JP2007064921A - Defect inspection equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a defect inspection apparatus capable of acquiring an image to be inspected with high accuracy and obtaining sufficient defect detection accuracy.
A first detection unit 17 that generates a first detection signal corresponding to the amount of illumination light, and a second detection signal that corresponds to the amount of image light from an inspection object illuminated by the illumination light. The second detection unit 16 to be generated and the first detection signal are converted into the first conversion signal by using the first conversion information, and the first conversion signal is illuminated by the first conversion information. A first conversion unit 51 configured to be proportional to or inversely proportional to the amount of light, and a second detection signal are converted into a second conversion signal using the second conversion information. A second conversion unit 52 configured so that the second conversion signal is proportional to the amount of image light based on the conversion information, and a correction unit 53 that corrects the second conversion signal using the first conversion signal; A defect detection unit for detecting a defect to be inspected based on the corrected second conversion signal. Yeah.
[Selection] Figure 3

Description

  The present invention relates to a defect inspection apparatus, and more particularly, to a defect inspection apparatus suitable for detecting a fine pattern defect such as a semiconductor photomask.

  One of the factors that reduce the yield of semiconductor devices such as LSIs is photomask defects. Therefore, with the miniaturization and high integration of semiconductor devices, it is important to improve defect detection accuracy.

  As a defect inspection apparatus, an apparatus that detects an image to be inspected such as a photomask with an image sensor and detects the defect by comparing the acquired image with a reference image is known. In such a defect inspection apparatus, when the light amount of the illumination light that illuminates the inspection target varies, the light amount of the image light from the inspection target also varies.

  In order to avoid the above-described problem, Patent Document 1 provides a light amount sensor for detecting the light amount fluctuation of the illumination light separately from the image sensor, and an image obtained by the image sensor according to the light amount fluctuation of the illumination light. It is corrected.

  However, in general, the input / output characteristics of the image sensor are different from the input / output characteristics of the light quantity sensor. In the conventional method described above, the difference between the input / output characteristics of the image sensor and the input / output characteristics of the light quantity sensor is not taken into consideration. A problem arises in that it is impossible to obtain a correct image.

As described above, the conventional defect inspection apparatus has a problem that it is difficult to acquire an image to be inspected with high accuracy, and sufficient defect detection accuracy cannot be obtained.
JP-A-4-362790

  An object of the present invention is to provide a defect inspection apparatus that can acquire an image to be inspected with high accuracy and can obtain sufficient defect detection accuracy.

  The defect inspection apparatus which concerns on one viewpoint of this invention is the illumination part which irradiates illumination light to test object, the 1st detection part which produces | generates the 1st detection signal according to the light quantity of the said illumination light, The said illumination light A second detection unit that generates a second detection signal corresponding to the amount of image light from the inspection object illuminated by the inspection object, and a first conversion of the first detection signal using the first conversion information. A first conversion unit for converting into a signal, wherein the first conversion unit is configured such that the first conversion signal is proportional or inversely proportional to the amount of illumination light according to the first conversion information; A second conversion unit that converts the second detection signal into a second conversion signal using the second conversion information, wherein the second conversion signal is converted into a light quantity of the image light by the second conversion information. A second conversion unit configured to be proportional to the first conversion signal, and the first conversion signal. Comprising a correcting unit for correcting the second conversion signal, and a defect detection section for detecting a defect of the inspection object based on the second conversion signal corrected by the correction unit.

  According to the present invention, an image to be inspected can be obtained with high accuracy, and sufficient defect detection accuracy can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a schematic configuration of a defect inspection apparatus according to an embodiment of the present invention. Hereinafter, the basic configuration and basic operation of the defect inspection apparatus according to the present embodiment will be described with reference to FIG.

  The photomask 11 to be inspected is placed on a table 12 that can move in the horizontal direction (X direction and Y direction) and the rotation direction (θ direction). An illumination unit including a light source 13 and an optical system 14 is provided above the photomask 11, and illumination light is irradiated to a mask pattern (for example, a mask pattern for an integrated circuit) 11a formed on the photomask 11. . Image light from the photomask 11 is incident on an image sensor (second detection unit) 16 formed of a photodiode array via a magnifying optical system 15.

  The image light incident on the image sensor 16 is photoelectrically converted, and the image sensor 16 outputs a photoelectric conversion signal (second detection signal) corresponding to the amount of light (light intensity) of the image light. The illumination light also enters the light quantity sensor (first detection unit) 17, and a photoelectric conversion signal (first detection signal) corresponding to the light quantity (light intensity) of the illumination light is output from the light quantity sensor 17. . The photoelectric conversion signals output from the image sensor 16 and the light amount sensor 17 are respectively input to the calculation unit 18, and the calculation unit 18 performs A / D conversion on the photoelectric conversion signal, and then performs processing described later.

  The position of the photomask 11 is controlled by moving the table 12. The table 12 is driven by an X motor 23a, a Y motor 23b, and a θ motor 23c by a control signal from a table control circuit 22 controlled by the control computer 21. Specifically, by sequentially moving the table 12 in the X direction and the Y direction, the divided areas of the photomask 11 are sequentially imaged on the image sensor 16 as shown in FIG. The moving position of the table 12 (that is, the position of the detection area of the photomask 11) is measured by the laser length measurement system 24 and sent to the position circuit 27. The photomask 11 is conveyed onto the table 12 from an autoloader 26 driven by an autoloader control circuit 25.

  In the calculation unit 18, calculation processing described later is performed, and image data of the pattern 11 a formed on the photomask 11 is calculated. The calculated image data is sent to the comparison circuit 28 together with the position data of the photomask 11 output from the position circuit 27.

  On the other hand, design data of the pattern 11 a formed on the photomask 11 is stored in the magnetic disk 29. This design data is read to the development circuit 31 via the control computer 21. The development circuit 31 converts the read design data into binary or multi-value image data, and the converted image data is sent to the reference circuit 32. The reference circuit 31 performs a filtering process on the converted image data. This is due to the following reason. That is, the image data output from the calculation unit 18 is in a state of being subjected to filter processing due to the resolution characteristics of the magnifying optical system 15 and the aperture effect of the photodiode array constituting the image sensor 16. Therefore, the image data converted from the design data is also subjected to filter processing so that the image data output from the calculation unit 18 and the image data converted from the design data can be accurately compared.

  In the comparison circuit 28, the image data output from the calculation unit 18 (hereinafter referred to as measurement image data for convenience) and the image data output from the reference circuit 32 (hereinafter referred to as reference image data for convenience) are as follows. Compare. First, sub-regions of appropriate sizes are cut out from the measurement image data and reference image data, respectively. Usually, overall alignment (overall alignment) is performed in advance on an image based on measurement image data and an image based on reference image data. For this reason, the positions of the cut out images are almost the same. However, due to the distortion of the photomask 11, the accuracy of the table 12, etc., there is usually a slight misalignment between the two images. Therefore, sub-regions of appropriate sizes are cut out, and alignment (area alignment) is performed for each sub-region so that the positional deviation between the sub-regions is as small as possible.

  In this way, the comparison circuit 28 compares the measured image data with the reference image data, and the defect of the pattern formed on the photomask 11 is detected based on the comparison result. For example, the difference between the measurement image data and the reference image data is obtained, and when the difference exceeds a predetermined value, it is determined as a defect. Such defect detection can be performed by the control computer 21, for example.

  Next, the process performed in the calculating part 18 is demonstrated with reference to the block diagram shown in FIG.

  The amount of illumination light applied to the photomask 11 is not always constant and varies depending on some cause. Therefore, when the standard light amount (standard light intensity) of the illumination light incident on the light amount sensor 17 is I and the variation rate of the illumination light is α, the light amount (light intensity) of the illumination light irradiated on the photomask 11 is αI. Become. The illumination light (light quantity αI) is photoelectrically converted by the light quantity sensor 17, and a photoelectric conversion signal G (αI) is output from the light quantity sensor 17. The input / output characteristics of the light quantity sensor 17 (relationship between the incident light quantity αI and the output voltage G (αI)) are not generally linear, and are, for example, input / output characteristics as shown in FIG.

  The photoelectric conversion signal G (αI) output from the light amount sensor 17 is input to the conversion unit (first conversion unit) 51. As shown in FIG. 5, the conversion unit 51 converts the input signal G (αI) so that the conversion signal (first conversion signal) output from the conversion unit 51 is proportional or inversely proportional to the incident light amount αI of the illumination light. Convert. Specifically, input / output characteristics of the light quantity sensor 17 are measured in advance, and conversion information (first conversion information) that can obtain the proportional or inverse proportional relationship is set in the conversion unit 51. As the conversion information, a conversion formula may be used, or a conversion table storing a relationship between an input signal and an output signal of the conversion unit 51 may be used.

  In the present embodiment, the conversion unit 51 is configured such that the conversion signal output from the conversion unit 51 is inversely proportional to the light amount αI of the illumination light, and the conversion signal (1 / α) is output from the conversion unit 51. It will be.

  On the other hand, image light having a light amount TαI is incident on the image sensor 17. T mainly represents the transmittance of illumination light in the photomask 11 (strictly speaking, an attenuation component in the magnifying optical system 15 and the like is also included). Image light (amount of light TαI) is photoelectrically converted for each pixel by the image sensor 16, and a photoelectric conversion signal F (TαI) is output for each pixel from the image sensor 16. The input / output characteristics of the image sensor 16 (the relationship between the incident light amount TαI and the output voltage F (TαI)) are generally not linear, and the input / output characteristics are different for each pixel. Therefore, the input / output characteristics of the image sensor 16 are as shown in FIG. 6, for example.

  The photoelectric conversion signal F (TαI) of each pixel output from the image sensor 16 is input to the conversion unit (second conversion unit) 52. As shown in FIG. 7, the conversion unit 52 converts the input signal F (TαI) so that the conversion signal (second conversion signal) output from the conversion unit 52 is proportional to the incident light amount TαI of the image light. . Specifically, the input / output characteristics of the image sensor 16 are measured in advance for each pixel, and conversion information (first conversion information) that can obtain the proportional relationship is set in the conversion unit 51 for each pixel. deep. Further, the conversion information is set so that the proportional relationship shown in FIG. 7 (the relationship between the incident light amount and the conversion output) is shared by the pixels. As the conversion information, a conversion formula may be used, or a conversion table storing the relationship between the input signal and the output signal of the conversion unit 52 may be used.

  Hereinafter, a specific method for obtaining the conversion information described above will be described in detail.

  First, image data Bo for a portion with low transmittance, image data Wo for a portion with high transmittance, and image data Mo_k with zero or more intermediate gradation values are acquired. Further, the ratio R of the light amount data to the reference light amount at the time of acquiring each image data is acquired.

If the input / output characteristics of the image sensor are linear, the input / output characteristics are determined using parameters x and y,
Bi = (x × Bo + y)
Wi = (x × Wo + y)
Mi_k = (x × Mo_k + y)
It becomes.

When the light amount is corrected for the sensor input values Bi, Wi, and Mi_k,
Bi × R
Wi x R
Mi_k × R
It becomes. These correction values can be obtained for the number of lines of image data for each sensor pixel.

Therefore, the average value of the image data is Bav, Wav, Mav_k,
Bi × R = Bav
Wi × R = Wav → (x, y) A = b
Mi_k × R = Mav_k
Using the coefficient matrix A and the average value vector b,
b × At × (A × At) ^ (− 1)
, X and y that minimize the deviation from the average value can be obtained. Using this, it is possible to calculate an inverse characteristic that optimizes the response of the image sensor with respect to the characteristic of the light quantity sensor. However, At represents the transposed matrix of A.

  Even if the equation used as a model of the sensor characteristics changes, the optimum parameter can be obtained in the same manner. Finally, select a model that minimizes the deviation from the average value. However, if the amount of deviation does not change much as the degree of freedom increases, a model with less degree of freedom is adopted.

Further, in actual correction, when o is an offset amount for setting the output value to a predetermined value,
Bo ′ = Wi × R + o
Wo ′ = Bi × R + o
Mo_k ′ = Mi_k × R + o
It becomes. The error (Bt−Bo ′) ^ 2+ (Wt−Wo ′) ^ 2+ (Mt_k) with respect to the target value Bt of the low transmittance portion, the target value Wt of the high transmittance portion, and the target value Mt_k of the intermediate gradation -Mo_k ') ^ 2
It is also possible to obtain the parameter of the model formula and the offset amount o at the same time so that is minimized.

  In the above discussion, instead of replacing the image sensor with a model, by replacing the characteristics of the light sensor with a model, it is possible to calculate an inverse characteristic that optimizes the characteristics of the light sensor with respect to the response of the image sensor. it can. Alternatively, a method of calculating an inverse function after preparing a test mask whose transmittance changes linearly and measuring sensor characteristics may be used.

  The conversion signal (1 / α) from the conversion unit 51 and the conversion signal (TαI) from the conversion unit 52 obtained as described above are multiplied by a multiplication unit (correction unit) 53. That is, the conversion signal (TαI) from the conversion unit 52 is corrected using the conversion signal (1 / α) from the conversion unit 51. As a result, the fluctuation component (α) based on the fluctuation of the amount of illumination light is removed from the conversion signal (TαI), and the correction signal TI is output from the multiplier 53. In the present embodiment, conversion processing is performed by the conversion unit 51 so that the conversion signal output from the conversion unit 51 is inversely proportional to the light amount (αI) of illumination light, and the conversion signal output from the conversion unit 52 is image light. The conversion unit 52 performs conversion processing so as to be proportional to the amount of light (TαI). Therefore, the fluctuation component (α) of the illumination light is removed only by performing the multiplication process by the multiplier 53. Thus, since the correction signal TI is obtained by removing the fluctuation component (α), an image of the pattern formed on the photomask 11 can be obtained with high accuracy without being affected by fluctuations in the amount of illumination light. can do.

  In addition, when the conversion part 51 is comprised so that the conversion signal output from the conversion part 51 may be proportional to the light quantity ((alpha) I) of illumination light, the conversion signal (for example, (alpha)) output from the conversion part 51, and conversion The conversion signal (TαI) output from the unit 52 has a simple proportional relationship. Therefore, also in this case, by using the conversion signal from the conversion unit 51 to correct the conversion signal from the conversion unit 52, the fluctuation component (α) based on the light amount fluctuation of the illumination light is converted from the conversion signal (TαI). Can be easily removed. Therefore, an image of the pattern formed on the photomask 11 can be obtained with high accuracy without being affected by fluctuations in the amount of illumination light.

  The signal TI output from the multiplication unit is input to the offset processing unit 54, and predetermined offset processing is performed. FIG. 8 is a diagram showing the relationship between the incident light amount (TαI) of image light and the output signal after the offset processing. As shown in FIG. 8, the offset value S is given to the output signal from the offset processing unit 54. Such an offset process is performed for the following reason. In the inspection of the photomask, the signal is largely dropped at the edge portion of the mask pattern, and a signal value lower than the black level signal value (the signal value of the light shielding portion) is output. Therefore, if the output of the multiplier 53 is used as it is, it becomes difficult to acquire an edge detection signal. By performing the offset process, the edge detection signal can be reliably acquired.

  The output signal from the offset processing unit 54 is sent to the comparison circuit 28 shown in FIG. 1, and as described above, the comparison circuit 28 compares the measured image data with the reference image data, and based on the comparison result. A defect of the pattern formed on the photomask 11 is detected.

  As described above, in this embodiment, the conversion signal is output from the conversion unit 52 after the conversion process is performed in the conversion unit 51 so that the conversion signal output from the conversion unit 51 is proportional or inversely proportional to the amount of illumination light. Is converted by the converter 52 so that is proportional to the amount of image light. Therefore, the fluctuation component of the illumination light can be surely and easily removed, and the pattern image formed on the photomask can be obtained with high accuracy without being affected by the fluctuation of the amount of illumination light. Therefore, it is possible to acquire an image of a photomask to be inspected with high accuracy and to obtain sufficient defect detection accuracy.

  The embodiment described above can be variously modified as described below.

(Modification 1)
In the above-described embodiment, the conversion information used for the conversion operation of the conversion unit 52 is fixed. However, the conversion information may be changed in order to cope with a change with time of the sensor. In this modification example, the conversion information is changed as shown in FIG. Hereinafter, the configuration and operation of this modification will be described with reference to FIG.

  The output signal from the offset processing unit 54 is sent to the determination unit 61, and it is determined whether or not a predetermined condition is satisfied. For example, it is compared with a reference value set in advance, and it is determined whether or not the difference from the reference value exceeds a predetermined value. If the predetermined condition is not satisfied, the conversion information calculation unit 62 calculates new conversion information, and sets the calculated new conversion information in the conversion unit 52. In this case, new conversion information for the conversion unit 51 may be calculated at the same time, and the calculated new conversion information may be set in the conversion unit 51.

  As described above, in this modified example, when the output signal from the offset processing unit 54 does not satisfy the predetermined condition, new conversion information is calculated. As a result, it is possible to accurately cope with changes with time of the sensor and the like, so that an image can be acquired with high accuracy and sufficient defect detection accuracy can be obtained.

  If the determination unit 61 determines that the predetermined condition is not significantly satisfied (for example, the difference from the reference value greatly exceeds the predetermined value), the sensor or the light source has failed. You may make it judge that it is.

(Modification 2)
Also in this modification, the conversion information used for the conversion operation of the conversion unit 52 is not fixed, but the conversion information is changed. In this modification example, the conversion information is changed as shown in FIG. Hereinafter, the configuration and operation of this modification will be described with reference to FIG.

  Data of the output signal from the offset processing unit 54 is sequentially stored in the signal data storage unit 63. The conversion information update unit 64 generates new conversion information using the signal data stored in the signal data storage unit 63, and updates the conversion information of the conversion unit 52 with the generated conversion information. That is, when the conversion process is performed by the conversion unit 52, the conversion information generated based on the conversion signal obtained by the conversion process prior to the conversion process is used.

  For example, the conversion information can be updated as follows. As shown in FIG. 2, the inspection region on the photomask 11 is divided into a plurality of stripe-shaped subregions, and the scanning direction (table moving direction) is controlled for each subregion. Therefore, when inspecting a certain sub-region, conversion information is generated using the signal data of the sub-region examined before that sub-region. However, as shown in FIG. 2, the scanning directions of adjacent sub-regions are opposite to each other (forward and backward directions). The trajectory may be slightly different between the forward direction and the backward direction. For this reason, if the conversion information is generated using the signal data of the immediately preceding (previous) sub-region, sufficient accuracy may not be obtained. In such a case, conversion information may be generated using the signal data of the previous sub-region. That is, conversion information may be generated using signal data of sub-regions in the same scanning direction.

  As described above, in this modified example, by sequentially updating the conversion information used for the conversion operation of the conversion unit 52, it is possible to always obtain an image with high accuracy and to obtain sufficient defect detection accuracy. Become.

(Modification 3)
In this modification example, a plurality of pieces of conversion information used for the conversion operation of the conversion unit 52 are prepared in advance, and optimum conversion information is selected from them. Hereinafter, the configuration and operation of this modification will be described with reference to FIG.

  The conversion information storage unit 65 stores a plurality of pieces of conversion information used for the conversion operation of the conversion unit 52. For example, since the image sensor 16 has individual differences, the conversion information differs depending on the image sensor 16. Therefore, conversion information is obtained in advance for each image sensor 16 scheduled to be used, and the obtained conversion information is stored in the conversion information storage unit 65. The selection unit 66 selects conversion information corresponding to the image sensor 16 to be used from the conversion information storage unit 65 and sets the selected conversion information in the conversion unit 52.

  In this way, in this modified example, since a plurality of pieces of conversion information are stored in advance and the optimum conversion information is selected, the trouble of calculating the conversion information each time can be saved, and the work efficiency of defect inspection can be saved. Can be improved.

(Modification 4)
In addition to a photomask having a light-shielding film formed on a light-transmitting substrate, a multi-layered mask in which a halftone film 72 and a light-shielding film 73 are formed on a light-transmitting substrate 71 as shown in FIG. is there. In such a multilayer structure mask, there is a large difference between the transmittance in the region A1 where only the halftone film 72 is formed and the transmittance in the region A2 where the halftone film 72 and the light shielding film 73 are formed. There is.

  Therefore, in the present modification example, the conversion information used for the conversion operation of the conversion unit 52 is different between the area A1 and the area A2. In other words, the region A1 is converted using the conversion information for the region A1, and the region A2 is converted using the conversion information for the region A2. Thereby, in this embodiment, an image can be acquired with higher accuracy, and sufficient defect detection accuracy can be obtained.

  In the above-described embodiment and its modification, the image is detected using the transmitted light from the photomask. However, the above-described case is also applied to the case where the image is detected using the reflected light from the photomask. It is possible to apply a method similar to the method.

  Moreover, in the above embodiment and its modification, although the photomask defect inspection was described as an example, the above-described defect inspection of the device pattern and circuit pattern formed on the semiconductor substrate (semiconductor wafer) was also described. It is possible to apply a method similar to the method. The above-described method can also be applied to the defect inspection of device patterns and circuit patterns on an active matrix substrate used in a liquid crystal display device.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Furthermore, the above embodiments include inventions at various stages, and various inventions can be extracted by appropriately combining the disclosed constituent elements. For example, even if several constituent requirements are deleted from the disclosed constituent requirements, the invention can be extracted as an invention as long as a predetermined effect can be obtained.

It is the block diagram which showed schematic structure of the defect inspection apparatus which concerns on embodiment of this invention. FIG. 4 is a diagram illustrating a divided region (sub-region) of a photomask according to the embodiment of the present invention. It is the block diagram shown about the process which concerns on embodiment of this invention and is performed in a calculating part. FIG. 6 is a diagram illustrating input / output characteristics of a light amount sensor according to an embodiment of the present invention. FIG. 6 is a diagram illustrating conversion characteristics related to a light amount sensor according to the embodiment of the present invention. FIG. 6 is a diagram illustrating input / output characteristics of an image sensor according to an embodiment of the present invention. FIG. 6 is a diagram illustrating conversion characteristics related to an image sensor according to the embodiment of the present invention. FIG. 10 is a diagram illustrating characteristics after offset processing according to the embodiment of the present invention. It is the block diagram shown about the process performed in the calculating part regarding the 1st modification of embodiment of this invention. It is the block diagram shown about the process performed in the calculating part regarding the 2nd modification of embodiment of this invention. It is the block diagram shown about the process performed in the calculating part regarding the 3rd modification of embodiment of this invention. It is the figure which showed the structure of the photomask concerning the 4th modification of embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Photomask 11a ... Mask pattern 12 ... Table 13 ... Light source 14 ... Optical system 15 ... Expansion optical system 16 ... Image sensor 17 ... Light quantity sensor 18 ... Calculation part 21 ... Control computer 22 ... Table control circuit 23a ... X motor 23b ... Y motor 23c ... θ motor 24 ... laser measurement system 25 ... autoloader control circuit 26 ... autoloader 27 ... position circuit 28 ... comparison circuit 29 ... magnetic disk 31 ... deployment circuit 32 ... reference circuit 51 ... conversion unit 52 ... conversion unit 53 ... Multiplier 54 ... Offset processing unit 61 ... Determination unit 62 ... Conversion information calculation unit 63 ... Signal data storage unit 64 ... Conversion information update unit 65 ... Conversion information storage unit 66 ... Selection unit 71 ... Translucent substrate 72 ... Halftone film 73 ... Light-shielding film

Claims (6)

An illumination unit for illuminating the inspection object with illumination light;
A first detection unit that generates a first detection signal corresponding to the amount of the illumination light;
A second detection unit that generates a second detection signal corresponding to the amount of image light from the inspection object illuminated by the illumination light;
A first conversion unit configured to convert the first detection signal into a first conversion signal using first conversion information, wherein the first conversion signal is converted into the illumination light by the first conversion information; A first converter configured to be proportional or inversely proportional to the amount of light;
A second conversion unit configured to convert the second detection signal into a second conversion signal using the second conversion information, wherein the second conversion signal is converted into the image light by the second conversion information; A second converter configured to be proportional to the amount of light;
A correction unit that corrects the second converted signal using the first converted signal;
A defect detection unit that detects the defect to be inspected based on the second conversion signal corrected by the correction unit;
A defect inspection apparatus comprising: The defect inspection apparatus according to claim 1, wherein the second conversion unit includes a conversion table in which the second conversion information is stored. A determination unit that determines whether or not the second conversion signal corrected by the correction unit satisfies a predetermined condition;
A conversion information calculation unit that calculates new second conversion information when it is determined that the corrected second conversion signal does not satisfy a predetermined condition;
The defect inspection apparatus according to claim 1, further comprising: A signal data storage unit for storing signal data based on the second conversion signal corrected by the correction unit;
A conversion information update unit that updates the second conversion information based on the signal data stored in the signal data storage unit;
The defect inspection apparatus according to claim 1, further comprising: A conversion information storage unit storing a plurality of the second conversion information;
A selection unit for selecting desired second conversion information from among the plurality of second conversion information stored in the conversion information storage unit;
The defect inspection apparatus according to claim 1, further comprising: The inspection object includes a first layer formed on a substrate and a second layer formed on the first layer;
The second conversion unit includes second conversions different from each other in a first region in which the first layer is formed and a second region in which the first layer and the second layer are formed. The defect inspection apparatus according to claim 1, wherein the second detection signal is converted into a second conversion signal using information.

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