Comparison of Thermal and Plasma-Enhanced ALD/CVD of Vanadium Pentoxide

Vanadium pentoxide was deposited by atomic layer deposition (ALD) from vanadyl-tri-isopropoxide (VTIP). Water or oxygen was used as a reactive gas in thermal and plasma-enhanced (PE) processes. For PE ALD, there was a wide ALD temperature window from 50 to 200 degrees C. Above 200 degrees C, VTIP decomposed thermally, resulting in the chemical vapor deposition (CVD) of vanadium pentoxide. The PE ALD reactions saturated much faster than during thermal ALD, leading to a growth rate of approximately 0.7 angstrom/cycle during PE ALD using H2O or O-2. Optical emission spectroscopy showed combustion-like reactions during the plasma step. X-ray diffraction was performed to determine the crystallinity of the films after deposition and after postannealing under He or O-2 atmosphere. Films grown with CVD at 300 degrees C and PE O-2 ALD at 150 degrees C were (001)-oriented V2O5 as deposited, while thermal and PE H2O ALD films grown at 150 degrees C were amorphous as deposited. The crystallinity of the PE O-2 ALD could be correlated to its high purity, while the other films had significant carbon contamination, as shown by X-ray photoelectron spectroscopy. Annealing under He led to oxygen-deficient films, while all samples eventually crystallized into V2O5 under O-2.