MOSFET with improved performance through induced net charge region in thick bottom insulator

A method for manufacturing a semiconductor power device, comprising:

• forming an epitaxial semiconductor region on a substrate doped with dopants of a first conductivity type,
• doping the epitaxial semiconductor region with dopants of the first type to a lower doping concentration than the substrate;
• forming a trench in the epitaxial semiconductor region;
• forming a body region in the epitaxial semiconductor region proximate the trench, wherein the body region is doped dopants of a second conductivity type that is opposite the first conductivity type;
• forming a source region of the first conductivity type proximate the trench such that the body region is between the source region and the epitaxial region, wherein a doping concentration of the source region is greater than a doping concentration of the epitaxial semiconductor region;
• forming a thick bottom insulator in a lower portion of the trench;
• forming an electrically conductive gate electrode in the trench above the thick bottom insulator, wherein the gate electrode is electrically insulated from a bottom of the trench by the thick bottom insulator and electrically insulated from sidewalls of the trench by a gate insulator;
• and
• deliberately inducing a region of net charge of the first conductivity type in the thick bottom insulator proximate an interface between the thick bottom insulator and the epitaxial semiconductor region, wherein the doping concentration of the epitaxial semiconductor region two to three times the doping concentration for an epitaxial semiconductor region in a conventional (unshielded) MOSFET device.