Intermixing reduction in ultra-thin titanium nitride/hafnium oxide film stacks grown on oxygen-inserted silicon and associated reduction of the interface charge dipole

Oxygen-insertion (OI) layers in Si were found to reduce the intermixing of a 3.0 nm titanium nitride (TiN)/3.5 nm hafnium oxide (HfO₂) film stack, as measured by secondary ion mass spectroscopy (SIMS), x-ray photoelectron spectroscopy (XPS), and high-resolution Rutherford backscattering spectroscopy (HR-RBS). In addition, a 5% reduction in HfO₂ film density and modification of in-gap state densities of bulk HfO₂ film were observed from HR-RBS and absorption spectra from spectroscopic ellipsometry (SE), respectively. Furthermore, the barrier height at HfO₂/Si was found to increase by 250 mV from Fowler–Nordheim (F–N) tunneling characteristics, and 172 mV lower flatband voltage (V_FB) was observed from capacitance–voltage (C–V) characteristics. These observations suggest that interfacial charge dipole formation of the high-k dielectric/metal gate (HKMG) stack on Si follows the O-vacancy model, in which charge dipole is explained as electrostatic energy stored at the interface from the intermixing process involving electron transition from oxygen vacancy in metal oxide to Si. OI-Si modifies the balance of the oxygen flux due to the supply of partially ionized oxygen in Si and, thus, leads to the reduction of the intermixing phenomena, modification of the resultant film properties, and reduction of the interfacial charge dipole. This discovery opens up a new technique for tuning HKMG electrical characteristics.