Preparation and plasma oxidation processing method of a semiconductor device

On the gate oxide film 102 on the silicon wafer 101, by forming a polysilicon to form a polysilicon electrode layer 103 (first electrode layer). On the polysilicon electrode layer 103 is formed of tungsten layer 105 (second electrode layer). Before forming the tungsten layer 105, formed in advance conductive barrier layer 104 on the polysilicon electrode layer 103. Thereafter, the silicon nitride layer 106 as an etching mask, etching is performed. Then, the exposed surface of the polysilicon layer 103 became exposed, by the plasma oxidation treatment process temperature using a processing gas containing oxygen gas and hydrogen gas and 300 ° C. or higher to form an oxide insulating film 107. Thus, without oxidizing the tungsten layer 105, selective oxidation process to the polysilicon electrode layer 103 can be performed.