In this work, the SiO₂ films on the silicon substrate with different orientations were first prepared by the low temperature process using the ECR plasma diffusion as a function of microwave power and oxidation time. Before and after thermal treatment, the surface morphology, Si/O ratio from physicochemical properties, and the electrical properties of the oxide films were also investigated. The oxidation rate increased with microwave power, while surface morphology showed the nonuniform due to etching. The film quality, therefore, was lowered with increasing the defect by etching and the content of positive oxide ions in the oxide films from bulk by higher self-DC bias. The content of positive oxide ions in the oxide films with different Si orientations showed Si(100) < Si(111) < poly Si. The defects in Si/SiO₂ interface of SiO₂ film could be decreased by annealing, while Q_it and Q_f were independent of thermal treatment and the dependent on concentration of reactive oxide ions and self-DC bias of substrate. At microwave power of 300, and 400 W, the high quality SiO₂ film that had lower surface roughness and defect in Si/SiO₂ interface was obtained. The value of interface trap density, then, was ∼9 x 10¹⁰ cm^-2 eV^-1