Failure mechanism of copper through-silicon vias under biased thermal stress

We report the failure of copper through-silicon via (TSV) under biased thermal stress. The time-dependent dielectric breakdown (TDDB) of the oxide liner in the TSV was measured to detect the migration of copper from TSV to silicon. The breakdown of the oxide liner occurred by thermal cracking followed by fast drift of copper ions through the crack. For the TSV structure, there were an initial decrease in the leakage current and then the breakdown of oxide, which is different from the 3-stage TDDB behavior observed in the planar metal-oxide-semiconductor (MOS) structure. Micro-cracks in the oxide liner at the top corner of TSV were observed after TDDB measurement, and the thermal cracking of the oxide was caused by the expansion of copper TSV at test condition. Finite element analysis showed the tensile stress of 670 MPa concentrated at the top corner of the TSV. The mechanism of TDDB in both TSV and planar MOS structures were also described comparatively.