JPS63311153A - Pattern inspecting apparatus - Google Patents

Abstract

PURPOSE:To perform inspection accurately regardless of a pattern, by stopping the position correcting operation in the direction of position deviation, when the amount of the data of the position deviation is less than a specified threshold value. CONSTITUTION:Binary coded video signals are stored into the shift registers of image memories 91A and 91B. Every time the image datum of one bit is inputted, the image signal is shifted by every one bit. When the signal is taken out of each position of the shift registers of the memories 91A and 91B, an image which is deviated in the X and Y directions with respect to a reference image is obtained. The images are taken out with delay circuits 92A and 92B and inputted into an exclusive OR circuit 93. The disagreed parts of the images, which are deviated by several bits, are detected and counted with a counter circuits 94. The counter circuit, of minimum count is identified with computing circuits 95A and 95B. When the rare of change in each of X and Y is less than a specified preset value, the output of the position deviation in that direction from a changing-rate computing circuit 96A or 96B is forcibly judged to be no deviation. The signal of the judgment is outputted to a position-deviation correcting circuit 97. In this way, inspection can be performed accurately regardless of a pattern to be inspected.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pattern inspection device, and in particular, a pattern inspection device that compares a plurality of two-dimensional patterns for semi-wet bodies, printed circuit boards, and circuit patterns used in their manufacture. The present invention relates to a pattern inspection device suitable for inspecting patterns for external defects.

[Conventional technology]

The image alignment method using exclusive OR, which is used in conventional pattern inspection equipment, calculates the number of mismatched parts between two images by shifting them by several bits in each of the X and Y directions from the reference image. The calculation was carried out using the counted value, and the discrepancy was unconditionally corrected to the minimum value. Therefore, if there is a pattern with a small count of mismatched portions in a part of the object to be inspected, malfunctions may occur due to defects in the object to be inspected or noise in the image signal.

[Problem that the invention seeks to solve]

The above-mentioned conventional device adds the counted values of the mismatched portions of multiple sets of images with shifted reference images, and when the added value is less than a certain value, it is determined that there is no effective pattern for alignment in the images. This prevents erroneous positioning by not performing the positioning.

However, no consideration has been given to preventing malfunctions in positioning two-dimensional images in individual directions. Therefore,
As shown in Figure 4(a), when the relative change rate is extremely small in an image where the count value change rate of the mismatched portion in each direction is large, alignment in the direction where the change rate is small is caused by disturbances such as noise. There was a problem of malfunction due to this.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pattern inspection apparatus that can perform accurate inspection without performing erroneous alignment operations even if there is a pattern whose positional deviation is difficult to detect in a part of the inspection target.

[Means for solving problems]

The above purpose is achieved by providing means for measuring the amount of positional deviation information for each correction direction, and means for stopping the positional correction operation in the corresponding direction when the amount of information is less than a certain threshold value. I made it.

[Effect]

As shown in FIG. 3, the minimum count value Ka in each direction
, A is calculated for the rate of change ΔK
)/ (2n + 1)...(1) ΔKy=(xat-1+ Ka, -2Ka, b)/(
2m +1 )...(2) When 8KX and ΔKy become less than a certain value, it is assumed that the amount of positional deviation information is small, and no positional deviation correction operation is performed in that direction. This prevents erroneous position correction due to noise or the like.

〔Example〕

The present invention will be explained in detail below with reference to the embodiment shown in FIGS. 1 and 2, and FIGS. 3 and 4.

FIG. 1 is a conceptual diagram showing an embodiment of the pattern inspection apparatus of the present invention, and FIG. 2 is a configuration diagram showing an embodiment of the positional deviation detection circuit of FIG. 1. In FIG. 1, two inspection objects IA and 1B (for example, printed circuit boards) having two-dimensional patterns are placed on fine adjustment tables 3A and 3B provided on an XY table 2 that is movable in the XY directions. Fixed. The two imaging devices 4A and 4B are the two inspection targets IA.
.

It is fixed at a position where the same pattern of IB is imaged.

The output signals of the imaging devices 4A and 4B are respectively binarized, passed through noise removal circuits 5A and 5B, and stored as binarized video signals in storage devices 6A and 6B arranged in a matrix. In step 7B, features corresponding to each pattern are extracted. These features are compared by a comparison/determination circuit 8, and if the two features completely match, it is determined that there is no defect, and if they do not match, it is determined that there is a defect.

In this comparative judgment method, two test objects LA and IB
In order to determine whether or not the patterns have the same features in very close positions, it is necessary to align the two patterns to be compared with high precision. Therefore, the noise removal circuit 5
The outputs of A and 5B are sent to the positional deviation detection circuit 9, the amount of positional deviation is measured, and the output is sent to the storage device 6B according to the measured amount of deviation.
The table drive section 31A corrects the amount of positional deviation and sends the output of the positional deviation detection circuit 9 to the table control circuit 10 each time the positional deviation is measured.

31B controls the fine adjustment tables 3A and 3B to correct accumulated positional deviations. Here, the positional deviation detection circuit 9 uses a circuit to which exclusive OR is applied.

In FIG. 2, the positional deviation detection circuit 9 includes an image memory 91A consisting of a plurality of shift registers, as shown in the figure.
, 91B, and a delay circuit 92A that virtually generates a plurality of sets of image shifts by changing the data extraction position of the shift register.

92B, an exclusive OR circuit 93 that detects the mismatched portions of the images, a counter circuit 94 arranged in a matrix that counts the mismatched portions of each image, and a counter circuit with the minimum counting side that detects each of X and Y. X is determined by the count values of the shift amount calculation circuits 95A and 95B that detect the shift amount in the direction of
, Y directions, and a positional deviation correction circuit 97 that determines whether or not to correct the amount of deviation based on the value of the change rate.

Next, an example of operation will be explained. Image memory 91A.

The shift register 91B includes the imaging device 4A in FIG.
A binarized video signal of the inspection object imaged by 4B and output through the noise removal circuits 5A and 5B is stored. Second
In the image memories 91A and 91B shown in the figure, the image signal is shifted by one bit each time one bit of image data is input. Therefore, by extracting signals from each position of the shift registers of the image memories 91A and 91B, an image shifted in the X and Y directions with respect to the reference image can be obtained. The output of each position of this shift register is delayed by a circuit 92A.

92B and inputs it to the exclusive OR circuit 93 to detect the mismatched portions of the images obtained by shifting the relationship between the two images by several bits, and the counter circuit 94 counts the mismatched portions of each image.

The positional deviation of the image is detected by determining the counter circuit with the minimum count value of the counter circuit 94 by the positional deviation amount calculation circuits 95A and 95B.

This positional deviation detection method is publicly known, but for example, in the case of an image pattern as shown in FIG. Since there are almost no defects, there is a drawback that a defective pattern exists in the inspection object or that a positional shift is erroneously detected due to disturbances such as noise.

In the embodiment of the present invention, focusing on the above-mentioned phenomenon, the change rate calculation circuits 96A and 96B of the positional deviation are calculated based on the positional deviation signals in the X and Y directions from the positional deviation amount calculation circuits 95A and 95B shown in FIG. As shown in FIG. 4, for the minimum count value, the x, y individual image shift change rate ((Ka, -□+Ka, n2 Ka, b)/
(2n + 1), (K −, one on b+, b−2Ka
, b)/(2m+1)), and if the rate of change in the individual directions of A signal for forcibly determining that there is no deviation is output to the positional deviation correction circuit 97.

In this way, in the positional deviation detection circuit 9 according to the embodiment of the present invention, the image positional deviation amount calculation circuit 95A is separately provided in each of the X and Y directions.
, 95B, and positional deviation change rate calculation circuits 96A, 96B.
By providing this, there is an effect that erroneous alignment operations can be prevented without being affected by the characteristics of the imaged pattern.

Although the present embodiment has been described in which everything is configured by hardware, the same effect can be obtained even if a part of the process is performed by software using a microprocessor.

〔Effect of the invention〕

As explained above, according to the present invention, even if there is a direction in the imaged pattern in which the sensitivity of position detection is low, an erroneous alignment operation is not performed, regardless of the pattern to be inspected. This has the effect of allowing accurate testing.

[Brief explanation of the drawing]

FIG. 1 is a conceptual diagram showing an embodiment of the pattern detection circuit of the present invention, FIG. 2 is a block diagram showing an embodiment of the positional deviation detection circuit of FIG. 1, and FIG. 3 is a conceptual diagram showing an embodiment of the pattern detection circuit of the present invention. An explanatory diagram of the rate calculation method, FIG. 4 is an image pattern diagram. IA, IB...Inspection object, 2...XY table, 3
A. 3B...fine adjustment table, 4A, 4B...imaging device,
5A, 5B...Noise detection circuit, 6A, 6B...Storage device, 7A, 7B...Feature extraction circuit, 8...Comparison/judgment circuit, 9...Positional deviation detection circuit, 10... Table control circuit, 91A, 91B... image memory, 92
A. 92B...Delay circuit, 93...Exclusive OR circuit,
94... Counter circuit, 95A, 95B... Deviation amount calculation circuit, 96A, 96B... Rate of change calculation circuit, 97
...Positional deviation correction circuit.

Claims (1)

[Claims] 1. An inspection object that has been roughly positioned in advance is captured as a two-dimensional image by an imaging device, and the reference two-dimensional image and the captured two-dimensional image are each stored in multiple storage elements.
In a pattern inspection device that has the function of sequentially inputting digitized image signals, calculating the exclusive OR of the two, calculating the amount of positional deviation between two-dimensional images, and correcting the position, A means for measuring the amount of positional deviation information,
A pattern inspection apparatus comprising: means for stopping a position correction operation in a corresponding direction when the amount of information is less than a certain threshold value.