Abstract:
A pattern evaluation method includes: acquiring data of a design pattern for an evaluation pattern to detect a first edge of the design pattern; acquiring an image of the evaluation pattern to detect a second edge of the evaluation pattern; dividing the first edge into first linear parts and first corner parts; performing matching of the first and second edges to obtain correspondence between the first and second edges; dividing the second edge into second linear parts and second corner parts based on the correspondence between the first and second edges; and evaluating the evaluation pattern based on at least one of the second linear parts and the second corner parts.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims benefit of priority under 35USC §119 to Japanese patent application No. 2008-027625, filed on Feb. 7, 2008, 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 evaluation method, a computer-readable recording medium, and a manufacturing method of a semiconductor device. 
     2. Related Background Art 
     A method of detecting an edge of an evaluation pattern to evaluate a shape of the pattern is extensively adopted in various industrial fields. For example, in manufacture a semiconductor device, accurately measuring a fine pattern formed by, e.g., a photolithography process, a film forming process, or an etching process is required to manufacture a fine device with an excellent yield ratio. CD measurement using a CDSEM (Critical Dimension Scanning Electron Microscope) has been conventionally extensively carried out as pattern measurement. 
     In recent years, to satisfy demands for realization of high performances or high functions of devices, not only sizes of patterns are miniaturized but also shapes of the same are becoming more complicated. To evaluate each of these patterns having complicated shapes, a shape of the entire pattern must be measured as different from the conventional CD measurement that measures a specific part of the pattern. For example, a technique of superimposing a design pattern obtained based on design data on an evaluation pattern to measure a difference between these patterns has been already carried out. However, as different from general industrial products, a pattern shape of a semiconductor device often greatly deviates from design data. In particular, since a corner part of the pattern is apt to be affected by an optical resolution of a pattern exposure device, forming such a right-angle part as that in the design pattern is difficult, and a rounded shape is generally obtained. Therefore, when measuring a difference in shape between an evaluation pattern and a design pattern, an influence of a corner part on a size is different from that of any other part on the same. The number of the corner parts in the pattern varies depending on complexity of the pattern, and hence a magnitude of the different is dependent on complexity of the pattern. This means that using the difference between the evaluation pattern and the design pattern is inappropriate to evaluate, e.g., a line pattern or a pattern in which line patterns are intricately coupled by using the same index. Therefore, corner parts of the pattern must be excluded from measurement of the difference when measuring the difference. 
     Here, achieving the above-explained object is not impossible by specifying a range of a specific part (the corner part) based on an operator&#39;s assist, but extracting each corner part of an actually formed semiconductor pattern by using human eyes is difficult as different from design data consisting of straight lines. Therefore, not only an accurate result cannot be obtained, but also a problem that a large individual difference occurs in accordance with a proficiency degree of each operator arises. Therefore, there can be also considered, e.g., an automation technique of using an image processing technology based on a computer to detect an edge of a pattern, calculating a local curvature thereof, and separating linear parts and corner parts in the pattern based on this curvature, thereby requiring no assist of an operator (Japanese patent laid open (kokai) 2005-098885). 
     However, according to the above-explained technique, if even a part of a pattern that should be evaluated as a linear part under normal conditions is deformed due to various processes, e.g., exposure conditions and a curvature is thereby locally increased, there can be considered a case that a contribution as a corner part to its difference is eliminated. Further, when exposure conditions are intentionally exerted at predetermined intervals to evaluate a pattern, since a pattern deformation degree differs in accordance with each pattern, a proportion of linear parts in a pattern edge differs between a largely-deformed pattern and a less-deformed pattern in the above-explained automation technique. As a result, there occurs a problem that using the difference as an evaluation index for a pattern deformation degree is difficult. 
     SUMMARY OF THE INVENTION 
     According to a first aspect of the present invention, there is provided a pattern evaluation method comprising: 
     acquiring data of a design pattern for an evaluation pattern to detect a first edge of the design pattern; 
     acquiring an image of the evaluation pattern to detect a second edge of the evaluation pattern; 
     dividing the first edge into first linear parts and first corner parts; 
     performing matching of the first and second edges to obtain correspondence between the first and second edges; 
     dividing the second edge into second linear parts and second corner parts based on the correspondence between the first and second edges; and 
     evaluating the evaluation pattern based on at least one of the second linear parts and the second corner parts. 
     According to a second aspect of the present invention, there is provided a computer readable recording media containing a program which allows a computer to execute a pattern evaluation processing, the program comprising: 
     acquiring data of a design pattern for an evaluation pattern to detect a first edge of the design pattern; 
     acquiring an image of the evaluation pattern to detect a second edge of the evaluation pattern; 
     dividing the first edge into first linear parts and first corner parts; 
     performing matching of the first and second edges to obtain correspondence between the first and second edges; 
     dividing the second edge into second linear parts and second corner parts based on the correspondence between the first and second edges; and 
     evaluating the evaluation pattern based on at least one of the second linear parts and the second corner parts. 
     According to a third aspect of the present invention, there is provided a manufacturing method of a semiconductor device comprising executing a manufacturing process of the semiconductor device with respect to a substrate when it is determined that a requested specification is satisfied as a result of evaluating an evaluation pattern formed on the substrate based on a pattern evaluation method, the pattern evaluation method includes: 
     acquiring data of a design pattern for an evaluation pattern to detect a first edge of the design pattern; 
     acquiring an image of the evaluation pattern to detect a second edge of the evaluation pattern; 
     dividing the first edge into first linear parts and first corner parts; 
     performing matching of the first and second edges to obtain correspondence between the first and second edges; 
     dividing the second edge into second linear parts and second corner parts based on the correspondence between the first and second edges; and 
     evaluating the evaluation pattern based on at least one of the second linear parts and the second corner parts. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings, 
         FIG. 1  is a flowchart for explaining an outline process of a pattern evaluation method according to a first embodiment of the present invention; 
         FIG. 2  is a view showing an example of an evaluation pattern; 
         FIG. 3  is a view showing a design pattern of the evaluation pattern depicted in  FIG. 2 ; 
         FIGS. 4 to 7  are explanatory views of the pattern evaluation method depicted in  FIG. 1 ; 
         FIG. 8  is a flowchart for explaining an outline process of a pattern evaluation method according to a second embodiment of the present invention; and 
         FIG. 9  is an explanatory view of the pattern evaluation method depicted in  FIG. 8 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Several embodiments according to the present invention will now be explained hereinafter with reference to the accompanying drawings. A case where an image of a fine pattern formed in a manufacturing process of a semiconductor device, e.g., a lithography process or an etching process is acquired by an imaging device, e.g., a CDSEM and this pattern image is evaluated will be taken as an example and explained hereinafter. However, the present invention is not restricted thereto, and it should be noted that the present invention can be applied to general pattern evaluation in other various industrial fields. It is also to be noted that a case where a top-down SEM image acquired by a CDSEM is used to evaluate an evaluation pattern will be taken as an example in the following embodiments, but the present invention is not restricted thereto and can be applied to an image acquired by any other device, e.g., an optical image acquisition device. However, since a pattern image must be acquired with a higher magnification in order to accurately evaluate a fine pattern of a semiconductor, using an SEM image is preferable at the present moment. 
     (1) First Embodiment 
     A first embodiment according to the present invention will now be explained with reference to  FIGS. 1 to 7 . 
       FIG. 1  is a flowchart for explaining an outline process of a pattern evaluation method according to this embodiment,  FIG. 2  shows an example of an evaluation pattern, and  FIG. 3  depicts a design pattern of the evaluation pattern illustrated in  FIG. 2 . 
     First, corner parts of a design pattern in  FIG. 3  are detected ( FIG. 1 , a step S 1 ). To achieve this detection, vertexes of a graphic in the design pattern are detected from design data. As a method of detecting vertexes, when the design data is supplied as a file such as GDS, since each vertex coordinate of a CAD (Computer Aided Design) graphic is written in this file, the vertexes can be read from this file. When a CAD graphic is given as image data in, e.g., a bitmap format obtained by spreading the GDS file, image processing for characteristic point detection must be used to detect the vertexes. Characteristic point detection is one of important element technologies in a machine vision technical field, and various methods have been already proposed, but just a cosine value judgment method is named herein. Of course, any other characteristic point detection methods can be used. 
     Then, as shown in  FIG. 4 , graphics each having a predetermined size, e.g., squares RT 1  to RT 6  are drawn with vertexes VT 1  to VT 6  of the CAD graphic extracted by one of the above-explained methods at the center, and an edge of the design pattern is divided into linear parts SD 1  to SD 6  and corner parts CD 1  to CD 6  ( FIG. 1 , a step S 2 ). A size of the square is adjusted based on a size of the entire pattern. In this embodiment, each square RT whose one side is 10 nm is used. As a result, intersections of the squares RT 1  to RT 6  and the edge of the CAD graphic are determined as a boundary, and the inner sides of the squares are determined as the corner parts CD 1  to CD 6  whilst the outer sides of the same are determined as the linear parts SD 1  to SD 6  to enable dividing the edge of the CAD graphic as shown in  FIG. 5 . Although the square RT is used to detect each corner part in this embodiment, the present invention is not restricted to this shape, and a graphic having any other shape, e.g., a rectangular shape, a circle, or an ellipse can be used. 
     Then, the evaluation pattern is divided into the linear parts and the corner parts based on matching of the evaluation pattern and the design pattern ( FIG. 1 , a step S 3 ). First, processing of matching the evaluation pattern depicted in  FIG. 2  with the design pattern shown in  FIG. 3  is executed. In this embodiment, distance matching proposed in Japanese Patent Application Laid-open No. 2006-275952 will be taken as an example and explained. The entire contents of Japanese Patent Application Laid-open No. 2006-275952 are herein incorporated in this specification by reference. In distance matching, an edge of an evaluation pattern must be detected prior to matching. Although various methods are proposed as a method of detecting an edge, this embodiment adopts a method proposed in Japanese Patent Application Laid-open No. 2003-178314 characterized in that even an entire edge of a complicated pattern can be rapidly and accurately detected without a manual assist, e.g., setting of an ROI (Region of Interest). The entire contents of Japanese Patent Application Laid-open No. 2003-178314 are also herein incorporated in this specification by reference. 
     Subsequently, matching of the thus detected edge of the evaluation pattern and the edge of the CAD graphic written in the design data is executed. In the distance matching processing adopted in this embodiment, a relative position of a distance map obtained by distance-conversion of the edge of the CAD graphic into a distance and the edge of the evaluation pattern is operated, a value obtained by an image arithmetic operation of the distance map, and edge data at this relative position is determined as a matching score, and a relative position where the value of the matching score becomes maximum is output as a matching coordinate. It is to be noted that the distance matching technique is used for positioning of the two patterns in this embodiment, but any other matching technique can be used. 
     Subsequently, processing of associating the edges of both the patterns with each other is executed. Although various methods can be considered to realize this processing, this embodiment uses a technique of robust point matching proposed in a paper “Haili Chui, An and Rangarajan, A new algorithm for non-rigid point matching, IEEE Conference on Computer Vision and Pattern Recognition (CVPR), volume II, 44-51, 2000”. 
       FIG. 6  shows a result obtained by performing such association. In the drawing, two points at both ends of each dotted line (EP 1 , EP 2 ), (EP 3 , EP 4 ), (EP 5 , EP 6 ), (EP 7 , EP 8 ), (EP 9 , EP 10 ), or (EP 11 , EP 12 ) correspond to two points associated with division points (DP 1 , DP 2 ), (DP 3 , DP 4 ), (DP 5 , DP 6 ), (DP 7 , DP 8 ), (DP 9 , DP 10 ), or (DP 11 , DP 12 ) depicted in  FIG. 5 , and are placed at equivalent positions on the two edges of the evaluation pattern and the design pattern. Furthermore, a sum total of lengths between ends of the respective point pairs represent a difference between the two patterns. 
     When the points EP 1  to EP 12  on the evaluation pattern associated with the points DP 1  to DP 12  at which the CAD pattern is divided into the linear parts and the corner parts are determined as division points in this manner, the evaluation pattern edge can be divided into linear parts SA 1  to SA 6  and corner parts of CA 1  to CA 6  as shown in  FIG. 7 . The divided evaluation patterns can be subjected to different evaluation methods ( FIG. 1 , a step S 4 ). In this embodiment, the linear parts SA 1  to SA 6  are subjected to roughness measurement, and the corner parts CA 1  to CA 6  are subjected to corner rounding measurement, thereby accurately performing pattern evaluation. As a measurement method for roughness or corner rounding, any existing method can be used. Respective averages or individual values of a plurality of thus obtained roughness and corner rounding measurement results for the evaluation pattern can be used as pattern evaluation indices. 
     (2) Second Embodiment 
     A second embodiment according to the present invention will now be explained with reference to  FIGS. 8 and 9 .  FIG. 8  is a flowchart for explaining an outline process of a pattern evaluation method according to this embodiment, and  FIG. 9  is an explanatory view of the pattern evaluation method depicted in  FIG. 8 . 
     In this embodiment, a case where a difference between a CAD pattern written in design data of a semiconductor pattern and an evaluation pattern is used as an evaluation index of the evaluation pattern will be taken as an example to be explained. 
     First, the method explained in the first embodiment is used to divide the evaluation pattern into linear parts and corner parts ( FIG. 8 , steps S 11  to S 14 ). In case of a semiconductor pattern, a pattern shape of a product generally greatly deviates from a CAD shape. The pattern is rounded especially at corner parts because of a restriction in, e.g., an optical resolution in pattern manufacture or a resolution of pattern transfer properties. Therefore, when using a difference from a CAD pattern as an evaluation index, it is desirable to divide an evaluation pattern into corner parts and linear parts and calculating a difference from a design pattern based on the linear parts only in the pattern. A sum total of distances between associated points on an edge divided as the linear parts may be output as a difference, but calculation is performed in accordance with the process depicted in  FIG. 8  when measuring a difference in the linear parts in the pattern in this embodiment. 
     First, corresponding linear parts are taken out from the design pattern and the evaluation pattern (a step S 15 ). Giving an explanation on the example according to the first embodiment, the linear parts SD 1  to SD 6  in the CAD pattern depicted in  FIG. 5  and the linear parts SA 1  to SA 6  in the actual pattern shown in  FIG. 7  are taken out. 
     Then, perpendicular lines VL are drawn from the design pattern toward the inner side and the outer side of the evaluation pattern at fixed intervals ( FIG. 8 , a step S 16 ).  FIG. 9  shows an example of the result. 
     Subsequently, a distance from a starting point of each perpendicular line VL on the design pattern to a point where this perpendicular line VL crosses the edge of the evaluation pattern is obtained ( FIG. 8 , a step S 17 ). At this time, a sign is set to a positive sign when the intersection is present on the outer side of the pattern, and the sign is set to a negative sign when the intersection is present on the inner side of the same. When the intersection is not found within a fixed distance, the distance is set to zero. 
     At last, all the distances are added (a step S 18 ). 
     As explained above, according to this embodiment, a value obtained by eliminating an influence of each corner part from a difference between the CAD pattern and the evaluation pattern can be accurately calculated in the above-explained process. 
     (3) Program 
     A series of processes in the pattern evaluation method according to the foregoing embodiment may be incorporated in a program executed by a computer, accommodated in a recording medium such as a flexible disk or a CD-ROM, and read and executed by the computer. As a result, the pattern evaluation method according to the present invention can be realized by using a general-purpose computer capable of executing image processing. The recording medium is not restricted to a portable medium, e.g., a magnetic disk or an optical disk, and a fixed type recording medium such as a hard disk drive or a memory may be used. Furthermore, a program having the above-explained series of processes in the pattern evaluation method incorporated therein may be distributed through a communication line, e.g., the Internet (including wireless communication). Moreover, a program having the series of processes in the pattern evaluation method incorporated therein may be encrypted, modulated, or compressed, and it may be distributed through a wire cable or a wireless line, e.g., the Internet or may be accommodated in a recording medium to be distributed in this state. 
     (4) Manufacturing Method of Semiconductor Device 
     Using the above-explained pattern evaluation method in the manufacturing process of a semiconductor device enables highly accurately evaluating a pattern in a short time, thereby manufacturing a semiconductor device with a higher yield ratio and a higher throughput. 
     More specifically, a substrate is sampled in units of production lot, and a pattern formed on the sampled substrate is evaluated based on the above-explained pattern evaluation method. When the pattern is determined as a non-defective pattern beyond a threshold value set based on a product specification as a result of the evaluation, the remaining manufacturing processes are continuously performed with respect to the entire production lot to which the substrate having the evaluated pattern formed thereon belongs. On the other hand, when the pattern is determined as a defective pattern as a result of the evaluation, rework processing is executed with respect to the production lot to which the substrate having the pattern determined as the defective pattern formed thereon belongs to if the rework processing is possible. When the rework processing is finished, a substrate is again sampled from this production lot to again evaluate a pattern. When the substrate sampled for reevaluation of the pattern is determined as a non-defective product, the remaining manufacturing processes are performed with respect to this production lot subjected to the rework processing. Additionally, when the rework processing is impossible, the production lot to which the substrate having the pattern determined as a defective pattern formed thereon belongs is discarded and, if a defect occurrence factor can be analyzed, a result of this analysis is fed back to a person in charge of design or a person in charge of upstream processes.