Method for forming trench MOSFET device with low parasitic resistance

A method of forming shallow and deep dopant implants adjacent source regions of a first conductivity type within an upper portion of an epitaxial layer in a trench MOSFET device, said method comprising:

• forming an patterned implantation mask over said epitaxial layer, said patterned implantation mask comprising a patterned insulating region, said patterned implantation mask covering at least a portion of said source regions, and said patterned implantation mask having apertures over at least portions of said epitaxial layer adjacent said source regions;
• forming shallow dopant regions by a process comprising:
• (a) implanting a first dopant of a second conductivity type at a first energy level within upper portions of said epitaxial layer Through said apertures and (b) diffusing said first dopant at elevated temperatures to a first depth from an upper surface of said epitaxial layer;
• forming deep dopant regions by a process comprising:
• (a) implanting a second dopant of said second conductivity type at a second energy level within upper portions of said epitaxial layer through said apertures and (b) diffusing said second dopant at elevated temperatures to a second depth from said upper surface of said epitaxial layer, wherein said first and second dopants can be the same or different, wherein said second energy level is greater than said first energy level, and wherein said second depth is greater than said first depth;
• and
• enlarging the apertures in said patterned insulating region.

A method of forming a device comprising plurality of trench MOSFET cells, said method comprising:

• providing an N-type silicon substrate;
• depositing an N-type silicon epitaxial layer over said substrate, said epitaxial layer having a lower majority carrier concentration than said substrate;
• etching trenches into said epitaxial region from an upper surface of said epitaxial layer;
• forming a silicon oxide region which lines at least a portion of said trenches;
• forming a doped polysilicon region within said trenches adjacent said silicon oxide region;
• forming P-type body regions within an upper portion of said epitaxial layer;
• forming N-type source regions within upper portions of said body regions adjacent said trenches;
• forming a patterned implantation mask over said epitaxial layer, wherein said patterned implantation mask has apertures over at least portions of said body regions adjacent said source regions, wherein said patterned implantation mask covers at least portions of said doped polysilicon region, wherein said patterned implantation mask covers at least portions of said source regions, and wherein said patterned implantation mask comprises a patterned masking layer disposed over a patterned BPSG region;
• forming shallow dopant regions by a process comprising:
• (a) implanting a first P-type dopant at a first energy level within upper portions of said body regions through said apertures and (b) diffusing said first dopant at elevated temperatures to a first depth from said upper surface of said epitaxial layer;
• forming deep dopant regions by a process comprising:
• (a) implanting a second P-type dopant at a second energy level within an upper portion of said body region through said apertures and (b) diffusing said second dopant at elevated temperatures to a second depth from said upper surface of said epitaxial layer, wherein said first P-type dopant and said second P-type dopant can be the same or different, wherein said deep and shallow dopant regions each has a higher majority carrier concentration than said body regions, wherein said second energy level is greater than said first energy level, and wherein said second depth is greater than said first depth;
• and
• enlarging the apertures in said patterned PBSG region by a wet blanket step.