A new auto-focus method in critical dimension measurement SEM

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We have developed a new auto-focus method using the image processing technology. This method consists of two steps. The first step is the preset of the objective lens condition with the feedback of Z-sensor. In the second step, the pattern recognition of a target hole pattern is performed prior to auto-focusing scan in order to scan E-beam accurately over the pattern. The measurement repeatability (3/spl sigma/) can be achieved within 3.9 nm. The pass rate of 98.7% can be realized in the present auto-focus method.

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