Vacuum annealing effects on the microstructure and properties of HfO2-based bilayer antireflective coatings by magnetron sputtering

Abstract

Hafnia (HfO2) retains thermal stability, mechanical resilience, and chemical resistivity, which makes it feasible in various high-tech applications in optics and integrated circuit technology. This work presents the effects of thermal annealing on the microstructure, optical performance, and wettability of HfO2/Al2O3 and HfO2/ZrO2 bilayer thin films prepared by magnetron sputtering. The films were deposited on silicon (Si) and glass substrates and then annealed at a certain temperature (300–500 °C) in the ambient vacuum condition for 5hrs. XRD results of as-deposited and annealed films revealed the polycrystalline nature of the monoclinic phase. The core level orbitals of Hf 4f, Zr 3d, and Al 2p spectra showed the formation of stoichiometric compositions of HfO2, ZrO2, and Al2O3 films and exhibited a slight shift in binding energy after annealing. The AFM and SEM analysis were utilized to inspect the roughness and surface morphology and correlated with the change in hydrophobicity to the self-cleaning nature of the prepared bilayer coatings. The observed upsurge in refractive indexes of the coatings is allied to the packing density that causes lattice contraction and enhances the attraction between dipoles. The negligible effect of negative temperature on the antireflection efficiency makes it suitable for future applications in optoelectronic, photovoltaic devices operated in a cold or humid environment.