JPS6410043B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an apparatus for detecting shape defects in a regular pattern of a unit aperture using a laser beam diffraction pattern spatial frequency filtering method. The present invention relates to a pattern defect inspection device.

In industrial products such as metal meshes, which have a regular arrangement pattern of unit apertures, the apertures are generally cut in the middle by edge lines at the edges, so that the apertures are connected by irregularly shaped unit apertures. Therefore, when using the laser light diffraction pattern spatial frequency filtering method, all edges are detected as defect shapes and must be distinguished from normal defects.

Herein, the present invention has as its object to provide a device from which to distinguish between normal defects and edges.

First, the basic configuration of the laser beam diffraction pattern spatial frequency filtering method will be explained with reference to FIG.

A laser beam 2 emitted from a laser oscillator 1 is expanded by a collimator 3 to become parallel light 4 and irradiated onto an object to be inspected 5 . The inspected object 5 is placed on the front focal plane of the Fourier transform lens 7, and the Fourier transform spectrum of the inspected object 5 is displayed on the back focal plane by the light 6 diffracted when passing through the inspected object 5. appear. A negative photographic film recording the Fourier transform spectral intensity distribution of the normal pattern (by the Fourier transform lens 7) of the inspected object 5, that is, a spatial frequency filter 8, is placed on the rear focal plane of the Fourier transform lens 7. Of the Fourier transform spectrum of the inspected object 5, only the spectrum corresponding to the normal pattern is absorbed by the spatial frequency filter 8, and the spectrum corresponding to the defective pattern is transmitted.

By the way, since this spatial frequency filter 8 is provided on the front focal plane of the inverse Fourier transform lens 10, the light 9 transmitted through the spatial frequency filter 8 is inversely Fourier transformed by the inverse Fourier transform lens 10, and then On the screen 11 placed on the back focal plane (inverse Fourier transform plane) of the conversion lens,
A spatially filtered inverse Fourier transform image appears, that is, an image of only the defective portion of the object 5 to be inspected. The above is the basic configuration of the spatial filtering method.

On the other hand, FIG. 2 shows an example of a pattern consisting of a regular array of rectangular unit openings, and a defect in such a pattern is defined as one whose size is greater than a predetermined value. Therefore, in the defect inspection apparatus using the spatial filtering method described in FIG.
4 appears on the re-diffraction image plane as a point whose brightness corresponds to the defect area. Furthermore, Figure 3E
shows a normal pattern.

Inspection pattern 5 appearing on the inverse Fourier transform surface
An image of only the defective portion of the reverse image is detected by a photodetector array 11, as shown in FIG. In other words, only the defective portion 15 appears as a bright spot, which is detected by the photodetector array 11.

Here, even if the pattern to be inspected 5 is translated within the parallel light 4 at right angles to the optical axis 12, there is no change in the Fourier transform pattern appearing on the back focal plane of the Fourier transform lens 7 due to the transfer law of Fourier transform. Therefore, even if the pattern to be inspected 5 is translated in parallel, only the spectrum corresponding to the normal pattern among the Fourier transform spectra of the pattern to be inspected 5 is absorbed by the spatial filter 8, and the spectrum corresponding to the defective pattern is absorbed by the spatial filter 8. is transparent. In this way, the inverse Fourier transform image moves in the opposite direction of the optical axis symmetry due to the parallel movement of the pattern to be inspected 5. In other words, the image of only the defective part of the inverse image of the pattern to be inspected 5 is placed between the optical axis 12 and the inverse Fourier transform image is moved in the opposite direction of the optical axis symmetry. moves on the inverse Fourier transform plane in the opposite direction of movement.

In FIG. 1, if the moving direction of the pattern to be inspected 5 is perpendicular to the plane of the paper, and the arrangement direction of the photodetector array 11 on the inverse Fourier transform plane is parallel to the plane of the paper, then the direction on the inverse Fourier transform plane is The moving defect image crosses the photodetector array 11 at right angles, and is detected as an output signal of the defect image.

Further, by installing a device in the present defect inspection apparatus that outputs information regarding the movement distance of the pattern to be inspected 5 as it moves, it is possible to know the position of a defect detected in the pattern to be inspected. To explain with an example, if the direction perpendicular to the moving direction of the pattern to be inspected is the X direction, and the parallel direction is the Y direction, the defect position component in the X direction is the defect image on the inverse Fourier transform plane. It can be detected by the position of the transverse unit photodetector in the photodetector array direction, and the Y direction is determined by the position scale on the fixed base and main body of the pattern to be inspected, and if high precision is required, the moire fringes of the diffraction grating. This can be detected by means such as providing a position displacement detection device or the like, or providing a rotary encoder on the drive shaft of a motor or the like for moving the pattern to be inspected. Besides these,
Since the pattern to be inspected moves at a constant speed, the defect position component in the Y direction can also be determined by counting time starting from the start of movement.

The photodetector array 11 is composed of a plurality of unit photodetectors 13 having rectangular openings, and the output signal obtained by moving the pattern to be inspected is binarized by a comparator having a threshold corresponding to the maximum allowable area of a defect. Defect detection is thereby performed.

In the manner described above, a signal corresponding to a defective portion in the pattern to be inspected is obtained.

However, in the above-mentioned signal, in addition to the regular pattern 50 shown in FIG. 5, the vertical edge 5Y and the horizontal edge 5X of the edge portion 16 are usually mixed with defects, so the present invention This is what we are trying to identify.

FIG. 6 is a plan view of the defect inspection apparatus to which the present invention is applied, viewed from the photodetector array 11 side. The Fourier transform lens and spatial frequency filter are omitted for clarity of explanation.

The photodetector array 11 is fixed, and the pattern moving device 62 that moves the pattern 50 is
It is moved in the Y-axis direction and the X-axis direction by a drive device 61, and its Y position and X position are determined by a Y position signal generator 63 and an X position signal generator 64, respectively.

As shown in FIG. 7, the pattern moving device 62 moves at a constant speed from 70 to 71 to move the Y axis, and from 71 to 72 moves the X axis by the length in the extending direction of the photodetector array 11 ( 72 and 73 move at a constant speed in the opposite direction on the Y axis, and repeat this to cover the entire surface of the pattern 50.

FIGS. 8 to 12 show an embodiment of the present invention.

According to the present invention, when the vertical and horizontal edges of a regular pattern on an inverse Fourier transform surface are detected by a photodetector array formed by arranging a plurality of unit photodetectors in a row, This device uses the fact that defects are detected continuously to distinguish them from normal defects that are not on edges.

Therefore, the regular pattern 50 is arranged at a right angle (Y
The constant speed movement in the X-axis direction and the pitch feed for the length of the photodetector array in the parallel (X-axis) direction are repeated.

Shape defect light incident on the photodetector array 11 is detected by a parallel detection multi-defect detection circuit 81 and then provided to an edge discrimination circuit 82 .

At the same time, according to the uniform velocity movement and pitch feeding, movement distance information of the regular pattern 50 is provided from the Y position signal generator 63 and the X position signal generator 64 to the edge discrimination circuit 82.

Shape defect light incident on the photodetector array 11 is amplified by an amplifier 20, and
The value converting circuit 21 converts it into a signal representing the presence or absence of a shape defect. This signal is sampled in the sampling circuit 22 by a clock pulse CK synchronized with position signals generated from the Y position signal generator 63 and the X position signal generator 64 in accordance with the uniform velocity movement and the pitch feed. This is DS1 of the timing chart shown in Figure 13.

AND gate 23 between DS1 and DS2
is for ignoring simultaneous defects in the X direction as an edge in the X direction, and the signal G applied to the AND gate 23 together with DS1 is generated by the simultaneous signal generation circuit shown in FIG.

In this embodiment, when three or more defects appear consecutively in both the X and Y directions, they are ignored as the edges in the X direction and the edges in the Y direction. Therefore, in the circuit shown in FIG. defective signal line
DS1 is connected to the same AND gate 24, and three or more defective signals DS are connected to the same AND gate 24.
1 is applied to the AND gate 23 in FIG. 9 via the NOR gate 25. As a result of this effect, as shown in the timing chart (FIG. 13), at the moment when three or more DS1s occur simultaneously, they are blocked by the gate signal G and become DS2.

Next, a circuit (FIG. 11) that ignores defects occurring continuously in the Y direction as edges in the Y direction will be described.
As for the operation of this circuit, only an outline will be given since FIG. 13 shows a detailed timing chart of each part. This circuit consists of a flip-flop 26 that constitutes a shift register, and a gate 27 that clears three consecutive defective signals when they are detected.
DS2 of the timing chart is composed of a flip-flop 28, a flip-flop 29 for ignoring defects following three consecutive defects, and a flip-flop 30 for resetting the circuit when the consecutive defects are interrupted. Five consecutive defective signals in (i) are ignored in the final output Q5.

FIG. 12 shows a portion where the true defect position is stored in accordance with the signal Q5 in which the edges in both the X and Y directions are ignored by the operation described above.

Pulse WCK synchronized with clock pulse CK is
Gate 31 only when a defect signal appears on Q5.
The signal passes through and becomes the write signal WR to the storage device 32. Signals from an X position signal generator 64 and a Y position signal generator 63 are connected to the data line of the storage device 32, and an address signal from the address generator 33 is applied to the address line. The address generator 33 generates a clock pulse.
It is synchronized with CK, and the address signal is counted up immediately after the WR signal is generated.

Thus, according to the present invention, the edges of a regular pattern of openings such as a metal mesh can be completely distinguished from normal defects, thereby improving reliability as a regular pattern defect inspection device and greatly increasing inspection efficiency. A leap forward has been recognized.

[Brief explanation of drawings]

Fig. 1 is a basic configuration diagram of the spatial filtering method, Fig. 2 is a diagram showing an example of a pattern consisting of a regular array of rectangular unit openings, and Figs. 3 A to E are diagrams showing defective and normal patterns. , FIG. 4 is an explanatory diagram of an image of a defective portion of the inverse image of the pattern to be inspected that appears on the inverse Fourier transform plane, and FIG.・
6 is a plan view of the defect detection part of the pattern of the defect detection device applied in the present invention; FIG. 7 is an explanatory diagram of the moving direction of the moving device;
8 to 12 are block diagrams of one embodiment of the present invention, and FIG. 13 is a timing chart of one embodiment. 1... Laser oscillator, 2... Laser beam, 3
...Collimator, 4...Parallel light, 5...Object to be inspected, 6...Diffracted light, 7...Fourier transform lens, 8...Spatial frequency filter, 9...Light transmitted through the filter 8, 10 ... Inverse Fourier transform lens, 11 ... Photodetector array (screen), 12 ... Optical axis, 13 ... Unit photodetector, 14 ... Slot, 15 ... Normal defect, 16 ... Marginal part, 20 ...Amplifier, 21...
Binarization circuit, 22...Sampling circuit, 32...
...Storage device, 33...Address generator, 50...
...regular pattern, 5Y...vertical edge, 5X...
... Lateral edge, 61 ... Drive device, 62 ... Pattern moving device, 63 ... Y position signal generator, 6
4...X position signal generator, 71-74...Movement path of pattern moving device 62, 81...Multi-defect detection circuit, 82...Edge discrimination device, 83...Defect position output.

Claims (1)

[Claims] 1. An apparatus for detecting shape defects in a regular pattern consisting of a regular array of unit apertures using a laser beam diffraction pattern spatial frequency filtering method, comprising: a. a photodetector array formed by arranging a plurality of photodetectors in a line; b. moving the regular pattern at a constant speed in a direction perpendicular to the photodetector array and in a parallel direction in a plane perpendicular to the optical axis; c. a multi-defect detection circuit that detects in parallel the shape defect light incident on the photodetector array; and d. the uniform velocity movement and pitch movement. a device that outputs movement distance information of the regular pattern according to the feeding; and a circuit for discriminating shape defect signals generated simultaneously in a plurality of unit photodetectors that are continuous perpendicularly to the direction of constant velocity movement from a lateral edge and distinguishing it from a shape defect portion. Regular pattern defect inspection device.