PURPOSE: To perform an etching with reproducibility by cleaning with nitrogen gas before and after the etching to blow off etching residues by the nitrogen gas, thereby always holding the environment in an etching chamber in a constant state.
CONSTITUTION: After a molybdenum silicide film on an etching wafer is etched with reactive gas which contains fluorine, an etching gas inlet hole 1a is closed, and all wafers are recovered. Thereafter, the valve of an exhaust hole 1b is closed. Even after the valve is closed, the chamber is maintained in considerably high vacuum. A gas inlet hole 1c is fully opened at one time to introduce compressed dry nitrogen gas from the hole 1c. The nitrogen is injected to a wall to be etched under considerable pressure to blow off a substance adhered to the wall. After the gas is fed for a predetermined time, the hole 1b is opened, and the nitrogen gas and the blown adhered articles are recovered. Thereafter, the hole 1c is closed, and the chamber is evacuated to the original pressure.