Automatic Focus Algorithm for IC Wafer Image Sampling by Adaptive Lifting Scheme Denoising

Abstract

High SNR (signal to noise ratio) image is deeply needed in the precise analysis of IC wafer micro-image; current denoising algorithms cant reach the analytic precision in some level. In tins paper, one image denoising algorithms is putted forward based on adaptive lifting scheme, the construction of Haar wavelet and CDF (2,2) is given, the signal is decomposed by wavelet base Haar or wavelet base CDF (2,2) adaptively along four directions (horizon, verticality, 45 degree and 135 degree) in the step of predicting, the wavelet coefficients are calculated separately at each direction, all the thresholds are gained using wavelet soft-thresholding principle, the optimal thresholds minimize the error of the result as compared to these the signal is decomposed along horizon and verticality. Finally the definition of the image is appraised with gray gradient judging function, the experimental data shows that the focus error is no more 4 um, the display definition of the image is improved.