Method to improve reliability of replacement gate device

1. A method of fabricating a gate stack for a semiconductor device, said method comprising steps of:

skipping a high temperature annealing step to activate implanted dopants of a source and/or drain before removing a dummy gate;

removing the dummy gate;

providing a replacement gate structure by performing steps of:

growing a high-k dielectric layer over an area vacated by the dummy gate;

depositing a thin metal layer over the high-k dielectric layer;

depositing a sacrificial layer over the thin metal layer;

performing a first rapid thermal anneal of the replacement gate structure and activating the implanted dopants of a source and/or drain at a high temperature of not less than 800° C.;

removing the sacrificial layer of the replacement gate structure; and

depositing a metal layer for gap fill.

2. The method of claim 1 , wherein performing the first rapid thermal anneal comprises annealing at a temperature between 800° C. and 1100° C., inclusive.

3. The method of claim 1 further comprising, after the step of removing the sacrificial layer:

removing the thin metal layer;

performing a second rapid thermal anneal at a temperature between 400° C. and 800° C., inclusive; and

re-depositing a thin metal layer over the high-k dielectric layer.

4. The method of claim 1 , wherein depositing the sacrificial layer comprises depositing a layer selected from poly-crystalline silicon and amorphous silicon.