Atomic layer deposition of aluminum oxyfluoride thin films with tunable stoichiometry

Atomic layer deposition (ALD) of aluminum oxyfluoride (AlO_xF_y) thin films was demonstrated at 150 °C. Trimethyl aluminum, water, and HF were used as the aluminum, oxygen, and fluorine sources, respectively. In situ quartz crystal microbalance studies were utilized to monitor the AlO_xF_y deposition. Two deposition pathways were explored to grow the AlO_xF_y thin films based on the HF exchange method and the nanolaminate method. Linear AlO_xF_y growth was observed during both deposition methods. The HF exchange method is based on the thermodynamically favorable fluorination of Al₂O₃ by HF. Compositional control was achieved either by changing the HF pressure during the HF exposure or by varying the thickness of the underlying Al₂O₃ layer prior to the HF exposure. The nanolaminate method is based on the sequential deposition of Al₂O₃ ALD and AlF₃ ALD layers. The ratio of the number of Al₂O₃ ALD cycles to the number of AlF₃ ALD cycles is the main parameter used to control the O and F concentrations. Ex situ x-ray photoelectron spectroscopy (XPS) depth-profiling and Rutherford backscattering spectroscopy measurements were used to determine the composition of the AlO_xF_y thin films. The XPS depth-profile measurements confirmed the uniform distribution of Al, O, and F throughout the AlO_xF_y films using both deposition methods. Both techniques could obtain a wide range of compositional tunability between Al₂O₃ and AlF₃. Physical sputtering rates were also observed to be dependent on the relative concentrations of O and F in the AlO_xF_y films. The physical sputtering rates at 3 keV varied from 0.03  to 0.28 Å/s for Al₂O₃ and AlF₃, respectively.