Structure and method of forming a dual-trench field effect transistor

A field effect transistor comprising:

• a semiconductor region of a first conductivity type having a thickness defined by the distance between upper and lower surfaces of the semiconductor region;
• a well region of a second conductivity type over the semiconductor region;
• a plurality of gate trenches each extending through the well region and terminating within an upper half of the semiconductor region;
• a plurality of source regions of the first conductivity type in an upper portion of the well region, the plurality of source regions flanking the sides of the plurality of gate trenches;
• and
• a plurality of stripe trenches each extending through the well region and terminating within a lower half of the semiconductor region at a depth above the bottom surface of the semiconductor region, each stripe trench being filled with a semiconductor material of the second conductivity type such that:
• (i) the filled stripe trench is contiguous with the well region, and (ii) the semiconductor material of the second conductivity type forms a PN junction with the semiconductor region.

A method of forming a field effect transistor comprising:

• forming a well region in a semiconductor region of a first conductivity type, the well region being of a second conductivity type and having an upper surface and a lower surface;
• forming a plurality of gate trenches extending into the semiconductor region to a depth below the lower surface of the well region;
• forming a plurality of stripe trenches extending through the well region and into the semiconductor region to a depth below that of the plurality of gate trenches, the plurality of stripe trenches being laterally spaced from one or more of the plurality of gate trenches;
• and
• at least partially filling the plurality of stripe trenches with a semiconductor material of the second conductivity type such that the semiconductor material of the second conductivity type forms a PN junction with a portion of the semiconductor region.