Self-aligned trench metal-alloying for III-V nFETs
After forming source/drain contact openings to expose portions of source/drain regions composed of an n-doped III-V compound semiconductor material, surfaces of the exposed portions of the source/drain regions are cleaned to remove native oxides and doped with plasma-generated n-type dopant radicals. Semiconductor caps are formed in-situ on the cleaned surfaces of the source/drain regions, and subsequently converted into metal semiconductor alloy regions. Source/drain contacts are then formed on the metal semiconductor alloy regions and within the source/drain contact openings.
1. A method of forming a semiconductor structure comprising:
forming source/drain regions on opposite sides of a gate structure and within a compound semiconductor channel layer, wherein the compound semiconductor channel layer is composed of a III-V compound semiconductor material and is located directly on a compound semiconductor substrate layer and wherein the source/drain regions are n-doped;
forming source/drain contact openings extending through an interlevel dielectric (ILD) layer that overlies the source/drain regions and laterally surrounds the gate structure, each of the source/drain contact openings exposing a portion of one of the source/drain regions;
removing native oxides from the top surface of the exposed portion of each of the source/drain regions to provide a treated source/drain surface;
performing plasma doping to introduce a free radical of an n-type dopant to the treated source/drain surface of each source/drain region, wherein the free-radical of the n-type dopant is selected from the group consisting of Sn radical, Te radicals and Si radicals;
forming, by selective epitaxy, a semiconductor cap only within the source/drain contact openings and extending upwards from the plasma doped and treated source/drain surface of each of the source/drain regions, wherein the removing of the native oxides and the selective epitaxy are performed in a same reactor chamber and wherein the semiconductor cap passivates the plasma doped and treated source/drain surface;
forming a metal layer over exposed surfaces of the ILD layer, the gate structure and each semiconductor cap;
forming metal semiconductor alloy regions within the source/drain contact openings by reacting an entirety of each semiconductor cap with the metal layer, wherein each of the metal semiconductor alloy regions is located at a bottom of one of the source/drain contact openings and in direct contact with a top surface of the exposed portion of one of the source/drain regions; and
forming source/drain contacts within the source/drain contact openings, each of the source/drain contacts contacting a top surface of one of the metal semiconductor alloy regions, wherein the source/drain contacts have a contact resistance that is lower than 5×10 −9 ohm-cm 2 , and wherein the source/drain regions comprise planar source/drain regions located within the compound semiconductor channel layer and raised source/drain regions, the raised source/drain regions having a same type of doping as the planar source/drain regions, and wherein each of the raised source/drain regions comprises a same III-V compound semiconductor material as the planar source/drain regions.
2. The method of claim 1 , wherein the treated source/drain surface of the exposed portion of each of the source/drain regions is essentially free of the native oxides.
3. The method of claim 1 , wherein the removing the native oxides comprises:
performing a wet etch using a diluted hydrofluoric acid (HF) solution; and
performing a dry etch using a hydrogen plasma process.
4. The method of claim 1 , wherein each of the semiconductor caps comprises Si, Ge or SiGe.
5. The method of claim 1 , wherein the compound semiconductor channel layer comprises GaAs, InAs, InP, InGaAs, InAlAs, InAlAsSb, InAlAsP or InGaAsP.
6. The method of claim 1 , wherein each of the raised source/drain regions comprises Si doped InGaAs.
7. The method of claim 1 , wherein the forming the planar source/drain regions are performed by implanting ion into portions of the compound semiconductor channel layer that are not covered by the gate structure.
8. The method of claim 1 , wherein the compound semiconductor channel layer is composed of a different compound semiconductor material than the compound semiconductor substrate layer.
9. The method of claim 8 , wherein the compound semiconductor channel layer comprises InGaAs, and the compound semiconductor substrate layer comprises InP.
10. The method of claim 1 , further comprising forming the gate structure on the compound semiconductor channel layer, wherein the forming the gate structure comprises:
forming a material stack including, from bottom to top, a gate dielectric layer, a gate electrode layer and a gate cap layer on the compound semiconductor channel layer; and
patterning the material stack to provide a gate stack including, from bottom to top, a gate dielectric, a gate electrode and a gate cap; and
forming a gate spacer on sidewalls of the gate stack.
11. The method of claim 1 , wherein the forming metal semiconductor alloy regions is performed by an anneal process.
12. The method of claim 1 , further comprising removing an unreacted portion of the metal layer after the forming the metal semiconductor alloy regions.
13. The method of claim 12 , further comprising a post-clean that removes any remnants of the metal layer from the exposed surfaces of the ILD layer in the source/drain contact openings.
14. The method of claim 13 , wherein the forming source/drain contacts within the source/drain contact opening comprises:
depositing a conductive material layer on the ILD layer and the metal semiconductor alloy regions to completely fill the source/drain contact openings; and
removing portions of the conductive material layer from a top surface of the ILD layer.
15. The method of claim 1 , wherein the source/drain regions are single crystalline and the semiconductor cap is also single crystalline.