Analysis device and analysis method

Abstract

This analysis device comprises: an optical scanner that irradiates a prescribed position on one surface of an object to be measured and scans said position; a photodetector that detects light reflected from the prescribed position as a result of light irradiation and outputs a detection signal; and an optical scanner control unit that controls the optical scanner. The optical scanner control unit has: a high-speed response circuit that responds with a first time constant; a low-speed response circuit that responds with a second time constant greater than the first time constant; and a changeover switch for selecting either the high-speed response circuit or the low-speed response circuit.

Description

Analysis device and analysis method

[0001] The present disclosure relates to an analysis device and an analysis method.

[0002] A known semiconductor failure analysis technique involves irradiating a predetermined position on one surface of a measurement object with light such as a laser and scanning the irradiated position. For example, in heat response analysis, a stimulus signal having a predetermined modulation frequency is applied to the measurement object, and the modulation of the intensity of reflected light due to differences in reflectivity on the surface of the measurement object caused by heat generated inside the measurement object is utilized for failure analysis (see Patent Document 1). In pattern image acquisition, an image based on the reflected light of the irradiated light is generated to visualize the structure formed on one surface of the measurement object. Other techniques include EOFM (EO Frequency Mapping) analysis, OBIRCH (Optical Beam Induced Resistance Change) analysis, and OBIC (Optical Beam Induced Current) analysis.

[0003] International Publication No. 2016 / 056110

[0004] An object of the present disclosure is to provide an analysis device and an analysis method that can perform failure analysis with high accuracy and smoothly according to the analysis technique.

[0005] (1) An analytical device according to one aspect of the present disclosure includes an optical scanning unit that irradiates light onto a predetermined position on one surface of an object to be measured and scans the position; an optical detection unit that detects light reflected at the predetermined position in response to the light irradiation and outputs a detection signal; and an optical scanning control unit that controls the optical scanning unit, wherein the optical scanning control unit has a high-speed response circuit that responds with a first time constant, a low-speed response circuit that responds with a second time constant that is larger than the first time constant, and a selector switch that selects either the high-speed response circuit or the low-speed response circuit.

[0006] The inventors have noted that the optimal time constant for optical scanning varies depending on the analysis method. For example, in heat response analysis, performing optical scanning with a time constant larger than the time constant for optical scanning in pattern image acquisition can improve the S / N ratio. On the other hand, in pattern image acquisition, performing optical scanning with a relatively small time constant can shorten the time required to acquire a pattern image. In an analysis device according to one aspect of the present disclosure, which takes into account the differences in appropriate time constants for each analysis method, a high-speed response circuit that responds with a first time constant and a low-speed response circuit that responds with a second time constant larger than the first time constant are provided, and one of the response circuits is selected by a selector switch. This configuration makes it possible to select a low-speed response circuit with a large time constant for the above-mentioned heat response analysis and a high-speed response circuit for pattern image acquisition, thereby selecting an appropriate response circuit depending on the analysis method. This allows, for example, to improve the S / N ratio in heat response analysis, etc., to perform high-precision failure analysis, and to perform fast (smooth) failure analysis in pattern image acquisition, etc. As described above, the analysis device according to one aspect of the present disclosure can perform failure analysis smoothly and with high accuracy according to the analysis method.

[0007] (2) The analysis device of (1) above further includes an application unit that applies a stimulus signal having a predetermined modulation frequency to the measurement object, and an analysis unit that generates a fever response image based on a detection signal output from the light detection unit when the stimulus signal is applied, and the selector switch may select the slow response circuit when the stimulus signal is applied to the measurement object by the application unit and the fever response image is generated by the analysis unit. With this configuration, the slow response circuit is selected in the fever response analysis that generates the fever response image, thereby appropriately improving the S / N ratio.

[0008] (3) In the analysis device described in (1) or (2), the application unit may apply a stimulus signal having a modulation frequency of 1 kHz to 20 kHz, inclusive. With this configuration, a fever response image can be appropriately generated in a frequency band that is less susceptible to shot noise.

[0009] (4) In the analysis device described in (3), the application unit may apply a stimulus signal having a modulation frequency of 6 kHz to 10 kHz, inclusive. With this configuration, a fever response image can be appropriately generated in a frequency band that is less susceptible to shot noise.

[0010] (5) The analysis device according to any one of (1) to (4) above may further include an analysis unit that generates a pattern image based on the detection signal output from the light detection unit, and the changeover switch may select the high-speed response circuit when the pattern image is generated by the analysis unit. With this configuration, the high-speed response circuit is selected when acquiring the pattern image, allowing for quick (smooth) processing.

[0011] (6) The analysis device according to any one of (1) to (5) above may further include an input unit that accepts a selection input of an analysis method from a user, and the selector switch may select either a fast response circuit or a slow response circuit depending on the analysis method accepted by the input unit. With this configuration, an appropriate response circuit can be selected depending on the analysis method based on the user's judgment.

[0012] (7) In the analyzer according to any one of (1) to (6) above, the selector switch may select either the high-speed response circuit or the low-speed response circuit according to the scanning speed of the optical scanning unit. With this configuration, an appropriate response circuit is selected according to the scanning speed, so that the response circuit selection can be performed more smoothly.

[0013] (8) In the analysis device according to any one of (1) to (7), the light may have a center wavelength in the range of 360 nm to 830 nm. With this configuration, thermal response analysis and pattern image acquisition can be performed appropriately.

[0014] (9) In the analysis device according to any one of (1) to (8), the first time constant may be 100 ns to 100 μs. With this configuration, for example, the high-speed response circuit can be operated at an appropriate speed to quickly acquire a pattern image.

[0015] (10) In the analysis device according to any one of (1) to (9), the second time constant may be 500 μs or more and 1 ms or less. With this configuration, for example, the slow response circuit can be operated at an appropriate speed to perform heat generation response analysis with high accuracy.

[0016] (11) An analysis method according to one aspect of the present disclosure is an analysis method performed by an analysis device, the analysis method including the steps of selecting, for optical scanning, a high-speed response circuit that responds with a first time constant or a low-speed response circuit that responds with a second time constant greater than the first time constant, irradiating a predetermined position on one surface of an object to be measured with light using the selected high-speed response circuit or low-speed response circuit to scan the position, and detecting light reflected at the predetermined position in response to the light irradiation and outputting a detection signal. Such an analysis method enables failure analysis to be performed smoothly and with high accuracy depending on the analysis technique.

[0017] According to the present disclosure, failure analysis can be performed smoothly and with high accuracy depending on the analysis method.

[0018] FIG. 1 is a configuration diagram of an analysis device according to the present embodiment; FIG. 2 is a diagram explaining the reason for providing an optical scanner control unit; FIG. 3 is a configuration diagram of an optical scanner control unit; FIG. 4 is a diagram explaining verification conditions; FIG. 5 is a diagram showing an example of a heat response image acquired by a high-speed response circuit and a low-speed response circuit; FIG. 6 is a graph showing pattern edge noise at each frequency; FIG. 7 is a graph showing the ratio of signal intensity of a heat response image to pattern edge noise at each frequency; and FIG. 8 is a diagram showing another example of a configuration diagram of an analysis device.

[0019] Hereinafter, this embodiment will be described in detail with reference to the drawings. In each drawing, the same or corresponding parts are designated by the same reference numerals, and duplicated explanations will be omitted.

[0020] As shown in FIG. 1 , the analysis apparatus 1 according to the embodiment is an analysis apparatus that analyzes a fault location in a measurement object MO, such as a semiconductor device SD, which is a device under test (DUT), by identifying the location of a heat source in the measurement object MO. A heat source is a heat-generating location inside the measurement object MO. If a short circuit or the like is present inside the measurement object MO when a signal is applied to the measurement object MO, the short circuit generates heat and becomes a heat source. In other words, the analysis apparatus 1 is a failure analysis apparatus that analyzes an abnormality, such as a short circuit, inside the measurement object MO by identifying the location of the heat source.

[0021] The device under test may be, for example, an integrated circuit having a PN junction such as a transistor (e.g., small scale integration (SSI), medium scale integration (MSI), large scale integration (LSI), very large scale integration (VLSI), ultra large scale integration (ULSI), giga scale integration (GSI)), a high current / high voltage MOS transistor, a bipolar transistor, or a memory storage device. In the following description, the device under test is assumed to be an integrated circuit.

[0022] In a semiconductor device SD, for example, an insulating film (SiO2 layer) is stacked on a Si substrate, and a process layer is further stacked on the insulating film, a wiring layer is stacked on the process layer, and a protective film is stacked on the wiring layer. Here, the location that may become a heat-generating point due to a short circuit is, for example, a device layer consisting of a process layer and a wiring layer. In this case, the device layer is the measurement object MO. Furthermore, one side of the measurement object MO is, for example, the surface of the wiring layer that contacts the protective film and the surface of the process layer that contacts the insulating film. Furthermore, if the device layer, the protective film, and the insulating film are also considered to be the measurement object MO, then one side of the measurement object MO is, for example, the surface of the protective film that contacts air and the surface of the insulating film that contacts the Si substrate. Furthermore, if the Si substrate is also considered to be the measurement object MO, then one side of the measurement object MO is, for example, the surface of the protective film that contacts air and the surface of the Si substrate that contacts air.

[0023] The analysis apparatus 1 includes a pulse generator 11 (applier), a light source 12, a photodetector 13 (light detector), a processor 14, a computer 15 (analyzer), an optical scanner 26 (light scanning unit), a display 28, an input unit 29, and an optical scanner controller 50 (light scanning controller). The semiconductor device SD is placed on a stage 25.

[0024] The pulse generator 11 outputs a modulation signal (stimulation signal) having a predetermined modulation frequency and applies the modulation signal to the measurement object MO of the semiconductor device SD. The semiconductor device SD is driven by the modulation signal applied by the pulse generator 11. Such a modulation signal may be, for example, a voltage or current modulated at a predetermined modulation frequency. Furthermore, if a short circuit exists within the measurement object MO, the application of the modulation signal causes the short circuit to generate heat and become a heat source. That is, the pulse generator 11 generates a heat source within the semiconductor device SD by applying the modulation signal to the measurement object MO. Based on a timing trigger signal input from the processing unit 14, the pulse generator 11 generates and outputs a modulation signal having the same frequency and phase as the timing trigger signal. The pulse generator 11 may apply a stimulation signal having a modulation frequency of 1 kHz to 20 kHz, preferably 6 kHz to 10 kHz, to the measurement object MO.

[0025] The light source 12 irradiates the measurement object MO with light (irradiation light). The light source 12 is configured with an SLD (Super Luminescent Diode). The light source 12 may be a laser light source such as an LD (Laser Diode), an LED (Light Emitting Diode), or a light source using a lamp light source. The irradiation light may be CW light or pulsed light. The irradiation light may be, for example, infrared light. In this case, the central wavelength of the irradiation light may be 830 nm or more and 2500 nm or less, such as 1300 nm. Alternatively, the irradiation light may be visible light having a central wavelength in the range of 360 nm or more and 830 nm or less. In this case, thinning the Si substrate of the semiconductor device SD makes it easier for the visible irradiation light to irradiate the device layer through the Si substrate.

[0026] Illumination light output from the light source 12 passes through a pinhole 16 and a lens 17 and enters a polarizer 18. The polarizer 18 transmits only illumination light polarized in a specific direction, and the illumination light that has passed through the polarizer 18 is entered into a polarization beam splitter (hereinafter referred to as a PBS) 19. The PBS 19 transmits light polarized in a specific direction and reflects light polarized in a specific direction. The PBS 19 reflects the illumination light that has passed through the polarizer 18 toward an optical scanner 26 (light irradiation unit). Note that the polarizer 18 does not necessarily have to be provided.

[0027] The optical scanner 26 is, for example, a galvanometer mirror scanner, a polygon mirror scanner, or a MEMS mirror scanner, and is controlled by the optical scanner control unit 50 so as to irradiate a desired position on the measurement object MO with light from the PBS 19. The optical scanner 26 irradiates a predetermined position on one surface of the measurement object MO with light from the PBS 19 and scans the position.

[0028] The illumination light output from the optical scanner 26 passes through the short-pass filter 27, passes through the λ / 4 plate 20 and the lens 21, and is then irradiated onto the measurement object MO of the semiconductor device SD. More specifically, the illumination light is irradiated onto a measurement point (predetermined position) set on the surface of the measurement object MO. The optical scanner 26 is not limited to being controlled to irradiate the light onto a predetermined position on the measurement object MO, and may scan the light one-dimensionally or two-dimensionally on the measurement object MO.

[0029] The light reflected from the measurement point in response to the irradiated light (reflected light) passes through the lens 21, short-pass filter 27, λ / 4 plate 20, and optical scanner 26 again before being input to the PBS 19. At this time, the short-pass filter 27 can block infrared light generated by the measurement object MO. Furthermore, the light input to the PBS 19 passes through the λ / 4 plate 20 twice, tilting its polarization direction, allowing the PBS 19 to transmit the reflected light. The reflected light passes through the lens 22 and pinhole 23 and is input to the photodetector 13. As described above, the optical system of this embodiment is a confocal optical system, configured to detect reflected light from a limited focal range. While the pinholes 16 and 23 are used in this embodiment, a confocal optical system may also be realized by using an optical fiber and utilizing the refractive index difference between the core and cladding.

[0030] The photodetector 13 detects the reflected light reflected from the surface of the measurement object MO in response to the irradiated light. The photodetector 13 also converts the detected reflected light into an analog detection signal and outputs it. The photodetector 13 may be an avalanche photodiode (APD), a photodiode (PD), a photomultiplier tube (PMT), or the like. When a heat source is generated, the refractive index of the material of the measurement object MO changes in response to the heat from the heat source, changing the reflectance at the surface of the measurement object MO. This change in reflectance at the surface of the measurement object MO over time is expressed as a change in the detection signal output from the photodetector 13 over time. In other words, the change in the detection signal output from the photodetector 13 over time changes depending on the speed of the thermal response of the measurement point to the heat source. Naturally, the speed of the thermal response of the measurement point to the heat source increases the closer the measurement point is to the heat source. The detection signal output by the photodetector 13 is input to the processing unit 14.

[0031] The processing unit 14 outputs a timing trigger signal to the pulse generator 11 and the computer 15. Based on the timing trigger signal, a modulated signal having the same frequency as the timing trigger signal and synchronized in phase with the timing trigger signal is generated by the pulse generator 11. Furthermore, when a detection signal is input, the processing unit 14 outputs the detection signal to the computer 15.

[0032] The computer 15 generates a heat generation response image based on the detection signal output from the photodetector 13 when a stimulus signal is applied. In the heat generation response analysis, a stimulus signal of a predetermined frequency is applied to the measurement object MO, and the photodetector 13 detects changes in reflectance on the surface of the measurement object MO associated with heat generation as the intensity of reflected light. The computer 15 then generates a heat generation response image corresponding to the detection signal from the photodetector 13. The computer 15 then analyzes the heat generation response image to identify the location of the heat source and identify abnormalities such as shorts. The computer 15 is connected to a display unit 28 that displays images such as analysis results and pattern images of the semiconductor device SD, and an input unit 29 for inputting analysis conditions.

[0033] The computer 15 sets measurement points on the surface of the measurement object MO. For example, the user uses the input unit 29 to specify at least one measurement point while looking at the display unit 28 on which a pattern image of the semiconductor device SD is displayed. The computer 15 may also set a measurement range on the surface of the measurement object MO. The pattern image may be, for example, an LSM image. The computer 15 sets position information (x coordinate and y coordinate) on the surface of the measurement object MO based on the position information of the specified measurement point.

[0034] Based on the position information of the set measurement points or measurement ranges, the computer 15 controls the optical scanner 26 via the optical scanner control unit 50. In detail, based on the position information of the measurement points or measurement ranges, the computer 15 controls the optical scanner 26 so that light is irradiated onto the measurement points on the surface of the measurement object MO.

[0035] The computer 15 generates a heat generation response image based on the detection signal and identifies the heat source position on the measurement object MO based on the heat generation response image. For example, the computer 15 derives the phase delay of the detection signal relative to the modulation signal to derive the distance from the point where light is reflected on the surface of the measurement object MO (measurement point) to the heat source position and identify the heat source position. Because the modulation signal has the same frequency and phase synchronization as the timing trigger signal, the computer 15 can derive the phase delay of the detection signal relative to the modulation signal based on the timing trigger signal and detection signal input from the processing unit 14. As described above, the phase of the detection signal changes depending on the distance from the measurement point to the heat source, so the phase delay of the detection signal relative to the modulation signal also changes depending on the distance from the measurement point to the heat source. Specifically, the phase delay of the detection signal increases in proportion to the distance from the measurement point to the heat source.

[0036] The computer 15 calculates the distance from the measurement point on the surface of the measurement object MO to the heat source from the derived phase delay amount. The computer 15 derives the distance from the measurement point to the heat source, for example, by multiplying the derived phase delay amount by a heat propagation speed determined according to the measurement object MO. Note that the computer 15 may store in advance a table that defines the correspondence relationship between the phase delay amount and the distance from the measurement point to the heat source, and derive the distance from the measurement point to the heat source based on the derived phase delay amount and the table.

[0037] The computer 15 analyzes the heat source position based on the derived distances from the measurement points to the heat source. Specifically, the computer 15 derives the phase delay amount of the detection signal at each of three measurement points on the surface of the measurement object MO and derives the distance from the measurement point to the heat source. The three-dimensional heat source position may then be uniquely identified based on the distances to the heat source at each of the three measurement points. For example, when identifying the heat source position from the phase delay amount at three measurement points, the computer 15 may analyze the heat source position by two-dimensionally mapping the phase delay amount at each measurement point. More specifically, the computer 15 may map the phase delay amount to the coordinates of each measurement point using the X-axis and Y-axis described above as the two axes of the coordinate system. In this case, even if there are two or more heat sources, the heat source position can be easily visually identified from the two-dimensional map.

[0038] As an analysis method different from the heat generation response analysis, the computer 15 may generate a pattern image (perform pattern image acquisition) based on the detection signal output from the photodetector 13. Furthermore, the computer 15 may perform EOFM (EO Frequency Mapping) analysis, OBIRC (Optical Beam Induced Resistance Change) analysis, OBIC (Optical Beam Induced Current) analysis, or the like as yet another analysis method.

[0039] 8 , the analysis apparatus according to the embodiment may be, for example, an analysis apparatus 1A that analyzes the internal operation of a measurement object MO, such as a semiconductor device SD, by identifying the generation of an electric field in the measurement object MO. For example, the analysis apparatus 1A that performs EOFM analysis includes a tester 11A (applier), a light source 12, a photodetector 13 (light detector), a processor 14, a computer 15 (analyzer), an optical scanner 26 (light scanning unit), a display 28, an input unit 29, and an optical scanner controller 50 (light scanning controller). The semiconductor device SD is placed on a stage 25.

[0040] The tester 11A of the analysis device 1A outputs a driving clock (stimulus signal) of a predetermined frequency (modulation frequency) and a test pattern (stimulus signal) that repeats at the same frequency (modulation frequency), and applies the driving clock and test pattern to the measurement object MO of the semiconductor device SD. The semiconductor device SD is driven by the driving clock and test pattern applied by the tester 11A. Driving by the driving clock and test pattern generates an electric field in transistors and other components inside the measurement object MO. That is, by applying the driving clock and test pattern to the measurement object MO, the tester 11A can generate an electric field inside the semiconductor device SD that changes at the modulation frequency. Because the generated electric field changes the reflectivity of the measurement object MO, EOFM analysis analyzes the internal operation of the semiconductor device SD from changes in the intensity of light reflected from one surface of the measurement object MO. At least one of the driving clock and the test pattern serves as the stimulus signal, and the frequency of the stimulus signal serves as the modulation frequency.

[0041] Next, the optical scanner control unit 50 that controls the optical scanner 26 based on a control signal from the computer 15 will be described in detail.

[0042] First, the reason for providing the optical scanner control unit 50 will be explained with reference to FIG. 2 . In recent years, with the increasing multilayering and integration of semiconductor devices, the importance of heat response analysis, which can appropriately analyze internal device failures even in multilayer devices, has increased. In a simulation using a 10 μm-thick semiconductor device, heat response analysis demonstrated that as the frequency of the applied stimulus signal was lowered, the reflection intensity (the intensity of reflected light detected by the photodetector 13) became more dominant than the optical shot noise, enabling the acquisition of clear heat response images with high signal intensity. In the simulation, clear heat response images were acquired at relatively low frequencies below 20 kHz, such as 15 kHz. This is thought to be due to the fact that at relatively high frequencies (e.g., frequencies higher than 20 kHz), heat generated inside the semiconductor device does not reach the surface of the semiconductor device as the semiconductor device becomes thicker, whereas at relatively low frequencies (e.g., frequencies below 20 kHz), heat reaches the surface of the semiconductor device even as the semiconductor device becomes thicker, allowing the heat response signal to be increased.

[0043] From the results of the above simulation, it was expected that the signal strength of the fever response image would be even higher if a stimulus signal with an even lower frequency, such as 10 kHz or less, were used. However, in reality, it was found that in the low-frequency range below 10 kHz, system noise due to vibrations of the optical scanner 26 and the like becomes dominant, and the signal of the fever response image is buried in the pattern edge noise associated with the system noise, resulting in a deterioration of the S / N ratio.

[0044] In FIG. 2( a), the horizontal axis represents the frequency of the stimulus signal, and the vertical axis represents the intensity of the reflected light or the amount of pattern edge noise. The graph shows the signal (reflected light) intensity and the pattern edge noise (system noise) indicated by the solid line when the stimulus signal frequency is 15 kHz and 10 kHz. As shown in FIG. 2( a), the signal amount (reflected light intensity) is greater at 10 kHz than at 15 kHz, but the pattern edge noise is large, so the signal is buried in the pattern edge noise. As a result, in the heat response image, the signal intensity 112 at 10 kHz shown in FIG. 2( c) is smaller (darker) than the signal intensity 111 at 15 kHz shown in FIG. 2( b). Similarly, the signal intensity 113 at 5 kHz shown in FIG. 2( d) and the signal intensity 114 at 1 kHz shown in FIG. 2( e) are also smaller than the signal intensity 111 at 15 kHz shown in FIG. 2( b) due to the influence of the pattern edge noise.

[0045] The inventors have found that in heat generation response analysis, when optical scanning is performed with a time constant (e.g., 500 μs or more and 1 ms or less) larger than the time constant (e.g., 100 ns or more and 100 μs or less) of optical scanning used in pattern image acquisition, it is possible to acquire a heat generation response image with an improved S / N ratio (a clear heat generation response image with high signal intensity). On the other hand, optical scanning with a large time constant (e.g., 500 μs or more and 1 ms or less) can interfere with other analysis methods, for example, by taking too long to acquire a pattern image.

[0046] Therefore, the inventors have adopted a configuration in which a high-speed response circuit that responds with a first time constant suitable for pattern image acquisition, etc., and a low-speed response circuit that responds with a second time constant (a time constant larger than the first time constant) suitable for heat generation response analysis, etc., are provided, and the high-speed response circuit and the low-speed response circuit are switched depending on the analysis method. That is, as shown in FIG. 3 , the optical scanner control unit 50 according to this embodiment has a high-speed response circuit 501, a low-speed response circuit 502, and a changeover switch 503.

[0047] The high-speed response circuit 501 is a response circuit that responds with a first time constant. The first time constant may be, for example, 100 ns or more and 100 μs or less. The high-speed response circuit 501 is selected by a changeover switch 503 when, for example, a pattern image is to be acquired.

[0048] The slow response circuit 502 is a response circuit that responds with a second time constant that is larger than the first time constant. The second time constant may be, for example, 500 μm or more and 1 ms or less. The slow response circuit 502 is selected by a selector switch 503 when, for example, a heat generation response analysis is performed.

[0049] The changeover switch 503 is a switch that selects either the high-speed response circuit 501 or the low-speed response circuit 502 .

[0050] The selector switch 503 may select the slow response circuit 502, for example, in response to a control signal from the computer 15, when a stimulus signal is applied to the measurement object MO by the pulse generator 11 and a heat response image is generated by the computer 15 (i.e., when a heat response analysis is performed).

[0051] The changeover switch 503 may select the high-speed response circuit 501 in response to a control signal from the computer 15 when a pattern image is generated by the computer 15 (that is, when a pattern image is acquired).

[0052] The selector switch 503 may select either the fast response circuit 501 or the slow response circuit 502 in response to a user-input selection of an analysis method. The user-input selection may be a user selection on a GUI. In this case, the input unit 29 accepts the user-input selection of an analysis method. The selector switch 503 may select either the fast response circuit 501 or the slow response circuit 502 in response to the analysis method accepted by the input unit 29. In this case, the user may select the fast response circuit 501 during heat generation response analysis, or the slow response circuit 502 during pattern image acquisition, in contrast to the above. For example, there may be cases where a slower acquisition of a pattern image is desired, and the optical scanner 26 may be controlled by the slow response circuit 502.

[0053] The changeover switch 503 may select either the high-speed response circuit 501 or the low-speed response circuit 502 according to the scanning speed (scanning speed) of the optical scanner 26. In this way, the changeover switch 503 may automatically switch the response circuit according to the scanning speed.

[0054] Such an analysis device 1 executes the following analysis method, which includes the steps of selecting a high-speed response circuit 501 that responds with a first time constant for optical scanning or a low-speed response circuit 502 that responds with a second time constant greater than the first time constant, irradiating light onto a predetermined position on one surface of the measurement object MO using the selected high-speed response circuit 501 or low-speed response circuit 502 to scan the position, and detecting light reflected at the predetermined position in response to the light irradiation and outputting a detection signal.

[0055] Next, the effects of the analysis device 1 according to this embodiment will be described.

[0056] The analytical device 1 according to this embodiment comprises an optical scanner 26 that irradiates light onto a predetermined position on one surface of the measurement object MO and scans the position, a photodetector 13 that detects light reflected at the predetermined position in response to the light irradiation and outputs a detection signal, and an optical scanner control unit 50 that controls the optical scanner 26. The optical scanner control unit 50 has a high-speed response circuit 501 that responds with a first time constant, a low-speed response circuit 502 that responds with a second time constant that is larger than the first time constant, and a changeover switch 503 that selects either the high-speed response circuit 501 or the low-speed response circuit 502.

[0057] The inventors have noted that the optimal time constant for optical scanning differs depending on the analysis method. For example, in heat response analysis, performing optical scanning with a time constant larger than the time constant for optical scanning in pattern image acquisition can improve the S / N ratio. On the other hand, in pattern image acquisition, performing optical scanning with a relatively small time constant can shorten the time required to acquire a pattern image. The analysis device 1 according to this embodiment, which takes into account the differences in the appropriate time constant for each analysis method, is provided with a high-speed response circuit 501 that responds with a first time constant and a low-speed response circuit 502 that responds with a second time constant larger than the first time constant, and one of the response circuits is selected by a selector switch 503. This configuration makes it possible to select the low-speed response circuit 502, which has a large time constant, for the above-mentioned heat response analysis, and the high-speed response circuit 501 for pattern image acquisition, thereby selecting an appropriate response circuit depending on the analysis method. This allows, for example, an improvement in the S / N ratio in heat response analysis, etc., to perform highly accurate failure analysis, and to perform failure analysis quickly (smoothly) in pattern image acquisition, etc. As described above, the analysis device 1 according to this embodiment can perform failure analysis smoothly and with high accuracy according to the analysis method.

[0058] The analysis device 1 further includes a pulse generator 11 that applies a stimulus signal having a predetermined modulation frequency to the measurement object MO, and a computer 15 that generates a heat response image based on a detection signal output from the photodetector 13 while the stimulus signal is applied, and the changeover switch 503 may select the slow response circuit 502 when the stimulus signal is applied to the measurement object MO by the pulse generator 11 and the heat response image is generated by the computer 15. With this configuration, the slow response circuit 502 is selected in the heat response analysis that generates the heat response image, and the S / N ratio can be appropriately improved.

[0059] The results of the verification experiment on the heat response image are described with reference to Figures 4 and 5. Figure 4 illustrates the verification conditions, showing a pattern image (top) and a cross-sectional structure (bottom) of the measurement object MO. As shown in the bottom diagram of Figure 4, a semiconductor device was used, consisting of a 525 μm Si substrate with a 2 μm insulating film (SiO2 layer) laminated thereon, with 1 μm of exposed Al wiring. The verification conditions were: resistance 4.6 Ω, applied voltage 0-360 mV (duty ratio 50%), stimulus signal frequency 8 kHz, scan magnification 20x × 4x (zoom) = 80x (effectively), laser wavelength 670 nm, laser power 0.46 mW, scan speed 0.33 ms / pixel, reference image amplitude increase, and photodetector 13 bandwidth 925 Hz.

[0060] FIG. 5 shows examples of heat response images acquired by the fast response circuit 501 and the slow response circuit 502 under the above-described verification conditions. FIG. 5( a) shows a heat response image acquired by the fast response circuit 501, and FIG. 5( b) shows a heat response image acquired by the slow response circuit 502. As shown in FIG. 5( a), when the fast response circuit 501 is used, pattern edge noise PN associated with system noise is clearly observed. On the other hand, as shown in FIG. 5( b), when the slow response circuit 502 is used, pattern edge noise is reduced, and almost only signal S is observed. Thus, in the verification experiment, it was confirmed that the S / N ratio in the heat response image can be improved by using the slow response circuit 502.

[0061] FIG. 6 is a graph showing the pattern edge noise at each frequency for the fast response circuit 501 and the slow response circuit 502. In FIG. 6, the horizontal axis represents the frequency of the stimulus signal, and the vertical axis represents the amount of pattern edge noise. In cutting-edge semiconductor devices, the increasing number of wiring layers allows the heat response signal to be increased by lowering the frequency of the modulation signal. However, as shown in FIG. 6, in the low-frequency range, system noise caused by factors such as mirror vibration becomes dominant, and there is a risk that the signal will be buried in the pattern noise. In this regard, as shown in FIG. 6, when the slow response circuit 502 is used, the region dominated by system noise on the low-frequency side can be reduced compared to when the fast response circuit 501 is used.

[0062] In the analysis device 1, the pulse generator 11 may apply a stimulation signal having a modulation frequency of 1 kHz to 20 kHz, or may apply a stimulation signal having a modulation frequency of 6 kHz to 10 kHz. With this configuration, a fever response image can be appropriately generated.

[0063] FIG. 7 is a graph showing the ratio of signal strength to pattern edge noise of the heat response image at each frequency. In FIG. 7, the horizontal axis represents frequency, and the vertical axis represents the signal strength / pattern edge noise value (ratio of signal strength to pattern edge noise). Under conditions generally similar to those of the above-described verification experiment, the frequency was varied to 5 kHz, 8 kHz, and 10 kHz, and the ratio of signal strength to pattern edge noise was measured for each of the fast response circuit 501 and the slow response circuit 502. As shown in FIG. 7, when the modulation frequency was in the range of 5 kHz to 10 kHz, the ratio of signal strength to pattern edge noise could be improved by using the slow response circuit 502. However, since a frequency band in which the signal amount is not buried in the pattern edge noise is optimal, it is more preferable that the modulation frequency be in the range of 6 kHz to 10 kHz, as described above.

[0064] The changeover switch 503 may select the high-speed response circuit 501 when a pattern image is generated by the computer 15. With this configuration, the high-speed response circuit 501 is selected when acquiring a pattern image, allowing for quick (smooth) processing.

[0065] The analysis device 1 may further include an input unit 29 that accepts an input of an analysis method selection from a user, and the selector switch 503 may select either the fast response circuit 501 or the slow response circuit 502 in accordance with the analysis method accepted by the input unit 29. With this configuration, an appropriate response circuit can be selected in accordance with the analysis method based on the user's judgment.

[0066] The changeover switch 503 may select either the high-speed response circuit 501 or the low-speed response circuit 502 depending on the scanning speed of the optical scanner 26. With this configuration, an appropriate response circuit is selected depending on the scanning speed, allowing for smoother response circuit selection.

[0067] In the analysis device 1, the light may have a central wavelength in the range of 360 nm to 830 nm. With this configuration, it is possible to appropriately perform thermal response analysis and pattern image acquisition.

[0068] In the analysis device 1, the first time constant may be 100 ns or more and 100 μs or less. With such a configuration, for example, the high-speed response circuit 501 can be operated at an appropriate speed that enables rapid acquisition of a pattern image.

[0069] In the analysis device 1, the second time constant may be 500 μs or more and 1 ms or less. With this configuration, for example, the slow response circuit 502 can be operated at an appropriate speed that allows heat generation response analysis to be performed with high accuracy.

[0070] The analysis method according to this embodiment is an analysis method performed by the analysis device 1, and includes the steps of selecting, for optical scanning, a high-speed response circuit 501 that responds with a first time constant or a slow-speed response circuit 502 that responds with a second time constant greater than the first time constant, irradiating light onto a predetermined position on one surface of the measurement object MO using the selected high-speed response circuit 501 or slow-speed response circuit 502 to scan the position, and detecting light reflected at the predetermined position in response to the light irradiation and outputting a detection signal. Such an analysis method allows for smooth and accurate failure analysis depending on the analysis technique.

[0071] 1, 1A...analysis device, 11...pulse generator (application unit), 11A...tester (application unit), 13...photodetector (light detection unit), 15...computer (analysis unit), 26...optical scanner (light scanning unit), 29...input unit, 50...optical scanner control unit (light scanning control unit), 501...high-speed response circuit, 502...low-speed response circuit, 503...changeover switch, MO...measurement object

Claims

1. An analytical device comprising: an optical scanning unit that irradiates light onto a predetermined position on one surface of an object to be measured and scans the position; an optical detection unit that detects light reflected at the predetermined position in response to the light irradiation and outputs a detection signal; and an optical scanning control unit that controls the optical scanning unit, wherein the optical scanning control unit has a high-speed response circuit that responds with a first time constant, a low-speed response circuit that responds with a second time constant that is larger than the first time constant, and a changeover switch that selects either the high-speed response circuit or the low-speed response circuit.

2. An analysis device as described in claim 1, further comprising: an application unit that applies a stimulus signal having a predetermined modulation frequency to the object to be measured; and an analysis unit that generates a heat-generating response image based on the detection signal output from the light detection unit when the stimulus signal is applied; wherein the changeover switch selects the slow response circuit when the stimulus signal is applied to the object to be measured by the application unit and the heat-generating response image is generated by the analysis unit.

3. The analysis device according to claim 2, wherein the application section applies the stimulus signal having the modulation frequency of 1 kHz to 20 kHz.

4. The analysis device according to claim 3, wherein the application section applies the stimulus signal having the modulation frequency of 6 kHz to 10 kHz.

5. An analysis device according to any one of claims 1 to 4, further comprising an analysis unit that generates a pattern image based on the detection signal output from the light detection unit, wherein the changeover switch selects the high-speed response circuit when the pattern image is generated by the analysis unit.

6. An analysis device according to any one of claims 1 to 5, further comprising an input unit that accepts a selection input of an analysis method from a user, wherein the changeover switch selects either the high-speed response circuit or the low-speed response circuit according to the analysis method accepted by the input unit.

7. An analysis device according to any one of claims 1 to 6, wherein the changeover switch selects either the high-speed response circuit or the low-speed response circuit according to the scanning speed of the optical scanning unit.

8. An analytical device according to any one of claims 1 to 7, wherein the light has a central wavelength in the range of 360 nm to 830 nm.

9. The analysis device according to any one of claims 1 to 8, wherein the first time constant is not less than 100 ns and not more than 100 μs.

10. An analysis device according to any one of claims 1 to 9, wherein the second time constant is not less than 500 μs and not more than 1 ms.

11. An analysis method performed by an analysis device, comprising the steps of: selecting, for optical scanning, a high-speed response circuit that responds with a first time constant or a low-speed response circuit that responds with a second time constant greater than the first time constant; using the selected high-speed response circuit or low-speed response circuit, irradiating light onto a predetermined position on one surface of an object to be measured and scanning the position; and detecting light reflected at the predetermined position in response to the irradiation of light and outputting a detection signal.

Images