JPH05158222A - Mask inspecting method - Google Patents

Abstract

PURPOSE:To improve sensitivity for detecting the defect of missize, on a mask inspecting method used for a photolithography. CONSTITUTION:This mask inspecting method has processes for catching two images formed on a mask and having equal patterns by a photodetector, respectively, and vertically or horizontally shifting one pattern image by the distance of the picture element size or below of the photodetector, and for having the back-and-white inversion of one of the pattern images, moving the other pattern image by the pitch of the relevant pattern, and inputting an image obtained by superimposing two pattern images into a comparator, and is constituted so that the asymmetry of a region except a part where two pattern images are superimposed, as the region outputted to the comparator as a signal, is obtained in an area ratio, and the defect of the missize of the pattern is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of inspecting a mask, and in recent years, the density of a mask (or reticle) has been required to increase with the increasing density of a semiconductor device. Therefore, it is necessary to improve the surface quality of the mask.

In particular, the most highly integrated state-of-the-art DRAM and the like are created according to the design rule (minimum pattern size) of the stepper, and the pattern cannot be resolved due to a minute defect which was not a problem in the past. Therefore, it has become important to improve the defect detection sensitivity in the mask surface automatic inspection device.

[0003]

2. Description of the Related Art In a conventional mask surface automatic inspection apparatus, a typical defect such as an isolated defect (residue of a light-shielding film, a pinhole) or an edge defect (a chipped edge or a protrusion of a patterned light-shielding film) is detected. The defect is detected by the following method.

For example, the images of two equal patterns formed on a mask are taken into a light receiving element such as a CCD, and at this time, the images of one pattern are inverted in black and white to superimpose the images of the two patterns, and there are defects. For example, by comparing the output black and white gradations (for example, 16 gradations) in an image of a certain pattern, it is judged that there is no defect if the left and right gradations are equal. Method, or to determine the position and number of defects by using the fact that a vector is generated in a certain direction along the edge of the pattern and the direction of the vector changes when there is a defect such as a chip or a protrusion on the edge. There is.

FIG. 2 is a block diagram showing an example of a mask surface inspection apparatus. In the figure, the light emitted from the mercury lamp 1 passes through the left and right lenses 2 and irradiates two equal patterns 4 on the reticle 3, and the lenses 5 focus the left and right patterns on the light receiving element 6.

The left and right image signals output from the light receiving elements are respectively image-processed and converted into a bit map 6, and one of the left and right bit maps is inverted in black and white, and the left and right bit maps are overlapped with each other by shifting the pitch of the pattern. Is entered.

At this time, if the comparator has an output signal, it is detected as a defect. Here, the above-mentioned typical defect has no problem because it has a defect detection capability of about the size of the pixel of the light receiving element, but a missize defect (a defect formed when the pattern dimension deviates from the intended dimension). For example, when two patterns having a missize in one of them are overlapped with being shifted by the pitch of the mask pattern, the size of the missize is twice the interval between the two patterns.

Therefore, on the contrary, half the size of the miss size
It is necessary to detect the pattern interval having the size of, and if this size is less than the size of the pixel of the light receiving element, the pattern cannot be detected. A conventional example will be specifically described below with reference to FIG.

3 (A) to 3 (C) are explanatory views of the miss size defect detection according to the conventional example. FIG. 3 (A) is an image of two real patterns having a missize in either one or a pattern captured by a light receiving element.

In FIG. 3B, the image of one pattern is reversed in black and white, and the images of the two patterns are shifted by the pitch of the mask pattern and superimposed. At this time, the images of the superimposed patterns are symmetrical. Here, when the two target patterns on the mask are separated by a distance that is an integer multiple of the array pitch, superposition may be shifted by an integer multiple of the array pitch.

In FIG. 3 (C), the superposed portion of the images of the two patterns is canceled and therefore is not output from the comparator,
The space area (hatched area) between the images of the two patterns is output to the comparator as a missize defect.

The distance A between the images of the two patterns cannot be detected when the size of the pixel of the light receiving element (about 0.25 μm) or less,
Therefore, the missize defect has a detection sensitivity of about 0.5 μm, which is twice that of the missize defect.

[0013]

In the conventional example, the minimum defect size of the miss size defect is twice the representative defect size, and the detection sensitivity is lowered.

An object of the present invention is to improve the detection sensitivity of missize defects.

[0015]

In order to solve the above-mentioned problems, the light-receiving element captures two images of the same pattern formed on the mask, and the image of one pattern is moved vertically or horizontally to the pixel size of the light-receiving element. The process of displacing the following distance and the image of either pattern is inverted in black and white, the image of either pattern is moved by the pitch of the pattern, and the image in which the images of the two patterns are superposed is displayed on the comparator. And the step of inputting, and detecting the pattern missize defect by obtaining the asymmetry of the area excluding the overlapping portion of the images of the two patterns, which is the area output as a signal to the comparator, by the area ratio. This is achieved by the mask inspection method.

[0016]

In the conventional example, the image signals of the two patterns respectively fetched from the left and right lenses are black-and-white inverted and superimposed by shifting the pattern pitch, but in the present invention, either the left or right signal is forced. By slightly shifting (for example, half of the pixel size of the light receiving element) vertically and horizontally, the patterns are overlapped on one side of the missize pattern to facilitate detection.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 (A) to 1 (D) are illustrations of missize defect detection according to an embodiment of the present invention. FIG. 1 (A) is an image of two real patterns having a missize in either one or a pattern captured by a light receiving element.

In FIG. 1 (B), when the two pattern images are superimposed by shifting the pattern pitches, the right image is shifted to the right by 0.125 μm, for example. In Fig. 1 (C), when the images of one pattern are inverted in black and white and the images of the two patterns are overlapped by shifting by the pitch of the patterns, the overlapping part of the images of the two patterns is canceled and the output from the comparator. Instead, the space area (hatched area) between the images of the two patterns is output as a missize defect from the comparator. At this time, the pattern image becomes asymmetrical as shown in the figure, and one side of the interval region of the pattern image is emphasized and becomes large.

In FIG. 1D, the missize defect is detected by comparing the left and right symmetry with respect to the right edge of the image of the left side pattern by the area ratio of the interval regions of the pattern image. In this case, if it is symmetrical, there will be no defect.

The detection sensitivity of the high-sensitivity mask surface inspection device is set to 0.
If it is 25 μm, the missize defect is 0.40 μm in the conventional example.
Although it could be detected only to some extent, in the embodiment, the detection sensitivity of 0.25 μm, which is equivalent to that of typical defects such as isolated defects and edge defects, was obtained.

[0021]

According to the present invention, the detection sensitivity of missize defects is improved. As a result, the quality of the reticle and mask was improved, which contributed to the improvement of manufacturing yield and reliability of high-density devices.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of missize defect detection according to an embodiment of the present invention.

FIG. 2 is a configuration diagram showing an example of a mask surface inspection apparatus.

FIG. 3 is an explanatory view of detection of a missize defect according to a conventional example.

[Explanation of symbols]

 1 Mercury lamp 2, 5 Lens 3 Inspected reticle 4 Pattern 6 Light receiving element 7 Bit map 8 Comparator

Claims (1)

[Claims] 1. A process of capturing images of two equal patterns formed on a mask by a light receiving element, and shifting one pattern image vertically or horizontally by a distance equal to or smaller than the pixel size of the light receiving element. And inverting the image of one of the patterns, moving the image of one of the patterns by the pitch of the pattern, and inputting the image in which the images of the two patterns are superimposed to a comparator. Inspection method for a mask, wherein a pattern missize defect is detected by obtaining the asymmetry of the area excluding the overlapping portion of the images of the two patterns, which is the area output as a signal to the container. .