Dummy fins and methods of forming thereof

A device comprising:

• a first transistor at a top surface of a semiconductor substrate, the first transistor comprising:
• a first channel region;
• and
• a first gate stack over and along sidewalls of the first channel region;
• a second transistor at the top surface of the semiconductor substrate, the second transistor comprising:
• a second channel region;
• and
• a second gate stack over and along sidewalls of the second channel region;
• and
• a dummy fin physically separating the first gate stack from the second gate stack, wherein the dummy fin comprises:
• a first film;
• and
• a second film over the first film, wherein a width of the dummy fin measured at a level of the second film is less than a width of the dummy fin measured at a level of the first film.

A method comprising:

• defining an opening between a first semiconductor fin and a second semiconductor fin;
• forming a dummy fin between the first semiconductor fin and the second semiconductor fin, forming the dummy fin comprising:
• depositing a first film in the opening;
• recessing the first film in the opening;
• depositing a second film in the opening over the first film;
• depositing a third film in the opening over the second film, the second film being disposed on sidewalls and a bottom surface of the third film;
• and
• etching the second film to at least partially remove the second film from the sidewalls of the third film;
• and
• forming a gate structure along sidewalls and top surfaces of the first semiconductor fin, the second semiconductor fin, and the dummy fin.