Patent ID: 6448555
Filing Date: 2002-09-10
Classification: H01J

Abstract:
An electron microscope having a scanning beam for irradiating a desired region on a specimen with a focused electron beam while scanning the beam in two dimensions, for detecting a first signal from the irradiated region, and for obtaining a first two-dimensional image based on the first signal, said electron microscope comprising:a first detector for detecting said first signal and means for repeating said scan and, at the same time, accumulating said first signal to perform a sequence of measurements for obtaining said first two-dimensional image; a second detector for detecting a second signal from said desired region at spaced intervals during the time period in which said sequence of measurements for obtaining said first two-dimensional image are gathered, said second signal being different from said first signal; means for obtaining a second two-dimensional image based on said second signal at the beginning of said sequence of measurements and storing said second two-dimensional image as a reference image; automatic means (i) for repeatedly at spaced intervals causing the second detector to obtain a second two-dimensional image based on said second signal as said sequence of measurements progresses and for storing the second two-dimensional image obtained as an image to be compared and (ii) for comparing said second two-dimensional image with said reference image and finding the direction and amount of the displacement of said second image from said reference image successively during the time period in which said sequence of measurements for obtaining said first two-dimensional image are gathered; and means for repeatedly modifying the region scanned with said electron beam according to the found direction and amount of displacement.