Investigation of the TiN gate electrode with tunable work function and its application for FinFET fabrication

The titanium nitride (TiN) gate electrode with a tunable work function has successfully been deposited on the sidewalls of upstanding Si-fin channels of FinFETs by using a conventional reactive sputtering. It was found that the work function of the TiN (φ_TiN) slightly decreases with increasing nitrogen (N₂) gas flow ratio, R_N = N₂/(Ar + N₂) in the sputtering, from 17% to 100%. The experimental threshold voltage (V_th) dependence on the R_N shows that the more R_N offers the lower V^th for the TiN gate n-channel FinFETs. The composition analysis of the TiN films with different R_N showed that the more amount of nitrogen is introduced into the TiN films with increasing R_N, which suggests that the lowering of φ_TiN with increasing R_N should be related to the increase in nitrogen concentration in the TiN film. The desirable V_th shift from -0.22 to 0.22 V was experimentally confirmed by fabricating n ⁺ poly-Si and TiN gate n-channel multi-FinFETs without a channel doping. The developed simple technique for the conformal TiN deposition on the sidewalls of Si-fin channels is very attractive to the TiN gate FinFET fabrication.