The influence of the precleaning process on the characteristics of SiO2 film grown by using electron cyclotron resonance (ECR) plasma oxidation at room temperature is presented in this work. We find that the growth rate, electrical properties, and reliability of the ECR plasma grown oxide is improved by this precleaning step. Two growth mechanisms are found which determine the electrical properties of the plasma grown oxide. The plasma damage is also discussed. We find that plasma oxidation produces little plasma damage in our experiments. Excellent ECR plasma grown silicon dioxide with good electrical properties and reliability characteristics are obtained by this precleaning technique.