A novel pre-processing approach for OPC using LSMR

In the integrated circuit manufacturing process, particularly in lithography, resolution enhancement techniques, such as optical proximity correction(OPC), are extremely important. To improve pattern fidelity and CD uniformity in lithography, it is necessary to generate appropriate sub-resolution assist feature(SRAF) and an initial mask as a pre-processing step for OPC. In this paper, we propose a novel method for generating an appropriate initial mask and SRAF, which we refer to as Quasi-Inverse Lithography Technique(QILT). The optical image intensity is expressed as a linear combination of the squares of the convolutions of the sum of coherent systems(SOCS) kernel and the mask function. Although solving this inverse problem directly is challenging, it can be reduced to a linear equation and solved approximately. To address this linear problem, we adopt the LSMR method, a conjugate residual method applied to the normal equation. This paper provides a detailed description of our method and demonstrates its effectiveness.