Direct Measurement of Distortion of Optical System of Lithography

In general, one of the methods used to measure distortion is to use the full image of the regular pattern. However, because of low accuracy, this method is mainly used for an optical system such as a camera.. In order to measure distortion with high accuracy less than 1um, one can use the method of measuring the exact position of a mask image. In this case, a high accuracy stage with a laser encoder is required. In this paper, we investigate measurement of the distortion of high accuracy with a simple manual stage. The main idea is that we split and measure the mask image with the overlapping area by using CCD or CMOS, and then we get an exact position of the mask image by integrating the adjacent split images. We use the Canny Edge Detection method to get the position information of the mask image and we researched the process to exactly calculate distortion by using coordinate transformations and a least square method.