Structure, optical properties and thermal stability of HfErO films deposited by simultaneous RF and VHF magnetron sputtering

Abstract

HfErO films are deposited on Si substrates by simultaneous radio frequency (RF) and very high frequency (VHF) magnetron sputtering technique. The content of the doped ingredient of Er and the body composition of HfO x are, respectively, controlled through the VHF and RF powers. Low content of Er doping in the HfErO films can be achieved, because the VHF source of 27.12 MHz has higher ion energy and lower ion flux than the RF source resulting in low sputtering rate in the magnetron sputtering system. The structure, optical properties and thermal stability of the HfErO films are investigated in this work. Results show that the doped content of Er is independently controlled by the VHF power. The oxygen vacancies are created by the Er incorporation. The hafnium in the HfErO films forms mixed valence of Hf2+ and Hf4+. The HfErO films are composed with the structures of HfO2, HfO and ErO x , which can be optimized through the VHF power. At high VHF power, the Hf–Er–O bonds are formed, which demonstrates that the Er atoms are doped into the lattice of HfO2 in the HfErO films. The HfErO films have bad thermal stability as the crystallization temperature decreases from 900 to 800 °C. After thermal annealing, cubic phase of HfO2 are stabilized, which is ascribed to the oxygen vacancies creation by the Er incorporation. The optical properties such as the refractive index and the optical band gap of the HfErO films are optimized by the VHF power.