Characterization of ultrathin sputtered SiO films on alumina by inelastic electron tunneling spectroscopy and atomic force microscopy

Abstract

Amorphous SiO films are prepared by radio-frequency planar magnetron sputtering in a background of argon. Inelastic electron tunneling spectra are presented of the films incorporated in Al/SiO/Pb tunnel junctions with the aluminium films pre- or post-oxidized relative to the SiO deposition stage. Both the aluminium and lead junction electrodes are evaporated in a standard oil diffusion pumped, liquid nitrogen trapped vacuum system at a base pressure of 10−7 Torr; aluminium oxidation is achieved either by admitting oxygen into the vacuum chamber or by performing a low power dc oxygen glow discharge. Spectra obtained are similar, but not identical, to those obtained for evaporated SiO films. Different types of silicon hydride species are observed depending on the environment to which the SiO films are exposed after their deposition. Possible reactions of the films with water vapor are discussed which could produce the observed hydrides which are also assigned. Reverse bias tunneling spectra provide strong evidence that the SiH species reside on the SiO surface, and it is shown that they can be removed by exposure of the surface to a gaseous glow discharge. Atomic force microscopy images are presented of SiO films supported on aluminium and alumina which indicate that their topography is not noticeably modified by exposure to the glow discharge, and that they possess a relatively uniform quasi two-dimensional island structure.