Comparison of hydrogen silsesquioxane development methods for sub-10 nm electron beam lithography using accurate linewidth inspection

Abstract

There is presently considerable interest in determining the resolution limits of hydrogen silsesquioxane as a negative tone electron beam resist. Various techniques for improving the resolution and contrast have been reported in the literature. These include the use of concentrated tetramethyl ammonium hydroxide, hot development, sodium hydroxide, salty development, and the use of dilute hydrofluoric acid dips. One difficulty in comparing the results from different research groups is that measurements are made using different electron microscopes working at various beam energies. Different groups frequently use different resist thickness and a variety of electron beam lithography tools operating at differing beam energies. These variations mean that useful comparisons at the nanometer scale are often not possible. This paper compares different development techniques using a unified inspection regime and a high contrast backscattered electron detector. The paper also considers important issues such as resist sensitivity, process latitude, and processing delay effects.