Filling of microvia with an aspect ratio of 5 by copper electrodeposition
By Lühn, O.; Hoof, C. Van; Ruythooren, W. & Celis, J.-P.
Published in Electrochimica Acta
2009
Abstract
The filling of microvias with a diameter of 5 µm and a depth of 25 µm (aspect ratio of 5) by copper electroplating was investigated. Filling experiments were evaluated by analyzing cross-sections of filled vias with scanning electron microscopy and focused ion beam. The fill-up evolution shows a bottom-up mechanism, also known as superfilling mechanism. The evolution of potential with time (chronopotentiometric measurements) was recorded during the fill-up process of vias and is interpreted based on potentiodynamic polarization measurements. The bottom-up fill mode is affected by the concentration of leveler inside the vias. A differential plating rate that is responsible for bottom-up plating, develops along the profile of the via on depletion of the leveler inside the vias. Since the depleted via is less inhibited, the local electrodeposition rate increases in the via. At the top part and outside the via, the electrodeposition rate is strongly inhibited due to a higher leveler concentration comparable to the one in the bulk electrolyte, what results in a low local electrodeposition rate. In this paper, the contribution of levelers to the bottom-up mechanism during the electrodeposition of copper in microvias is investigated. The observed microstructure supports the superfilling mechanism.