A New Failure Mechanism: Al-Si Bond Pad Whisker Growth During Life Test

The results are presented of a study conducted to determine reasons for and kinetics of the growth of thin aluminum whiskers from the bond pads of semiconductors. These whiskers were found to grow to lengths of up to 200 µm from thin-film aluminumsilicon on N-type silicon gate metal-oxide semiconductors (NMOS). Whisker growth was found to be due to the compressive stress generated in the metal during wire bonding. The problem is complicated by the presence of silicon grains in the Al-Si film and was found only on parts using gold ball bonds. The growth rate is temperature dependent with a thermal activation energy of 0.7 eV. Copper doping of the metallization as well as the use of aluminum ultrasonically bonded wires were both found to effectively prevent whisker growth.