A New Level-Set-Based Inverse Lithography Algorithm for Process Robustness Improvement with Attenuated Phase Shift Mask

Inverse lithography technology (ILT) is one of the promising resolution enhancement techniques (RET), as the advanced integrated circuits (IC) technology nodes still use the 193nm light source. Among all the algorithms for ILT, the level-set-based ILT (LSB-ILT) is a feasible choice with good production result in practice. However, existing ILT algorithms optimize mask at nominal process condition without giving sufficient attention to the process variations, and thus the optimized masks show poor performance with focus and dose variations. In this paper, we put forward a new LSB-ILT algorithm for process robustness improvement with attenuated Phase Shift Mask (att-PSM) which is extensively used in the semiconductor foundries. In order to account for the process variations in the optimization, we adopt a new form of the cost function by adding the objective function of process variation band (PV band) to the nominal cost. The test patterns are from the M1 layer of a 28nm layout. Experimental results show that our new algorithm has a larger process window (PW) and reduces the process manufacturability index (PMI) by 41.37% compared with the LSB-ILT algorithm without PV band consideration.