Rapid growth of tungsten nanosheets on TiN surfaces for high-k metal gate devices: a first-principles study

As semiconductor devices scale to the nanometer level, high-k metal gate (HKMG) technology is widely adopted, but power consumption becomes problematic due to effective work function (EWF) shifts caused by interface dipoles at high-k dielectrics. Inserting an Al₂O₃ layer at the dielectric/gate interface reduces power consumption by adjusting the EWF, but it significantly slows W gate deposition. Experimentally, introducing a TiN layer on Al₂O₃ promotes fast and uniform W growth, yet the underlying mechanism remains unclear. Here, density functional theory calculations reveal the nucleation and growth of W on Al₂O₃ and TiN surfaces. We identify stable AlO(II)-terminated Al₂O₃(001), TiN(001), and N-terminated TiN(111) surfaces and their most stable W adsorption sites. As more W atoms adsorb, a W cluster forms on Al₂O₃ and a W nanosheet develops on TiN, with stronger W adsorption on TiN during nucleation. In the growth step, W binds more strongly to the W nanosheet than to the W cluster, further accelerating W deposition. These strong W adsorption on TiN are attributed to the robust W-N bonding, forming uniform W metal nanosheets. Our findings clarify the nucleation and growth mechanisms of W deposition and suggest the optimal surface for cost-efficient HKMG production with improved electrical performance.