beam as illumination light to be irradiated onto the EO sensor 109. The laser device 101 irradiates an object with the generated laser beam through, for example, an optical fiber. The laser beam irradiated onto the EO sensor 109 is, for example, a visible light laser.

[0012] The collimator lens 102, the ¼ wavelength plate 103, the ½ wavelength plate 104, the PBS 105, the ¼ wavelength plate 106, the ½ wavelength plate 107, and the mirror 108 are disposed on the output optical path of the laser device 101. The collimator lens 102, the ¼ wavelength plate 103, the ½ wavelength plate 104, the PBS 105, the ¼ wavelength plate 106, the ½ wavelength plate 107, and the mirror 108 can operate as a wavefront matching optical system for matching the wavefront of the output light of the laser device 101 with the light irradiation surface of the EO sensor 109. The PBS 105, the ¼ wavelength plate 106, the ½ wavelength plate 107, and the mirror 108 can also operate as a detection optical system for converting the modulation of the polarization state output from the EO sensor 109 into intensity modulation.

[0013] Collimator lens 102 outputs the laser light incident from laser device 101 as parallel light. The laser light emitted from collimator lens 102 is circularly polarized by quarter wave plate 103 and half wave plate 104. This circularly polarized light travels straight through PBS 105, passes through quarter wave plate 106 and half wave plate 107, and then has its optical axis bent by mirror 108. The light with the bent optical axis is perpendicularly incident on EO sensor 109.

[0014] Furthermore, the mirror 108 reflects the light incident from the EO sensor 109 in the direction of the half-wave plate 107 .

[0015] The EO sensor 109 is an electro-optical element sensor that changes birefringence when an electric field is applied. For example, the EO sensor 109 is made of an isotropic crystal plate such as ZnTe or LiNO3. The EO sensor 109 is disposed near a device under test (DUT) D so as to receive an electric field generated in the DUT. When light is incident on the EO sensor 109, the EO sensor 109 polarizes the incident light with a birefringence according to the strength of the electric field received from the DUT, and emits the polarized light in the direction of the mirror 108.

[0016] The oscillator 110 generates a carrier wave. The carrier wave is, for example, a sine wave with a frequency fc. The frequency fc is a high frequency such as 10 GHz.

[0017] The frequency divider / phase shifter 111 generates an amplitude modulated wave by dividing and phase shifting the carrier wave. The amplitude modulated wave is, for example, a sine wave with a modulation frequency fam. The modulation frequency fam is set to a frequency lower than the frame rate of the camera 115. For example, the modulation frequency fam is set to a frequency equivalent to ¼ of the frame rate of the camera 115.

[0018] The amplitude modulator 112 as a test signal application section generates a test signal by amplitude modulating a carrier wave with an amplitude modulated wave. Then, the amplitude modulator 112 applies the test signal to one of the probe electrodes 118, 119, and 120 via the demultiplexer 113. In FIG. 1, an example is shown in which the amplitude modulator 112 applies the test signal to the probe electrode 119.

[0019] The demultiplexer 113 selects, based on instructions from the computer 117, one of the probe electrodes 118, 119, and 120 to which the test signal from the amplitude modulator 112 is to be applied, and outputs the test signal to the selected probe electrode.

[0020] The probe electrodes 118, 119, and 120 are arranged on the surface of the substrate D opposite to the surface facing the EO sensor 109, with a gap between them and the substrate D. The probe electrodes 118, 119, and 120 are electrostatically coupled to the substrate D, and apply the test signal output from the amplitude modulator 112 to the substrate D in a non-contact manner. As described above, the substrate D is a substrate to which it is not necessary to apply a signal of a specific operating frequency, and is, for example, an interposer. In this case, the probe electrodes 118, 119, and 120 are arranged near the respective connection pads of the interposer.

[0021] The imaging lens 114 is disposed on the reflected light path of the PBS 105 and causes the light incident from the PBS 105 to form an image on the pixels of the camera 115 .

[0022] Camera 115 has an image sensor consisting of many pixels, and captures the light imaged through imaging lens 114 to obtain a digital pixel signal. The image sensor is, for example, a CMOS image sensor. As will be described later, camera 115 captures one frame at a frame rate equivalent to 4 fam input from amplitude modulator 112.

[0023] The signal processing unit 116 is, for example, a digital signal processing unit (DSP), and performs signal processing on the pixel signals obtained by the camera 115. The signal processing includes processing for quadrature demodulation.

[0024] 2 is a diagram showing a configuration of an example of a signal processing unit 116. The example of the signal processing unit 116 has a cosine component integrator 1161, a low-pass filter (LPF) 1162, a sine component integrator 1163, a low-pass filter (LPF) 1164, and a multiplexer 1165. Here, the signal processing unit 116 may be configured integrally with the computer 117.

[0025] The cosine component integrator 1161 multiplies the input signal by the cosine component cos2πft. f is a frequency and is equal to the modulation frequency fam. t is the elapsed time from the start of imaging by the camera 115. The cosine component integrator 1161 may multiply the input signal by a pseudo cosine component instead of by the cosine component cos2πft. The pseudo cosine component is a square wave approximating the cosine wave cos2πft with an amplitude of ±1. For example, when multiplying the input signal of one cycle (four frames) obtained by the camera 115 by a pseudo cosine component, the cosine component integrator 1161 multiplies the input signal of the first frame by +1, the input signal of the second frame by +1, the input signal of the third frame by -1, and the input signal of the fourth frame by -1. Here, an operation equivalent to that of the cosine component integrator 1161 may be performed by digital calculation.

[0026] The LPF 1162 removes harmonic components generated by the product of the input signal from the camera 115 and a cosine component. An operation equivalent to that of the LPF 1161 may be performed by digital calculation using a finite impulse response (FIR) filter, an infinite impulse response (IIR) filter, or the like.

[0027] The sine component integrator 1163 multiplies the input signal by the sine component sin2πft. f is a frequency and is equal to the modulation frequency fam. t is the elapsed time from the start of imaging by the camera 115. The sine component integrator 1163 may multiply the input signal by a pseudo sine component instead of multiplying the input signal by the cosine component sin2πft. The pseudo sine component is a square wave approximating the sine wave sin2πft with an amplitude of ±1. For example, when multiplying the input signal of one cycle (four frames) obtained by the camera 115 by a pseudo sine component, the sine component integrator 1163 multiplies the input signal of the first frame by -1, the input signal of the second frame by +1, the input signal of the third frame by +1, and the input signal of the fourth frame by -1. Here, an operation equivalent to that of the sine component integrator 1163 may be performed by digital calculation.

[0028] The LPF 1164 removes harmonic components generated by the product of the input signal from the camera 115 and a sine component. An operation equivalent to that of the LPF 1164 may be implemented by digital calculation using an FIR filter, an IIR filter, or the like.

[0029] The multiplexer 1165 combines the input signals from the LPF 1162 and the LPF 1164 and outputs the combined signals to the computer 117 .

[0030] The computer 117 is a computer that controls the operation of the test apparatus 1. The computer 117 calculates the amplitude and phase of the return light that indicates the change in the birefringence of the EO sensor 109 from the output of the signal processing unit 116, for example. The computer 117 also displays the calculated amplitude and phase of the return light as an image. In addition, the computer 117 can also control the operation of the laser device 101 and the oscillator 110.

[0031] 3 is a diagram showing an example of the configuration of the computer 117. The computer 117 is, for example, a personal computer, and has, as hardware, a processor 1171, a memory 1172, a storage 1173, an input interface 1174, and an output interface 1175. The processor 1171, the memory 1172, the storage 1173, the input interface 1174, and the output interface 1175 are connected to a bus.

[0032] The processor 1171 is a processor that controls the overall operation of the computer 117. The processor 1171 can perform various processes by executing a program stored in the storage 1173, for example. The processor 1171 is, for example, a CPU. The processor 1171 may be an MPU, a GPU, or the like. Furthermore, an ASIC, an FPGA, or the like may be used instead of the processor 1171. The processor 1171 may be a single CPU, or the like, or may be multiple CPUs, or the like.

[0033] The memory 1172 includes a ROM and a RAM. The ROM is a non-volatile memory. The ROM stores a startup program and the like for the computer 117. The RAM is a volatile memory. The RAM is used as a working memory during processing in the processor 1171, for example.

[0034] The storage 1173 is, for example, a storage such as a hard disk drive or a solid state drive. The storage 1173 stores various programs, such as a test program 1173a, executed by the processor 1171. In addition, the storage 1173 may store calculated values ​​of the amplitude and phase of the return light and / or image data representing the same.

[0035] The input interface 1174 is an input device such as a touch panel, a keyboard, a mouse, etc. When the input interface 1174 is operated, a signal corresponding to the operation is input to the processor 1171 via the bus. The processor 1171 performs various processes according to the signal. The input interface 1174 may be used by an operator who operates the test apparatus 1 to make various settings related to the test apparatus 1. The various settings include, for example, settings of the carrier frequency fc and the modulation frequency fam.

[0036] The output interface 1175 includes a display device such as a liquid crystal display, an organic electroluminescence display, or the like. The output interface 1175 may be used to display the calculated amplitude and phase values ​​of the return light and / or an image representing them. The output interface 1175 may also include an output device for various information such as a printer instead of or in addition to the display device. Here, the display device or the like of the output interface 1175 does not necessarily need to be provided in the computer 117, and may be an external display device or the like that can communicate with the computer 117.

[0037] Next, a description will be given of the operation of the test apparatus 1. Fig. 4 is a flow chart showing an example of a test method using the test apparatus 1. Here, the following test method will be described taking a continuity test of an interposer as an example.

[0038] In step S1, the computer 117 irradiates the substrate D with laser light. In step S2, the computer 117 assigns 1 to the probe electrode number n. In step S3, the computer 117 sends a control signal to the demultiplexer 113 to select the probe electrode n and apply a test signal to the probe electrode n. In step S4, the computer 117 starts imaging with the camera 115. The pixel signal of each pixel of the camera 115 is subjected to processing for quadrature demodulation in the signal processing unit 116. Thereafter, the processed pixel signal data is stored in, for example, the memory 1172 of the computer 117. The processing of steps S3 and S4 may be performed simultaneously. In step S5, the computer 117 calculates the amplitude and phase of the return light for the image corresponding to the probe electrode number n.

[0039] The processing of steps S1-S5 will be specifically described below. First, computer 117 controls oscillator 110 to start outputting a carrier wave. Amplitude modulator 112 generates a test signal by amplitude modulating the carrier wave with an amplitude modulated wave generated by frequency divider / phase shifter 111. Amplitude modulator 112 also sends a frame rate signal (=4 fam) to camera 115. The test signal generated by amplitude modulator 112 is applied in a non-contact manner to one connection pad provided on the back surface of the interposer via demultiplexer 113 and a probe electrode with probe electrode number n, probe electrode 119 in FIG. 1.

[0040] Laser light emitted from laser device 101 is collimated by collimator lens 102. The light that has passed through collimator lens 102 passes through quarter-wave plate 103 and half-wave plate 104 to become circularly polarized light. This circularly polarized light is separated by entering PBS 105. The polarized light component that has passed through PBS 105 is polarized by quarter-wave plate 106 and half-wave plate 107, and then reflected by mirror 108 to enter EO sensor 109.

[0041] A test signal with a frequency of fc±fam is applied to the substrate D. As a result, an electric field whose intensity varies with the frequency fc±fam is generated on the surface of the substrate D depending on the state of continuity of the substrate D. For example, in a continuity test of an interposer, an electric field whose intensity varies with the frequency fc±fam is generated on the surface pad connected to the pad on the back side of the interposer to which the electric field is applied by the probe electrode, and if there is no continuity, no electric field is generated on the surface pad. Also, if an electric field is observed on a surface pad that is not actually connected to a pad on the back side, it can be determined that the wiring inside the interposer is short-circuited.

[0042] As described above, the EO sensor 109 is disposed near the substrate D so as to change the birefringence at the frequency fc±fam upon receiving an electric field from the substrate D. Therefore, when the reflected light from the mirror 108 enters the EO sensor 109, the reflected light is locally modulated in its polarization state according to the birefringence characteristics of the EO sensor 109. Therefore, the return light from the EO sensor 109 contains light components with frequencies fc±fam in addition to the frequency components of the original laser light.

[0043] The return light from the EO sensor 109 is reflected by the mirror 108. Thereafter, the modulation of the polarization state of the return light is converted to intensity modulation by passing through the half-wave plate 107, the quarter-wave plate 106, and the PBS 105. Then, this return light is imaged on the pixels of the camera 115 via the imaging lens 114. Since the camera 115 captures images at a frame rate equivalent to 4 fam, the camera 115 captures the light of the frequency fam component. The light of the frequency fam component is light that reflects the birefringence characteristics of the EO sensor 109, i.e., the state of the electric field of the substrate D.

[0044] After the camera 115 has completed capturing one frame, the signal processing unit 116 performs, as a process for orthogonal demodulation, a process of multiplying the pixel signal of each pixel of the camera 115 by a cosine component or a pseudo cosine component and then removing high frequency components, and a process of multiplying the pixel signal by a sine component or a pseudo sine component and then removing high frequency components. The signal processing unit 116 transfers the cosine component pixel signals and sine component pixel signals obtained by these processes to the computer 117 in association with the pixel positions. The computer 117 stores the data transferred from the signal processing unit 116 in, for example, the memory 1172.

[0045] Here, the camera 115 captures the return light at a frame rate equivalent to four times the modulation frequency fam. That is, four frames are required to capture one cycle of the return light. After the four frames are captured, the computer 117 calculates the amplitude and phase of the return light for the probe electrode number n from the cosine component pixel signal and the sine component pixel signal obtained by the signal processing unit 116. Specifically, the computer 117 calculates the integral value of each of one cycle of the cosine component pixel signal and the sine component pixel signal. Then, the computer 117 calculates the amplitude A of the return light from the sum of the squares of the integral value of one cycle of the cosine component pixel signal and the integral value of one cycle of the sine component pixel signal based on the following formula (1). The computer 117 also calculates the phase P of the return light from the ratio of the integral value of one cycle of the cosine component pixel signal and the integral value of one cycle of the sine component pixel signal based on the following formula (2). Here, M in formula (1) is the amplitude of the integrated cosine component pixel signal and the sine component pixel signal.

number

[0046] Here, we return to the explanation of FIG. 4. In step S6, the computer 117 adds +1 to the probe electrode number n. In step S7, the computer 117 judges whether the probe electrode number n is nend. nend is a number representing the last probe electrode. In step S7, if the probe electrode number n is not the last probe electrode number nend, the process returns to step S3. In this case, the operations from steps S3 to S5 are performed on the next probe electrode. In step S7, if the probe electrode number n is the last probe electrode number nend, the process ends. At this time, for example, the computer 117 may display the amplitude and phase information as a two-dimensional image on the display device by assigning pixel values ​​according to the magnitude of the amplitude and phase to each of the amplitude and phase calculated for each pixel of the camera 115. As described above, the image representing the amplitude and phase information is an image representing the state of the electric field on the surface of the interposer as the substrate D. The conductive or non-conductive state of the interposer can be grasped from the distribution of the amplitude and phase. Specifically, the computer 117 recognizes in advance the expected positions of the pads on the surface that will be detected when a test signal is applied to each probe electrode from the design data of the interposer. If the positions of high electric fields in an electric field amplitude image of the interposer surface when an electric field is applied to each probe electrode match the expected positions, it is understood that the wiring in the interposer is connected normally. If they do not match the expected positions, it is understood that the wiring in the interposer is disconnected or the wiring in the interposer is short-circuited.

[0047] As described above, in the embodiment, in a test that does not require application of a signal of a specific operating frequency to the board, the laser light is not modulated, and a modulated test signal is applied to the board. By setting the modulation frequency of the test signal at this time to a frequency lower than the frame rate of the camera, the state of the electric field of the board accompanying the application of the test signal can be captured as an image by the camera. In addition, in the embodiment, modulation of the laser light is not required. Therefore, the test device of the embodiment has a simple configuration that does not require an MZM or the like for modulating the laser light. Furthermore, in the embodiment, since modulation of the laser light is not required, there is no loss of power of the laser light due to modulation of the laser light. As a result, the S / N ratio of the image obtained by the camera can be improved.

[0048] In the embodiment, the test signal is applied in a non-contact manner by electrostatic coupling between the substrate and the probe electrode. Therefore, the test can be performed even in a situation where it is difficult to contact the probe electrode due to the small connection pad of the substrate. Furthermore, by using a modulated test signal, the test signal can be applied with low loss by increasing the carrier frequency even if the coupling capacitance between the substrate and the probe electrode is small.

[0049] (Modification) Modifications of the embodiment will be described below. (Variation 1) In the embodiment, the test signal is applied in a non-contact manner using capacitive coupling, but the test signal does not necessarily have to be applied in a non-contact manner.

[0050] (Variation 2) If the size of the substrate is large relative to the size of the EO sensor or if the angle of view of the camera is narrow, the test for the entire area of ​​the substrate cannot be completed in one test. In this case, the test may be performed multiple times by changing the EO sensor and the irradiation position of the laser light.

[0051] (Variation 3) Furthermore, the embodiments do not specifically mention the medium between the probe electrode and the substrate, and between the substrate and the EO sensor. If the test were to be performed in air, air would be present between the probe electrode and the substrate, and between the substrate and the EO sensor. Since the dielectric constant of air is small, if air is present between the probe electrode and the substrate, and between the substrate and the EO sensor, the loss at each location would be large.

[0052] Here, it is known that the coupling loss is inversely proportional to the coupling capacitance. In order to reduce the coupling capacitance between the probe electrode and the substrate and between the substrate and the EO sensor, the space between the probe electrode and the substrate and the space between the substrate and the EO sensor may be filled with a medium having a dielectric constant greater than that of air. Specifically, the space may be filled with a medium having a relative dielectric constant greater than 1. For example, as shown in FIG. 5, the coupling loss can be reduced by performing a test while the substrate is immersed in a medium having a relative dielectric constant greater than 1, such as water 121.

[0053] (Variation 4) In the embodiment, the camera captures images at a frame rate equivalent to 4fam, which is four times the modulation frequency fam. In this case, the camera captures images of 1 / 4 period of the return light in one frame.

[0054] Fig. 6 is a conceptual diagram showing quadrature demodulation of pixel signals of four frames when the phases of the cosine component pixel signal and the sine component pixel signal are shifted from the phase of the test signal. 4m+1, 4m+2, 4m+3, and 4m+4 (m is an integer equal to or greater than 0) in Fig. 6 represent frame numbers. Furthermore, IN in Fig. 6 indicates an example of a pixel signal input to the signal processing unit 116, COS in Fig. 6 indicates an example of a cosine component pixel signal corresponding to IN, and SIN in Fig. 6 indicates an example of a sine component pixel signal corresponding to IN. In practice, the pixel signal, the cosine component pixel signal, and the sine component pixel signal are treated as digital values. Specifically, the digital value of the pixel signal in each frame is the average value of the intensity of light received in the same frame.

[0055] As shown in Figure 6, if the cosine and sine component pixel signals are out of phase with respect to the phase of the test signal, the cosine and sine component pixel signals will not be zero in any of frames 4m+1, 4m+2, 4m+3, and 4m+4. In this case, four frames of imaging are required to demodulate the return light.

[0056] On the other hand, if the phases of the cosine component pixel signal and the sine component pixel signal are not shifted from the phase of the test signal, when the amplitude of one of the cosine component pixel signal and the sine component pixel signal is maximum, the amplitude of the other will be zero. In this case, one of Mcos(2πft) and Msin(2πft) in equation (1) will be zero, so the amplitude of the returning light can be found only from the non-zero one of the cosine component pixel signal and the sine component pixel signal. In such a case, the amplitude of the returning light can be found by imaging two frames instead of four frames.

[0057] Fig. 7 is a conceptual diagram showing orthogonal demodulation of pixel signals of two frames when the phase of the test signal and the phase of the cosine component pixel signal are the same. 2m+1, 2m+2, 2(m+1)+1, and 2(m+1)+2 (m is an integer equal to or greater than 0) in Fig. 7 represent frame numbers. Furthermore, IN in Fig. 7 indicates an example of a pixel signal input to the signal processing unit 116, COS in Fig. 7 indicates an example of a cosine component pixel signal corresponding to IN, and SIN in Fig. 7 indicates an example of a sine component pixel signal corresponding to IN. In practice, the pixel signal, the cosine component pixel signal, and the sine component pixel signal are treated as digital values. Specifically, the digital value of the pixel signal in each frame is the average value of the intensity of light received in the same frame.

[0058] As shown in Figure 7, when the phase of the test signal and the phase of the cosine component pixel signal are the same, the cosine component pixel signal will be the maximum value and the sine component pixel signal will be zero in all frames 2m+1, 2m+2, 2(m+1)+1, and 2(m+1)+2. Therefore, from equation (1), the amplitude A of the returned light is Mcos(2πft). Therefore, the amplitude of the electric field can be calculated by capturing two frames.

[0059] In order to match the phase of the test signal with the phase of the cosine component pixel signal or the sine component pixel signal, it is sufficient to shift the timing at which the camera 115 starts imaging by φ. This φ can be the phase P shown in equation (2). Alternatively, φ can be obtained by repeatedly capturing the above-mentioned four frames of images while shifting the timing at which the camera 115 starts imaging, and finding the shift time at which either the cosine component pixel signal or the sine component pixel signal is maximized. After the value of φ is determined, there is basically no need to adjust φ. This is because a small shift in φ has almost no effect on the results of quadrature demodulation.

[0060] FIG. 8 is a diagram showing an example of the configuration of a test apparatus according to the fourth modification. The configuration of the test apparatus 1 according to the fourth modification is basically the same as the configuration of the test apparatus 1 according to the embodiment shown in FIG. In the fourth modification, the computer 117 notifies the frequency divider / phase shifter 111 of the value of the shift time φ for the timing of starting imaging by the camera 115. The camera 115 of the fourth modification performs imaging at the same frame rate equivalent to 4fam, delayed by φ from the application of the test signal and the irradiation of the laser light. However, since imaging is completed in two frames, the modulation frequency of the test signal applied to the interposer can be improved to 2fam, which is twice that of the embodiment.

[0061] In this way, the amplitude of the return light can be calculated by capturing two frames in Modification 4. This is expected to reduce the test time.

[0062] Here, in the fourth modification, it is not necessary to obtain the amplitude of the return light by orthogonal demodulation. Specifically, the amplitude may be obtained from the difference between pixel signals for two frames, i.e., one period. When such a configuration is adopted, the signal processing unit 116 may include a frame memory 1166 consisting of frame memories A and B that accumulate pixel signals for two frames, and a difference calculation unit 1167 that calculates the difference between the pixel signals accumulated in the frame memory A and the pixel signals accumulated in the frame memory B, as shown in FIG. 9. With such a configuration, the configuration of the signal processing unit 116 can be simplified.

[0063] The present invention is not limited to the above-mentioned embodiment, and various modifications can be made in the implementation stage without departing from the gist of the invention. In addition, the embodiments may be implemented in appropriate combination, and in that case, the combined effect can be obtained. Furthermore, the above-mentioned embodiment includes various inventions, and various inventions can be extracted by combinations selected from the multiple components disclosed. For example, if the problem can be solved and the effect can be obtained even if some components are deleted from all the components shown in the embodiment, the configuration from which the components are deleted can be extracted as an invention. [Explanation of symbols]

[0064] 1 Test equipment, 101 Laser device, 102 Collimator lens, 103 1 / 4 wave plate, 104 1 / 2 wave plate, 104 Polarizing beam splitter (PBS), 106 1 / 4 wave plate, 107 1 / 2 wave plate, 109 Electro-optical (EO) sensor, 110 Oscillator, 111 Divider / phase shifter, 112 Amplitude modulator, 113 Demultiplexer, 114 Imaging lens, 115 Camera, 116 Signal processing unit, 117 Computer, 118, 119, 120 Probe electrode, 121 Water, 1161 Cosine component integrator, 1162 Low-pass filter (LPF), 1163 Sine component integrator, 1164 Low-pass filter (LPF), 1165 Multiplexer, 1171 Processor, 1172 Memory, 1173 storage, 1174 input interface, 1175 output interface.

Claims

1. an electro-optic sensor disposed adjacent to a substrate under test, the electro-optic sensor receiving an electric field from the substrate and changing a birefringence characteristic; a test signal applying unit that applies a modulated test signal to the substrate; a light source that irradiates the electro-optical sensor with illumination light; a camera that receives illumination light from the light source and captures a return light of the illumination light that is emitted from the electro-optical sensor when the test signal is applied to the board; A test apparatus comprising:

2. 2. The test device according to claim 1, wherein the test signal application section generates the test signal by modulating a carrier wave with an amplitude modulated wave having a modulation frequency lower than a frame rate of the camera.

3. 3. The test device according to claim 2, wherein the camera captures the returned light at a frame rate corresponding to a frequency four times the modulation frequency.

4. 3. The test device according to claim 2, wherein the camera captures the return light at a frame rate corresponding to twice the modulation frequency by shifting an image capture start timing by an amount corresponding to a phase of the return light.

5. 2. The test apparatus according to claim 1, wherein the test signal application section is disposed near the substrate and applies the test signal in a non-contact manner from a probe electrode that is electrostatically coupled to the substrate.

6. 2. The test device according to claim 1, wherein a medium having a relative dielectric constant greater than that of air is interposed between the substrate and the electro-optical sensor.

7. 6. The test device according to claim 5, wherein a medium having a relative dielectric constant greater than that of air is interposed between the substrate and the probe electrode.

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