Low hydrogen content silicon nitride films deposited at room temperature with a multipolar ECR plasma source

Silicon nitride layers with very low hydrogen content (less than 1 atomic percent) were deposited at near room temperature, from N2 and SiH4, with a multipolar electron cyclotron resonance plasma. The influences of pressure and nitrogen flow rate on physical and electrical properties were studied in order to minimize the hydrogen and oxygen content in the layers. The optimized layers were characterized by a refractive index of 1.98, a dielectric constant of 7.2, and Si/N ratio values of 0.78. The layers exhibited very good dielectric strength, which was confirmed by large breakdown fields of 12 MV/cm, very high resistivities of 1016 Omega cm, and maximum charges to breakdown values of 90 C/cm2. Increasing the deposition pressure and decreasing the N2 flow improved the SiN/Si interface, due to increased oxygen incorporation. The dominant conduction mechanism in the layers was the Poole-Frenkel effect. The critical field and the trap energy had similar dependencies on deposition pressure. Fowler-Nordheim tunneling occurred at high gate biases, for the layers deposited at the highest pressure of about 22 mTorr

Electrical characterisation of gate dielectrics deposited with multipolar electron cyclotron resonance plasma source

Silicon oxide films have been deposited by plasma-enhanced chemical vapour deposition, at glass compatible temperatures. A multipolar electron cyclotron resonance plasma (ECR) source with SiH4/He and N2O was used. The electrical properties of the films were determined by means of C-V and I-V measurements. The dependencies of the electrical properties on gas-flow ratio and pressure were investigated. Critical electric fields as high as 6 MV/cm and net oxide charge densities as low as 1×1011 ions/cm2 have been obtained for the optimal deposition conditions. The oxide integrity versus CVD conditions was investigated by charge to breakdown measurements. MOSFETs have been fabricated in order to test the dielectric quality

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

Silicon nitride layers obtained by ECR PECVD

It has been found that good quality silicon nitride films can be deposited at room temperature, with an alternate electron cyclotron resonance (ECR) plasma source, called multipolar ECR. The effects of several deposition conditions on physical and electrical properties were studied in order to optimise the deposition process.\ud The layers were characterised by a refractive index of 1.97, dielectric constant of 7.1, Si/N ratio values of around 0.78 and very low hydrogen content (under 1%). The lowest oxygen contamination (2%) was obtained for the highest nitrogen flow. A decrease in refractive index was observed at high pressure, probably because of insufficient energy to dissociate the nitrogen molecules. The density of interface charge was estimated to be in the range of 3-11•1011 cm-2 and the breakdown field was calculated to be around 12 MV/cm.\u