Etch stop layer formation in metal gate process

1. A method of forming a semiconductor device comprising:

forming a metal gate conductor of a gate structure on a channel portion of a semiconductor substrate, wherein the metal gate conductor is comprised of a catalytic metal;

forming a gate dielectric cap on the metal gate conductor with an atomic layer deposition process that includes only half reactions of a silanol containing precursor, the gate dielectric cap comprised of at least silicon and oxygen, wherein the gate dielectric cap is catalyzed by the catalytic metal so that edges of the gate dielectric cap are aligned with a sidewall of the metal gate conductor, wherein the thickness of the gate dielectric cap is self limited to less than 20 nm; and

forming contacts to at least one of a source region and a drain region that are on opposing sides of the gate structure, wherein the gate dielectric cap obstructs the contacts from contacting the metal gate conductor.

2. The method of claim 1 , wherein the gate dielectric cap comprises SiO 2 , SiCO, SiCNO, SiON or a combination thereof.

3. The method of claim 1 , wherein the gate structure further comprises a gate dielectric layer between the channel portion of the semiconductor substrate and the metal gate conductor.

4. The method of claim 3 , wherein forming of the metal gate conductor comprises:

forming a replacement gate structure on the channel portion of the semiconductor substrate;

forming a dielectric spacer on opposing sides of the replacement gate structure;

forming the source region and the drain region in the semiconductor substrate;

forming an interlevel dielectric over the semiconductor substrate having an upper surface that is coplanar with the replacement gate structure;

removing the sacrificial gate structure to provide an opening to the channel portion of the semiconductor substrate;

forming the gate dielectric layer on sidewalls of the opening and a base of the opening on the channel portion of the semiconductor substrate; and

forming the metal gate conductor on the gate dielectric layer filling the opening.

5. The method of claim 4 , wherein the replacement gate structure is comprised of a aluminum containing gate conductor.

6. The method of claim 1 , wherein the catalytic metal is selected from the group consisting of aluminum (Al), hafnium (Hf), zirconium (Zr), titanium (Ti), tantalum (Ta), tungsten (W) and a combination thereof.

7. The method of claim 1 , wherein the catalytic metal is deposited by sputtering.

8. The method of claim 1 , wherein the silanol containing precursor comprises tris (tert-butyloxyl) silanol and the gate dielectric cap comprises silicon oxide.

9. The method of claim 1 , wherein the silanol containing precursor comprises bis (tert-butyloxyl) alkyl silanol and the gate dielectric cap comprises silicon-oxycarbide (SiCO).

10. The method of claim 1 , wherein the silanol containing precursor comprises bis-(tert-butyloxyl aminoalkyl silanol and the gate dielectric cap comprises silicon carbon nitro-oxide (SiCNO).

11. The method of claim 4 , wherein the forming of the contacts comprises etching a via opening through the interlevel dielectric to each of the source region and the drain region, wherein the etching is selective to the gate dielectric cap, the dielectric spacer, and the source region and the drain region; and

forming the interconnect in each via opening in direct contact with each of the source region and the drain region.