Paper AS+BI+MI+NS+SA+SS-WeM2
XPS Depth Profiling of SrTiO₃ and HfO₂ with Small Argon Clusters

Wednesday, November 1, 2017, 8:20 am, Room 13

Metal oxides are employed in a wide variety of functional applications. There is currently strong technological interest in strontium titanate (SrTiO₃) and hafnium oxide (HfO₂) due to their specific band gaps and high dielectric constants. SrTiO₃ is being studied for use in photocatalysis, energy storage and electronic sensors, whilst HfO₂ is widely employed for optical coatings and optoelectronic device applications. Both materials are regularly deposited as thin films and doped to optimise their properties for the application. An accurate determination of thin film composition is paramount to the understanding and optimisation of device performance.

In this work, thin films of SrTiO₃ and HfO₂ have been deposited onto silicon substrates and XPS depth profiles have been performed through the thin films using both monatomic and cluster argon ion bombardment. The monatomic Ar⁺ profiles were performed using an incident ion energy of 500 eV and the gas cluster ion beam (MAGCIS) profiles were recorded using8 keV Ar₁₀₀₀⁺ and 8 keV Ar₁₅₀⁺ for SrTiO₃ and HfO₂ respectively. For HfO₂ the optimum results were found when the MAGCIS ion beam was incident upon the sample at a glancing angle. These MAGCIS conditions yielded excellent retention of the original SrTiO₃ and HfO₂ stoichiometry during the profile, with no evidence of preferential sputtering or ion beam induced reduction. Using 500 eV Ar⁺,however, resulted in the preferential sputtering of oxygen leading to the presence of sub-oxide states in the XPS spectra of Ti in SrTiO₃ and Hf and HfO₂. The depth resolution was similar between the monatomic and cluster ion depth profiles for both thin film materials. Using the same incident ion beam angle, the etch rate for 8 keV Ar₁₀₀₀⁺ was only 2.5 times lower than that for 500 eV Ar⁺. The results will be discussed in the light of known ion beam effects when sputtering metal oxide materials.