Multiple-stage optical proximity correction

Standard industry practice in model-based optical proximity correction is to use a single-stage model in which mask, optical projection, resist, and etch effects are lumped together [J.P. Stirniman, M.L. Rieger, SPIE Proc. Optical/Laser Microlithography X, Vol. 3051, p294, 1997.] Through the 130nm node, where optical projection and resist effects dominated proximity errors, the single-stage model approach has proven to be a convenient, accurate and efficient methodology. A disadvantage of this approach is its lack of modularity. If any one component of the process changes, a new lumped model must be built, usually by shooting a new set of test wafers from which to collect calibration data. Staged correction, in which corrections for different process steps are carried out sequentially, has become an appealing alternative to single-stage correction for the 130 nm node, 100 nm node and beyond. In addition to providing potential "mix and match" capabilities, the component corrections can be better optimized for unique behaviors in the constituent process steps. Thus, the overhead of sequencing through separate corrections can be offset by increased correction efficiency at each step to achieve accuracy equal to, or better than, that of a single stage correction with a lumped model. Separate corrections for etch and for litho/resist have been put into use in the industry and an additional stage for mask correction has also been considered. In this paper we demonstrate advantages of staged correction over the traditional single-stage correction. Advantages and disadvantages of different staged correction flows will be examined, with particular emphasis on the flow where an etch correction is followed by a lithography correction.