Method of fabricating a gallium nitride merged P-I-N schottky (MPS) diode by regrowth and etch back
View Patent ↗An MPS diode includes a III-nitride substrate characterized by a first conductivity type and a first dopant concentration and having a first side and a second side. The MPS diode also includes a III-nitride epitaxial structure comprising a first III-nitride epitaxial layer coupled to the first side of the substrate, wherein a region of the first III-nitride epitaxial layer comprises an array of protrusions. The III-nitride epitaxial structure also includes a plurality of III-nitride regions of a second conductivity type, each partially disposed between adjacent protrusions. Each of the plurality of III-nitride regions of the second conductivity type comprises a first section laterally positioned between adjacent protrusions and a second section extending in a direction normal to the first side of the substrate. The MPS diode further includes a first metallic structure electrically coupled to one or more of the protrusions and to one or more of the second sections.
1. A method for fabricating an MPS diode, the method comprising:
providing a III-nitride substrate of a first conductivity type having a first surface and a second surface opposing the first surface;
forming a first III-nitride epitaxial layer of the first conductivity type coupled to the first surface of the III-nitride substrate, the first III-nitride epitaxial layer having a first surface adjacent the first surface of the III-nitride substrate and a second surface opposing the first surface;
forming a mask pattern coupled to the second surface of the first III-nitride epitaxial layer to define etch areas;
etching the etch areas to form a plurality of recessed regions extending to a predetermined depth into the first III-nitride epitaxial layer;
regrowing a second III-nitride epitaxial layer that fills the recessed regions and extends to a predetermined height from the second surface of the first III-nitride epitaxial layer, wherein the second III-nitride epitaxial layer is lattice matched with the first III-nitride epitaxial layer;
forming a second mask pattern coupled to the second III-nitride epitaxial layer to define second etch areas;
etching the second etch areas to define a plurality of regrown regions extending in a direction normal to the second surface of the first III-nitride epitaxial layer and to expose a plurality of portions of the first III-nitride epitaxial layer;
forming a first metallic structure electrically coupled to one or more of the plurality of regrown regions and one or more of the exposed portions of the first III-nitride epitaxial layer; and
forming a second metallic structure electrically coupled to the second surface of the III-nitride substrate.
2. The method of claim 1 wherein the first metallic structure comprises a Schottky contact to the exposed portions of the first III-nitride epitaxial layer and an ohmic contact to the one or more of the plurality of regrown regions.
3. The method of claim 1 wherein the exposed plurality of portions of the first III-nitride epitaxial layer are individually interspersed between the plurality of regrown regions.
4. The method of claim 1 wherein a lateral width of each of the plurality of regrown regions measured in the plane of the second surface of the first III-nitride epitaxial layer is greater than a lateral width of each of the exposed plurality of portions of the first III-nitride epitaxial layer measured in the plane of the second surface of the first III-nitride epitaxial layer.
5. The method of claim 1 wherein the III-nitride substrate is characterized by a first dopant concentration and the first III-nitride epitaxial layer is characterized by a second n-type dopant concentration less than the first dopant concentration.
6. The method of claim 1 wherein at least one of the plurality of regrown regions is configured to provide edge termination to a semiconductor device.
7. The method of claim 1 wherein at least one of the plurality of regrown regions is configured to provide a junction termination extension to a semiconductor device.
8. The method of claim 1 wherein:
the first III-nitride epitaxial layer is GaN; and
the first conductivity type is n-type.
9. The method of claim 1 wherein:
each of the plurality of regrown regions comprises a first section and a second section;
the first section, of each of the plurality of III-nitride regions, is disposed between portions of the first III-nitride epitaxial layer; and
the second section, of each of the plurality of III-nitride regions, extends beyond a height of portions of the first III-nitride epitaxial layer and has a width greater than a width of a corresponding first section such that the second section overhangs the corresponding first section.
10. The method of claim 9 wherein the first section of each of the plurality of regrown regions has a thickness measured in a direction normal to the first surface of the III-nitride substrate, and the thickness is between 0.1 microns and 5 microns.
11. The method of claim 1 wherein the first III-nitride epitaxial layer is formed to have a thickness measured in a direction normal to the first surface of the III-nitride substrate, and the thickness is between 0.5 microns and 100 microns.
12. The method of claim 11 wherein the thickness is between 5 microns and 100 microns.
13. The method of claim 1 wherein:
the plurality of regrown regions have a doping concentration in a range from 10 17 to 2×10 20 cm −3 ;
the first III-nitride epitaxial layer has a doping concentration in a range from 10 17 to 2×10 20 cm −3 ; and
the III-nitride substrate has a doping concentration in a range from 10 17 to 1×10 20 cm −3 .