High-speed copper filling within high aspect ratio through holes in polymer substrates

In this work, we presented a "bottom-up" and a "two-step" electrodeposition formulas for copper filling within high aspect through polymer holes (TPHs), which are needed for integrating flexible bio-micro-electro-mechanical system (bio-MEMS) sensors with conventional CMOS circuits. By using the "two-step" electrodeposition formula, a void-free copper filling is successfully realized for TPHs with the diameter of 20 μm and height of 125 μm in a common plating solution. The void-free filling effect was attributed to the preformed "V" profile after the first-step deposition. The filling time is reduced by about 80% than that of the "bottom-up" filling formula. The results suggest that the "two-step" deposition mode can be a potential solution to the long time of the through polymer holes filling.