Profile reconstruction in sputter depth profiling

Quantification of measured sputtering profiles in terms of atomic monolayer accuracy can only be accomplished by applying appropriate methods of deconvolution or profile reconstruction. Of the different approaches developed to adequately describe the depth resolution function, the so-called mixing-roughness-information depth (MRI)-model has proved its usefulness in many applications including both secondary ion mass spectrometry (SIMS) and Auger electron spectroscopy (AES). The MRI model is governed by three fundamental and physically well-defined parameters: atomic mixing length, roughness and information depth. Application examples are presented for depth profiling of GaAs/AlAs delta layers and thicker layers showing an accuracy of 0.2 monolayers. First order non-linear effects like preferential sputtering can be corrected by a composition dependent relation between sputtering time and sputtered depth. A non-linear relationship between intensity and elemental concentration can be corrected by a composition-dependent sensitivity factor, as in secondary ion cluster profiling. However, segregation and compound formation effects causing inhomogeneous elemental distribution in the mixing zone are difficult to include and are the main reason for the present limitations in MRI model applications.