Gate leakage current reduction and improved reliability with an ultra-thin Ti layer for low-power applications

This study analyzed the physical and electrical characteristics of the interface reactions between hafnium-based high-k gate dielectrics and a TiN-based metal gate. Decreasing the N₂ gas flow ratio (R_N2 = N₂/Ar+N₂) from the physical-vapor-deposited TiN decreased the gate leakage current (J_G) and the effective work function (EWF) of the metal gate. X-ray photoelectron spectroscopy analysis confirmed that TiN deposited with a lower R_N2 condition can be easily oxidized to form TiO_x at the gate oxide and metal gate interface after annealing at 1050 °C. This newly created oxide layer can prevent oxygen diffusion from the gate oxide through TiN to the TiN/poly-silicon interface, resulting in improved gate oxide quality. Inserting a thin Ti layer (< 1 nm) on the gate oxide formed a TiO_x layer without a change in EWF, indicating that TiN composition variation followed the same trend as capacitance equivalent thickness (CET) versus J_G. Therefore, an oxygen-blocking layer can have the same effect as gate oxide quality improvement for both scenarios—low R_N2 of TiN and the thin Ti insertion—due to decreased oxide charge density. The Ti insertion process was associated with improved gate oxide leakage, negligible CET increase (0.2 Å), and gate oxide reliability, including time-dependent dielectric breakdown characteristics due to the blockage of oxygen up-diffusion.