Automatic Focusing and Astigmatism Correction Method based on Fourier Transform of Scanning Electron Microscope Images

概要

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A new method for automatic focusing and astigmatism correction of electron optics has been proposed. The method consists of the following 6 steps : (1) Obtain scanning electron microscope (SEM) images i_1(x, y), i_2(x, y) under two focusing conditions. (2) Obtain Fourier transformed images of i_1(x, y) and i_2(x, y), I_1(k_x, k_y) and I_2(k_x, k_y). (3) Obtain a characteristic function R(k_x, k_y) = ln(I_1(k_x, k_y)/I_2(k_x, k_y)). (4) Repeat the above steps under different focusing conditions. (5) From the change in R(k_x, k_y), calculate the change in beam sharpnesses in different directions. (6) Correct the astigmatism and adjust the focus. R(k_x, k_y) is independent of the sample shape, and is independent of the beam shape in the case of a character beam. Therefore, this method can be applied both to a SEM and to an electron beam writer with a character beam.
社団法人応用物理学会の論文
1999-02-15