Patent ID: 8387560

Claim:
A plasma processing unit comprising: a processing vessel having an opening on a ceiling side thereof, and capable of creating a vacuum therein; a stage disposed in the processing vessel, for placing thereon an object to be processed; a top plate made of a dielectric, the top plate being hermetically fitted in the opening and allowing a microwave to pass therethrough; a planar antenna member disposed on or above the top plate, the planar antenna member being provided with a plurality of microwave radiating holes for radiating a microwave for plasma generation toward an inside of the processing vessel; a slow-wave member disposed on or above the planar antenna member, for shortening a wavelength of a microwave; and a microwave interference restraining part disposed on a lower surface of the top plate such that the lower surface of the top plate consists of a flat surface except at the microwave interference restraining part, the microwave interference restraining part separating the lower surface into a plurality of concentric zones, wherein the microwave interference restraining part consists of three or more concentric ridges having a same cross section and a same predetermined pitch, the microwave interference restraining part is spaced apart from a periphery of the lower surface of the top plate, toward the center of the lower surface, the pitch of the three or more concentric ridges is within a range from 1/10 to ⅓ times the length of a wavelength λ of a microwave in the slow-wave member, and the microwave interference restraining part has an inner diameter within a range from 1.5 to 2.5 times the length of the wavelength λ of the microwave in the slow-wave member.