Résumé dans la langue de publication, traduction non disponible A device and method used for etching, ashing, CVD, etc., at the time of manufacturing large scale integrated circuits (LSI) and liquid crystal displays (LCD). The device is a plasma treatment device provided with a dielectric plate for microwave waveguide, a microwave introducing window counterposed to the dielectric plate, and a reaction vessel in which a sample stage is so positioned that the table faces to the microwave introducing window. The device has a recessed section in the area of the microwave introducing window facing the sample stage. In the method, a sample is treated with a plasma by using the plasma treatment device. The plasma density in the area facing the sample and the treating speed of the sample with the plasma are increased. When etching a fine hole pattern, the pattern missing is improved. Therefore, a semiconductor device having a fine pattern can be manufactured and, at the same time, the manufacturing yield of the device, etc., is improved.