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For low k1 lithography process, some minor facotrs' impacts are strongly enhanced such as MEEF, lens distortion, wafer topography, pattern density and so on. How to minimize those impacts becomes more and more important. Unfortunately those impacts are not controlled by lithography process itself and caused by other modules such as layout design, integration schemes, mask making, film deposition, CMP and so on. A method to reduce those impacts is quietly needed. DFM (Design for Manufacturability) is a popular and effective approach to get more robust process by reducing pattern loading effect. In this paper, we will show our study on wafer local topography in low k1 lithography process. Products with sub-90nm design rules and different device structures are processed by pure KrF process. The maximum 0.82NA KrF scanner tools are used. The k1 factor is low enough to enhance the impacts. By using DFM solutions, we had resolved these issues and the process window are obviously improved.

Amid continuing reduction in average wafer sale price, in the past 30 years, the industry witnesses continuous shrink in production design rules in order to gain performance per unit area on each silicon wafer. While the mainstream wafer production is at 65 and 45 nm with 300 mm diameter wafers, to maintain cost competitiveness, 200 mm wafer companies also start to explore production feasibility under groundrules smaller than 110 nm while maintain the cost advantages in KrF exposure tools systems. The k1 factor under 110 nm with 248 nm illumination will be below 0.35. For example, at 90 nm, at 0.80 NA, the k1 factor is 0.29, which owns the same level of complexity in optical proximity correction compared to 65 nm at 0.93 NA with 193 nm exposure tools. However, due to that the KrF photoresists are originally designed for ground rules greater than 110 nm, such as, 130 nm structures, it is relatively unknown how feasible it is to extend their performance below 110 nm. In this paper, we will show our initial study in CD process window and CD through pitch performance at 90 nm groundrule for 3 critical layers - Active, Gate poly and Contact. The wafer data in process window and optical proximity will be analyzed and compared with performance specifications of the current exposure tools.