JPH10163283A - Method for aligning lsi image - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an aligning method by which an LSI observing/measuring device, such as the electron beam tester, can align an observed image required for automatic operation, etc., with a low error probability. SOLUTION: Wiring contours 13 and 23 are extracted against an observed picture 11 showing a two-dimensional shape obtained by controlling the position of an LSI observing/measuring device to a prescribed spot of an LSI and the layout data 21 of the LSI. Then, two-dimensional closed areas 15 and 25 formed of the wiring contours 13 and 23 are extracted, and the closed area extracted from the observed picture is compared with that extracted from the layout data. For combinations which are discriminated to have possibilities of coincidence between both closed areas, the degree of coincidence between whole wirings in both areas is evaluated in a positional relation 37 where the wirings in both areas lie upon another, the combination having the highest degree of coincidence is found, and the positional relation corresponding to the combination is used as the optimum positional relation 39 between obtained observed pictures.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for aligning an observation image representing a two-dimensional shape of an LSI required for an automatic operation or the like in an LSI observation / measurement apparatus such as an electron beam tester, and in particular, It relates to an alignment method that does this with low error probability.

[0002]

2. Description of the Related Art In an LSI observation / measurement device such as an electron beam tester, when an observation image is obtained by controlling an imaging position at a specified position, there is no guarantee that an image exactly matching the specified position can be obtained. Generally, an image having a slightly shifted position is obtained. For this reason, in order to accurately align the position with the designated portion, it is necessary to compare the observed image with the layout data of the designated position of the LSI to grasp the positional relationship. In general, an image obtained by observing a two-dimensional shape of an LSI has image quality deterioration such as noise, distortion, and blur. Therefore, the observed image and the layout data are compared overall and comprehensively to obtain the highest matching degree. There is a need for a method for grasping such mutual positional relationships.

[0003] As a rudimentary method for this purpose,
There is a method in which the overall degree of coincidence is evaluated while shifting the relative position of the two images little by little, and the amount of deviation when the degree of coincidence is maximized is determined as a necessary position correction amount. Is shifted little by little, so that a very large processing time is required when the range in which the positional shift can occur is large.

In connection with such alignment, a method for aligning an electron beam tester image of an LSI with an LSI mask diagram at high speed is disclosed in a literature (Okubo et al., "EB Automatic Positioning Method for LSI Wiring in EB Tester". Consideration ”,
Materials for the 117th meeting of the JSPS 132 Committee, pp.
153-158). According to the method, contours of wiring and the like in an electron beam tester image are adjusted for each direction, and the distribution of contours in the direction perpendicular to the X-axis and the Y-axis is projected, and the projection amount for two images for each axis is projected. Are compared to calculate a displacement amount or the like. According to this method, the distribution of contour lines such as wiring is decomposed in each of the X and Y axes for each direction to calculate a one-dimensional displacement, and thus the degree of coincidence is adjusted while shifting the position little by little in a two-dimensional space. It can be done faster than the method.

[0005]

In the above method, when the observed image is largely shifted from the designated position, an erroneous positional shift may be introduced. In the above-described method, the amounts of the contours of the wiring and the like projected on the X axis and the Y axis for each direction are used. However, depending on the type of the integrated circuit element or the observation location therein, the distribution amount may be substantially similar in coordinates even though the wiring in the X-axis or Y-axis direction is different. Although there is no problem when the number of observed images is about one or two wirings, there is a possibility that an erroneous positional shift amount may be calculated when the observed image is shifted by several wires or more, an example of which is shown.

FIGS. 8A and 8B are schematic diagrams showing a distribution of observed images and contour lines in a conventional example, wherein FIG. 8A is a schematic diagram of a wiring image of an LSI, and FIG. FIG.

FIG. 8 shows an example of a target image which leads to an erroneous displacement amount in the above-described conventional method. Although an image obtained by actually observing an LSI has image quality degradation, it is not represented in this example but is represented schematically. As shown in FIG. 8 (a), in this observation image, there are two vertical wirings on the right and left sides from the center, respectively, and correspondingly, four wirings on the right and left sides respectively. There is a contour line in the Y-axis direction. FIG.
FIG. 8B shows the amount of projection of the contour in the Y-axis direction on the X-axis in the target image in FIG.
The distribution corresponding to each of the four contour lines in the Y-axis direction on the right and left sides of (a) is similar to that shown in FIG.
In the determination based on (b), there is a possibility that the displacement in the X-axis direction is erroneously grasped.

An object of the present invention is to provide an L-beam tester such as an electron beam tester.
It is an object of the present invention to provide a positioning method in which a positioning of an observation image required for an automatic operation or the like in an SI observation / measurement apparatus can be performed with low possibility of error.

[0009]

According to the method of aligning an LSI image of the present invention, an imaging image is moved to a desired observation point on an LSI to obtain an observation image representing a two-dimensional shape of the LSI. A corresponding wiring outline is extracted from the observed image and the layout data of the LSI, a two-dimensional closed region formed by the extracted wiring outline is extracted, and an extracted from the closed region and the layout data extracted from the observed image. The possibility of shape matching between the determined closed areas is determined, and for the combination of closed areas determined to be likely to match, the entire wiring of the observed image and the layout data The degree of coincidence when the entire wiring is superimposed is evaluated, and a positional relationship that maximizes the degree of coincidence of the entire wiring is obtained.

In the process of extracting the wiring outline from the observation image,
The shape of the two-dimensional wiring outline may be approximated by a combination of line segments according to a predetermined method, and the line segment may be extracted as the wiring outline, and the extraction may be performed. Only the extracted closed region may be extracted, and the possibility of shape matching may be determined for the extracted closed region. As a method of extracting only the closed region having a predetermined size or more, at least one of the wiring contours is extracted. On the side, a wiring contour having no intersection of the wiring contour or bent of the wiring contour over a predetermined length or more may be obtained, and a closed region including the corresponding wiring contour may be extracted.

In the determination of the possibility of matching of the shape between the closed region of the observation image and the closed region of the layout data,
The possibility of matching the shapes of the closed regions may be determined by comparing feature values including at least one of the vertical size, the horizontal size, and the number of vertices of each closed region. , It is determined whether the comparison of the feature quantity including at least one of the horizontal dimension and the number of vertices satisfies a predetermined set value, and only the combinations satisfying the criterion can be matched in detail. May be determined,
The determination of the possibility of matching the shapes of the closed regions and the subsequent operations may be performed only on the combinations of the closed regions including the differences in the respective positions within the range that can occur as the positional deviation in the observation image.

Further, as a method of obtaining a positional relationship in which the degree of coincidence of the entire wiring is the highest, a plurality of combinations in which the possibility of coincidence of the shape of the closed region is determined are compared with the closed region of the observed image and the closed region of the layout data. As a positional relationship with overlapping, priority is given to a common one among a plurality of positional relationships obtained from each combination, and the degree of coincidence of the overall wiring positional relationship under each positional relationship is evaluated. May be obtained with the highest degree of matching.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail. FIG. 1 is a flowchart for explaining an embodiment of an LSI positioning method according to the present invention. In the figure, reference numeral 11 denotes an observed image, 12 denotes a process of extracting a wiring outline of the observed image, and 13 denotes an extracted wiring. Contour, 14 is a closed region extraction process, 15 is an extracted closed region, 21 is layout data, 22 is a wiring data extraction process of layout data, 2
3 is an extracted wiring outline, 24 is a process of extracting a closed area, 2
5 is an extracted closed region, 36 is a process of determining the possibility of matching the shape of the closed region, 37 is a determined positional relationship, 38 is a process of evaluating the degree of matching of the entire wiring, and 39 is an optimal positional relationship evaluated. .

First, a wiring contour extraction 12 is performed from the obtained observation image 11. The observation image 11 is an image of a two-dimensional shape of an LSI obtained by an analysis device such as an electron beam tester, and FIG. 2 shows an LSI image according to an embodiment of the present invention.
5 is an electron micrograph (SEM photograph) of an example of an observed image of the wiring of FIG. The extraction of the wiring outline to be compared with the image is performed based on the analysis of the data of the luminance value of each point in the target range. 3A and 3B are schematic diagrams showing a method for analyzing image data according to the present invention. FIG. 3A is a schematic diagram showing a part of the brightness of each section of an image expressed in a range from 0 (black) to 255 (white). FIG. 4B is a distribution diagram of a luminance analysis value obtained by comparing the luminance of each part divided in FIG.

In the wiring contour extraction 12, a wiring contour is extracted from the observation image 11. In the case of the observation image of the electron beam tester, as shown in FIG. 2, the luminance is relatively higher at the wiring contour than at other parts in the vicinity. As shown in FIG. 3A, the observation image is divided into predetermined sizes, and the luminance of each division is measured. Considering that most wiring in the LSI is vertical or horizontal, the luminance in the X-axis direction and the Y-axis direction is higher than the other coordinate values before and after, and has the maximum luminance among them. By extracting points, it is possible to extract points representing the wiring contours for the wiring in the vertical and horizontal directions, respectively. Whether or not the luminance is relatively higher than the others may be set and operated as appropriate.

For example, a description will be given of a case where a wiring contour is extracted in the X-axis direction with respect to a luminance distribution extracted from an observation image (part) as shown in FIG. When the value of the luminance is higher than the other preceding and succeeding sections by 30 or more and the section having the maximum luminance is extracted in the X-axis direction, and the extracted section is displayed as 1 and the other sections are displayed as 0, The extracted section as shown in FIG. 3B is displayed as 1.

The data of the wiring contour can be represented by a two-dimensional bit map as shown in FIG. 3B. It may be approximated by one or more line segments by a predetermined method, and in subsequent operations, the line segments may be regarded as contours and used. That is, since the line segment is represented only by the coordinates of the start point and the end point, the use of the line segment makes it possible to reduce the amount of data and perform various operations at high speed.

In addition, since noise and a break in the wiring contour occur in the observed image, it is effective to remove a wiring contour having a length equal to or less than a certain length or to connect a break in the wiring contour having a certain length or less. . FIG. 4 shows an example in which the wiring outline is extracted from the image of FIG. 2 and further approximated by a line segment as a two-dimensional image. FIG. 4 shows the electron microscope of FIG. This is a halftone image of the wiring contour displayed on the display after extracting and processing the wiring contour from the observed image. In the figure, the wiring contour portion is white and the others are black.

When the directions of the wiring contours in the vertical and horizontal directions are slightly inclined from the orthogonal lines as shown in FIG.
Based on those average inclinations, it is possible to correct the orientation so that the orientation is more accurate in the vertical and horizontal directions. FIG.
Is a halftone image of the wiring outline displayed on the display after correction is made so that the vertical and horizontal directions of the wiring outline in FIG. 4 are orthogonal to each other.

On the other hand, extraction 22 of the wiring outline from the layout data 21 to be compared is also performed. The layout data 21 is data of a layout design for the LSI, and the data represents the shape of each wiring. For layout data, it is sufficient to extract the outline of the wiring from the data limited to the upper layer appearing in the observed image of the LSI, and there is a possibility that the position may deviate from the position specified when acquiring the observed image of the LSI. Based on the largest possible range, it is preferable to determine a range where there is a possibility of overlapping, and to extract a wiring contour within the range.

In the next extraction of closed regions 14 and 24, sections surrounded by the wiring contours 13 and 23 are extracted. Originally, the observation image 11 or the layout data 21 contains a very large number of closed regions, but it is desirable to extract only the closed regions having a certain size or more in order to reduce the number of extracted regions. Vertical,
It is preferable to extract only those having a certain size or more based on the minimum value, average value, product, and the like of the horizontal dimension.

Further, as a method for extracting only such a closed region having a certain size or more, a portion of the wiring contour which does not cross or bend over a certain length on either side is searched. Is preferably extracted. In general, a large closed area in an LSI often includes a long straight section in a wiring contour constituting the closed area. Such a portion can be detected as a portion of the wiring contour having no intersection or bend over a certain length on either side. Then, by obtaining only a closed region extracted by tracing the wiring contour with the detected portion of the wiring contour as a starting point, a closed region having a certain size or more can be obtained. FIG. 6 shows an example of extracting a closed area having a size equal to or larger than the wiring contour of FIG.
Shown in FIG. 6 is a diagram showing a closed area which is displayed on a display and shows a closed area extracted by a predetermined method from the wiring outline after correcting the wiring outline of FIG. 5 so that the vertical direction and the horizontal direction are orthogonal to each other. Are halftone images.

In the next possibility of matching the shape of the closed region 36, it is determined whether there is a possibility that the closed region 15 extracted from the observed image and the closed region 16 extracted from the layout data have the same shape. Is determined. Basically, the positions may be adjusted between the two closed regions, the degree of overlap of the wiring contours when the two regions are overlapped is evaluated, and the determination may be made based on the evaluation value.

The position can be adjusted by calculating the position difference based on the difference between the coordinates of one or both of the leftmost end and the rightmost end of the two, and the coordinates of one or both of the uppermost end and the lowermost end. . By using the difference between the coordinates of one of the leftmost and rightmost ends of the two, and the coordinates of one of the uppermost and lowermost ends, the deviation of the coordinates of both can be corrected, both the leftmost and rightmost ends of the two, and the uppermost and lowermost ends By using the difference between the two coordinates, it is possible to correct not only the difference in the coordinates but also the difference in the magnification of the X coordinate and the Y coordinate when the shapes of the two coincide with each other.

FIGS. 7A and 7B are schematic diagrams of a closed region extracted from the observed image and the layout data. FIG. 7A is a schematic diagram of the closed region extracted from the observed image, and FIG. 7B is a schematic diagram of the closed region extracted from the layout data. schematic diagram of a closed region corresponding to a),
(C) is a schematic diagram of a similar closed region extracted from layout data.

For example, determination 36 of the possibility of shape matching with a closed region from an observation image as shown in FIG. 7A and a closed region from layout data as shown in FIG. When the relationship 37 is grasped, the leftmost X coordinate value 57 of the closed region from the observed image, the X coordinate value -400 of the leftmost position of the closed region from the layout data, and the leftmost X coordinate value of the closed region from the observed image are obtained. If the rightmost X-coordinate value 67 and the leftmost X-coordinate value -300 of the closed area from the layout data are treated as coincident, each (rightmost X-coordinate value)-(leftmost X-coordinate value) Since the values are 10 and 100, it can be seen from the ratio that the difference in the magnification of the X coordinate is 0.1, and the positional relationship when the two coincide with each other is as follows.

(X coordinate on observation image side) = 0.1 × (X coordinate on layout side) +97 Similarly, it can be seen that the Y coordinate is as follows.

(Y coordinate on observation image side) = 0.1 × (Y coordinate on layout side) +89 In this manner, the positions of the closed regions can be matched.

As a method of evaluating the degree of overlap of the wiring outlines constituting the closed region, an evaluation value can be derived by integrating the results by any one or a combination of the following. (A) A positive or negative evaluation is given to a wiring contour from an observation image depending on whether or not a wiring contour from layout data exists near a corresponding position. (B) Positive or negative evaluation is given depending on whether or not the wiring outline from the observed image exists near the corresponding position while the wiring outline from the layout data exists.

By judging the evaluation values obtained by these using a set threshold value, it is possible to judge the possibility of matching.

For example, for the closed regions in FIGS. 7A and 7B, a wiring outline from layout data exists near a corresponding position with respect to a wiring outline from an observed image.
Further, since the wiring outline from the layout data exists near the position corresponding to all the wiring outlines from the observation image, a high evaluation value can be derived. FIG.
In the closed area of FIG. 7A and FIG. 7C, the position of the wiring outline from the observation image and the position of the wiring outline from the layout data are different in the lower right part. Absent, this gives a negative rating and can lead to a lower rating than in the former case.

It takes some time to evaluate and determine the degree of overlap of the wiring contours constituting such a closed region. For this reason, it may be determined whether or not there is a possibility that the shape of the closed region matches according to the vertical and horizontal dimensions of the closed region or the feature amount such as the number of vertices. As a result, the possibility of matching can be determined in a short time. In addition, first, it is determined whether or not the shape of the closed region has a possibility of matching based on the vertical and horizontal dimensions of the closed region, or the feature amount such as the number of vertices, and a combination of the closed regions for which the matching possibility is determined is determined. A method may be adopted in which the degree of overlap between the wiring contours constituting the closed region is evaluated and determined only for this.

As a combination of the closed regions for evaluating the possibility of matching of the shapes, based on a range that can occur as a positional shift in the observed image, a closed region whose difference in position is included in the range is included. It is preferable to limit the number of combinations to the combinations and compare the possibility of matching of the shapes of the closed regions only for such combinations. This can reduce the number of sets of closed regions for which the possibility of matching is evaluated.

In the evaluation 38 of the degree of coincidence of the entire wiring, the combination of the closed areas determined to have the possibility of coincidence is superimposed on the entire wiring under a positional relationship such that they overlap with each other. To evaluate.

The method of matching the positional relationship is the same as the method of matching the positions described as the basic method for determining the possibility of matching the shapes of the closed areas, that is, one of the leftmost and rightmost ends of the two. A method of calculating and correcting a difference in position based on a difference in coordinates of one or both of the uppermost end and the lowermost end may be used, and the entire wiring may be overlapped with the same positional relationship. Further, when evaluating the degree of overlap of the wiring contours in the closed area, a slight shift may be measured, and the positional relationship may be further corrected based on this, and then the entire wiring may be overlapped.

As for the evaluation of the degree of overlap of the entire wiring, as in the evaluation of the degree of overlap of the wiring outlines for determining the possibility of the shape match of the closed area, the evaluation value is obtained by integrating the following one or a combination of the evaluation values. I can guide you. (A) A positive or negative evaluation is given to a wiring contour from an observation image depending on whether or not a wiring contour from layout data exists near a corresponding position. (B) Positive or negative evaluation is given according to whether or not the wiring outline from the observed image exists near the corresponding position while the wiring outline from the layout data exists.

Such a coincidence evaluation is performed for a combination of a plurality of closed regions, and if a positional relationship with respect to the combination that leads to the best evaluation value is obtained, an optimal position between the observed image and the layout data is obtained. The relationship 39 is obtained.

It is necessary to evaluate the degree of coincidence of the entire wiring for each of the combinations for which the possibility of coincidence of the shapes of the two-dimensional closed regions has been determined under the positional relationship where the two overlap. Absent. For a positional relationship that is the same as or close to the positional relationship that has already been tried, the evaluation of the matching degree of the entire wiring may be omitted.

Further, of the plurality of positional relationships corresponding to the plurality of combinations determined to have the possibility of coincidence, the degree of coincidence of the entire wiring is allowed under each positional relationship by a priority number from the most common positional relationship. And the positional relationship with the highest degree of matching may be obtained based on this. By adopting such a method, the number of times of evaluating the matching degree of the entire wiring is further reduced,
The positional relationship can be derived without error.

With the above-described method, the positional relationship between the observed image and the layout data can be derived with a low possibility of error.

[0041]

According to the method of the present invention, a closed region is further extracted from each of the wiring contours extracted from the observation image and the layout data, and an optimum positional relationship is determined from the possibility of matching the shape of the closed region. Since it is determined, even if the position of the observed image is shifted by more than several wires, there is an effect that the position can be adjusted with a lower possibility of error than the conventional method.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining an embodiment of an LSI alignment method according to the present invention.

FIG. 2 is an electron microscope photograph (SEM photograph) of an example of an observed image of an LSI wiring according to an embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating a method for analyzing image data according to the present invention. (A) shows that the brightness of each section of the image is 0.
FIG. 9 is a schematic distribution diagram of a part represented in a range from (black) to 255 (white). (B) is a distribution diagram of a brightness analysis value obtained by comparing the brightness of each part divided in (a) with the surroundings on a predetermined basis.

FIG. 4 is a halftone image of a wiring contour extracted from the electron microscope observation image of FIG. 2 of the present invention, processed, and displayed on a display.

5 is a halftone image of the wiring outline displayed on the display after the wiring outline of FIG. 4 has been corrected so that the vertical direction and the horizontal direction are orthogonal to each other.

FIG. 6 is a diagram showing a closed area extracted on a display from a wiring outline obtained by correcting the wiring outline of FIG. 5 so that the vertical direction and the horizontal direction are orthogonal to each other, and displaying the closed area on a display; It is a halftone image of a contour.

FIG. 7 is a schematic diagram of a closed region extracted from an observation image and layout data. (A) is a schematic diagram of a closed region extracted from an observation image. (B) is a schematic diagram of a closed region corresponding to (a) extracted from layout data.
(C) is a schematic diagram of a similar closed region extracted from layout data.

FIG. 8 is a schematic diagram showing a distribution of observed images and contour lines in a conventional example. (A) is a schematic diagram of a wiring image of an LSI.
(B) is a distribution diagram of a contour line in the Y-axis direction of the wiring of (a).

[Explanation of symbols]

 REFERENCE SIGNS LIST 11 observation image 12 wiring outline extraction process of observation image 13 extracted wiring outline 14 closed area extraction process 15 extracted closed region 21 layout data 22 layout data wiring outline extraction process 23 extracted wiring outline 24 closed Region extraction process 25 Extracted closed region 36 Process of determining the possibility of matching the shape of the closed region 37 Determined positional relationship 38 Evaluation process of the degree of coincidence of the entire wiring 39 Optimal positional relationship evaluated

Claims (8)

[Claims] 1. An imaging position is moved to a desired observation point on an LSI to obtain an observation image representing a two-dimensional shape of the LSI, and a corresponding one of the obtained observation image and the layout data of the LSI is obtained. Extracting a two-dimensional closed region formed by the extracted wiring outlines, and extracting a two-dimensional closed region between the closed region extracted from the observation image and the closed region extracted from the layout data. The possibility of shape matching is determined, and for the combination of the closed regions determined to be likely to match, the entire wiring of the observation image and the entire wiring of the layout data are superimposed in a positional relationship where the two overlap. A method for evaluating the degree of coincidence in a case where the degree of coincidence is obtained to obtain a positional relationship that maximizes the degree of coincidence of the entire wiring. 2. In the process of extracting the wiring outline from the observed image, the shape of the two-dimensional wiring outline is approximated by a combination of line segments according to a predetermined method, and the line segment is extracted as a wiring outline. 2. The method according to claim 1, wherein the step (a) is performed. 3. The method according to claim 1, wherein in the extraction of the closed region, only the closed region having a size equal to or larger than a predetermined size is extracted, and the determination of the possibility of shape matching is performed on the extracted closed region. 3. The method for positioning an LSI image according to 1. 4. A method for extracting only a closed area having a size equal to or greater than a predetermined size, wherein at least one side of the wiring outline does not cross the wiring outline or bend the wiring outline over a predetermined length. 4. The LSI according to claim 3, wherein an outline is obtained, and a closed region including the corresponding wiring outline is extracted.
Image alignment method. 5. The method according to claim 5, wherein in the determination of the possibility of matching of the shapes between the closed region of the observation image and the closed region of the layout data, the vertical size, the horizontal size, and the number of vertices of each closed region are selected. 2. The method according to claim 1, wherein the likelihood of matching of the two shapes is determined by comparing feature amounts including at least one of the two. 6. The method according to claim 1, wherein in the determination of the possibility of matching of the shape between the closed region of the observation image and the closed region of the layout data, the vertical size, the horizontal size, and the number of vertices of each closed region are selected. 6. The method according to claim 5, wherein it is determined whether or not the comparison of the feature amounts including at least one of the predetermined values satisfies a predetermined set value, and the possibility of matching of the shapes of both combinations is determined in detail only for a combination satisfying the set value. LSI image alignment method. 7. The method according to claim 1, wherein the determination of the possibility of matching of the shape between the closed region of the observation image and the closed region of the layout data is performed within a range that can occur as a position shift in the observation image. The method according to claim 1, wherein the determination of the possibility of matching the shape of the closed region and the subsequent operation are performed only for the combination of the closed regions including a difference in position. 8. As a method of obtaining a positional relationship that maximizes the degree of coincidence of the entire wiring, a plurality of combinations in which the likelihood of the shape of the closed area is determined are determined by comparing the closed area and the layout of the observed image with each other. As a positional relationship where the closed region of the data overlaps, a common one among a plurality of positional relationships obtained from each combination is prioritized, and the degree of coincidence of the positional relationship of the entire wiring under each positional relationship is evaluated. And
2. The method according to claim 1, wherein a positional relationship having the highest matching degree is obtained based on the information.
3. The method for positioning an LSI image according to 1.