Study on an inspection method of repeated pattern

LCD(Liquid Crystal Display) became one of the most popular display devices in these days. The TFT(Thin Film Transistor) substrate is the key part of active matrix LCD. TFT is an electrical device to activate a displaying cell. To display an image precisely, several millions of identical transistors are patterned on a wide glass panel. Since a minute damage on the pattern can causes a serious defect to display, it is important to inspect the pattern precisely. Taking the advantage of the fact that the pattern of good cell should be identical to that of adjacent cells, it would be a convenient way to compare a cell with its neighbor cells to find a defect. In practical applications, if the period of repetition could be represented as an integer number of digitized image pixel, it would be possible to find a damaged pixel readily. However, the period of pattern depends on the product size and cannot be determined as an integer always. In this paper, so called, pseudo-matching magnification algorithm has been introduced to solve the problem. A digital image was magnified and period of pattern can be determined as an integer from the processed image. It has been shown that the defects could be enhanced after the preprocessing of digital image. As a result, a TFT-pattern inspection system has been developed and it has been shown the proposed method is compatible for the inspection of repeated pattern.