JP2003214820A - Method and apparatus for inspecting stroke width - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for inspecting a stroke width in which an accurate inspection of the stroke width of a formed pattern can be realized. <P>SOLUTION: The method for inspecting the stroke width comprises the steps of totalizing the degrees of differences of the stroke widths, obtaining an inspected value based on the totalized degree, and comparing the inspected value with a threshold value by a deciding circuit 9. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a line width inspection method and apparatus capable of inspecting the line width of a pattern drawn on a photomask or the like used in manufacturing a semiconductor device with high accuracy. .

[0002]

2. Description of the Related Art With the evolution of LSI, semiconductor circuits are inevitably required to have a high density. In order to manufacture such a high-density semiconductor circuit, it is necessary to make the exposure performed in the manufacturing process highly accurate. For that purpose, a highly accurate photomask must be used. For the photomask, layout design is performed by using an LSI design CAD tool.
It is manufactured by creating layout data, converting the LSI layout data into EB (Electron Beam) data, and inputting the EB data into a photomask drawing device. The photomask thus manufactured is subjected to a pattern defect inspection by measuring the line width of a predetermined (designated) portion by a pattern defect inspection device (line width measuring device), and the measured value is designated. The line width accuracy of the pattern formed on the photomask is assured by determining whether or not it is within the allowable range from the obtained dimension value and using only the acceptable product. The pattern defect inspection apparatus compares image data (sensor data) of a pattern to be inspected formed on a photomask or the like with reference data which is design data used when designing this image pattern, and A defect in the inspection pattern is detected.

FIG. 6 is a block diagram showing an example of the structure of a line width inspection apparatus which is a conventional pattern defect inspection apparatus. As shown in FIG. 6, the structure of the line width measuring device is as follows: an image pickup device 31 such as a CCD line sensor for picking up an image of a pattern to be inspected formed on a photomask or the like to obtain an image signal; An A / D converter 32 for A / D converting the image signal from A to D to generate sensor data is provided. On the other hand, design data used as an inspection pattern is developed into a bit pattern, and the image capturing device 31 uses the image capturing position as an image capturing position. A reference data generation circuit 33 is provided which inputs corresponding position data and generates reference data corresponding to a pattern to be inspected using this position data.

The sensor data and the reference data obtained by these are configured so that the line width comparison circuit 34 compares them and the defective portion is output.

The line width comparing circuit 34 includes a line width measuring circuit 35,
36 and a line width comparison / determination circuit 37. As illustrated in FIG. 2, the line width measuring circuits 35 and 36 measure the line width for each pixel from the images of the sensor data and the reference data. That is, the edges 14a and 14b that are the ends of the line for line width measurement are recognized from the pattern, a cross-sectional profile is taken at the recognized edge positions, and the positions of the edges 14a and 14b are detected from the profile with an accuracy of less than a pixel. Ask. Edge 14a of the obtained pair,
The line width is measured by the line width comparison / determination circuit 37 by calculating the distance between the positions of 14b. Edge 14a, 1
The position of 4b is calculated with a precision equal to or less than the pixel by linearly interpolating the position where the profile crosses the thresholds of the edges 14a and 14b. Thereby, the abnormal data of the line width formed in the pattern is detected.

[0006]

However, in the above-described conventional line width inspection method, the line width is measured for each pixel from the images of the sensor data and the reference data. The line width is measured by obtaining the essence position with an accuracy of a pixel or less, but the optical resolution, the pixel resolution, the quantization accuracy of A / D conversion,
Moreover, the accuracy at the time of measurement is determined by factors such as electrical noise. Therefore, when a highly accurate inspection of the line width of the pattern is required, it is difficult to improve the accuracy by the conventional method of measuring each pixel.

On the other hand, with regard to the quality control (target value and variation) of the line width of the pattern formed on the mask, with the miniaturization of semiconductor circuits, increasingly precise specifications are required. In particular, as the wavelength of the light source of the stepper is in the deep ultraviolet region, the number of patterns formed on the mask is 10 nm.
It has been found that the abnormal line width of 1 affects the yield of wafers.

For the management of the line width of the pattern formed on the mask, a method of measuring and managing several points on the mask by SEM or the like may be used. But,
With this method, the line width of the pattern cannot be confirmed over the entire surface of the mask. For the place where the line width abnormality of the pattern occurs, it is not possible to find out where on the mask the abnormality occurs. Therefore, there is an increasing demand for highly accurate pattern line width inspection over the entire surface of the mask.

The present invention has been made in view of these circumstances, and an object thereof is to provide a line width inspection method and an apparatus therefor capable of realizing highly accurate inspection of the line width of a formed pattern.

[0010]

According to the means of the invention of claim 1, the sensor data obtained by imaging the object to be inspected and the reference data electrically developed from the CAD data are compared to each other. In a line width inspection method for inspecting the line width of a pattern formed on an inspection body, an imaging step of capturing an image of the inspection body and dividing the imaged pattern formed on the inspection body to form an inspection region And a line width difference detection step of obtaining a line width difference for each pixel by comparing the line width data for each pixel captured in the sensor data for each inspection region. And a frequency counting step of counting the frequency of the line width difference, an inspection value calculating step of obtaining an inspection value based on the counted frequency, and comparing the inspection value with a threshold value set from the reference data. And the judgment process The line width inspection method characterized in that it has.

According to the means of the invention according to claim 2,
The inspection value is an average value of a difference in line width between the sensor data and the reference data, which is a line width measuring method.

According to the means of the invention according to claim 3,
The inspection value is a difference between a maximum value and a minimum value of the line width of the reference data or a standard deviation value, which is a line width measuring method.

According to the means of the invention according to claim 4,
Imaging means for imaging the inspected object to obtain sensor data from the pattern of the inspected object, and reference data generating means for electrically developing CAD data to obtain reference data of the pattern of the inspected object. And a line width measuring device having a comparing means for comparing the line widths from the sensor data and reference data, wherein the comparing means has a function of measuring the line width of the pattern and the sensor data of the pattern. The comparison means has a function of obtaining a difference in line width from the reference data, and the comparison means is connected to a frequency counting means for counting the frequency of the line width difference within a certain inspection region. Is connected to an average value calculating means for obtaining an average value of the line width difference, and to the average value calculating means is connected a determining means for comparing the average value of the line width difference with a threshold value. Line width measuring device A.

According to the means of the invention according to claim 5,
The inspection area is specified by an inspection area dividing unit that divides the inspection object at predetermined intervals.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An example of an embodiment of a line width inspection device of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the structure of a line width inspection apparatus. The line width inspection device is a CCD that captures an image of a pattern to be inspected formed on a photomask, which is an object to be inspected, as an image signal, as an input line of sensor data.
An image pickup device 1 such as a line sensor, and an A / D device for A / D converting an image signal from the image pickup device 1 to generate sensor data.
The D converter 2 is provided. On the other hand, as an input line of the design data used as the inspection pattern, the design data is developed into a bit pattern, and the position data corresponding to the image capturing position of the image pickup apparatus 1 is input, and the position data is used to inspect the pattern. A reference data generation circuit 3 for generating corresponding reference data is provided. The reference data generation circuit 3 and the output side of the A / D converter 2 are both connected to the comparison circuit 4.

To the output side of the comparison circuit 4, a frequency counting circuit 7 for connecting the frequencies of the line width differences is connected. Data is also input to the frequency counting circuit 7 from the inspection area dividing circuit 6, and an average value calculating circuit 8 is connected to the output side of the frequency counting circuit 7. A determination circuit 9 is connected to the output side of the average value calculation circuit 8.

The comparison circuit 4 comprises line width measuring circuits 11 and 12 and a line width comparison circuit 13. As illustrated in FIGS. 2A and 2B, the line width measuring circuits 11 and 1
In 2, the line width is measured for each pixel from the images of the sensor data and the reference data. That is, from the pattern data, the edges 14 that become the pair of ends of the line for measuring the line width.
a, 14b are recognized, and the recognized edges 14a, 14b are recognized.
2B, a cross-sectional profile depending on the illuminance is taken, and the edges 14a, 1
The position of 4b is obtained with an accuracy of a pixel or less. The line width is measured by calculating the distance between the obtained edge positions 14a and 14b of the pair. The positions of the edges 14a and 14b are calculated with the accuracy of pixels or less by linearly interpolating the positions where the profile crosses the threshold values of the edges 14a and 14b.

The line width comparison circuit 13 uses the sensor data and CA.
The difference between the line widths of the patterns formed on the object to be inspected is calculated by comparing the D data with the reference data electrically developed.

The inspection area dividing circuit 6 is a circuit for dividing the inspection area into a predetermined size. As shown in the explanatory views of FIGS. 3A to 3C, first, as shown in FIG. First, the mask 15 as the inspection object is first divided into strips called inspection stripes 16. During the actual inspection, the inspection stripe 16 is scanned from left to right and from right to left. Next, as shown in FIG. 3B, the inspection stripe 16 is vertically and horizontally divided into units having a predetermined division width to form an inspection region 17. As a result, as shown in FIG. 3C, a plurality of patterns 18 formed on the mask 15 are present in each vertically and horizontally divided inspection region 17.

The frequency totalizing circuit 7 includes a divided inspection area 1
This is a circuit for counting the frequency of the difference between the line widths of the sensor data and the reference data in units of 7.

The average value calculation circuit 8 is a circuit for obtaining the average value of the line width difference from the frequency of the line width difference as the inspection value.

The determination circuit 9 is a circuit that compares the average value of the line width difference with a threshold value to detect a line width abnormal portion and outputs line width abnormal data.

Next, the line width measurement by the above line width inspection apparatus will be described. FIG. 4 is a flowchart showing steps of line width measurement by the line width inspection device.

First, as shown in FIG. 3A, the inspection stripe 16 is vertically and horizontally divided into units of a predetermined division width with respect to the mask 15 which is the object to be inspected to form an inspection region 17 ( S1).

Next, as shown in FIG. 3C, which shows the position of the pattern 18 where the line width can be measured in the inspection area 17, the inspection point in the inspection area 17 is specified (S2). It should be noted that a plurality of patterns 18 to be measured are present at the inspection location according to the type of the pattern 18 formed on the mask 15.

Next, the inspection of the pattern 18 at the inspection location
As shown by the arrows in FIG. 5A, the width in the X direction and the Y direction of each pattern 18 is inspected (S3). In this inspection, first, as shown in FIG. 5B, which shows a portion where the line width is actually measured by taking the X direction as an example, the line width is measured for one pattern 18 and the pixel is measured. A plurality of line widths are measured according to the number of pixels.
The same applies to the Y direction.

The line width difference is detected by summing up the line width measurement results measured for each pixel (S4). Based on this, the frequencies for each detected line width difference are totaled (S5). Further, as an inspection value, the average value of the frequencies is obtained from the counting result of the frequencies (S
6). FIG. 5C is a graph showing the frequency distribution of the line width differences obtained by measuring and totalizing the line widths of the patterns 18 existing in the divided inspection area 17. In the normal portion of the line width, the frequency distribution of the line width difference is distributed around 0 nm as in the CAD data which is the reference data. On the other hand, in the line width irregular portion, the frequency distribution of the line width difference is distributed around 25 nm, which is deviated from the reference data.

Next, it is determined whether or not the average value of the frequencies is within a predetermined threshold value. If it is within the threshold value, the result is passed, and if it is desired to exceed the threshold value, the result is rejected ( S
7). If the line width abnormality is simply determined from the line width measurement result, the abnormal portion and the normal portion may not be sufficiently divided, and when the abnormal portion is detected, the normal portion may be detected together. Occur. Therefore, in the method of the present invention, as an example of the inspection value, the average value of the line width of the normal portion and the abnormal portion of the line width is obtained for each inspection area 17. In the case of the graph shown in FIG. 5C, the average values are 0 nm and 25 nm, respectively. By obtaining the average value, the variation component appearing in the line width distribution is reduced. Therefore, if this average value is determined with a threshold value of 30 m, for example, an abnormal portion having a line width of 50 nm can be detected in units of the inspection area 17 without misjudging a normal portion. As a result, as shown in FIG. 5D, the inspection area 17a in which the line width abnormality has occurred can be accurately detected.

As described above, according to the above-described embodiment, the line width inspection is performed by determining the average value of the line width differences calculated in the constant inspection area 17, and therefore the conventional method is used. As in the method, the random variation component that occurs when measuring the difference in line width, which occurs when it is obtained for each pixel, is reduced. As a result, it has become possible to inspect an abnormal line width portion that cannot be detected by the conventional method with a high accuracy equal to or less than the variation accuracy of the conventional measurement accuracy.

In the above embodiment, the average value is calculated as the inspection value from the frequency distribution of the line width difference, and the average value is compared with the threshold value to inspect the line width abnormality. Instead of the average value as the value, the maximum value (threshold value) of the line width of the normal portion may be used to compare with the maximum value of the line width of the measured pattern to detect the line width abnormality.

The same effect can be obtained by comparing and inspecting the difference between the maximum and minimum values of the line width of the pattern measuring portion or the standard deviation and the like.

[0033]

According to the present invention, an abnormal line width of a pattern can be detected with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a line width inspection device of the present invention.

2A and 2B are explanatory diagrams of line width measurement.

3A to 3C are explanatory views of the operation of the inspection area dividing circuit.

FIG. 4 is a flowchart showing the steps of line width measurement according to the present invention.

5A to 5D are explanatory views of pattern inspection.

FIG. 6 is a configuration diagram showing a configuration of a conventional line width inspection device.

[Explanation of symbols]

1 ... Imaging device, 4 ... Comparison circuit, 6 ... Inspection area dividing circuit,
7 ... Frequency totaling circuit, 8 ... Average value calculating circuit, 9 ... Judgment circuit, 11, 12 ... Line width measuring circuit, 13 ... Line width comparing circuit,
14a, 14b ... Edge, 17 ... Inspection area, 18 ... Pattern

Claims (5)

[Claims] 1. A line for inspecting a line width of a pattern formed on the inspection object by comparing sensor data obtained by imaging the inspection object with reference data electrically developed from CAD data. In the width inspection method, an imaging step of imaging the inspection object, an inspection area forming step of dividing an imaged pattern formed on the inspection object to form an inspection area, and the sensor data for each inspection area. A line width difference detecting step of obtaining line width difference of each pixel by comparing the line width data of each pixel taken in, and a frequency totalizing step of totaling the frequency of the obtained line width difference. A line width including an inspection value calculation step of obtaining an inspection value based on the counted frequency and a determination step of making a determination by comparing the inspection value with a threshold value set from the reference data. Inspection method. 2. The line width measuring method according to claim 1, wherein the inspection value is an average value of a difference in line width between the sensor data and the reference data. 3. The line width measuring method according to claim 1, wherein the inspection value is a difference between a maximum value and a minimum value of the line width of the reference data or a standard deviation value. 4. An imaging means for imaging the inspected object to obtain sensor data from the pattern of the inspected object, and a CA for obtaining reference data of the pattern of the inspected object.
A line width measuring device comprising: a reference data generating unit that electrically develops D data; and a comparing unit that compares the line widths from the sensor data and the reference data, wherein the comparing unit is a line of the pattern. It has a function of measuring the width and a function of obtaining the difference in line width between the sensor data of the pattern and the reference data, and the comparison means collects the frequency of the difference in line width within a certain inspection region. A frequency counting means is connected, and an average value calculating means for calculating an average value of line width differences is connected to the frequency counting means, and the average value calculation means compares the average value of the line width differences with a threshold value. A line width measuring device having a determination means connected thereto. 5. The line width measuring apparatus according to claim 4, wherein the inspection area is specified by an inspection area dividing unit that divides the inspection object at predetermined intervals.