FORMATION OF THIN FILM

摘要

PURPOSE:To prevent a reactive product thin film from forming on an ultraviolet light transmission window without coating oil or the like by applying a bias voltage of a discharge starting voltage or lower to a first electrode and a second electrode provided on the window or near the window or ultraviolet light source. CONSTITUTION:A power source 11 is so provided as to apply a bias voltage to between a first electrode 4 and a second electrode 2 provided on an ultraviolet light transmission window or near the window or ultraviolet light source. Ion species or active species slightly charged in which reactive product contained in reaction gas becomes solid is separated from the window 5 or near the light source 6 by a bias voltage applied to between the electrodes 4 and 2. Thus, an optical CVD method can be applied to a wide semiconductor device to simply obtain a semiconductor device having preferably boundary characteristic without damage on a base of the feature of the optical CVD method.