Patent ID: 7700440

Claim:
A method of manufacturing a metal-oxide-semiconductor (MOS) transistor, comprising: providing a substrate; forming a buried layer of a heavily doped first conductivity type on the substrate; forming a covering layer of the first conductivity type on the buried layer; forming a body region of a second conductivity type in the covering layer; forming a trench having a bottom surface and side surfaces and extending vertically downward from the top surface of the covering layer into the buried layer, wherein the bottom surface of the trench lies in the buried layer; performing an etching back process to remove the liner oxide on the bottom surface but not on the side surfaces of the trench; forming a liner oxide on the side surfaces and the bottom surface of the trench; filling a semiconductor material of the first conductivity type as a source/drain region within the trench to contact the buried layer at the bottom surface of the trench, leaving a space in the top portion of the trench; forming a gate on the body region and the covering layer; and forming a source/drain region within the body region.