Silicon dioxide films depostied at low temperatures using a remote plasma plasma enhanced chemicall vapor depostion(RPECVD) is annealed by a rapid thermal processing(RTP) in nitrogen ambient to enhance the reliability of silicon dioxide. The nitridation of silicon dioxide film is analyzed by thermodynamic calcyation. RTP decreases film thickness due to a densification and increases a refractive index but the oxide surface roughness is increased at thigh RTP temperature above 80$0^{circ}C$. After RTP, the breakdown field strength is increased by the substitution of strained Si-O bonds with relaxed Si-N bonds as a form of S$i_2$$N_2$O. The thermodynamci analysis is a useful guide to account for the experimental results.