Patent ID: 7172675

Claim:
A plasma processing apparatus comprising: (a) an observation window installed at a sidewall of a processing room thereof, the observation window comprising: (i) a through hole with an opening facing the processing room; (ii) a transparent member installed at a side of the hole opposite to the processing room; and (iii) a magnetic pole pair having two different magnetic poles disposed opposite each other with the hole interposed there between, the magnetic pole pair being configured to have a sufficient magnetic field strength to prevent electrons which form plasma in the processing room from reaching the transparent member through the hole; (b) a laser irradiating unit at a side of the observation window opposite the processing room, the laser irradiating unit irradiating a laser light into the processing room through the observation window; and (c) a laser detecting unit detecting a reflected light or a scattered light through the observation window, the reflected light or the scattered light being generated when the laser light irradiated into the processing room is irradiated to floating particles in the plasma, wherein the observation window has a surface having a curvature substantially the same as that of an inner wall of the processing room; a first end of the hole adjoining the transparent member has a height corresponding to about 1.5Â° when viewed at an observation target location in the processing room; and the height of the opening of a second end of the hole facing the processing room is smaller than that of the first end, wherein the observation target is located near a perimeter of a holder of a wafer to be processed at a farther end of the wafer to be processed with respect to the observation window.