Nanosheet transistor having abrupt junctions between the channel nanosheets and the source/drain extension regions

1. A method of performing fabrication operations to form a nanosheet field effect transistor (FET) device, wherein the fabrication operations include:

forming a nanosheet stack over a substrate;

wherein the nanosheet stack comprises a plurality of channel nanosheets;

wherein the plurality of channel nanosheets includes a first channel nanosheet having a first end region, a second end region, and a central region positioned between the first end region and the second end region;

wherein the first end region, the second end region, and the central region each comprises a first type of semiconductor material;

wherein, when the first type of semiconductor material is at a first temperature, the first type of semiconductor material has a first diffusion coefficient for a dopant; and

converting the central region to a second type of semiconductor material;

wherein, when the second type of semiconductor material is at the first temperature, the second type of semiconductor material has a second diffusion coefficient for the dopant.

2. The method of claim 1 , wherein:

the first type of semiconductor material includes a first concentration of a first semiconductor; and

the second type of semiconductor material includes a second concentration of the first semiconductor.

3. The method of claim 2 , wherein the first concentration is less than the second concentration.

4. The method of claim 3 , wherein:

the first type of semiconductor material comprises a first SiGe alloy;

the first semiconductor comprises Ge;

the second type of semiconductor material comprises a second SiGe alloy; and

the second semiconductor comprises Ge.

5. The method of claim 1 , wherein converting the central region to the second type of semiconductor material comprises:

depositing a donor layer on the central region; and

exposing the donor layer and the central region to an anneal in an inert gas ambient;

wherein the anneal initiates a chemical reaction between the donor layer and the central region; and

wherein a result of the chemical reaction comprises converting the central region from the first type of semiconductor material to the second type of semiconductor material.

6. The method of claim 5 , wherein the first type of semiconductor material comprises a first SiGe alloy having a first Ge concentration.

7. The method of claim 6 , wherein the second type of semiconductor material comprises a second SiGe alloy having a second Ge concentration.

8. The method of claim 7 , wherein the first Ge concentration is less than the second Ge concentration.

9. The method of claim 1 , wherein the fabrication operations further include:

forming a source or drain (S/D) region over the substrate;

wherein the S/D region is communicatively coupled to the first end region;

doping the S/D region with the dopant; and

forming a junction between the first end region and the central region by applying an anneal at the first temperature to the S/D region and the first end region, wherein the anneal is configured to diffuse the dopant from the S/D region through the first end region that comprises the first type of semiconductor material having the first diffusion coefficient for the dopant.

10. The method of claim 9 , wherein:

the first type of semiconductor material comprises a first SiGe alloy having a first Ge concentration; and

the second type of semiconductor material comprises a second SiGe alloy having a second Ge concentration;

wherein the first Ge concentration is less than the second Ge concentration.

11. The method of claim 10 , wherein the first diffusion coefficient is greater than the second diffusion coefficient.

12. A method of performing fabrication operations to form a nanosheet field effect transistor (FET) device, wherein the fabrication operations include:

forming a nanosheet stack over a substrate;

wherein the nanosheet stack comprises a plurality of channel nanosheets;

wherein the plurality of channel nanosheets includes a first channel nanosheet having a first end region, a second end region, and a central region positioned between the first end region and the second end region;

wherein the first end region, the second end region, and the central region each comprises a first type of semiconductor material;

wherein, when the first type of semiconductor material is at a first temperature, the first type of semiconductor material has a first diffusion coefficient for a dopant;

forming a source or drain (S/D) region over the substrate;

wherein forming the S/D region comprises epitaxially growing the S/D region from the first end region such that the S/D region is communicatively coupled to the first end region;

doping the S/D region with the dopant;

converting the central region to a second type of semiconductor material;

wherein, when the second type of semiconductor material is at the first temperature, the second type of semiconductor material has a second diffusion coefficient for the dopant; and

forming a junction between the first end region and the central region by applying a first anneal at the first temperature to the S/D region and the first end region, wherein the first anneal is configured to diffuse the dopant from the S/D region through the first end region that comprises the first type of semiconductor material having the first diffusion coefficient for the dopant;

wherein the first diffusion coefficient is greater than the second diffusion coefficient.

13. The method of claim 12 , wherein:

the first type of semiconductor material includes a first concentration of a first semiconductor; and

the second type of semiconductor material includes a second concentration of the first semiconductor.

14. The method of claim 13 , wherein the first concentration is less than the second concentration.

15. The method of claim 14 , wherein:

the first type of semiconductor material comprises a first SiGe alloy;

the first semiconductor comprises Ge;

the second type of semiconductor material comprises a second SiGe alloy; and

the second semiconductor comprises Ge.

16. The method of claim 12 , wherein converting the central region to the second type of semiconductor material comprises:

depositing a donor layer on the central region; and

exposing the donor layer and the central region to a second anneal in an inert gas ambient;

wherein the second anneal initiates a chemical reaction between the donor layer and the central region; and

wherein a result of the chemical reaction comprises converting the central region from the first type of semiconductor material to the second type of semiconductor material.

17. The method of claim 16 , wherein:

the first type of semiconductor material comprises a first SiGe alloy having a first Ge concentration;

the second type of semiconductor material comprises a second SiGe alloy having a second Ge concentration; and

the first Ge concentration is less than the second Ge concentration.