Patent ID: 7326995

Claim:
A trench MIS device comprising: a substrate of a first conductivity type; an epitaxial layer of a second conductivity type on the substrate, an interface between the epitaxial layer and the substrate forming a first PN junction; a trench extending into the epitaxial layer from a surface of the epitaxial layer, the trench having a bottom in the epitaxial layer above the interface between the substrate and the epitaxial layer; a gate positioned in the trench; a gate insulating layer along a sidewall of the trench; a bottom insulating layer on a bottom of the trench, the bottom insulating layer being thicker than the gate insulating layer and abutting the gate insulating layer, the gate being electrically insulated from the epitaxial layer by the gate insulating layer and the bottom insulating layer; a drain-drift region of the first conductivity type in the epitaxial layer, the drain-drift region extending between the trench and the interface between the epitaxial layer and the substrate, the drain-drift region forming a second PN junction with a remaining portion of the epitaxial layer, the second PN junction extending between the trench and the first PN junction, the second PN junction being aligned with a location where the bottom insulating layer and the gate insulating layer meet.