Upscaling Challenges of HIPIMS for Directional Deposition
May 1, 2017 12:00 am
Ionized deposition based on HIPIMS has been successfully developed for barrier and copper seed layers in Through Silicon Vias with very high aspect ratios of 10:1 and up to 20:1. However, upscaling to larger substrate sizes like 300 mm wafers generated several process challenges. In HIPIMS with static deposition mode the required pulse peak currents get quite high due to large target areas. The substrate bias had to ensure that a high fraction of the ionized metal is directed towards the substrate and not towards the target, because for materials with high sputter yield the ionization degree is reduced by self-sputtering. For uniformity optimization the contributions of metal ions and metal atoms had to be treated separately to achieve uniform seed layers in the vias and in the field of the substrate. The new process was applied to 200 x 10 μm vias on 300 mm wafers and the seed layers were enforced by Cu electroplating. The results were analyzed by cross-section SEM prior to and after electroplating. X-ray tomography was applied for nondestructive inspection of the entire wafer and to demonstrate that all vias had been properly seeded in the entire depth of the via.