JPH10281722A - Pattern coordinate measuring method and apparatus - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To reduce an error of a stage position due to a stage vibration or the like and to measure a coordinate position of a pattern with high accuracy. SOLUTION: Light from a light source 6 is illuminated on a sample 2, and the reflected light is imaged on a CCD camera 7. The CPU 10 controls the driving of the XY stage 1 to move the pattern 3 on the sample 2 to a position observable by the CCD camera 7 and then stops. The image of the pattern 3 captured by the CCD camera 7 is digitally converted by the A / D converter 9, stored in the frame memory 8, and analyzed by the CPU 10 to calculate the pattern position on the image. On the other hand, at the timing when the image of the pattern 3 is captured by the CCD camera 7, the value of the laser interferometer 5 is sampled at a constant cycle, and the average value of the stage position is calculated. The position coordinates of the pattern 3 on the sample 2 are obtained from the average value of the position of the stage 1 and the pattern position on the image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for measuring the position coordinates of a fine pattern formed on a sample surface such as a mask or a reticle, and more particularly, to a method for measuring the position coordinates of a pattern with high accuracy of about 2 nm. The present invention relates to a pattern coordinate measuring method and a pattern coordinate measuring apparatus suitable for a semiconductor manufacturing field which needs to be measured.

[0002]

2. Description of the Related Art Conventionally, in the step of inspecting whether a pattern on a sample such as a mask or a reticle is formed accurately, the sample is placed on an XY stage and
The pattern to be measured by the stage is moved to a position where an image can be formed on a video camera, and at a certain moment when an image is captured by the video camera, the position of the XY stage is measured by a laser interferometer. And the position of the pattern on the image obtained from the image captured by the video camera, the position coordinates of the pattern on the sample have been obtained.

[0003]

However, even while an image is being captured by a video camera, the stage position constantly fluctuates due to vibration or the like. For this reason, in the above-mentioned conventional method, in the measurement of the stage position by the laser interferometer, it is not possible to obtain highly accurate pattern position coordinates due to the influence of the stage position fluctuation due to vibration or the like.

[0004] Therefore, as a solution of the prior art,
A method is conceivable in which an image is captured into a video camera in a shorter time by using a flash light from a strobe light source to reduce the influence of the stage position fluctuation. However, even if there is no fluctuation in the position of the stage, the value of the laser interferometer fluctuates due to the effects of air fluctuations in the optical path of the laser interferometer. May not accurately indicate the stage position, and this improvement method cannot ensure sufficient accuracy.

SUMMARY OF THE INVENTION It is an object of the present invention to reduce the error of the stage position due to the stage vibration and the like due to the fluctuation of the air in the optical path for measuring the stage position, and to make it possible to measure the coordinates of the pattern with high accuracy.

[0006]

In order to achieve the above object, a first pattern coordinate measuring method according to the present invention comprises placing a sample on which a pattern is formed on a stage and stopping the stage at a desired position. During the image capturing period in which the pattern image is captured by the CCD camera, the position detection of the stage is sampled, and the average value of the sampled detection values of the stage position and the pattern position on the image are determined from the image captured by the CCD camera. And the position coordinates of the pattern on the sample are obtained.

[0007] The position of the stage on which the sample is placed is not constant but slightly fluctuates due to vibration or the like. A laser interferometer or the like is usually used to detect the stage position. However, the detected value of the stage position always fluctuates due to air fluctuation in the optical path to be measured. Therefore, the detection value of the stage position includes a position error due to vibration of the stage or the like, and a length measurement error of the stage position due to air fluctuation in the optical path or the like. Therefore, during the image capturing period by the CCD camera, sampling of the stage position detection is performed at appropriate time intervals, and the average value obtained by averaging the detected values of many sampled stage positions is used as the stage position. The error included in the detection value of the above can be reduced as much as possible.

According to a second method of measuring the pattern coordinates of the present invention, a sample on which a pattern is formed is placed on a stage, the stage is stopped at a desired position, and a plurality of pattern images are captured by a CCD camera. During the image capture period, sampling of the stage position detection is performed, and the average value of the sampled stage position detection values and the pattern position on the image obtained from the plurality of images captured by the CCD camera are obtained. The position coordinates of the pattern on the sample are obtained.

[0009] In the method of the second invention, similarly to the method of the first invention, the average of the detected values of many sampled stage positions is used, and the stage value included in the detected value of the stage position is used. The length error of the stage position due to the position error due to the vibration of the laser and the air fluctuation in the optical path is reduced. The analog image information stored in the form of electric charges by the CCD is A / D converted to digital image data and analyzed, but the A / D conversion is performed due to quantization errors and noise during the A / D conversion. An error occurs. Therefore, in the present invention, the A / D
By using the images of a plurality of pattern images to be converted, for example, by superimposing these images, dividing and averaging the image data to obtain a pattern position on the image, the A / D conversion is performed. Conversion error can be reduced.

[0010] The first pattern coordinate measuring apparatus of the present invention comprises:
An apparatus for performing the method of the first invention,
A stage on which a sample on which a pattern is formed can be mounted and movable, a laser interferometer for detecting the amount of movement of the stage, an illumination optical system for illuminating the pattern, and a pattern image illuminated by the illumination optical system An image forming optical system for forming an image on a CCD camera, and an image based on an average value of the values of the laser interferometer sampled during an image capturing period in which a pattern image is captured by the CCD camera and image data captured by the CCD camera. And a data processing unit for calculating the position of the pattern on the sample.

A second pattern coordinate measuring apparatus according to the present invention is an apparatus for carrying out the method according to the second invention, comprising a stage on which a pattern-formed sample is placed and movable. A laser interferometer for detecting the amount of movement of the stage, an illumination optical system for illuminating the pattern, an imaging optical system for imaging a pattern image illuminated by the illumination optical system on a CCD camera, and the CCD camera Calculating a pattern position on an image from an average value of the values of the laser interferometer sampled during an image capturing period for capturing a plurality of pattern images and a plurality of image data captured by a CCD camera, A data processing unit for obtaining the position coordinates of the pattern on the sample.

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a schematic configuration diagram showing an embodiment of a pattern coordinate measuring device according to the present invention.

In FIG. 1, reference numeral 1 denotes an XY stage on which a sample 2 on which a pattern 3 is formed can be mounted and two-dimensionally moved. The position of the XY stage 1 is
X measured by the laser interferometer 5
The measurement value at the position of the -Y stage 1 is input to the CPU 10. On the other hand, the light emitted from the light source 6 is
And illuminates the pattern 3 through the objective lens 4, and the reflected light passes through the objective lens 4, the half mirror 11, is reflected by the mirror 12, and is reflected by the CCD camera 7.
An image is formed on the surface. The image of the pattern 3 captured by the CCD camera 7 is digitally converted by the A / D converter 9, stored in the frame memory 8, and analyzed by the CPU 10.

Next, a specific method of measuring pattern coordinates will be described. The CPU 10 controls a motor (not shown) for driving the XY stage 1 to move the pattern 3 to a position where the pattern 3 can be observed by the CCD camera 7. When the movement is completed, the CPU 10 issues an image accumulation start command to the CCD camera 7 (the electronic shutter of the CCD camera 7 is opened), and at the same time, starts sampling the value of the laser interferometer 5 at a constant sampling interval. I do. After a certain period of time, the CPU 10 issues a command to the CCD camera 7 to end image storage and output an image, and at the same time ends sampling of the value of the laser interferometer 5.

FIG. 4 is a timing chart showing the timing of capturing an image of a pattern by the CCD camera 7 and the timing of measuring the position of the XY stage 1 by the laser interferometer 5. 4 (1), the image capturing period T ₁ shown in (a), FIG. (1), X at a constant sampling interval as shown in (b)
-The position of the Y stage 1 is measured. The image capture period is about 1/15 second to 1/60 second, and the sampling interval is about 1 millisecond to 1 microsecond.

In response to an image output command from the CPU 10,
The image output from the CCD camera 7 to the A / D converter 9 is digitally converted by the A / D converter 9 and then stored in the frame memory 8. FIG. 2 shows the frame memory 8
FIG. 3 is an image diagram of the pattern 3 developed above, and FIG. 3 is a profile diagram showing a luminance change of a certain horizontal line 13 in FIG. 3, the intersection of the appropriate threshold L ₀ and profile is defined as the edge position of the pattern, when e1, e2, respectively, the pattern position e on the frame memory 8, and e = (e1 + e2) / 2.

The size k of one pixel of the frame memory 8 on the surface of the sample 2 is known. If the stage position obtained by averaging the values of the laser interferometer 5 sampled by the CPU 10 is s, the pattern sample The coordinates x on the surface are x = s-k · e. Thus, the position coordinate of the pattern in the x direction is 2n
It is required with high precision of about m. Similarly, the pattern coordinate position in the y direction can be obtained.

In this embodiment, the CPU 10 instructs the CCD camera 7 to store an image.
The result is the same even if the CPU 10 starts sampling the value of the laser interferometer 5 in response to the image accumulation command from the camera 7.

Further, as shown in FIG. 4 (2), the image capture period T ₂ by the CCD camera 7 captures an image of a pattern of a plurality at a predetermined period (three in FIG. 4 (2)), A pattern position on an image may be calculated from image data obtained by superimposing and averaging a plurality of A / D-converted images. In this way, as shown in FIG. 4 (3), as compared with the case of calculating the pattern position on the image in substantially the same image capture period T ₃ captures one image, A /
A / D conversion errors due to quantization and noise during D conversion are averaged, and A / D conversion errors can be reduced.

Further, as shown in FIG. 4 (4), by performing the sampling of the position measurement at a plurality of times each image capture of the image capture period T _4, and calculates the respective average values, further these average values In this case, since it takes a long time to calculate the average value, sampling is continued during the image capturing period as shown in FIG. It is preferable from the viewpoint of quick measurement to calculate the average value collectively for all of the above.

[0021]

As is apparent from the above description, the present invention has the following effects. During the image capture period for storing the image of the pattern image with the CCD camera, the value of a measuring device such as a laser interferometer that measures the position of the stage is sampled, and the measured values of the sampled stage position are averaged. Therefore, it is possible to reduce a position error due to a stage vibration or the like and a length measurement error due to an air fluctuation in an optical path being measured, and to greatly improve the coordinate measurement accuracy of the pattern.

Also, by capturing images of a plurality of patterns with a CCD camera and performing image processing based on image data of a plurality of pattern images to be A / D-converted, quantization errors, noise, and the like are caused. An error at the time of A / D conversion can be reduced, and the measurement accuracy of the coordinate position of the pattern can be further improved.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing an embodiment of a pattern coordinate measuring device according to the present invention.

FIG. 2 is an image diagram showing an example of a pattern image developed in a frame memory of FIG. 1;

FIG. 3 is a profile diagram showing a luminance change of one horizontal line in the frame memory of FIG. 2;

FIG. 4 is a waveform chart showing an example of timings of capturing a pattern image by a CCD camera and sampling an XY stage position by a laser interferometer in the apparatus of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 XY stage 2 Sample 3 Pattern 4 Objective lens 5 Laser interferometer 6 Illumination light source 7 CCD camera 8 Frame memory 9 A / D converter 10 CPU

Claims (4)

[Claims] A sample on which a pattern is formed is placed on a stage, the stage is stopped at a desired position, and sampling of position detection of the stage is performed during an image capturing period in which a pattern image is captured by a CCD camera. Obtaining a position coordinate of the pattern on the sample by obtaining an average value of the detected values of the sampled stage positions and a pattern position on the image from the image captured by the CCD camera. Coordinate measurement method. 2. A stage on which a sample on which a pattern is formed is placed on a stage, the stage is stopped at a desired position, and a plurality of pattern images are captured by a CCD camera during an image capturing period. Sampling is performed, the average value of the sampled stage position detection values and the pattern position on the image are obtained from the plurality of images captured by the CCD camera, and the position coordinates of the pattern on the sample are obtained. A method for measuring pattern coordinates, characterized in that: 3. A stage on which a sample on which a pattern is formed is mounted and movable, a laser interferometer for detecting the amount of movement of the stage, an illumination optical system for illuminating the pattern, and an illumination optical system. CC illuminated pattern image
An image forming optical system for forming an image on a D camera, and an average value of the values of the laser interferometer sampled during an image capturing period in which the pattern image is captured by the CCD camera and image data captured by the CCD camera. A pattern processing device for calculating a pattern position and obtaining a position coordinate of the pattern on the sample. 4. A stage on which a sample on which a pattern is formed can be mounted and movable, a laser interferometer for detecting an amount of movement of the stage, an illumination optical system for illuminating the pattern, and an illumination optical system CC illuminated pattern image
An imaging optical system for forming an image on a D camera, an average value of the values of the laser interferometer sampled during an image capturing period in which a plurality of pattern images are captured by the CCD camera, and a CCD
A pattern processing apparatus for calculating a pattern position on an image from a plurality of pieces of image data captured by a camera and obtaining a position coordinate of the pattern on the sample.