| 摘要 |
PROBLEM TO BE SOLVED: To provide an autofocus deciding method which can make a focusing even if a specimen has a surface which can be regarded as a flat plate. SOLUTION: The autofocus method includes the steps of: causing focal condition of the charged-particle beam to be varied in steps over the specimen; scanning a strip-shaped region over the specimen with the charged-particle beam whenever the focal condition is varied; storing data obtained concomitantly with the scanning and a focus value corresponding to this focal condition into a memory as image data; reading the image data from the memory and dividing the data into plural sets of data on a data domain such that the sets of data correspond to plural subregions; finding characteristics of brightness at plural kinds of focus values for each of the plural sets of data; accumulating characteristics of a certain kind among the plural kinds of characteristics for each focus value; averaging the accumulated characteristics and taking the averaged characteristics as a focus function; approximating the focus function by a quadratic curve; finding a focus value at a peak point from the quadratic curve; and setting the focal condition of the charged-particle beam based on the found focus value. COPYRIGHT: (C)2009,JPO&INPIT
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