Proximity effect correction in electron-beam lithography

Abstract

Electron-beam fabrication offers several important advantages for lithography, including a capability of geometries smaller than one micrometer, a high adaptability to automation and the ability to write directly on a Si wafer without the need for a mask. However, for submicron patterns, a proximity effect is observed by the behavior of incident electrons in a resist. In electron-beam lithography the exposure intensity distribution (hereafter EID) is an essential physical quantity for implementing a proximity effect correction. There are many correction methods and several methods have been tried to correct for practical devices. However, the variation of the EID along the distance into the resist from the surface is neglected, and only a two-dimensional EID is presented in those articles. The present paper describes experimental and theoretical study on a correction method of the proximity effect which contains the consideration of the three-dimensional profile of a resist. It has been found from a Monte Carlo simulation that a cross-sectional profile can be controlled by an additional exposure at the vicinity of a pattern edge. With this method, for example, an undercut resist pattern, which is suitable for a lift-off process, can be obtained, avoiding as a whole the overdose on a pattern. A 0.5 μm line and space pattern with 1 μm thickness PMMA has been easily obtained, namely, when under-developed, the wall profile of the resist becomes rather steep, and when properly developed, the profile becomes undercut.