JP2000195458A - Electron microscope and inspection method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron microscope capable of automatically detecting a defect and observing high resolution without requiring to specify a defect position by using an inspection device in advance. SOLUTION: When detecting a singular point on an inspection picture 17 obtained by picking up an image of a specimen to be inspected with an electron microscope on which a periodical pattern is formed, the inspection picture is split into plural partial pictures 20 of the same size, a difference processing between small regions 19 separated for one period or plural periods of a pattern formed on the specimen is applied to find the sum of the differences in each partial picture, and the singular point 18 exists in the partial picture 20 in which the sum of the difference is maximum.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope and an inspection method for inspecting a pattern defect or a foreign substance or storing observation information on a fine pattern such as an LSI wafer, a TFT or a mask.

[0002]

2. Description of the Related Art With the advance of semiconductor manufacturing technology in recent years, in a semiconductor device manufacturing inspection, defects and foreign substances which need to be inspected (hereinafter collectively referred to simply as "defects") are reduced in size. It has become difficult to detect or observe defects using a microscope. Therefore, conventionally, in high-resolution observation of defects, a defect occurrence device is specified in advance using a defect inspection device (or a foreign material inspection device), and based on information such as a coordinate origin and a defect coordinate provided by the defect inspection device, 2. Description of the Related Art Defects are observed with high resolution using an electron microscope with a coordinate function or the like. Japanese Patent Application Laid-Open No. Hei 9-139406 is a patent that takes these systemizations into consideration. In this electron microscope system, the visual field of the electron microscope is moved on the basis of the defect information provided by the inspection device, and the obtained inspection 2
Pattern matching, difference processing, etc. are performed between the next electronic image and two reference secondary electronic images obtained from the coordinates in the equivalent chip of the adjacent chip, and a defect is automatically determined as a singular point. To detect.

[0003]

In order to observe a defect at a high resolution with the above-mentioned electron microscope system, it is necessary to specify a defect position in advance using a defect inspection apparatus. In the process of manufacturing a semiconductor device, when inspecting a minute defect that cannot be detected by an optical defect inspection device, or when it is necessary to inspect only a certain position on a substrate of the semiconductor device, Since the location where the defect has occurred cannot be specified, the observation field of the electron microscope is moved to a specific area that a human wants to inspect, and the defect is visually detected and observed. In such a case, there is a problem that the automatic inspection as in the above-described system cannot be performed because the defect is not specified by the defect inspection apparatus.

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art, and it is intended to automatically detect a defect and perform high-resolution observation without having to specify a defect position in advance using an inspection apparatus. It is an object of the present invention to provide an electron microscope and an inspection method which can be performed. Further, the present invention provides an electron microscope that enables defect detection and high-resolution observation in an inspection area without irradiating an unnecessary electron beam to a reference area other than the inspection area on the sample and causing damage thereto, and It is intended to provide an inspection method.

[0005]

Means for Solving the Problems The present inventors have found that a defect such as a semiconductor memory formed on a semiconductor wafer or a pattern formed by repetition of the same fine pattern or a foreign substance attached to the pattern has a periodicity. The present invention has been achieved by focusing on the fact that the pattern can be perceived as disorder.

That is, the electron microscope of the present invention comprises an inspection point registration means for registering an inspection position of a sample to be inspected on the electron microscope, and an automatic detection of an abnormal portion of an inspection image taken at the registered inspection position as a singular point. And an observation processing unit that obtains information on the singular point detected by the singular point automatic detecting unit. The inspection image is captured using secondary electrons, reflected electrons, or secondary and reflected electrons emitted from the sample by electron beam irradiation. The electron microscope may include a visual field automatic setting unit that automatically sets a microscope visual field region based on advance information on the abnormal part. Here, the prior information on the abnormal portion includes inspection coordinates, generated defect size, minimum defect detection size, defect category, cluster, generated process name, and the like. Inspection coordinates among these pieces of prior information are used to set the visual field position of the electron microscope. Also,
The generated defect size, minimum defect detection size, category, cluster, etc. are used to set the field of view of the electron microscope, and can also be used to select only an arbitrary generation step, size, cluster, etc., and perform singularity automatic detection. Used.

[0007] The observation processing means may have a function of storing observation information and incidental information about the detected singular point. Here, the observation information refers to image information, and the incidental information includes the size and area of a defect or a foreign substance, a projection length in the X direction, a projection length in the Y direction, a category, and the like. The observation processing means may have a function of changing the observation conditions of the electron microscope according to the detection result by the singular point automatic detection means. With this function, the observation magnification of the electron microscope can be changed so that the entire singular point can be observed, for example, according to the size, distribution, and spread of the detected singular point. For example, when the detected singular points are widely distributed, the observation magnification is lowered so that the whole can be seen.

[0008] The singular point automatic detection means can detect a singular point by using the period information of the pattern formed on the sample to be inspected. In addition, the singularity automatic detection means,
A singular point can be detected by detecting disturbance of the periodic pattern formed on the sample to be inspected. More specifically, the singularity automatic detection means creates a plurality of partial images obtained by dividing the inspection image by one or more periods of the pattern using the period information of the pattern formed on the sample to be inspected. In addition, a singular point can be detected by performing a difference process between corresponding small areas of a plurality of partial images.

Alternatively, the singular point automatic detection means divides the inspection image into a plurality of partial images of the same size, and within each partial image, only one or a plurality of periods of the pattern formed on the sample to be inspected. The sum of the differences is obtained by performing the difference processing between the separated small areas, and the singular point can be detected assuming that the singular point exists in the partial image in which the sum of the differences is maximum.

[0010] In the electron microscope, the small area may be composed of one pixel or a plurality of pixels. The electron microscope may be a scanning electron microscope, but may be another type of electron microscope, such as a transmission electron microscope or a scanning transmission electron microscope. In the inspection method of the present invention, in the inspection method for detecting a singular point of a sample to be inspected on which a periodic pattern is formed, pattern disorder is detected using pattern cycle information, and the pattern has disorder. It is characterized in that a position is detected as a singular point.

According to the inspection method of the present invention, there is provided an inspection method for detecting a singular point on an inspection image obtained by imaging an inspection sample on which a periodic pattern is formed with an electron microscope. The method is characterized in that a plurality of partial images divided in one cycle or a plurality of cycles are created, and a singular point is detected by performing difference processing between corresponding small areas among the plurality of partial images.

According to the inspection method of the present invention, there is provided an inspection method for detecting a singular point on an inspection image obtained by imaging an inspection sample on which a periodic pattern is formed with an electron microscope. Divided into multiple sub-images,
In each partial image, a difference processing is performed between small areas separated by one cycle or a plurality of cycles of a pattern formed on the sample to be inspected to obtain a sum of differences, and a portion where the sum of the differences is maximum It is characterized in that a singular point exists in the image.

In the above inspection method, the small area may be composed of one pixel, or may be composed of a plurality of pixels. The present invention does not require information on the location of a defect or foreign matter generated by a defect inspection device or a foreign material inspection device, and detects a defect in a periodic pattern in an electron microscope image (inspection image) of a region to be inspected on a sample. And the position of foreign matter. As described above, since an abnormal portion of the pattern is detected as a singular point only from the electron microscope image of the inspection area, a reference image to be compared with the electron microscope image of the inspection area is not required. Therefore, the region on the sample other than the region to be inspected is not irradiated with the electron beam in order to acquire the reference image, so that damage to the sample due to the electron beam irradiation can be minimized.

According to one aspect of the present invention, for example, a defect present on a semiconductor wafer is captured on an electronic computer at an optimum inspection and observation magnification by a secondary electron image of an arbitrary region on the wafer.
From the captured secondary electron image, the location of the defect is automatically detected as a singular point by a detection method using pattern period information configured on the wafer such as design rules,
The singular point is automatically observed at the optimum magnification, and the observed image and incidental information are stored as electronic information. This makes it possible to automatically perform the process from defect detection (including foreign matter detection) or observation to storage of an image in an arbitrary area on the sample to be inspected.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. Hereinafter, a defect inspection of a memory pattern formed on a semiconductor wafer will be described as an example. However, the present invention is not limited to the defect of the pattern on the semiconductor wafer, but can be applied to the inspection of a defect, a foreign substance, and the like on an arbitrary sample having a periodic pattern.

FIG. 1 is a block diagram showing the configuration of an electron microscope according to the present invention. The electron microscope 4 includes an inspection point registration unit 1, a singular point automatic detection unit 2, a singular point information processing and
An observation processing unit 3 is provided. The electron microscope 4 can be typically a scanning electron microscope, but may be another type of electron microscope such as a transmission type or a scanning transmission type. The operator of the electron microscope registers the inspection point on the semiconductor wafer to be inspected on the electron microscope by the inspection point setting means 1. The field of view of the electron microscope 4 automatically moves to the registered inspection point. Then, the singular point automatic detection means 2 automatically detects the singular point (defect or foreign matter), and the image information of the detected singular point is processed by the information processing / observation processing means 3.

The information processing / observation processing unit 3 acquires and stores an electron microscope image of the detected singular point, and calculates the size, area, projection length in the X direction, and Y direction of the singular point from the acquired image information. For example, a process of acquiring and storing additional information such as a projection length and a category of the image is performed. Information processing / observation processing means 3
Further, according to the size, distribution, and spread of the singularity detected by the singularity automatic detection means 2, the observation conditions such as the observation magnification of the electron microscope 4 are changed so that the entirety can be observed. The inspection point to be registered in the electron microscope may be determined by using information on defective foreign matter coordinates obtained by using the abnormal part inspection apparatus.

FIG. 2 is a flowchart for explaining a processing procedure of an example of the defect detection and high-resolution observation processing according to the first embodiment of the present invention. First, the sample is aligned with the electron microscope sample stage based on the design data or the coordinate information provided from the abnormal part inspection apparatus (S11). Next, an inspection point is registered on the electron microscope (S12). The registration of the inspection point is performed by creating a map of the semiconductor wafer on the electron microscope and registering the coordinate data of the inspection point by the operator or by registering the coordinates obtained from the abnormal part inspection apparatus.

FIG. 3 is a diagram showing an example of the inspection point registration screen. A method for registering and setting inspection points will be described with reference to FIG. Inspection point setting window 3 for electron microscope
In step 7, a wafer map 32 of the semiconductor wafer to be inspected is created, and an inspection chip 33 on the map 32 is designated. In the figure, the test chip 33 is shaded and the non-test chip 34 is displayed in white. Further, the inspection coordinates (X, Y) in the inspection chip 33 are input to the in-chip coordinate value input area 35, and the inspection point is registered in the electron microscope with the inspection point setting button 36. The inspection coordinates in the inspection chip 33 may be set using a mouse cursor or the like on the image while viewing the image of the chip of the electron microscope. In this case, the coordinates in the inspection chip are automatically set. Further, the method of registering the inspection points is not limited to the method shown in FIG. 3, and any method may be used as long as coordinates can be set.

Returning to FIG. 2, when a pattern is observed on a substrate to be inspected by an electron microscope, such as a semiconductor wafer in the middle of a manufacturing process, the coordinates within a chip adjacent to the chip including the inspection point or the coordinates within the chip. The field of view of the electron microscope is moved to the reference point using the coordinates in the equivalent cell in the adjacent cell as a reference point (S13), and a secondary electron image is taken into a computer as a reference image (S14). The observation magnification of the electron microscope automatically sets the observation magnification at which the minimum defect size desired by the operator can be detected because the minimum detectable defect size depends on the observation magnification of the electron microscope. If the inspection point is a coordinate obtained from the abnormal part inspection apparatus, the maximum magnification is set to allow the coordinate error of the inspection apparatus, the coordinate error of the electron microscope, and the coordinate error between the inspection apparatus and the electron microscope. For example, in the case of a defect having a large size, the maximum magnification is changed so that the defect is included in the image. Alternatively, in the case where the category indicating the type of defect such as a scratch, a peeling, or a foreign substance is a densely distributed category such as a scratch, if the same category exists in an arbitrarily set peripheral area, the defect existing area is determined. It is possible to change to the included magnification.

Next, the visual field of the electron microscope is moved to the inspection point registered on the electron microscope (S15). After that, the secondary electron image of the inspection point is captured as an inspection image at the same observation magnification as when the reference image was obtained (S16), and an image comparison is performed between the two images by a pattern matching method or the like, and a singular point (defect) ) Is specified (S17). In the subsequent determination in step 18, if a singular point is detected, the detected point is set as the observation center, the maximum magnification that can be observed is set, and information processing and observation processing of the singular point such as image storage and length measurement are performed. (S19). The observation magnification at this time may be a previously set observation magnification. Thereafter, the observation image at the optimum magnification is stored on a computer as electronic information. Not only images but also detected singularities (defects)
It is also possible to simultaneously store additional information such as the size and projection length (horizontal direction, vertical direction).

If the existence of a singular point cannot be confirmed in the processing of step 17, the processing proceeds from step 18 to step 20.
To determine whether to perform a re-inspection for that inspection point. Whether the reinspection is performed may be determined by the operator each time, or the reinspection may be always performed. Which mode is to be set can be set in advance. When re-examination,
Returning from step 20 to step 13, the reference image and the inspection image are acquired again, and the singular point is automatically detected. At this time, the chip for acquiring the reference image may be changed to another chip. If the re-inspection is not performed, the process proceeds from step 20 to step 21 as it is. Before proceeding from step 20 to step 21, an inspection image in which a singular point is not recognized may be stored so that it can be checked again later. The reference image is stored together with the inspection image depending on the operator's request.

Next, proceeding to step 21, it is determined whether or not the inspection point for which singularity detection has been performed is the last inspection point registered in step 12, and step 13 is performed until all inspection points have been inspected. Is repeated. Here, the reference image and the inspection image do not necessarily need to be secondary electron images, and may be reflected electron images or mixed images of reflected electrons and secondary electrons. The automatic detection processing of the singular point performed in step 17 is not limited to the pattern matching processing between two images, and any method may be used as long as the automatic detection of the pattern singular point is possible.

Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a view for explaining the singular point automatic detection processing according to the present embodiment, and FIG. 5 is a flowchart showing the flow of the processing. In the second embodiment, an abnormal portion having a disordered pattern periodicity is automatically detected as a singular point only from an inspection image without using a reference image. The registration of the inspection point is performed as described above with reference to FIG.

The semiconductor memory formed on the semiconductor wafer is formed by repeating the same pattern as schematically shown in FIG. In the singular point automatic detection of this embodiment, the position information of the inspection point set in advance as described above is read (S31 in FIG. 5), and the visual field of the electron microscope is moved to one of the inspection points (S3).
2) Inspection image (secondary electron image) 17 of the inspection point is taken into the computer (S33). Now, in the inspection image 17, as schematically shown in FIG.
Shall exist. Next, as shown in FIG. 4B, the inspection image is divided into a number of small areas 19 (S3).
4). The small area 19 may be constituted by one pixel, or one small area 19 may be constituted by a plurality of pixels. When one small area is formed by a plurality of pixels, for example, one small area can be formed by m × m pixels, but the shape of the small area does not necessarily have to be a square. Further, it is not necessary to determine the size and shape of the small region 19 particularly in association with the pattern cycle of the semiconductor memory. Each small area 19 is quantified by a gray level value obtained by dividing the image density (secondary electron intensity) of the small area into an arbitrary gradation (S35).

Next, as shown in FIG. 4C, the inspection image 17 is divided into windows 20 of the same shape including an appropriate number of small regions 19 (S36). Then, based on the repetition information (period information) of the pattern formed on the semiconductor wafer, such as the design rule, as shown in FIG. Calculate the difference between the gray level values of. At this time, window 2
It is preferable that 0 includes a repeating pattern of two or more cycles. Thus, in each window 20,
In the window, the sum of the differences of the gray level values between the small areas separated by one cycle from each other is calculated (S37). The processing in step 37 is performed until it is determined in step 38 that processing has been completed for all windows.

If no defect exists in the inspection image 17, the same image, that is, a small area 19 having the same gray level appears in the window 20 every cycle.
The difference in gray level value between the small areas is ideally zero. On the other hand, if a defect exists in the inspection image 17, the gray level of the small area 19 one cycle apart in the window 20 differs, so that the difference in the gray level value between the small areas 19 increases. Therefore, the window showing the feature that the total sum of the gray level values between the small areas is the largest is regarded as a defective window, and the center of the field of the electron microscope is moved to the center of the unique window (S39). Is changed to the optimal magnification at which imaging can be performed, an observation process is performed as shown in FIG. 4E, and the image is stored (S4).
0). At this time, information processing for acquiring additional information about the singular point such as the size, area, projection length in the X direction, projection length in the Y direction, and category of the singular point is performed, and the result is stored together with the image. You may. Thereafter, it is determined whether or not the inspection point is the last inspection point read in step 31 (S41). If any inspection points for which inspection has not been completed remain, the flow returns to step 32 to return to the next inspection point. Move the field of view and perform the same processing.

The distance between the small areas 19 for obtaining the gray level difference in the window 20 is not necessarily limited to one cycle, but may be any two or three cycles within a range not exceeding the size of the window 20. Can be set to the cycle. The singular point automatic detection method of this embodiment can be similarly applied to an automatic inspection of an unprocessed semiconductor wafer by arbitrarily setting a period. Further, the inspection image 17 is not necessarily a secondary electron image, but may be a reflected electron image, a mixed image of reflected electrons and secondary electrons, or the like.

Next, a third embodiment of the present invention will be described with reference to FIG. The third embodiment is an embodiment in which a plurality of windows are created from an inspection image based on periodic information of a pattern formed on a semiconductor wafer such as a design rule, and a singular point is automatically detected. The inspection point of the semiconductor wafer to be inspected is set on an electron microscope, for example, as described with reference to FIG.

In the same manner as in the above embodiment, a secondary electron image at a test point of a semiconductor memory pattern formed on a wafer is taken into a computer as a test image 17 and the test image is taken as one pixel or a fixed number of pixels. , The secondary electron intensity of each small area 19 is quantified by a gray level value divided into an arbitrary gradation. Next, a plurality of windows 31a and 31b are created from the inspection image 17 in an arbitrary cycle unit. Since the windows 31a and 31b are created based on the same cycle, the same pattern exists at the corresponding position of each window, and there is no need to perform position matching such as pattern matching before the difference processing. Therefore, these windows 31
The difference processing of the gray level value is performed between the small areas 19 corresponding to a and 31b, and the small area having the largest difference is detected as a singular point. Thereafter, the center of the visual field of the electron microscope is moved to the detected singular point, the observation magnification is changed to the optimum magnification, an electron microscope image is obtained, and the obtained observation image is stored as electronic information on an electronic computer. At this time, the size of the singular point,
Information processing for acquiring additional information about a singular point such as an area, a projection length in the X direction, a projection length in the Y direction, and a category may be performed, and the result may be stored together with the image.

In the third embodiment, two windows 31
When the difference processing of a and 31b is performed, it is possible to specify a small area having a large difference, but it is not possible to specify in which window a singular point (defect) exists. However, when combined with the second embodiment in which the presence or absence of a singular point in a window is detected by taking the sum of the gray level value differences between corresponding small areas one or several cycles apart in one window, It can be determined that a singular point exists on the window side showing the characteristic that the sum of the gray level values between the regions is the largest. Thus, when the third embodiment and the second embodiment are combined, the number of windows required for specifying a singular point (defect) is at least two. As a result, it is possible to acquire an image with a defect centered on the screen with higher accuracy than in the case of the second embodiment alone.

The detection method of the third embodiment is similarly effective for automatic observation and automatic inspection of an unprocessed semiconductor wafer by setting the cycle arbitrarily. The inspection image does not need to be a secondary electron image, and may be a reflected electron image, a mixed image of a reflected electron and a secondary electron image, or the like.

[0033]

According to the present invention, it is possible to automatically perform from detection or observation of a foreign substance or a defect in an arbitrary area to storage of an image. Further, by detecting a singular point from one inspection image without using a reference image, it is possible to prevent the sample from being irradiated with an electron beam and the number of times of moving the stage.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an electron microscope according to the present invention.

FIG. 2 is a flowchart of an example of a defect detection and high-resolution observation process according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an example of an inspection point registration screen.

FIG. 4 is a diagram illustrating a method for automatically detecting a singular point according to a second embodiment of the present invention.

FIG. 5 is a flowchart illustrating a flow of a process according to a second embodiment.

FIG. 6 is a diagram illustrating a method for automatically detecting a singular point according to a third embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inspection point setting means, 2 ... Singular point automatic detection means, 3 ... Singular point information processing / observation processing means, 4 ... Electron microscope, 17
... inspection image, 18 ... defect, 19 ... small area, 20 ... window, 31a, 31b ... window, 32 ... wafer map, 33 ... inspection chip, 34 ... non-inspection chip, 35 ...
In-chip coordinate input area, 36 ... step for setting inspection point, 37
… Inspection point setting window

Claims (13)

[Claims] 1. An inspection point setting means for setting an electron microscope visual field at an inspection position on a sample to be inspected, and a singular point automatic detection for automatically detecting an abnormal portion of an inspection image picked up at the inspection position as a singular point And an observation processing unit for obtaining information on the singular point detected by the singular point automatic detection unit. 2. The electron microscope according to claim 1, further comprising an automatic visual field setting unit that automatically sets a visual field area of the microscope based on prior information on the abnormal part. 3. The electron microscope according to claim 1, wherein the observation processing unit has a function of storing observation information and incidental information about the detected singular point. 4. An electron microscope according to claim 1, wherein said observation processing means has a function of changing observation conditions according to a detection result by said singular point automatic detection means. 5. The singular point automatic detecting means detects a singular point using period information of a pattern formed on a sample to be inspected. Item electron microscope. 6. The method according to claim 1, wherein the singular point automatic detecting means detects a singular point by detecting a disturbance of a periodic pattern formed on the sample to be inspected. Item electron microscope. 7. The singularity automatic detection means creates a plurality of partial images obtained by dividing the inspection image by one or more periods of the pattern using period information of the pattern formed on the sample to be inspected. The electron microscope according to claim 1, wherein a singular point is detected by performing a difference process between corresponding small regions among the plurality of partial images. 8. The singularity automatic detection means divides the inspection image into a plurality of partial images having the same size, and in each partial image, one period or a plurality of periods of a pattern formed on a sample to be inspected. The difference processing is performed between small areas separated by a period to obtain the sum of the differences, and the detection of the singular point is performed assuming that the singular point exists in the partial image having the maximum sum of the differences. The electron microscope according to claim 1. 9. The electron microscope according to claim 7, wherein the small area is composed of a plurality of pixels. 10. In an inspection method for detecting a singular point of a sample to be inspected on which a periodic pattern is formed, a pattern disturbance is detected by using the pattern period information, and a position at which the pattern exists is detected. An inspection method characterized by detecting as a singular point. 11. An inspection method for detecting a singular point on an inspection image obtained by imaging a sample to be inspected on which an periodic pattern is formed with an electron microscope, wherein the inspection image includes one or more periods of the pattern. An inspection method comprising: creating a plurality of partial images delimited by, and performing a difference process between corresponding small regions among the plurality of partial images to detect a singular point. 12. An inspection method for detecting a singular point on an inspection image obtained by imaging an inspection sample on which an periodic pattern is formed with an electron microscope, wherein the inspection image has a plurality of partial images of the same size. Divided into
In each partial image, a difference processing is performed between small areas separated by one cycle or a plurality of cycles of a pattern formed on the sample to be inspected to obtain a sum of differences, and a portion where the sum of the differences is maximum An inspection method characterized by detecting a singular point assuming that a singular point exists in an image. 13. The inspection method according to claim 11, wherein the small area includes a plurality of pixels.