Method for production of semiconductor device

A method for producing a semiconductor device, said method comprising the steps of:

• forming a hard mask layer on a semiconductor substrate, the substrate including a source region;
• forming a resist layer over said hard mask;
• patterning said resist layer to form an opening in the resist layer;
• etching said hard mask to form an opening therein in registry with said opening in said resist layer;
• removing said resist layer;
• forming a side wall mask on a sidewall of said mask opening;
• forming a trench which extends from said opening in said opening in said hard mask to said source region using said side wall mask and said hard mask layer as a mask;
• removing said side wall mask;
• coating a sidewall and floor of said trench with an insulating film;
• forming a gate electrode by filling said trench and said mask opening with a gate electrode material;
• removing said hard mask to expose a portion of said gate electrode extending above a surface of said substrate;
• forming a side wall on the side wall of said gate electrode;
• and
• forming a drain region below the surface of said semiconductor substrate adjacent to said gate electrode.