Atomic layer deposition of aluminum oxyfluoride thin films with tunable stoichiometry

Abstract

Atomic layer deposition (ALD) of aluminum oxyfluoride (AlOxFy) 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 AlOxFy deposition. Two deposition pathways were explored to grow the AlOxFy thin films based on the HF exchange method and the nanolaminate method. Linear AlOxFy 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 AlOxFy thin films. The XPS depth-profile measurements confirmed the uniform distribution of Al, O, and F throughout the AlOxFy 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 AlOxFy films. The physical sputtering rates at 3 keV varied from 0.03 to 0.28 Å/s for Al2O3 and AlF3, respectively.