Depth resolution and preferential sputtering in depth profiling of delta layers

Abstract

The influence of different sputtering rates between a delta layer of A in a surrounding matrix of B on the depth resolution function of A is studied for delta layers of monoatomic thickness using the Mixing-Roughness-Information-depth (MRI) model. The two extreme cases of preponderant atomic mixing and of preponderant roughness as well as mixed cases yield different results. Whereas the effect of the preferential sputtering rate ratio of A and B, rA/B, is practically zero for preponderant roughness, it is strongly pronounced if atomic mixing prevails. The strength of the dependence of the depth resolution on rA/B is governed by the relative contribution of the apparent mixing length w/rA/B to the total depth resolution. For a delta layer of component A, the depth resolution Δz(A) decreases with rA/B > 1 and vice versa. For rA/B ≠ 1, the mixing part of the depth resolution function becomes surface concentration dependent and therefore loses its applicability in the convolution integral. As a further consequence, the interfacial depth resolution gets different for A/B and B/A interfaces. In case of similar magnitude of roughness and mixing parameters, a similar but more moderate influence of rA/B on the depth resolution as compared to preponderant mixing is obtained.