Effects of surface structure on depth resolution of AES depth profiles of Ni/Cr multilayers

The influence of surface topography and crystalline structure on the depth resolution of Auger electron spectroscopy (AES) depth profiles of Ni/Cr mul tilayers was studied on three different samples sputter deposited onto smoo th Si(lll) substrates: an Ni/Cr multilayer composed of 16 alternating Ni an d Cr layers with a single layer thickness of similar to 30 nm, and the same Ni/Cr multilayer covered either with a smooth amorphous Ta2O5 layer simila r to 50 nm thick or a crystalline Al layer with an average thickness of sim ilar to 40 nm and a relatively large average surface roughness (R-a = 21.5 nm) in comparison with the first two samples (R-a <1 nm), All three types of samples were AES depth profiled with (1 rpm) and without sample rotation, using two symmetrically inclined 1 keV Ar+ ion beams at t wo different ion incidence angles of 47 degrees and 80 degrees, The AES dep th profiles obtained at an ion incidence angle of 47 degrees on stationary Ni/Cr and a-Ta2O5/Ni/Cr multilayer samples with smooth surfaces showed shar p interfaces with a depth resolution of approximately the same order of mag nitude. However, due to surface microroughness induced by ion sputtering, a slight monotonous degradation of the depth resolution with sputter depth w as observed on both samples, In contrast, AES depth profiling of the Al/Ni/ Cr stationary sample with the initially rough crystalline Al surface layer caused in-depth topographical changes of the Ni/Cr multilayer, and the orig inally sharp internal interfaces were strongly broadened. The optimal depth resolution was obtained by rotational depth profiling of the samples at an ion incidence angle of similar to 80 degrees, The values of depth resoluti on were independent of the sputter depth, and were of the same order of mag nitude for all three types of samples, lying between 4.5 and 8.0 mm, An ato mic force microscopy study of as-deposited and selected ion-sputtered sampl es showed that use of a grazing incidence angle and sample rotation during AES depth profiling promoted a smoothing effect and reduced the microroughn ess of the initially rough sample surface. Copyright (C) 2000 John Wiley & Sons, Ltd.