JPH1183431A - Coordinate center position determination device for image pickup optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device for correctly determining the coordinate center position of an image-pickup optical system. SOLUTION: The pinhole image of a pinhole plate 2 irradiated by a light source 1 is imaged on a sample 5 surface, and is picked up together with the pattern of the sample 5 surface by an image pickup system. Since the position of a focused pinhole on the sample 5 surface is definite, this position can be used as the coordinate center position of the image pickup optical system. Even if the imaging position on the image pickup element 8 face of the sample 5 is changed by the optical axis position change of a variable power part 7, measurement can be conducted without influence of the optical axis position change of the variable power part 7 by determining the coordinate of the image pickup optical system referring the position of the pinhole image.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for determining a coordinate center position of an imaging optical system when digitizing an image of a sample and performing image processing.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, a target circuit pattern is extracted by taking an image of a wafer surface with an imaging optical system and performing image processing on the imaged data.
Based on this, dimension measurement and alignment are performed.

FIG. 5 schematically shows an image pickup optical system used for this purpose. In FIG. 5, the surface of a sample 5 is imaged by an objective lens 4, and a beam splitter 3, a mirror 6
, The magnification can be changed as appropriate by the magnification changing unit 7, and an image is taken by an image pickup device (for example, a CCD). The magnification unit 7
A plurality of optical systems having different magnifications are provided, and necessary optical systems are appropriately selected and used. As described above, since the variable magnification section 7 has the movable section, it is inevitable that the optical axis position changes when the magnification is changed.

As a result, if the magnification of the variable magnification unit 7 is changed, the optical axis of the entire image pickup optical system will be shifted.
It is unclear which element in the imaging element 8 is located at the coordinate center position of the imaging optical system. Therefore, there is a problem that it is unclear which point should be used as a reference, especially when performing alignment.

Conventionally, in order to solve this problem, a reticle line drawing mark is projected on a sample surface, the image is detected by an imaging optical system, and the detected image is used as a reference for the position of the imaging optical system. Image processing has been performed. That is, in FIG. 5, the reticle line mark plate 9 is disposed immediately after the light source 1. On the reticle line mark plate 9,
As shown in FIG. 6, four cross-shaped reticle line drawing marks are engraved, and the images are formed on the surface of the sample 5 and are imaged together with the surface image of the sample 5 by the imaging optical system.

In an image processing system, the positions of four reticle line drawing marks are detected, and the intersection of a line (reticle line) connecting two sets of opposing reticle line drawing marks is determined as the coordinate center point of the imaging optical system. Is recognized. According to this method, since the position of the reticle line drawing mark on the sample 5 is constant, the coordinate center position of the imaging optical system can be correctly recognized even if the optical axis of the zoom unit 7 is shifted. A reticle line is displayed on the display device (not shown) together with the image of the sample surface taken.

[0007]

As described above,
In the related art, the coordinate center position of the imaging optical system is determined by detecting the position of a reticle line drawing mark by image processing. Therefore, an error due to the image recognition accuracy of the reticle line drawing mark causes a shift of the reference position of the imaging optical system, which is a problem particularly when the sample is measured by performing alignment.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an apparatus for accurately determining a coordinate center position of an image pickup optical system.

[0009]

A means for solving the above-mentioned problem is an apparatus for determining a coordinate center position of an image pickup optical system in an apparatus for digitizing a picked-up image of a sample and performing image processing, wherein the apparatus is provided immediately after a light source. A pinhole, an optical system that forms an image of the pinhole on the surface of the sample, an imaging optical system that images the surface of the sample and stores the image in an image memory, and an image operation processing unit. The processing device includes a coordinate center position determining unit that determines the position of the image memory where the center of the image of the pinhole exists as the coordinate center position of the imaging optical system, wherein the coordinate center of the imaging optical system is It is a position determining device.

According to this apparatus, the image of the pinhole formed on the surface of the sample is picked up by the image pickup optical system, and the position where the image exists is determined as the coordinate center position. Compared to conventional methods using image recognition,
The coordinate center position of the imaging optical system can be determined with accurate accuracy.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an outline of an example of an embodiment of the present invention. In FIG. 1, the difference from the prior art of FIG. 5 is that the reticle line mark plate 9 in FIG.
The only difference is that a pinhole plate 2 is provided in place of. Therefore, the same components as those in FIG. 5 are denoted by the same reference numerals, and description thereof will be omitted.

As shown in FIG. 2, the pinhole plate 2 has a very small pinhole at the center, and an image of the pinhole illuminated by the light source 1 is formed on the surface of the sample 5, and The image is captured by the imaging optical system together with the pattern on the five surfaces. Since the position of the pinhole image formed on the surface of the sample 5 is constant, this position can be used as the coordinate center position of the imaging optical system. That is, even if the imaging position of the sample 7 on the imaging element 8 surface changes due to the change of the optical axis position of the magnification unit 7, the coordinates of the imaging optical system are determined based on the position of the image of the pinhole, thereby changing the position. Double part 7
Can be measured without being affected by the change in the optical axis position.

FIG. 3 is a schematic diagram showing an example of the configuration of a system for displaying a captured image and a coordinate center point of an imaging optical system on a monitor screen in the embodiment of the present invention.
The pattern on the surface of the sample 5 and the image of the pinhole imaged by the imaging device 11 (same as the imaging device 8 in FIG. 1) are converted into digital data by the A / D converter 12 and stored in the image memory 13. Image operation processing unit 14
Calculates the center of the pinhole image by processing such as extracting the pinhole image from the data in the image memory 13 and calculating the center of gravity thereof, and sets the position corresponding to the center as the coordinate center position of the imaging optical system. Then, as shown in FIG. 4, an image of the center position mark 21 is generated at the coordinate center position,
An image of the cross line 22 is generated vertically and horizontally with the image as the center, and written in the image memory 13.

The contents of the image memory 13 are converted into video signals by a D / A converter 16 and displayed on a monitor screen 17. Therefore, on the monitor screen 17, the surface pattern of the imaged sample 5, the center position mark 21, and the cross line 22 are displayed in an overlapping manner.

When replacing the scaling unit 7, the control computer 15 transmits the image processing operation unit 1 through the local bus.
4 to issue a command to determine the center position of the coordinates of the imaging optical system each time.

[0016]

As described above, according to the present invention, a pinhole provided immediately after a light source, an optical system for forming an image of the pinhole on the sample surface, and an image obtained by imaging the sample surface An imaging optical system for storing in a memory, and an image processing device, wherein the image processing device determines a position of the image memory where the center of the image of the pinhole exists as a coordinate center position of the imaging optical system. Since the determination unit is provided, it is possible to determine the coordinate center position of the imaging optical system with more accurate accuracy as compared with the conventional method based on image recognition of the reticle line drawing mark.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of an embodiment of the present invention.

FIG. 2 is a view showing a pinhole plate used in the apparatus shown in FIG.

FIG. 3 is a schematic diagram illustrating an example of a configuration of a system that displays a captured image and a coordinate center point of an imaging optical system on a monitor screen in the embodiment of the present invention.

FIG. 4 is a diagram showing an example of a center position mark and a crosshair displayed on a monitor screen.

FIG. 5 is a diagram showing an outline of a conventional imaging optical system for imaging a wafer surface.

FIG. 6 is a view showing a reticle line mark plate used in the apparatus shown in FIG. 5;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Light source 2 ... Pinhole plate 3 ... Beam splitter 4 ... Objective lens 5 ... Sample 6 ... Mirror 7 ... Magnification unit 8 ... Image sensor 9 ... Reticle line mark plate 11 ... Image sensor 12 ... A / D converter 13 ... Image Memory 14 Image processing unit 15 Control computer 16 D / A converter 17 Monitor screen

Claims (1)

[Claims] 1. An apparatus for determining a coordinate center position of an imaging optical system in an apparatus for digitizing an image of a sample and performing image processing, wherein a pinhole provided immediately after a light source and an image of the pinhole are determined. An optical system that forms an image on the surface of the sample, an imaging optical system that captures an image of the surface of the sample and stores the image in an image memory, and an image operation processing unit. An apparatus for determining a coordinate center position of an imaging optical system, comprising a coordinate center position determining unit for determining an existing image memory position as a coordinate center position of the imaging optical system.