Comparison of the sputter rates of oxide films relative to the sputter rate of $SiO2$

There is a growing interest in knowing the sputter rates for a wide variety of oxides because of their increasing technological importance in many different applications. To support the needs of users of the Environmental Molecular Sciences Laboratory, a national scientific user facility, as well as our research programs, the authors made a series of measurements of the sputter rates from oxide films that have been grown by oxygen plasma-assisted molecular beam epitaxy, pulsed laser deposition, atomic layer deposition, electrochemical oxidation, or sputter deposition. The sputter rates for these oxide films were determined in comparison with those from thermally grown $SiO2$⁠, a common reference material for sputter rate determination. The film thicknesses and densities for most of these oxide films were measured using x-ray reflectivity. These oxide films were mounted in an x-ray photoelectron or Auger electron spectrometer for sputter rate measurements using argon ion sputtering. Although the primary objective of this work was to determine relative sputter rates at a fixed angle, the measurements also examined (i) the angle dependence of the relative sputter rates, (ii) the energy dependence of the relative sputter rates, and (iii) the extent of ion beam induced reduction for some oxides. Oxide films examined include $SiO2$⁠, $Al2O3$⁠, $CeO2$⁠, $Cr2O3$⁠, $Fe2O3$⁠, $HfO2$⁠, In–Sn oxide, $Ta2O5$⁠, $TiO2$ (anatase, rutile, and amorphous), and ZnO. The authors found that the sputter rates for the oxides can vary up to a factor of 2 (usually lower) from that observed for $SiO2$⁠. The ratios of sputter rates relative to those of $SiO2$ appear to be relatively independent of ion beam energy in the range of 1–4 kV and for incident angles $<50°$⁠. As expected, the extent of ion beam induced reduction of the oxides varies with the sputter angle.