Electronic conduction processes in SiO₂ films obtained by ECR PECVD

Low temperature dielectrics are desired for realising thin-film-transistors on glass or plastic substrates. In the past silicon dioxide layers with stoichiometric composition and good electrical properties were deposited without substrate heating with an Electron Cyclotron Resonance Plasma source. This work is focused on determining the conduction mechanisms in the deposited films. The temperature dependence of the current density - electric field characteristics were studied and Fowler-Nordheim was found to be the dominant conduction mechanism in SiO2 films deposited with low silane flow and at low pressure. For higher silane flows and higher pressures, the current travels via traps in the oxide bandgap. Constant current stress measurements confirmed that low silane flow (5 sccm) and low pressure (4 mTorr) are ideal deposition conditions. For aluminium-gate capacitors with SiO2 deposited at optimised parameters, a charge to breakdown of 1 C/cm2 was found, comparable with the values obtained for thermally grown oxide.