Novel Cu plating formula for filling through silicon vias

Through-silicon-via (TSV) technology has been employed for three-dimensional (3D) packaging of multi-chips. A high interwafer interconnect density can be achieved with a minor area penalty. Having shorter signal paths between dies make it possible to improve the system´s performance by permitting the system to run faster, alleviate interconnect delay problems, it also consumes less power. Copper has been selected as the through-chop material because of its compatibility with conventional multilayer. If the top surface profile of the copper deposit inside the TSV is V-shaped, then a seam may exist at the via center after electroplating. Alternatively, it should have no seam inside the filled TSV, if the top surface profile of the copper deposit inside the TSV is U-shaped after electroplating. In this regard, it is supposed that the top surface profile of the deposited copper inside the TSV during plating is one of the key points to achieve voidand seam-free filling. In this study, the void-free copper filling of TSVs with an aspect ratio of 3.5, where the diameter is 20 ?m and the depth is 70 ?m, by copper electroplating was investigated. A novel plating formula was developed in order to achieve the U-shaped copper filling during plating. Filling performance of the novel plating formula was evaluated by examining cross-section of the filled TSVs using an optical microscope (OM). The effects of chemical and physical interactions between the plating additives and fluid dynamics were characterized by using a potentiostat with a three-electrode cell. We used two rotation speeds of working electrode (WE) to simulate the fluid motion around the wafer. One was fixed at 1000 rpm to simulate the fluid motion outside the TSV. The other was fixed at 100 rpm to simulate the fluid motion inside the TSV. Electrochemical analyses show that the filling mechanism obey a model of convection-dependent adsorption (CDA) behavior. The novel copper plating formula led to the bottom-up beh- avior looking like an elevator, that is, the top surface profile of the copper deposit filled in the TSV always was a flat plane during plating. Besides, the sidewall shrinkage due to copper deposition was insignificant during plating. This filling behavior is totally different from that of a conventional copper plating formula for via filling, which usually behaves a zipper-type filling mode and thus causes a seam formation at the center of the filled TSV. This invention of this work can make sure of no void and seam in the filled TSV. Thus, the reliability of the TSV can be greatly improved.