Surface Segregation of Non-Bonding Impurities in Gold-Silicon Preforms

Stable, uniform and strong adhesives which have good thermal conductivity and are capable of severe temperature and mechanical stresses are required for highly reliable LSI devices. Au-2% Si "eutectic" preforms which are used to bond LSI devices to substrates have two serious problems: (1) Voids of significant size are created in the preform layer during the bonding operation and (2) bonding is non-uniform and some-times non-existent. Using Auger Electron Spectroscopy (AES), Secondary Ion Mass Spectroscopy (SIMS), and Quadrupole Mass Analysis (QMA) of the gases released when the preform material melted, we show that the lack of adherence of Au-2% Si preforms is due primarily to the surface segregation and compound formation of bulk impurities, notably oxygen, carbon and silicon.