Characterisation of thin films of silicon rich oxides

Abstract

The electrical characteristics of a Metal-Semi-insulator-Semiconductor diode have been comprehensively studied at various temperatures. In particular the electrical, structural and compositional properties of the semi-insulator, silicon-rich-oxide (SRO), have been thoroughly investigated. The SRO films were all deposited by atmospheric pressure chemical vapour deposition, (APCVD), at 650 C with silane (SiH(_4)) and nitrous oxide (N(_2)O) reactant gases and a carrier gas of nitrogen. The reactant gas ratio, γ, was held at 0.22 and the deposition time varied between 0.5 and 8 minutes. The effects of film thickness, film annealing, forming, top contact metal (i.e. work function difference), top contact metal area, substrate material and temperature on the electrical characteristics in both forward and reverse bias have been reported. Various techniques have been employed to elucidate the physical and structural properties of the SRO film. These include: Auger Electron Spectroscopy; Secondary Ion Mass Spectroscopy; Glow Discharge Optical Emission Spectroscopy; Scanning Electron Microscopy; Transmission Electron Microscopy; Rutherford Backscattering Spectroscopy; Optical Ellipsometry and Alpha Step Analysis. A model for the structure of SRO films has been put forward. The films are thought to be extremely random in structure, containing many voids with a gradual variation in composition from substrate to top metal contact. Various models for conduction in the SRO film were investigated over a range of electric fields and temperatures to determine the predominant conduction mechanism for a particular set of conditions. Conduction in SRO is thought to be dominated by Schottky emission across the SRO-substrate interface. Once this Schottky barrier is conducting, at suitably high biases, conduction across the remainder of the device is thought to be by thermionic emission at high temperatures and by a Poole-Frenkel process at low temperatures.