Plasma processing apparatus

A plasma processing apparatus that includes an external circuit of a power meter or a signal meter electrically connected via a line to an electrical member within a processing vessel in which a plasma process is performed, wherein the plasma processing apparatus is configured to reduce or block a noise of a predetermined frequency introduced from the electrical member into the line toward the external circuit by a filter provided on the line,

• wherein the filter comprises:
• an air core coil;
• a cylindrical external conductor, accommodating or surrounding the air core coil, and in combination with the air core coil, configured to form a distributed constant line in which parallel resonance of multiple frequencies corresponding to multiple parallel resonance frequencies occurs;
• and
• first comb teeth and second comb teeth, all of which are made of an insulating material and are selectively inserted into winding gaps of the air core coil,
• wherein each of the first comb teeth has a thickness smaller than a standard thickness, which is a comb tooth thickness that allows a uniform winding gap over an entire length of the air core coil, and wherein the first comb teeth are inserted into one or more zones that are arranged separately in a longitudinal direction of a central axis of an air core coil winding to shift one or more of the plural parallel resonance frequencies to a lower frequency range in a frequency-impedance characteristic of the filter,
• wherein each of the second comb teeth has a thickness equal to or larger than the standard thickness, and wherein the second comb teeth are inserted into the winding gaps in which the first comb teeth are not inserted, and
• wherein the thickness of each of the first and the second comb teeth is measured longitudinally relative to the central axis of the air core coil winding.