Effects of the oxygen precursor on the electrical and structural properties of $HfO2$ films grown by atomic layer deposition on Ge

We report on the growth by atomic layer deposition of $HfO2$ films on HF-last treated Ge(001) substrates using $HfCl4$ as a Hf source and either $O3$ or $H2O$ as oxygen sources. The choice of the oxygen precursor strongly influences the structural, chemical, and electrical properties of the $HfO2$ films: Those grown using $H2O$ exhibit local epitaxial growth, a large amount of contaminants such as chlorine and carbon, and a large frequency dispersion of the capacitance-voltage $(C–V)$ characteristics. Films grown using $O3$ are good insulators and exhibit well-shaped $C–V$ curves with a minimum frequency dispersion of the accumulation capacitance. Moreover, they are smoother, less crystallized, and with a lower contaminant content than those grown using $H2O$⁠. However, the use of $O3$ leads to the formation of a $2nm$ thick layer, possibly $GeOx$⁠, at the $HfO2∕Ge$ interface.