Fast proximity correction with zone sampling

Proximity effects cause integrated circuit features to be distorted when compared to the original mask pattern. These effects are becoming widely recognized as serious barriers to achieving effective half-micrometer and smaller wafer lithography processes. A promising remedy for proximity effects is to adjust mask feature shapes to compensate for predictable distortions in the wafer lithography process. Proximity effects are systematic -- the effects on a pattern repeat when printed with the same equipment under the same process conditions. Predicting proximity distortions is a non-trivial problem. The distortions are functions of the size and shape of each feature as well as the sizes, shapes, and spacings of nearby features. Imaging characteristics of the exposure tool, resist and etch characteristics, and effects from the underlying substrate all contribute to wafer feature distortions. We present a general method for computing proximity-corrected shapes. A technique we call "zone sampling" provides accurate models of proximity behaviors with optimum computational efficiency. Proximity behavior for arbitrary layout configurations is derived from two-dimensional density measurements (zone samples) computed from IC layout pattern data. Zone sampling provides a complete "behavior model" of combined, non-linear proximity effects, including optical, process, and underlying substrate mechanisms.