Computational Lithography

Chapter 8

Other RET Optimization Techniques

As a supplemental to the OPC and PSM optimization algorithms discussed in Chapters 5 and 7, a variety of techniques to improve the performance of OPC and PSM optimizations are described in this chapter. First, a double patterning method is developed based on the generalized PSM optimization framework described in Section 5.4. Second, a post-processing based on 2D discrete cosine transform (DCT) is presented to simultaneously reduce the complexity of the mask pattern and the output pattern error. Finally, a photoresist tone reversing method is described to print extremely sparse patterns on the wafer.

8.1 Double-Patterning Method

In Section 5.4, a generalized PSM optimization algorithm is developed to design multiphase PSMs capable of generating mask patterns with arbitrary Manhattan geometries. Although this approach is effective in eliminating the phase conflict, it usually results in a phase-shifting mask, which is difficult to fabricate [40, 41]. In the event that multiphase masks are difficult to fabricate, but the goal is to still synthesize masks with arbitrary geometry, a double patterning PSM optimization method is developed in this section. At each stage the PSM masks are constrained to have two phases. The two-stage patterning method can lead to high-fidelity output pattern reproduction at the expense of a more complex exposure process. Thus, the double patterning optimization method is an alternative to the multiphase PSM ...