Termination for trench MIS device having implanted drain-drift region
View Patent ↗A trench MIS device is formed in a P-epitaxial layer that overlies an N-epitaxial layer and an N+ substrate. In one embodiment, the device includes an N-type drain-drift region that extends from the bottom of the trench to the N-epitaxial layer. Preferably, the drain-drift region is formed at least in part by fabricating spacers on the sidewalls of the trench and implanting an N-type dopant between the sidewall spacers and through the bottom of the trench. The drain-drift region can be doped more heavily than the conventional “drift region” that is formed in an N-epitaxial layer. Thus, the device has a low on-resistance. The device can be terminated by a plurality of polysilicon-filled termination trenches located near the edge of the die, with the polysilicon in each termination trench being connected to the mesa adjacent the termination trench. The polysilicon material in each termination trenches.
1. A method of forming a semiconductor die containing an MIS device comprising:
providing a semiconductor substrate;
forming an epitaxial layer of a first conductivity type on said substrate, said substrate having a net doping concentration of a second conductivity type opposite to said first conductivity type such that forming the epitaxial layer creates a PN junction between said substrate and said epitaxial layer;
etching a plurality of trenches in said epitaxial layer thereby forming a plurality of mesas between said trenches and between one of said trenches and an edge of said die, said trenches extending from a surface of said epitaxial layer and having bottoms in said epitaxial layer above said PN junction, said trenches comprising at least one active trench and a plurality of termination trenches, said termination trenches being located between said at least one active trench and said edge of said die, said mesas comprising at least one active mesa and a plurality of termination mesas said at least one active mesa bordering said at least one active trench, each of said termination mesas bordering at least one of said termination trenches;
introducing a dopant of said second conductivity type through the bottoms of said active trenches and said termination trenches to form a region of said second conductivity type extending between each of said trenches and said substrate;
forming a gate dielectric layer on the walls of said trenches;
introducing a conductive material into said trenches;
implanting a dopant of said second conductivity type into said epitaxial layer so as to form a source region adjacent said at least one active trench;
forming a second dielectric layer over the surface of said epitaxial layer;
masking and etching said second dielectric layer so as to form an opening over, each of said termination trenches and said termination mesas, respectively;
depositing a metal layer over said second dielectric layer, said metal layer flowing into said openings;
masking and etching said metal layer so as to form a plurality of termination metal layers, said termination metal layers being electrically isolated from each other, each of said termination metal layers extending into an opening over one of said termination trenches and an opening over a termination mesa bordering said one of said termination trenches so as to electrically connect the conductive material in said one of said termination trenches and with said termination mesa bordering said one of said termination trenches.
2. The method of claim 1 comprising implanting a dopant of said first conductivity type through said openings in said second dielectric layer over said termination mesas to form contact regions.
3. The method of claim 1 wherein providing a semiconductor substrate comprises forming a second epitaxial layer of said second conductivity type on a semiconductor member of said second conductivity type.
4. The method of claim 1 comprising masking and etching said second dielectric layer so as to form an opening over said source region.
5. The method of claim 4 wherein depositing a metal layer causes metal to flow into said opening in said second dielectric layer over said source metal layer.
6. The method of claim 5 wherein masking and etching said metal layer forms a source metal layer, said source metal layer being in electrical contact with said source region, said source metal layer being isolated from each of said termination metal layers.
7. A method of forming a semiconductor die containing an MIS device comprising:
providing a semiconductor substrate of a first conductivity type;
forming an epitaxial layer of a first conductivity type on said substrate;
implanting a dopant of a second conductivity type into said epitaxial layer so as to create a PN junction in said epitaxial layer;
etching a plurality of trenches in said epitaxial layer thereby forming a plurality of mesas between said trenches and between one of said trenches and an edge of said die, said trenches extending from a surface of said epitaxial layer and having bottoms in said epitaxial layer below said PN junction, said trenches comprising at least one active trench and a plurality of termination trenches, said termination trenches being located between said at least one active trench and said edge of said die, said mesas comprising at least one active mesa and a plurality of termination mesas, said at least one active mesa bordering said at least one active trench, each of said termination mesas bordering at least one of said termination trenches;
forming a gate dielectric layer on the walls of said trenches;
introducing a conductive material into said trenches;
implanting a dopant of said first conductivity type into said epitaxial layer so as to form a source region adjacent said at least one active trench;
forming a second dielectric layer over the surface of said epitaxial layer;
masking and etching said dielectric layer so as to form an opening over each of said termination trenches and said termination mesas, respectively;
depositing a metal layer over said second dielectric layer, said metal layer flowing into said openings;
masking and etching said metal layer so as to form a plurality of termination metal layers, said termination metal layers being electrically isolated from each other, each of said termination metal layers extending into an opening over one of said termination trenches and an opening over a termination mesa bordering said one of said termination trenches so as to electrically connect the conductive material in said one of said termination trenches with said termination mesa bordering said one of said termination trenches.
8. The method of claim 7 comprising implanting a dopant of said second conductivity type through said openings in said second dielectric layer over said termination mesas to form contact regions.
9. The method of claim 7 comprising masking and etching said second dielectric layer so as to form an opening over said source region.
10. The method of claim 9 wherein depositing a metal layer causes metal to flow into said opening in said second dielectric layer over said source metal layer.
11. The method of claim 10 wherein masking and etching said metal layer forms a source metal layer, said source metal layer being in electrical contact with said source region, said source metal layer being isolated from each of said termination metal layers.