X-ray micro-beam diffraction determination of full stress tensors in Cu TSVs

We report the first non-destructive, depth resolved determination of the full stress tensor in Cu through-silicon vias (TSVs), using synchrotron based micro-beam X-ray diffraction. Two adjacent Cu TSVs were studied; one deliberately capped with SiO₂, the other without (uncapped). Both Cu TSVs were found to be in a state of tensile hydrostatic stress that fluctuated considerably with depth. The average hydrostatic stress across the capped and the uncapped Cu TSVs was found to be (99 MPa ± 13 MPa) and (118 MPa ± 18 MPa), respectively. This apparent disparity between the mean hydrostatic stresses is attributed to local differences in their microstructure, and not to the differences in capping.