Inspection device

Abstract

The inspection apparatus of the present application includes: a light source that generates light; a light amplifier that amplifies input light and outputs the light; an optical system (an objective lens, an imaging optical system, and a scanning optical system) that irradiates light from the light source to a semiconductor device and guides light from the semiconductor device to the light amplifier; and a light detector that detects light output from the light amplifier, the light amplifier amplifying input light in an unsaturated manner.

Description

Technical Field

[0001] One aspect of the present invention relates to an inspection device. Background Technology

[0002] There is a known inspection device that irradiates a driven semiconductor device with laser light and detects the intensity modulation of the reflected light, thereby performing fault analysis on the semiconductor device (see, for example, Patent Document 1).

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2007-64975 Summary of the Invention

[0006] The problem the invention aims to solve

[0007] In recent years, with the improvement of semiconductor device performance, there has been a demand for an inspection device capable of detecting broadband phenomena involving higher frequency bands. Specifically, for example, there is a demand for an inspection device capable of accurately detecting minute jitter (e.g., jitter of about 10 ps) in transistors that switch at speeds below 10 ps.

[0008] One aspect of the present invention is made in view of the above-mentioned actual situation, and the object is to provide an inspection device that can accurately detect broadband phenomena.

[0009] Technical means to solve the problem

[0010] An inspection apparatus according to one aspect of the present invention comprises: 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 light from the semiconductor device to the optical amplifier; and a photodetector that detects light output from the optical amplifier, wherein the optical amplifier amplifies the input light in an unsaturated manner.

[0011] In one aspect of the inspection apparatus of the present invention, light from a semiconductor device is input to an optical amplifier, which amplifies and outputs the light within an unsaturated range, and the light output from the optical amplifier is detected in a photodetector. Typically, the amount of light irradiating the semiconductor device is reduced to a level that does not damage the semiconductor device. Therefore, although the amount of light returning from the semiconductor device is also reduced, there is a concern that the detection accuracy may be reduced due to the noise (thermal noise) of the detection system when the amount of returning light is small. Therefore, conventionally, photodetectors with a multiplication layer that amplifies the returning light have been used as photodetectors. However, with photodetectors having a multiplication layer, the capacitance becomes relatively large, making them unsuitable for measuring high-speed signals (detecting high-frequency phenomena). In this respect, in one aspect of the inspection apparatus of the present invention, as described above, since the optical amplifier is provided separately from the photodetector, and the light amplified by the optical amplifier is detected in the photodetector, the signal amplification to ensure detection accuracy can be performed by the optical amplifier, and the amplified light can be detected by the photodetector. In this configuration, since a photodetector with a relatively small capacitance and no multiplication layer can be used as the photodetector, high-frequency phenomena can be detected. Furthermore, in one aspect of the inspection apparatus of the present invention, light is amplified by an optical amplifier within an unsaturated range. In a saturated state, the minute signals contained in the input light disappear after amplification, raising concerns about the inability to properly detect these minute signals. In this respect, by amplifying light within an unsaturated range, minute phenomena can be accurately detected based on the output light containing the minute signals. As described above, an inspection apparatus according to one aspect of the present invention can accurately detect broadband phenomena including high-frequency bands.

[0012] An optical amplifier can also amplify the input light by making the change in the output light intensity linear with respect to the input light intensity. Because of this linear relationship between the input and output light, the phenomenon of reflected light from semiconductor devices can be accurately detected.

[0013] An optical amplifier can also amplify the input light by increasing the output light intensity to more than half of the maximum output light intensity. This allows for both preventing saturation and maximizing the amplification, thus ensuring the accuracy of phenomenon detection.

[0014] An optical amplifier can also amplify the input light in such a way that the shot noise contained in the output light exceeds the thermal noise of the photodetector. In this way, by amplifying the light in a manner that makes the noise contained in the light greater than the noise of the photodetector, the noise contained in the light (shot noise or relative intensity noise) becomes dominant, thereby preventing the detection accuracy from being degraded by the noise (thermal noise) of the photodetector.

[0015] An optical amplifier can also have an amplifying element of a length that satisfies the condition of amplifying the input light in an unsaturated manner. Thus, the input light can be appropriately amplified under the condition of being set in an unsaturated manner.

[0016] The optical amplifier can also be a semiconductor amplifier, a fiber optic amplifier, or a cone amplifier. Therefore, it is possible to appropriately amplify light within the aforementioned unsaturated range.

[0017] A photodetector can also be a PIN photodiode. Thus, by using a PIN photodiode with relatively small capacitance as a photodetector, high-frequency phenomena can be detected.

[0018] Photodetectors can also be configured to detect light in frequency bands above 8 GHz. This allows for the detection of high-frequency phenomena.

[0019] The effects of the invention

[0020] According to one aspect of the present invention, an inspection device capable of accurately detecting broadband phenomena can be provided. Attached Figure Description

[0021] Figure 1 This is a structural diagram of an inspection device according to an embodiment of the present invention.

[0022] Figure 2 yes Figure 1 The diagram shows the configuration of the optical measurement unit included in the inspection device.

[0023] Figure 3 This is a graph showing the input and output characteristics of the optical amplifier. Detailed Implementation

[0024] Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Furthermore, identical or equivalent parts are labeled with the same symbols in the various figures, and repeated descriptions are omitted.

[0025] [First Implementation]

[0026] like Figure 1As shown, the inspection device 1 of the first embodiment is a device used to inspect a semiconductor device D, specifically the object being measured and the device under test (DUT), i.e., the location of an abnormality in the semiconductor device D. More specifically, the inspection device 1 determines the location of the fault using a photodetector technique called EOP (Electro Optical Probing) or EOFM (Electro Optical Frequency Mapping). The semiconductor device D can be an integrated circuit (IC) with PN junctions such as transistors, or a large-scale integrated circuit (LSI), i.e., a logic device, a memory device, an analog device, or a mixed-signal device combining these, or a power semiconductor device (power device) such as a high-current / high-voltage MOS (Metal Oxide Semiconductor) transistor, a bipolar transistor, or an IGBT (Insulated Gate Bipolar Transistor).

[0027] The inspection device 1 includes a test head 2, a test plate 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, a light measurement unit 12, a digitization unit 13, a control device 14, and an input / output device 15. The stage 5, objective lens 6, turret 7, imaging optical system 8, and scanning optical system 9 are housed in a dark box 4. The stage 5 serves to hold all the components housed within the dark box 4.

[0028] Test head 2 mounts semiconductor device D via test board 3 and repeatedly applies specific operating pulse signals to semiconductor device D. Semiconductor device D is driven by these test signals. Test head 2 includes, for example, a pulse generator for generating operating pulse signals to drive semiconductor device D, a test unit for inputting operating pulse signals to semiconductor device D, and a power supply. Test board 3 is a semiconductor substrate on which semiconductor device D is mounted. Test board 3 includes peripheral chips, circuits, and terminals required for the operation of semiconductor device D.

[0029] The scanning optical system 9 receives the light source 121 (reference) from the optical measurement unit 12 via the optical fiber 10. Figure 2 The light emitted from the light source 121 is guided to the imaging optical system 8. Specifically, the light from the light source 121 passes through the optical coupler 122 (see reference 8). Figure 2The light emitted from the light source 121 of the light measurement unit 12 illuminates (scans) a selected area on the semiconductor device D. This selected area is a point or region selected by the user. The scanning unit 11 controls the scanning optical system 9 based on the control device 14, ensuring that the light illuminates the selected area. The light emitted from the light source 121 of the light measurement unit 12 illuminates (scans) the selected area.

[0030] The imaging optical system 8 receives light emitted from the light source 121 of the light 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 light measurement unit 12 onto the semiconductor device D. The objective lens 6 is configured to allow switching between a low-magnification objective lens (e.g., 5x) and a high-magnification objective lens (e.g., 50x) via the turret 7. The reflected light (return light) from the semiconductor device D is input to the light measurement unit 12 via the objective lens 6, the imaging optical system 8, the scanning optical system 9, and the optical fiber 10. Thus, the objective lens 6, the imaging optical system 8, and the scanning optical system 9 illuminate the semiconductor device D with the light from the light source 121 of the light measurement unit 12, and guide the reflected light (return light) from the semiconductor device D to the optical amplifier 123 of the light measurement unit 12 (see reference). Figure 2 ) optical system.

[0031] like Figure 2 As shown, 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.

[0032] Light source 121 operates via a power supply (not shown), generating and outputting light that illuminates semiconductor device D. This light can be coherent or incoherent. For example, an SLD (Super Luminescent Diode), ASE (Amplified Spontaneous Emission), or LED (Light Emitting Diode) light source can be used as light source 121. The light output from light source 121 is guided to scanning optical system 9 via optical coupler 122 and optical fiber 10. Optical coupler 122 is a PBS (Polarizing Beam Splitter) type optical coupler or a circulator type optical coupler. If optical coupler 122 is a PBS type optical coupler, a λ / 4 waveplate can be installed inside scanning optical system 9. Alternatively, if optical coupler 122 is a circulator type optical coupler, a λ / 2 waveplate can be installed inside scanning optical system 9. Alternatively, an optical splitter can be used instead of optical coupler 122. Alternatively, a Faraday rotator can be installed inside the scanning optical system 9 instead of the waveplate described above.

[0033] Optical amplifier 123 receives reflected light (return light) from semiconductor device D via optical fiber 10 and optical coupler 122, amplifies the intensity of the reflected light (input light), and outputs amplified light. Optical amplifier 123 can be, for example, a semiconductor amplifier, fiber optic amplifier, SOA (Solid Optical Amplifier), tapered amplifier, auxiliary optical amplifier, etc. Alternatively, optical amplifier 123 can also be an amplifier using crystals, gases, liquids, or other materials as the laser medium. The output light from optical amplifier 123 is input to photodetector 124 via optical fiber 10.

[0034] Figure 3 This is a graph showing the input and output characteristics of the optical amplifier 123. Figure 3In the diagram, the horizontal axis represents the input light quantity to the optical amplifier 123, and the vertical axis represents the output light quantity from the optical amplifier 123. The gain of the optical amplifier 123 is determined to a specific value per wavelength based on the characteristics of the component (optical amplifier). Furthermore, the upper limit of the light intensity that can be output from the optical amplifier 123 is also determined. Therefore, when the intensity of the input light to the optical amplifier 123 exceeds a certain value, optical amplification is suppressed, and the light cannot be amplified according to the determined gain. In this case, even if the intensity of the input light to the optical amplifier 123 increases, the intensity of the amplified light remains constant, and the optical amplification characteristic of the optical amplifier 123 becomes non-linear. Thus, the state in which the optical amplification characteristic of the optical amplifier 123 becomes non-linear is called the state in which the optical amplifier 123 becomes gain saturated. The so-called gain saturation of the optical amplifier 123 at a certain wavelength means that at that wavelength, all the charge that could contribute to light amplification is used up, thus suppressing light amplification.

[0035] Figure 3 The input light 1 is light of unsaturated intensity from the optical amplifier 123. Figure 3 The input light 2 is light of saturated intensity to 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, thus linearly amplifying the input light 1. In this case, as... Figure 3 As shown, the input light 1 contains a tiny signal ( Figure 3 The portion showing the range of "amplitude" is also linearly amplified. Since the output light at this time contains ASE light (naturally emitted light), the noise increases slightly. On the other hand, when input light 2 is input to optical amplifier 123, since optical amplifier 123 becomes gain saturated, the optical amplification characteristics of optical amplifier 123 become nonlinear, and optical amplifier 123 outputs input light 2 at its output limit. In this case, as... Figure 3 As shown, the tiny signal (tiny fluctuations) contained in the input light 2 is compressed and disappears.

[0036] The amplification of an optical amplifier depends on the excited electron density and the length of the amplifier. Since electrons in the ground state absorb light, the aforementioned excited electron density specifically refers to the electron density in the excited state minus the electron density in the substrate state. The longer the optical amplifier, the more collisions occur between excited electrons and photons, resulting in a greater amplification.

[0037] The so-called saturation of an optical amplifier is equivalent to the amplification and utilization of excited electrons. As a result, near the output of the optical amplifier, the density of excited electrons is lower than the density of ground-state electrons. The maximum output of the amplified light depends on the excited electron density; for an optical fiber amplifier, it depends on the intensity of the excitation light, and for an SOA, it depends on the intensity of the supplied current (excitation current). In an optical amplifier, by increasing the excitation light or excitation current, the density of excited electrons can be increased, thereby improving the amplification.

[0038] Here, increasing the excitation light or excitation current of the optical amplifier increases the maximum output simultaneously with the density of excited electrons. That is, when the amplification changes due to variations in the density of excited electrons caused by changes in the excitation light, the maximum output also changes simultaneously. Therefore, simply changing the excitation light is insufficient to properly switch between saturated and unsaturated states of the light. Therefore, to prevent output light saturation, an amplification element with appropriate gain for the input light, i.e., an amplification element with an appropriate amplification length, can be used. Furthermore, attenuating the input light can also prevent output light saturation, but since this degrades the signal-to-noise ratio (S / N), the amplification length of the amplification element can be appropriately designed as described above.

[0039] As described above, when the input light is amplified in an unsaturated manner, a small amount of noise will be superimposed on the amplified input light. This is called the noise floor, and although it depends on the amplification method, it is, for example, around 5 to 10 dB. The gain of the optical amplifier 123 is set to be at least greater than its gain.

[0040] The optical amplifier 123 amplifies the input reflected light in an unsaturated manner. That is, the optical amplifier 123 amplifies the reflected light within a range where it is unsaturated and does not saturate the photodetector. The optical amplifier 123 amplifies the input light in a manner that makes the change in the amount of output light relative to the amount of input reflected light linear. For example, the optical amplifier 123 amplifies the input light in a way that the amount of output light is greater than half of the maximum output light amount. Additionally, for example, the optical amplifier 123 may amplify the input light in a way that the shot noise contained in the output light exceeds the thermal noise of the photodetector 124. Furthermore, the optical amplifier 123 has an amplifying element of a length that satisfies the condition of amplifying the input light in an unsaturated manner as described above.

[0041] The photodetector 124 is an optical sensor that detects the light output from the optical amplifier 123. The photodetector 124 is a high-speed optical signal detection sensor, specifically configured to detect light in frequency bands, for example, 8 GHz and above. The photodetector 124 is, for example, a PIN photodiode. When using an optical sensor capable of detecting high-speed optical signals (e.g., a PIN photodiode), the incident fiber 10 and optical coupler 122, etc., can be constructed from a combination of single-mode fibers to serve as the input to the single-mode fiber. Alternatively, they can be constructed from an optical system consisting of a semi-reflective mirror, a polarizing beam splitter, or a collimator. Furthermore, the photodetector 124 can also be configured to detect broadband signals, such as those above 8 GHz, such as an avalanche photodiode, a photomultiplier tube, or a region imaging sensor. 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 a 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.

[0042] Return to Figure 1 The digitization unit 13 waveforms the amplified signal input from the high-frequency amplifier 125 and outputs it. The digitization unit 13 is constructed using, for example, a digitizer, an oscilloscope, or an FPGA (Field Programmable Gate Array). The waveform signal output by the digitization unit 13 is input to the control device 14.

[0043] The control device 14 controls the scanning unit 11 and the digitization unit 13. The control device 14 generates a waveform (analyzed image) based on the waveform signal obtained from the digitization unit 13, and inputs this analyzed image to the input / output device 15. The input / output device 15 includes an input device such as a keyboard or mouse for user input of measurement conditions, and a display device such as a monitor for displaying measurement results to the user. The input / output device 15 displays the analyzed image input from the control device 14. From this analyzed image, jitter can be measured, and image (waveform) conversion can be confirmed, allowing for the identification of fault locations.

[0044] Next, the effects of the inspection device 1 in this embodiment will be explained.

[0045] First, the configuration of the comparative example inspection apparatus and its problems will be explained. The reflectivity of light in the active components of semiconductor devices such as LSIs, such as transistors, is low, typically below 10%. If such semiconductor devices are irradiated with strong light, there is a concern that transistors and other devices may be damaged by the incident light. Therefore, the amount of light irradiating the semiconductor device is reduced to a level that does not damage the semiconductor device. For example, when using a solid-state lens with one or more apertures, the upper limit of the amount of irradiated light is several mW, and the upper limit of the reflected light (return light) is approximately 0.1 mW. Furthermore, for ideal measurement, the shot noise of the light can be greater than the thermal noise of the measuring instrument (e.g., a photodetector). In the comparative example inspection apparatus (ordinary inspection apparatus), in order to reduce the amount of returned light as described above and make the shot noise greater than the thermal noise, a photodetector with a multiplication layer that amplifies the returned light (e.g., an APD (Avalanche PhotoDetector)) is used. By using such a photodetector, the shot noise can be greater than the thermal noise, resulting in high-precision inspection.

[0046] In recent years, with the improvement of semiconductor device performance, there has been a demand for inspection devices capable of detecting broadband phenomena including higher frequency bands. Specifically, for example, there is a demand for inspection devices capable of accurately detecting minute jitter (e.g., jitter of about 10 ps). In this regard, in inspection devices with photodetectors as described in the comparative example above, the capacitance of the photodetector becomes relatively large, making high-speed signal detection (detection of high-frequency phenomena) impossible. Specifically, the photodetector of the comparative example (e.g., an APD) has a multiplication layer between the P-layer and N-layer, and a strong electric field is applied to this multiplication layer. In photodetectors with a multiplication layer to which a strong electric field is applied, the capacitance becomes relatively large, making high-speed signal detection (detection of high-frequency phenomena) impossible.

[0047] As a solution to such problems, the inspection device 1 of this embodiment includes: a light source 121 that generates light; a light 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 semiconductor device D with the light from the light source 121 and guides the light from the semiconductor device D to the light amplifier 123; and a light detector 124 that detects the light output from the light amplifier 123, wherein the light amplifier 123 amplifies the input light in an unsaturated manner.

[0048] In the inspection apparatus 1 of this embodiment, since the optical amplifier 123 is provided separately from the photodetector 124, and the light amplified by the optical amplifier 123 is detected in the photodetector 124, the signal amplified by the optical amplifier 123 can be amplified to ensure detection accuracy, and the amplified light can be detected by the photodetector 124. In this configuration, since a photodetector without a multiplication layer and with relatively small capacitance (e.g., a PIN photodiode) can be used as the photodetector 124, high-frequency band phenomena (e.g., a band around 20 GHz exceeding 10 GHz) can be detected. Furthermore, in the inspection apparatus 1 of this embodiment, the light is amplified by the optical amplifier 123 within an unsaturated range. In a saturated state, the small signals contained in the input light will disappear after amplification, raising concerns about the inability to properly detect these small signals. In this respect, by amplifying the light within an unsaturated range, small phenomena (e.g., jitter) can be correctly detected based on the output light containing small signals. As described above, the inspection apparatus 1 of this embodiment can accurately detect broadband phenomena containing high-frequency bands.

[0049] The optical amplifier 123 can also amplify the input light by making the change in the amount of output light relative to the amount of input light linear. Thus, because there is a linear relationship between the input and output light, the phenomenon of reflected light from the semiconductor device D can be accurately detected.

[0050] The optical amplifier 123 can also amplify the input light by increasing the output light intensity to more than half of the maximum output light intensity. This allows for a significant increase in amplification while avoiding saturation, thus ensuring the accuracy of phenomenon detection.

[0051] The optical amplifier 123 can also amplify the input light in such a way that the shot noise contained in the output light exceeds the thermal noise of the photodetector 124. In this way, by amplifying the light in such a way that the noise contained in the light is greater than the noise of the photodetector 124, the noise contained in the light (shot noise or relative intensity noise) becomes dominant, thereby preventing the detection accuracy from deteriorating due to the noise (thermal noise) of the photodetector 124.

[0052] The optical amplifier 123 can have an amplifying element of a length that satisfies the condition of amplifying the input light in an unsaturated manner. Thus, the input light can be appropriately amplified under the condition of being set in an unsaturated manner.

[0053] The optical amplifier 123 can also be a semiconductor amplifier, a fiber optic amplifier, or a cone amplifier. Therefore, light amplification within the aforementioned unsaturated range can be appropriately performed.

[0054] The photodetector 124 can also be a PIN photodiode. Thus, by using a PIN photodiode with relatively small capacitance as a photodetector, high-frequency phenomena can be detected.

[0055] The photodetector 124 can also be configured to detect light in the frequency band above 8 GHz. Therefore, high-frequency phenomena can be detected.

[0056] Symbol Explanation

[0057] 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. An inspection device, wherein, have: A light source, which produces light; An optical amplifier amplifies the input light and outputs it. An optical system that illuminates a semiconductor device with light from the light source and guides light from the semiconductor device to the optical amplifier; as well as A photodetector that detects light output from the optical amplifier. The optical amplifier amplifies the input light in an unsaturated manner. The optical amplifier amplifies the input light in such a way that the shot noise in the output light exceeds the thermal noise of the photodetector.

2. The inspection device as claimed in claim 1, wherein, The optical amplifier amplifies the input light in such a way that the change in the amount of output light relative to the amount of input light is linear.

3. The inspection device as claimed in claim 1, wherein, The optical amplifier amplifies the input light in such a way that the output light intensity is greater than half of the maximum output light intensity.

4. The inspection device as claimed in claim 2, wherein, The optical amplifier amplifies the input light in such a way that the output light intensity is greater than half of the maximum output light intensity.

5. The inspection device according to any one of claims 1 to 4, wherein, The optical amplifier has an amplifying element whose length satisfies the condition of amplifying the input light in an unsaturated manner.

6. The inspection device as claimed in any one of claims 1 to 4, wherein, The optical amplifier is a semiconductor amplifier, a fiber optic amplifier, or a cone amplifier.

7. The inspection apparatus as claimed in claim 5, wherein, The optical amplifier is a semiconductor amplifier, a fiber optic amplifier, or a cone amplifier.

8. The inspection device as claimed in any one of claims 1 to 4, wherein, The photodetector is a PIN photodiode.

9. The inspection device as claimed in claim 5, wherein, The photodetector is a PIN photodiode.

10. The inspection apparatus as claimed in claim 6, wherein, The photodetector is a PIN photodiode.

11. The inspection apparatus as claimed in claim 7, wherein, The photodetector is a PIN photodiode.

12. The inspection device according to any one of claims 1 to 4, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

13. The inspection apparatus as claimed in claim 5, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

14. The inspection apparatus as claimed in claim 6, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

15. The inspection apparatus as claimed in claim 7, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

16. The inspection apparatus as claimed in claim 8, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

17. The inspection apparatus as claimed in claim 9, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

18. The inspection apparatus as claimed in claim 10, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

19. The inspection apparatus as claimed in claim 11, wherein, The photodetector is configured to detect light in the frequency band above 8 GHz.

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