Inspection device and inspection method

Abstract

An inspection device includes: a characteristic signal acquisition unit that outputs a characteristic signal; a noise signal output unit that outputs a noise signal including noise included in a test voltage; a filter for filtering the noise signal; a parameter setting unit for adjusting a parameter of the filter in a direction in which the difference between the noise included in the characteristic signal and the noise included in the noise signal after the filtering decreases; a noise reduction unit that, after the parameter has been adjusted, reduces the noise of the characteristic signal according to a noise signal that has been filtered and outputs the characteristic signal after the noise reduction as information for detecting an abnormal part; and a beam emission unit for emitting a beam at a semiconductor device.

Description

Inspection device and inspection method

[0001] This application claims priority to Japanese Application No. 2023-056888, filed March 31, 2023, and incorporates by reference all of the contents of said Japanese application.

[0002] Patent Documents 1 to 3 disclose noise removal in the Optical Beam Induced Resistance Change (OBIRCH) measurement method. Of these, Patent Documents 2 and 3 disclose methods for removing noise caused by external power supplies. Patent Documents 4 to 6 disclose methods for removing noise in failure analysis based on changes in the electrical characteristics of semiconductor devices due to light irradiation, such as the LIVA / TIVA measurement method or the OBIC measurement method, which are similar to the OBIRCH measurement method.

[0003] Japanese Patent Application Publication No. 2012-242157 Japanese Patent Application Publication No. 2020-34440 Japanese Patent Application Publication No. 2021-043156 U.S. Patent Application Publication No. 2002 / 163352 U.S. Patent No. 6,169,408 U.S. Patent No. 4,588,950

[0004] There are methods for analyzing failures and the like based on changes in the electrical characteristics of a test object due to beam irradiation, such as the OBIRCH measurement method and the OBIC measurement method. In these methods, noise contained in the test voltage or test current applied to the test object may be superimposed on the measurement results. Usually, in these methods, the change in the signal obtained from the test object as the measurement result is weak, so if noise is superimposed on the signal, accurate measurement becomes difficult.

[0005] Therefore, it is conceivable to remove noise from the measurement result signal, as in the devices or methods disclosed in Patent Documents 1 to 6, for example. However, the characteristics (e.g., waveform, magnitude, or frequency) of the noise superimposed on the measurement result signal change depending on the electrical characteristics of the test object. For example, when measuring multiple types of test objects, there is variation in the electrical characteristics of the test objects. In such cases, the characteristics of the noise superimposed on the measurement result signal change in various ways, making it difficult to effectively reduce the noise.

[0006] The present disclosure aims to provide an inspection device and an inspection method that can effectively reduce noise superimposed on a signal of a measurement result even when there is variation in the electrical characteristics of a test object.

[0007] [1] An inspection device according to the present disclosure includes: a characteristic signal acquisition unit that acquires a characteristic signal indicating electrical characteristics of an inspection area in a test specimen to which a test voltage or a test current is applied; a noise signal output unit that outputs a noise signal that includes noise contained in the test voltage or the test current applied to the inspection area; a filter that performs filtering on the noise signal; a parameter setting unit that changes filter parameters such that the difference between the noise contained in the characteristic signal and the noise contained in the filtered noise signal becomes smaller; a noise reduction unit that reduces noise in the characteristic signal by the noise signal that has been filtered after the parameters have been changed by the parameter setting unit, and outputs the noise-reduced characteristic signal as information for detecting abnormalities in the inspection area; and a beam irradiation unit that irradiates a beam onto the inspection area when the characteristic signal acquisition unit acquires the characteristic signal before noise reduction that is the basis of the characteristic signal output as information from the noise reduction unit.

[0008]

[11] An inspection method according to the present disclosure includes a first characteristic signal acquisition step of acquiring a first characteristic signal indicating an electrical characteristic of an inspection area of ​​a test object while applying a test voltage or a test current to the inspection area; a first noise signal generation step of generating a first noise signal including noise contained in the test voltage or the test current applied to the inspection area; a first filtering step of filtering the first noise signal using a filter; a parameter setting step of changing filter parameters in a direction that reduces the difference between the noise contained in the first characteristic signal and the noise contained in the filtered first noise signal; The method includes a second characteristic signal acquisition step of acquiring a second characteristic signal indicating an electrical characteristic of the inspection area while applying a test current and irradiating the inspection area with a beam; a second noise signal generation step of generating a second noise signal containing noise contained in the test voltage or test current applied to the inspection area; a second filtering step of filtering the second noise signal using the filter after parameter change; and a noise reduction step of reducing noise in the second characteristic signal by the filtered second noise signal and outputting the noise-reduced second characteristic signal as information for detecting abnormalities in the inspection area.

[0009] In the inspection device of [1] above and the inspection method of

[11] above, filter parameters are changed in a direction that reduces the difference between the noise contained in the characteristic signal and the noise contained in the noise signal after filtering. As a result, when a beam is irradiated onto an area to be inspected and a characteristic signal is acquired, the difference or ratio between the characteristic signal and the noise signal can be calculated, for example, to reduce the noise superimposed on the characteristic signal, i.e., the signal resulting from the measurement. According to these devices and methods, the filter parameters are changed in accordance with the electrical characteristics of the object, so that noise can be effectively reduced even if the electrical characteristics of the object vary. Then, abnormalities in the area to be inspected can be accurately detected based on the characteristic signal with reduced noise.

[0010] [2] In the inspection apparatus of [1] above, the beam irradiator may irradiate the inspection area with a beam even when the characteristic signal acquirer acquires a characteristic signal used to change parameters in the parameter setting unit.

[12] Similarly, in the inspection method of

[11] above, the first characteristic signal acquirer may acquire the first characteristic signal while irradiating the inspection area with a beam. This makes it possible to make the state of the specimen when acquiring a characteristic signal (first characteristic signal) for changing filter parameters the same as the state of the specimen when acquiring a characteristic signal (second characteristic signal) for detecting an abnormality.

[0011] [3] In the inspection apparatus of [1] above, the beam irradiation unit may not irradiate the inspection area with a beam when the characteristic signal acquisition unit acquires the characteristic signal used to change the parameters in the parameter setting unit.

[13] Similarly, in the first characteristic signal acquisition step in the inspection method of

[11] above, the first characteristic signal may be acquired without irradiating the inspection area with a beam. This shortens the beam irradiation time, thereby reducing the risk of damage to the specimen due to beam irradiation.

[0012] [4] In the inspection device of any one of [1] to [3] above, the characteristic signal and the filtered noise signal used in the parameter setting unit may be digital signals, and the parameter setting unit may determine the parameters by digital calculation.

[14] Similarly, in the inspection method of any one of

[11] to

[13] above, the first characteristic signal and the filtered first noise signal used in the parameter setting step may be digital signals, and the parameters may be determined by digital calculation in the parameter setting step. This allows for easy and accurate parameter calculation.

[0013] [5] In the inspection device of [4] above, the noise signal input to the filter may be a digital signal, and the filter may be a digital filter.

[15] Similarly, in the inspection method of

[14] above, the first noise signal and the second noise signal input to the filter may be digital signals, and the filter may be a digital filter. This makes it easy to change parameters.

[0014] [6] In the inspection device of [4] or [5] above, the parameter setting unit may include an evaluation value calculation unit that calculates an evaluation value representing the degree of difference between the noise included in the characteristic signal and the noise included in the filtered noise signal, and a parameter calculation unit that calculates a parameter that reduces the difference based on the evaluation value.

[16] Similarly, in the inspection method of

[14] or

[15] above, the parameter setting step may include an evaluation value calculation step that calculates an evaluation value representing the degree of difference between the noise included in the first characteristic signal and the noise included in the filtered first noise signal, and a parameter calculation step that calculates a parameter that reduces the difference based on the evaluation value. This makes it possible to preferably calculate a parameter that reduces the difference between the noise included in the characteristic signal and the noise included in the filtered noise signal.

[0015] [7] In the inspection device of any one of [1] to [6] above, the parameter setting unit may change parameters so that a difference between noise contained in the characteristic signal and noise contained in the filtered noise signal approaches zero.

[17] Similarly, in the parameter setting step of the inspection method of any one of

[11] to

[16] above, parameters may be changed so that a difference between noise contained in the first characteristic signal and noise contained in the filtered first noise signal approaches zero. This makes it possible to reduce noise more effectively.

[0016] [8] The inspection device according to any one of [1] to [7] above may further include a control unit that fixes the filter parameters after the parameter setting unit changes the parameters.

[18] Similarly, the inspection method according to any one of

[11] to

[17] above may further include a step of fixing the filter parameters after the parameter setting step and before the second filtering step. This allows for stable detection of abnormalities in the inspection area.

[0017] [9] In the inspection device of any one of [1] to [8] above, the beam irradiation unit may irradiate a light beam as the beam.

[19] Similarly, in the inspection method of any one of

[11] to

[18] above, the beam may be a light beam. This makes it possible to more safely change the electrical characteristics of the inspection area of ​​the subject.

[0018]

[10] In the inspection device of any one of [1] to [9] above, the characteristic signal acquisition unit may acquire, as the characteristic signal, a current generated in the inspection area by application of a test voltage or a voltage generated in the inspection area by application of a test current.

[20] Similarly, in the inspection method of any one of

[11] to

[19] above, the first characteristic signal acquisition step and the second characteristic signal acquisition step may acquire, as the first characteristic signal and the second characteristic signal, a current generated in the inspection area by application of a test voltage or a voltage generated in the inspection area by application of a test current, respectively. This enables accurate detection of abnormalities in the inspection area using the OBIRCH measurement method.

[0019] According to the inspection device and inspection method of the present disclosure, even when there is variation in the electrical characteristics of the test object, it is possible to effectively reduce noise superimposed on the signal of the measurement result.

[0020] FIG. 1 is a schematic diagram showing the configuration of an inspection apparatus according to an embodiment. FIG. 2 is a block diagram showing a specific example of the configuration of the inspection apparatus. FIG. 3 is a block diagram showing a transversal filter structure as an example of an FIR filter structure. FIG. 4 is a flowchart showing an example of a method for adjusting filter coefficients based on evaluation values. FIG. 5 is a block diagram showing another specific example of the configuration of the inspection apparatus. FIG. 6 is a flowchart showing the operation of the inspection apparatus according to an embodiment. FIG. 7 is a diagram showing a circuit used in simulations. FIG. 8 is a graph showing a noise waveform. FIG. 9 is a graph showing the time waveform of noise included in a noise signal output from a filter and the time waveform of noise included in a characteristic signal. FIG. 10 is a graph showing the time waveform of noise included in a characteristic signal after filter parameters have been adjusted and the time waveform of noise included in the characteristic signal after noise subtraction. FIG. 11 is a graph showing an enlarged portion of FIG. 10. FIG. 12 is a flowchart showing the operation of an inspection apparatus and an inspection method according to a modified example.

[0021] Hereinafter, embodiments of an inspection device and an inspection method according to the present disclosure will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are given the same reference numerals, and duplicated explanations will be omitted.

[0022] FIG. 1 is a diagram schematically illustrating the configuration of an inspection apparatus 1 according to an embodiment of the present disclosure. The inspection apparatus 1 of this embodiment is an apparatus that uses the OBIRCH method to inspect a semiconductor device S as a test object for defects. The semiconductor device S as a test object is, for example, an electronic device such as a semiconductor integrated circuit. Alternatively, the test object may be, for example, an electronic component such as a capacitor. In this case, in the following description, all references to the semiconductor device S will be interpreted as "electronic component." In the inspection apparatus 1, an external power supply device 2 applies a test voltage or test current to an inspection area of ​​the semiconductor device S. Simultaneously, a beam irradiation unit 10 irradiates the inspection area of ​​the semiconductor device S with a beam B and scans the inspection area with the beam B. A characteristic signal Sa1 indicating the electrical characteristics of the inspection area is extracted from the semiconductor device S in response to the application of the test voltage or test current. When the beam B scans the inspection area of ​​the semiconductor device S, the temperature of the beam-irradiated location changes, changing the resistivity of the location. Therefore, if current is flowing through the location without any abnormality, the value of the characteristic signal will fluctuate due to irradiation with beam B. The inspection device 1 detects an abnormal location in the inspection area of ​​the semiconductor device S based on the presence or absence or degree of change in the characteristic signal Sa1 when beam B is scanned.

[0023] The external power supply 2 is a DC power supply that converts commercial AC power into DC power. The external power supply 2 is, for example, a switching power supply. The external power supply 2 outputs, for example, a test voltage or test current that is constant over time. The inspection device 1 may also be equipped with an internal power supply instead of the external power supply 2.

[0024] The inspection apparatus 1 includes a beam irradiation section 10, an inspection unit 20, and a control unit 30. The beam irradiation section 10 irradiates and scans a beam B onto an inspection area of ​​a semiconductor device S. The beam B is, for example, a light beam, and in one example, a laser beam. The light beam does not necessarily have to be coherent light, and may be incoherent light. The beam B does not necessarily have to be a light beam, and may be radiation such as infrared rays, ultraviolet rays, X-rays, or gamma rays, an electron beam, or ultrasound.

[0025] In one embodiment, the beam irradiation unit 10 includes a beam source 11, a beam scanning unit 12, and a microscope 13. When the beam B is a laser beam, the beam source 11 is, for example, a semiconductor laser or a solid-state laser. When irradiating the semiconductor device S with incoherent light, the beam source 11 may be an SLD (Super Luminescent Diode) or an ASE light source. The beam source 11 generates and emits the beam B. The beam scanning unit 12 is disposed on the optical path of the beam B emitted from the beam source 11. The beam B emitted from the beam source 11 is incident on the beam scanning unit 12. The beam scanning unit 12 irradiates the inspection area with the beam B via the microscope 13 and scans the beam B in a predetermined direction. The beam scanning unit 12 performs, for example, a raster scan in a plane perpendicular to the optical axis direction. The microscope 13 focuses the beam B to a microscopic spot diameter. The microscope 13 obtains an image of the irradiated area by the reflected light of the irradiated beam B.

[0026] The inspection unit 20 detects abnormalities in the inspection area of ​​the semiconductor device S based on the characteristic signal Sa1 acquired from the inspection area of ​​the semiconductor device S. The inspection unit 20 has a sample stage 21, a noise signal output unit 22, a characteristic signal acquisition unit 23, a filter 24, a noise reduction unit 25, and a parameter setting unit 26.

[0027] A semiconductor device S is placed on the sample stage 21. The semiconductor device S placed on the sample stage 21 is positioned at the focal position of the microscope 13. The sample stage 21 has an input terminal and an output terminal. The input terminal of the sample stage 21 is connected to the output terminal of the external power supply 2 via wiring 21a. The semiconductor device S placed on the sample stage 21 is electrically connected to the output terminal of the external power supply 2 through the sample stage 21. A test voltage or test current is applied from the external power supply 2 to the inspection area of ​​the semiconductor device S via the wiring 21a. A characteristic signal Sa1 that indicates the electrical characteristics of the inspection area, which is generated in the inspection area of ​​the semiconductor device S in response to the application of the test voltage or test current, is output from the output terminal of the sample stage 21. The characteristic signal Sa1 is, for example, an analog signal, such as a voltage signal.

[0028] The input terminal of the noise signal output unit 22 is electrically connected to the input terminal of the sample stage 21. That is, the noise signal output unit 22 is electrically connected to the output terminal of the external power supply 2, and is connected in parallel with the semiconductor device S and the sample stage 21 when viewed from the output terminal of the external power supply 2. The noise signal output unit 22 inputs a test voltage or test current to be applied to an area to be inspected of the semiconductor device S. The noise signal output unit 22 outputs a noise signal Sb1 containing noise contained in the test voltage or test current. The noise contained in the noise signal Sb1 has substantially the same waveform and substantially the same frequency band as the noise contained in the test voltage or test current. The noise signal Sb1 output from the noise signal output unit 22 is, for example, a digital signal.

[0029] The characteristic signal acquisition unit 23 is electrically connected to the output terminal of the sample stage 21. That is, the characteristic signal acquisition unit 23 is connected to the external power supply 2 through the sample stage 21 and the semiconductor device S. The characteristic signal acquisition unit 23 acquires a characteristic signal Sa1 from the semiconductor device S. The characteristic signal Sa1 is a current generated in the inspection area when a test voltage is applied, or a voltage generated in the inspection area when a test current is applied. The characteristic signal acquisition unit 23 outputs a characteristic signal Sa2 corresponding to the characteristic signal Sa1. The characteristic signal Sa2 is, for example, a digital signal indicating the magnitude of the characteristic signal Sa1.

[0030] The filter 24 receives the noise signal Sb1 from the noise signal output unit 22. The filter 24 performs filtering on the noise signal Sb1. The filter 24 is, for example, a digital filter. The transfer function of the filter 24 is determined by a plurality of parameters. The filter 24 outputs a noise signal Sb2 generated by filtering the noise signal Sb1. If the filter 24 is a digital filter, the noise signal Sb2 is a digital signal.

[0031] The noise reduction unit 25 reduces the noise contained in the characteristic signal Sa2 using the noise signal Sb2 that has been filtered by the filter 24. Specifically, the noise reduction unit 25 reduces the noise contained in the characteristic signal Sa2 by calculating the difference (or ratio) between the noise signal Sb2 and the characteristic signal Sa2. This calculation is, for example, a digital calculation. The noise reduction unit 25 outputs a characteristic signal Sa3, which is a signal obtained by reducing the noise from the characteristic signal Sa2. The characteristic signal Sa3 is, for example, a digital signal.

[0032] The parameter setting unit 26 adjusts, i.e., changes, multiple parameters of the filter 24. The parameter setting unit 26 adjusts the multiple parameters of the filter 24 in a direction that reduces the difference between the noise included in the characteristic signal Sa2 and the noise included in the noise signal Sb2. The parameter setting unit 26 may adjust the multiple parameters of the filter 24 so that the difference between the noise included in the characteristic signal Sa2 and the noise included in the noise signal Sb2 approaches zero. In one embodiment, the parameter setting unit 26 inputs the characteristic signal Sa3 from the noise reduction unit 25, and adjusts the multiple parameters of the filter 24 in a direction that reduces (or approaches zero) the noise included in the characteristic signal Sa3. In one example, the parameter setting unit 26 determines each of the multiple parameters by digital calculation.

[0033] After the plurality of parameters have been adjusted, the noise reduction unit 25 again receives the noise signal Sb2 that has been filtered by the filter 24. The noise reduction unit 25 reduces the noise in the characteristic signal Sa2 using the noise signal Sb2. The noise reduction unit 25 outputs the characteristic signal Sa3 after the noise reduction as information for detecting abnormalities in the inspection region of the semiconductor device S.

[0034] The control unit 30 controls the beam irradiation unit 10 and the inspection unit 20. The control unit 30 presents information to an operator based on the characteristic signal Sa3 output from the noise reduction unit 25. The information is information for detecting abnormalities in the inspection area of ​​the semiconductor device S. In one embodiment, the control unit 30 includes a control unit 31 and a display unit 32. The control unit 31 is connected to the beam scanning unit 12, the microscope 13, the noise reduction unit 25, the parameter setting unit 26, and the display unit 32. The control unit 31 controls the scanning of the beam B by the beam scanning unit 12, the acquisition of an image of the semiconductor device S by the microscope 13, the adjustment of multiple parameters by the parameter setting unit 26, and the display of information by the display unit 32. After the adjustment of the multiple parameters by the parameter setting unit 26, the control unit 31 may output a control signal to the parameter setting unit 26 to fix the multiple parameters of the filter 24. The control unit 31 displays the distribution of the electrical characteristics of the semiconductor device S on the display unit 32 based on the characteristic signal Sa3 output from the noise reduction unit 25. The electrical characteristics of the semiconductor device S change as the beam B is irradiated and scanned. The display unit 32 is, for example, a display such as an LCD monitor. The control unit 31 physically includes a computer including a processor (Central Processing Unit) such as a CPU, recording media such as Random Access Memory (RAM) and Read Only Memory (ROM), a communication module, and input / output devices such as a mouse and a keyboard. The control unit 31 may include multiple computers. The control unit 31 may also be configured using a Field Programmable Gate Array (FPGA), an application specific integrated circuit (ASIC), a system on a chip (SoC), a microcomputer, or the like.

[0035] Fig. 2 is a block diagram showing a specific example of the configuration of the inspection apparatus 1. Fig. 2 shows a configuration for applying a test voltage to an area under inspection of a semiconductor device S. In the example shown in Fig. 2, the positive electrode (potential SV+) of the external power supply 2 is connected to a node 51, and the negative electrode (potential SV-) of the external power supply 2 is connected to a node 52. The node 51 is electrically connected to one end of the area under inspection of the semiconductor device S. The node 52 is electrically connected to the other end of the area under inspection of the semiconductor device S. As a result, the voltage between the positive and negative electrodes of the external power supply 2 is applied to the area under inspection of the semiconductor device S as a test voltage.

[0036] The characteristic signal acquisition unit 23 includes a current-voltage conversion unit 231 and an A / D converter 232. In the illustrated example, the current-voltage conversion unit 231 is provided between the node 52 and the semiconductor device S. The current-voltage conversion unit 231 includes, for example, a shunt resistor. The current-voltage conversion unit 231 generates a signal SA1, which is an analog signal and a voltage signal. The signal SA1 is a signal corresponding to the magnitude of a current (corresponding to the characteristic signal Sa1 shown in FIG. 1) generated in an area to be inspected of the semiconductor device S due to application of a test voltage. The current-voltage conversion unit 231 may be provided between the node 51 and the semiconductor device S. The A / D converter 232 is electrically connected to the output terminal of the current-voltage conversion unit 231. The A / D converter 232 converts the signal SA1 output from the current-voltage conversion unit 231 into a digital signal SD1. The signal SD1 corresponds to the characteristic signal Sa2 shown in FIG. 1. The A / D converter 232 operates in synchronization with the clock CL output from the clock circuit 53 .

[0037] The noise signal output unit 22 includes an amplifier 221 and an A / D converter 222. In the example shown in FIG. 2, the amplifier 221 is a differential input amplifier having two input terminals. One of the two input terminals is electrically connected to node 51. The other of the two input terminals is electrically connected to node 52. In one example, these input terminals are connected (short-circuited) to the positive and negative electrodes of the external power supply 2, respectively, via substantially zero electrical resistance. In this case, the test voltage output from the external power supply 2 is input directly to these input terminals. The amplifier 221 amplifies the voltage between the two input terminals and outputs an amplified signal SA2. The signal SA2 is an analog signal and a voltage signal. The A / D converter 222 is electrically connected to the output terminal of the amplifier 221. The A / D converter 222 converts the signal SA2 output from the amplifier 221 into a digital signal SD2. The signal SD2 corresponds to the noise signal Sb1 shown in FIG. 1. The A / D converter 222 operates in synchronization with the clock CL output from the clock circuit 53. That is, the clock CL is a common clock for the A / D converters 222 and 232.

[0038] The filter 24 receives the signal SD2 output from the A / D converter 222. The filter 24 filters the signal SD2 and outputs the filtered signal as a signal SD3. The signal SD3 corresponds to the noise signal Sb2 in FIG. 1. The filter 24 is, for example, a finite impulse response (FIR) filter. FIG. 3 is a block diagram showing a transversal filter structure as an example of an FIR filter structure. The filter 24 shown in FIG. 3 has M delay elements 61(0) to 61(M-1), (M+1) filter coefficient blocks 62(0) to 62(M), and one adder 63. Each of the filter coefficient blocks 62(0) to 62(M) includes a filter coefficient b ０ ~b Ｍ The delay elements 61(0) to 61(M-1) are arranged in series in this order. The input signal to the first delay element 61(0) is filtered by the filter coefficient b０ The output signal from the delay element 61(0) is multiplied by the filter coefficient b １ After that, the output signal from the delay element 61(m) is multiplied by the filter coefficient b ｍ＋１ The multiple output signals multiplied by the filter coefficients are all added together by an adder 63. The signal after addition by the adder 63 becomes the signal SD3 output from the filter 24 shown in FIG. 2. In this example, the multiple parameters of the filter 24 mentioned above are (M+1) filter coefficients b ０ ~b Ｍ Refers to...

[0039] Referring again to FIG. 2, the noise reduction unit 25 includes a subtraction unit 251. The subtraction unit 251 subtracts the signal input to the input terminal 251a from the signal input to the input terminal 251b, and outputs the remaining signal from the output terminal 251c. The noise reduction unit 25 performs this calculation digitally. The input terminal 251b receives the signal SD1. The input terminal 251a receives the signal SD3. Therefore, the subtraction unit 251 outputs a signal SD4 indicating the difference between the signal SD1 and the signal SD3. The signal SD4 corresponds to the characteristic signal Sa3 shown in FIG. 1.

[0040] The parameter setting unit 26 determines a plurality of parameters of the filter 24 by repeated calculation. The plurality of parameters of the filter 24 are repeatedly adjusted when the control signal HLD provided from the control unit 31 is at a first level (e.g., a high level). The plurality of parameters of the filter 24 are fixed when the control signal HLD is at a second level (e.g., a low level). The parameter setting unit 26 has an evaluation value calculation unit 261 and a parameter calculation unit 262. The evaluation value calculation unit 261 calculates an evaluation value. The evaluation value represents the degree of difference between the noise contained in the signal SD1 (i.e., the characteristic signal Sa2) and the noise contained in the signal SD3 (i.e., the noise signal Sb2) after filtering by the filter 24. For example, an evaluation value that decreases as the difference between these noises decreases is used. The time series data of the signal SD1 is expressed as y=(y ０ , y １ , y ２ , ..., y ｋ), and the time series data of the signal SD2 is x=(x ０ , x １ , x ２ , ..., x ｋ ), and the time series data of the signal SD3 is x'=(x ０ ', x １ ', x ２ ',...,x ｋ In this case, the evaluation function f Eval (x', y, N) is set, for example, as in the following mathematical formula (1). N represents the length of the data string used to calculate the evaluation value E. The evaluation function for calculating the evaluation value E is not limited to this. The parameter calculation unit 262 calculates a plurality of parameters (filter coefficients b ０ ~b Ｍ ) is calculated.

[0041] FIG. 4 shows the filter coefficient b ０ ~b Ｍ 1 is a flowchart showing an example of a method for adjusting the filter coefficient b. First, in step ST11, the parameter setting unit 26 starts parameter adjustment when it confirms that the control signal HLD from the control unit 31 has reached the first level. In step ST12, the evaluation value calculation unit 261 calculates the evaluation value E based on the value of x'-y output from the subtraction unit 251. At this time, the filter coefficient of the filter 24 is b ０ ~b Ｍ As a function for calculating the evaluation value E, for example, the evaluation function f Eval (x', y, N) is used. At this time, the variable j is set to an initial value (for example, 0). In step ST13, the parameter calculation unit 262 calculates the filter coefficient b ｊ The value of b ｊ +Δb (Δb is a predetermined change amount). Then, in step ST14, the evaluation value calculation unit 261 calculates the evaluation value E ｊ ' is calculated. ｊ The function for calculating ' also includes, for example, the evaluation function f Eval(x', y, N) is used. Then, the parameter calculation unit 262 calculates the filter coefficient b ｊ The value of the variable j is returned to its original value. If the variable j does not reach M (step ST15: NO), 1 is added to the variable j (step ST16). Then, the evaluation value calculation unit 261 and the parameter calculation unit 262 repeat the above-mentioned steps ST13 and ST14. As a result, when the variable j reaches M (step ST15: YES), the time-series data of the evaluation value E'=(E ０ ', E １ ', E ２ ', ..., E Ｍ ') is obtained.

[0042] Thereafter, in step ST17, the parameter calculation unit 262 calculates time series data g relating to the difference between the time series data E' of the evaluation value and the original evaluation value E = (E, E, E, ..., E). Then, in step ST18, the parameter calculation unit 262 calculates the filter coefficient b = (b ０ , b １ , b ２ , ..., b Ｍ ) is changed to b-αg, where α is a constant that affects the convergence of the optimization calculation. α can be determined, for example, according to Newton's method.

[0043] In step ST19, the parameter setting unit 26 checks the control signal HLD from the control unit 31. As long as the control signal HLD is at the first level (step ST19: NO), the parameter setting unit 26 repeats the above-described steps ST12 to ST18. As a result, the optimum filter coefficient b=(b ０ , b １ , b ２ , ..., b Ｍ When the control signal HLD becomes the second level (step ST19: YES), the parameter setting unit 26 ends the search and fixes the filter coefficient b.

[0044] In this way, the parameter setting unit 26 finds the optimal parameter (filter coefficient b) by alternately repeating the calculation of the evaluation value E by the evaluation value calculation unit 261 and the calculation of the parameter (filter coefficient b) by the parameter calculation unit 262. The length of the period during which the control signal HLD is at the first level, in other words, the time during which the parameter setting unit 26 searches for the optimal filter coefficient b, is set in advance to a time sufficient for the calculation to converge. The length of the period during which the control signal HLD is at the first level is, for example, 5 seconds. This time is set in advance depending on the processing capabilities of the noise reduction unit 25 and the parameter setting unit 26.

[0045] FIG. 5 is a block diagram showing another specific example of the configuration of the inspection apparatus 1. FIG. 5 shows a configuration for applying a test current to an area under inspection of a semiconductor device S. The example shown in FIG. 5 differs from the example shown in FIG. 2 in the following respects and is identical to the example shown in FIG. 2 in other respects. The characteristic signal acquisition unit 23 does not include the current-voltage conversion unit 231 shown in FIG. 2, but includes an A / D converter 232 and a differential amplifier 233. The A / D converter 232 is electrically connected to nodes 51 and 52 via the differential amplifier 233. The A / D converter 232 inputs a voltage proportional to the voltage across the area under inspection of the semiconductor device S. The voltage across the area under inspection is a voltage generated by application of the test current. The A / D converter 232 outputs a signal SD1, which is a digital signal corresponding to this voltage across the area under inspection. In this example, the noise signal output unit 22 includes a current-voltage conversion unit 223. The current-voltage conversion unit 223 is provided between the external power supply 2 and the semiconductor device S. The current-voltage conversion unit 223 includes, for example, a shunt resistor. The current-voltage conversion unit 223 outputs a signal SA1, which is a voltage signal corresponding to the magnitude of the test current. The amplifier 221 is electrically connected to the output terminal of the current-voltage conversion unit 223. The amplifier 221 amplifies the signal SA1 and outputs an amplified signal SA2.

[0046] 6 is a flowchart showing the operation of the inspection device 1 according to this embodiment. The operation of the inspection device 1 and the inspection method according to this embodiment will be described with reference to FIG.

[0047] First, a first characteristic signal acquisition step ST21, a first noise signal generation step ST22, and a first filtering step ST23 are performed. In the first characteristic signal acquisition step ST21, while applying a test voltage or test current from the external power supply 2 to the inspection area of ​​the semiconductor device S, the characteristic signal acquisition unit 23 acquires a characteristic signal Sa1, which is an analog signal, as a first characteristic signal indicating the electrical characteristics of the inspection area. The characteristic signal acquisition unit 23 outputs a characteristic signal Sa2, which is a digital signal corresponding to the characteristic signal Sa1. The characteristic signal Sa2 is used to adjust parameters in the subsequent parameter setting step ST24. In this first characteristic signal acquisition step ST21, the characteristic signal Sa1 is acquired without irradiating the inspection area with the beam B. In the first noise signal generation step ST22, the noise signal output unit 22 generates a noise signal Sb1, which is a digital signal, as a first noise signal containing noise contained in the test voltage or test current applied to the inspection area of ​​the semiconductor device S. After the first noise signal generating step ST22, in a first filtering step ST23, the filter 24 filters the noise signal Sb1 and outputs a noise signal Sb2. The filter 24 is, for example, a digital filter.

[0048] The order of the first characteristic signal acquisition step ST21 and the step group consisting of the first noise signal generation step ST22 and the first filtering step ST23 is not limited to the above. The first characteristic signal acquisition step ST21 may be performed after the first noise signal generation step ST22 and the first filtering step ST23, or the first characteristic signal acquisition step ST21 may be performed simultaneously with the first noise signal generation step ST22 and the first filtering step ST23.

[0049] Subsequently, in a parameter setting step ST24, the parameter setting unit 26 performs digital calculations to adjust the parameters (filter coefficients b) of the filter 24 in a direction that reduces the difference between the noise contained in the characteristic signal Sa2 and the noise contained in the filtered noise signal Sb2. In one example, in the parameter setting step ST24, the parameters are adjusted so that the difference between the noise contained in the characteristic signal Sa2 and the noise contained in the filtered noise signal Sb2 approaches zero.

[0050] The parameter setting step ST24 includes an evaluation value calculation step ST241 and a parameter calculation step ST242. In the evaluation value calculation step ST241, the evaluation value calculation unit 261 calculates an evaluation value E. The evaluation value E represents the degree of difference between the noise contained in the characteristic signal Sa2 and the noise contained in the filtered noise signal Sb2. In the parameter calculation step ST242, the parameter calculation unit 262 calculates a parameter that reduces the difference based on the evaluation value E. Until a predetermined time has elapsed, i.e., while the control unit 31 keeps the control signal HLD at the first level, the first filtering step ST23, the evaluation value calculation step ST241, and the parameter calculation step ST242 are repeated many times. As a result, the parameters of the filter 24 gradually converge. After the predetermined time has elapsed, the control unit 31 sets the control signal HLD to the second level. This ends the repeated calculation, and the parameters of the filter 24 are fixed (parameter fixation step ST25).

[0051] Subsequently, a second characteristic signal acquisition step ST26, a second noise signal generation step ST27, and a second filtering step ST28 are performed. In the second characteristic signal acquisition step S26, similar to the first characteristic signal acquisition step S21, a test voltage or test current is applied from the external power supply 2 to the inspection area of ​​the semiconductor device S. Additionally, in the second characteristic signal acquisition step S26, the beam irradiation unit 10 irradiates and scans the inspection area with beam B. Then, while applying the test voltage or test current and scanning with beam B, the characteristic signal acquisition unit 23 again acquires a characteristic signal Sa1, which is an analog signal, as a second characteristic signal indicating the electrical characteristics of the inspection area. The characteristic signal Sa1 is the characteristic signal before noise reduction. The characteristic signal before noise reduction serves as the basis for a characteristic signal Sa3 output from the noise reduction unit 25 in the subsequent noise reduction step ST29. The characteristic signal acquisition unit 23 outputs a characteristic signal Sa2, which is a digital signal corresponding to the characteristic signal Sa1. In a second noise signal generating step ST27, the noise signal output unit 22 generates a noise signal Sb1 again as a second noise signal containing noise contained in the test voltage or test current applied to the inspection target region of the semiconductor device S. After the second noise signal generating step ST27, in a second filtering step ST28, the filter 24 after parameter adjustment performs filtering on the noise signal Sb1 and outputs a noise signal Sb2.

[0052] The order of the second characteristic signal acquisition step ST26 and the step group consisting of the second noise signal generation step ST27 and the second filtering step ST28 is not limited to the above. The second characteristic signal acquisition step ST26 may be performed after the second noise signal generation step ST27 and the second filtering step ST28, or the second characteristic signal acquisition step ST26 may be performed simultaneously with the second noise signal generation step ST27 and the second filtering step ST28.

[0053] Next, a noise reduction step ST29 is performed. In the noise reduction step ST29, the noise reduction unit 25 reduces the noise in the characteristic signal Sa2 using the noise signal Sb2 that has been filtered in the second filtering step ST28. The noise reduction unit 25 outputs the noise-reduced characteristic signal Sa3 as information for detecting an abnormality in the inspection area. The control unit 30 presents the operator with information for detecting an abnormality in the inspection area of ​​the semiconductor device S based on the characteristic signal Sa3 output from the noise reduction unit 25.

[0054] The effects achieved by the inspection apparatus 1 and inspection method according to the present embodiment described above will now be described. In the inspection apparatus 1 and inspection method according to the present embodiment, the parameters of the filter 24 are adjusted to reduce the difference between the noise contained in the characteristic signal Sa2 and the noise signal Sb2 after filtering. This allows, when the inspection area is irradiated with the beam B and the characteristic signal Sa1 is acquired, to calculate, for example, the difference or ratio between the characteristic signal Sa2 and the noise signal Sb2, thereby reducing the noise superimposed on the characteristic signal Sa3, i.e., the measurement result signal. According to the inspection apparatus 1 and inspection method according to the present embodiment, the parameters of the filter 24 are adjusted according to the electrical characteristics of the semiconductor device S, thereby effectively reducing noise even if the electrical characteristics of the semiconductor device S vary. Furthermore, abnormalities in the inspection area can be accurately detected based on the noise-reduced characteristic signal Sa3.

[0055] As in the present embodiment, in the first characteristic signal acquisition step ST21, the characteristic signal Sa1 may be acquired without irradiating the inspection area with the beam B from the beam irradiation unit 10. In this case, the irradiation time of the beam B can be shortened, thereby reducing the risk of damage to the semiconductor device S due to irradiation with the beam B.

[0056] As in the present embodiment, the characteristic signal Sa2 and the filtered noise signal Sb2 used in the parameter setting unit 26 (parameter setting step ST24) may be digital signals, and the parameter setting unit 26 (in parameter setting step ST24) may determine the parameters by digital calculation, thereby enabling easy and accurate calculation of the parameters.

[0057] As in this embodiment, the noise signal Sb1 input to the filter 24 may be a digital signal, and the filter 24 may be a digital filter, which makes it possible to easily adjust the parameters.

[0058] As in the present embodiment, the parameter setting unit 26 may include an evaluation value calculation unit 261 that calculates an evaluation value E that indicates the degree of difference between the noise included in the characteristic signal Sa2 and the noise included in the filtered noise signal Sb2, and a parameter calculation unit 262 that calculates a parameter that reduces the difference based on the evaluation value E. Similarly, the parameter setting step ST24 may include an evaluation value calculation step ST241 that calculates an evaluation value E that indicates the degree of difference between the noise included in the characteristic signal Sa2 and the noise included in the filtered noise signal Sb2, and a parameter calculation step ST242 that calculates a parameter that reduces the difference based on the evaluation value E. This makes it possible to preferably calculate a parameter that reduces the difference between the noise included in the characteristic signal Sa2 and the noise included in the filtered noise signal Sb2.

[0059] As described above, the parameter setting unit 26 (at parameter setting step ST24) may adjust the parameters so that the difference between the noise contained in the characteristic signal Sa2 and the noise contained in the filtered noise signal Sb2 approaches zero, thereby enabling more effective noise reduction.

[0060] As in the present embodiment, the inspection apparatus 1 may include a control unit 31 that fixes the parameters of the filter 24 after the parameters are adjusted by the parameter setting unit 26. Similarly, the inspection method may include a parameter fixing step ST25 that fixes the parameters of the filter 24 after the parameter setting step ST24 and before the second filtering step ST28. This allows for stable detection of abnormalities in the inspection area.

[0061] As in the present embodiment, the beam irradiation unit 10 may irradiate the semiconductor device S with a light beam. Similarly, in the inspection method, the beam irradiated to the semiconductor device S may be a light beam. In this case, the electrical characteristics in the inspection area of ​​the semiconductor device S can be changed more safely compared to when the beam is something other than a light beam (such as an electron beam or an X-ray beam).

[0062] As in the present embodiment, the characteristic signal acquiring unit 23 (in the first characteristic signal acquiring step ST21 and the second characteristic signal acquiring step ST26) may acquire, as the characteristic signal Sa1, a current generated in the inspection area when the test voltage is applied, or a voltage generated in the inspection area when the test current is applied, thereby enabling accurate detection of abnormalities in the inspection area using the OBIRCH measurement method.

[0063] The control unit 31 may have a storage area for storing adjusted parameters of the filter 24. This allows previously adjusted parameters to be read and used according to the type of semiconductor device S. This reduces the number of parameter adjustments and shortens the time required for inspection. Adjusted parameters may be provided to the parameter setting unit 26 from the storage area of ​​the control unit 31 according to the type of semiconductor device S to be inspected. Alternatively, the control unit 31 may store a plurality of adjusted parameter sets corresponding to a plurality of types of semiconductor device S, and when inspection starts, the parameter setting unit 26 may set the plurality of parameter sets in the filter 24 in order, so that the most suitable parameter set is ultimately selected.

[0064] Various types of semiconductor devices S may be prepared before inspection, and parameter sets suitable for each semiconductor device S may be collected by steps ST21 to ST24 shown in FIG. 6 . Then, using the collected parameter sets, machine learning may be used to learn the relationship between noise patterns and optimal parameters, creating an inference device. This allows the noise signal Sb1 to be input to the inference device during inspection, and optimal parameters to be calculated in a short time, thereby shortening the time required for inspection. Alternatively, steps ST21 to ST24 may be performed using the parameters calculated by the inference device as initial values, thereby shortening the time required for parameter adjustment and shortening the time required for inspection. [Example]

[0065] Here, the results of a simulation of the effects of the above embodiment will be described. Fig. 7 is a diagram showing a circuit used in this simulation. In this circuit, a resistor is provided as the semiconductor device S. An ammeter 231a and a low-pass filter 231b are provided as the current-voltage conversion unit 231. The low-pass filter 231b is a delay element used during current-voltage conversion. A square element 261a and an integral element 261b are provided in series as the evaluation value calculation unit 261.

[0066] FIG. 8 is a graph showing the waveforms of noise contained in the characteristic signal Sa2 and the noise signal Sb2. In FIG. 8, the vertical axis represents noise intensity (arbitrary units), and the horizontal axis represents the irradiation position (number) of the beam B within the inspection area. In FIG. 8, noise waveform G11 represents the noise waveform contained in the noise signal Sb2 output from the filter 24, and noise waveform G12 represents the noise waveform contained in the characteristic signal Sa2 output from the current-voltage conversion unit 231. Part (a) of FIG. 9 is an enlarged view of region C1 in FIG. 8. Part (b) of FIG. 9 is an enlarged view of region C2 in FIG. 8. Referring to FIGS. 8 and 9, it can be seen that the magnitude of the noise contained in the noise signal Sb2 gradually approaches the magnitude of the noise contained in the characteristic signal Sa2 as the irradiation position of the beam B moves, in other words, as time passes.

[0067] Fig. 10 is a graph showing a time waveform A12 of noise contained in the characteristic signal Sa2 after the parameters of the filter 24 have been adjusted, and a time waveform A13 of noise contained in the characteristic signal Sa3 after noise subtraction. In Fig. 10, the vertical axis represents noise intensity (arbitrary units), and the horizontal axis represents the irradiation position (number) of the beam B within the inspection area. Fig. 11 is a graph showing an enlarged portion of Fig. 10. Referring to Figs. 10 and 11, it can be seen that the spike-like noise contained in the characteristic signal Sa2 is effectively reduced in the characteristic signal Sa3. [Modification]

[0068] In the above embodiment, in the first characteristic signal acquisition step ST21, the characteristic signal Sa1 is acquired without irradiating the inspection area with the beam B from the beam irradiation unit 10. This is not limited to this configuration, and in the first characteristic signal acquisition step ST21, the characteristic signal Sa1 may be acquired while irradiating and scanning the inspection area with the beam B from the beam irradiation unit 10. This makes it possible to make the state of the semiconductor device S when acquiring the characteristic signal Sa1 for changing the parameters of the filter 24 the same as the state of the semiconductor device S when acquiring the characteristic signal Sa1 for detecting an abnormal portion of the semiconductor device S. Therefore, for example, even if irradiation with the beam B increases the average temperature of the entire semiconductor device S and changes the characteristics of the semiconductor device S, the parameters can be set appropriately.

[0069] In the above embodiment, the first filtering step ST23, the evaluation value calculation step ST241, and the parameter calculation step ST242 are repeated until a predetermined time has elapsed. Then, after the predetermined time has elapsed, the control unit 31 sets the control signal HLD to the second level in the parameter fixation step ST25, thereby fixing the parameters of the filter 24. This is not limiting, and the control unit 31 may set the control signal HLD to the second level in the parameter fixation step ST25 after the evaluation value E has converged within a predetermined range, thereby fixing the parameters of the filter 24.

[0070] In the above embodiment, the parameters of the filter 24 are set, and then information for detecting abnormalities in the inspection area of ​​the semiconductor device S is presented to the operator. This configuration is not limited to this. If the operator determines that the information for detecting abnormalities in the inspection area of ​​the semiconductor device S contains a large amount of noise while it is being presented to the operator, the parameters of the filter 24 may be adjusted as needed. FIG. 12 is a flowchart showing the operation of the inspection apparatus 1 and an inspection method of this configuration. First, the parameters of the filter 24 are set to predetermined values, and then the characteristic signal acquisition step ST31, the noise signal generation step ST32, the filtering step ST33, and the noise reduction step ST34 are performed. The details of the characteristic signal acquisition step ST31, the noise signal generation step ST32, the filtering step ST33, and the noise reduction step ST34 are the same as those of the second characteristic signal acquisition step ST26, the second noise signal generation step ST27, the second filtering step ST28, and the noise reduction step ST29 described above. If the operator determines that the information for detecting an abnormality contains a large amount of noise, the operator performs a stop input operation (step ST35), which causes the irradiation of beam B to be stopped (step ST36). Then, with the information for detecting an abnormality being presented to the operator, adjustment of the parameters of filter 24 is started. The subsequent operations are the same as those shown in FIG. 6.

[0071] 12 , the control unit 31 may determine the stop input operation in step ST35 instead of the operator. That is, if the control unit 31 determines that the information for detecting an abnormality contains a large amount of noise, the stop input operation may be performed, thereby stopping the irradiation of the beam B. The control unit 31 may determine the amount of noise based on the magnitude of the high-frequency component contained in the characteristic signal Sa3 (or contained in the information). Alternatively, if the control unit 31 determines that the information for detecting an abnormality contains a large amount of noise, the control unit 31 may suggest to the operator that the parameters of the filter 24 be adjusted, and the parameter adjustment may be started in response to the stop input operation from the operator.

[0072] In the above embodiment, the characteristic signal Sa3 after noise reduction is not output as information for detecting an abnormality while the parameters of the filter 24 are being adjusted. However, the present invention is not limited to this embodiment, and the characteristic signal Sa3 after noise reduction may be output as information for detecting an abnormality while the parameters of the filter 24 are being adjusted. In other words, the information for detecting an abnormality may be presented to the operator and the parameters of the filter 24 may be adjusted in parallel.

[0073] The inspection device and inspection method according to the present disclosure are not limited to the above-described embodiment, and various other modifications are possible. For example, in the above embodiment, an FIR filter is used as the filter 24. Although an FIR filter is a stable filter in principle, the type of filter 24 is not limited to this. For example, the filter 24 may be a moving average filter or an infinite impulse response (IIR) filter. A moving average filter is also a stable filter like an FIR filter. An IIR filter can realize a more complex filter.

[0074] In the above embodiment, the characteristic signal Sa2 and the noise signal Sb1 are digital signals, and the filter 24 is a digital filter. However, the inspection device and inspection method according to the present disclosure are not limited to this configuration. The characteristic signal Sa2 and the noise signal Sb1 may be analog signals, and the filter 24 may be an analog filter.

[0075] In the above embodiment, an example of the inspection device and the inspection method performing OBIRCH measurement has been described. The inspection device and the inspection method according to the present disclosure may also perform OBIC measurement, which generates a photovoltaic current in a semiconductor by irradiating the semiconductor with a beam. Even in this case, the same effects as those described above can be achieved.

[0076] 1... inspection device, 2... external power supply device, 10... beam irradiation unit, 11... beam generation source, 12... beam scanning unit, 13... microscope, 20... inspection unit, 21... sample stage, 21a... wiring, 22... noise signal output unit, 23... characteristic signal acquisition unit, 24... filter, 25... noise reduction unit, 26... parameter setting unit, 30... control unit, 31... control unit, 32... display unit, 51, 52... node, 53... clock circuit, 61(0) to 61(M-1)... delay elements, 62(0) to 62(M)... filter coefficient block, 63... adder, 221... amplifier, 222, 232... A / D converter, 223, 231... current-voltage conversion unit, 231a...ammeter, 231b...low-pass filter, 233...differential amplifier, 251...subtraction unit, 251a, 251b...input terminal, 251c...output terminal, 261...evaluation value calculation unit, 261a...squaring element, 261b...integral element, 262...parameter calculation unit, A11, A12, A13...time waveform, B...beam, CL...clock, G11, G12...noise waveform, HLD...control signal, S...semiconductor device, S21...first characteristic signal acquisition step, S26...second characteristic signal acquisition step, Sa1, Sa2, Sa3...characteristic signal, SA1, SA2, SD1, SD2, SD3, SD4...signal, Sb1, Sb2...noise signal.

Claims

1. a characteristic signal acquiring unit that acquires a characteristic signal that indicates an electrical characteristic of an area under test in a test subject to which a test voltage or a test current is applied; a noise signal output unit that outputs a noise signal containing noise included in the test voltage or the test current applied to the inspection target area; a filter for filtering the noise signal; a parameter setting unit that changes parameters of the filter in a direction that reduces the difference between noise included in the characteristic signal and noise included in the noise signal after the filtering process; a noise reduction unit that reduces noise in the characteristic signal by the noise signal that has been subjected to the filtering process after the parameters have been changed by the parameter setting unit, and outputs the characteristic signal after the noise reduction as information for detecting an abnormality in the inspection area; a beam irradiation unit that irradiates the inspection area with a beam when the characteristic signal acquisition unit acquires the characteristic signal before noise reduction, which is the basis of the characteristic signal output as the information from the noise reduction unit; An inspection device comprising:

2. 2. The inspection device according to claim 1, wherein the beam irradiating section irradiates the inspection area with the beam even when the characteristic signal acquiring section acquires the characteristic signal used to change the parameter in the parameter setting section.

3. 2. The inspection device according to claim 1, wherein the beam irradiating section does not irradiate the inspection area with the beam when the characteristic signal acquiring section acquires the characteristic signal used to change parameters in the parameter setting section.

4. the characteristic signal and the filtered noise signal used in the parameter setting unit are digital signals; The inspection device according to claim 1 , wherein the parameter setting unit determines the parameters by digital calculation.

5. 5. The inspection device according to claim 4, wherein the noise signal input to the filter is a digital signal, and the filter is a digital filter.

6. The parameter setting unit an evaluation value calculation unit that calculates an evaluation value that indicates the degree of difference between the noise included in the characteristic signal and the noise included in the noise signal after the filtering process; a parameter calculation unit that calculates the parameter that changes the difference in a direction that reduces the difference based on the evaluation value; The inspection device according to claim 4 , further comprising:

7. The inspection device according to any one of claims 1 to 6, wherein the parameter setting unit changes the parameters so that a difference between the noise contained in the characteristic signal and the noise contained in the noise signal after the filtering process approaches zero.

8. 7. The inspection device according to claim 1, further comprising a control unit that fixes the parameters of the filter after the parameters are changed by the parameter setting unit.

9. 7. The inspection device according to claim 1, wherein the beam irradiation unit irradiates a light beam as the beam.

10. The inspection device according to any one of claims 1 to 6, wherein the characteristic signal acquisition unit acquires, as the characteristic signal, a current generated in the inspection area when the test voltage is applied, or a voltage generated in the inspection area when the test current is applied.

11. a first characteristic signal acquiring step of acquiring a first characteristic signal indicating an electrical characteristic of an inspection area of ​​a test object while applying a test voltage or a test current to the inspection area; a first noise signal generating step of generating a first noise signal including noise contained in the test voltage or the test current applied to the inspection area; a first filtering step of filtering the first noise signal using a filter; a parameter setting step of changing parameters of the filter in a direction that reduces a difference between noise included in the first characteristic signal and noise included in the first noise signal after the filtering process; a second characteristic signal acquiring step of acquiring a second characteristic signal indicating an electrical characteristic of the inspection area while applying the test voltage or the test current to the inspection area and irradiating the inspection area with a beam; a second noise signal generating step of generating a second noise signal including noise contained in the test voltage or the test current applied to the inspection area; a second filtering step of filtering the second noise signal using the filter after changing parameters; a noise reduction step of reducing noise in the second characteristic signal by the second noise signal that has been subjected to the filtering process, and outputting the noise-reduced second characteristic signal as information for detecting an abnormality in the inspection area; 12. A testing method comprising:

12. 12. The inspection method according to claim 11, wherein in the first characteristic signal acquiring step, the first characteristic signal is acquired while irradiating the inspection area with a beam.

13. 12. The inspection method according to claim 11, wherein in the first characteristic signal acquiring step, the first characteristic signal is acquired without irradiating the region to be inspected with a beam.

14. the first characteristic signal and the filtered first noise signal used in the parameter setting step are digital signals; The inspection method according to claim 11, wherein the parameter setting step determines the parameters by digital calculation.

15. 15. The inspection method according to claim 14, wherein the first noise signal and the second noise signal input to the filter are digital signals, and the filter is a digital filter.

16. The parameter setting step includes: an evaluation value calculation step of calculating an evaluation value representing a degree of difference between noise included in the characteristic signal and noise included in the first noise signal after the filtering process; a parameter calculation step of calculating the parameter that changes the difference in a direction that reduces the difference based on the evaluation value; The inspection method according to claim 14, comprising:

17. The inspection method according to any one of claims 11 to 16, wherein in the parameter setting step, the parameters are changed so that a difference between the noise contained in the first characteristic signal and the noise contained in the first noise signal after the filtering process approaches zero.

18. The inspection method according to any one of claims 11 to 16, further comprising the step of fixing the parameters of the filter after the parameter setting step and before the second filtering step.

19. The inspection method according to any one of claims 11 to 16, wherein the beam is a light beam.

20. 17. The inspection method according to claim 11, wherein in the first characteristic signal acquisition step and the second characteristic signal acquisition step, a current generated in the inspection area by application of the test voltage, or a voltage generated in the inspection area by application of the test current, is acquired as the first characteristic signal and the second characteristic signal, respectively.