Transistor gate structure and method of forming

A transistor comprising:

• a first nanostructure over a semiconductor substrate;
• a second nanostructure over the first nanostructure;
• a gate dielectric surrounding the first nanostructure and the second nanostructure;
• and
• a gate electrode over the gate dielectric, wherein the gate electrode comprises:
• a work function metal around the first nanostructure and the second nanostructure;
• a barrier layer on the work function metal;
• and
• a fill metal over the barrier layer, wherein the fill metal has a higher concentration of fluorine than the barrier layer.

A method comprising:

• depositing a gate dielectric around a first nanostructure and a second nanostructure, the first nanostructure is disposed over the second nanostructure;
• depositing a work function metal over the gate dielectric;
• depositing a barrier layer over the work function metal, wherein depositing the barrier layer comprises a first atomic layer deposition (ALD) process, and wherein the first ALD process does not use any fluorine-comprising precursors;
• and
• depositing a fill metal over the barrier layer, wherein depositing the fill metal comprises using a fluorine-comprising precursor.