Feasibility study of Cu paste printing technique to fill deep via holes for low cost 3D TSV applications

In this study, we report a unique Cu paste printing technique to replace Cu electroplating. The new technique is simple, fast, low cost, and high efficiency to fill holes with high aspect ratio. Moreover, overburden Cu is almost absent, and a small amount of remaining paste can be easily removed, so that the expensive CMP step can be omitted. We used TSV substrates having Ø10μm x 80μm in diameter and depth. Via walls were coated with a PECVD SiO
₂
layer. The SiO
₂
surface was further coated with a primer layer by dipping in a solution of organometallic complex for the purpose of an adhesion promotor and a diffusion barrier layer. Cu paste was made of submicron Cu particles. The paste composition was carefully adjusted to ensure filling quality. Printing of the Cu paste was carried out by vacuum assisted printing followed by centrifugation process to remove solvent from the paste and to improve particle packing. The printed TSV were annealed at 250 °C in air and in successive reducing ambient to achieve good sintering and concomitantly minimize inherent shrinkage. The same paste was screen-printed on Si-SiO
₂
/Cu seed substrates and annealed under the same condition as for the TSV to evaluate the electrical resistivity.