Method and system for fabricating edge termination structures in GaN materials
View Patent ↗A method for fabricating an edge termination, which can be used in conjunction with GaN-based materials, includes providing a substrate of a first conductivity type. The substrate has a first surface and a second surface. The method also includes forming a first GaN epitaxial layer of the first conductivity type coupled to the first surface of the substrate and forming a second GaN epitaxial layer of a second conductivity type opposite to the first conductivity type. The second GaN epitaxial layer is coupled to the first GaN epitaxial layer. The substrate, the first GaN epitaxial layer and the second GaN epitaxial layer can be referred to as an epitaxial structure.
1. A method for fabricating an edge termination structure, the method comprising:
providing a GaN substrate of a first conductivity type, the GaN substrate having a first surface and a second surface, the first surface opposite the second surface in a vertical dimension;
forming a first GaN epitaxial layer of the first conductivity type coupled to the first surface of the GaN substrate; and
forming an insulating region in a first portion of the first GaN epitaxial layer, wherein the insulating region extends vertically through at least 90% of the first GaN epitaxial layer to separate an active device region of the first GaN epitaxial layer from an outer region of the first GaN epitaxial layer;
wherein the insulating region circumscribes the active device region.
2. The method of claim 1 wherein the insulating region extends vertically through the first GaN epitaxial layer and into the GaN substrate.
3. The method of claim 1 further comprising:
forming a second GaN epitaxial layer of a second conductivity type opposite the first conductivity type, the second GaN epitaxial layer being coupled to the first GaN epitaxial layer;
wherein the insulating region also extends vertically through the second GaN epitaxial layer.
4. The method of claim 3 further comprising forming a metallic structure electrically coupled to a portion of the second GaN epitaxial layer, wherein the metallic structure comprises an Ohmic contact to the second GaN epitaxial layer.
5. The method of claim 3 wherein:
the GaN substrate is characterized by a first n-type dopant concentration;
the first GaN epitaxial layer is characterized by a second n-type dopant concentration less than the first n-type dopant concentration; and
the second GaN epitaxial layer is characterized by a p-type dopant concentration greater than the second n-type dopant concentration and less than the first n-type dopant concentration.
6. The method of claim 1 wherein forming the insulating region comprises a plurality of ion implantations into the first GaN epitaxial layer, each ion implantation step being performed at a different energy such that corresponding implanted profiles overlap vertically to form a substantially continuous implanted region.
7. The method of claim 1 wherein forming the insulating region comprises:
etching a trench in the vertically into the first GaN epitaxial layer, and
filling the trench with an insulating material.
8. The method of claim 7 wherein:
the insulating material comprises insulating GaN; and
filling the trench comprises selective epitaxial growth.
9. The method of claim 7 wherein the insulating material comprises a dielectric material.
10. The method of claim 1 further comprising forming a metallic structure electrically coupled to a second portion of the first GaN epitaxial layer, wherein the metallic structure comprises a Schottky contact to the second portion of the first GaN epitaxial layer.
11. The method of claim 1 further comprising forming a metallic structure electrically coupled to the second surface of the GaN substrate.
12. A method of fabricating a vertical power device structure, the method comprising:
forming an epitaxial structure by:
providing a III-nitride substrate of a first conductivity type characterized by a first dopant concentration; and
forming a first III-nitride epitaxial layer of the first conductivity type having a thickness and coupled to a first surface of the III-nitride substrate;
defining regions of the epitaxial structure by forming an insulating region of the epitaxial structure, wherein the insulating region electrically separates a device region of the epitaxial structure from an outer region of the epitaxial structure; and
forming one or more active devices using at least the device region of the epitaxial structure, wherein the insulating region extends vertically through at least 90% of the thickness of the first III-nitride epitaxial layer.
13. The method of claim 12 further comprising forming a Schottky metallic structure coupled to the first III-nitride epitaxial layer.
14. The method of claim 12 further comprising:
forming a second III-nitride epitaxial layer of a second conductivity type coupled to the first III-nitride epitaxial layer; and
forming an Ohmic metallic structure coupled to the second III-nitride epitaxial layer.
15. The method of claim 12 further comprising forming an Ohmic metallic structure coupled to a second surface of the III-nitride substrate.
16. The method of claim 12 wherein the insulating region circumscribes the one or more active devices.
17. The method of claim 12 wherein the first III-nitride epitaxial layer is characterized by a second dopant concentration less than the first dopant concentration.
18. The method of claim 12 wherein forming the insulating region comprises:
etching a trench vertically into the first III-nitride epitaxial layer; and
filling the trench with an insulating material.
19. A semiconductor structure comprising:
a GaN substrate having a first surface and a second surface opposing the first surface, wherein the GaN substrate is characterized by a first conductivity type and a first dopant concentration;
a first GaN epitaxial layer of the first conductivity type coupled to the second surface of the GaN substrate, wherein the first GaN epitaxial layer comprises:
an active device region;
an outer region; and
an insulating region disposed between the active device region and the outer region, the insulating region having a thickness greater than 90% of a thickness of the first GaN epitaxial layer.
20. The semiconductor structure of claim 19 further comprising a second GaN epitaxial layer of a second conductivity type coupled to the first GaN epitaxial layer.
21. The semiconductor structure of claim 20 wherein the active device region includes a PN diode, the PN diode comprising at least a portion of the first GaN epitaxial layer and at least a portion of the second GaN epitaxial layer.
22. The semiconductor structure of claim 19 wherein the active device region comprises a Schottky contact electrically coupled to a portion of the first GaN epitaxial layer.
23. The semiconductor structure of claim 22 wherein the Schottky contact extends laterally over at least a portion of the insulating region.
24. The semiconductor structure of claim 19 wherein the active device region includes one or more elements of a vertical JFET.
25. The semiconductor structure of claim 19 wherein the active device region includes at least a portion of a vertical Schottky diode.
26. The semiconductor structure of claim 19 further comprising a field plate coupled to the active device region, the field plate extending laterally over at least a portion of the insulating region.
27. The semiconductor structure of claim 19 wherein the insulating region circumscribes the active device region.
28. The semiconductor structure of claim 19 wherein:
a depletion region is formed adjacent to the insulating region when the semiconductor structure is reverse biased; and
a thickness of the depletion region is less than the thickness of the insulating region.