Optimization of process pressure for reactive electron beam evaporation of the HfO2 thin film for electro-optical applications

Hafnium dioxide (HfO2) thin films are widely used in optical applications due to their ultraviolet transparent nature. E-beam evaporation is the main deposition technique for the deposition of HfO2 used in optical applications. To provide the industrial deposition rate, HfO2 thin films are deposited with reactive evaporation of metallic hafnium. These depositions suffer from the incident change in vacuum atmosphere and result with unwanted absorption at thin films. This study focuses on keeping the pressure value constant at all times of deposition via changing the oxygen flow rate. In this way, HfO2 thin films are deposited at different pressure levels and the obtained thin films are characterized by structural and optical techniques. Thin films are obtained at different levels of crystallinity which become stronger when the deposition is carried out at low process pressure. Also, at low process pressure, depositions result with Hf-rich HfO film formation, which is obtained from x-ray photoelectron spectroscopy analysis. Higher process pressure depositions result with bigger particle formation and this cause more surface irregularity and rough surface formation. Optical measurements show that higher refractive index inhomogeneity is formed when the deposition is carried out at high oxygen flow rates and, oppositely, high absorption at thin films occurs when the oxygen flow rate is low. There is a balance to get good optical characteristics, which is obtained at 1.2 × 10−4 mbar process pressure.