Copper Through Silicon Vias Studied by Photo-elastic Scanning Infrared Microscopy

The in-plane stress distribution in copper through silicon vias (TSV) ensembles of different design has been studied by the scanning infrared stress explorer (SIREX). SIREX is a reflection-based plane polarimeter particularly developed for the high-resolution stress state visualization in silicon-based electronic and mechanic devices. The SIREX method is based on the principle of stress-induced birefringence. We demonstrate that the silicon crystal matrix around the TSV is optically anisotropic with a stress distribution being similar to fields which are known from point-like stress sources. The maps of optical anisotropy have been converted into maps of difference of principal stress components Δσ with a resolution of a few kPa. We show that magnitude and direction of Δσ depend on the geometrical design of the TSV, in particular on length and diameter. The average radial profile of magnitude is discussed. In consequence, we offer a promising tool and method for the non-destructive evaluation of TSV structures in view of their stress characteristics and integrity.