Experimental study of line-end shortening

Line end shortening is a phenomenon originating from a combination of imperfect aerial image formation of the line end and acid diffusion in chemically amplified resists. For geometries at 0.25 micrometers and below, line end shortening has become a concern in photolithography. Because of the complex coupling between the optical effect and the acid diffusion, accurate and reliable prediction of line end shortening form theory is difficult. Experimental characterization of line end shortening is thus required. In this study, line end shortening was measured on OPAL CD SEM using a special measurement algorithm. Our experimental results show that both NA and (sigma) affect line end shortening, higher (sigma) are preferred to reduce line end shortening. PEB time has little effect on line end shortening, while line end shortening increases with PEB temperature only when it reaches a chemical mechanism transition temperature. The most effective way to minimize and control line end shortening is through optical proximity correction. By optimizing the serif size, not only the desired line end dimension can be achieved, but also its process latitude is greatly improved.