Surface Acidity-Induced Inherently Selective Atomic Layer Deposition of Tantalum Oxide on Dielectrics

Selective deposition shows a great perspective for the downscaling of nanoelectronics. In this work, inherently selective atomic layer deposition (ALD) of tantalum oxide was studied on a series of oxide substrates. The Ta2O5 films linearly grow on acidic oxides of MnO2, SiO2, and Ta2O5, while there are long nucleation delays on basic oxides such as Al2O3 and HfO2. The inherent selectivity is induced through acidity differences which influence the reaction path, and the H-transfer reaction is a key factor. The Ta(OEt)5 precursor with alkaline ligands tends to chemically adsorb on acidic SiO2 surfaces through H-transfer reaction between surface hydroxyls and precursor molecules. Through H-transfer reaction, the ligands of the Ta(OEt)5 precursor are dissociated into ethanol molecules and the remaining intermediates are strongly chemisorbed on the surface, initiating the following nucleation. However, it is hard to nucleate on basic Al2O3 and HfO2 substrates because the H-transfer reaction is blocked. Moreover, robust selectivity only exists within the ALD temperature window, which highlights that tuning deposition temperature is also an effective way to amplify selectivity. The obstruction of H-transfer reaction on basic oxides provides a new strategy for inherently selective ALD, which will expand the selective toolbox of nanofabrication for next-generation nanoelectronic applications.