Effect of Substrate Potential on Al2O3 Films Prepared by Electron Beam Evaporation

Abstract

In previous experiments the authors explored the deposition of Al2O3 films on silicon by electron-beam evaporation. These films exhibited unstable offset voltages, measured by C–V techniques, and poor radiation resistance. This paper describes the continuation of this study, with the discovery that electrostatic charges developed on the substrates during the electron-beam deposition process play a significant role in affecting the electrical and physical film properties. These investigations indicate that the buildup of negative charge from stray electrons on insulating substrates apparently repels oxygen ions thus altering the stoichiometry of the final film. Control of this charge buildup alters both the electrical and optical properties of the Al2O3 films. Al2O3 films varying in shades of brown to completely clear are produced by altering the electrostatic fields from −22 V (for the darkest films) measured between substrate and ground to less than −2 V between substrate and ground (for the clearest films). Ultraviolet spectra, radiation results, and C–V data indicate that a significant amount of dissociation takes place from the evaporant source during the electron-beam deposition.