An unique method is used to produce a low energy nonthermalized fast neutral radical beam wliich can activate the SiO2 surface for chemical reaction at the desired incident energy. The fast neutral beam energy is continuously adjustable (2eV<Ek<200eV) and the beam flux is typically 5×1015cm−2 sec−1(∼4L). An uniform large diameter plasma is also made for the production of neutral beam covering 5”wafer and larger. Large diameter neutral beam single wafer reactor is feasible with off-the-shelf pumping technology.