Inspection Equipment

Abstract

This inspection device comprises: a light source that emits light; an optical amplifier that amplifies the inputted light and outputs the resultant light; an optical system (an objective lens, an image-forming optical system, and a scan optical system) that irradiates a semiconductor device with the light from the light source and guides the light from the semiconductor device to the optical amplifier; and an optical detector that detects the light outputted from the optical amplifier. The optical amplifier amplifies the inputted light so as not to be saturated.

Description

[Technical field]

[0001] One aspect of the present invention relates to an inspection apparatus. [Background technology]

[0002] 2. Description of the Related Art There is known an inspection apparatus that performs a failure analysis of a semiconductor device by irradiating a laser beam onto the semiconductor device in operation and detecting the intensity modulation of the reflected light (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2007-64975 A Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, with the improvement of the performance of semiconductor devices, there is a demand for inspection equipment that can detect broadband phenomena including higher frequency bands. Specifically, there is a demand for inspection equipment that can accurately detect minute jitter (e.g., jitter of about 10 ps) in transistors switching at a speed of less than 10 ps.

[0005] One aspect of the present invention has been made in consideration of the above-described circumstances, and has an object to provide an inspection device capable of accurately detecting a wideband phenomenon. [Means for solving the problem]

[0006] An inspection device according to one embodiment of the present invention includes a light source that generates light, an optical amplifier that amplifies and outputs the input light, an optical system that irradiates a semiconductor device with light from the light source and guides the light from the semiconductor device to the optical amplifier, and a photodetector that detects the light output from the optical amplifier, and the optical amplifier amplifies the input light so as not to saturate it.

[0007] In the inspection device according to one aspect of the present invention, light from a semiconductor device is input to an optical amplifier, the light is amplified and output within a range that does not cause saturation in the optical amplifier, and the light output from the optical amplifier is detected by a photodetector. Usually, the amount of light irradiated to a semiconductor device is reduced to a degree that does not destroy the semiconductor device. Therefore, the amount of light returned from the semiconductor device is also reduced, but when the amount of light returned is small, there is a risk that the detection accuracy will decrease due to the influence of noise (thermal noise) in the detection system. For this reason, a photodetector having a multiplication layer that amplifies the returned light has been used as a photodetector in the past. However, a photodetector having a multiplication layer has a relatively large capacity, and is therefore not suitable for measuring high-speed signals (detecting phenomena in a high frequency band). In this regard, in the inspection device according to one aspect of the present invention, as described above, an optical amplifier is provided separately from the optical detector, and the light amplified in the optical amplifier is detected by the optical detector, so that the amplification of the signal to ensure the detection accuracy is performed by the optical amplifier, and the detection of the amplified light can be performed by the optical detector. In such a configuration, a photodetector having no multiplication layer and a relatively small capacity can be used as the photodetector, so that a phenomenon in a high frequency band can be detected. In addition, in the inspection device according to one aspect of the present invention, the light is amplified by the optical amplifier within a range that does not cause saturation. In the case of saturation, a small signal contained in the input light disappears after amplification, and the small signal may not be detected properly. In this respect, by amplifying the light within a range that does not cause saturation, even a small phenomenon can be accurately detected based on the output light containing a small signal. As described above, the inspection device according to one aspect of the present invention can accurately detect a wide band phenomenon including a high frequency band.

[0008] The optical amplifier may amplify the input light so that the change in the amount of output light with respect to the amount of input light is linear. In this way, the input light and the output light have a linear relationship, so that the phenomenon related to the return light from the semiconductor device can be accurately detected.

[0009] The optical amplifier may amplify the input light so that the amount of output light is greater than half the maximum amount of light that can be output. This allows the amplification rate to be sufficiently large while avoiding saturation, and ensures the accuracy of phenomenon detection.

[0010] The optical amplifier may amplify the input light so that the shot noise contained in the output light exceeds the thermal noise of the photodetector. In this way, by amplifying the light so that the noise contained in the light is greater than the noise associated with the photodetector, the noise contained in the light (shot noise and relative intensity noise) becomes dominant, and it is possible to prevent the detection accuracy from being deteriorated due to the influence of the noise associated with the photodetector (thermal noise).

[0011] The optical amplifier may have an amplifying element with a length that satisfies the condition for amplifying the input light without saturating it, thereby making it possible to appropriately amplify the input light under the condition set so as not to cause saturation.

[0012] The optical amplifier may be a semiconductor amplifier, an optical fiber amplifier, or a tapered amplifier, which allows the optical amplification to be appropriately performed within the above-mentioned non-saturation range.

[0013] The photodetector may be a PIN photodiode. In this way, a PIN photodiode having a relatively small capacitance is used as the photodetector, making it possible to detect a phenomenon in a high frequency band.

[0014] The photodetector may be configured to detect light in a frequency band of 8 GHz or higher, thereby making it possible to detect phenomena in high frequency bands. Effect of the Invention

[0015] According to one aspect of the present invention, it is possible to provide an inspection device capable of accurately detecting a broadband phenomenon. [Brief description of the drawings]

[0016] [Figure 1] 1 is a configuration diagram of an inspection device according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a configuration diagram of an optical measurement unit included in the inspection device of FIG. [Diagram 3] FIG. 2 is a diagram showing input / output characteristics of an optical amplifier. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and duplicated explanations will be omitted.

[0018] [First embodiment] As shown in Fig. 1, the inspection apparatus 1 according to the first embodiment is an apparatus for inspecting a semiconductor device D, which is a measurement target and a device under test (DUT), such as identifying an abnormality location in the semiconductor device D. More specifically, the inspection apparatus 1 identifies a fault location by an optical probing technique called EOP or EOFM. The semiconductor device D may be an integrated circuit (IC) having a PN junction such as a transistor, a logic device which is a large scale integrated circuit (LSI), a memory device, an analog device, or a mixed signal device which is a combination of these, or a power semiconductor device (power device) such as a high current / high voltage MOS transistor, a bipolar transistor, or an IGBT.

[0019] The inspection device 1 includes a tester head 2, a test board 3, a stage 5, an objective lens 6, a turret 7, an imaging optical system 8, a scanning optical system 9, a scanning unit 11, an optical measurement section 12, a digitizing unit 13, a control device 14, and an input / output device 15. The stage 5, the objective lens 6, the turret 7, the imaging optical system 8, and the scanning optical system 9 are housed in a dark box 4. The stage 5 is a platform that holds each component housed in the dark box 4.

[0020] The tester head 2 mounts a semiconductor device D via a test board 3 and repeatedly applies a predetermined operating pulse signal to the semiconductor device D. The semiconductor device D is driven by the test signal. The tester head 2 has, for example, a pulse generator that generates an operating pulse signal for driving the semiconductor device D, a tester section that inputs the operating pulse signal to the semiconductor device D, and a power supply. The test board 3 is a semiconductor substrate on which the semiconductor device D is mounted. The test board 3 has peripheral chips, circuits, terminals, etc. required for the operation of the semiconductor device D.

[0021] The scanning optical system 9 receives light emitted from a light source 121 (see FIG. 2) of the optical measurement unit 12 via the optical fiber 10, and guides the light to the imaging optical system 8. In detail, the light from the light source 121 passes through an optical coupler 122 (see FIG. 2) and is guided to the scanning optical system 9 by the optical fiber 10. The fiber end of the optical fiber 10 may be, for example, an APC type in order to reduce reflected light. The scanning optical system 9 has an optical scanner including an optical scanning element such as a galvanometer mirror or a MEMS (micro electro mechanical system) mirror. The scanning optical system 9 irradiates (scans) a selected area on the semiconductor device D with the light emitted from the light source 121 of the optical measurement unit 12. The selected area is a spot or area selected by a user. The scanning unit 11 controls the scanning optical system 9 under the control of the control device 14 so that the light is irradiated to a spot in the selected area.

[0022] The imaging optical system 8 receives light emitted from the light source 121 of the optical measurement unit 12 via the scanning optical system 9, and guides the light to the objective lens 6. The objective lens 6 is a lens that focuses the light from the light source 121 of the optical measurement unit 12 onto the semiconductor device D. The objective lens 6 is configured to be switchable between a low-magnification objective lens (e.g., 5x) and a high-magnification objective lens (e.g., 50x) by the turret 7. The reflected light (return light) from the semiconductor device D is input to the optical measurement unit 12 via the objective lens 6, the imaging optical system 8, the scanning optical system 9, and the optical fiber 10. In this way, the objective lens 6, the imaging optical system 8, and the scanning optical system 9 are optical systems that irradiate the light from the light source 121 of the optical measurement unit 12 onto the semiconductor device D, and guide the reflected light (return light) from the semiconductor device D to the optical amplifier 123 (see FIG. 2) of the optical measurement unit 12.

[0023] As shown in FIG. 2, the optical measurement unit 12 includes a light source 121, an optical coupler 122, an optical amplifier 123, a photodetector 124, and a high-frequency amplifier 125.

[0024] The light source 121 is operated by a power source (not shown) and generates and outputs light to be irradiated onto the semiconductor device D. The light may be coherent or incoherent. For example, a super luminescent diode (SLD), an amplified spontaneous emission (ASE) light source, or a light emitting diode (LED) may be used as the light source 121. The light output from the light source 121 is guided to the scanning optical system 9 via an optical coupler 122 and an optical fiber 10. The optical coupler 122 is a polarizing beam splitter (PBS) type optical coupler or a circulator type optical coupler. When the optical coupler 122 is a PBS type optical coupler, a λ / 4 wave plate may be provided inside the scanning optical system 9. When the optical coupler 122 is a circulator type optical coupler, a λ / 2 wave plate may be provided inside the scanning optical system 9. An optical splitter may be used instead of the optical coupler 122. Moreover, inside the scanning optical system 9, a Faraday rotator may be provided in place of the above-mentioned wave plate.

[0025] The optical amplifier 123 receives reflected light (return light) from the semiconductor device D via the optical fiber 10 and the optical coupler 122, amplifies the intensity of the reflected light (input light), and outputs the amplified light. The optical amplifier 123 is, for example, a semiconductor amplifier, an optical fiber amplifier (optical fiber amplifier), a SOA (Solid Optical Amplifier), a tapered amplifier (tapered amplifier), a booster optical amplifier, or the like. The optical amplifier 123 may also be an amplifier that uses a crystal, gas, liquid, or the like as a laser medium. The output light output by the optical amplifier 123 is input to the photodetector 124 via the optical fiber 10.

[0026] FIG. 3 is a diagram showing the input / output characteristics of the optical amplifier 123. In FIG. 3, the horizontal axis indicates the amount of light input to the optical amplifier 123, and the vertical axis indicates the amount of light output from the optical amplifier 123. The gain of the optical amplifier 123 is set to a specific value for each wavelength according to the characteristics of the element (optical amplifier). In addition, an upper limit of the intensity of light that can be output from the optical amplifier 123 is also set. Therefore, when the intensity of the input light to the optical amplifier 123 becomes greater than a certain value, the optical amplification is suppressed, and the optical amplifier 123 is no longer able to amplify light according to the set gain. In this case, even if the intensity of the input light to the optical amplifier 123 becomes greater, the intensity of the amplified light becomes constant, and the optical amplification characteristics of the optical amplifier 123 become nonlinear. The state in which the optical amplification characteristics of the optical amplifier 123 are nonlinear in this way is the state in which the optical amplifier 123 is gain saturated. The optical amplifier 123 being gain saturated at a certain wavelength means that all the charges that can contribute to the amplification of light at that wavelength are used up, and the optical amplification is suppressed.

[0027] The input light 1 in FIG. 3 is light with an intensity that does not saturate the optical amplifier 123. The input light 2 in FIG. 3 is light with an intensity that saturates the optical amplifier 123. When the input light 1 is input to the optical amplifier 123, the optical amplification characteristic of the optical amplifier 123 becomes linear, and the input light 1 is linearly amplified. In this case, as shown in FIG. 3, the small signal contained in the input light 1 (the part shown in FIG. 3 as the range of "amplitude") is also linearly amplified. In this case, the output light contains ASE light (spontaneous emission light), so noise increases slightly. On the other hand, when the input light 2 is input to the optical amplifier 123, the optical amplifier 123 becomes gain saturated, so the optical amplification characteristic of the optical amplifier 123 becomes nonlinear, and the input light 2 is output at the output limit of the optical amplifier 123. In this case, as shown in FIG. 3, the small signal (small fluctuation) contained in the input light 2 is compressed and disappears.

[0028] The amplification factor of an optical amplifier depends on the density of excited electrons and the length of the optical amplifier. Since ground-state electrons absorb light, the above-mentioned excited electron density is, in detail, the density of excited-state electrons minus the density of ground-state electrons. The longer the optical amplifier is, the more collisions between excited-state electrons and photons occur, and the greater the amplification factor becomes.

[0029] An optical amplifier becomes saturated when the density of excited state electrons near the output of the optical amplifier becomes lower than the density of ground state electrons as a result of excited state electrons being used for amplification. The maximum output of the amplified light depends on the density of excited electrons, which in the case of an optical fiber amplifier depends on the intensity of the pump light, and in the case of an SOA depends on the intensity of the supplied electric current (excitation current). In an optical amplifier, the density of excited electrons can be increased and the amplification rate can be raised by increasing the pump light or pump current.

[0030] Here, when the pumping light or pumping current for the optical amplifier is increased, the density of pumped electrons and the maximum output also increase. That is, when the density of pumped electrons is changed by changing the pumping light or the like to change the amplification factor, the maximum output also changes at the same time. For this reason, the saturated / non-saturated state of light cannot be appropriately switched by only changing the pumping light or the like. Therefore, in order to prevent the output light from being saturated, an amplifying element having an appropriate gain for the input light, that is, an amplifying element having an appropriate amplification length, may be used. Note that the configuration in which the output light is not saturated can also be achieved by attenuating the input light, but since this deteriorates the S / N ratio, the amplification length of the amplifying element may be appropriately designed as described above.

[0031] As described above, when the input light is amplified so as not to cause saturation, minute noise is superimposed on the output light after amplification. This is called the noise floor, and although it depends on the amplification method, it is, for example, about 5 to 10 dB. The gain of the optical amplifier 123 is set to at least exceed this.

[0032] The optical amplifier 123 amplifies the input reflected light so as not to saturate the reflected light. That is, the optical amplifier 123 amplifies the reflected light within a range that does not saturate the optical amplifier 123 and does not saturate the photodetector. The optical amplifier 123 amplifies the input light so that the change in the amount of output light relative to the amount of input reflected light becomes linear. For example, the optical amplifier 123 may amplify the input light so that the amount of output light becomes greater than half the maximum amount of light that can be output. Also, for example, the optical amplifier 123 may amplify the input light so that the shot noise contained in the output light exceeds the thermal noise of the photodetector 124. The optical amplifier 123 has an amplifying element with a length that satisfies the condition for amplifying the input light so as not to saturate it, as described above.

[0033] The photodetector 124 is an optical sensor that detects the light output from the optical amplifier 123. The photodetector 124 is an optical sensor that detects high-speed optical signals, and is configured to be able to detect light in a band of 8 GHz or more, for example. The photodetector 124 is, for example, a PIN photodiode. When an optical sensor (for example, a PIN photodiode) that can detect high-speed optical signals is used, the input is made to a single mode fiber, so the optical fiber 10 for input and the optical coupler 122, etc. may all be configured as a combination of single mode fibers, but may also be configured as an optical system combining a half mirror, a polarizing beam splitter, and a collimator. The photodetector 124 may be, for example, an avalanche photodiode, a photomultiplier tube, an area image sensor, or the like configured to be able to detect a wide band signal of 8 GHz or more. The photodetector 124 outputs a detection signal (electrical signal). The detection signal output by the photodetector 124 is input to the high-frequency amplifier 125 via the high-frequency cable 16. The high-frequency amplifier 125 amplifies the detection signal input from the photodetector 124 and outputs it as an amplified signal.

[0034] Returning to Fig. 1, digitizing unit 13 converts the amplified signal input from high frequency amplifier 125 into a waveform and outputs the waveform. Digitizing unit 13 is composed of, for example, a digitizer, an oscilloscope, an FPGA, etc. The waveform signal output from digitizing unit 13 is input to control device 14.

[0035] The control device 14 is a device that controls the scan unit 11 and the digitizing unit 13. The control device 14 generates a waveform (analysis image) based on the waveform signal obtained from the digitizing unit 13, and inputs the analysis image to the input / output device 15. The input / output device 15 has input devices such as a keyboard and a mouse into which the user inputs measurement conditions and the like, and a display device such as a monitor for showing the user the measurement results and the like. The input / output device 15 displays the analysis image input from the control device 14. From the analysis image, it is possible to measure jitter and check the switching image (waveform), and identify the location of a fault, etc.

[0036] Next, the effects of the inspection device 1 according to this embodiment will be described.

[0037] First, the configuration of the inspection device according to the comparative example and the problems associated with the configuration will be described. The reflectance of light of an active device on a semiconductor device such as an LSI, for example, a transistor, is not large, being about 10% or less. If strong light is applied to such a semiconductor device, the device such as a transistor may be destroyed by the incident light. For this reason, the amount of light irradiated onto the semiconductor device is made small enough to prevent the semiconductor device from being destroyed. For example, when a solid immersion lens that realizes a numerical aperture of 1 or more is used, the amount of light irradiated is set to an upper limit of several mW, and the upper limit of the reflected light (return light) in that case is about 0.1 mW. For ideal measurement, the shot noise of light may be made larger than the thermal noise of a measuring instrument (more specifically, a photodetector, etc.). In the inspection device (general inspection device) according to the comparative example, a photodetector (for example, a photodetector such as an APD) having a multiplication layer that amplifies the return light is adopted in order to make the shot noise larger than the thermal noise in a configuration in which the amount of return light is small as described above. By using such a photodetector, the shot noise can be made larger than the thermal noise, and highly accurate inspection can be performed.

[0038] Here, in recent years, with the improvement of the performance of semiconductor devices, there is a demand for an inspection device capable of detecting a wideband phenomenon including a higher frequency band. Specifically, for example, there is a demand for an inspection device capable of accurately detecting minute jitter (for example, jitter of about 10 ps). In this regard, in an inspection device having a photodetector according to the above-mentioned comparative example, the capacity of the photodetector is relatively large, so that high-speed signal detection (detection of a phenomenon in a high frequency band) cannot be performed. Specifically, a photodetector according to the comparative example (for example, an APD) has a multiplication layer between a P layer and an N layer, and a strong electric field is applied to the multiplication layer. In a photodetector having a multiplication layer to which a strong electric field is applied, the capacity becomes relatively large, so that high-speed signal detection (detection of a phenomenon in a high frequency band) cannot be performed.

[0039] To solve such problems, the inspection device 1 of this embodiment includes a light source 121 that generates light, an optical amplifier 123 that amplifies and outputs the input light, an optical system (objective lens 6, imaging optical system 8, and scanning optical system 9) that irradiates the light from the light source 121 onto a semiconductor device D and guides the light from the semiconductor device D to the optical amplifier 123, and a photodetector 124 that detects the light output from the optical amplifier 123, and the optical amplifier 123 amplifies the input light so as not to saturate it.

[0040] In the inspection device 1 according to the present embodiment, an optical amplifier 123 is provided in addition to the photodetector 124, and the light amplified by the optical amplifier 123 is detected by the photodetector 124. Therefore, the signal amplification for ensuring the detection accuracy is performed by the optical amplifier 123, and the amplified light can be detected by the photodetector 124. In such a configuration, a photodetector (e.g., a PIN photodiode) having a relatively small capacity without a multiplication layer can be used as the photodetector 124, so that a phenomenon in a high frequency band (e.g., a band of about 20 GHz, exceeding 10 GHz) can be detected. In addition, in the inspection device 1 according to the present embodiment, the light is amplified by the optical amplifier 123 within a range that does not cause saturation. In the case of saturation, a minute signal contained in the input light disappears after amplification, and the minute signal may not be detected appropriately. In this regard, by amplifying the light within a range that does not cause saturation, it is possible to accurately detect even a minute phenomenon (e.g., jitter, etc.) based on the output light containing a minute signal. As described above, according to the inspection device 1 according to the present embodiment, a wide band phenomenon including a high frequency band can be accurately detected.

[0041] The optical amplifier 123 may amplify the input light so that the change in the amount of output light with respect to the amount of input light is linear. In this way, the input light and the output light have a linear relationship, so that the phenomenon related to the return light from the semiconductor device D can be accurately detected.

[0042] The optical amplifier 123 may amplify the input light so that the amount of output light is greater than half the maximum amount of light that can be output. This allows the amplification rate to be sufficiently large while preventing saturation, and ensures the accuracy of phenomenon detection.

[0043] The optical amplifier 123 may amplify the input light so that the shot noise contained in the output light exceeds the thermal noise of the photodetector 124. In this way, by amplifying the light so that the noise contained in the light becomes larger than the noise related to the photodetector 124, it is possible to prevent the noise contained in the light (shot noise and relative intensity noise) from becoming dominant and the detection accuracy from being deteriorated due to the influence of the noise related to the photodetector 124 (thermal noise).

[0044] The optical amplifier 123 may have an amplifying element with a length that satisfies the condition for amplifying the input light without saturating it, thereby making it possible to appropriately amplify the input light under the condition set so as not to cause saturation.

[0045] The optical amplifier 123 may be a semiconductor amplifier, an optical fiber amplifier, or a tapered amplifier, which can appropriately amplify light within the above-mentioned non-saturation range.

[0046] The photodetector 124 may be a PIN photodiode. In this way, by using a PIN photodiode with a relatively small capacitance as the photodetector, it is possible to detect phenomena in a high frequency band.

[0047] The photodetector 124 may be configured to be capable of detecting light in a band of 8 GHz or higher, thereby making it possible to detect phenomena in high frequency bands. [Explanation of symbols]

[0048] 1... inspection device, 6... objective lens (optical system), 8... imaging optical system (optical system), 9... scanning optical system (optical system), 121... light source, 123... optical amplifier, 124... photodetector.

Claims

1. A light source that generates light; an optical amplifier that amplifies and outputs input light; an optical system that irradiates a semiconductor device with light from the light source and guides the light from the semiconductor device to the optical amplifier; a photodetector for detecting light output from the optical amplifier; The optical amplifier amplifies the input light so as not to saturate the light, The optical amplifier amplifies the input light so that shot noise contained in the output light exceeds thermal noise of the photodetector.

2. 2. The inspection device according to claim 1, wherein the optical amplifier amplifies the input light so that a change in the amount of output light relative to the amount of input light becomes linear.

3. 3. The inspection device according to claim 1, wherein the optical amplifier amplifies the input light so that the amount of output light is greater than half the maximum amount of light that can be output.

4. 4. The inspection device according to claim 1, wherein said optical amplifier has an amplifying element having a length that satisfies a condition for amplifying said input light without saturating said light.

5. 5. The inspection device according to claim 1, wherein the optical amplifier is a semiconductor amplifier, an optical fiber amplifier, or a tapered amplifier.

6. 6. The inspection device according to claim 1, wherein the photodetector is a PIN photodiode.

7. 7. The inspection device according to claim 1, wherein the photodetector is configured to be capable of detecting light in a band of 8 GHz or higher.

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