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 CuSO₄/ 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 CuSO₄, and 0.3 M CH₃COOH under stagnant conditions. Increasing [TNBT] to 80 ppm and [Cl^-] to 120 ppm in the presence of 0.3 M CH₃COOH 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 CuSO₄, 80 ppm Cl^-, 0.6MH₂SO₄, 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.