A New Autofocus Using Image Processing Techniques in Critical Dimension Measurement SEM

摘要

We have developed a new autofocus method us- ing image processing techniques. This method consists of two steps. The first step is the preset of an objective lens condition with the aid of the feedback of Z-sensor. Next, a hole pattern to be measured is detected using the pattern recognition. In the second step, the E-beam is shifted to the center of hole pattern and scanned across the axis of a pattern. The exciting current of the objective lens is changed at constant intervals, where the cen- ter position of the range is the preset value of the Z-sensor.