Method of manufacturing a source/drain feature in a multi-gate semiconductor structure

1. A method of manufacturing a semiconductor device, comprising:

forming a fin structure in which first semiconductor layers and second semiconductor layers are alternately stacked;

forming a sacrificial gate structure over the fin structure;

etching a source/drain region of the fin structure, which is not covered by the sacrificial gate structure, thereby forming a source/drain trench;

laterally etching the first semiconductor layers through the source/drain trench;

forming an inner spacer layer, in the source/drain trench, at least on lateral ends of the etched first semiconductor layers;

forming a seeding layer on the inner spacer layer; and

growing a source/drain epitaxial layer in the source/drain trench, wherein the growing of the source/drain epitaxial layer includes growing the source/drain epitaxial layer from the seeding layer and from lateral ends of the second semiconductor layers.

2. The method of claim 1 , wherein the seeding layer is partially embedded in the inner spacer layer.

3. The method of claim 1 , wherein the forming of the inner spacer layer includes:

depositing the inner spacer layer in the source/drain trench, thereby covering lateral ends of the second semiconductor layers; and

partially removing the inner spacer layer to expose the lateral ends of the second semiconductor layers.

4. The method of claim 1 , wherein the forming of the seeding layer includes:

epitaxially growing the seeding layer on the inner spacer layer, wherein the seeding layer covers lateral ends of the second semiconductor layers; and

partially removing the seeding layer from the lateral ends of the second semiconductor layers.

5. The method of claim 1 , further comprising:

after the forming of the seeding layer, oxidizing the inner spacer layer.

6. The method of claim 1 , wherein the growing of the source/drain epitaxial layer includes:

growing a first epitaxial layer directly from the seeding layer; and

growing a second epitaxial layer directly from the first epitaxial layer, wherein the second epitaxial layer has a higher dopant concentration than that of the first epitaxial layer.

7. The method of claim 1 , wherein the inner spacer layer includes germanium.

8. The method of claim 1 , wherein the seeding layer includes undoped silicon.

9. The method of claim 1 , wherein the seeding layer includes amorphous silicon.

10. The method of claim 1 , further comprising:

removing the sacrificial gate structure, thereby forming a gate trench;

removing the first semiconductor layers from the gate trench, thereby exposing the second semiconductor layers in the gate trench; and

forming a metal gate structure engaging the exposed second semiconductor layers.

11. A method of manufacturing a semiconductor device, comprising:

forming a fin extruding from a substrate, the fin having a plurality of sacrificial layers and a plurality of channel layers, wherein the sacrificial layers and the channel layers are alternately arranged;

removing the sacrificial layers and the channel layers from a source/drain region of the fin, thereby forming a source/drain trench;

depositing a first semiconductor layer in the source/drain trench;

depositing a second semiconductor layer on the first semiconductor layer;

partially removing the first semiconductor layer and the second semiconductor layer to expose the channel layers in the source/drain trench;

oxidizing the first semiconductor layer; and

epitaxially growing a source/drain feature from the second semiconductor layer.

12. The method of claim 11 , wherein the second semiconductor layer has a dielectric constant higher than that of the oxidized first semiconductor layer.

13. The method of claim 11 , wherein the first semiconductor layer includes silicon germanium and the second semiconductor layer includes silicon.

14. The method of claim 11 , wherein after the partially removing of the first semiconductor layer and the second semiconductor layer, remaining portions of the second semiconductor layer are surrounded by the first semiconductor layer.

15. The method of claim 11 , wherein the depositing of the first semiconductor layer and the depositing of the second semiconductor layer both include an epitaxial growing process.

16. The method of claim 11 , further comprising:

removing the sacrificial layers from a channel region of the fin, thereby forming a gate trench; and

forming a gate structure engaging the channel layers in the gate trench.

17. A method of manufacturing a semiconductor device, comprising:

forming a stack of alternately vertically arranged first semiconductor layers and second semiconductor layers;

patterning the stack in forming a fin;

etching a portion of the fin in forming a trench;

depositing a spacer layer on sidewalls of the trench;

depositing a semiconductive material layer covering the spacer layer in the trench;

partially removing the semiconductive material layer from portions of the spacer layer that are deposited on lateral ends of the second semiconductor layers;

etching the portions of the spacer layer and exposing the lateral ends of the second semiconductor layers; and

growing an epitaxial feature in the trench, wherein the growing of the epitaxial layer includes directly growing the epitaxial layer from remaining portions of the semiconductive material layer.

18. The method of claim 17 , wherein the remaining portions of the semiconductive material layer are partially embedded in the spacer layer.

19. The method of claim 17 , further comprising:

after the partially removing of the semiconductive material layer, oxidizing the spacer layer.

20. The method of claim 19 , wherein the oxidized spacer layer includes silicon germanium oxide.