Abstract: A plasma processing unit of the invention includes: a processing container, and a first electrode disposed in the processing container. The first electrode has: a plurality of gas-dispersion holes for supplying a process gas into the processing container, and an opening for a measurement light. A second electrode is arranged on one side of and a predetermined gap away from the gas-dispersion holes and the opening of the first electrode. A power source unit applies electric power between the first electrode and the second electrode and generates plasma between the first electrode and the second electrode. An optical path of a window member adjacently communicates with the other side of the opening for the measurement light. The gas-dispersion holes are formed into a predetermined arrangement, and the opening is formed separately from the gas-dispersion holes without disturbing the arrangement of the gas-dispersion holes.

Abstract: A method of detecting an etching depth of a target object includes the steps of irradiating an etching layer of the target object that is being etched in an etching section with light having a plurality of components differing from each other in a wavelength, detecting a plurality of interference light components differing from each other in the wavelength and having an intensity periodically changed by the light components reflected from an upper surface of the etching layer and a surface of the etching section, applying a frequency analysis to these interference light components so as to obtain the frequency of each of these interference wave forms in which the intensity forms the amplitude, calculating an etching rate corresponding to each interference wave form by using the frequency of the interference wave form, and obtaining an etching depth from the etching rate.

Abstract: A method of detecting an etching depth of a target object includes the steps of irradiating an etching layer of the target object that is being etched in an etching section with light having a plurality of components differing from each other in a wavelength, detecting a plurality of interference light components differing from each other in the wavelength and having an intensity periodically changed by the light components reflected from an upper surface of the etching layer and a surface of the etching section, applying a frequency analysis to these interference light components so as to obtain the frequency of each of these interference wave forms in which the intensity forms the amplitude, calculating an etching rate corresponding to each interference wave form by using the frequency of the interference wave form, and obtaining an etching depth from the etching rate.