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.

Highlights

  • The transition from aluminium to copper metallisation schemes in semiconductor technologies was one of the major breakthroughs for the industry, as it offered significant improvements in performance while enabling a reduction in feature sizes.1 a major challenge is the fast diffusion of copper toward the silicon device at relatively low temperatures (

  • The influence of post-deposition annealing and composition on the oxidation behaviour of TiW thin films was investigated using a combination of soft X-ray photoelectron spectroscopy (SXPS) and hard X-ray photoelectron spectroscopy (HAXPES)

  • Surface-sensitive SXPS measurements reveal that longer annealing times result in a greater accumulation of titanium at the TiW/air interface

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Summary

Introduction

The transition from aluminium to copper metallisation schemes in semiconductor technologies was one of the major breakthroughs for the industry, as it offered significant improvements in performance while enabling a reduction in feature sizes.1 a major challenge is the fast diffusion of copper toward the silicon device at relatively low temperatures (

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