PURPOSE: To remarkably reduce the hydrogen content in a silicon oxide film by depositing a thin film from a raw gas contg. a geseous silicon halide and oxygen, treating the thin film in a gaseous hydrogen atmosphere and repeating the process.

CONSTITUTION: An Si wafer 103 is heated, gaseous SiH4 107 is introduced into a reaction vessel 101, gaseous N2O 108 as the oxygen-contg. gas is introduced, and a silicon oxide film is deposited in 5 thickness at 3Torr for 3sec. The vessel 101 is evacuated to 5×10-7Torr by an evacuating device 104, gaseous F2 diluted to 5% with He is introduced, and the film is treated with gaseous F2 at 3Torr for 2sec. The vessel is evacuated to 5×10-7Torr. The process is repeated 100 times, and a silicon oxide film having 500 thickness is deposited. The content of gaseous H2 in the film is measured by the multipath reflection infrared analysis and measured result is 6×1019cm-3.