JP6002486B2 - Pattern measuring method and pattern measuring apparatus - Google Patents

Description

The present invention relates to a pattern measuring apparatus that measures a pattern dimension based on a signal obtained by irradiating a sample with a charged particle beam, and more particularly to a pattern measuring apparatus suitable for measuring a hole pattern.

In the manufacturing process of a semiconductor element, a technique for measuring, inspecting, and evaluating a pattern formed with a scanning electron microscope is widely used. In recent years, with the high integration of patterns, the patterns to be inspected have been miniaturized. Under such circumstances, the pattern shape actually formed may be different from the design drawing. For example, a pattern that should be a perfect circle may be formed by being deformed.
Even if the profile of the pattern thus formed is acquired using a polar coordinate expansion, the edge is detected and measured, depending on the profile acquisition direction, it is not perpendicular to the edge. There was a problem that the edge could not be detected. In Patent Document 1, a figure reflecting a pattern shape is created from a pattern image, density distribution data on a straight line perpendicular to the tangent of the outline is obtained at the intersection of the center of gravity of the figure and the outline, and the density It is described that pattern edge coordinates are detected from distribution data.

JP 2001-91231 A (corresponding US Pat. No. 6,480,807)

In the pattern measurement method disclosed in Patent Document 1, circle, ellipse, and oval patterns can be measured, but the profile acquisition position is searched for on a straight line from the center of gravity position of the pattern.
In the case of a pattern with a curved or elongated shape such as a circle or ellipse, other edges that are not the measurement target may be located between the center of gravity and the edge, depending on the measurement purpose. Appropriate measurement results may not be obtained.
In the following, a pattern measurement method and a pattern measurement device for the purpose of enabling proper measurement even when it is difficult to specify a measurement start point or measurement end point such as a curved closed figure pattern will be described. To do.

As one aspect for achieving the above object, the following is a pattern measuring device including an arithmetic processing unit that measures a pattern formed on a sample based on a signal obtained by a charged particle beam device, The arithmetic processing unit specifies a plurality of center positions between one edge of the pattern and another edge, and measures a first length of the pattern along the plurality of center positions, A second length corresponding to half of a dimension between edges in a direction intersecting the line segments along the plurality of center positions from the length of the line segments along the plurality of center positions starting from the edge The length between the end of the line segment of the third length and the edge of the pattern is obtained in a plurality of directions, and the statistical value of the length in the plurality of directions is obtained. Of the fourth length calculated based on the third length and the third length A pattern measuring device for obtaining the first length based on the total is proposed.

According to the above configuration, it is possible to perform appropriate measurement even for a pattern in which it is difficult to specify the measurement start point and the measurement end point.

The figure which shows the example of 1 structure of a scanning electron microscope system. The figure which shows the example in which the setting of the measurement reference | standard (measurement start point, measurement end point) on the basis of a gravity center position fails. The flowchart which shows a pattern measurement process. The flowchart which shows the process of pinpointing the center position of the curved vertically long pattern. The figure which shows an example of the curved vertically long pattern. The figure which shows an example of a brightness | luminance profile acquisition position. The figure which shows an example of a brightness | luminance profile and its differential waveform. The figure which shows an example of the vertically long pattern by which the center position was specified. The figure which shows the example which sets the detection direction of an edge based on specification of a center position. The figure which shows the edge part of the vertically long pattern by which the center point was specified. The figure which shows the example which extracts a brightness | luminance profile in several directions on the basis of the center point set to the edge part of a vertically long pattern. The flowchart which shows the process of measuring the horizontal width of a pattern based on specification of the center position of the curved vertically long pattern. The flowchart which shows the process of adding the length of the edge part of the curved vertically long pattern, and the length of the pattern center part, and calculating | requiring pattern length. The figure which shows the relationship between the angle when a pattern edge part expand | deploys polar coordinates, and r-theta. The figure which shows an example of the pattern measurement apparatus containing a scanning electron microscope.

Below, for a vertically long pattern that is mainly curved, a differential profile is created in a direction intersecting the longitudinal direction of the pattern, and the profile is horizontally moved while moving vertically until there is no peak of the differential profile. To obtain the center coordinate between the peaks of the two differential profiles, acquire the profile in the vertical direction of the line connecting the center coordinates, perform edge detection, calculate the lateral length measurement value, The center point is the position that has moved half the length of the measured value in the horizontal direction in the direction of the line connecting the central coordinates from the position where the center no longer exists, and edge detection is performed by expanding polar coordinates from the center point. An embodiment of a method and apparatus for obtaining the distance from the edge to the edge and using the sum of the distances between the center points as the length measurement value in the vertical direction will be described.
An example of the configuration of a scanning electron microscope system is shown in FIG. In the following description, a scanning electron microscope will be described as an example. However, the present invention is not limited to this, and can be applied to other charged particle beam apparatuses such as a focused ion beam apparatus. Reference numeral 101 denotes a housing part of an electron microscope, and an electron beam 103 emitted from an electron gun 102 is converged by an electron lens and irradiated onto a sample 105. By the electron beam irradiation, the intensity of secondary electrons or reflected electrons generated from the sample surface is detected by the detector 106 and amplified by the amplifier 107. Reference numeral 104 denotes a deflector that moves the position of the electron beam, and the electron beam 103 is raster-scanned on the sample surface by the control signal 108 of the control computer 110.
The signal output from the amplifier 107 is AD converted in the image processor 109 to create digital image data. Reference numeral 111 denotes a display device that displays the image data. The image processing processor 109 has an image memory for storing digital image data, an image processing circuit for performing various image processing, and a display control circuit for performing display control. Input means 112 such as a keyboard and a mouse is connected to the control computer 110. In the image processor 109 and the control computer 110 described above, pattern measurement processing described later is performed. In this embodiment, an example in which the image processor 109 and the control computer 110 are included in one arithmetic processing device 113 will be described. However, each processing may be performed by different arithmetic processing devices.
The length measurement value is obtained by the following method for the hole pattern of the electron microscope image taken from the electron microscope. In the deformed hole pattern as shown in FIG. 2, there is a case where the profile cannot be acquired correctly by the method of acquiring the profile radially from the position of the center of gravity. For example, as shown in FIG. 2, there are cases where the edge of the pattern and the profile acquisition direction are parallel, or where the edge of the pattern is overlapped with the edge before the edge position to be detected. In such a case, the edge cannot be correctly detected by the conventional method, but it can be detected at the edge position of the pattern by using the method of this embodiment. FIG. 15 is a diagram illustrating an example of a pattern measurement system including the electron microscope housing unit 101. The measurement system includes a control device 1501 that controls the electron microscope and processes signals obtained by the electron microscope, an arithmetic processing device 113 that executes arithmetic processing based on the electronic signals obtained by the control device 1501, and An input means (input device) 112 including a display device 111 is included. The arithmetic processing unit 113 includes an arithmetic processing unit 1502 for executing arithmetic processing to be described later, and a memory 1503 for storing arithmetic processing conditions and signal information obtained by an electron microscope.
FIG. 3 is a flowchart showing a pattern measurement process. In this embodiment, after measuring the horizontal width of a vertically long curved pattern, the vertical length (vertical width) is measured based on the horizontal width information, so a signal waveform (profile) is acquired by an electron microscope (step) 301) After performing horizontal width measurement (step 302) using the profile, a process of performing vertical width measurement (step 303) is executed.
FIG. 5 is a diagram illustrating an example of a hole pattern to be measured. As shown in the figure, a perfect circle has a shape that is elongated and curved in the vertical direction. The cross mark in FIG. 5 is a detection position (measurement reference position), and is set within the contour of the pattern in order to execute processing described later. The outline (rectangular part) of FIG. 5 represents the length measurement cursor, and the measurement process is executed inside this.
First, as shown in FIG. 6, the luminance profile creation unit 1504 forms a signal waveform as illustrated in the upper part of FIG. 7 for the measurement reference position based on the detection signal stored in the memory 1503 (FIG. 4). Steps 401 and 402). Two peaks appear in this luminance profile, indicating the position of one edge located on the right side of the pattern and the other edge located on the left side of the pattern.
In this example, the brightness profile is obtained in the horizontal direction at the cursor center position of the length measurement cursor indicating the area to be measured, and the obtained brightness profile is used in the direction from the cursor center position to the end of the cursor. A differential profile is calculated (step 403). The profile shape is as shown in the lower part of FIG. Since the differentiation processing unit 1505 performs differentiation processing in the left direction and the left direction starting from the cursor center position, as illustrated in FIG. 7, it is possible to form a symmetrical differential waveform. . Next, the pattern measuring unit 1509 measures the distance between two positive peaks in the differential profile using a threshold method or the like, and the center specifying unit 1506 calculates the midpoint of the two positive peaks based on the measurement result. (Step 404).
The above processing is performed until the positive peak no longer exists in each direction while moving the profile acquisition position upward and downward (step 405), starting from the center position of the cursor. For example, a predetermined threshold may be set for the presence or absence of a positive peak, and it may be determined that the peak does not exist when the peak falls below the threshold. The fact that the positive peak does not occur means that the profile acquisition position is located in the portion where the signal change from the inside of the pattern (part where the luminance is low) to the pattern edge (part where the luminance is high) disappears. . That is, the profile acquisition position is arranged on the upper edge or lower edge of the pattern. At the upper and lower ends of the pattern, there is only a change from a portion with high luminance (edge) to a portion with low luminance (outside the pattern edge), so only a negative peak appears. In this example, the upper end position and the lower end position of the pattern are specified based on such a principle. The midpoint of the two negative peaks at the position where the positive peak no longer exists is recorded.
Next, as shown in FIG. 8, a plurality of midpoints of the two positive peaks (midpoint inside the pattern) and two midpoints of the negative peaks (midpoint of the pattern upper end and lower end) are connected in the order of the Y coordinate. A line (hereinafter, center line) is created (step 406).
Through the processing as described above, an approximate center line of the curved pattern can be obtained. Next, the edge detection unit 1507 performs edge detection in the direction of a predetermined relative angle (90 degrees in this example) with respect to the center line with reference to the center line (step 1201 in FIG. 12). . As illustrated in FIG. 9, this process is performed on two spaces separated by a center line (in the middle point of the two positive peaks, as shown in FIG. Edge detection is performed in the direction of the bisector of the angle of the angle.) The midpoint of the two edge points detected by the edge detection unit 1507 is set as a new center point (step 1202). The pattern measuring unit 1509 calculates a length measurement value in the horizontal direction from the average value of a plurality of distances between the detected edges (step 1203). This average value is defined as the width of the pattern. If the pattern edge is partially missing and the peak height of the positive peak is not sufficient, it is not a mere arithmetic mean, but other statistics such as a weighted average operation using the peak height as a weighting factor. Processing may be performed.
Next, the center identifying unit 1506 moves the midpoint from the midpoint of the negative peak located at the approximate pattern end to the midpoint of the positive peak one lower (in the pattern internal direction or the cursor center position direction). The pattern moves to half the length (L / 2 (second length) in FIG. 10) of the horizontal width of the pattern (L in FIG. 10), that is, the position of the center point in FIG. This process is performed at both ends (step 1301). The length of the center line between the two center points can be defined as the pattern length excluding the pattern end. In order to obtain the overall length later, the pattern dimension measuring unit 1509 causes the memory 1503 to store the length (third length) of the center line between the two center points.
Next, as shown in FIG. 11, the polar coordinate development unit 1508 performs 90-degree polarization coordinate development on the left and right with reference to a direction opposite to the middle point of the positive peak one level below the center point shown in FIG. 10. (Step 1303). Polar coordinate development is performed, edge detection is performed on the obtained image, the distance between the start point and the edge point at the time of polar coordinate development is calculated, and the average value of the distances is obtained (step 1304). More specifically, when the center line is set to 0 degree, the image between the edge on the edge side of the pattern and the center point is developed in the r-θ coordinate system. FIG. 14 is a diagram showing an example of an image developed in polar coordinates. Since the edge 1401 varies in distance from the center point due to variations in noise and edge shape, the average value 1402 is calculated to suppress the influence of noise or the like (the distance measured at the tip (the fourth length measurement value)). ))) Is calculated. Note that other statistical processing such as weighted average calculation may be performed on the pattern edge.
The average value (measured value of the tip (or measured value of the two tips if both the upper and lower ends are present)) and the length of the center line (between the two center points) The total value of the center line length) is the length measurement value in the vertical direction (first length), that is, the vertical width of the pattern. With the above processing, the horizontal width and vertical width of the pattern are calculated.
According to this embodiment, a pattern in which an edge parallel to the half line starting from the center of gravity position exists, a pattern in which an edge parallel to the half line starting from the center of gravity position exists, It is possible to provide a method and an apparatus capable of measuring pattern dimensions even for a pattern having a shape in which another edge exists between a half line as a starting point and an edge position to be detected.

DESCRIPTION OF SYMBOLS 101 Body part of electron microscope 102 Electron gun 103 Electron beam 104 Deflector 105 Sample 106 Electron detector 107 Amplifier 108 Control signal 109 Image processor 110 Control computer 111 Display device 112 Input means

Claims (3)

In a pattern measuring apparatus including an arithmetic processing unit that measures a pattern formed on a sample based on a signal obtained by a charged particle beam apparatus,
The arithmetic processing unit generates a plurality of luminance profiles on a plurality of straight lines in the same direction at different positions in a direction intersecting with the edge of the closed figure pattern formed by the linear edges. A plurality of center positions of the two peaks are specified based on the plurality of luminance profiles that appear, and a pattern start point and a pattern end point are specified based on the plurality of luminance profiles in which one peak appears. Measuring a first length of a virtual line segment between the pattern start point and the pattern end point along the center position ,
For each of the start point side of the pattern and the end point side of the pattern, a second length corresponding to half of the dimension between two edges located on a line segment orthogonal to the virtual line segment is set to the virtual line segment. The third length is obtained by removing from the length of
With respect to each of the pattern start point and pattern end point, the range of −90 degrees to +90 degrees when the direction of the virtual line segment is set to 0 degrees with reference to the end of the third length virtual line segment. The length between the edge positions in a plurality of directions and the end of the third imaginary line segment is obtained, and the length between the plurality of edge positions and the end of the third imaginary line segment The pattern measuring device is characterized in that the first length is obtained on the basis of the total of the fourth length and the third length obtained based on the statistical value. In claim 1,
The arithmetic processing unit differentiates the luminance profile toward a first direction from the reference position inside the closed figure pattern toward the edge and a second direction opposite to the first direction. based on the differential waveform obtained by the pattern measuring apparatus characterized that you detect said peak. In claim 2,
The arithmetic processing unit, wherein the position at which the positive peak is exhausted differential waveform pattern start, and a pattern measuring apparatus characterized that you identify a pattern end point.