METHOD OF PRODUCING A SEMICONDUCTOR DEVICE

A method of producing a semiconductor substrate, particularly one having a buffer coat layer and sealed in a mold resin, is disclosed. The method patterns a polyimide film, etches an insulating film or passivation film using the resulting polyimide pattern as a mask, and then ashes the polyimide pattern by oxygen plasma to thereby obviate the influence of an etchant used for etching. Therefore, the method is capable of reducing the corrosion of portions where a metallic wiring pattern is exposed to the outside. Because the oxygen ashing step is followed by heat treatment, the influence of oxygen which would lower the adhesion strength between the polyimide pattern and a mold resin is eliminated. As a result, tight adhesion of the polyimide pattern to the mold resin is insured. Further, when a first heat treatment is effected after the patterning of the polyimide film, a solvent in the polyimide film is evaporated. This reduces degassing in the event of the etching of the passivation film which immediately follows the first heat treatment.