Vertical lithography: controlling resist profiles in optical lithography with a large area electron beam

Abstract

An electron beam exposure method is described which provides a means of controlling the wall slope and edge profiles of developed patterns in photoresist. The method utilizes a large area, uniform (and near monoenergetic) electron beam exposure system with a programmable accelerating voltage and a precise electron beam dose monitor. Conventional optical lithography patterning is followed by a blanket electron beam exposure. Several variations of the process are described where the photoresist is exposed with the blanket electron beam before or after the development of the resist. The resist is exposed at selected doses of different accelerating voltages inducing a graded solubility at different depths in the resist layer. The process can be used advantageously for achieving undercut profiles in resist for lift- off patterning. Further refinements of the process can be used for micromachining applications and creating three dimensional molds for micromechanical structures.