Silicon oxide films have been deposited with remote plasma chemical vapour deposition (RPCVD) at low temperatures (<300 degrees C) from SiH4-N2O. The effect of a gas-phase reaction on the SiO2 film properties and Si/SiO2 interface was investigated. As the partial pressure ratio was increased above N2O/SiH4 = 4, a gas-phase reaction with powder formation was observed, which degraded film properties, increased surface roughness, and decreased deposition rate. When N2O/SiH4<4, there was no detectable IR absorption in the film associated with hydrogen-related bonds (Si-OH and Si-H) but when N2O/SiH4>4, the incorporation of Si-OH bond became significant and Si1+, intermediate state silicon at the interface, was more abundant. The oxide fixed charge, interface trap density, surface roughness and leakage current were increased when there was powder formation in the gas phase. High plasma power also favoured the powder formation in the gas phase. C-V and I-V characteristics were measured and it was shown that these electrical properties were directly related to the process condition and material properties of the oxide and the Si/SiO2 interface.