Measuring the roughness of buried interfaces by sputter depth profiling

We report results of high-resolution sputter depth profiling of an alternating MgO/ZnO nanolayer stack grown by atomic layer deposition (ALD) of 5.5 nm per layer. We used an improved dual beam time-of-flight secondary ion mass spectrometer to measure 24Mg+ and 64Zn+ intensities as a function of sample depth. Analysis of depth profiles by the mixing-roughness-information model yields a 1.5 nm nanolayer interfacial roughness within the MgO/ZnO multilayer. This finding was cross-validated using specular x-ray reflectivity. Such an analysis further suggested that the 1.5 nm roughness corresponds to native/jig-sawed interfacial roughness rather than interfacial interdiffusion during the ALD growth.