PURPOSE: To generate a stable plasma even if a treating chamber is increased in its diameter by altering a passing ratio of a microwave for at least two modes in a circular propagation space increased in its diameter in which microwaves of a plurality of modes can be existed.
CONSTITUTION: A mode filter 13 is disposed forward in a microwave advancing direction from a quartz bell-jar 3 in a circular waveguide 2d. The filter 13 is formed as a mode filter 13a in which a plurality of circular-arc metal plates having different curvatures are disposed in a metal cylinder. The cylinder and the plates have longitudinal directions in a direction parallel to a magnetic field to be generated from a solenoid coil 8. When the filter 13a is used, only the electric field perpendicular to the plates can be passed. Thus, influence to a desired mode is reduced, and mixture of other mode can be prevented.
WATANABE SEIICHI
OGAWA YOSHIFUMI
