Atmospheric pressure plasma (APP) systems operate at atmospheric pressure and low temperatures, eliminating the need for vacuum systems such as vacuum chambers and pumps. In this paper, we studied that silicon dioxide thin films were formed at room temperature (25 ^oC) and 400 ^oC by APP processes on silicon wafers. A mixture of hexamethyldisilazane, oxygen, helium, and argon was supplied to the plasma apparatus to form the SiO₂ layer. It was observed that a heat insulating layer having a thickness of about 22 nm at 25 ^oC and about 75 nm at 400 ^oC was formed. Although the surface was clean in samples treated at 400 ^oC, small grains were observed in samples processed at room temperature. However, no void or defect in all samples is observed inside the thin film from the surface. The physical property of the SiO₂ thin film carried out by measuring refractive index and density. The experimental refractive index of silicon dioxide grown by applying heat can be fitted to the Sellmeier equation. Also, the film density of the sample at 400 ^oC using a XRR was observed to be 2.25 g/cm³, similar to that of the glass, but that of the sample treated at room temp. was very low at 1.68 g/cm³. We also investigated the voltage-dependent current change in the oxide material. The SiO₂ layer coated at room temperature showed a breakdown electrical field of 2.5 MV/cm, while oxides deposited at 400 ^oC showed a characteristic of 9.9 MV/cm

Keywords: Silicon oxide, Atmospheric pressure plasma, Hexamethylidisilazane, Room temperature, 400 ^oC