Depth dependences of the ion bombardment induced roughness and of the interdiffusion coefficient for Si/Al multilayers

Depth dependences of the ion bombardment induced roughness and of the interdiffusion coefficient observed by Auger electron spectroscopical (AES) depth profiling of stationary as-deposited and annealed Si/Al multilayered specimens were evaluated by fitting calculated concentration–depth profiles to measured ones. The model used for calculation of the concentration–depth profile accounts for the instrumental smearing (interface broadening) upon AES depth profiling and, if relevant, interdiffusion. The instrumental smearing incorporates the effects of atomic mixing, roughness, escape depth of the Auger electrons, and preferential sputtering. The depth profile recorded from a stationary as-deposited Si/Al multilayered specimen was fitted by assuming, additionally, that the ion bombardment induced roughness increases with the sputter depth, keeping the other fitting parameters (including the inherent surface roughness) equal to the values determined for a rotating specimen. The roughness values determined by fitting to the measured depth profiles agree well with those determined directly by atomic force microscopy (AFM). Interdiffusion at the Si/Al interfaces was induced by annealing the specimens isothermally in an argon atmosphere at 120 8C for 240 min, 135 8C for 60 min, and 150 8C for 20 min. It was found that interdiffusion across interfaces near the surface of the multilayer is more pronounced than across interfaces in the deeper part of the layer. To account for this depth dependence of the extent of interdiffusion, calculated depth profiles for the annealed specimens were fitted to measured ones by assuming that diffusion annealing can be described as an additional ‘‘roughening’’ of the interfaces. As a result, values of the interdiffusion coefficient as a function of the depth beneath the surface were obtained. The depth dependence of the interdiffusion coefficient was discussed in terms of the microstructural development. # 2003 Elsevier B.V. All rights reserved.