| 摘要 |
The invention relates to a method for focusing an object in e.g. a scanning electron microscope. A first image of an object is acquired using a first focal value F 1 , and the defocus dF 1 of the image is estimated by comparing the image with a series of through-focus images of a master object. Said through-focus series comprises images of similar areas of another, similar object. The focus of the SEM is now corrected by setting the focal value to F 1 - dF 1 . However, as known to the person skilled in the art, there is a chance that the correct value is F 1 + dF 1 , as equal amounts of under- and over focus give very similar images. Therefore the defocus is estimated again, and when the defocus is larger than the first defocus, the focal value is set to F 1 + dF 1 .
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