Work function tuning in TiAlN thin films by trace Al doping for CMOS-compatible metal gates

With continued scaling of semiconductor devices, integrating high-k dielectrics with metal-gate electrodes is essential to overcome the limitations of conventional Si-based MOSFETs. Titanium nitride (TiN), widely employed as a gate material due to its low resistivity and robust thermal and chemical stability, typically exhibits an effective work function (EWF) of 4.7–4.9 eV, favoring p-type devices. However, n-type MOSFETs require lower values. To address this, we investigated the EWF modulation of TiN by incorporating trace aluminum (Al) through thermal atomic layer deposition (ALD). TiAlN thin films were deposited at 300 °C using a supercycle-based thermal ALD process. Tetrakis(dimethylamido)titanium and NH3 were employed for TiN growth, while trimethylaluminum enabled controlled Al incorporation. By restricting AlN cycles to <10% of the total, the Al content was tuned below 10 at. %. The resulting films achieved resistivities as low as ∼5000 μΩ cm without plasma assistance or postannealing. A sharp increase in resistivity and oxygen uptake occurred beyond nine AlN cycles, attributed to insulating Al–O/Al–N bonds and Ti–Al oxynitride formation. Importantly, the EWF decreased systematically from 4.90 to 4.45 eV, as extracted from flatband voltage measurements using the traced oxide method. This controllable EWF shift highlights TiAlN as a dual-compatible metal-gate electrode for both p- and n-type MOSFETs. Owing to its conformal growth, compositional tunability, and compatibility with low-temperature processes, the ALD-based TiAlN approach provides a promising strategy for next-generation device platforms, including gate-all-around FETs and complementary FETs, where precise work function engineering is critical.