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

Abstract

The influence of surface topography and crystalline structure on the depth resolution of Auger electron spectroscopy (AES) depth profiles of Ni/Cr multilayers was studied on three different samples sputter deposited onto smooth Si(111) substrates: an Ni/Cr multilayer composed of 16 alternating Ni and Cr layers with a single layer thickness of ∼30 nm, and the same Ni/Cr multilayer covered either with a smooth amorphous Ta 2 O 5 layer ∼50 nm thick or a crystalline Al layer with an average thickness of ∼40 nm and a relatively large average surface roughness (R a = 21.5 nm) in comparison with the first two samples (R a < I 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 two different ion incidence angles of 47° and 80°. The AES depth profiles obtained at an ion incidence angle of 47° on stationary Ni/Cr and a-Ta 2 O 5 /Ni/Cr multilayer samples with smooth surfaces showed sharp interfaces with a depth resolution of approximately the same order of magnitude. However, due to surface microroughness induced by ion sputtering, a slight monotonous degradation of the depth resolution with sputter depth was 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 originally 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 ∼80°, The values of depth resolution were independent of the sputter depth, and were of the same order of magnitude for all three types of samples, lying between 4.5 and 8.0 nm. An atomic force microscopy study of as-deposited and selected ion-sputtered samples showed that use of a grazing incidence angle and sample rotation during AES depth profiling promoted a smoothing effect and reduced the microroughness of the initially rough sample surface.