JP2014016361A - Pattern dimension calculation method and image analysis device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a calculation of a pattern dimension in any local position of a contour line or a specific part thereof easily, and to obtain an image data analysis capable of accurately calculating a representative dimension value of the contour line.SOLUTION: The pattern dimension calculation method according to the present invention is configured to: create coordinate data of each apex of polygon contour data to be obtained on the basis of image data imaged by a scanning electron microscope; calculate a region where contour data on an inspection target pattern and rectangle data for measuring a length are overlapped with each other; calculate a target dimension value from an area of the overlapped region; upon calculating the target dimension value, generate an auxiliary line perpendicular to a counter side crossing the rectangular overlapped region of the rectangle data for measuring the length in the overlapped region; divide the overlapped region into a plurality of trapezoidal regions by drawing a vertical line from each apex of which the coordinate data is created with respect to the auxiliary line; calculate an area of the overlapped region from a total sum of areas of each trapezoidal region; and divide the area of the overlapped region by a dimension of a side serving as the rectangle data for measuring the length and not crossing the contour data and thereby calculate the target dimension value.

Description

  The present invention relates to a pattern dimension calculation method and an image analysis apparatus, for example, a method for calculating a dimension measurement value from a contour line of a pattern extracted from a captured image of an electron microscope, and an apparatus for evaluating the dimension measurement value.

  Conventionally, it is known to measure a pattern on a semiconductor integrated circuit using CAD (Computer Aided Design) data and exposure simulation data. Since the CAD data and the exposure simulation data indicate the ideal shape of the semiconductor element, the semiconductor manufacturing process can be evaluated by comparing the actually formed patterns.

  On the other hand, with the miniaturization of semiconductor elements, it is difficult to form a pattern in an ideal shape. For this reason, it is becoming more important to consider the conditions for semiconductor manufacturing from the design stage using a lithography aware tool such as exposure simulation. Lithography-aware tools need to input data on dimensions and shapes of actually formed semiconductor patterns, and there is an increasing demand for inputting more measurement items and highly accurate data. The size and shape data of the semiconductor pattern is calculated from the pattern of the image captured by the scanning electron microscope.

  Conventionally, basic dimensions for evaluating the shape of a semiconductor pattern are representative values such as a pattern length and a hole radius. This is calculated from the pattern of the image picked up by the length measuring scanning electron microscope. In lithography-aware tools, there is an increasing demand for inputting measurement data for more items for pattern-related evaluation and manufacturing-related simulations such as exposure simulation. Patterns captured with a length-measuring scanning electron microscope High-precision contour data is extracted from the image and input to a lithography-aware tool.

JP 2002-229179 A

  However, in the lithography-aware tool, there are various problems when contour data is input instead of representative values such as pattern length and hole radius.

  For example, when calculating a local pattern dimension from an outline, there are many setting items for calculation, and accuracy is insufficient. Therefore, there is a problem that it is impossible to cope with a case where pattern dimension calculation is desired at an arbitrary local position from the contour line.

  In addition, the lithography-aware tool may require only a specific portion of the contour line, not the contour line of the entire captured pattern, but there is a problem that it is difficult to cut out a local region from the entire contour line. .

  Furthermore, in order to create a highly accurate contour line, it is necessary to compare and evaluate it with the dimension value measured by a conventional measuring instrument, but the contour line (two-dimensional data: which part of the dimension There is a problem that it is difficult to compare and evaluate between a dimensional value such as a length and the like, which is difficult to specify as a representative value.

  The present invention has been made in view of such a situation, and can easily calculate a pattern dimension at an arbitrary local position of a contour line or a specific part, and can also accurately represent a representative dimension value of a contour line pattern. The image data analysis that can be obtained well is realized.

  In order to solve the above problems, the present invention discloses a pattern dimension calculation method for obtaining a target dimension value of an inspection target pattern from contour data obtained from image data of the inspection target pattern. In this pattern dimension calculation method, the image processing unit converts each vertex of the polygonal contour data obtained based on the image data captured by the scanning electron microscope into coordinate data, and the contour data of the inspection target pattern and the length measurement rectangle The overlapping area with the data is calculated, and the target dimension value is calculated from the area of the overlapping area. When calculating the target dimension value, the image processing unit generates an auxiliary line perpendicular to the opposite side intersecting the rectangular overlapping area of the length measurement rectangular data in the overlapping area, and overlaps the auxiliary line. The overlapping area is divided into a plurality of trapezoidal areas by drawing a perpendicular line from each vertex converted into the coordinate data of the area. Further, the image processing unit calculates the area of the overlapping region from the sum of the areas of the trapezoidal regions, and divides the area of the overlapping region by the dimension of the side that is the rectangular data for length measurement and does not intersect with the contour data. The target dimension value is calculated.

  Further features of the present invention will become apparent from the following detailed description and the accompanying drawings.

  According to the present invention, it is possible to easily calculate a pattern dimension at an arbitrary local position of a contour line or a specific part, and to obtain a representative dimension value of the contour line pattern with high accuracy.

It is a block diagram which shows the structure outline | summary of a length measuring scanning electron microscope. It is a figure which shows the dimension calculation method of the outline by embodiment of this invention. It is a figure which shows the method to compare the length measurement value with the dimension of an outline by embodiment of this invention. It is a flowchart for demonstrating the detail of an outline dimension value calculation process. It is a flowchart for demonstrating the process which compares an actual length measurement value and the calculated value of an outline. It is the figure which showed the dimension calculation method of the outline which is an Example of this invention.

  The present invention discloses a method for easily and accurately obtaining a dimension value (representative value or average value) of an outline pattern of an electron microscope image.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be noted that this embodiment is merely an example for realizing the present invention, and does not limit the technical scope of the present invention. In each drawing, the same reference numerals are assigned to common components.

<Configuration of image data analyzer>
FIG. 1 is a block diagram showing a schematic configuration of an image data analysis apparatus according to an embodiment of the present invention. In FIG. 1, the electron microscope 101 is included in a part of the configuration of the image data analysis apparatus 100. However, the configuration is not limited to this, and the configuration is such that image data separately acquired by the electron microscope apparatus is input and analyzed. There may be.

  The image data analysis apparatus 100 according to the present embodiment includes a scanning electron microscope 101, a design data storage unit 112, a control system 110, an image processor 109, and a display device 111.

  In FIG. 1, an electron beam 103 emitted from an electron gun 102 in an electron microscope 101 is converged by an electron lens 113 and irradiated onto a sample 105. The intensity of secondary electrons 114 or reflected electrons generated from the surface of the sample 105 due to electron beam irradiation is detected by the electron detector 106 and amplified by the amplifier 107. The deflector 104 that moves the irradiation position of the electron beam 103 raster scans the electron beam 103 on the surface of the sample 105 in response to the control signal 108 of the control system 110. The image processor 109 AD-converts the signal output from the amplifier 107 to create digital image data. The display device 111 is a device that displays image data.

  In the semiconductor chip design data 112 such as CAD data, an area to be inspected can be arbitrarily designated. In addition, the sample stage control device 116 can move the sample stage 115 with respect to the electron beam 103. The display device 111 can display the electron microscope image 118 obtained by imaging the sample 105 and the contour line 117 extracted from the captured image by the image processor 109.

  The image processor 109 can calculate the electron microscope image pattern dimension value 120 from the electron microscope image 118, and can calculate the contour line pattern average dimension value 119 from the contour 117. The contour line pattern can be extracted by applying an edge enhancement filter such as a Sobel filter to the microscope image (SEM image). Details of the contour line (edge) pattern extraction are described in, for example, Japanese Patent Application Laid-Open Nos. 2001-338304 and 2002-31525.

  The display device 111 can display a comparison result 121 between the electron microscope image pattern dimension value 120 and the contour line pattern average dimension value 119. The comparison result will be described later. For example, it is the difference between the electron microscope image pattern average dimension value 120 and the contour line pattern average dimension value 119.

  The control system 110 performs control for imaging and inspection of the semiconductor wafer and communication with the image processor 109 using the design data 112 and the information on the area to be inspected. A system comprising an electron microscope 101, an image processor 109, a control system 110, a display device 111, and a device for storing design data 112 has a communication means for exchanging data.

<Calculation of contour line average (representative) dimension value>
FIG. 2 is a diagram illustrating a method (concept) for calculating the line pattern contour average dimension value 119 based on the data of the line pattern contour 202 extracted from the image captured by the length measurement scanning electron microscope.

  The contour line data 201 indicates a contour line of a pattern within a predetermined range of an image captured by the length measurement scanning electron microscope, and a line pattern contour line 202 is included therein. In FIG. 2, the shaded area is an area surrounded by the line pattern outline 202. As described above, the extraction of the line pattern outline has been conventionally performed, and can be extracted using image binarization, thinning processing, etc. after differential filter calculation by image processing. Further, the extracted contour line can be converted into a data format that can be read by a CAD tool such as GDSII.

  When data analysis is performed using an analysis tool such as a lithography-aware tool, it is necessary to obtain the width of the line pattern contour 202 in the horizontal direction. It may be necessary to determine the width of a specific area depending on the purpose. When the line width is obtained with a length measuring scanning electron microscope, a width within a specific range called a length measuring box is calculated from the image. A length measurement box 203 is obtained by converting a length measurement box on an image captured by a length measurement scanning electron microscope onto contour data 201. Here, the measurement box 203 is rectangular. The length measurement box height 204 is the length of the length measurement box in the vertical direction.

  When the line pattern outline 202 and the measurement box 203 are overlapped, an overlapping region 231 is obtained. The overlapping area 231 is a closed polygon having the intersections 206, 207, 208, and 209 and the vertices 210, 211, 212, and 213 of the line pattern outline 202 as vertices, and is an area with hatched portions in the figure. In order to obtain the area of this figure, an auxiliary line 205 is created. Here, the auxiliary line 205 is perpendicular to the upper and lower sides of the rectangle. The overlap region 231 can be divided into six trapezoid regions 215, 216, 217, 218, 219, and 220 by dropping perpendicular lines from the vertices 210, 211, 212, and 213 of the line pattern outline 202 to the auxiliary line 205. It is. The area of the trapezoidal region 215 can be calculated by the trapezoid upper base length 221, the trapezoid lower base length 222, the trapezoid height 223, and the formula 224. Here, the trapezoid upper base length 221 is the distance between the vertex 206 and the auxiliary line 205, the trapezoid lower base length 222 is the distance between the vertex 210 and the auxiliary line 205, and the trapezoid height 223 is the distance between both perpendicular lines. Calculation is possible. The areas of the six trapezoidal regions 215, 216, 217, 218, 219, and 220 can be calculated by the same method. Accordingly, the area of the overlapping region 231 can be calculated by calculating the total sum of the areas of the six trapezoidal regions 215, 216, 217, 218, 219, and 220 using Expression 225. The average length 228 in the measurement box can be calculated by the area of the overlapping region 231, the measurement box height 204, and the equation 227. This method is a method for accurately calculating the size of the local region of the contour line.

  The above processing is shown in a flowchart in FIG. First, the image processor 109 acquires the electron microscope image 118 within the scanning range of the electron beam (step S401). Further, the image processor 109 acquires the contour data 201 by the method described above based on the electron microscope image 118 acquired in step S401 (step S402). Further, the image processor 109 arranges the length measurement box 203 on the contour line data 201 acquired in step S402 (step S403).

  Subsequently, the image processor 109 divides the area 231 surrounded by the measurement box 203 and the line pattern outline 202 of the outline data 201 into a plurality of trapezoid areas 215 to 220 (step S404). In addition, the image processor 109 calculates the area of each trapezoidal region 215 to 220 using the formula 224 (see FIG. 2) (step S405). Then, the image processor 109 obtains the sum of the areas of the trapezoidal areas using Expression 225 (Step S406). Further, the image processor 109 calculates the contour line pattern average value 119 using the equation 227, and stores it in a memory (not shown) (step S407).

<Method for calculating the outline dimension difference>
FIG. 3 illustrates a method (concept) for calculating the contour line dimension difference 321 between the length measurement value 315 calculated from the captured image 301 of the scanning electron microscope (length measurement SEM) and the dimension value 320 calculated from the contour line data 316. FIG.

  A method for calculating the length measurement value 315 calculated from the captured image 301 of the length measurement scanning electron microscope is an existing method. A line pattern 302 is present in the captured image 301, a length measurement box 303 is set, and the width of the internal line pattern is calculated.

  As a method for obtaining the length measurement value 315, for example, there is a method in which the length measurement box 303 is divided into a plurality of lengths and averaged. FIG. 3 shows an example of dividing into five pieces. Since an image picked up by the length-measuring scanning electron microscope has noise, the 1 pix image profile 306 has much noise, and it is difficult to calculate a stable line width. Therefore, the line profiles of a plurality of pixels are integrated to create a line profile with improved S / N like the integrated profile 307. Further, there is a method of performing a smoothing process on the integrated profile 307 and setting the distance of a place such as 50% of the maximum value of the peak of the line profile 308 to the line width.

  Further, an average of the line widths 310, 311, 312, 313 and 314 calculated by this method is taken, and a length measurement value 315 for the length measurement box 303 is calculated. There are multiple types of this method even in the existing methods. There are various methods for extracting contour lines. There are a plurality of types of methods for both the measurement line width calculation method and the contour line extraction method, and the line width and the position of the contour line differ depending on the type.

  However, as described above, it may be necessary to make the difference between them as small as possible. Therefore, it is necessary to calculate the average length 119 in the measurement box by the method of FIG. 2 and compare it with the measurement value 315. The contour line data 316 is extracted from the captured image 301. A line pattern outline 317 is an outline of the line pattern 302. The measurement box 318 is obtained by converting the measurement box 303 into the coordinates of the contour line data 316. The average length 320 in the measurement box in the measurement box 318 of the line pattern outline 317 can be calculated by the method of FIG. Further, the equation 321 makes it possible to calculate an outline dimension difference that allows confirmation of the position of the outline on the basis of the length measurement value 315 according to the conventional method. When the dimensional difference is within a predetermined range (for example, an error within 1%), it can be evaluated that the average length 320 can be used as a representative dimensional value.

  The above processing is shown in a flowchart in FIG. First, the image processor 109 acquires the electron microscope image 301 within the scanning range of the electron beam (step S501). Further, the image processor 109 sets the length measurement box 310 on the electron microscope image 301 so as to determine the length measurement range (step S502). Further, the image processor 109 divides the measurement box 310 vertically into a plurality of regions 305 at predetermined width intervals (step S503).

  The image processor 109 acquires the line profile 306 for each region obtained in step S503 (step S504), and further acquires the line profile 307 obtained by integrating the line profiles (step S505). Subsequently, the image processor 109 performs a smoothing process on the integrated line profile 307 (step S506).

  Further, the image processor 109 acquires the length measurement value (line width) 309 from the smoothed integrated line profile 308 in each region (step S507), and the line width average value of the length measurement values 310 to 314 in each region. Is calculated (step S508). The line width 309 is obtained, for example, by measuring the half-value width of each local maximum value of the profile indicating the edge portion.

  Further, the image processor 109 uses the average line width value obtained in step S508 as the electron microscope image pattern dimension value, and calculates the difference between this and the contour line pattern average dimension value obtained in the process of FIG. S509). Then, the image processor 109 determines whether the dimensional difference is equal to or less than a predetermined value A% (step S510). If the dimensional difference is equal to or less than the predetermined value A%, the contour line pattern average dimension value is used as a representative dimension value. (Step S511), and if it is larger than the predetermined value A%, it is determined that the contour line pattern average dimension value cannot be used as the representative dimension value (step S512). The contour line pattern average dimension value determined not to be used as the representative dimension value is erased from the memory. In this case, the contour line pattern average dimension value may be calculated by changing the measurement position and executing the process of FIG. 4 again.

<Summary>
In this embodiment, contour data is acquired from image data (electron microscope image) of an inspection target pattern, and the target dimension value of the inspection target pattern is obtained from the contour data. That is, the image processor divides the overlapping area into a plurality of trapezoidal areas (see FIG. 2), calculates the area of the overlapping area from the sum of the areas of each trapezoidal area, and outlines the area of the overlapping area with the measurement box. The side that does not intersect with the data (in FIG. 2, it is the vertical side of the measurement box. When the contour data extends horizontally instead of vertical as shown in FIG. 2, it becomes the horizontal side of the measurement box. ) To calculate the target dimension value. By executing such a calculation, the local average dimension value can be obtained easily and accurately.

  In the present embodiment, the image processor compares the length measurement value obtained by actually measuring the image data with the target dimension value calculated from the contour data obtained from the image data, and displays the comparison result on the display unit. To display. As a result, the user can determine whether or not the target dimension value from the contour data can be used as an index. Further, it is possible to compare the length measurement value according to the conventional method and the dimension value from the contour line in one system. Further, when the dimensional difference between the length measurement value and the target dimension value is within a predetermined range, it may be determined that the target dimension value can be used as the dimension representative value, and the determination result may be displayed on the display unit. This eliminates the need for the user to bother to determine whether or not the user can use it.

  The present invention can also be realized by a program code of software that realizes the functions of the embodiments. In this case, a storage medium in which the program code is recorded is provided to the system or apparatus, and the computer (or CPU or MPU) of the system or apparatus reads the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the program code itself and the storage medium storing the program code constitute the present invention. As a storage medium for supplying such program code, for example, a flexible disk, CD-ROM, DVD-ROM, hard disk, optical disk, magneto-optical disk, CD-R, magnetic tape, nonvolatile memory card, ROM Etc. are used.

  Also, based on the instruction of the program code, an OS (operating system) running on the computer performs part or all of the actual processing, and the functions of the above-described embodiments are realized by the processing. May be. Further, after the program code read from the storage medium is written in the memory on the computer, the computer CPU or the like performs part or all of the actual processing based on the instruction of the program code. Thus, the functions of the above-described embodiments may be realized.

  Also, by distributing the program code of the software that realizes the functions of the embodiment via a network, the program code is stored in a storage means such as a hard disk or memory of a system or apparatus, or a storage medium such as a CD-RW or CD-R And the computer of the system or apparatus (or CPU or MPU) may read and execute the program code stored in the storage means or the storage medium when used.

101 ... Scanning electron microscope (measurement SEM)
109 ... Image processor 110 ... Control system 111 ... Display device 112 ... Design data storage unit

Claims (3)

A pattern dimension calculating method for obtaining a target dimension value of the inspection target pattern from contour data obtained from image data of the inspection target pattern,
An image processing unit converting each vertex of polygonal contour data obtained based on the image data captured by a scanning electron microscope into coordinate data;
The image processing unit calculates an overlapping area between the contour data of the inspection target pattern and the rectangular data for length measurement, and calculates the target dimension value from the area of the overlapping area,
In the step of calculating the target dimension value, the image processing unit generates an auxiliary line in the overlapping area that is perpendicular to the opposite side that intersects the overlapping area of the rectangle of the length measurement rectangular data, and the auxiliary line The overlap area is divided into a plurality of trapezoid areas by drawing a perpendicular from each vertex converted to the coordinate data of the overlap area, and the area of the overlap area is calculated from the sum of the areas of the trapezoid areas, The pattern dimension calculation method characterized in that the target dimension value is calculated by dividing the area of the overlapping region by the dimension of the side that is the length measurement rectangular data and does not intersect the contour data.   The pattern size calculation method according to claim 1, wherein the image processing unit displays the target dimension value together with at least one of the image data and the contour data on a display unit. From the contour data obtained from the image data of the inspection target pattern, an image analysis device for obtaining the target dimension value of the inspection target pattern,
Each vertex of the polygonal contour data obtained based on the image data imaged by the scanning electron microscope is converted into coordinate data, and an overlapping area between the contour data of the inspection target pattern and the rectangular data for measurement is calculated, An image processing unit that calculates the target dimension value from the area of the overlapping region;
A display unit for displaying the target dimension value calculated by the image processing unit,
The image processing unit generates an auxiliary line in the overlapping area that is perpendicular to the opposite side that intersects the rectangular overlapping area of the length measurement rectangular data, and the coordinate data of the overlapping area with respect to the auxiliary line. The overlapping area is divided into a plurality of trapezoidal areas by drawing a perpendicular line from each vertex, and the area of the overlapping area is calculated from the sum of the areas of each trapezoidal area, and the area of the overlapping area is used for the length measurement. An image analysis apparatus characterized in that the target dimension value is calculated by dividing by a dimension of a side that is rectangular data and does not intersect with the contour data.

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