EFFECTS OF CRYSTALLINITY ON DEPTH RESOLUTION IN SPUTTER DEPTH PROFILES

For sputter depth profiling the effect of the layer crystallinity on the resolution of the underlying interfaces was investigated. By applying D. Onderdelinden's model of monocrystal sputtering (Appl. Phys. Lett. 8, 189 (1966); Can. J. Phys. 46, 739 (1968)) and J. Lindhard's approach to axial ion channelling (Phys. Lett. 12, 126 (1965); K. Dan. Vidensk. Selsk. Mat. Fys. Medd. 34, No. 14 (1965)) to textured and non-textured polycrystalline layers, it is shown that the interface resolution under these layers is largely affected by the channelling of incident ions. The strong dependence of channelling on the orientation of individual grains leads to extremely non-uniform erosion and poor interface resolution. This model of polycrystalline layer sputtering reproduces well the dependence of depth profile shape and depth resolution on layer thickness, ion energy and incidence angle, as shown for sputter depth profiling through textured aluminium layers by inert gas ions. In the case of higher ion masses, the observed effects are slightly overestimated by the model, as anticipated from the inherent limitations of the Lindbard and the Onderdelinden approaches. The implications of channelling for depth profiles of polycrystalline layers are discussed and conclusions are drawn for appropriate selection of sputter parameters to ensure optimum depth resolution. The effects of sample temperature, continuous rotation of the sample during sputter erosion and reactive ion sputtering are also discussed.