Avalanche capability improvement in power semiconductor devices

A power semiconductor device comprising a plurality of trench MOSFETs, wherein each of said trench MOSFETs further comprising:

• a substrate of a first conductivity type;
• an epitaxial layer of said first conductivity type over said substrate, wherein said epitaxial layer having a lower doping concentration than said substrate;
• a plurality of gate trenches extending into said epitaxial layer, wherein each of said gate trenches has a first insulation layer lining its inner surface and a doped poly-silicon layer thereon;
• a body region of a second conductivity type surrounding sidewall of each of said gate trenches between every two adjacent of said gate trenches;
• a source region of said first conductivity type near top surface of said body region, wherein said source region surrounds top portion of sidewall of each of said gate trenches, and has a higher doping concentration than said epitaxial layer;
• a second insulation layer disposed over said epitaxial layer and covering outer surface of said doped poly-silicon layer;
• a source-body contact trench locating between every two adjacent of said gate trenches, opened through said second insulation layer and said source region, and extended into said body region;
• a body ohmic contact doped region of said second conductivity type formed within said body region, surrounding at least bottom of each said source-body contact trench and having a higher doping concentration than said body region;
• at least one avalanche capability enhancement doped region of said second conductivity type disposed underneath each said body ohmic contact doped region, wherein said avalanche capability enhancement doped region has a higher doping concentration than said body region but a lower doping concentration than said body ohmic contact doped region;
• a metal plug filling in each said source-body contact trench;
• a source metal disposed covering top surface of said second insulation layer;
• and
• a drain metal disposed on rear side of said substrate.