Stability and diffusion dynamics of TiW/Cu heterostructures investigated by X-ray photoelectron spectroscopy Anna Regoutz, Curran Kalha Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK Power semiconductor devices are key to enabling our move towards electric mobility. With the advent of copper metallisation schemes to enable improved performance and smaller feature sizes, diffusion barriers have become crucial to avoid interdiffusion between the metallisation and underlying dielectric and semiconductor structures. One of the most widely established barrier materials is the binary pseudo-alloy of titanium–tungsten (TiW). However, it is prone to degradation via out-diffusion of titanium at high temperatures posing a major reliability challenge. To capture the interdiffusion phenomena occurring, this work presents a combination of ex- and in-situ soft and hard X-ray photoelectron spectroscopy. [1-3] Device heterostructures consisting of a Si/SiO 2 /Ti x W 1-x /Cu material stack, with the Ti x W 1-x layer acting as a diffusion barrier between Si and Cu, were investigated before and after annealing at temperatures up to 400°C. Ti within the diffusion barrier is shown to be highly mobile during annealing, diffusing out of the barrier and accumulating at the Cu surface. Core level spectra are able to follow both changes in relative atomic concentrations as well as local chemical environments. Longer annealing duration promotes a greater out-diffusion and, if exposed to air, the formation of thicker Ti oxide over layers. A clear correlation between the out-diffusion observed and the initial Ti concentration in the TiW is also found. The presented results provide crucial evidence for the relationship between TiW barrier integrity and composition, delivering insights into the physical and chemical mechanisms underlying both their effectiveness and remaining limitations. References 1. Thermal and oxidation stability of TixW1−x diffusion barriers investigated by soft and hard x-ray photoelectron spectroscopy.C. Kalha, S. Bichelmaier, N. K. Fernando, J. V. Berens, P. K. Thakur, T.-L. Lee, J. J. Gutiérrez Moreno, S. Mohr, L. E. Ratcliff, M. Reisinger, J. Zechner, M. Nelhiebel, and A. Regoutz, Journal of Applied Physics 129, 195302 (2021) 2. Evaluation of the thermal stability of TiW/Cu heterojunctions using a combined SXPS and HAXPES approach.C. Kalha, M. Reisinger, P. K. Thakur, T.-L. Lee, S. Venkatesan, M. Isaacs, R. G. Palgrave, J. Zechner, M. Nelhiebel, and A. Regoutz, Journal of Applied Physics 131, 165301 (2022) 3. Capturing the dynamics of Ti diffusion across TixW1−x heterostructures using X-ray photoelectron spectroscopy.C. Kalha, P. K. Thakur, T.-L. Lee, M. Reisinger, J. Zechner, M. Nelhiebel, and A. Regoutz, arXiv:2301.02577 (2023)
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