PURPOSE: To efficiently remove impurities existing in the surface layer of a silicon substrate so as to realize surface treatment which can completely remove a halogen or natural oxide film from the surface of the substrate by irradiating the surface with ultraviolet rays in a hydrogen atmosphere after continuously and alternately performing an oxidizing and oxygen removing processes on the surface of the substrate.

CONSTITUTION: After a wafer 6 is placed on a wafer carrying system 4, the wafer 6 is efficiently oxidized by using an oxidizing gas excited by ultraviolet rays of ≥16Onm in wavelength. In addition, an oxide formed on the wafer 6 is efficiently removed by using an oxide removing gas excited by ultraviolet rays. These processes are simultaneously or alternately performed. Then the molecular species which is used at the time of oxide removal and coupled with or adsorbed to the surface of the wafer 6 is removed by irradiating the surface of the wafer 6 with ultraviolet rays in a hydrogen atmosphere. Therefore, surface treatment which can completely remove halogen, such as fluorine, chlorine, etc., natural oxide film, etc., by efficiently removing such impurities as metals, organic compounds, etc., from the surface layer of the wafer 6 can be realized.