Theoretical analysis of line-edge roughness using FFT techniques

Although the line-edge roughness of resist patterns is becoming a serious problem as the size of resist patterns are decreased, quantitative analysis has rarely been seen so far. We investigated the line-edge roughness of ArF resist patterns using the FFT (Fast Fourier Transform) method. We found that all-the observed line-edge roughness had a specific FFT spectrum shape composed of a flat area at low frequency and a 1/root f component area at high frequency. The amount of line-edge roughness is independent of dose and linewidth but has a strong dependence on defocus. The patterns formed using TSI (Top-Surface Imaging) also have similar FFT spectrum shapes. Based on these findings, we proposed a line-edge roughness simulation method that achieves the observed FFT spectrum.