Self-aligned contact structure for replacement metal gate
A metallic top surface of a replacement gate structure is oxidized to convert a top portion of the replacement gate structure into a dielectric oxide. After removal of a planarization dielectric layer, selective epitaxy is performed to form a raised source region and a raised drain region that extends higher than the topmost surface of the replacement gate structure. A gate level dielectric layer including a first dielectric material is deposited and subsequently planarized employing the raised source and drain regions as stopping structures. A contact level dielectric layer including a second dielectric material is formed over the gate level dielectric layer, and contact via holes are formed employing an etch chemistry that etches the second dielectric material selective to the first dielectric material. Raised source and drain regions are recessed. Self-aligned contact structures can be formed by filling the contact via holes with a conductive material.
1. A semiconductor structure comprising:
a field effect transistor including a raised source region and a raised drain region and located on a substrate;
a gate level dielectric layer comprising a first dielectric material and overlying a gate electrode of said field effect transistor;
a contact level dielectric layer comprising a second dielectric material and overlying said gate level dielectric layer; and
a contact via structure electrically shorted to one of said raised source region and raised drain region and extending through said contact level dielectric layer and said gate level dielectric layer as a single contiguous structure, wherein a lower portion of said contact via structure embedded within said gate level dielectric layer is narrower than an upper portion of said contact via structure embedded within said contact level dielectric layer along a horizontal direction parallel to a direction of a channel of said field effect transistor, said lower portion of said contact via structure has a lateral width that decreases with an increase in a vertical distance from a horizontal plane including an interface between said substrate and said gate level dielectric layer, said lateral width being measured between sidewalls of said lower portion of said contact via structure along a horizontal direction that is parallel to said horizontal plane.
2. The semiconductor structure of claim 1 , wherein said upper portion of said contact via structure has a substantially uniform width.
3. The semiconductor structure of claim 1 , wherein sidewalls of said lower portion of said contact via structure have a non-zero taper angle.
4. The semiconductor structure of claim 3 , wherein said one of said raised source region and raised drain region has another taper angle that is not less than said taper angle.
5. The semiconductor structure of claim 3 , wherein said sidewalls of said lower portion of said contact via structure are located within same planes as faceted crystallographic surfaces of said one of said raised source region and raised drain region.
6. The semiconductor structure of claim 3 , further comprising a metal-semiconductor alloy region contacting a bottom surface of said contact via structure, wherein sidewalls of said metal-semiconductor alloy region have a same taper angle as said non-zero taper angle.
7. The semiconductor structure of claim 1 , wherein said lower portion of said contact via structure has sidewalls having a taper angle relative to a surface normal of the interface between said substrate and said gate level dielectric layer.
8. The semiconductor structure of claim 1 , wherein said raised source region and said drain region includes a second semiconductor material that is different from a first semiconductor material of said channel.
9. The semiconductor structure of claim 8 , wherein all interfaces between said gate level dielectric layer and said contact level dielectric layer are within a same horizontal plane.
10. The semiconductor structure of claim 1 , wherein a horizontal cross-sectional area of said lower portion of said contact via structure decreases with said increase in said vertical distance from said horizontal plane.
11. The semiconductor structure of claim 1 , wherein said upper portion of said contact via structure has a substantially uniform width that is invariant with translation along a vertical direction that is perpendicular to said interface between said substrate and said gate level dielectric layer.
12. The semiconductor structure of claim 1 , wherein said upper portion of said contact via structure and said lower portion of said contact via structure comprise a same conductive material.
13. The semiconductor structure of claim 12 , wherein said same conductive material is selected from a metal, a conductive metallic nitride, and a conductive metallic carbide.
14. The semiconductor structure of claim 1 , wherein said one of said raised source region and raised drain region has a crystallographic facet that contacts said contact level dielectric layer.
15. The semiconductor structure of claim 14 , wherein a surface of said lower portion of said contact via structure is within a same plane as said crystallographic facet.
16. The semiconductor structure of claim 14 , wherein said crystallographic facet is within a plane that is not orthogonal to, or parallel to, said interface between said substrate and said gate level dielectric layer.
17. The semiconductor structure of claim 14 , wherein an angle between said plane containing said crystallographic facet and a vertical direction is in a range from 5 degrees to 75 degrees.
18. The semiconductor structure of claim 14 , further comprising a metal semiconductor alloy region contacting a bottom surface of said contact via structure, wherein a surface of said metal semiconductor alloy region is within a plain containing said crystallographic facet.
19. The semiconductor structure of claim 1 , wherein said lower portion of said contact via structure includes a surface that is located within a same plane as a crystallographic facet of said one of said raised source region and said raised drain region.