Replacement metal gate FinFET

1. A method for fabricating a field effect transistor device, the method comprising:

depositing a hardmask layer over a semiconductor layer, the semiconductor layer disposed on an insulator layer;

depositing a metallic alloy layer over the hardmask layer;

defining a semiconductor fin by patterning and removing portions of the metallic alloy layer, the hardmask layer, and the semiconductor layer to expose portions of the insulator layer and define the semiconductor fin on the insulator layer;

depositing a dummy gate stack material layer conformally on exposed portions of the insulator layer, the semiconductor fin, the hardmask layer and the metallic alloy layer;

patterning a dummy gate stack by removing portions of the dummy gate stack material using an etching process that selectively removes exposed portions of the dummy gate stack material without appreciably removing portions of the metallic alloy layer;

forming sidewall spacers adjacent to the dummy gate stack, such that the both the sidewall spacers and the dummy gate stack are disposed on the metallic alloy layer;

removing exposed portions of the metallic alloy layer not covered by the sidewall spacers and the dummy gate stack;

forming source and drain regions on exposed regions of the semiconductor fin;

removing the dummy gate stack;

removing portions of the metallic alloy layer exposed from the removal of the dummy gate stack, thereby leaving first and second portions of the metallic alloy layer disposed on opposing ends of the hardmask layer, such that bottom surfaces of the sidewall spacers are formed on the first and second portions of the metallic alloy layer; and

forming a gate stack conformally over exposed portions of the insulator layer and the semiconductor fin.

2. The method of claim 1 , wherein the patterning and removing the portions of the metallic alloy layer, the hardmask layer, and the semiconductor layer includes:

forming a mandrel material layer over the metallic alloy layer;

patterning and removing portions of the mandrel material layer to expose portions of the metallic alloy layer and define a mandrel arranged on the metallic alloy layer;

forming mandrel spacers adjacent to the mandrels, the mandrel spacers arranged on the metallic alloy layer;

removing the mandrels to expose portions of the metallic alloy layer; and

removing the portions of the metallic alloy layer, the hardmask layer, and the semiconductor layer using an etching process that does not appreciably remove portions of the mandrel spacers.

3. The method of claim 1 , wherein the forming the source and drain regions on the exposed regions of the semiconductor fin includes performing an epitaxial growth process.

4. A method for fabricating a field effect transistor device, the method comprising:

depositing a hardmask layer over a semiconductor layer, the semiconductor layer disposed on an insulator layer;

depositing a metallic alloy layer over the hardmask layer;

defining a semiconductor fin by patterning and removing portions of the metallic alloy layer, the hardmask layer, and the semiconductor layer to expose portions of the insulator layer and define the semiconductor fin on the insulator layer;

depositing a dummy gate stack material layer conformally on exposed portions of the insulator layer, the semiconductor fin, the hardmask layer and the metallic alloy layer;

patterning a dummy gate stack by removing portions of the dummy gate stack material using an etching process that selectively removes exposed portions of the dummy gate stack material without appreciably removing portions of the metallic alloy

forming sidewall spacers adjacent to the dummy gate stack, such that the both the sidewall spacers and the dummy gate stack are disposed on the metallic alloy layer;

removing exposed portions of the metallic alloy layer not covered by the sidewall spacers and the dummy gate stack;

forming source and drain regions on exposed regions of the semiconductor fin;

removing the dummy gate stack;

removing portions of the metallic alloy layer exposed from the removal of the dummy gate stack; and

forming a gate stack conformally over exposed portions of the insulator layer and the semiconductor fin;

wherein the removing-portions of the metallic alloy layer exposed from the removal of the dummy gate stack includes performing an isotropic etching process operative to remove the metallic alloy layer and form a cavity defined by the spacer, the hardmask layer and the source or drain region.

5. The method of claim 4 , wherein the method further includes, removing exposed portions of the hardmask layer following the removal of the dummy gate stack and the removal of the exposed portions of the metallic alloy layer.

6. The method of claim 4 , wherein the method further includes, removing the exposed portions of the hardmask layer with an anisotropic etching process following the removal of the dummy gate stack and the removal of the exposed portions of the metallic alloy layer.

7. The method of claim 4 , wherein the method further includes, removing the exposed portions of the hardmask layer with an isotropic etching process following the removal of the dummy gate stack and the removal of the exposed portions of the metallic alloy layer.