Method for manufacturing a semiconductor device and suppressing the generation of bulk microdefects near the substrate surface layer

A method for manufacturing a semiconductor device having in a semiconductor substrate of one conductivity type a deep island-like diffusion layer of the opposite conductivity type, said method suppressing the generation of bulk microdefects near the substrate surface layer and comprising the steps of:

• selectively forming in the semiconductor substrate of one conductivity type a deep island-like impurity diffusion layer of the opposite conductivity type, including the substeps of,
• forming an oxide film on the semiconductor substrate;
• forming a resist pattern on the oxide film;
• implanting an impurity ion into the substrate at a predetermined location;
• forming a well by heating the substrate at a temperature greater than 1100.degree. C. in a gas comprising H.sub.2 and one of N.sub.2, Ar, Ne, He or a mixture thereof;
• and
• removing the oxide film;
• forming a field oxide film, serving as an element isolation layer, next to the impurity diffusion layer;
• forming a first gate, serving as a capacitor, on the semiconductor substrate;
• forming a second gate, serving as a switching transistor, on the semiconductor substrate and connected in parallel with the first gate;
• forming an insulation layer for insulating the first gate from the second gate;
• and
• forming a passivation film for protecting an element uppermost on the insulation layer.