Atomic layer deposition of hafnium and zirconium oxyfluoride thin films

Hafnium and zirconium oxyfluoride films may act as effective protective coatings during plasma processing. The low molar volume expansion/contraction ratios and the small estimated strain values versus fluorination/oxidation suggest that hafnium and zirconium oxyfluorides can serve as protective coatings in both fluorine and oxygen plasma environments. To demonstrate the procedures for depositing these films, hafnium and zirconium oxyfluorides with tunable stoichiometry were grown using atomic layer deposition (ALD) at 150 °C. Tetrakis(dimethylamido)hafnium and tetrakis(ethylmethylamido)zirconium were used as the metal precursors. H₂O and HF were employed as the oxygen and fluorine precursors, respectively. MO_xF_y (M = Hf and Zr) films were grown using two deposition mechanisms: the nanolaminate method and the HF exchange method. In situ quartz crystal microbalance studies were employed to monitor the MO_xF_y growth. Both deposition methods observed a linear MO_xF_y growth at 150 °C. The nanolaminate method is defined by the sequential deposition of MO_x ALD and MF_y ALD layers. Compositional tunability was achieved by varying the ratio of the number of MO_x ALD cycles to the number of MF_y ALD cycles in the nanolaminate. The HF exchange method is based on the thermodynamically favorable fluorination reaction of MO_x by HF. Variable oxygen-to-fluorine concentrations in these films were obtained either by changing the HF pressure or by varying the thickness of the underlying MO_x ALD layers. Ex situ Rutherford backscattering spectroscopy measurements were utilized to determine the composition of the various MO_xF_y thin films. Both deposition techniques displayed a wide range of compositional tunability from HfO₂ to HfF₄ and ZrO₂ to ZrF₄. In addition, the physical sputtering rates of MO_xF_y films were estimated from the film removal rates during ex situ x-ray photoelectron spectroscopy depth profiling. The physical sputtering rates increased with F concentration in the MO_xF_y films.