Gate structures in transistors and method of forming same

A method comprising:

• depositing a gate dielectric over a first semiconductor material, wherein the first semiconductor material extends from a first source/drain region to a second source/drain region, wherein a width of the first source/drain region is greater than a width of the first semiconductor material in a top-down view;
• depositing a first conductive metal over the gate dielectric, wherein the first conductive metal comprises fluorine;
• forming a protective capping layer over the first conductive metal, wherein the protective capping layer is formed in-situ with the first conductive metal;
• and
• diffusing fluorine from the first conductive metal into the gate dielectric while the protective capping layer covers the first conductive metal.

A method comprising:

• depositing a first conductive material over a gate dielectric on a substrate;
• depositing a second conductive material over the first conductive material, wherein depositing the second conductive material comprises flowing a fluorine-containing precursor;
• forming a silicon capping layer over the second conductive material;
• performing a thermal treatment to diffuse fluorine from the second conductive material into the gate dielectric through the first conductive material, wherein the thermal treatment further diffuses silicon from the silicon capping layer into the gate dielectric through the first conductive material;
• removing the silicon capping layer;
• and
• after removing the silicon capping layer, depositing one or more metal layers over the gate dielectric to form a gate electrode.