PURPOSE: To remove metal contaminants without wetting a silicon wafer with water and to prevent the formation of an unstable natural oxide film by a method wherein gas containing HCl gas and/or O3 gas is fed to the wafer to oxidize the metal contaminants being adhered on the wafer and after that, inert gas is fed and is exhausted along with the oxidized metal contaminants.

CONSTITUTION: Gas containing HCl gas and/or O3 gas is fed to a silicon wafer 3 in a pressure reducing chamber 1 or at normal pressures to oxidize metal contaminants being adhered on the wafer 3 at normal temperatures or while the wafer 3 is heated and after that, inert gas is fed and is exhausted along with the oxidized metal contaminants. The supply sources of the gases have respectively a flow rate controller 4 and the flow rates of the gases are controlled by the controllers 4 so that the gases to be fed to the wafer are produced into the optimum composition according to the conditions of the wafer 3. Thereby, the metal contaminants can be removed without wetting the wafer 3 with water and the formation of a natural oxide film can be prevented.