JPH0420166B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pattern defect inspection method for a pattern in which light-transmitting unit patterns such as mesh stripes are regularly and repeatedly arranged.

An optical Fourier transform spatial filter method is known as a method for inspecting defects in regular repeating patterns as described above. FIG. 1 shows the principle. Laser light emitted from a laser head 1 is irradiated onto a test pattern 5 as coherent parallel light through a condenser lens 2, a pinhole plate 3, and a collimator lens 4. The light that has passed through the transparent portion of the pattern is then passed through the Fourier transform lens 6 to produce an optical Fourier transform spectrum of the pattern to be tested 5 at the focal point. The spatial filter 7 has a light shielding pattern created by photographically recording the Fourier transform spectrum, and shields the spectrum of the normal test pattern 5. If there is a pattern defect in the light irradiation part of the test pattern 5, the light from that part passes through the spatial filter 7 and forms a defect image at the position of the screen or detector 9 by the inverse Fourier transform lens 8. By visually detecting this defect image or using a photodetector, it is possible to easily detect only the defective portion of the pattern.

This inspection method optically extracts only the defective parts of the repeating pattern, so it does not require a precise mechanism or electrical defect extraction circuit, and is easy to implement.
Also, compared to methods using video signal processing used in pattern inspection, high-speed inspection is easier. On the other hand, since the pattern to be inspected corresponds to the pattern of the spatial filter, it is necessary to prepare a spatial filter for each type of pattern to be inspected. Arrangement angle, shape of light transmitting unit pattern,
There are limitations such as the inability to inspect patterns that change in size, etc., and this has been an obstacle to practical application.

The present invention aims to eliminate these drawbacks by improving the spatial filter, expand the types of patterns that can be inspected in the defect inspection method using the Fourier transform spatial filter method, and improve the efficiency. A spatial filter is formed by combining images of optical Fourier transform spectra of transmitted light from a plurality of different pattern parts such as repeating pitches of unit patterns, and has a light shielding part that blocks all of the optical Fourier transform spectra. It was discovered that the intended purpose could be achieved by using the present invention, and the present invention was completed based on this knowledge.

That is, the gist of the present invention is to irradiate a pattern in which light-transmitting unit patterns are regularly and repeatedly arranged with parallel light, to block the diffracted light generated by the defect-free repeating pattern, and to block the light from the defective portions of the pattern. In a pattern defect detection method that includes a spatial filter that allows light to pass through and detects the transmitted light visually or with a photodetector, the spatial filter may be a plurality of patterns in which the repeating pitch, etc. of light-transmitting unit patterns differs within the inspection area. This pattern defect detection method is characterized by using a spatial filter that is formed by combining images of optical Fourier transform spectra of partially transmitted light and has a light shielding part that blocks all of the optical Fourier transform spectra.

Hereinafter, the present invention will be explained in detail.

Before explaining the present invention, the relationship between the pattern to be inspected and the pattern of a conventional photographic spatial filter will be explained.

FIG. 2 shows an example of a repeating pattern having a striped light transmitting unit pattern of equal pitch and equal opening width. In the figure, p indicates the repeating pitch of the pattern, a indicates the opening width, and 10 indicates the light transmitting unit pattern. Next, FIG. 3 shows a light-shielding pattern of a photographic spatial filter for detecting pattern defects in the repetitive pattern shown in FIG.

In the pattern of the imaging spatial filter shown in Figure 3, the pitch Pf of the dot row corresponding to the Fourier transform spectrum of the transmitted light of the test pattern is determined by the repetition pitch p of the test pattern, and the dot diameter d The change in is determined by the aperture width a of the unit pattern (slit shape). Therefore, if the repetition pitch or aperture width of the test pattern is different, the Fourier transform spectrum of the normal pattern and the spatial filter pattern will not match, and the light from the normal pattern will pass through the spatial filter and reach the detection part, resulting in a problem with S for defect identification. /N ratio decreases, making it impossible to perform highly accurate detection.

In the present invention, an improved spatial filter as shown in the fourth figure, which is an improved spatial filter as shown in the third figure, is used.

In this improved spatial filter, dots corresponding to a striped light transmittance unit pattern (not shown) with a repeating pitch _p1 are displayed at the pitch _pf1 , and dots corresponding to a striped light transmittance unit pattern (not shown) with a repeating pitch p1 are displayed at the pitch _pf1 . Light transmitting unit pattern (not shown)
A dot corresponding to is displayed at pitch p _f2 , and the dots are continuous. Further, dots of a higher order than the above-mentioned dots are displayed in a continuous bar shape. That is, in this improved spatial filter, the optical Fourier transform spectrum of the transmitted light of multiple types of pattern portions consisting of light transmittance unit patterns arranged with an arrangement pitch that gradually changes in the range p ₁ ≦ p ≦ p ₂ This is a composite display of rows of dots corresponding to the image. Therefore, with this improved spatial filter,
The repeating pitch p of the test pattern is between p ₁ and _{p 2} , and the width of the stripe is such that o<a<p.It is possible to block light from the normal striped pattern and at the same time allow light from the defective part to pass through. It is. According to this improved spatial filter, it is possible to repeatedly inspect various striped patterns of equal pitch and equal aperture width, where the pitch p is p ₁ ≦p≦p ₂ and the aperture width a is o<a<p. If the range in which the repeated pitch p changes is within the range p ₁ ≦p≦p ₂ , it is possible to inspect a pattern in which the pitch p and the aperture width a gradually change within the inspection area.

As described above, the transmitted light of multiple types of pattern portions in which the repeating pitch, arrangement angle, shape, size, etc. of each unit pattern, etc. of the light-transmitting unit patterns gradually change in the inspection area as shown in the fourth figure. Using a spatial filter that is formed by combining images of the optical Fourier transform spectrum and has a light shielding part that shields all of the optical Fourier transform spectrum,
It is possible to detect defective portions of patterns in which the repeating pitch, arrangement angle, shape, size, etc. of each unit pattern gradually change depending on the location.

FIG. 5 now shows another improved spatial filter for use in the present invention.

In the improved spatial filter shown in Fig. 5, the image of the optical Fourier transform spectrum of the transmitted light of a repeating pattern with a repeating pitch p = p ₁₁ and the optical Fourier transform spectrum of the transmitted light of a repeating pattern with a repeating pitch p = p ₁₂ are obtained. It has a light-shielding part formed by combining it with an image. Therefore, this single spatial filter can detect defects in both the p=p ₁₁ repeating pattern and the p=p ₁₂ repeating pattern.

As described above, the light shielding system which blocks all of the optical Fourier transform spectra formed by combining the images of the optical Fourier transform spectra of the transmitted light of the plurality of regularly repeated patterns to be inspected as shown in FIG. using a spatial filter with a
It is possible to detect defects in a plurality of types of regularly repeated patterns.

Although the above examples are examples of one-dimensional repeating patterns, the same effect can be achieved with two-dimensional repeating patterns, such as mesh patterns.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of the optical Fourier transform spatial filter method, Fig. 2 is a plan view of a repeating pattern, Fig. 3 is a plan view of a photographic spatial filter pattern for detecting defects in the pattern shown in Fig. 2, Fourth
The figure is a plan view of an example of the improved spatial filter used in the present invention, and FIG. 5 is a plan view of another example of the improved spatial filter used in the present invention. p...Repetition pitch of the test pattern, a...
Aperture width, p _f ... Pitch of spatial filter pattern corresponding to repetition pitch p, d ... Dot diameter, p _f1 ... Pitch of Fourier transform spectrum when p = p ₁ , p _fd ... p = p Pitch of Fourier transform spectrum when ₂ .

Claims (1)

[Scope of Claims] 1. A pattern in which light-transmitting unit patterns are regularly and repeatedly arranged is irradiated with parallel light to block the diffracted light generated by the defect-free repeating pattern and to pass the light from the defective part of the pattern. In a pattern defect detection method in which a spatial filter is provided and the transmitted light is detected visually or with a photodetection device, the spatial filter is used to detect multiple types of pattern portions in which the repeating pitch etc. of light transmitting unit patterns are different within the inspection area. A pattern defect detection method comprising using a spatial filter formed by combining images of optical Fourier transform spectra of transmitted light and having a light shielding portion that blocks all of the optical Fourier transform spectra. 2 The repeating pitch and arrangement angle of the light transmitting unit pattern within the inspection area as the spatial filter;
and formed by combining images of optical Fourier transform spectra of transmitted light of multiple types of pattern portions in which the shape, size, etc. of each unit pattern gradually changed.
Using a spatial filter having a light shielding part that blocks all of the optical Fourier transform spectrum, the repetition pitch, arrangement angle, and
2. The pattern defect detection method according to claim 1, wherein defective portions of patterns in which the shape, size, etc. of each unit pattern gradually change are detected. 3 A space having a light-shielding portion that blocks all of the optical Fourier-transformed spectra formed by combining images of optical Fourier-transformed spectra of transmitted light of multiple types of regular repeating patterns to be inspected as the spatial filter. using a filter,
2. The pattern defect detection method according to claim 1, wherein defect portions of a plurality of types of regularly repeated patterns are detected using a common spatial filter.