A process for prevention of low temperature oxide growth over gold coated backside of silicon wafer

A process for the stabilization of gold film deposited on the back of silicon wafers was developed whereby low-temperature migration of silicon through gold and its oxidation could be prevented. The process consisted of rapid thermal alloying of a sputtered gold film deposited over a fine-ground backside of silicon wafer. The alloying was done at 400°C in an inert environment for a duration of 30 s. The effectiveness of this treatment was demonstrated by improved wetting of an aged, alloyed film with melted gold preform used in gold-silicon eutectic die bonding compared with a nonalloyed specimen. Rapid thermal alloying at 400°C in an inert atmosphere was found to be the most effective means of stabilizing the gold-coated wafer backside. Convection alloying was found to induce some surface oxidation. Surface finish had a notable effect on the resistance to oxidation of the alloyed film; smoother finish was found to be better. Evaporated gold film was found to have a thin underlying SiO₂ layer. Such a structure would be a potential hazard to the reliability of die bonding. In such a case, sputtering would be the preferred method of gold deposition