Fast and Cost-Effective Superconformal Filling of High Aspect Ratio through Glass Vias Using MTT Additive

Abstract

Cu superconformal filling of through glass vias (TGV) of aspect ratios (AR) 6 and 10 for glass interposer applications is achieved at greatly reduced times of about 1 h and 4 h, respectively, compared to about 3 h and 12 h in the past. The DC electroplating is carried out in the presence of the additive thiazolyl blue tetrazolium bromide (MTT) in acidic (pH 2 to 4) copper methane sulfonate (CuMSA)/Cl− formulations. The applied plating conditions enable the ‘butterfly’ mechanism that nucleates hemispherical or X-shaped Cu plugs in the TGV's centers while keeping the thickness on external surfaces low. Plugs are formed in AR 6 TGV's in as little as 12 min, after which the plating can be viewed as the filling of double-sided blind vias. Issues with imperfections trapped in the plugs have been addressed by decreasing the current around the time of plug formation, then increasing it for the rest of the process. In order to fill AR 10 holes much longer times at lower current density are needed. Larger diameter AR 4 TGV's have been also successfully filled with Cu. Lab scale quantities of MTT are 8 to 14 times less expensive than the competing additives NTBC and TNBT, respectively.