Copper Superfilling without a Copper Pad at the Microvia Bottom Due to Reduced Graphene Oxide (rGO) Coating

Abstract

Reduced graphene oxide(rGO) has outstanding thermal and electrical conductivity. Compared to electroless (ELS)copper plating process, rGO grafting process is more environmentally friendly because ELS copper plating solution contains toxic species (i.e. formaldehyde as a reducer) and precious metal (i.e., Pd as a catalyst). rGO grafting process has less step than ELS deposition process, which makes it has a great prospect. Particularly, if the copper pad at microvia bottom was removed before the rGO grafting process and the sidewall and the bottom of the microvia were coated with rGO, the copper superfilling exhibited more excellent compared with ELS copper deposition process. This special process is related to the physical property of rGO. In other word, the issue of seam formation between the filled copper and the copper pad due to ELS deposition process is solved. Moreover, this approach also can be used to perform copper pillar plating, which exhibits excellent bottom-up deposition in the photoresistant hole. In this work, copper pad at the microvia bottom was removed by piranha solution at first. To enhance the filling performance, the effect of sonication in graphene oxide(GO)solution and plating time were discussed. In addition, the effect of the sidewall roughness of the microvia was evaluated to inference the exact nucleation position of plated copper the mechanism thereof. Result show that, the brand-new copper super-filling process was expected to replace the ELS copper deposition process in the future. Keyword Microvia, Electroplating, reduced Graphene Oxide, Copper superfilling References : Pei, S. F.; Cheng, H. M., The reduction of graphene oxide. Carbon 2012, 50 (9), 3210-3228.Chen, P. Y.; Sodhi, J.; Qiu, Y.; Valentin, T. M.; Steinberg, R. S.; Wang, Z. Y.; Hurt, R. H.; Wong, I. Y., Multiscale Graphene Topographies Programmed by Sequential Mechanical Deformation. Advanced Materials 2016, 28 (18), 3564-+.