PURPOSE: To remove deposit which was deposited out of a plasma producing area owing to gas flow through a plasma etching process, by making an earth shield which has controlled the spread of plasma to be at the same potential as that of an electrode which applies a voltage in the plasma etching.

CONSTITUTION: In the thin film formation being performed owing to plasma decomposition, an earth shield 9 is connected through both contacts A and C to the earth so that the spread of the plasma is effectively controlled. On the other hand, in plasma etching being performed, the earth shield 9 is connected through both contacts A and B to a power source to be at the same potential as that of an electrode 2, so that the plasma is made to be sufficiently spread. As a result, the deposit which was deposited out of a plasma producing area owing to gas flow is effectively etched away by the plasma etching.