A processing apparatus of the present invention has a mounted chamber holding a semiconductor wafer and having members for work-processing the substrate under any of heating, plasma and process gas or a combination of them, in which a film of Al2O3 and Y2O3 is formed on an inner wall surface of the chamber and on those exposed surface of the members within the chamber and has a high-corrosion resistance and insulating property and, when the process gas is introduced onto a processing surface of a semiconductor wafer and diffused into it, any product is less liable to be deposited on a plasma generation area and on those members held within the chamber.