Upscaling challenges of HIPIMS for directional deposition

Ionized deposition based on HIPIMS has been developed for barrier and copper seed layers in Through Silicon Vias with very high aspect ratios of 10:1 and up to 20:1. By upscaling to larger substrates - beginning with 300mm wafers - several challenges appear. In stationary HIPIMS tools the required pulse peak currents are rising and the pulse current rise times should be as short as possible. The substrate bias has to ensure that a high fraction of the ionized metal is directed towards the substrate and not towards the target, since especially for materials with high sputter yield the ionization degree is reduced by self-sputtering. For the 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 process has been applied to 200x10µm vias and the seed layers have been enforced by Cu electroplating. The result has been analyzed by cross-section SEM prior to and after electroplating. X-ray tomography has been applied to nondestructively inspect the entire 300mm wafer and to demonstrate that all vias have been properly seeded in the entire depth of the via.