Trench MOSFET having improved breakdown and on-resistance characteristics

A power MOSFET comprising:

• a semiconductor substrate of a first conductivity type;
• an epitaxial layer overlying the substrate, a trench being formed in the epitaxial layer;
• and
• a gate positioned in the trench and electrically isolated from the epitaxial layer by an insulating layer which extends along a bottom and a sidewall of the trench;
• the epitaxial layer comprising:
• a source region of the first conductivity type, the source region being located adjacent a top surface of the epitaxial layer and the sidewall of the trench;
• a body of the second conductivity type, the second conductivity type dopant of the body forming a PN junction with the first conductivity type dopant of the substrate, the PN junction being substantially coincident with the interface between the epitaxial layer and the substrate;
• and
• a drain region of the first conductivity type extending between the substrate and the bottom of the trench.

A power MOSFET comprising:

• a semiconductor substrate of a first conductivity type;
• an epitaxial layer overlying the substrate, the epitaxial layer being generally of a second conductivity type opposite to the first conductivity type;
• a trench extending from a surface of the epitaxial layer, through the epitaxial layer and into the substrate;
• a gate positioned in the trench and electrically isolated from the epitaxial layer by an insulating layer which extends along a bottom and a sidewall of the trench;
• and
• a source region of the first conductivity type in the epitaxial layer, the source region being located adjacent a top surface of the epitaxial layer and the sidewall of the trench.