Three-dimensional (3D) IC chip stacking has been proposed for a long time. An interposer designed between two chips for interconnection [i.e., through silicon vias (TSVs)] is a bridge for vertical signal transmission. Recently, reduced Graphene Oxide (rGO) has also been developed because it not only is a good conductor, but also it can be grafted onto the surface of many substrates and makes them be conductive through rGO grafting process. TSV is a silicon-based substrate, so self-assembled monolayer (SAM) of amino-silane is usually used as an adhesive layer in the rGO grafting process, and it can form a thin film with positive charges, which can adsorb the functional groups of GO sheets due to charge attraction. After GO is grafted onto the surface, a chemical reducer is used to reduce the grafted GO to rGO. However, silane must be dissolved in an organic solvent for stabilization. Otherwise, it easily forms “islands” on the surface, which then cause non-uniform and discontinuous rGO film. In this work, deionized water was employed to replace the organic solvent to dissolve the amino-silane. Effects of operating parameters, surface treatments and modifications on rGO grafting performance were investigated to improve the uniformity and continuity of the grafted rGO using several analysis methods and instruments, like water contact angle, atomic force microscopy(AFM) and conductive atomic force microscopy(C-AFM), etc. Cross-section images of TSVs after copper and cobalt electroplating were also used to evaluate the filling performance and uniformity. Eventually, a stable and optimized aqueous rGO grafting process is developed and can be used as a conducting layer of TSV for copper and cobalt superfilling.

Keywords:

Through Silicon Via, Electroplating, reduced Graphene Oxide, 3D IC

Reference:

1. Songfeng, and C. Hui-Ming, “The Reduction of Graphene oxide ”, Carbon., 2012, 50, 3210-3228.

Figure1. Scheme of the rGO grafting process. TSV was immersed in Beaker A for surface pre-treatment, surface modification with amino-silane was carried out in Beaker B, the GO grafting step was performed in Beaker C, and GO reduction was conducted in Beaker D.