Epitaxy source/drain regions of FinFETs and method forming same
A method includes forming isolation regions extending into a semiconductor substrate, and recessing the isolation regions, so that portions of semiconductor strips between the isolation regions protrude higher than the isolation regions to form semiconductor fins. The method further includes recessing the semiconductor fins to form recesses, epitaxially growing a first semiconductor material from the recesses, etching the first semiconductor material, and epitaxially growing a second semiconductor material from the first semiconductor material that has been etched back.
1. A method comprising:
forming isolation regions extending into a semiconductor substrate, wherein the forming the isolation regions comprises:
in a common etching process, etching the semiconductor substrate to form two first trenches and a second trench between the two first trenches;
forming a hard mask layer comprising first bottom portions extending to bottoms of the two first trenches, and a second bottom portion extending to a bottom of the second trench;
performing an etching step, wherein both the two first bottom portions and the second bottom portion are exposed to an etchant used in the etching step, and the first bottom portions and portions of the semiconductor substrate directly underlying the first bottom portions are etched to extend the two first trenches down, and the second bottom portion protects a portion of the semiconductor substrate directly underlying the second bottom portion; and
filling the two first trenches and the second trench with a dielectric material to form isolation regions;
recessing the isolation regions, so that portions of semiconductor strips between the isolation regions protrude higher than the isolation regions to form semiconductor fins;
recessing the semiconductor fins to form recesses;
epitaxially growing a first semiconductor material from the recesses;
etching the first semiconductor material; and
epitaxially growing a second semiconductor material from the first semiconductor material that has been etched back.
2. The method of claim 1 , wherein the etching the first semiconductor material is performed after the epitaxially growing the first semiconductor material.
3. The method of claim 1 , wherein the second semiconductor material is different from the first semiconductor material.
4. The method of claim 3 , wherein the second semiconductor material has a higher n-type impurity concentration than the first semiconductor material.
5. The method of claim 3 , wherein the second semiconductor material has a higher p-type impurity concentration than the first semiconductor material.
6. The method of claim 1 , wherein the second semiconductor material grown starting from different recesses merge with each other, and the first semiconductor material grown starting from different recesses do not merge with each other.
7. The method of claim 1 , wherein the etching back comprises an anisotropic etching.
8. The method of claim 1 , wherein the etching back comprises an isotropic etching.
9. A method comprising:
forming a first isolation region between a first semiconductor fin and a second semiconductor fin, with the first isolation region has a first bottom surface;
forming a second isolation region on an outer side of the first semiconductor fin, wherein the first and the second isolation regions are on opposite sides of the first semiconductor fin, wherein the second isolation region has a second bottom surface lower than the first bottom surface;
etching the first isolation region to form a middle recess extending from a top surface of the first isolation region into the first isolation region, wherein the first isolation region comprises opposite portions on opposite sides of the middle recess;
forming a gate stack on the first semiconductor fin and the second semiconductor fin;
etching the first semiconductor fin and the second semiconductor fin to form a first recess and a second recess;
growing a first epitaxy region and a second epitaxy region from the first recess and the second recess, respectively;
etching back the first epitaxy region and the second epitaxy region; and
growing a third epitaxy region and a fourth epitaxy region based on the first epitaxy region and the second epitaxy region, respectively.
10. The method of claim 9 , wherein the etching back the first epitaxy region and the second epitaxy region is performed when the first epitaxy region and the second epitaxy region are spaced apart from each other.
11. The method of claim 9 , wherein the etching back the first epitaxy region and the second epitaxy region is performed when the first epitaxy region and the second epitaxy region have been joined with each other.
12. The method of claim 9 , wherein the third epitaxy region and the fourth epitaxy region join with each other, with an air gap is sealed underneath the joined third and fourth epitaxy regions.
13. The method of claim 9 , wherein the forming the first isolation region and the forming the second isolation region are performed in a common etching process, wherein trenches in which an entirety of the first isolation region and a top portion of the second isolation region are formed in the common etching process.
14. The method of claim 9 , wherein the forming the first isolation region and the forming the second isolation region are performed in different processes, with the first isolation region and the second isolation region being formed of different materials.
15. A method comprising:
forming a gate stack on a semiconductor fin;
forming gate spacers on sidewalls of the gate stack and fin spacers on sidewalls of the semiconductor fin;
etching the fin spacers;
growing an epitaxy region based on the semiconductor fin to form a first portion of a source/drain region, wherein the epitaxy region extends into a space left by the etched fin spacers;
etching the epitaxy region;
further growing the epitaxy region; and
forming a silicide region on a top surface of the epitaxy region.
16. The method of claim 15 , wherein the fin spacers are directly over isolation regions, and the method further comprises, after the fin spacers are removed, further recessing the isolation regions.
17. The method of claim 15 , wherein the etching the epitaxy region is performed using a process gas free from silicon and germanium containing process gases.
18. The method of claim 15 , wherein the etching the epitaxy region is performed using HCl as a process gas.
19. The method of claim 15 , wherein the growing the epitaxy region is performed using a first process gas comprising silicon or germanium and a second process gas comprising HCl.
20. The method of claim 12 , wherein the air gap comprises a bottom portion extending into the first isolation region, with the middle recess forming the bottom portion of the air gap.