Al 2 O 3 Films Prepared by Electron-Beam Evaporation of Hot-Pressed Al2O3 in Oxygen Ambient

Abstract

This paper describes the deposition as well as the electrical and physical evaluation of Al2O3 films on silicon substrates prepared by reactively evaporating Al2O3 in an oxygen ambient. The Al2O3 was evaporated using an electron-beam gun. Several ambient parameters were varied in order to obtain their effects on film properties. Variations in the substrates preheating, in temperature of the substrates during evaporation, and rates of evaporation were made. Measurement of MOS capacitance vs voltage provided data concerning the interface properties between oxide and silicon as well as conduction of the Al2O3 with applied bias conditions. These measurements indicated that mobile charge manifested by offset voltage in the C-V plots could be reduced below 7×1011 e/cm2 either by post heat treatments or deposition on heated substrates. The dielectric constant of these films at 100 kHz ranged between 7.6 and 7.8. Ellipsometry measurements show that the index of refraction varies from 1.72 to 1.55 as the deposition parameters were altered. X-ray analysis indicates that these films are fundamentally amorphous or are finely grained polycrystalline. Etching of the films in buffered HF suggests some degree of porosity. It may be generally concluded that the films produced by electron-beam evaporation were oxygen deficient and less dense than bulk. This result suggests that the Al2O3 source dissociates during the electron-beam evaporation. Obtaining stoichiometric Al2O3 onto silicon substrates requires the confinement of the evaporant and the reactive ambient in a chamber below the substrate.