Charge balance field effect transistor

A method of forming a MOSFET comprising:

• providing a substrate of a first conductivity type;
• forming an epitaxial layer of a second conductivity over the substrate;
• forming a trench extending through the epitaxial layer and terminating in the substrate;
• performing a two-pass angled implant of dopants of the first conductivity type to thereby form a region of first conductivity type along the trench sidewalls;
• forming a shield electrode in a lower portion of the trench such that an upper portion of the shield electrode extends in the epitaxial layer and a lower portion of the shield electrode extends in the substrate, the shield electrode being insulated from the epitaxial layer and the substrate by a shield dielectric;
• forming a gate dielectric layer along upper sidewalls of the trench;
• forming a gate electrode in the trench over but insulated from the shield electrode;
• performing a threshold voltage adjust implant of dopants of the second conductivity type to thereby convert the conductivity type of a portion of the region of the first conductivity type extending along upper sidewalls of the trench to the second conductivity type;
• and
• forming source regions of the first conductivity type flanking each side of the trench.

A MOSFET comprising:

• a trench extending into a semiconductor region;
• a shield electrode in a lower portion of the trench, the shield electrode being insulated from the semiconductor region by a shield dielectric;
• a gate electrode in an upper portion of the trench, the gate electrode being over but insulated from the shield electrode;
• wherein the semiconductor region comprises:
• a substrate of a first conductivity type;
• a first silicon region of a second conductivity type over the substrate, the first silicon region having a first portion extending to a depth intermediate a top surface and a bottom surface of the gate electrode, the first silicon region having a second portion extending to a depth intermediate a top surface and a bottom surface of the shield electrode;
• a second silicon region of the first conductivity type between the trench and the second portion of the first silicon region, the second silicon region having a laterally-graded doping concentration decreasing in a direction away from the trench sidewalls;
• and
• a source region of the first conductivity type in the first silicon region, the source region being adjacent the trench.