Structure and method for improving access resistance in U-channel ETSOI
The present invention provides for a method of fabricating a semiconductor device, the method includes depositing a nitride layer on an ETSOI layer; forming a dummy gate over the nitride layer; forming nitride gate spacers from the nitride layer; growing a sacrificial layer on the ETSOI layer, the sacrificial layer composing a material that can be at least partially converted to a metal layer by a metal-bearing gas; forming refractory metal contacts using the sacrificial layer and a consumptive process; depositing an oxide protect layer on the refractory metal contacts; removing the dummy gate using a mask and etch process combined with chemical-mechanical polishing (CMP); etching the ETSOI layer to form a U-shaped channel; and depositing the final gate stack into the U-shaped channel.
1. A method of fabricating a semiconductor device comprising:
forming nitride gate spacers adjacent to a dummy gate located on an ETSOI layer;
growing a sacrificial layer on the ETSOI layer, the sacrificial layer comprising a material that is able to be converted to a metal layer by a metal-bearing gas;
forming refractory metal contacts from the sacrificial layer by introducing the metal-bearing gas to the sacrificial layer, wherein forming the refractory metal contacts additionally forms a vertically graded layer in a top layer of the ETSOI layer;
depositing an oxide protect layer on the refractory metal contacts;
removing the dummy gate using a mask and etch process combined with chemical-mechanical polishing (CMP);
etching the ETSOI layer to form a U-shaped channel that extends below the vertically graded layer; and
depositing a final gate stack into the U-shaped channel.
2. The method of claim 1 , wherein the U-shaped channel is doped through an open cavity prior to depositing the final gate stack.
3. The method of claim 1 , wherein the refractory metal contacts are selected from a group consisting of tungsten, tantalum, platinum, molybdenum, iridium, and niobium.
4. The method of claim 1 , further comprising monitoring the formation of the refractory metal contacts by measuring at least one of a concentration, a partial pressure, and an amount of reaction products formed during the sacrificial layer consumptive process.
5. The method of claim 1 , wherein the sacrificial layer has a nonplanar structure prior to forming the refractory metal contacts.
6. The method of claim 1 , further comprising forming a source region and a drain region, wherein a drive-in anneal process is applied to facilitate dopant diffusions.
7. The method of claim 1 , wherein the sacrificial layer is fully converted to a metal layer by a metal-bearing gas.
8. The method of claim 1 , wherein the dummy gate is polished back to leave a planar top surface.
9. The method of claim 1 , wherein the source region and the drain region is formed within the exposed ETSOI layer adjacent to the final gate stack.
10. The method of claim 1 , wherein the oxide protect layer is removed after the final gate stack is formed.