Role of Incorporated Hydrogen and Sputtered Grain Size on Tin Whiskering

(Part A) The structure zone (SZ) scheme allows for modification of the grain size of sputter deposited thin films by adjustment of the substrate temperature during deposition. Previous work by this group on whiskering has been done exclusively on room temperature sputter-deposited tin (Sn) films with a homologous temperature Ts/Tm = 0.6, where Ts is the substrate deposition temperature and Tm is the melting point of Sn (232°C). Such Zone T depositions result in a fine-grained Sn microstructure with an average grain size ~ 1 μm. In current experiments, we explore the impact on whisker growth of Sn films produced from other portions of SZ space by depositing films at a variety of (higher) substrate temperatures having Zone 2 and Zone 3 Sn microstructures, which have more columnar growth and average measured grain sizes of ~ 3 and 4.5 μm, respectively. (Part B) The role of incorporated hydrogen on the growth of tin (Sn) whiskers is currently unknown, despite suspicions for years that it plays a role in whisker incubation and growth processes. The presence of hydrogen is of particular concern for electrodeposited films, where the plating bath contains considerable amounts of hydrogen-containing molecules which are incorporated into the deposited thin film. In this work we have investigated the role of hydrogen in whiskering by implanting a roughly uniform distribution (~ 2 × 10¹⁹/cm³) of 550 keV protons into ~1.5 micron sputtered Sn films (on Si) by a particle accelerator. Prior to the implant, the Sn films were deposited under both tensile and compressive intrinsic stress conditions and each specimen had an implanted and (masked, control) non-implanted side. It is early in the incubation period, but results to date indicate no significant differences in whisker number densities between implanted and non-implanted film regions.