Efficient Mask Design for Inverse Lithography Technology Based on 2D Discrete Cosine Transformation (DCT)

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An efficient algorithm is proposed for fast synthesis of low complexity model-based inverse lithography technology (ILT) and phase shift masks (PSM) to improve the resolution and pattern fidelity in optical microlithography. The patterns on the mask are transformed into frequency space using 2D discrete cosine transformation (DCT). The solution space is thus changed to frequency space from real space. By cutting off high frequency components in DC spectrum, the dimension of the solution space is greatly reduced. Using a gradient-based algorithm, we solve the inverse problem in incoherent and partial coherent imaging systems with binary, 6%EPSM and APSM mask. Good fidelity images are achieved.