Formation of High Resistivity Phases of Nickel Silicide at Small Diffusion Region

An increase in the sheet resistance at small diffusion regions is caused by the formation of high resistivity phases of nickel silicide. The increase in the sheet resistance strongly depends on the size of diffusion region at which nickel silicide is formed. On the condition under which NiSi is formed at large diffusion regions, Ni₃Si₂ is formed at small N* diffusion regions and NiSi₂ is formed at small N* diffusion regions. The uniformity of sheet resistance at small N* diffusion regions is improved by increasing the first anneal temperature. The uniformity of sheet resistance at small N* diffusion regions is not improved enough by increasing the first or second anneal temperature. It is considered that the transformation from Ni₃Si₂ to NiSi₂ occurs at small N* diffusion region between 500degC and 550degC.