Infrared and optical emission spectroscopy study of atmospheric pressure plasma-enhanced spatial ALD of Al2O3

Atmospheric-pressure Plasma-Enhanced spatial Atomic Layer Deposition (PE-s-ALD) is a high-throughput technique for synthesizing thin films at low temperatures for large area applications. The spatial separation of the ALD half-reactions and the use of an atmospheric pressure plasma as the reactant give rise to complex surface chemistry which is not yet well understood. Here, we employed gas-phase infrared spectroscopy and optical emission spectroscopy (OES) to study the underlying chemistry of the PE-s-ALD process of Al2O3 films grown at 80 C using Al(CH3)3 and an Ar-O2 plasma. We identified the reaction products and investigated their dependence on the exposure time of the substrate to the precursor. Infrared absorbance spectra show CO, CO2, H2O, and CH4 as the main ALD reaction byproducts originating from (i) combustion-like reactions of the methylated surface with O plasma radicals and O3 and (ii) a concurrent latent thermal ALD component due to produced and/or residual H2O molecules. In addition, CH2O and CH3OH were identified as reaction by-products either originating at the surface or formed in the plasma. The OES spectra provide a corroborative proof of the combustive nature of the PE-s-ALD
reactions showing OH and CH emissions arising during the spatial ALD process while excited O species are being consumed.