Influence of target microstructure on the propensity for whisker growth in sputter‐deposited aluminum alloy films

Sputtering target microstructure can significantly affect the reliability of integrated circuit metallizations through the growth of aluminum single‐crystal whiskers during sputter deposition at substrate temperatures in excess of 400 °C. Whisker densities in the film ranged from over 1500 to 133 cm−2 as the aluminum–silicon–copper alloy target microstructure was varied from a low to a high concentration of second‐phase precipitates. The mechanism by which the micro‐ structure of the sputtering target influences the propensity for whisker growth in the deposited film is proposed to be the emission of silicon–silicon and aluminum–copper dimers by the target. These dimers nucleate second‐phase precipitates in the growing film which reduces grain boundary mobility and suppresses film stress relief by hillocking. The film stress is consequently relieved by the rapid growth of the aluminum single‐crystal whiskers.