Transistor gate structures and methods of forming the same

A device comprising:

• a channel region;
• a gate dielectric on the channel region;
• a first work function metal on the gate dielectric, the first work function metal having a first concentration of non-metal elements;
• a second work function metal on the first work function metal, the second work function metal different from the first work function metal, the second work function metal having a different thickness than the first work function metal, the second work function metal having a second concentration of the non-metal elements;
• an adhesion metal on the second work function metal, the adhesion metal having a third concentration of the non-metal elements, the third concentration greater than the first concentration and the second concentration;
• and
• a fill metal on the adhesion metal.

A method comprising:

• forming a first nanostructure and a second nanostructure;
• forming a gate dielectric having a first portion around the first nanostructure and having a second portion around the second nanostructure;
• depositing one or more work function metals over the gate dielectric, the work function metals completely filling an opening between the first portion of the gate dielectric and the second portion of the gate dielectric, the work function metals comprising impurities, the impurities comprising metalloids or nonmetals;
• applying a purification treatment to the work function metals, the purification treatment reducing a first concentration of the impurities in the work function metals;
• after applying the purification treatment to the work function metals, depositing an adhesion metal over the work function metals, the adhesion metal comprising the impurities;
• and
• depositing a fill metal over the adhesion metal.