In this study, we report a new method for achieving depth resolved determination of the full stress tensor in buried Cu through-silicon vias (TSVs), using synchrotron based X-ray micro-diffraction technique. Two adjacent Cu TSVs were analyzed; one capped with SiO2 (170nm) and the other without. The uncapped Cu TSV was found to have higher stresses with an average hydrostatic stress value of 151±37 MPa, as compared to the capped Cu TSV which had a value of 99±30 MPa. Finite element based parametric analysis of the effect of cap thickness on TSV stress were also performed. The differences in the stresses in the adjacent Cu TSVs were attributed to their microstructural differences and not to the presence of a cap layer. Based on the experimentally determined stresses, the stresses in the surrounding Si for both Cu TSVs were calculated and the MOSFET keep-out-zone (KOZ) from the Cu TSV was estimated. The MOSFET keep-out-zone is influenced by the microstructural variations in their neighboring Cu TSVs, thus, should be accounted for in KOZ design rules.
Citation: IEEE Transactions on Electron Devices
Pub Type: Journals