Effectiveness of Barrier Layer Metallizations in Long Term High Temperature Endurance Tests on Wire Bond Interconnections

Abstract

Silicon on insulator (SOI) device technology has been shown to be capable of functioning satisfactorily at operating temperatures of >200°C, with device lifetimes of 5 y at 225°C being declared. One of the key areas governing the lifetime of the packaged electronic devices is the reliability of the wire bond interconnection between the device and the package or substrate connection. Extended temperature storage testing at 250°C of packaged SOI devices has highlighted end of life failure modes associated with wire bond connections. SOI devices are normally supplied with an aluminum based bond pad metallization, which are not suitable for direct connection of Au wire at operating temperatures of >125°C, due to the formation of Au-Al intermetallics. It is possible to postprocess silicon wafers to deposit barrier and connection materials to create a monometallic Au-Au joint at the surface. For long term endurance at temperatures >200°C, the effectiveness of the barrier layer in preventing diffusion of the aluminum bond pad metallization to interact with the Au is a critical factor. This paper presents results of studies carried out on two postprocess metallization systems Au/TiW and Au/Pd/Ni deposited onto aluminum bond pads, which have been Au wire bonded and exposed to 250°C temperature storage for up to 13,000 h. The results have shown that the barrier layers are not effective in preventing diffusion of the aluminum bond pad metallization to create Au-Al based intermetallics. The results are compared with Al-1%Si wire bonding to the aluminum bond pad, where the second wedge bond is attached to a Au/Ni plated metallization, where the degradation appears to be less severe. Recommendations for designing stable wire bond interconnection systems for extended high temperature operation will be presented.