Superconformal Filling of High Aspect Ratio through Glass Vias (TGV) for Interposer Applications Using TNBT and NTBC Additives

Cu superconformal filling of through glass vias (TGV) of aspect ratios (AR) 6:1 and 10:1 for glass interposer applications is achieved by DC electroplating in the presence of the additives tetranitroblue tetrazolium Cl − (TNBT) and nitroblue tetrazolium Cl − (NTBC) in acidic CuSO 4 / Cl − formulations. Filling takes place by the so-called 'butterfly' mechanism that nucleates hemispherical or X-shaped Cu plugs in the centers of TGV's while keeping the thickness on external surfaces low. Holes of AR 6:1 are filled in 3 h at 2.5 mA.cm −2 , using a bath composed of 40 ppm TNBT, 80 ppm Cl − , 0.88 M CuSO 4 , and 0.3 M CH 3 COOH under stagnant conditions. Increasing [TNBT] to 80 ppm and [Cl − ] to 120 ppm in the presence of 0.3 M CH 3 COOH allows filling of 10:1 AR holes in 12.5 h at 1.0 mA.cm −2 while maintaining thin surface plating. In the case of NTBC, 6:1 holes are filled in 4–5 h at 2.5–4.0 mA.cm −2 , and 10:1 holes are filled in 12–13 h at 1.0 to 1.5 mA.cm −2 in a slowly stirred bath containing 0.88 M CuSO 4 , 80 ppm Cl − , 0.6 M H 2 SO 4, and 45–50 ppm NTBC. Optimization of bath composition is necessary to avoid void-formation in the holes. Effects of composition on overvoltage and Cu surface topography are discussed.