DEPTH PROFILING OF NONCONDUCTIVE OXIDIC MULTILAYERS WITH PLASMA-BASEDSNMS IN HF-MODE

Multilayer structures such as CuO/Al2O3/SnO2/SiO2 or CuO/SiO2/SnO2/SiO 2 are developed to operate as gas sensor devices. To optimize the gas- selective CuO/Al2O3 or CuO/SiO2 membranes on top of the gas sensitive SnO2 layer, plasma-based secondary neutral mass spectrometry (plasma S NMS) was used to investigate the thickness, the stoichiometry and puri ty of the layers as well as the thermal stability of their interfaces for different preparation methods. However, the electrical conductivit y of such multilayer samples is too low to avoid the sample being char ged up during depth-profiling with stationary sputtering. SNMS was fou nd to be well suited to analyze such multilayers, provided a high freq uency mode (HFM) is employed. Intermediate annealing after each deposi tion step turned out to be a prerequisite to avoid interdiffusion whic h can appear as a consequence of the usual operating temperature (300 degrees C) of such metal oxide gas sensors. (C) 1998 Elsevier Science S.A. All rights reserved.