Exploring Ru Compatibility With Al-Ge Eutectic Wafer Bonding

Abstract

We explore compatibility of Ru with Al-Ge eutectic wafer bonding. We first present experiments to check for the presence of Ru ternary alloy poisoning inhibiting Al-Ge melting as well as evaluations of Al-Ge melt wettability on Ru and diffusion outcomes following bond-simulating anneals. Results show that Ru is stable with no observed microstructural changes or dissolution in the melt, indicating no ternary poisoning for the applied thermal budget. Ru was found to act as an effective barrier offering good melt wettability in all considered configurations with Al and Ge. From inspection of the binary constituents of Al-Ge-Ru we propose that Al-Ge eutectic melting temperature will decrease marginally for Ru contamination in a 1-2% range before a drastic increase in melting temperature (>10°C/% Ru) at higher Ru compositions. We then demonstrate wafer-level packaged 200 mm devices and MEMS with strong bond outcomes of devices bearing Ru contacts. We conclude that Ru has high compatibility with Al-Ge eutectic bonding.