JPH075116A - Pattern inspection equipment - Google Patents

Abstract

PURPOSE:To increase the yield by making a decision of normal when a pattern having inappropriate profile is present at a place deviated from a correct position. CONSTITUTION:The pattern inspection equipment comprises a sample (a) provided with a large number of patterns regularly on the surface thereof, means (b) for picking up the surface image of the sample (a), means (c) for storing the image, means (d) for setting a window opening at a position determined while taking account of the regularity of patterns, and means (e) for superposing the window on the image stored in the memory means (c) and measuring the positional relationship between a target pattern and peripheral patterns. The pattern inspection equipment further comprises a first decision means (f) for deciding whether the profile of pattern is normal or abnormal based on the image stored in the memory means (c), and a second decision means (g) for outputting the decision results from the first decision means, as it is, when the measurements of the position measuring means (e) satisfy the regularity whereas making a decision of normality regardless of the decision results from the first decision means (f) when the regularity is not satisfied.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pattern inspection apparatus, and more particularly to a pattern inspection apparatus suitable for inspecting a high density printed circuit board. For example, a printed circuit board used in a large-sized computer is provided with a large number of miniaturized patterns for mounting surface-mounted components and connecting layers of a multilayer board.

FIG. 15 is an external view of a main portion of this type of printed circuit board. On the circuit board 1, linear patterns 2 for signal lines and power supply lines are formed and arranged with a predetermined regularity. Further, a large number of miniaturized patterns 3 (circular or rectangular patterns; hereinafter represented by “circular patterns”) are formed.
The diameter of the circular pattern 3 is minute, for example, about 200 μm, and the arrangement interval is extremely narrow, about 600 μm to 700 μm. Therefore, the size of the substrate 1 is, for example, 5
Assuming 0 cm x 50 cm, approximately 800 x 800 = 6
An enormous number of circular patterns 3 of 40,000 are formed, and the quality of such a large number of circular patterns 3 is judged, that is, the presence or absence of "inappropriate shape", "positional deviation", "copper residue", etc. is visually checked. When observed with, not only is it not possible to obtain sufficient accuracy, but it also involves considerable difficulty and is not realistic.

Therefore, there is a demand for a highly accurate inspection device capable of automatically determining the quality of a pattern without relying on visual inspection.

[0004]

2. Description of the Related Art FIG. 16 is a block diagram of a conventional pattern inspection apparatus. In this figure, 10 is a light source, 11 is a sample (printed circuit board), 12 is a CCD (Charge Coupled Device) camera for capturing a plane image of the sample 11, and 13 is a C.
A binarization circuit that converts the output of the CD camera 12 into a binarized image signal, 14 is a storage circuit (image memory) that two-dimensionally develops and stores the binarized image signal, 15 is a length measurement circuit, 16
Is a coding circuit for coding the output of the length measuring circuit 15 (hereinafter, "length measuring value"), and 17 is a defect dictionary referred to by the output of the coding circuit 16.

Here, as shown in FIG. 17A, the length measuring circuit 15 measures the shape of a plurality of circular patterns 18 to 24 (however, the number and arrangement are examples). It is a thing. Specifically, from the center of the pattern of interest (the circular pattern 18 for convenience), the length measurement lines 18a to
18 h is extended to measure the distance from the center of the pattern of interest 18 to the edge of the pattern, and the measurement result is radial coded and collated with the defect dictionary 17. For example, when the distances for each length measurement line are not uniform, the pattern of interest 18
If the shape is an improper shape other than a circle, the defect dictionary 17 outputs a signal indicating "defect".

[0006]

However, in such a conventional pattern inspection apparatus, since the pattern normality / abnormality is determined only based on the shape of the pattern of interest, the determination is excessive and the yield is increased. There was a problem that it could not be improved. That is, as in the case of FIG. 17B, when the pattern 25 having an improper shape is present at a proper position, it should be judged as abnormal, as shown in FIG. 17C. When the pattern 26 having an improper shape is present at a place deviating from the proper position, the improper shape pattern 26 is like dust, so that it does not become an obstacle unless it is peeled off and moved. It is safe to use. Therefore,
In the case of FIG. 17B, it should be determined as “normal” rather than as “abnormal” in terms of improving the yield. [Purpose] Therefore, the present invention avoids excessive determination by adding the positional relationship of patterns to the determination material, and determines, for example, that a pattern having an improper shape is present at a place deviating from the proper position as normal. The objective is to make a judgment and improve the yield.

[0007]

In order to achieve the above object, the present invention provides a sample a having a large number of regularly arranged patterns on its surface as shown in the principle diagram of FIG.
A photographing means b for photographing a surface image of the sample a, a storage means c for holding the image, a window setting means d for setting a window opened at a position taking into account the regularity of the numerous patterns, Position measurement means e for measuring the positional relationship between the pattern of interest and the pattern around it by superimposing the window on the image held in the storage means c, and the pattern based on the image held in the storage means c First judging means f for judging whether the shape is normal or abnormal
When the measurement result of the position measuring means e satisfies the regularity, the determination result of the first determining means f is output as it is, while when it is not satisfied, the first determination is performed. It is characterized in that it is provided with a second judging means g which outputs normal regardless of the judgment result of the means f.

[0008]

In the present invention, if the position of the pattern of interest is improper, that is, if it is out of the regularity of the pattern, it is uniformly determined as normal regardless of the determination result of the pattern shape. Therefore, for example, when an improperly-shaped pattern exists at a position deviating from the proper position (see FIG. 17).
(See (c)) is also determined to be normal, and the yield is improved.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. 2 to 14 are views showing an embodiment of the pattern inspection apparatus according to the present invention. First, the configuration will be described. Figure 2
In the figure, 30 is a light source, 31 is a sample (for example, a printed circuit board), 32 is a CCD camera (imaging means), 33 is a binarization circuit, 34 is a storage circuit, 35 is a length measurement circuit, and 36 is a first dictionary (first 1 is a determining means), 37 is a second dictionary, 38 is a defect determining circuit (second determining means), 39 is a placement detecting circuit (window setting means), and 40 is a placement determining circuit (position measuring means).

On the surface of the sample 31, a minute size circular (or rectangular) pattern arranged at least with a predetermined regularity is formed, and transmitted light is illuminated from the back surface by using a light source 30 such as a halogen lamp. The surface image of the sample 31 is C
The analog image signal photographed by the CD camera 32 and output from the CCD camera 32 is converted into a binarized signal by the binarization circuit 33, and then stored in the storage circuit 34. The stored content (image) of the storage circuit 34 is the length measurement circuit 35.
Are sequentially transferred to the placement detection circuit 39, and the required processing is performed in each.

The length measuring circuit 35 measures the pattern shape in the image. Specifically, the length measuring circuit 35 detects the center pixel of the pattern of interest and measures the distance from the center pixel to the edge of the pattern of interest. It measures in multiple directions. For example, if the length measurement values in each direction are substantially equal, it can be determined that the pattern is a normal circular pattern (that is, a proper shape), while if the length measurement values in each direction are not uniform (unequal), a pattern other than a circular pattern (that is, a proper shape) is used. It can be determined that the shape is inappropriate. The length measurement value is radially coded by a coding circuit (not shown), and the first dictionary 36 and the second dictionary 37 are referred to using this code. If it is the code of the proper shape pattern, a signal indicating "normal" (hereinafter referred to as "candidate signal") is extracted from both dictionaries, while if it is the code of the improper shape pattern, "1" is retrieved from the first dictionary 37. A candidate signal indicating “abnormal” and a candidate signal indicating “normal” are extracted from the second dictionary 37. These first and second dictionaries 3
The candidate signals extracted from 6 and 37 are both sent to the defect determination circuit 38, and one of them is selected by the defect determination circuit 38 according to the output of the arrangement determination circuit 40, and is output as a pass / fail result.

Placement detection circuit 39 and placement determination circuit 40
Sets a detection window (hereinafter referred to as “window”) that opens at a position that takes into account the regularity of many patterns formed on the surface of the sample 31, and superimposes this window on the image held in the memory circuit 34. And measures the positional relationship between the pattern of interest and the pattern around it and has a function as a window setting means and a position measuring means.

FIG. 3A shows, as an example, seven openings 41.
FIG. 47 is a conceptual view of a window having ˜47, in which a central opening 41 corresponds to a pattern of interest, and openings 42 to 4 around it.
7 corresponds to each pattern located around the target pattern. FIG. 3B is a state diagram in which the image held in the storage circuit 34 and the window are superposed, and the white circles are patterns. The pattern arrangement has regularity, and the window opening position also has similar regularity. Therefore, when the window opening 41 is located on the target pattern 48 as shown by A in the figure, the other openings are also located on the surrounding patterns 49 to 54. That is, the target pattern 48 and the six patterns 49 around it.
If the positional relationship of ~ 54 is correct, all the openings 41-47 of the window will hit the pattern, and the number of hits in this case is "7", which is the same as the number of openings. Also,
When there is a pattern defect 55 as shown in B in the figure, the opening 45 in the pattern defect portion has no hit, and the number of hits in this case is “7-1 = 6”. Further, as shown by C in the figure, when there is a pattern 56 having an improper position, only one opening (for example, 41) is hit and other openings are not hit. Therefore, the number of hits in this case is " 1 ”. Note that FIG. 4 is a correspondence diagram between the openings 41 to 47 and the target pattern, and the window output, that is, the number of hits is given to the central pixel of the plurality of pixels forming the target pattern.

FIG. 5 shows an example of a hardware configuration for realizing a window. In this example, 11 shift registers 57 to 67 are connected in series. One square of the shift register corresponds to one pixel of the image data, and five squares marked with a symbol S or C are set to form seven openings S1 to S7. Note that C is a square representing the seven openings S1 to S7. FIG. 6 shows such an opening S
It is a conceptual diagram of the window which has 1-S7. The central opening S1 includes cells C11 and S12 to S15, and the five openings S2 to S7 in the periphery thereof are each made of Si.
Includes squares from 1 to Si5 (where i is an opening number; 2 to 7). The number of squares is set to an appropriate number (here, five) capable of distinguishing the substrate and the pattern from the image data.

Here, when the opening S7 is located on the pattern, the five squares S71 to S forming the opening S7 are formed.
All 75 hit the pattern. Therefore, the opening S7
The maximum number of hits will be "5". Alternatively, the opening S
When 7 is located on the substrate, all of the five squares S71 to S75 forming this opening S7 do not hit the pattern. Therefore, the number of hits of the opening S7 becomes the minimum value "0". However, such a maximum value and a minimum value are not always obtained, and depending on the unevenness of illumination and the degree of unevenness of the substrate or pattern surface, the maximum number of hits is "5" even when the opening S7 is located on the pattern. , Or the number of hits may be larger than the minimum value “0” even when the opening S7 is located on the substrate. If one opening is formed by about 5 squares, the pattern and the substrate can be distinguished without any trouble even in such a case.

FIG. 7 is a block diagram of an arrangement determination circuit 40 having a pattern / board identification function. In this figure,
A signal from a square forming each opening (“1” if the pattern hits, “0” if no hit) is added by the adder 76 for each opening, and then compared with a predetermined threshold value by the comparator 77. It The threshold value is “3”, for example, and when the addition result of the adder 76 is “3” or more, the comparator 77 outputs “1”. That is, if the addition result is in the range of "3" to "5", it is determined to be a pattern, and if it is in the range of "2" to "0", it is determined to be a substrate. The determination results (pattern; "1", substrate determination; "0") for each of the openings S1 to S7 are again added by the adder 78, and the addition result (which becomes the value of the pattern of interest) is determined by the comparator 79. It is compared with a threshold value (an appropriate value obtained by an experiment or the like). When the threshold is exceeded,
It is determined that the positional relationship between the pattern of interest and the surrounding pattern is a proper arrangement that satisfies the regularity (“1” is output).
Alternatively, if the threshold value is not exceeded, it is determined that the layout is improper (“0” is output).

As shown in FIG. 8, the output ("1" or "0") of the arrangement determining circuit 40 is either a candidate signal from the first dictionary 36 or a candidate signal from the second dictionary 37. Is input to the defect determination circuit 38, which selects the candidate signal from the first dictionary 36 when the output of the placement determination circuit 40 is “1”, that is, when the placement is appropriate. On the other hand, when the output of the arrangement determination circuit 40 is “0”, that is, when the arrangement is inappropriate, the candidate signal from the second dictionary 36 is selected and output.

Here, the first dictionary 36 and the second dictionary 37.
The content of is shown in FIG. 9, for example. When inputting radial code 1 (disconnection), radial code 2 (short circuit) or radial code 3 (thin), both dictionaries output candidate signals indicating "abnormal", but radial code 4
When (copper remaining) is input, the first dictionary 36 outputs a candidate signal indicating “abnormal”, while the second dictionary 37 outputs a candidate signal indicating “normal”.

This means that when the quality determination is performed using two pieces of shape information and arrangement information, the first dictionary 36 and the second dictionary 36 are used.
The content of the first dictionary 36 is the same as the content of the second dictionary 37 when the quality determination is performed using only the shape information (in other words, the arrangement information is not required). Means to That is, when the determination result of the placement determining circuit 40 is “1” (appropriate placement), the candidate signal (“abnormal”) from the first dictionary 36 is selected by the defect determining circuit 38, as shown in FIG. On the other hand, when the determination result of the placement determining circuit 40 is “0” (inappropriate placement), the candidate signal (“normal”) from the second dictionary 37 is the defect determining circuit as shown in FIG. Selected at 38.

Therefore, as in the case of FIG. 17B, when the pattern 25 having an improper shape is present at the proper position, the judgment result of the arrangement judging circuit 40 becomes "1", and the first judgment is made.
The defect determination circuit 38 selects the candidate signal (“abnormal”) from the dictionary 36. On the other hand, as shown in FIG. 17C, when the pattern 26 having the inappropriate shape and the inappropriate shape exists, the determination result of the placement determining circuit 40 becomes “0”, and the candidate from the second dictionary 37 is obtained. The signal (“normal”) is selected by the defect determination circuit 38. As a result, even if the pattern has an improper shape, its position is not correct, that is,
If it exists at a position outside the regularity of the pattern, it can be determined as normal and the yield can be improved.

According to the above window, one opening in the center and six openings around it are combined, so that, for example, as shown in FIG. 12, a pattern corresponding to one opening 41 in the center. Is inconvenient if it is located in the peripheral part (hatched part) of the image. That is, in this case, some of the surrounding openings 42 to 47 (four in the example of C in the drawing, 42, 45, 46, and 47) are out of the image, so the number of hits is reduced by that amount, and the pattern Even though it is located on the upper side, it will be erroneously determined to be on the substrate. To avoid this, if even one pattern hits in the image of the hatched portion, "1" is forcibly given to the opening outside the image.

Further, in the embodiment, the two dictionaries 36 and 37 are used.
The output of is selected by the defect judgment circuit.
The present invention is not limited to this. For example, FIG.
As shown in FIG. 3, one dictionary may be provided with a flag (0: reference, 1: not reference) as to whether or not to refer to the arrangement information. In FIG. 13, reference numeral 50 is a dictionary including a flag indicating whether to reference a candidate signal and arrangement information,
The candidate signal (abnormal) extracted from the dictionary 50 is sent to the first defect determination circuit 51 and the second defect determination circuit 52, and the candidate signal logically inverted from abnormal to normal by the inversion circuit 53 is 1 defect determination circuit 51. The placement determination result of the first defect determination circuit 51 is “1”.
If it is (appropriate placement), a non-inverted candidate signal (abnormal) is selected, or the placement determination result is "0" (unsuitable position).
If so, the output of the inverting circuit 53, that is, "normal" is selected. In the second defect determination circuit 52, the flag is "1".
The candidate signal (abnormal) from the dictionary 50 is selected in the case of (not referring to the placement information), and the output of the first defect determination circuit 51 is selected in the case of the flag being “0” (reference to the placement information). .

According to such a configuration, the same operation as that of the above-described embodiment can be obtained, and since there is one dictionary, the configuration can be simplified. Although the above embodiment assumes a window having one opening in the center and six openings around it, the shape of the window is not limited to this. The point is to match the regularity of the target pattern. For example, a cross-shaped array as shown in FIG. 14A, a multi-intersection array as shown in FIG. 14B, and a crossover array as shown in FIG. 14C. Various modifications are conceivable, such as a rectangular array, a rhombic array as shown in FIG. 14D, or a square array as shown in FIG. 14E.

[0024]

According to the present invention, since the positional relationship of patterns is added to the judgment material, excessive judgment can be avoided and, for example, a pattern having an improper shape exists at a position deviated from the proper position. The case can be determined to be normal, and the yield can be improved.

[Brief description of drawings]

FIG. 1 is a principle configuration diagram of the present invention.

FIG. 2 is an overall block diagram of an embodiment.

FIG. 3 is a conceptual diagram of a detection window (window) according to an embodiment.

FIG. 4 is a correspondence diagram of a window and a pattern of interest according to an embodiment.

FIG. 5 is a configuration diagram of a window using a shift register according to an embodiment.

FIG. 6 is a correspondence diagram of each opening of the window and the grid of the shift register according to the embodiment.

FIG. 7 is a configuration diagram of a placement determination circuit according to an embodiment.

FIG. 8 is a configuration diagram of a main portion including first and second dictionaries and a defect determination circuit according to an embodiment.

FIG. 9 is a conceptual diagram of first and second dictionaries of one embodiment.

FIG. 10 is a state diagram in the case of proper placement determination according to an embodiment.

FIG. 11 is a state diagram of an improper arrangement according to an embodiment.

FIG. 12 is a diagram illustrating an inconvenience at an image end portion according to the embodiment.

FIG. 13 is a configuration diagram when one dictionary according to an embodiment is used.

FIG. 14 is another configuration diagram of the window according to the embodiment.

FIG. 15 is an external view of a main part of a printed circuit board.

FIG. 16 is a block diagram of a conventional example.

FIG. 17 is a pattern inspection state diagram of a conventional example.

[Explanation of symbols]

 31: sample 32: CCD camera (imaging means) 34: storage circuit (storage means) 39: placement detection circuit (window setting means) 35: placement determination circuit (position measurement means) 36: first dictionary (first determination) Means) 38: Defect judging circuit (second judging means)

Claims (1)

[Claims] 1. A sample having a large number of regularly arranged patterns on its surface, b) a photographing means for photographing a surface image of the sample, and c) a storage means for holding the image. d) window setting means for setting a window to be opened at a position taking into account the regularity of the plurality of patterns, and e) superposing the window on the image held in the storage means, and the pattern of interest and its surrounding pattern. Position measuring means for measuring the positional relationship of f), f) first judging means for judging whether the pattern shape is normal or abnormal based on the image held in the storing means, and g) the measurement result of the position measuring means. If the regularity is satisfied, the determination result of the first determination means is output as it is, while if it is not satisfied, the determination result of the first determination means is displayed. A pattern inspecting device comprising: a second determining unit that outputs a normal state.