Group III-N transistors 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:
an anchor disposed over the substrate;
a first and second group III-N device layer stack physically separated from each other by the anchor, and each stack with a c-axis extending in opposite directions from the anchor and substantially parallel to a surface plane of the substrate; 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, wherein the channel semiconductor layer has a conduction band offset from the anchor material.
2. The III-N FET of claim 1 , wherein the anchor further comprises a silicon fin having sidewalls with a (111) or (110) surface, the sidewalls substantially perpendicular to the III-N device layer stack c-axis.
3. The III-N FET of claim 2 , wherein the channel semiconductor layer comprises InGaN with 20% In, or less.
4. The III-N FET of claim 2 , wherein the silicon fin has a top surface minimum dimension of no more than 20 nm and wherein the sidewalls have a z-height no greater than 100 nm.
5. The III-N FET of claim 1 , wherein the anchor further comprises a silicon-based dielectric fin.
6. The III-N FET of claim 5 , wherein the 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.
7. The III-N FET of claim 1 , wherein the 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.
8. The III-N FET of claim 7 , wherein the 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.
9. 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.
10. The III-N FET of claim 9 , wherein the transition layer further comprises at least one of: a crystalline oxide, AlN, AlInN, or AlGaN.
11. 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 a first crystalline transition layer on the first sidewall and a second crystalline transition layer on the second sidewall;
epitaxially growing a first III-N semiconductor channel layer over the first transition layer and a second III-N semiconductor channel layer over the second transition layer;
epitaxially growing a first III-N semiconductor polarization layer over the first III-N semiconductor channel and a second III-N semiconductor polarization layer over the second III-N semiconductor channel; and
forming a gate stack over the first and second polarization layers, wherein the method comprises at lest one of:
growing an InGaN material as the III-N semiconductor channel layers;
removing the silicon fin subsequent to epitaxially growing at least the transition layers; or
converting the silicon fin to a silicon-based dielectric material subsequent to epitaxially growing at least the transition layer.
12. The method of claim 11 , wherein the method comprises removing the silicon fin with a selective etch chemistry subsequent to epitaxially growing the transition layers, channel layers, and polarization layers.
13. The method of claim 11 , wherein the method comprises converting the silicon fin into a silicon-based dielectric subsequent to epitaxially growing the transition layers, channel layers, and polarization layers.
14. The method of claim 13 , 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.
15. The method of claim 11 , 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.
16. The method of claim 11 , wherein forming the gate stack further comprises:
depositing one or more gate dielectric layer over the polarization layers 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.
17. The method of claim 16 , wherein depositing the one or more gate dielectric layers further comprises depositing the a gate dielectric layer on a side of the transition layer opposite the III-N semiconductor channel layer.
18. The method of claim 11 , wherein epitaxially growing the first and second crystalline transition layers further comprises growing at least one of: a crystalline oxide and a III-N semiconductor to a thickness less than 100 nm, wherein the first and second semiconductor channel layers are grown to a thickness less than 50 nm, and wherein the first and second polarization layers are grown to a thickness less than 10 nm.