PURPOSE: To ensure the capture of contaminated material, to obtain the passive state, to prevent deterioration of the characteristics of a silicon film even if it is contaminated to some extent and to improve the resistance to the contamination by distributing contaminant capturing atoms in the silicon oxide film formed on a semiconductor substrate approximately uniformly.

CONSTITUTION: A silicon oxide film 14 is exposed in a semiconductor device 10. The semiconductor device 10 in this state is held with a holder 22 in a reaction chamber 20. Infrared rays are vertically projected on the silicon oxide film 14 through a transmitting window 24 from infrared ray lamps 14. Under this state chlorine gas is introduced through a gas introducing pipe 27. Phosphine gas is introduced through a gas introducing pipe 28. As a result, chlorine atoms and phosphorus atoms are distributed in the silicon oxide film 14 at a uniform temperature. Alkali metal and alkali earth metal are captured with the chlorine atoms, and heavy metals such as iron, nickel and copper are captured in the form of the compound with the phosphorus atoms. The metals are made to be the passive state.