Patent ID: 6965687

Claim:
A size checking method comprising: a first step of reading image data on a reference pattern and recognizing an edge direction of the reference pattern on the basis of pixel values detected at edge portions which are end portions as viewed in a width direction of the reference pattern; a second step of detecting edge points corresponding to the end portions as sub-pixels on the basis of the pixel values detected at the edge portions, and calculating a widthwise dimension of the reference pattern from the edge points; a third step of acquiring image data on a pattern under inspection; a fourth step of detecting edge points at each of edge portions which are end portions as viewed in a width direction of the pattern under inspection, said edge points of the pattern under inspection being detected with respect to edge portions located at the same position as the edge portions whose widthwise dimension is calculated by use of the reference pattern, and of calculating the widthwise dimension of the pattern under inspection, said edge points of the pattern under inspection as starting points; a fifth step of determining whether or not the pattern under inspection is defective on the basis of the widthwise dimension of the reference pattern and the widthwise dimension of the pattern under inspection; a sixth step of preparing a frequency distribution with respect to a dimensional error obtained on the basis of the widthwise dimension of the reference pattern and the widthwise dimension of the pattern under inspection, and varying a threshold value used in the second step when the edge points are detected as sub-pixels; said fifth step including, calculating a dimensional error on the basis of the difference between the widthwise dimension of the pattern under inspection and the widthwise dimension of the reference pattern, and determining an abnormal state when a value obtained by adding an offset value to the dimensional error is out of an allowable range; and said sixth step including, preparing a frequency distribution with respect to the dimensional error, which is based on both the widthwise dimension of the pattern under inspection and the widthwise dimension of the reference pattern, and varying the offset value or a threshold value which is that of either the reference pattern or the pattern under inspection, and which used in the second step when the edge points are detected as sub-pixels, on the basis of the frequency distribution.