A new method for the determination of the diffusion-induced concentration profile and the interdiffusion coefficient for
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A new Auger electron spectroscopical sputter depth profiling method was developed to determine the interdiffusion coefficient for the initial stage of diffusion annealing of thin films. The method is based on (i) adoption of an interdiffusion model appropriate for the specimen investigated and (ii) convolution of an accordingly calculated diffusion-induced concentration profile with the smearing effects due to atomic mixing, surface/interface roughness, escape depth of the Auger electrons, and preferential sputtering. The diffusion-induced concentration profile and the interdiffusion coefficient are determined by fitting in an iterative least-squares procedure of the calculated Auger electron spectroscopical depth profile to the measured one. The method was applied to bilayered and multilayered structures, exhibiting dominant grain-boundary diffusion and dominant volume diffusion, respectively. A very small extent of interdiffusion, characterized by diffusion distances as small as 1 nm, could be quantified.
I. INTRODUCTION
Auger electron spectroscopy (AES) in combination with ion sputtering (“depth profiling”) has been widely used for the determination of interdiffusion coefficients in thin solid films.1–5 However, if the diffusion length is only a few nanometers, as in the case of the initial diffusion process, the concentration-profile broadening effects due to this method of analysis and the intrinsic surface/interface roughness of the film cannot at all be neglected as compared to the diffusion-induced broadening. Thereby, well-known methods for diffusion coefficient determination by AES sputter depth profiling of thin films, as the center-gradient method1 and the interface-width method,2 become unreliable. The broadening effects in AES depth profiling are mainly the surface/interface roughness of the film as resulting from film growth, the atomic mixing due to the sputtering, the escape depth of the Auger electrons, and the preferential sputtering. Further, the ion beam sputtering induced roughness can possibly be one of the broadening effects.6,7 These broadening
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0430 J. Mater. Res., Vol. 19, No. 11, Nov 2004
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effects can be taken into account by the convolution of the true concentration-depth profile with the smearing (“depth resolution”) function. The recently developed so-called mixing-roughness-information depth (MRI) model provides a suitable description of the smearing function.8 Thereby, an AES depth profile can be calculated as would be measured from a specimen containing a certain concentration-depth profile. On this basis, the true concentration-depth profile can in principal be retrieved from the measured AES depth profile in an iterative least-squares procedure where an assumed description for the true concentration-depth profile is adopted and refined until agreement of measured and calculated AES depth profiles has been achieved. The interdiff
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