JPH071232B2 - Image defect detection method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image defect detection method applicable to a defect inspection apparatus that automatically inspects a wiring pattern on a printed circuit board, a semiconductor integrated circuit, or the like.

(Prior Art) As a method of automatically inspecting a wiring pattern on a printed circuit board or a semiconductor integrated circuit, an image pattern to be inspected and a reference image pattern are compared with each other, and if a difference more than a predetermined value is found, the pattern is detected. A method of determining that the inspection image pattern has a defect is often used. With this test method,
Accurate alignment of the image pattern to be inspected with the reference image pattern is extremely important, but both the image pattern to be inspected and the reference image pattern have slight expansion and contraction, so both patterns are completely covered over the entire range. Cannot be superposed on each other, and good superposition can be achieved only in a narrow range to some extent.
Therefore, as disclosed in Japanese Patent Laid-Open No. 61-278914, the image pickup area is made to have an appropriate size so that good overlaying can be performed in the area, and the image pattern to be inspected and the reference image are firstly formed. Even after performing pattern alignment, a method of performing optimal alignment for the area and inspecting each time the imaging area is moved is performed. However, the conventional inspection method first performs alignment using the image pattern in the image pickup area, and then compares the image pattern to be inspected with the reference image pattern to detect a defect. On the other hand, there was a problem that it required two scans, which required a long time for the inspection.

(Problems to be Solved by the Invention) An object of the present invention is to perform high-speed image defects that can perform alignment and defect detection at the same time by performing one scan, and can shorten the inspection time accordingly. It is to provide a detection method.

(Means for Solving the Problem) In order to achieve the above object, in the image defect detection method of the present invention, a long strip-shaped comparison area is provided in the horizontal scanning direction, and the image pattern to be inspected and the reference image are provided in the comparison area. The defect is detected while comparing the patterns with each other, and at the same time, the displacement amount between the image pattern to be inspected and the reference image pattern is measured in the displacement amount detection area provided in the comparison area. The position correction is performed on the next comparison area adjacent in the vertical scanning direction. In the next comparison area, the position is corrected in this way, and the defect is detected again, and the position deviation amount is measured in the position deviation amount detection area inside the defect detection area, and the position of the next comparison area is calculated based on the position deviation amount. Matching is done. In this way, the defect inspection is performed in the state where the current comparison area is aligned based on the positional deviation amount of the immediately preceding positional deviation amount detection area.

In this method, the alignment is performed based on the positional shift amount of the immediately preceding pattern, not the current positional shift amount of the pattern in the comparison area. Therefore, strictly speaking, the comparison inspection is performed in the state where there is a slight positional shift. Will be done. However, the positional deviation does not occur suddenly but gradually, and the length in the vertical scanning direction is sufficiently short because the comparison area is long in the horizontal scanning direction. There is little change in the position shift at. Furthermore, since the amount of misalignment can be measured with high accuracy of 1 bit or less, if the misregistration correction of 1 bit is performed when the immediately preceding misregistration amount detection result is 0.5 bits or more, the actual position can be adjusted. The amount of displacement is always suppressed to 1 bit or less, and alignment can be performed without any practical problems.

(Operation, Example) Hereinafter, one example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram of a pattern defect detecting apparatus according to a comparison method of an embodiment of the present invention. In the figure, the pattern 1 to be inspected is linearly imaged in the horizontal scanning direction by the one-dimensional camera 2 and is sent in the vertical scanning direction by the motor 7 to form a strip-shaped area S (hatched in FIG. 1). The part marked with) is to be inspected. The belt-shaped area S can be moved in the horizontal scanning direction by the motor 8. When inspecting a wide pattern in the horizontal direction, the whole area is divided into a plurality of belt-shaped areas and the inspection is performed for each belt-shaped area. I am supposed to do it. Hereinafter, a case of inspecting one strip area will be described.

The video signal of the pattern to be inspected obtained by the one-dimensional camera 2 is binarized by the binarization circuit 3 to be the image pattern signal to be inspected, and the defect determining section 5 and the displacement measuring section 6
to go into. On the other hand, the reference image pattern (binary image) is stored in the memory 4
The signal, which is stored in advance, is read line by line in synchronization with the scanning of the one-dimensional camera 2, and is supplied to the defect determination unit 5 and the positional deviation amount measurement unit 6. Further, the values of the horizontal direction (X direction) positional deviation amount ΔX and the vertical direction (Y direction) positional deviation amount ΔY are input to the address control unit 9 by the positional deviation amount measuring unit 6 and the reference image pattern is extracted from the memory 4. The address is controlled so that the position of the reference image pattern is superimposed on the position of the image pattern to be inspected. As described above, in this embodiment, since the position of the memory is controlled to correct the position, unlike the case where the position is corrected by mechanical movement, the position can be corrected instantaneously. Next, how the image defect detection of the present invention is performed with such an apparatus configuration will be described with reference to FIG. FIG. 2 conceptually shows the area of the image pattern to be inspected. In this figure, W shows the imaging range of the one-dimensional camera 2, and as the pattern 1 to be inspected is sent by the motor 7, Image data of new lines are obtained one after another in the vertical scanning direction, and the inspection is sequentially performed. Therefore, the upper end of FIG. 2 is the tip position of the inspection area. Also, in FIG. 2, A1
.About.A3 indicate displacement amount detection areas, and C1 to C3 indicate comparison areas. B1 to B3 are parts for performing calculation for obtaining the amount of positional deviation. As can be seen from FIG. 2, the comparison area C is a strip-shaped area that is long in the horizontal scanning direction, and the positional deviation amount detection area A is provided inside the comparison area C. The comparison areas C1, C2, C3 are all the same size, and the displacement amount detection areas A1, A2, A3 are also all the same size. Although not shown in the figure, the inspected image pattern and the reference image pattern are preliminarily aligned by some means. A method using an alignment mark is generally used for aligning the head portion, but the details are omitted because it is not the main point of the present invention. In this way, since the top part is aligned, in the comparison area C1, from the first line to the last line, the defect detection is performed by comparing the inspected image pattern and the reference image pattern with the same positional relationship. Part 5 will take place. On the other hand, in parallel with the defect detection, in the misregistration amount detection area A1, data for obtaining the misregistration amount between the inspected image pattern and the reference image pattern is collected from the first line to the last line. It Next, the position shift amount and the address amount to be corrected are calculated based on the data, but these calculations are completed within the range of B1. Even though the position alignment at the beginning is possible, the position deviation amount detection area A1 may be slightly displaced as a whole, and if the position deviation amount in the position deviation amount detection area A1 is 0.5,
If the number of bits is equal to or larger than 1 bit, an address correction amount of 1 bit can be obtained. If the displacement amount of the displacement amount detection area A1 is 1.5 bits or more, it is necessary to correct the address of 2 bits, but it is necessary to correct the address of 2 bits as described above. If the size setting of the deviation amount detection area A is bad, the feeding accuracy of the motor 7 is bad, there is a problem with the optical system, etc., the size is properly selected, and the feeding with high accuracy and the correct optical system selection If this is done, the address correction amount will be within 1 bit at most.

A reference image retrieved from memory according to the address correction amount obtained in the portion of B1 in a short time until the scanning of the last row of the comparison area C1 is completed and before the start of the scanning of the next comparison area C2. The address of the pattern is switched, and the defect detection in the new alignment state comparison area C2 and the data collection for the measurement of the positional deviation amount in the positional deviation amount detection area A2 are performed. Further, in the portion B2, the amount of displacement and the amount of address correction are calculated. Then, the address switching in the memory is performed until the scanning of the last row of the comparison area C2 ends and the scanning of the first row of the next comparison area C3 starts. Thereafter, the same operation is repeated, and when the feeding of the pattern 1 to be inspected is completed, the inspection is completed.

As described above, in the present invention, the current position adjustment is performed using the position shift amount of the immediately previous area, but the position shift gradually occurs, and the position shift amount detection area A and the comparison area C are It is short enough in the vertical direction, and the position is corrected immediately when there is a displacement of 0.5 bits or more, so the actual displacement amount is within 1 bit, and the alignment is performed with sufficient accuracy for practical use. Can be done.

Although the one-dimensional camera is used as the imaging device in the present embodiment, it is not necessarily limited to the one-dimensional camera.
The same thing can be done by dividing one screen into horizontally long comparison areas by using a three-dimensional so-called television camera.

(Effects of the Invention) As described above, according to the image defect detection method of the present invention, it is possible to perform alignment with practically sufficient accuracy, and
Since the scanning is required only once, it is possible to reduce the inspection time by about half as compared with the conventional method, and the effect is extremely great.

[Brief description of drawings]

FIG. 1 is a block diagram of a pattern inspection apparatus which is an embodiment of the present invention, and FIG. 2 is an explanatory diagram for explaining the operation of the present invention. 1 ... Inspected pattern, 2 ... One-dimensional camera 3 ... Binarization circuit, 4 ... Memory 5 ... Defect determination section, 6 ... Position deviation amount measurement section 7,8 ... Motor, 9,10 ...... Address control unit A ...... Area shift amount detection area, C ...... Comparison area

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-60-138921 (JP, A) JP-A-63-128241 (JP, A) JP-A-58-30645 (JP, A)

Claims (1)

[Claims] 1. An image defect detection method for detecting a defect by comparing an image pattern to be inspected with a reference image pattern, and an inspection is performed while sequentially performing alignment with a pre-aligned state as a start state. In the image defect detection method of the progressive method, a strip-shaped area that is long in the horizontal scanning direction of an image is defined as a comparison area, and defect detection is performed while comparing the inspected image pattern and the reference image pattern with each other in the comparison area. At the same time, the displacement amount between the image pattern to be inspected and the reference image pattern is measured in the displacement amount detection area provided in the comparison area, and in the next comparison area adjacent to the current comparison area in the vertical scanning direction, In the state where the position is corrected based on the position shift amount, the defect detection and the position shift amount measurement are performed, and then this operation is repeated until the end. An image defect detection method characterized by simultaneously performing alignment and defect detection.