Comparison of AlF3 thin films grown by thermal and plasma enhanced atomic layer deposition

Films of aluminum fluoride (AlF3) deposited by thermal and plasma enhanced atomic layer deposition (PEALD) have been compared using in situ multiwavelength ellipsometry (MWE) and monochromatic x-ray photoelectron spectroscopy (XPS). The AlF3 films were grown using cyclic exposures of trimethylaluminum, hydrogen fluoride, and H radicals from a remote H2 inductively coupled plasma. Films were characterized in situ using MWE and XPS for growth rate, film composition, and impurity incorporation. The MWE showed a growth rate of 1.1 and 0.7 Å per cycle, at 100 °C, for thermal and plasma enhanced ALD AlF3 films, respectively. Carbon incorporation was below the XPS detection limit. The plasma enhanced ALD AlF3 film showed the presence of Al-Al chemical states, in the Al 2p scans, suggesting the presence of Al-rich clusters with a concentration of 14%. The Al-rich clusters are thought to originate during the hydrogen plasma step of the PEALD process. Finally, the Al-rich clusters were not detected in thermal ALD AlF3 films using the same precursors and substrate temperature.