Trench MOS device having a termination structure with multiple field-relaxation trenches for high voltage applications

A semiconductor device, comprising:

• a semiconductor substrate having at least one trench MOS device located in an active region of the semiconductor substrate;
• a plurality of trench cells only located in a termination region of the semiconductor substrate adjacent to the active region of the semiconductor substrate, the plurality of trench cells extending from a boundary between the active and termination regions toward an edge of the semiconductor substrate;
• a termination trench formed in the termination region on a side of the plurality of trench cells remote from the active region;
• a first oxide layer lining the plurality of trench cells and the termination trench;
• a conductive spacer located adjacent a sidewall of the termination trench nearest the plurality of trench cells;
• a second oxide layer formed in the termination trench and contacting a sidewall of the conductive spacer;
• a first conductive layer formed on a backside surface of the semiconductor substrate;
• and
• a second conductive layer located atop the active region and the termination region, a portion of the second conductive layer located in the termination region defining a field plate.

A method of forming a semiconductor device, comprising:

• forming at least one trench MOS device located in an active region of a semiconductor substrate,
• forming a plurality of trench cells located in a termination region of the semiconductor substrate adjacent to the active region of the semiconductor substrate,
• the plurality of trench cells extending from a boundary between the active and termination regions toward an edge of the semiconductor substrate,
• forming a termination trench in the termination region of the semiconductor substrate on a side of the plurality of trench cells remote from the active region,
• forming a conductive spacer located adjacent a sidewall of the termination trench nearest the plurality of trench cells, forming a first oxide layer in the termination trench which contacts a sidewall of the conductive spacer,
• forming a first conductive layer on a backside surface of the semiconductor substrate,
• forming a second conductive layer located atop the active region;
• and
• forming a first conductive layer on a backside surface of the semiconductor substrate,
• wherein the plurality of trench cells are filled with a conductive material up to a top surface of a plurality of mesas, wherein the second conductive layer extends from the active area as a continuous layer and completely covering the plurality of trench cells and at least a portion of the termination trench such that the second conductive layer, the conductive spacer and a field plate formed in the termination region are electrically coupled to one another.