Silicon Nitride whose thickness is about $100AA$by the ellipsometer was successfully formed by the Plasma reaction. Nitrogen Plasma was formed by applying the 200KHz, 500Watt power between the two electroes and nitridation of silicon was carried out directly on the top of the silicon wafer. Thus Silicon Nitride formed was oxidized to from oxynitrides and their electrical characterlstice were analyzed by measuring I-V curves and capacitances. Through ESCA depth profiles, the chemical composition changes before and after the oxidation wers analyzed.