An evaluation of test structures for measuring the contact resistance of 3-D bonded interconnects

This paper evaluates test structures designed to characterise electrical contacts between interconnect on bonded wafers. Both simulation and experimental measurements are used to explore the capability of a stacked Greek cross type test structure to extract the contact resistivity (p_c) between two bonded conductive layers. It is concluded from the simulations and actual electrical measurements of the benchmark Kelvin structures that the stacked Greek cross can only be used where there is a relatively high specific contact resistivity. For the structures evaluated in this study, this was found to be greater than p_c ≥ 9.0 x 10^-7 Ω-cm².