Stacked nanowires
Techniques for producing stacked SiGe nanowires using a condensation process without parasitic Ge nanowires as an undesired by-product. In one aspect, a method of forming SiGe nanowires includes the steps of: forming a stack of alternating Si and SiGe layers on a wafer; patterning fins in the stack; selectively thinning the SiGe layers in the fins such that the Si and SiGe layers give the fins an hourglass shape; burying the fins in an oxide material; and annealing the fins under conditions sufficient to diffuse Ge from the SiGe layers in the fins to the Si layers in the fins to form the SiGe nanowires. A FET device and method for formation thereof are also provided.
1. A field effect transistor (FET) device, comprising:
at least one stack of silicon germanium (SiGe) nanowires;
a gate at least partially surrounding a portion of each of the SiGe nanowires that serves as a channel region of the FET device, wherein portions of the SiGe nanowires extending out from the gate serve as source and drain regions of the FET device, and wherein the SiGe nanowires have a uniform diameter throughout the source, drain, and channel regions of the FET device; and
inner spacers between the channel region and the source and drain regions, wherein the inner spacers have an hourglass shape in between the SiGe nanowires.
2. The FET device of claim 1 , wherein the inner spacers are formed from an oxide material.
3. The FET device of claim 1 , wherein the gate fully surrounds the portion of each of the SiGe nanowires in a gate-all-around (GAA) configuration.
4. The FET device of claim 1 , wherein the gate is a metal gate.
5. The FET device of claim 4 , wherein the gate comprises an n-type workfunction setting metal.
6. The FET device of claim 5 , wherein the n-type workfunction setting metal is selected from the group consisting of: titanium nitride and tantalum nitride.
7. The FET device of claim 4 , wherein the gate comprises a p-type workfunction setting metal.
8. The FET device of claim 7 , wherein the p-type workfunction setting metal is tungsten.
9. The FET device of claim 1 , wherein the gate only partially surrounds the portion of each of the SiGe nanowires.
10. The FET device of claim 9 , further comprising:
an oxide material between the SiGe nanowires which physically supports the SiGe nanowires in the channel region and in the source and drain regions of the FET device.
11. The FET device of claim 1 , further comprising:
a gate dielectric separating the SiGe nanowires from the gate.
12. The FET device of claim 11 , wherein the gate dielectric is disposed as a conformal layer on the SiGe nanowires.
13. The FET device of claim 11 , wherein the gate dielectric is selected from the group consisting of: hafnium oxide and lanthanum oxide.
14. The FET device of claim 1 , further comprising:
epitaxial SiGe on the portions of the SiGe nanowires extending out from the gate in the source and drain regions of the FET device.
15. The FET device of claim 14 , wherein the epitaxial SiGe fully surrounds the portions of the SiGe nanowires extending out from the gate in the source and drain regions of the FET device.
16. The FET device of claim 14 , wherein the epitaxial SiGe is doped with an n-type dopant.
17. The FET device of claim 14 , wherein the epitaxial SiGe is doped with a p-type dopant.
18. The FET device of claim 1 , wherein the SiGe nanowires comprise from about 10% to about 60% germanium (Ge), and ranges therebetween.