POSITIVE AND NEGATIVE RESISTLESS LITHOGRAPHY OF GAAS BY ELECTRON-BEAM EXPOSURE AND THERMAL CL-2 ETCHING

Positive and negative lithographic patterns have been produced in epitaxial layers of GaAs, achieved by electron beam writing and subsequent etching by Cl2 gas at elevated temperatures. A latent image is formed in the native oxide which is either less resistant to thermal Cl2 etching (positive pattern) or more resistant to thermal Cl2 etching (negative pattern), depending on the electron beam dose. The pattern is stable in air for at least several weeks. The tone of the pattern also depends on the electron beam accelerating voltage, the etching conditions, and the thickness and initial state of the native oxide. Significant changes in the resulting lithography are due to changes in an oxide only a few monolayers thick. Both positive and negative patterns can be produced in adjacent areas with high contrast by variation of the electron-beam does. Initial Auger analysis suggests that chemical rearrangement of the native oxide occurs with electron beam exposure. The discovery that the native oxide on GaAs acts as both positive and negative resists opens tremendous possibilities for in situ processing and device fabrication.