Method for regrown source contacts for vertical gallium nitride based FETS

1. A method for forming an alignment contact, the method comprising:

providing a III-nitride substrate;

epitaxially growing a first III-nitride layer on the III-nitride substrate, wherein the first III-nitride layer is characterized by a first conductivity type;

forming a plurality of III-nitride fins on the first III-nitride layer, wherein each the plurality of III-nitride fins is separated by one of a plurality of first recess regions and characterized by a fin surface, wherein the plurality of III-nitride fins are characterized by the first conductivity type;

forming a III-nitride gate layer disposed between adjacent III-nitride fins of the plurality of III-nitride fins, wherein a surface of the III-nitride gate layer is substantially coplanar with the fin surface;

epitaxially regrowing a III-nitride source contact portion on each of the plurality of III-nitride fins; and

forming a source contact structure on the III-nitride source contact portions.

2. The method of claim 1 wherein the III-nitride substrate comprises an n-GaN substrate.

3. The method of claim 1 wherein the first III-nitride layer and the plurality of III-nitride fins comprise an n-GaN epitaxial layer.

4. The method of claim 1 , further comprising, prior to forming the plurality of III-nitride fins, forming a hardmask on the fin surface of each of the plurality of III-nitride fins.

5. The method of claim 1 wherein sidewalls of each of the plurality of III-nitride fins are aligned with an m-plane and the fin surface is aligned with a c-plane.

6. The method of claim 1 wherein epitaxially regrowing the III-nitride source contact portion comprises performing a self-limiting growth process on top of each of the plurality of III-nitride fins and the epitaxially regrown III-nitride source contact portion is characterized by an isosceles triangle shape having a base angle in a range between 58 degrees and 65 degrees in a cross-section view.

7. A method for forming an alignment contact, the method comprising:

providing a III-nitride substrate;

epitaxially growing a first III-nitride layer on the III-nitride substrate, wherein the first III-nitride layer is characterized by a first conductivity type;

forming a first hardmask layer on the first III-nitride layer;

forming a plurality of III-nitride fins on the first III-nitride layer using the first hardmask layer as a mask, wherein each of the plurality of III-nitride fins are separated by one of a plurality of first recess regions and characterized by a fin surface, wherein the plurality of III-nitride fins are characterized by the first conductivity type;

epitaxially growing a III-nitride gate layer having a second conductivity type opposite to the first conductivity type in the plurality of first recess regions, wherein a surface of the III-nitride gate layer is substantially coplanar with the fin surface;

forming a first dielectric layer on the first hardmask layer and the III-nitride gate layer, wherein the first dielectric layer comprises a contact region aligned with each of the plurality of III-nitride fins and a gate region aligned with the III-nitride gate layer;

forming a photoresist layer on the gate region of the first dielectric layer;

etching the contact region of the first dielectric layer using the photoresist layer as a mask to form a second recess region, wherein an upper surface of each of the plurality of the III-nitride fins and a portion of upper surface of the III-nitride gate layer surrounding each of the plurality of III-nitride fins are exposed from a bottom surface of the second recess region;

removing the photoresist layer;

epitaxially regrowing a III-nitride source contact portion in the second recess region; and

removing the first dielectric layer.

8. The method of claim 7 wherein a width of the contact region is at least three times of that of a width of each of the plurality of III-nitride fins.

9. The method of claim 7 , further comprising:

forming a source metal mask layer having an opening aligned with the III-nitride source contact portion on each of the plurality of III-nitride fins;

forming a first source metal layer coupled to the III-nitride source contact portion;

forming a second source metal layer coupled to the first source metal layer;

forming a third source metal layer coupled to the second source metal layer; and

removing the source metal mask layer.

10. The method of claim 7 wherein epitaxially regrowing the III-nitride source contact portion comprises performing a self-limiting growth process on top of each of the plurality of III-nitride fins.

11. The method of claim 7 wherein the III-nitride source contact portion is characterized by an isosceles triangle shape having a base angle in a range between 58 degrees and 65 degrees in a cross-section view.

12. The method of claim 7 wherein the III-nitride gate layer is disposed in the plurality of first recess regions between adjacent III-nitride fins of the plurality of III-nitride fins.