Group III-N transistor on nanoscale template structures
A III-N semiconductor channel is formed on a III-N transition layer formed on a ( 111 ) or ( 110 ) surface of a silicon template structure, such as a fin sidewall. In embodiments, the silicon fin has a width comparable to the III-N epitaxial film thicknesses for a more compliant seeding layer, permitting lower defect density and/or reduced epitaxial film thickness. In embodiments, a transition layer is GaN and the semiconductor channel comprises Indium (In) to increase a conduction band offset from the silicon fin. In other embodiments, the fin is sacrificial and either removed or oxidized, or otherwise converted into a dielectric structure during transistor fabrication. In certain embodiments employing a sacrificial fin, the III-N transition layer and semiconductor channel is substantially pure GaN, permitting a breakdown voltage higher than would be sustainable in the presence of the silicon fin.
1. A III-N field effect transistor (FET) disposed on a silicon substrate, the FET comprising:
a dielectric anchor disposed over the substrate;
a first and second group III-N device layer stack physically separated from each other by the dielectric anchor; and
a gate stack disposed over the III-N device layer stacks to control a conductivity of a channel semiconductor layer in each of the III-N device layer stacks.
2. The III-N FET of claim 1 , wherein the channel semiconductor layer comprises InGaN with 20% In, or less.
3. The III-N FET of claim 1 , wherein the dielectric anchor comprises a silicon-based dielectric fin.
4. The III-N FET of claim 3 , wherein the dielectric anchor further comprises silicon dioxide in contact with a first crystalline transition layer disposed between the silicon dioxide and a first of the semiconductor channel layers, the silicon dioxide in further contact with a second crystalline transition layer disposed between the silicon dioxide and a second of the semiconductor channel layers.
5. The III-N FET of claim 1 , wherein the dielectric anchor further comprises a gate dielectric layer, and wherein the gate dielectric layer is further disposed over a III-N polarization layer of each of the III-N device layer stacks.
6. The III-N FET of claim 5 , wherein the dielectric anchor further comprises a gate electrode material, and wherein the gate dielectric layer is disposed between the gate electrode material and each of the first and second III-N device layer stacks.
7. The III-N FET of claim 1 , wherein each of the III-N device layer stacks further comprises:
a channel semiconductor layer of GaN disposed on a transition layer; and
a polarization layer of AlN, AlInN, AlGaN, or AlInGaN disposed on the GaN channel semiconductor layer.
8. The III-N FET of claim 7 , wherein the transition layer further comprises at least one of: a crystalline oxide, AlN, AlInN, or AlGaN.
9. A method of forming a III-N field effect transistor (FET), the method comprising:
forming a silicon fin over a substrate, the silicon fin having first and second sidewalls with a ( 111 ) surface or a ( 110 ) surface;
epitaxially growing first and second III-N semiconductor device stacks on the first and second sidewalls, respectively, of the silicon fin, wherein each of the first and second III-N semiconductor device stacks comprises a III-N channel semiconductor layer; and
forming a gate stack over the first and second III-N semiconductor device stacks, wherein the method comprises at least one of:
growing an InGaN material as the III-N semiconductor channel layers;
removing the silicon fin subsequent to epitaxially growing the first and second III-N semiconductor device stacks; or
converting the silicon fin to a silicon-based dielectric material subsequent to epitaxially growing the first and second III-N semiconductor device stacks.
10. The method of claim 9 , wherein the method comprises removing the silicon fin with a selective etch chemistry subsequent to epitaxially growing the first and second III-N semiconductor device stacks.
11. The method of claim 9 , wherein the method comprises converting the silicon fin into a silicon-based dielectric subsequent to epitaxially growing the first and second III-N semiconductor device stacks.
12. The method of claim 11 , wherein converting the silicon fin into a silicon-based dielectric further comprises exposing a top surface of the silicon fin to a plasma or thermal oxidation process.
13. The method of claim 9 , wherein forming the fin further comprises:
patterning an isolation region around a portion of the substrate silicon having a width no more than 20 nm; and
recessing the isolation region to provide the first and second sidewalls with a height of no more than 100 nm, and wherein the method further comprises:
forming a structural support disposed along a length of the fin prior to removing or converting the silicon fin into the silicon-based dielectric material.
14. The method of claim 9 , wherein forming the gate stack further comprises:
depositing one or more gate dielectric layer over the first and second III-N semiconductor device stacks using an atomic layer deposition process; and
depositing one or more gate electrode layer over the gate dielectric layer using an atomic layer deposition process.
15. The method of claim 14 , wherein depositing the one or more gate dielectric layers further comprises depositing the gate dielectric layer on a side of a transition layer opposite the III-N semiconductor channel layer.