Structure and method for metal gate stack oxygen concentration control using an oxygen diffusion barrier layer and a sacrificial oxygen gettering layer

A process of forming an integrated circuit, comprising the steps of:

• forming a dummy PMOS gate stack and a dummy NMOS gate stack, wherein said dummy PMOS gate stack includes a PMOS gate dielectric layer, a PMOS gate work function metal layer and a PMOS dummy gate layer, and said dummy NMOS gate stack includes a NMOS gate dielectric layer, a NMOS gate work function metal layer and a NMOS dummy gate layer;
• removing said PMOS dummy gate layer and said NMOS dummy gate layer;
• performing a low temperature oxidation process on the NMOS gate work function metal layer and the PMOS gate work function metal layer;
• after performing the low temperature oxidation process, forming an oxygen diffusion barrier layer over said PMOS gate work function metal layer;
• forming an oxygen getter layer over said NMOS gate work function metal layer, wherein said oxygen getter layer is blocked from said PMOS gate work function metal layer by said oxygen diffusion barrier layer;
• performing a getter anneal process with the oxygen diffusion barrier layer over the PMOS gate work function metal layer and the oxygen getter layer over the NMOS gate work function metal layer;
• and
• forming an NMOS metal gate over said NMOS gate work function metal layer and a PMOS metal gate over said PMOS gate work function metal layer.