Low cost through silicon via (TSV) technology is a key enabler for the future performance growth of various semiconductor devices. Deep etching and solder filling for TSV through pre-stacked silicon wafers make the TSV process much simpler. Polymer insulator also contributes to stress reduction and conformal insulation. In this paper, we investigate the barrier effect of polymer insulators on metal diffusion through the polymer into a silicon device by using various simple test specimens. It is found that although tin and indium showed some diffusion in the polymer materials, gold, silver, and bismuth showed little diffusion after excess annealing. We conclude that various popular solders such as SnAg, SnBi, and SnIn can be adopted as the solder via material with low risk of metal contamination in silicon.