PURPOSE: To prevent aluminum from melting due to galvanic action by plasma etching the aluminum and then electrically eliminating charge stored on a semiconductor substrate by an ionizer.

CONSTITUTION: An ionizer 104 for generating N+ and N- ions ionized through an N2 pipe 105 is connected to an etching chamber 101. After one batch of etchings are finished, the N+ and N- ions ionized by the ionizer 104 are fed through the pipe 105 into the chamber 101. Thus, positive ions on the surface of a semiconductor substrate charged during the etching are neutralized by the N- ions. Then, it can prevent aluminum from melting due to galvanic action.