Depth profiling of thin gate dielectric films was studied. For SiON films profiled with 300 eV Cs + at ∼75° roughening was not observed at 3 nm, but depth scale discrepancies suggest that roughening-induced sputter rate variations are present. Profiles of ZrO 2 and HfO 2 films sputtered with Cs show a unique behavior of sputter-induced roughness going through a maximum in the Si under the oxide film. This roughness influences the Cs concentration, which in turn affects the ion yields. Profiling the ZrO 2 and HfO 2 films with O 2 + appears to be compromised by the presence of radiation-enhanced diffusion that leads to large decay lengths of the Zr + or Hf + signals.