On the Issue of Work Function Tuning of Nickel Silicide Gates

The mechanism of work function tuning in NixSiy gates was investigated critically. Furthermore, the role of the underlying dielectric (SiO2 and high-k materials) was also evaluated and it was found that the work function tuning mechanism strongly depends upon the concentration of SiO2 in the dielectric. Ternary alloy silicides NixTa1-xSi and NixPt1-xSi were investigated as possible gates for NMOS and PMOS application repectively. Phi m of 4.27eV and 5.1eV was achieved for the cases of Ta rich and Pt rich silicides on SiO2. However , the window of Phi m range reduced as hafnium was added to the dielectric such that for the case of HfO2 dielectric, the range reduced to 200meV. We attribute this to Fermi level pinning due to increase in Hf+Si bonds. Critical investigation of the role of dielectric-metal gate interface was carried out. Results of varying the Ni and Si composition on SiO2, HfO2 and HfSiOx dielectrics and resulting variation of EOT and Phi m are compared. We report dielectric surface related possible phase modulation of NixSiy gates. To understand the co-relation of EOT variation with work function of the metal gate, top interface of HfSiOx was modulated and the results of such modulation affected increase in the Phi m tuning.