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Instruments / Technical Area	Publication Details	Published	Actions
I09-Surface and Interface Structural Analysis	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 , A. Regoutz Journal Of Applied Physics 131 DOI: 10.1063/5.0086009 Diamond Proposal Number(s): [24248] Open Access Show Abstract ▼ Abstract: Power semiconductor device architectures require the inclusion of a diffusion barrier to suppress or at best prevent the interdiffusion between the copper metallization interconnects and the surrounding silicon substructure. The binary pseudo-alloy of titanium–tungsten (TiW), with >70 at. % W, is a well-established copper diffusion barrier but is prone to degradation via the out-diffusion of titanium when exposed to high temperatures (≥400 ∘C). Here, the thermal stability of physical vapor deposited TiW/Cu bilayer thin films in Si/SiO2(50 nm)/TiW(300 nm)/Cu(25 nm) stacks were characterized in response to annealing at 400 ∘C for 0.5 h and 5 h, using a combination of soft and hard x-ray photoelectron spectroscopy and transmission electron microscopy. Results show that annealing promoted the segregation of titanium out of the TiW and interdiffusion into the copper metallization. Titanium was shown to be driven toward the free copper surface, accumulating there and forming a titanium oxide overlayer upon exposure to air. Annealing for longer timescales promoted a greater out-diffusion of titanium and a thicker oxide layer to grow on the copper surface. However, interface measurements suggest that the diffusion is not significant enough to compromise the barrier integrity, and the TiW/Cu interface remains stable even after 5 h of annealing.	Apr 2022
I09-Surface and Interface Structural Analysis	Thermal and oxidation stability of Tix W1−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 , A. Regoutz Journal Of Applied Physics 129 DOI: 10.1063/5.0048304 Diamond Proposal Number(s): [19885] Open Access Show Abstract ▼ Abstract: 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.	May 2021

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