Inverse Lithography with Structured Sub-Resolution Assist Features

With the continuous advancement of semiconductor manufacturing technology, integrated circuits now incorporate billions of mask pattern data. In the event of non-compliance with mask design rules before manufacturing, the entire mask needs to be re-optimized to address mask rule violations, incurring significant resource and time costs. In this paper, we address mask rule violations of width, space, minimum areas during the optimization process by constructing structured sub-resolution assist features (SRAFs) and incorporating them into the optimization process of inverse lithography technology (ILT) using the level-set method. An initial mask is calculated by combining the structured SRAFS and the optical proximity correction (OPC) region of the main features which excludes the SRAFs outside of the spacing spec. Level-set based IL T is further implemented incorporating mask rule checks (MRC) and corrections during the optimization process: features with spacing violations are merged while features with width violations are expanded to a structured formation; the contour of the detected non-compliant locations are fixated, while allowing the contour of the MRC-compliant features to evolve. This ensures that features already corrected will not experience new or previously encountered violations during the subsequent optimization iterations. Upon completion of the level set optimization, structured SRAFs with fixed widths will be defined. Simulation results indicate that the inclusion of mask rule check and correction dose compromise pattern fidelity with comparable performance, it can effectively solve the problem of mask rule violation. Furthermore, by constructing structured SRAFs, mask complexity is significantly reduced.