Backside TSV protrusion induced by thermal shock and thermal cycling

This paper reports on thermal-mechanical failures of through-silicon-vias (TSVs), in particular, for the first time, the protrusions at the TSV backside, which is exposed after wafer bonding, thinning and TSV revealing. Temperature dependence of TSV protrusion is investigated based on wide-range thermal shock and thermal cycling tests. While TSV protrusion on the TSV frontside is not visible after any of the tests, protrusions on the backside are found after both thermal shock tests and thermal cycling tests at temperatures above 250°C. The average TSV protrusion height increases from ~0.1 μm at 250°C to ~0.5 μm at 400°C and can be fitted to an exponential function with an activation energy of ~0.6eV, suggesting a Cu grain boundary diffusion mechanism.