Low temperature oxidation process of Si(100) substrates using atomic oxygen has been proposed. For the generation of atomic oxygen, microwave plasma remotely attached on the oxidation chamber was used. In the microwave plasma, the large amount of rare gas and a small amount of 02 gas mixture was supplied. The existence of the large amount of rare gas controls the plasma energy to some restricted values associated with the metastable states of the rare gas. Consequently, using Kr as mixed rare gas, atomic oxygen were efficiently generated instead of excited 02 molecules with any vibrational or ionized states. The oxidation kinetics of crystalline Si using this process was shown to be diffusion limiting, even if the oxide thickness was less than several nm. The activation energy of B, which is referred to as the parabolic rate constant, was found to be as low as 0.14eV In addition, lower interface trap density of 2.6 × 1011/cm2/eV at the mid gap could be achieved for the as-grown SiO2/Si(100) interface at the processing temperature of 500C.