Fluoride Contamination Induced ${\rm NiSi}_{2}$ Film Formation in a Gate NiSi Line

Undulate high-resistance nickel silicide film is found in a gate electrode of a logic device. The undulate film is caused by fluoride contamination derived from a chemical dry-cleaning process for silicon (Si) substrate prior to nickel (Ni) sputtering. The undulate film was composed of a thicker nickel monosilicide (NiSi) film nearby a Si hillock and a thinner nickel disilicide (NiSi₂) film on the hillock. These results indicate that fluoride contamination impeded Ni diffusion during the initial silicidation. At the same time, vacancies are left by excess Ni diffusion at a clean Ni-Si interface. Then, the thin nickel silicide film is transformed into NiSi₂ because of the excess thermal budget during the second silicidation. Where the vacancies filled up by Si, a Si hillock is formed.