High quality SiO₂ with atomic flat interface was grown on SiC rapidly at room temperature with growth rate of over 3 nm/min using high pressure (~6 kPa) microwave plasma oxidation method. Thermodynamic calculation reveals that high pressure atomic oxygen is helpful to remove the residual carbon and suppress the SiO (g) desorption and oxygen vacancy formation, and thus maintain a fast growth rate and high quality. Atomically flat interface with very low Dit (<; 5 xl0¹⁰ cm-²eV^-1) comparable to SiO₂/Si interface is demonstrated.