Patent ID: 7745289

Claim:
A method of forming a field effect transistor, comprising: epitaxially forming a substrate cap region of a first conductivity type silicon over and in contact with a substrate of the first conductivity type silicon; epitaxially forming a body region of a second conductivity type silicon over and in contact with the substrate cap region; forming a plurality of trenches each extending at least through the body region; lining the sidewalls and bottom of each trench with a dielectric material; at least partially filling each trench with a conductive material; and forming a plurality of source regions of the first conductivity type in an upper portion of the body region, wherein during one or more temperature cycles, dopants of the first conductivity type in the substrate cap region out-diffuse into a lower portion of the body region to form an out-diffusion region of the first conductivity type extending from an interface between the body region and the substrate cap region into the body region such that a spacing between the source regions and the out-diffusion region defines a length of a channel region of the field effect transistor.