Hafnium carbide formation in oxygen deficient hafnium oxide thin films

TL;DR

This study demonstrates that oxygen-deficient hafnium oxide thin films readily form hafnium carbide at relatively low temperatures during vacuum annealing, influenced by residual carbon and oxygen vacancies.

Contribution

It reveals that oxygen vacancies significantly lower the formation energy of hafnium carbide, impacting the stability of hafnia-based devices under thermal conditions.

Findings

HfC$_x$ forms at 600°C in oxygen-deficient films

Fully stoichiometric HfO$_2$ does not form HfC$_x$ under same conditions

Residual carbon and oxygen vacancies facilitate carbide formation

Abstract

On highly oxygen deficient thin films of hafnium oxide (hafnia, HfO$_{2-x}$) contaminated with adsorbates of carbon oxides, the formation of hafnium carbide (HfC$_x$) at the surface during vacuum annealing at temperatures as low as 600 {\deg}C is reported. Using X-ray photoelectron spectroscopy the evolution of the HfC$_x$ surface layer related to a transformation from insulating into metallic state is monitored in situ. In contrast, for fully stoichiometric HfO$_2$ thin films prepared and measured under identical conditions, the formation of HfC$_x$ was not detectable suggesting that the enhanced adsorption of carbon oxides on oxygen deficient films provides a carbon source for the carbide formation. This shows that a high concentration of oxygen vacancies in carbon contaminated hafnia lowers considerably the formation energy of hafnium carbide. Thus, the presence of a sufficient amount of residual carbon in resistive random access memory devices might lead to a similar carbide formation within the conducting filaments due to Joule heating.