Patent ID: 8404559

Claim:
A semiconductor device production method comprising: forming a LOCOS oxide film in a surface portion of a silicon layer by a LOCOS method; forming an impurity region in the silicon layer by introducing an impurity into the silicon layer; sequentially removing parts of the LOCOS oxide film and the silicon layer to form a trench for isolation of the impurity region after the formation of the LOCOS oxide film and the impurity region; forming an SiN layer of SiN and an SiO 2 layer of SiO 2 in this order on the silicon layer prior to the formation of the trench after the formation of the LOCOS oxide film and the impurity region; and forming an opening in the SiN layer and the SiO 2 layer for selectively exposing a surface of the LOCOS oxide film by a photolithography and etching process; wherein the trench is formed by etching the LOCOS oxide film and the silicon layer by using the SiN layer and the SiO 2 layer as a mask after the formation of the opening.