Abstract:
A pattern shape evaluation method includes acquiring an image of an evaluation target pattern including a plurality of element patterns; detecting edge of the evaluation target pattern from the image; classifying the detected edge of the evaluation target pattern into a plurality of evaluation target pattern edge groups; acquiring edge of a reference pattern serving as an evaluation standard for the element patterns; classifying the edge of the reference pattern into a plurality of reference pattern edge groups; selecting a reference pattern edge group to be aligned with the edge of the evaluation target pattern from the classified reference pattern edge groups; aligning the edge of the selected reference pattern edge group with the edge of the evaluation target pattern; and evaluating the shape of the evaluation target pattern by use of the result of the alignment.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority under 35 USC §119 to Japanese patent application No. 2006-110120, filed on Apr. 12, 2006, the contents of which are incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pattern shape evaluation apparatus, a pattern shape evaluation method, a semiconductor device manufacturing method, and a program. 
     2. Related Background Art 
     Heretofore, in evaluating a pattern of a semiconductor device, an image of the pattern is acquired, the width of the pattern is measured at an arbitrary place from the obtained image, and the width is compared with a preset specification. However, when the shape of the pattern is complicated, it is impossible to know a change in the whole shape of the pattern if the dimensional measurement is carried out at one place alone. The number of measurement points has to be increased to know the overall change, but this decreases the throughput of the measurement. 
     In order to solve the above-mentioned problem, there have been proposed various methods for comparing the shape of a pattern with data serving as an evaluation standard. These proposals include a pattern shape evaluation method which comprises: acquiring an image of an actual pattern which is an evaluation target by, for example, a scanning electron microscope (SEM); and acquiring the edge of the evaluation target pattern from the acquired image; superposing this edge on, for example, design data or lithography simulation data for the pattern. 
     For example, there is a method which comprises: aligning the edge of an evaluation pattern with design data before measuring the distance of a difference therebetween, and evaluating how faithfully to the design data the actual pattern is formed, thereby judging whether the sample is good or bad, and there is also a method which compares the edge of an actual pattern with a lithography simulation result to verify the accuracy of a simulation model. There is another method which comprises: providing in advance an allowable range (tolerance data) in design data; aligning the edge of an evaluation target pattern with the tolerance data to check whether the edge of the evaluation pattern is within the allowable range, thereby judging whether the evaluation target pattern is good or bad. In any of these evaluation methods, the accuracy of aligning (matching) the evaluation target pattern with a reference pattern greatly influences the evaluation. 
     However, the shape of a pattern on an actual wafer is often distorted with respect to design data, and this cause difficulty in the alignment. Moreover, the degree of the distortion is not uniform among a plurality of patterns present in an acquired image, and unpredictable distortions are also found. For example, there is a case where the position of only one at the end of a plurality of line patterns arranged in parallel to each other has moved from the design data due to, for example, the influence of etching or an aberration of an exposure unit. If such an actual pattern is to be superposed on the design data, a situation arises where matching suitable for evaluation can not be achieved due to the influence of the moved actual pattern. If the distance of a difference between the design data and the evaluation pattern is measured in such a case, an actual change of the shape to which a positional difference in matching is added is calculated as the distance of the difference. 
     Here, it is possible to provide in advance an evaluation region (region of interest: hereinafter simply referred to as “ROI”.) to prevent the inclusion of a pattern which has produced a positional difference so that matching is carried out only within this ROI. However, when the amount of the positional difference has changed due to a change of process conditions, questionable patterns may be contained in an assumed ROI. Moreover, in the case of a pattern having a complicated shape instead of the above-mentioned simple line pattern, it is not possible for a rectangular ROI to deal with such a pattern, and a problem arises in which the setting of the ROI itself becomes troublesome. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a pattern shape evaluation method comprising: 
     acquiring an image of an evaluation target pattern including a plurality of element patterns; 
     detecting edge of the evaluation target pattern from the image; 
     classifying the detected edge of the evaluation target pattern into a plurality of evaluation target pattern edge groups; 
     acquiring edge of a reference pattern serving as an evaluation standard for the element patterns; 
     classifying the edge of the reference pattern into a plurality of reference pattern edge groups; 
     selecting a reference pattern edge group to be aligned with the edge of the evaluation target pattern from the classified reference pattern edge groups; 
     aligning the edge of the selected reference pattern edge group with the edge of the evaluation target pattern; and 
     evaluating the shape of the evaluation target pattern by use of the result of the alignment. 
     According to a second aspect of the present invention, there is provided a program which is stored in a computer-readable medium and which causes a computer to execute a pattern shape evaluation method, the pattern shape evaluation method comprising: 
     acquiring an image of an evaluation target pattern including a plurality of element patterns; 
     detecting edge of the evaluation target pattern from the image; 
     classifying the detected edge of the evaluation target pattern into a plurality of evaluation target pattern edge groups; 
     acquiring edge of a reference pattern serving as an evaluation standard for the element patterns; 
     classifying the edge of the reference pattern into a plurality of reference pattern edge groups; 
     selecting a reference pattern edge group to be aligned with the edge of the evaluation target pattern from the classified reference pattern edge groups; 
     aligning the edge of the selected reference pattern edge group with the edge of the evaluation target pattern; and 
     evaluating the shape of the evaluation target pattern by use of the result of the alignment. 
     According to a third aspect of the present invention, there is provided a semiconductor device manufacturing method comprising executing a process of manufacturing a semiconductor device on a substrate when a pattern to be inspected formed on the substrate for a semiconductor device is judged to satisfy required specifications of the semiconductor device as a result of an evaluation by a pattern shape evaluation method, the pattern shape evaluation method including: 
     acquiring an image of an evaluation target pattern including a plurality of element patterns; 
     detecting edge of the evaluation target pattern from the image; 
     classifying the detected edge of the evaluation target pattern into a plurality of evaluation target pattern edge groups; 
     acquiring edge of a reference pattern serving as an evaluation standard for the element patterns; 
     classifying the edge of the reference pattern into a plurality of reference pattern edge groups; 
     selecting a reference pattern edge group to be aligned with the edge of the evaluation target pattern from the classified reference pattern edge groups; 
     aligning the edge of the selected reference pattern edge group with the edge of the evaluation target pattern; and 
     evaluating the shape of the evaluation target pattern by use of the result of the alignment. 
     According to a fourth aspect of the present invention, there is provided a pattern shape evaluation apparatus comprising: 
     an edge detecting unit which is provided with an image of an evaluation target pattern including a plurality of element patterns to detect the edge of the evaluation target pattern from the image; 
     an edge labeling unit which classifies the edge of the detected evaluation target pattern into a plurality of evaluation target pattern edge groups; 
     a design data labeling unit which is provided with data on the edge of a reference pattern serving as an evaluation standard for the element patterns and which classifies the edge of the reference pattern into a plurality of reference pattern edge groups; 
     a selecting unit which selects a reference pattern edge group to be aligned with the edge of the evaluation target pattern from the classified reference pattern edge groups; 
     an alignment unit which aligns the edge of the selected reference pattern edge group with the edge of the evaluation target pattern; and 
     a pattern shape evaluation unit which evaluates the shape of the evaluation target pattern by use of the result of the alignment. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a block diagram showing a schematic configuration of a pattern shape evaluation apparatus in one embodiment according to the present invention; 
         FIG. 2  is a flowchart showing a schematic procedure of a pattern shape evaluation method in a first embodiment according to the present invention; 
         FIG. 3  is a schematic diagram showing one example of an observation image of an evaluation target pattern; 
         FIG. 4  is a diagram showing one example of edge data for the evaluation target pattern detected from the observation image shown in  FIG. 3 ; 
         FIG. 5  is a diagram showing design data for the evaluation target pattern shown in  FIG. 3 ; 
         FIG. 6  is a diagram showing one example of the result of grouping and labeling the edge of a reference pattern; 
         FIG. 7  is a diagram showing reference pattern edge groups selected for alignment; 
         FIG. 8  is a diagram showing one example of the result of aligning the selected reference pattern edge groups with the edge of the evaluation target pattern; 
         FIG. 9  is a diagram showing one example of the result of aligning according to a prior art; 
         FIG. 10  is a diagram explaining a modification of the first embodiment of the pattern shape evaluation method according to the present invention; 
         FIG. 11  is a flowchart showing a schematic procedure of the pattern shape evaluation method shown in the modification in  FIG. 10 ; 
         FIGS. 12A to 12C  are explanatory diagrams for a “positional difference amount”; 
         FIG. 13  is a flowchart showing a schematic procedure of a pattern shape evaluation method in a second embodiment according to the present invention; 
         FIG. 14  is a diagram showing a part of the edge group extracted from the reference pattern within a reference image shown in  FIG. 6 ; 
         FIG. 15  is a diagram explaining one example of the alignment of the reference pattern edge group with an evaluation pattern edge group in the pattern shape evaluation method shown in  FIG. 13 ; 
         FIG. 16  is a diagram showing another part of the edge group extracted from the reference pattern within a reference image shown in  FIG. 6 ; 
         FIG. 17  is a diagram explaining another example of the alignment of the reference pattern edge group with the evaluation pattern edge group in the pattern shape evaluation method shown in  FIG. 13 ; 
         FIG. 18  is a flowchart showing a schematic procedure of a pattern shape evaluation method in a third embodiment according to the present invention; and 
         FIG. 19  is a flowchart showing a schematic procedure of a pattern shape evaluation method in a fourth embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Several embodiments of the present invention will hereinafter be described with reference to the drawings. 
     (1) One Embodiment of Pattern Shape Evaluation Apparatus 
       FIG. 1  is a block diagram showing a schematic configuration of a pattern shape evaluation apparatus in one embodiment according to the present invention. A pattern shape evaluation apparatus  1  shown in  FIG. 1  comprises a controller  10 , a memory MR 1 , a pattern image acquirer  12 , a pattern edge detector  14 , a pattern edge labeler  16 , a design data memory  22 , a design data labeler  24 , a matching unit  30  and a pattern shape evaluator  50 . 
     The memory MR 1  is connected to the controller  10 , and stores a program in which there is written an inspection recipe for executing a pattern shape evaluation method according to the present invention described later. 
     The controller  10  is not only connected to the memory MR 1 , but also connected to the pattern image acquirer  12 , the pattern edge detector  14 , the pattern edge labeler  16 , the design data memory  22 , the design data labeler  24 , the matching unit  30  and the pattern shape evaluator  50 . The controller  10  generates control signals and supplies the control signals to the respective sections to control the entire apparatus, and reads the program of the inspection recipe from the memory MR 1 , thereby executing inspection procedures on the basis of the program. 
     The pattern image acquirer  12  is not only connected to the pattern edge detector  14  but also connected to an unshown SEM unit and an optical imagining unit, and acquires, from these units, an image of an evaluation target pattern such as an SEM image or an optical microscopic image, and then supplies this image to the pattern edge detector  14 . The pattern edge detector  14  is connected to the pattern edge labeler  16 , and detects the edge of the evaluation target pattern from the image supplied from the pattern image acquirer  12 , and then supplies the edge to the pattern edge labeler  16 . The pattern edge labeler  16  is connected to the matching unit  30 , and classifies (labels) the edge of the evaluation target pattern into evaluation target pattern edge groups and supplies the result of grouping to the matching unit  30 . 
     The design data memory  22  stores design data for the evaluation target pattern. The design data labeler  24  is connected to the design data memory  22  and the matching unit  30 . The design data labeler  24  takes the design data out of the design data memory  22 , develops a linear image to generate a reference pattern, classifies (labels) the edge thereof into reference pattern edge groups, and supplies the result of grouping to the matching unit  30 . 
     The matching unit  30  includes an edge group selector  32 , a group associator  34 , an aligner  36 , a positional difference amount calculator  38  and a weighting unit  42 , and is connected to the pattern shape evaluator  50 . The edge group selector  32  selects edge groups to be aligned among the reference pattern edge groups. The aligner  36  aligns the reference pattern edge groups with the evaluation target pattern so that they are brought into proximity to each other, thereby aligning the selected reference pattern with the evaluation target pattern. The positional difference amount calculator  38  calculates, as the amount of a positional difference, a difference between standard coordinates of the image of the reference pattern and standard coordinates of the image of the evaluation target pattern, at the time of the alignment by the aligner  36 . The weighting unit  42  is provided with the result of calculating the positional difference amount from the aligner  36 , and weights each of the reference pattern edge groups in accordance with the degree of the positional difference amount. The group associator  34  uses the result of the alignment to associate the evaluation target pattern edge groups with the reference pattern edge groups, and supplies the result of the association to the pattern shape evaluator  50 . From the result of the association supplied from the matching unit  30 , the pattern shape evaluator  50  compares the evaluation target pattern with the reference pattern, thereby evaluating the shape of the evaluation target pattern. 
     The operation of the pattern shape evaluation apparatus  1  shown in  FIG. 1  will be described as an embodiment of the pattern shape evaluation method according to the present invention. 
     (2) First Embodiment of Pattern Shape Evaluation Method 
       FIG. 2  is a flowchart showing a schematic procedure of a pattern shape evaluation method according to the present embodiment. It is to be noted that a case will hereinafter be taken as an example where the shape of a pattern is evaluated using an SEM image acquired by an SEM unit, but the present invention is not limited thereto and can be applied an image acquired by any other unit such as an optical image acquiring unit. However, the use of the SEM image is preferable at the present moment because it is necessary to acquire an image of a pattern with higher magnification in order to evaluate the shape of a micropattern of a semiconductor. 
     First, a sample in which an evaluation target pattern is formed is brought in the SEM unit, and an image of the pattern is acquired (step S 1 ) and supplied to the pattern image acquirer  12 . Thus, for example, an observation image as shown in  FIG. 3  is obtained. As shown in  FIG. 3 , four kinds of patterns TP 1  to TP 4  are present in the observation image. In the present embodiment, the four kinds of patterns TP 1  to TP 4  shown in the observation image correspond to, for example, element patterns. In addition, the edges of the patterns are shining white because emission efficiency of a secondary electron increases at the edges of the patterns. 
     Next, the pattern edge detector  14  detects an edge corresponding to the contour of the evaluation target pattern from data on the acquired image ( FIG. 2 , step S 2 ). Since the edge of the evaluation target pattern is shining white in the observation image as described above, the edge can be extracted using binarization by a threshold value of intensity in the simplest method. However, any other method may be used such as a method using a sobel filter, a method using a canny filter, a method by template matching (Japanese Patent Publication Laid-open No. 2003-178314), a method in which a threshold for data is determined on the basis of intensities of signals in the vicinity of the edge of a pattern to extract an edge (threshold value method), and a linear approximation method. By the above citation, the contents of Japanese Patent Publication Laid-open No. 2003-178314 are incorporated in the specification of the present application. One example of edge data obtained as described above is shown in an inspection image GT 2  in  FIG. 4 . 
     Subsequently, the pattern edge labeler  16  labels the obtained edge after grouping ( FIG. 2 , step S 3 ). In the present embodiment, the edge is divided into four groups forming element patterns, which are labeled as “α”, “β”, “γ” and “δ”. 
     On the other hand, the design data labeler  24  carries out data acquisition ( FIG. 2 , step S 4 ), edge acquisition (step S 5 ) and labeling (step S 6 ) for the reference data as well almost simultaneously with or in parallel with the procedure in steps S 1  to S 3 . An example is shown in  FIG. 5  in which there is developed, in a diagrammatic view, design data which corresponds to that for the evaluation target pattern shown in  FIG. 3  and which is stored in the memory  22 . In a reference image GR 2  in  FIG. 6 , there is shown one example of the result of acquiring edge data corresponding to the edge of the reference pattern from the image data in  FIG. 5  (step S 5 ), and grouping and labeling the edge (step S 6 ). In the example shown in  FIG. 6 , the edge is divided into four reference pattern edge groups forming element patterns as in the evaluation target pattern, which are labeled as “a”, “b”, “c” and “d”. 
     Next, the edge group selector  32  compares the evaluation target pattern edge groups with the reference pattern edge groups (step S 7 ), and selects reference pattern edge groups to be aligned with the evaluation target pattern edge groups among the reference pattern edge groups (step S 8 ). In the present embodiment, in accordance with the purpose of the shape evaluation and required specifications of a product, an operator makes a selection and issues an instruction to the edge group selector  32 . Here, a reference pattern edge group is excluded which is considered to have a high risk of decreasing the accuracy of alignment due to a larger positional difference and a higher degree of a shape change than those of the other element patterns as a result of the comparison between the evaluation target pattern edge groups and the reference pattern edge groups, such that the reference pattern edge groups to be aligned are selected. In the case of a comparison between the example shown in  FIG. 4  and the example shown in  FIG. 6 , the three reference pattern edge groups “a”, “b” and “c” are to be aligned which remain after the exclusion of the reference pattern edge group “d” having a high degree of the shape change as shown in  FIG. 7 . 
     Subsequently, the aligner  36  aligns the selected reference pattern edge groups “a”, “b” and “c” with the edge groups of the evaluation target pattern so that their edges are superposed on each other as much as possible (step S 9 ). In the present embodiment, as a method of matching, it is desirable to use, for example, a method proposed in Japanese patent laid open (kokai) 2005-098885 which uses the distance between the edges. By this citation, the contents of the specification of the above-mentioned application are incorporated in the present application. However, other methods may be used as long as such methods allow the superposition with accuracy. One example of the result of such alignment is shown in  FIG. 8 . Then, the group associator  34  associates the evaluation target pattern edge groups with the reference pattern edge groups using the result of the alignment in the procedure described above. In the example shown in  FIG. 8 , “a” is associated with “α”, “b” is associated with “β”, and “c” is associated with “γ”. 
     Next, the result of the association is sent from the group associator  34  to the pattern shape evaluator  50 , and the pattern shape evaluator  50  compares the reference pattern selected for alignment with the corresponding evaluation target pattern, thereby evaluating the shape of the evaluation target pattern (step S 10 ). 
     Thus, according to the present embodiment, attention is focused on a part of the pattern of the reference data in order to exclude the influence of a pattern (the element pattern labeled as the edge group “δ” in the example shown in  FIG. 4 ) in which the degree of the shape change is higher than those of the other patterns, such that it is possible to highly accurately align the reference pattern with the evaluation target pattern. In  FIG. 9 , there is shown one example of the result of aligning the evaluation target pattern of the present embodiment with the reference pattern according to a prior art. As shown in  FIG. 9 , the accuracy of alignment has heretofore been extremely low because the alignment of the evaluation target pattern with the reference pattern is carried out for all the element patterns without narrowing down the reference patterns in accordance with the difference in the degree of the shape change. As apparent from a comparison between  FIG. 9  and  FIG. 8 , it is possible to evaluate the pattern shape with high accuracy according to the present embodiment because the alignment can be carried out with high accuracy. 
     In the embodiment described above, a form has been shown in which the shape evaluation is implemented for the reference pattern edge groups “a”, “b” and “c” other than the excluded reference pattern edge group “d” in  FIG. 6 . However, as shown in  FIG. 10 , the alignment may be carried out only using the reference pattern edge groups “a”, “b” and “c”, and then the reference pattern edge group “d” excluded during the alignment may be compared with the evaluation target pattern edge group “δ” to evaluate the shape of the evaluation target pattern edge group “δ”. The procedure of such a modification is shown in a flowchart of  FIG. 11 . The substantial difference between the procedure shown in  FIG. 11  and the procedure in  FIG. 2  only lies in the last step S 20 , and for other steps,  10  is added to the numbers of the steps in the procedure in  FIG. 2 , so that these steps are substantially the same as those in the procedure in  FIG. 2 . 
     (3) Second Embodiment of Pattern Shape Evaluation Method 
     While the operator specifies the reference pattern edge group used in the alignment in the embodiment described above, the present embodiment provides a method comprising calculating the amount of the positional difference of edge groups corresponding to each other between the reference pattern and the evaluation target pattern, and using the obtained positional difference amount to automatically specify a pattern. 
     Here, the definition of the “positional difference amount” is clarified. The positional difference amount is the amount indicating a difference between a standard point of the image of the evaluation target and a standard point of the standard image (reference image), and is expressed by, for example, horizontal and vertical distances between the standard points. 
     To explain more specifically using  FIGS. 12A to 12C , when the evaluation target pattern is a cross pattern, a standard point RPt of an evaluation image GT 4  incorporating the evaluation target pattern and a standard point RPr of a reference image GR 4  which is an image of the reference pattern for providing a standard for the shape evaluation of the evaluation target pattern are located in the center of the images. A reference pattern Pr is disproportionately located in an upper left direction of the drawing with respect to the standard point RPr within the reference image GR 4  in  FIG. 12A , while an evaluation target pattern Pt is disproportionately located in a lower right direction of the drawing with respect to the standard point RPt within the evaluation image GT 4  in  FIG. 12B . In this case, when the alignment is carried out so that the evaluation target pattern Pt is superposed on the reference pattern Pr, a difference is produced between the standard points RPt and RPr with no correspondence therebetween, as shown in  FIG. 12C . The positional difference amount quantitatively expresses this difference, which can be expressed by, for example, horizontal and vertical distances between these standard points RPt and RPr. In the pattern shape evaluation apparatus  1  shown in  FIG. 1 , the positional difference amount calculator  38  included in the matching unit  30  calculates, as the positional difference amount, a difference (Δx, Δy) between standard coordinates of the image of the reference pattern and standard coordinates of the image of the evaluation target pattern, during the alignment by the aligner  36 . It is to be noted that the images, for example, the reference image GR 4  in  FIG. 12A  and the evaluation image GT 4  in  FIG. 12B  do not need to be the same in size (field of view) in calculating the positional difference amounts. 
       FIG. 13  is a flowchart showing a schematic procedure of a pattern shape evaluation method in the present embodiment. 
     In the procedure of  FIG. 13 , for steps from step S 21  of acquiring an image of the evaluation target pattern to step S 26  of labeling the reference pattern,  20  is simply added to the numbers of steps S 1  to S 6  in the procedure in  FIG. 2 , so that the procedure in these steps is substantially the same as the procedure in steps S 1  to S 6 , and explanation below starts in step S 27 . 
     The aligner  36  of the matching unit  30  aligns the labeled edge of the evaluation target pattern with the labeled edge of the reference pattern (step S 27 ). Then, the group associator  34  associates the edge groups with each other using the result of this alignment (step S 28 ). To explain using the examples in  FIGS. 3 to 6  as is, “a” is associated with “α”, “b” is associated with “β”, “c” is associated with “γ”, and “d” is associated with “δ”. 
     Subsequently, the aligner  36  again aligns the associated edge groups with each other, and the positional difference amount calculator  38  calculates the positional difference amount for each case (step S 29 ). A reference image GR 2   d  shown in  FIG. 14  shows the edge group d extracted from the reference pattern within the reference image GR 2  shown in  FIG. 6 . When the reference pattern edge group “d” in  FIG. 14  is only aligned with the edge group “δ” within the evaluation target pattern shown in  FIG. 4 , these are matched as shown in  FIG. 15 . Further, a reference image GR 2   a  shown in  FIG. 16  shows the edge group “a” extracted from the reference pattern within the reference image GR 2 . When this edge group “a” is only aligned with the edge group “α” within the evaluation target pattern shown in  FIG. 4 , these are matched as shown in  FIG. 17 . It is understood from a contrast between  FIG. 15  and  FIG. 17  that the positional difference amount in the matching of the edge group “d” with “δ” is obviously different from the positional difference amount in the matching of the edge group “a” with “α”. The positional difference amount calculator  38  carries out such matching and calculation of the positional difference amounts for all of the edge groups, and the edge group selector  32  compares the positional difference amounts in the respective groups and detects whether there is an edge group whose positional difference amount is greater than those of the other groups ( FIG. 13 , step S 30 ). To take an example of a specific method, a threshold value may be provided to a deviation obtained from an average value of the positional difference amounts of all the edge groups, so that an edge group exceeding this threshold value is determined as the edge group whose positional difference amount is relatively large. 
     Then, the reference pattern is again aligned with the evaluation target pattern except for the edge group whose positional difference amount is determined to be large (step S 31 ), and the shape of the evaluation target pattern is evaluated as in the first embodiment described above (step S 32 ). 
     Thus, according to the present embodiment, the positional difference amount is calculated between edge groups corresponding to each other, and the reference pattern is aligned with the evaluation target pattern except for the edge group whose positional difference amount is large, so that high-speed and highly accurate shape evaluation can be automatically achieved without depending on the level of the skills of the operator. 
     (4) Third Embodiment of Pattern Shape Evaluation Method 
       FIG. 18  is a flowchart showing a schematic procedure of a pattern shape evaluation method in the present embodiment. 
     The present embodiment is characterized by the procedure shown in steps S 50  and S 51  in  FIG. 18 . For other steps in the procedure in  FIG. 18 ,  20  is added to the numbers of the steps in the processing procedure in the third embodiment shown in  FIG. 13 , so that these steps are substantially the same. Therefore, the procedure shown in steps S 50  and S 51  in  FIG. 18  will be described below. 
     That is, after completion of realignment and calculation of the positional difference amount (step S 49 ), the weighting unit  42  of the matching unit  30  weights each edge group in accordance with the calculated positional difference amount (step S 50 ). This weighting is set so that, for example, a deviation is obtained for each edge group from an average value of the positional difference amounts of all the edge groups and so that the weights are greater for the element patterns whose deviation is smaller. Using the weights thus given, the reference pattern edge group is again aligned with the evaluation target pattern edge group (step S 51 ). Finally, the pattern shape is evaluated between the edge groups (step S 52 ). 
     Thus, according to the present embodiment, each edge group is weighted in accordance with the positional difference amount, and it is thus possible to achieve the alignment free of the influence of the edge group having a large deviation of the positional difference amount. As a result, the accuracy of the pattern shape evaluation can be further increased. 
     (5) Fourth Embodiment of Pattern Shape Evaluation Method 
     While the reference pattern edge groups to be aligned are selected by a comparison between the evaluation target pattern edge groups and the reference pattern edge groups in the first embodiment described above, it is possible in some cases to experientially judge in advance by the reference pattern data alone that there is a high risk of decreasing the accuracy of alignment. For example, in the case of an isolated line pattern, it is possible to predict the occurrence of a significant positional difference at a particular end. In such a case, the reference pattern group judged to have a high risk of decreasing the accuracy of alignment is excluded without comparing the edge groups with each other as shown in step S 7  in  FIG. 2 , such that the reference pattern edge groups to be aligned can be selected. A procedure of a pattern shape evaluation method according to such an embodiment is shown in a flowchart of  FIG. 19 . The difference between the procedure shown in  FIG. 19  and the procedure in  FIG. 2  is that there is no step in the procedure in  FIG. 19  which corresponds to step S 7  in  FIG. 2 , and that step S 68  corresponding to step S 8  in  FIG. 2  is only inserted between step S 66  and step S 69  without using the result of labeling in step S 63 . For other steps in  FIG. 19 ,  60  is added to the numbers of the steps in the procedure in  FIG. 2 , so that these steps are substantially the same as those in the procedure in  FIG. 2 . 
     (6) Program 
     A series of procedures of the pattern shape evaluation method in the embodiments described above may be incorporated in a program to be executed by a computer, stored as a recipe file in a recording medium such as a flexible disk or a CD-ROM, and read into and executed by the computer. This makes it possible to achieve the pattern shape evaluation method according to the present invention by use of a general-purpose control computer capable of image processing. The recording medium is not limited to a portable medium such as a magnetic disk or an optical disk, and may be a fixed recording medium such as a hard disk drive or a memory. Further, the program incorporating the series of procedures of the pattern shape evaluation method described above may be distributed via a communication line (including wireless communication) such as the Internet. Moreover, the program incorporating the series of procedures of the pattern shape evaluation method described above may be distributed in an encrypted, modulated or compressed state via a wired line such as the Internet or a wireless line or in a manner stored in a recording medium. 
     (7) Semiconductor Device Manufacturing Method 
     When the pattern shape evaluation method described above is used in a process of manufacturing a semiconductor device, the shape of a pattern can be evaluated with high accuracy and in a short time, such that the semiconductor device can be manufactured with higher yield and throughput. 
     More specifically, a semiconductor substrate is extracted per production lot, and a pattern formed on the extracted semiconductor substrate is evaluated by the pattern shape evaluation method described above. When the semiconductor substrate exceeds a threshold value set in accordance with the specifications of a product and is judged as a nondefective product as a result of the evaluation, the rest of the manufacturing process is continuously executed for the whole production lot to which the evaluated semiconductor substrate belongs. On the other hand, when the semiconductor substrate is judged as a defective product as a result of the evaluation and can be reworked, rework processing is executed for the production lot to which the semiconductor substrate judged as the defective product belongs. When the rework processing is finished, the semiconductor substrate is extracted from the production lot, and the shape of the pattern is again evaluated. If the extracted semiconductor substrate is judged as a nondefective product as a result of the reinspection, the rest of the manufacturing process is executed for the production lot finished with the rework processing. In addition, when the rework processing is impossible, the production lot to which the semiconductor substrate judged as the defective product belongs is disposed of. When the cause of the defect can be analyzed, results of the analysis are fed back to a person in charge of designing, a person in charge of an upstream process or the like. 
     While the embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and can be modified in various manners within the technical scope thereof and carried out. For example, the design data is used to prepare the reference pattern in the embodiments described above, but the present invention is not limited thereto, and lithography simulation data may be used or an image taken from the actual pattern may be used.