Electron Beam Lithography

Electron beam lithography is of the highest resolution in nanoscale patterning. It works the same way as optical lithography by exposure of a polymer resist but does not need a mask. Its high resolution patterning is ensured by finely focused beam size. This chapter starts by explaining the principle of electron optics as well as the ten basic configurations and six key specifications of an electron beam lithography system. The feature unique to electron beam lithography is the electron scattering in solid materials and the associated proximity effect. Using the author’s own Monte Carlo simulation program, such effect is vividly explained by simulated electron scattering trajectories and point spread function of deposited electron energy in resist. Methods to correct such proximity effect are also presented. A range of resist materials used in electron beam lithography are discussed such as polymethylmethacrylate (PMMA) and hydrogen silsesquioxane (HSQ), chemically amplified resists, inorganic resists, even ice as a resist, as well as some special development processes which can help to enhance the lithography resolution. Based on the author’s own experience, ten factors that can influence the ultimate resolution of electron beam lithography are explained. While electron beam lithography is primarily for small batch patterning and mostly used in scientific research, high-throughput patterning is possible by variable shaped beam and multi-beam systems. The final part of this chapter explains how they are employed for making DUV and EUV optical lithography masks in the latest IC manufacturing.