Quantification of sputtering induced surface roughness in AES depth profiling of polycrystalline Ni/Cr multilayers

Ion bombardment induced surface roughening takes place during AES sputter depth profiling of polycrystalline thin metal films, caused by different sputtering yields of the differently oriented grains with lattices in channelling or non-channelling directions. This effect is the main source of the degradation of depth resolution upon sputtering. In order to remedy this effect and to improve the depth resolution, sample rotation is often applied during depth profiling. In this study, the depth resolution of AES depth profiles obtained from stationary and rotating specimens are compared on the basis of the so-called mixing-roughness-information depth (MRI)-model. The system chosen is a well-studied Ni/Cr multilayer composed of 16 alternating Ni and Cr layers with a single layer thickness of 30 nm. AES depth profiles obtained from both stationary and rotating specimens are fitted by the MRI model by varying three physically well-defined parameters: atomic mixing length w, roughness s and information depth l. The depth profile recorded from stationary specimen is fitted by assuming, additionally, that the ion sputtering induced roughness s increases with an exponent of less than 1/2 of the sputtered depth, leaving the other two parameters (as depth independent) equal to those determined from the rotating specimen. Authors)