Method of forming a multi-layer epitaxial source/drain region having varying concentrations of boron and germanium therein

1. A method comprising:

depositing a first dummy gate over and along sidewalls of a first fin, the first fin extending from a substrate;

forming a first gate spacer along a sidewall of the first dummy gate;

forming a first recess in the first fin adjacent the first gate spacer; and

epitaxially growing a first source/drain region in the first recess, the first source/drain region having a first layer and a second layer, the first layer having a higher germanium concentration than the second layer, the first layer having a lower boron concentration than the second layer, the first layer being the innermost layer of the first source/drain region, an outer surface of the second layer of the first source/drain region having more than eight facets in a first plane, the first plane being orthogonal to a top surface of the substrate, the first layer having a boron concentration in a range from 3E20 cm −3 to 5E20 cm −3 , the second layer having a boron concentration in a range from 6E20 cm −3 to 1E21 cm −3 .

2. The method of claim 1 , wherein epitaxially growing the first source/drain region in the first recess comprises epitaxially growing the first source/drain region in the first recess with a first ratio of etchant precursors to deposition precursors, the first ratio being in a range from 0.05/1 to 0.25/1.

3. The method of claim 1 , wherein an intersection of adjacent facets on the outer surface of the first source/drain region form a first angle, the first angle being in a range from 140° to 180°.

4. The method of claim 1 further comprising:

replacing the first dummy gate with a functional gate stack disposed over and along sidewalls of the first fin.

5. The method of claim 1 further comprising:

forming an etch stop layer over the first source/drain region and on a sidewall of the first gate spacer;

forming a first interlayer dielectric over the etch stop layer;

forming a second interlayer dielectric over the first interlayer dielectric;

etching a hole through the first and second interlayer dielectrics and the etch stop layer; and

forming a first conductive contact in the hole, the first conductive contact being electrically coupled to the first source/drain region.

6. The method of claim 5 , wherein the first conductive contact physically contacts a top surface of the first source/drain region for a first distance in a first plane, the first plane being orthogonal to a top surface of the substrate and perpendicular to a longitudinal axis of the first fin, a widest portion of the first source/drain region in the first plane being separated by a second distance, the first distance being in a range of 30% to 70% of the second distance.

7. The method of claim 1 , wherein the facets on the outer surface of the first source/drain region are along (111), (113), and (119) planes.

8. The method of claim 1 , wherein the second layer is the outermost layer of the first source/drain region.

9. The method of claim 1 , wherein the first layer has the highest germanium percentage of any layer in the first source/drain region.

10. A method comprising:

forming a first dummy gate over and along sidewalls of a first fin extending upwards from a substrate;

forming gate spacers along sidewalls of the first dummy gate and the first fin;

etching a first recess in the first fin adjacent the first dummy gate, the gate spacers being on opposing sides of the first recess;

epitaxially growing a first source/drain region in the first recess with a first ratio of etchant precursors to deposition precursors, the first ratio being in a range from 0.05/1 to 0.25/1, the first source/drain region contacting the gate spacers on opposing sides of the first recess, the first source/drain region having a top surface extending above a top surface of the gate spacers on opposing sides of the first recess, wherein epitaxially growing the first source/drain region in the first recess further comprises:

epitaxially growing a first epitaxial layer from the first fin in the first recess; and

epitaxially growing a second epitaxial layer from the first epitaxial layer, the second epitaxial layer having a greater concentration of boron than the first epitaxial layer, the first epitaxial layer having a greater concentration of germanium than the second epitaxial layer, the second epitaxial layer being the outermost layer of the first source/drain region; and

replacing the first dummy gate with a first functional gate stack disposed over and along sidewalls of the first fin.

11. The method of claim 10 , wherein an outer surface of the first source/drain region has more than eight facets in a first plane, the first plane being orthogonal to a top surface of the substrate.

12. The method of claim 10 , wherein the first epitaxial layer is the innermost layer of the first source/drain region.

13. A method comprising:

forming a first fin extending from a substrate;

forming a first gate stack over and along sidewalls of the first fin;

forming a first gate spacer disposed along a sidewall of the first gate stack; and

forming a first epitaxial source/drain region in the first fin and adjacent the first gate spacer, an outer surface of the epitaxial first source/drain region having more than eight facets in a first plane, the first plane being orthogonal to a top surface of the substrate, wherein the first epitaxial source/drain region comprises:

a first epitaxial layer on the first fin, the first epitaxial layer having a first doping concentration of boron; and

a second epitaxial layer on the first epitaxial layer, the second epitaxial layer having a second doping concentration of boron, the second doping concentration being greater than the first doping concentration, the first epitaxial layer having a higher germanium concentration than the second epitaxial layer, the first epitaxial layer being the innermost layer of the first epitaxial source/drain region, the first epitaxial layer having a boron concentration in a range from 3E20 cm −3 to 5E20 cm −3 , the second epitaxial layer having a boron concentration in a range from 6E20 cm −3 to 1E21 cm −3 .

14. The method of claim 13 further comprising:

forming a second fin extending from a substrate;

forming a second gate stack over and along sidewalls of the second fin;

forming a second gate spacer disposed along a sidewall of the second gate stack; and

forming a second source/drain region in the second fin and adjacent the second gate spacer, the second source/drain region comprising a third epitaxial layer, the third epitaxial layer having a different material composition than the first and second epitaxial layers.

15. The method of claim 13 , wherein the facets on the outer surface of the epitaxial first source/drain region are along (111), (113), and (119) planes.

16. The method of claim 13 further comprising:

forming an etch stop layer over the first epitaxial source/drain region and on a sidewall of the first gate spacer;

forming a first interlayer dielectric over the etch stop layer;

forming a second interlayer dielectric over the first interlayer dielectric; and

forming a first conductive contact extending through the first and second interlayer dielectrics and the etch stop layer, the first conductive contact being electrically coupled to the first epitaxial source/drain region.

17. The method of claim 13 , wherein the first epitaxial source/drain region contacts the first gate spacer.

18. The method of claim 13 , wherein an intersection of adjacent facets on the outer surface of the first epitaxial source/drain region form a first angle, the first angle being in a range from 140° to 180°.

19. The method of claim 13 , wherein the second epitaxial layer is the outermost layer of the first epitaxial source/drain region.

20. The method of claim 13 , wherein the first epitaxial layer has the highest germanium percentage of any layer in the first epitaxial source/drain region.