Pattern inspecting method and pattern inspecting device

Details Pattern inspecting method and pattern inspecting device Pattern inspecting method and pattern inspecting device

1999-02-22

2001-04-24

Bella, Matthew C. (Department: 2621)

Image analysis

Applications

Manufacturing or product inspection

C382S147000, C382S172000, C382S205000

Reexamination Certificate

active

06222935

ABSTRACT:

This is a Continuation-in-Part of International Application PCT/JP98/02838 with an international filing date of Jun. 25, 1998.
1. Field of the Invention
The present invention relates to a pattern inspection method of inspecting patterns of printed wiring boards, printed circuit boards, or the other articles with patterns, and an apparatus therefor.
2. Disclosure of the Prior Art
Printed wiring boards or printed circuit boards are usually manufactured through a plurality of manufacturing stages. As an example, a plan view of a printed wiring board is shown in FIG.
23
. In a first stage, circuit patterns
2
are formed on substrates
1
, and also through holes
3
or via-holes
4
are formed. In a second stage, a metal such as gold is plated on IC connecting pads
5
, and solder-resist patterns
6
or silk-printing patterns (letter
7
and mark
8
) are formed. In
FIG. 23
, the numeral
6
E designates an edge of the solder-resist pattern
6
.
In the first stage, defects such as short circuit, chipping, projection, pinhole, residual copper, thickening, thinning, position shift of through-hole, and disconnection of circuit pattern are inspected. These inspections can be carried out by an automatic inspection apparatus. However, since over-detection of defects frequently occurs, confirmation is needed after the automatic inspection. Thus, there is room for further improvement of the inspection reliability.
On the other hand, in the second stage, defects such as position shift, bleeding, and blur of solder-resist pattern, position shift, bleeding and blur of silk-printing pattern, projection, contamination, roughness, adherence of extraneous substance, and chipping of pad are inspected. A visual inspection by the naked eye, or using a magnifying glass is usually performed to inspect these defects. In particular, the inspection of the pads
5
needs to find a fine defect having a size within a range of about 5 to 20 &mgr;m. For this purpose, it is preferred to perform a visual inspection by using a microscope with a magnifying power of 10 to 40. However, due to the visual inspection by human, there are problems such as a low inspection efficiency and individual variations in inspection standard.
In the past, there are various kinds of methods of automatically inspecting patterns. For example, an inspection method of a circuit pattern is disclosed in Japanese Patent Early Publication [KOKAI] No. 9-178442. In this method, a defect of a pattern to be inspected is detected according to a comparison with a reference data obtained by taking images of a plurality of reference patterns. However, since careful consideration is not given to the preparation of the reference data, it is not sufficient to provide high inspection accuracy. In addition, it is desired to provide a pattern inspection method capable of coping with the following situations.
With respect to a specific pattern classification such as circuit pattern, solder-resist pattern, or silk-printing pattern, there is a case that a large acceptable amount of position shift is set. In such case, it is needed to perform the inspection while considering the acceptable amount of position shift.
There is a case that an acceptable defect-size of solder-resist pattern is much different from the acceptable defect-size of silk-printing pattern or IC connecting pad. For example, as shown in
FIG. 23
, although defects A such as a projection, contamination and a chipping, of the pads
5
are very fine, they are decided as bad quality. On the other hand, since defects B such as a pinhole, residual copper and a large chipping, of the circuit pattern
2
do not come into problem with respect to circuit pattern width, they are decided as good quality. Although a defect C is a fine flaking of the solder resist pattern
6
, it is decided as bad quality. In addition, the inspection accuracy may be influenced by different inspecting conditions, e.g., lighting conditions. Thus, it is needed to perform the inspection while considering the kinds of defects and the inspecting condition.
There is a case that it is desired to decide a printed article having a bright spot, in a dark large area as bad quality, and as good quality a printed article having a bright spot at an edge of a dark large area, a printed article having a bright spot in a dark small area, or a printed article having a bright spot in a large area of neutral tint.
There is a case that a configuration or position of a thin line of a specific color has important information. In such a case, it is needed to inspect a specific region according to a severe inspection standard and the other region according to an average inspection standard.
SUMMARY OF THE INVENTION
A primary object of the present invention is to provide an improved pattern inspection method, which is capable of coping with the above-explained situations. That is, the pattern inspection method includes the following steps. A plurality of pattern classifications are provided according to pixel-value ranges of a reference-image data obtained from at least one reference pattern. Reference-data preparing parameters are set every pattern classification. With respect to each of pixels of the reference-image data, values of the pixel and required neighbor pixels defined around the pixel are compared with the pixel-value ranges. When the pixel and the neighbor pixels are within a single pixel-value range, the pixel is decided as a uniform portion, and the reference data of the pixel is prepared according to the reference-data preparing parameters of the pattern classification corresponding to the single pixel-value range. When at least one of the neighbor pixels is included in a different pixel-value range from the pixel, the pixel is decided as a step portion, and internal and external pattern classifications of the step portion are determined, so that the reference data of the pixel is prepared according to the reference-data preparing parameters of at least one of the internal and external pattern classifications. Thus, the reference data of each pixel of the reference-image data is obtained. Next, an inspection-image data is obtained by taking an image of a pattern to be inspected, and then is compared with the reference data to detect a defect of the pattern. The pattern inspection method of the present invention improves the reliability of pattern inspection and prevents over-detection of defects.
In a preferred embodiment of the present invention, the pixel and the neighbor pixels are arranged in an M×M-pixel window in which “M” is an integer, and the pixel is disposed at a center of the pixel window. In particular, it is preferred that the pattern inspection method also includes a re-checking treatment of the uniform portion. In the re-checking treatment, a re-checking parameter is set every pattern classification. With respect to the pixel decided as the uniform portion by using the M×M-pixel window, the re-checking parameter corresponding to the pattern classification of the pixel is compared with the integer “M” of the M×M-pixel window. When the re-checking parameter has a larger integer “N” than the integer “M”, an N×N-pixel window having the pixel as a center pixel and neighbor pixels arranged around the pixel is provided. Pixel values in the N×N-pixel window are checked to cancel the decision of the uniform portion when at least one value of the neighbor pixels of the N×N-pixel window is included in a different pixel-value range from the center pixel. This re-checking treatment improves the reliability of the decision of the uniform portion. In particular, this re-checking step is useful to prevent the occurrence of wrong inspection at the vicinity of a pattern edge of silk-printing pattern or solder-resist pattern.
It is preferred to obtain the reference-image data according to one of first and second methods, as explained below. In the first method, images of a plurality of reference patterns are taken to prepare image data. After adjusting positions of the image data, an

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