Reactive sputtering followed by N-2, NH3, O-2, and NO post-deposition annealing (PDA) of SiO2 on 4H-SiC was investigated in this study. The results of ellipsometry, an etching test, and X-ray photoemission spectroscopy showed that N-2 and NH3 PDA nitrified the SiO2. Devices using N-2 and NH3 PDA exhibited a high gate leakage current and low breakdown field due to oxygen vacancies and incomplete oxynitride. SiO2/4H-SiC MOS capacitors were also fabricated and their electrical characteristics measured. The average breakdown fields of the devices using N-2, NH3, O-2, and NO PDA were 0.12, 0.17, 4.71 and 2.63 MV/cm, respectively. The shifts in the flat-band voltage after O-2 and NO PDA were 0.95 and -2.56 V, respectively, compared with the theoretical value. The extracted effective oxide charge was -4.11 x 10(11) cm(-2) for O-2 PDA and 1.11 x 10(12) cm(-2) for NO PDA. NO PDA for 2 h at 1200 degrees C shifted the capacitance-voltage curve in the negative direction. The oxygen containing PDA showed better electrical properties than non-oxygen PDA. The sputtering method described can be applied to 4H-SiC MOS fabrication.