Thermal and oxidation stability of TixW1−x diffusion barriers investigated by soft and hard x-ray photoelectron spectroscopy

The binary alloy of titanium-tungsten (TiW) is an established diffusion barrier in high-power semiconductor devices, owing to its ability to suppress the diffusion of copper from the metallization scheme into the surrounding silicon substructure. However, little is known about the response of TiW to high-temperature events or its behavior when exposed to air. Here, a combined soft and hard x-ray photoelectron spectroscopy (XPS) characterization approach is used to study the influence of post-deposition annealing and titanium concentration on the oxidation behavior of a 300 nm-thick TiW film. The combination of both XPS techniques allows for the assessment of the chemical state and elemental composition across the surface and bulk of the TiW layer. The findings show that in response to high-temperature annealing, titanium segregates out of the mixed metal system and upwardly migrates, accumulating at the TiW/air interface. Titanium shows remarkably rapid diffusion under relatively short annealing timescales, and the extent of titanium surface enrichment is increased through longer annealing periods or by increasing the bulk titanium concentration. Surface titanium enrichment enhances the extent of oxidation both at the surface and in the bulk of the alloy due to the strong gettering ability of titanium. Quantification of the soft x-ray photoelectron spectra highlights the formation of three tungsten oxidation environments, attributed to WO2, WO3, and a WO3 oxide coordinated with a titanium environment. This combinatorial characterization approach provides valuable insights into the thermal and oxidation stability of TiW alloys from two depth perspectives, aiding the development of future device technologies.C.K. acknowledges the support from the Department of Chemistry, UCL. N.K.F. acknowledges support from the Engineering and Physical Sciences Research Council (No. EP/L015277/1). J.J.G.M. and S.M. acknowledge the support from the FusionCAT project (No. 001-P-001722) co-financed by the European Union Regional Development Fund within the framework of the ERDF Operational Program of Catalonia 2014–2020 with a grant of 50% of total cost eligible, the access to computational resources at MareNostrum and the technical support provided by BSC (No. RES-QS-2020-3-0026). L.E.R. acknowledges support from an EPSRC Early Career Research Fellowship (No. EP/P033253/1) and the Thomas Young Centre under Grant No. TYC-101. A.R. acknowledges the support from the Analytical Chemistry Trust Fund for her CAMS-UK Fellowship. We acknowledge Diamond Light Source for time on Beamline I09 under Proposal No. SI19885-1. The authors would like to thank Dave McCue, I09 beamline technician, for his support of the experiments.Peer Reviewed"Article signat per 13 autors/es: 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"Postprint (author's final draft