JP2002261136A - Method for inspecting foreign matter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and surely determine whether foreign matters are critical to a process for forming a pattern. SOLUTION: A secondary electron profile 29 only for the foreign matters is obtained from a secondary electron profile 28 of the foreign matters portion in a sample image 26 and a secondary electron profile 27 of the same portion in a reference image 21. By examining the overlapping 30 of peak waveforms of the secondary electron profile 27 only for the pattern and the secondary electron profile 29 only for the foreign matters, positions where the foreign matters 25a comes in contact with the pattern 23 is detected and whether the foreign matters are critical to the process is determined.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a foreign substance or a defect present on a sample surface by using a scanning electron microscope.

[0002]

2. Description of the Related Art Since a plurality of semiconductor LSIs and memories are formed on a substrate such as a silicon wafer at a time,
Using an optical microscope or a scanning electron microscope, an inspection method is used to compare adjacent IC chips or partial IC chips with the same pattern shape, and if there is a difference, extract that part as a defect. Have been. Such an inspection method is described in, for example, JP-A-61-82107, JP-A-3-209843, and JP-A-5-258703. In this method, from the defect detection to the classification, the extracted image is automatically extracted and learned from the teaching image according to a predetermined algorithm, and the classification is performed based on the learning result.

[0003]

In the prior art, an electron beam is scanned at each location with reference to a location having a similar pattern shape in the vicinity of the location to be measured, and signals obtained (such as secondary electrons and Defects or foreign matter (hereinafter collectively referred to as foreign matter) by constructing a sample image from reflected electrons) and binarizing a difference image obtained by comparing each sample image.
Is determined. Then, the extracted foreign matter is classified into a plurality of groups determined based on a teaching image created in advance. For example, foreign substances having similar parameters such as color, shape, and contrast are classified into the same group. The information on the foreign matter classified in this way is used for analyzing the source of the foreign matter.

On the other hand, foreign matter present on a pattern of a semiconductor device may or may not be fatal in a process. For example, when a foreign substance exists over two line patterns, a pattern short circuit occurs, which is fatal. It is also fatal if a foreign substance is present in the hole pattern and blocks the hole. On the other hand, if the foreign matter exists in a space portion other than on the pattern, it is not fatal and does not pose a problem in the process formation at this time.

In the above-described foreign matter discrimination method, since the detected foreign matter is classified only based on the characteristic amount, it cannot be determined whether the foreign matter is fatal to the process. A chip having a fatal defect is highly likely to eventually become a defective product, which causes a reduction in yield. An object of the present invention is to provide a method for easily and surely determining whether a detected foreign matter is fatal to a process in view of the problems of the related art.

[0006]

According to the present invention, a secondary electron profile of a foreign material portion in a sample image is compared with a secondary electron profile of the same portion in a reference image to determine how the foreign material exists in the pattern. Is to determine whether Since the sample image is based on the premise that a single foreign substance is displayed at the center of the image, if the electron beam is scanned in the X-axis direction so as to pass through the center of the image, a secondary electron profile including the foreign substance will always be obtained. Obtainable. At this time, if a foreign substance is present on the pattern, a secondary electron profile obtained by adding both the pattern and the foreign substance is obtained. Therefore, the pattern is formed using the secondary electron profile of only the pattern obtained from the reference image. The secondary electron profile of the foreign matter is separated, and each profile is compared to determine whether the presence state of the foreign matter is fatal to the pattern.

When it is not possible to determine whether or not the image is fatal only by the secondary electron profile at the center of the image, for example, when the shape of the foreign matter is a bar, an arbitrary shape is determined in the Y-axis direction from the center of the image. By detecting the secondary electron profile at a plurality of locations and comparing the secondary electron profile with the same location in the reference image, the shape of the foreign substance can be grasped more accurately. Furthermore, it is also possible to detect the edge from the secondary electron profile of the foreign matter obtained from the difference between the secondary electron profile of the sample image and the reference image and measure the size of the foreign matter.

That is, the foreign matter inspection method according to the present invention comprises:
Scanning the inspection area where the foreign matter of the sample on which the pattern is formed is present with an electron beam, to obtain a secondary electron profile of the pattern including the foreign matter, and another area having the same pattern as the inspection area. Scanning an area where no foreign matter exists with an electron beam to obtain a secondary electron profile of a pattern containing no foreign matter; and obtaining a secondary electron profile of a pattern containing foreign matter and a secondary electron profile of a pattern containing no foreign matter. Obtaining the secondary electron profile of the foreign matter and comparing the secondary electron profile of the foreign matter with the secondary electron profile of the pattern containing no foreign matter to determine whether the foreign matter is fatal in the pattern formation process. And a judging step.

In the judging step, if there is a portion where the peak waveform of the secondary electron profile of the foreign matter contacts or overlaps with the peak waveform of the secondary electron profile of the pattern containing no foreign matter, the foreign matter contacts the pattern at that portion. It can be determined that they overlap the pattern.

In the determining step, the edge position of the peak waveform of the secondary electron profile of the foreign matter contacts the edge position on the foreign matter side of the peak waveform of the secondary electron profile of the pattern containing no foreign matter or exceeds the edge position. When it is present on the pattern side, it may be determined that foreign matter is in contact with the pattern or overlaps the pattern at that location.

In the foreign matter inspection method of the present invention, when it is determined that one foreign matter contacts or overlaps two or more lines simultaneously with respect to the line and space pattern, the foreign matter is fatal in the pattern forming process. Is determined to be the target. In the foreign matter inspection method of the present invention,
When it is determined that the foreign matter overlaps the hole pattern, the foreign matter is determined to be fatal in the pattern forming process. In the foreign matter inspection method of the present invention, the distance between both edges of the peak waveform of the secondary electron profile of the foreign matter may be obtained as the size of the foreign matter.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a configuration example of a scanning electron microscope (SEM) used in the foreign substance classification method of the present invention.
The primary electron beam 4 extracted by the voltage V1 applied to the cathode 1 and the first anode 2 is accelerated by the voltage Vacc applied to the second anode 3, and advances to the subsequent lens system. The primary electron beam 4 is converged as a minute spot on a wafer (sample) 7 held on a sample table 15 by a converging lens 5 and an objective lens 6 controlled by a lens control power supply 14, and is deflected by a two-stage deflection coil 8. The wafer 7 is scanned two-dimensionally. Further, the moving stage 16 is provided with the control means 1.
The sample stage 15 can be moved by the control signal from 7 to change the position where the electron beam 4 scans the wafer 7. The scanning signal of the deflection coil 8 is controlled by a deflection control device 9 according to the observation magnification.

A secondary electron 10 generated from a sample by a primary electron beam 4 scanned on a wafer 7 is converted into a secondary electron detector 11.
Is detected by The secondary electron information detected by the secondary electron detector 11 is amplified by the amplifier 12, processed by the computer 18, and displayed as an image on a display device such as the CRT 13. At this time, the contrast of the image
By performing the processing in step 8, the secondary electron profile 20 is displayed. The secondary electron profile is obtained by dividing the color tone of the entire image into 256 tones and converting the numerical value into a numerical value, and extracting and displaying only the scan portion in the X-axis direction.

The computer 18 instructs the control means 17 based on the information on the foreign object coordinates passed from the foreign object inspection device 19 to move the stage so that the foreign object is located at the center of the visual field. According to the present invention, a secondary electron profile is obtained at the same pattern portion of a foreign substance image in which a foreign substance is located at the center of the visual field and a reference image that does not include the foreign substance, and the secondary electron profiles of the foreign substance and the pattern are compared based on a difference between these. Thus, it is determined how the foreign matter exists with respect to the pattern and is fatal in the process.

FIG. 2 is a flowchart showing an example of the flow of a process for judging whether or not a foreign matter is fatal from the secondary electron profile of the foreign matter image acquired using the semiconductor SEM and the secondary electron profile of the reference image. is there. The figure also shows the determination method for the case of a hole pattern and the case of a line pattern.

First, as a step 1, the foreign matter inspection device 19
Read the coordinate data of the foreign matter measured in step. The coordinate data is transferred from the foreign matter inspection device 19 to the SEM through a recording medium such as a floppy (registered trademark) disk or a network connection. In the next step 2, the wafer 7 subjected to the foreign substance inspection by the foreign substance inspection device 19 is loaded. After loading, in step 3, the stage is moved to the location of the foreign substance based on the read coordinate data of the foreign substance, and a foreign substance image is obtained.

In the prior art, the chip moves to the next chip and obtains a reference image containing no foreign matter at the same position in the chip as the foreign matter image. Then, a difference image is obtained from the foreign matter image and the reference image and binarized to extract a foreign matter image. The foreign substances having similar characteristics are classified based on the characteristic amounts of the foreign substances thus obtained. According to the present invention, in addition to obtaining a feature amount of a foreign substance by comparing a foreign substance image and a reference image as in the conventional method, the secondary electron profile is used to determine how the foreign substance exists in the pattern, This is to determine whether the process is fatal to the formation process.

After acquiring the foreign matter image in step 3, a secondary electron profile of the foreign matter part is acquired in step 4 by image contrast processing. What is image contrast processing?
The color tone of the image is divided into 256 tones between white and black, and is subjected to numerical processing. At that time, white has the highest value and black has the lowest value. Next, in step 5, the reference coordinate of the adjacent chip or the like is moved to obtain a reference image of only a pattern that does not include a foreign substance.
Similarly, in step 6, a secondary electron profile of only the pattern containing no foreign matter is obtained from the reference image.

From these two types of secondary electron profiles, a secondary electron profile of only the foreign matter excluding the pattern can be obtained by numerically taking a difference in step 8. Further, in step 8, the contact position between the pattern and the foreign matter is detected by comparing the secondary electron profile of the foreign matter only with the reference secondary electron profile of the pattern only.

In step 9, the type of the pattern is determined. If the pattern is a hole pattern, the process proceeds to step 10. If a foreign substance is present on the pattern, it is determined that the pattern is all fatal, and the other cases are non-fatal. In the case of a line pattern, the process proceeds from step 9 to step 11. If there is no more than one contact point between the foreign matter and the pattern, it is non-fatal, and if it is in contact with the line at two or more places across two lines, the foreign matter Is determined to be fatal to the pattern. By performing these determination processes at the same time as the classification of the foreign matter based on the characteristic amount of the conventional technique, it is possible to classify the foreign matter comprehensively, and it is expected that the classification accuracy is further improved.

3 to 3 based on the processing flow shown in FIG.
7, a method for classifying foreign matter according to the present invention will be specifically described. Based on the position information of the foreign matter obtained from the foreign matter inspection device 19 such as an optical inspection device, the stage of the scanning electron microscope moves to a chip having the foreign matter on the wafer 7 and scans an electron beam. The foreign object image 26 is obtained. Since the stage is moved based on the information on the foreign substance coordinates, a foreign substance image 26 in which the foreign substance 25 is located substantially at the center is obtained.
Usually, in a semiconductor wafer, a large number of chips having the same pattern shape are formed on the entire surface of the wafer. Therefore, if the semiconductor wafer is moved to a chip next to the chip from which the foreign matter image is obtained, the same pattern shape as the foreign matter image is shown. The reference image 21 without any foreign matter can be obtained.

When foreign matter is present in a semiconductor sample having a line-and-space pattern in which a plurality of lines 23 separated by a space portion 22 are arranged, it is important to determine how the foreign matter is positioned with respect to the line 23. Becomes FIG.
As shown in (1), when the foreign matter 25a is in contact with only one line, no short circuit occurs between the lines, and the presence of the foreign matter is not fatal to pattern formation. This is determined by the following method. Profile acquisition location 2 in the X-axis direction so as to pass through the center of foreign matter image 26
4 is selected and the secondary electron profile 28 is acquired on the line. The secondary electron profile 28 means that the color is relatively white as the signal intensity is higher. Similarly,
The profile acquisition part 24 is selected so as to pass through the center part of the reference image 21, and the secondary electron profile 27 of only the line and space pattern is acquired.

By subtracting the secondary electron profile 27 of the reference image from the secondary electron profile 28 obtained in the foreign substance image 26 by numerical calculation, a secondary electron profile 29 of only the foreign substance 25a can be obtained. Here, by measuring the distance between both ends of the peak waveform from the secondary electron profile 29 of only the foreign matter 25a, the foreign matter 25a is measured.
The size 31a of a can be obtained. Further, by comparing the secondary electron profile 29 of only the foreign matter with the secondary electron profile 27 of the pattern only, the location where the peak waveforms of the two secondary electron profiles 27 and 29 overlap, that is, the line pattern 23 and the foreign matter The location where 25a is in contact is detected. In the case of the example shown in FIG.
The location 30 where the peak waveforms of the two secondary electron profiles 27 and 29 overlap is only one location on the left line. Thus, the foreign matter 25a is determined to be non-fatal because it is in contact with only the left line in the figure and is not in contact with two lines at the same time.

Next, referring to FIG. 4, a description will be given of a case where a foreign substance exists over two lines of a line-and-space pattern and is fatal. As in the case shown in FIG. 3, the secondary electron profiles 28 and 27 are acquired in the foreign matter image 26 and the reference image 21, and the secondary electron profile 27 of the reference image is subtracted from the secondary electron profile 28 of the foreign matter image. A secondary electron profile 29 of only the foreign matter 25b is obtained. Here, the size 31b of the foreign matter 25b can be obtained by measuring the distance between both edges of the peak waveform from the profile 29 of only the foreign matter. Furthermore, the secondary electron profile 2 of only the foreign matter
9 and a pattern-only secondary electron profile 27 are superimposed and compared to obtain two secondary electron profiles 2.
A position where the peak waveforms 7 and 29 overlap with each other, that is, a position where the line pattern 23 and the foreign matter 25b are in contact with each other is detected. In this example, two secondary electron profiles 2
It can be seen that the peak waveforms 7 and 29 overlap at a total of two locations, a location 30a on the left line and a location 30b on the right line. Thus, the foreign matter 25b is determined to be simultaneously overlapping both the left and right lines in the drawing, and is determined to be fatal.

In the case of the elongated foreign matter 25c as shown in FIG. 5, it is possible to judge whether the foreign matter is fatal or non-fatal to the pattern forming process based on only the secondary electron profile of the central portion of the foreign matter image 26. Can not. In such a case, a plurality of lines 24a, 24b, 24c,.
a, 24b, 24c,... on the secondary electron profile 28
a, 28b, 28c,... (only three secondary electron profiles 28a, 28b, 28c are shown in FIG. 5). At this time, since it is assumed that the foreign matter 25c exists at the center of the foreign matter image 26, it is determined that the foreign matter existing on an arbitrary line that is translated in the Y direction from the center of the image is one foreign matter. . Further, in the reference image, the lines 24a, 24b, 24c,
Are acquired on a plurality of lines corresponding to... (Only one secondary electron profile 27 is shown in FIG. 5).

The difference between the secondary electron profile corresponding to each of the foreign image and the reference image is obtained,
The secondary electron profiles 29a, 29b, 29c,... Of only the foreign substances on the lines 24a, 24b, 24c,.
To get. Thereafter, by comparing the secondary electron profile 27 of only the pattern acquired from the reference image and the secondary electron profiles 29a, 29b, 29c,... Of only the foreign substance, the peak waveforms of the two secondary electron profiles overlap. Places 30c, 30d, 30 where the line pattern 23 and the foreign matter 25c overlap each other
e is detected, and the foreign matters 25c and the line 23 are integrated.
And overlapping places 30f and 30g are obtained. When the overlapping portion between the foreign object 25c and the line exists on two or more lines, the foreign object is determined to be fatal. In the case of the example shown in FIG. 5, the overlapping place 30 between the foreign matter 25c and the line 23
Since e and 30f are present on two different lines, the foreign matter 25c is determined to be fatal to the pattern forming process. Also, the secondary electron profile 29 of the foreign matter
a, 29b, 29c,..., the outermost peak edges P1, P2 can be recognized as foreign matter edges, and the size 31c of the foreign matter can be measured from the interval between the peak edges.

FIG. 6 is an explanatory diagram of another method for determining whether or not a fatal condition has occurred using information on a contact portion between a foreign matter and a pattern. The case where the peak due to the line pattern 23 and the peak due to the foreign substance 25 coexist in the secondary electron profile 28 acquired from the foreign substance image 26 will be described with the electron beam scanning direction as the X axis.

The edges B and C (B <C) of the peak waveform of the secondary electron profile indicating the presence of the foreign matter 25 are the difference between the secondary electron profile acquired from the foreign matter image and the secondary electron profile acquired from the reference image. Can be specified by the secondary electron profile of only the foreign matter obtained from the above. Edge B is a left rising point of the secondary electron profile of the foreign matter, and edge C is a right rising place of the secondary electron profile of the foreign matter. Also, the inner edges A and D (A <D) of the peak waveform of the secondary electron profile of the line pattern on both the left and right sides of the foreign matter can be specified from the secondary electron profile of the reference image. An edge A is a right rising point of a secondary electron profile of a line pattern existing on the left side of the foreign matter, and an edge D is a left rising point of a secondary electron profile of a line pattern existing on the right side of the foreign matter.

If the foreign matter 25 does not contact or overlap the line pattern 23, or if it touches or overlaps only one line, it is non-fatal. At this time, looking at the magnitude relationship of the X coordinates of the peak edges A, B, C and D, the former is A <B and C <D, and the latter is B ≦ A and C <D or A <B and D ≦ C Is considered non-fatal. If the foreign matter is in contact with two or more line patterns, it is fatal.
When represented by the magnitude relation of the X coordinates of B, C, and D, B ≦ A and D
It is determined to be fatal only when ≤C.

In the case of FIG. 6A, the peak edges A, B,
The magnitude relation between C and D is A <B and C <D. In this case, since the foreign matter 25 is located between the two lines and does not contact any of the lines, it is determined to be non-fatal. In the case of FIG. 6B, A = B and C = D. In this case, the foreign matter 25 is in contact with two adjacent lines and is determined to be fatal. In the case of FIG.
A ≧ B and C <D. In this case, the foreign matter is in contact with only one of the lines, and is determined to be non-fatal. In the case of FIG. 6D, A ≧ B and C ≧ D. In this case, the foreign matter is in contact with two adjacent lines and is determined to be fatal. In the case of FIG. 6E, A ≧ B and C ≧ D. Also in this case, the foreign matter is in contact with two adjacent lines and is determined to be fatal.

FIG. 7 is an explanatory diagram of a method of judging whether a foreign substance present at the location of the hole pattern is fatal or non-fatal. A hole pattern 33 exists in the reference image 21. When the foreign matter 25d exists on the hole 33,
Fatal in the pattern formation process. The determination as to whether or not a foreign substance exists on the hole is also performed as shown in FIG.
Up to step 9 is the same as in the case of the line pattern.
Secondary electron profile 2 obtained from the same part of reference image 21 from secondary electron profile 28 obtained from foreign matter image 26
By subtracting 7, the secondary electron profile 29 of only the foreign matter 25d is obtained. Here, by measuring the distance between both edges of the peak waveform from the secondary electron profile 29 of only the foreign matter 25d, the size 31 of the foreign matter 25d is obtained.
d can be obtained.

As in the case of the line-and-space pattern, by comparing the secondary electron profile 29 of only the foreign matter 25d and the secondary electron profile 27 of only the hole 33, the contact point between the foreign matter and the hole pattern is determined. To detect. That is, two secondary electron profiles 2
A location 30h where the 7, 29 peak waveforms overlap is detected. In the case of a hole pattern, if any foreign matter exists on the hole pattern 33, it is determined that all are foreign.

Considering this by the magnitude of the X coordinate position of the edges A and D (A <D) of the peak waveform representing the hole 33 and the edges B and C (B <C) of the peak waveform representing the foreign matter 25d, C <A and D when is not in contact with the hole
<B, otherwise the foreign material covers part or all of the hole. Therefore, based on the information of the edges A and D (A <D) of the hole 33 obtained from the peak waveform of the secondary electron profile and the edges B and C (B <C) of the peak waveform representing the foreign matter 25d, the foreign matter is formed in the hole pattern. Is determined to be non-fatal if and only if C <A and D <B,
In all other cases, it is determined to be fatal.

[0034]

According to the present invention, it is possible to easily and reliably determine whether or not a foreign matter is fatal to a pattern by comparing the secondary electron profiles of the foreign matter and the pattern. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration example of a scanning electron microscope used in a foreign substance classification method of the present invention.

FIG. 2 is a flowchart illustrating an example of the flow of a process for determining whether a foreign matter is fatal.

FIG. 3 is a diagram showing an example of a secondary electron profile in a sample image and a reference image.

FIG. 4 is an explanatory diagram showing an example in which a foreign substance exists over a line pattern.

FIG. 5 is an explanatory diagram showing an example in a case where the foreign matter is in a rod shape.

FIG. 6 is an explanatory diagram of a fatal / non-fatal determination method based on a peak position relationship between a foreign substance and a line pattern.

FIG. 7 is an explanatory diagram of a fatal / non-fatal determination method when a foreign substance exists on a hole pattern.

[Explanation of symbols]

1: cathode, 2: first anode, 3: second anode, 4: primary electron beam, 5: converging lens, 6: objective lens, 7: wafer,
8: deflection coil, 9: deflection controller, 10: secondary electron beam, 11: secondary electron detector, 12: amplifier, 13: CR
T, 14: lens control power supply, 15: sample stage, 16: moving stage, 17: Hama device, 18: computer, 1
9: Foreign substance inspection device, 20: secondary electron profile, 2
1: reference image, 22: space portion, 23: line pattern, 24: line profile acquisition position, 25: foreign matter, 26: foreign matter image, 27: secondary electron profile of reference image, 28: secondary electron profile of foreign matter image , 2
9: secondary electron profile of foreign matter, 30: contact point between pattern and foreign matter, 31: foreign matter size

Continued on the front page (72) Inventor Shunsuke Koshihara 1040 Ma, Ishiki, Hitachinaka City, Ibaraki Prefecture Inside Hitachi Science Systems, Ltd. (72) Inventor Kazuo Aoki 882, Ichimo, Hitachinaka-shi, Ibaraki F-term in Hitachi Instruments Measuring Instruments Group (reference) 2G001 AA03 BA07 CA03 GA04 HA13 JA07 JA13 KA03 LA11 MA05 PA03 PA11 2G051 AA51 AB01 AC21 BA20 DA07 EA03 EA08 EC01 EC10 4M106 AA01 BA02 CA41 DB05 DB18 DB21 DJ18 DJ20 DJ26 5B057 AA03 BA01 DA03 DA13 DB02 DB09 DC04 DC16 DC22 DC33

Claims (6)

[Claims] 1. A step of scanning an inspection area where a foreign substance is present on a sample on which a pattern is formed with an electron beam to obtain a secondary electron profile of the pattern including the foreign substance, and having the same pattern as the inspection area. Scanning an area other than the area where no foreign matter is present with an electron beam to obtain a secondary electron profile of a pattern containing no foreign matter; and a secondary electron profile of the pattern containing the foreign matter and not including the foreign matter. Obtaining a secondary electron profile of the foreign matter from the secondary electron profile of the pattern; and comparing the secondary electron profile of the foreign matter with the secondary electron profile of the pattern containing no foreign matter, whereby the foreign matter is fatal in the pattern forming process. And a determining step of determining whether or not the foreign matter is correct. 2. The foreign matter inspection method according to claim 1,
In the determining step, if there is a place where the peak waveform of the secondary electron profile of the foreign matter contacts or overlaps with the peak waveform of the secondary electron profile of the pattern not containing the foreign matter, the foreign matter contacts the pattern or the pattern at that place. A foreign matter inspection method, characterized in that it is determined that the foreign matter overlaps with. 3. The foreign matter inspection method according to claim 1, wherein
In the determination step, the edge position of the peak waveform of the secondary electron profile of the foreign matter contacts the edge position on the foreign matter side of the peak waveform of the secondary electron profile of the pattern that does not include the foreign matter, or the edge position of the pattern exceeds the edge position. The foreign matter is determined to be in contact with or overlapping the pattern at that location. 4. The foreign matter inspection method according to claim 1, wherein when it is determined that one foreign matter contacts or overlaps two or more lines simultaneously with respect to the line and space pattern, A foreign matter inspection method, wherein the foreign matter is determined to be fatal in a pattern forming process. 5. The foreign matter inspection method according to claim 1, wherein when it is determined that the foreign matter overlaps the hole pattern, the foreign matter is determined to be fatal in the pattern forming process. Foreign matter inspection method. 6. The foreign matter inspection method according to claim 1, wherein a distance between edges at both ends of a peak waveform of a secondary electron profile of the foreign matter is obtained as a size of the foreign matter. Foreign matter inspection method.