Estimation of electron probe profile from SEM image through wavelet multiresolution analysis for inline SEM inspection

We propose an analytical estimation method of the electron probe profile from an SEM image through the wavelet analysis of the multiscale information for inline SEM inspection. Defocused electron probe profiles are calculated based on wave optical theory. The calculated profiles are well approximated with the distributions composed of several Gaussian distributions with different center positions and variances. Analytical equations to estimate standard deviations of blurring Gaussian functions included in the defocused electron probe profile from a sequence of wavelet transform modulus maxima are derived. By using a noisy blurred step edge signal, the estimation accuracy was evaluated as a function of SNR with the standard deviation of blurring Gaussian function as a parameter. The accuracy of better than 15% is obtained when the SNR becomes larger than 10. Our analytical estimation method is applied to the simulated secondary electron intensity profile blurred with the defocused electron probe profile. The probe profile similar to the calculated one is estimated.