Patent ID: 8072027

Claim:
A semiconductor device, comprising: a semiconductor substrate containing a source region in an upper portion of the substrate; a dual trench structure in an upper portion of the substrate, wherein the dual trench structure contains: a plurality of discrete lower trenches separated by a mesa between adjacent lower trenches, the lower trenches having sidewalls extending in both an x- and a y-direction; and an upper trench overlying the lower trenches, the upper trench having sidewalls extending in the y direction that are longer than the sidewalls extending in the x direction; an oxide layer located on the bottom, sidewall of the lower trenches, and sidewall of the upper trench; a first conductive or semi-conductive layer located on the oxide layer in the lower trenches; and a second conductive or semi-conductive layer located on the first conductive or semi-conductive layer and the mesa.