Patent ID: 7807531

Claim:
A method for manufacturing a semiconductor device comprising: forming a trench in a semiconductor wafer; forming a gate silicon dioxide layer on an entire surface of said semiconductor wafer; depositing a first gate layer on said gate silicon dioxide layer; etching back said first gate layer to form a first gate electrode on a sidewall of the trench of said semiconductor wafer via said gate silicon dioxide layer; depositing an insulating layer on an entire surface of said semiconductor wafer after said first gate electrode is formed, said insulating layer excluding silicon dioxide and having different etching characteristics from those of silicon dioxide; etching back said insulating layer using said gate silicon dioxide layer as an etching stopper, so that said insulating layer is left on a bottom of the trench of said semiconductor wafer via said gate silicon dioxide layer and is surrounded by said first gate electrode; forming a second gate electrode layer on an entire surface of said semiconductor wafer after said insulating layer is etched back; and etching back said second gate electrode layer using said gate silicon dioxide layer as an etching stopper to form a second gate electrode buried in the trench of said semiconductor wafer, said second gate electrode being in contact with said first gate electrode and said insulating layer.