Controlling threshold voltages through blocking layers

A method comprising:

• forming a transistor comprising:
• depositing a work-function layer over a semiconductor region;
• depositing a capping layer over the work-function layer;
• depositing a fluorine-blocking layer over the capping layer;
• removing the fluorine-blocking layer;
• and
• forming a metal-filling layer over the capping layer, wherein the metal-filling layer comprises a same metal as the fluorine-blocking layer.

A method comprising:

• depositing a work-function layer comprising titanium and aluminum;
• forming a titanium nitride layer over the work-function layer;
• forming a first tungsten layer over and in physical contact with the titanium nitride layer;
• removing the first tungsten layer through etching, with the titanium nitride layer used as an etch stop layer;
• and
• forming a second tungsten layer over the titanium nitride layer.