Method and structure for metal gates

A method of forming a semiconductor device, comprising:

• receiving a substrate and first and second gate structures over the substrate, wherein the first and second gate structures include first and second trenches respectively;
• forming a gate dielectric layer in the first and second trenches;
• forming a barrier layer over the gate dielectric layer;
• forming an oxide layer over the barrier layer, wherein the oxide layer includes one of:
• tantalum oxide, titanium oxide, and niobium oxide;
• and
• forming a first work function metal layer over the oxide layer.

A method of forming a semiconductor device, comprising:

• providing a substrate, the substrate including first and second trenches;
• forming a gate dielectric layer in the first and second trenches;
• forming a barrier layer over the gate dielectric layer;
• forming an oxide layer over the barrier layer;
• forming a first work function metal layer over the oxide layer;
• forming a masking element over the first work function metal layer in the second trench;
• etching the first work function metal layer in the first trench;
• and
• forming a second work function metal layer over the oxide layer in the first trench, wherein the second work function metal layer is different from the first work function metal layer.