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

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 alu...