Abstract
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.
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