Patent ID: 6903412

Claim:
A metal-insulator-semiconductor (MIS) device comprising: a semiconductor substrate including a trench extending into said substrate from a surface of said substrate; a drain region of a first conductivity type; and a body region of a second conductivity type opposite to said first conductivity type adjacent to at least a portion of a sidewall of said trench; wherein said trench is lined with an oxide layer, said oxide layer comprising a first section, a second section and a transition region between said first and second sections, said first section being adjacent at least a portion of said drain region, said second section being adjacent at least a portion of said body region, a thickness of said oxide layer in said first section being greater than a thickness of said oxide layer in said second section, a thickness of said oxide layer in said transition region decreasing gradually from said first section to said second section, a PN junction between said body region and said drain region intersecting said trench at a point adjacent said transition region of said oxide layer, said PN junction extending downward from said trench and reaching a level below said bottom of said trench at a location where said PN junction is horizontal.