Asymmetric source and drain structures in semiconductor devices
The present disclosure provides semiconductor devices with asymmetric source/drain structures. In one example, a semiconductor device includes a first group of source/drain structures on a first group of fin structures on a substrate, a second group of source/drain structures on a second group of fin structures on the substrate, and a first gate structure and a second gate structure over the first and the second group of fin structures, respectively, the first and second groups of source/drain structures being proximate the first and second gate structures, respectively, wherein the first group of source/drain structures on the first group of fin structures has a first source/drain structure having a first vertical height different from a second vertical height of a second source/drain structure of the second group of source/drain structures on the second group of fin structures.
1. A method for forming a semiconductor device, comprising:
etching a first and a second source/drain structures on a first and a second fin structures in a first and a second active region, respectively, on a substrate by an etching gas mixture including a sulfur containing passivation gas, wherein the etching gas mixture etches the first source/drain structure at a faster etching rate than etching the second source/drain structure, the etching forming the first source/drain structure in the first active region having a first vertical height less than a second vertical height formed in the second source/drain structure in the second active region, wherein the first source/drain structure is n-type and the second source/drain structure is p-type.
2. The method of claim 1 , wherein the sulfur containing passivation gas selectively reacts with the second source/drain structure in the second active region, forming a passivation layer on the second source/drain structure while patterning the first source/drain structure in the first active region.
3. The method of claim 2 , wherein the sulfur containing passivation gas is carbonyl sulfide.
4. The method of claim 1 , further comprising:
prior to etching the first and the second source/drain structures, forming a third source/drain structure neighboring the first source/drain structure in the first active region, and forming a fourth source/drain structure neighboring the second source/drain structure in the second active region, wherein the third source/drain structure has a third vertical height greater than a fourth vertical height of the fourth source/drain structure.
5. The method of claim 4 , wherein a first step height is defined between the third vertical height and the first vertical height in the first active area, and a second step height is defined between the fourth vertical height and the second vertical height in the second active area, wherein the first step height is at least about 5% higher than the second step height.
6. The method of claim 1 , wherein the etching gas mixture comprises a carbon fluorine gas, an oxygen containing gas, and a carbonyl sulfide gas.
7. The method of claim 1 , wherein the etching gas mixture comprises carbon fluorine gas.
8. A method for forming a semiconductor device, the method comprising:
forming a first fin on a substrate;
forming a second fin on the substrate;
epitaxially growing a first source/drain region on the first fin;
epitaxially growing a second source/drain region on the second fin, wherein the first source/drain region has a first vertical height greater than a second vertical height of the second source/drain region;
forming a first dielectric layer over the first source/drain region and the second source/drain region; and
etching the first dielectric layer, the first source/drain region and the second source/drain region, wherein the etching etches the first source/drain region at a faster rate than the second source/drain region, wherein the etching exposes an outer sidewall of the first source/drain region.
9. The method of claim 8 , wherein after etching the first source/drain region has a first step height greater than a second step height of the second source/drain region.
10. The method of claim 9 , wherein a ratio of the first step height to the second step height is greater than 1.1.
11. The method of claim 10 , wherein the first vertical height is 8% to 20% greater than the second vertical height.
12. The method of claim 8 , wherein the first source/drain region is n-type and the second source/drain region is p-type.
13. The method of claim 8 , wherein etching is performed using a carbon fluorine gas, an oxygen containing gas, an inert gas, and a passivation gas.
14. The method of claim 13 , wherein:
the carbon fluorine gas is CF 4 ,
the oxygen containing gas is O 2 ,
the inert gas is Ar, and
and the passivation gas is COS.
15. A method for forming a semiconductor device, the method comprising:
forming a first fin on a substrate;
forming a second fin on the substrate;
epitaxially growing a first source/drain region on the first fin;
epitaxially growing a second source/drain region on the second fin;
forming a first dielectric layer over the first source/drain region and the second source/drain region;
forming a first opening and a second opening in the first dielectric layer, wherein forming the first opening and the second opening comprises etching the first dielectric layer, the first source/drain region and the second source/drain region, wherein the etching etches the first source/drain region at a faster rate than the second source/drain region; and
forming a first contact in the first opening and a second contact in the second opening, wherein a first contact area between the first contact and the first source/drain region is greater than a second contact area between the second contact and the second source/drain region, wherein the first contact has a point that abuts the first source/drain region, the point being above the first fin, wherein the first contact extends laterally from the point to an outermost edge of the first source/drain region in a direction perpendicular to the first fin.
16. The method of claim 15 , wherein, after forming the first opening and the second opening, a first step height of the first source/drain region is greater than a second step height of the second source/drain region.
17. The method of claim 16 , wherein, prior to forming the first opening and the second opening, a first vertical height of the first source/drain region is greater than a second vertical height of the second source/drain region.
18. The method of claim 15 , forming the first opening and the second opening comprises etching using a sulfur containing gas.
19. The method of claim 18 , wherein forming the first opening and the second opening forms a passivation layer over the second source/drain region while etching the first source/drain region.
20. The method of claim 15 , wherein after forming the first opening and the second opening, a first height of remaining portions of the first source/drain region is less than a second height of remaining portions of the second source/drain region.