Gas phase chemical thermodynamics calculation as a first step for understanding of non-stoichiometric HfOx formation mechanism in ALD

Abstract

The dependence of hafnium oxide stoichiometry from the water time in the thermal atomic layer deposition (ALD) using TDMAH and water as reactant was shown. Non-stoichiometric hafnium oxide (HfO_x) is observed over the entire range of water step time from 10 ms to 1000 ms. The HfO_x formation is caused by interaction of hafnium oxide surface with organic products of ALD reactions during the layer growth. An increase in water exposure leads to growth in the proportion of redox reactions with water and a decrease in the proportion of redox reactions with hafnium oxide. This promotes a shift of the stoichiometry index x in the oxide composition HfO_x towards higher values. Additionally, to competitive redox reactions with water and hafnium oxide the stoichiometry index change can be caused by the adsorption of carbon dioxide with the subsequent carbonates formation. Which in turn leads to a decrease in the catalytic ability of hafnium oxide and a decrease in redox reactions.