Crystal orientation engineering to achieve consistent nanowire shapes

1. A semiconductor structure comprising:

a column of horizontally-oriented nanosheet transistors, each of the nanosheet transistors having a respective channel segment of semiconductor crystalline nanosheet material sheathed by gate stack material; and

a substrate supporting the column,

wherein the channel segments of semiconductor crystalline nanosheet material have a diamond cubic crystal structure and which is oriented such that {111} planes of the nanosheet material are horizontal.

2. The structure of claim 1 , wherein the column comprises a plurality of the nanosheet transistors.

3. The structure of claim 1 , wherein the gate stack material comprises a gate conductor sheathing the channel segment of each of the nanosheet transistors and spaced from the channel segment of each of the nanosheet transistors by a gate dielectric material.

4. The structure of claim 3 , wherein each of the nanosheet transistors further includes source and drain regions disposed on opposite ends of the of the channel segments longitudinally,

wherein all of the source regions are connected in parallel, all of the drain regions are connected in parallel, and all of the gate conductors are connected in parallel.

5. The structure of claim 3 , further comprising a second column of the horizontally-oriented nanosheet transistors,

wherein each of the nanosheet transistors further includes source and drain regions disposed on opposite ends of the of the channel segments longitudinally,

wherein all of the source regions are connected in parallel, all of the drain regions are connected in parallel, and all of the gate conductors are connected in parallel.

6. The structure of claim 1 , wherein the semiconductor crystalline nanosheet material is silicon or a silicon alloy.

7. A method of making a semiconductor structure, comprising:

providing a substrate; and

forming a column of horizontally-oriented nanosheet transistors supported on the substrate, each of the nanosheet transistors having a respective channel segment of semiconductor crystalline nanosheet material sheathed by gate stack material,

wherein the channel segments of semiconductor crystalline nanosheet material have a diamond cubic crystal structure and which is oriented such that { 111 } planes of the nanosheet material are horizontal.

8. The method of claim 7 , wherein the column comprises a plurality of the nanosheet transistors.

9. The method of claim 7 , wherein the gate stack material comprises a gate conductor sheathing the channel segment of each of the nanosheet transistors and spaced from the channel segment of each of the nanosheet transistors by a gate dielectric material.

10. The method of claim 9 , wherein each of the nanosheet transistors further includes source and drain regions disposed on opposite ends of the of the channel segments longitudinally,

wherein all of the source regions are connected in parallel, all of the drain regions are connected in parallel, and all of the gate conductors are connected in parallel.

11. The method of claim 9 , further comprising forming a second column of the horizontally-oriented nanosheet transistors,

wherein each of the nanosheet transistors further includes source and drain regions disposed on opposite ends of the of the channel segments longitudinally,

wherein all of the source regions are connected in parallel, all of the drain regions are connected in parallel, and all of the gate conductors are connected in parallel.

12. The method of claim 7 , wherein the forming of the column of the horizontally-oriented nanosheet transistors comprises:

forming on the substrate a column of layers including at least one silicon layer each spaced from a next layer below, each of the silicon layers being oriented such that { 111 } planes of the silicon layers are horizontal;

annealing the column of layers to round corners of the channel segment of each of the silicon layers in the stack; and

sheathing the channel segment of each of the silicon layers in the stack with the gate stack material.

13. The method of claim 12 , wherein the gate stack material comprises a gate conductor sheathing the channel segment of each of the nanosheet transistors and spaced from the channel segment of each of the nanosheet transistors by a gate dielectric material,

and wherein the forming of the column of the horizontally-oriented nanosheet transistors further comprises:

forming source and drain regions on opposite ends of the of the channel segments longitudinally;

connecting all of the source regions in parallel;

connecting all of the drain regions in parallel; and

connecting all of the gate conductors in parallel.

14. The method of claim 12 , wherein the forming on the substrate a column of layers including at least one silicon layer each spaced from a next layer below comprises:

forming on the substrate a stack of silicon layers alternating with layers of a sacrificial material, including at least one silicon layer and at least one layer of the sacrificial material below each of the silicon layers and above the substrate;

patterning the stack to form a column of the alternating silicon layers and layers of the sacrificial material; and

removing the sacrificial material at least below a respective channel segment of each of the silicon layers in the column.

15. The method of claim 14 , wherein the substrate has a top surface of silicon oriented such that { 111 } planes of the top surface of silicon are horizontal,

wherein the sacrificial material has a diamond cubic crystal structure,

and wherein the forming on the substrate a stack of silicon layers alternating with layers of a sacrificial material, comprises growing the stack of layers epitaxially on the substrate.

16. The method of claim 15 , wherein the sacrificial material is SiGe.

17. An intermediate structure comprising:

a substrate; and

a plurality of parallel ridges supported by the substrate,

wherein each of the ridges comprises a plurality of layers of silicon alternating with layers of SiGe, and wherein each of the ridges comprises at least one layer of SiGe below each silicon layer of the plurality of silicon layers and above the substrate,

and wherein the silicon layers have a diamond cubic crystal structure, which is oriented such that { 111 } planes of the silicon layers are horizontal.

18. The intermediate structure of claim 17 , wherein the SiGe layers are oriented such that { 111 } planes of the SiGe layers are horizontal.

19. The intermediate structure of claim 18 , wherein the substrate has a top surface of { 111 }-oriented silicon,

and wherein the SiGe layers are formed by epitaxial growth on the substrate.