Estimation of electron beam profile from SEM image by using wavelet multiresolution analysis

Abstract

We have tried to estimate the electron beam profile from a scanning electron microscope (SEM) image by using Wavelet multiresolution analysis for in-process SEM inspection. At first, an ideal secondary electron (SE) profile for step edge is calculated by using the Monte Carlo simulator. Then the SE profiles observed by the electron beam with Gaussian profiles are simulated with the electron beam diameter as a parameter. Wavelet analyzed results of SE profiles show that it is possible to estimate the size of electron beam profile from the Wavelet coefficient of SE profile. Next we apply the proposed estimation method to SEM images of test pattern. The procedure is as follows. 1) Noise included in SEM images is reduced by using the denosing method by Wavelet transform. 2) The SE profile for edge is extracted from a SEM image and is normalized. 3) The normalized SE profile is decomposed by Wavelet multiresolution analysis. 4) By comparing the obtained Wavelet coefficient of SE profile with the relation between the electron beam diameter and the Wavelet coefficient, the electron beam profile is estimated. Proposed procedure was applied to the SEM image of test pattern to obtain the beam profile.