Effects of post-metallisation annealing on surface–interfacial and electrical properties of HfO₂/Ge stacks modified in situ with SiO₂ interfacial layer

The effects of post-metallisation annealing (PMA) at 400 °C for 30 min in an NH₃ ambient on the interfacial and electrical properties of a structure consisting of a Ge substrate coated with HfO₂ by atomic layer deposition with a 3-nm-thick SiO₂ interfacial layer formed in situ by a sputtering technique were evaluated. X-ray diffraction and x-ray photoelectron spectroscopy analyses confirmed the crystallinity of HfO₂ and chemical bonding of the HfO₂/SiO₂/Ge interface before and after the annealing. Clear stretch-free distinct capacitance–voltage curves were observed for the sample after the PMA. According to the electrical measurements, the sample after the PMA exhibited a large dielectric constant (k ̃ 17), low interface trap density (D _it = 1.8 × 10¹² cm² eV⁻¹), and small oxide charge (Q _eff = 2.54 × 10¹² cm² eV⁻¹). The gate leakage current of the PMA device determined using the current–voltage curve was approximately 0.1 × 10⁻⁴ A cm⁻² at V _g+ = +1 V. These results suggest that the SiO₂ interfacial layer formed in situ and NH₃−PMA significantly improved the structural, interfacial, and electrical characteristics of the HfO₂/Ge stacks for future Ge-based complementary metal–oxide–semiconductor device applications. (paper)