Method to improve reliability of replacement gate device

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

after removal of a dummy gate, providing a replacement gate structure by performing steps of:

growing a high-k dielectric layer over the replacement gate structure;

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 high-k dielectric layer, the thin metal layer, and the sacrificial layer at a high temperature not less than 800° C.;

performing a millisecond anneal;

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;

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

depositing a metal layer for gap fill.

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