PURPOSE: To carry out high-quality etching by forming a bulkhead window at a waveguide side with small-dielectric-constant quartz and a bulkhead window at a plasma reaction chamber side with alumina which is anti-corrosive against chemical reaction.

CONSTITUTION: Double bulkheads with windows made of a different materials are formed between a waveguide 12 connected to a plasma generation equipment 11 and a plasma generation chamber 16. The bulkhead window 13 at the waveguide 12 side is made of small dielectric constant quartz and the bulkhead window 15 at the plasma generation chamber 16 side is made of alumina which is anti-corrosive against chemical reaction. Then, the bulkhead window 13 is low in loss against microwave power so a temperature is not raised and the quartz is not corroded by chemical reaction because no direct contact with a reaction gas is made. The bulkhead window 15 is difficult to be chemical by reacted with the reaction gas and no conventional corrosion nor generation of dust exists. This enables high-quality etching.