Depth profiling of non-conductive oxidic multilayers with plasma-based SNMS in HF-mode

Abstract Multilayer structures such as CuO/Al 2 O 3 /SnO 2 /SiO 2 or CuO/SiO 2 /SnO 2 /SiO 2 are developed to operate as gas sensor devices. To optimize the gas-selective CuO/Al 2 O 3 or CuO/SiO 2 membranes on top of the gas sensitive SnO 2 layer, plasma-based secondary neutral mass spectrometry (plasma SNMS) was used to investigate the thickness, the stoichiometry and purity of the layers as well as the thermal stability of their interfaces for different preparation methods. However, the electrical conductivity of such multilayer samples is too low to avoid the sample being charged up during depth-profiling with stationary sputtering. SNMS was found to be well suited to analyze such multilayers, provided a high frequency mode (HFM) is employed. Intermediate annealing after each deposition step turned out to be a prerequisite to avoid interdiffusion which can appear as a consequence of the usual operating temperature (300°C) of such metal oxide gas sensors.