Simulating ion sputtered depth profiles in Auger electron spectroscopy
Yohannes Tesfamicael, Biniam
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Recent developments in advanced materials technology are mainly based on the progress in surface and interface science. These surface and interface properties of materials greatly affect and control the overall properties of the materials. The reliable performance of multilayered thin- film structures in many technological applications like microelectronics, for instance depends upon the mechanical and chemical stability of the interfaces. Hence, appropriate study and analysis of the interfaces is an important aspect that has to be carried out with great precision. Depth profiling is one of the most powerful mechanisms in the analysis of surface and interfaces of thin multilayered structures. This depth profiling is accomplished by surface analytical techniques like AES and XPS accompanied by ion sputtering. The principal aim of this depth profiling is to investigate the distribution of elemental concentration with depth. The ion etching of the sample during the depth profiling, however, imposes some effects on the shape of the profile. The major causes for the profile distortion comes from Atomic mixing, Interface roughness, Information depth of the secondary emission and preferential sputtering in multicomponent systems. A model (MRI) that is often used in literature to simulate depth profiles in Auger electron spectroscopy takes into account the effect of atomic mixing, interface roughness and information depth. One of the radiation-induced factors limiting depth resolution is preferential sputtering. In this study the model was modified to incorporate the effect of preferential sputtering on the distortion of the depth profile. Although preferential sputtering is an exponential function it was treated as independent of the other contributing functions and in such a way as to add to the total depth resolution in quadrature, according to an error propagation law. One application of the model is in the determination of interdiffusion parameters in annealed multilayered thin film structures. In the experimental part of this study a Cu/Ni multilayer structure was evaporated onto a silicon substrate. The samples were annealed for different times in the temperature range 250 to 350ºC. This was followed by Auger depth profiling using Ar + sputtering with 3 keV primary ions at an angle 60º to the surface normal. Deconvolution of the overlapping Cu and Ni Auger spectra were performed followed by the calibration of the depth and concentration scales. In the process of simulating the measured depth profile the modified model yielded the contributions of atomic mixing, information depth, interface roughness and the ratio of the sputtering yields of Cu and Ni. The value of the interface roughness, expected to be a function of annealing temperature and time, was used to calculate the interdiffusion coefficient. The diffusion parameters Do = 4x10 -14 m 2 /s and the activation energy Q=69kJ/mol agrees excellently with values available in literature where grain boundary diffusion is the dominant diffusion process. These results confirm the successful modification of the MRI model.