A study on the intermetallic growth of fine-pitch Cu pillar/SnAg solder bump for 3D-TSV interconnection

The IMC growth of fine pitch Cu pillar/SnAg solder bumps used for the chip to chip eutectic bonding of 3D-TSV interconnection was investigated. Most of SnAg solder was rapidly consumed by Cu-Sn intermetallic compound (IMC) growth during the eutectic bonding process. The composition of the IMC phase were identified as Cu-Au-Sn ternary phase and the main TEM diffraction patterns were well matched with the Cu₆Sn₅ crystal structure and the two week diffraction spots between every two strong spots matched with the superlattice of Au atoms. As a result, it was proved that the Cu-Au-Sn ternary IMCs were (Cu, Au)₆Sn₅. In the case of a large solder joint such as BGA (Ball Grid Array) or CSP (Chip Scale Package), most of the Au deposited on a metal pad was dissolved in the melting solder region due to relatively little Au content. However, in the case of TSV Cu pillar/SnAg solder bump jointed on the Au coated Cu pad, Au atoms were completely dissolved in the solder and participated in the IMC reaction due to the very small amount of solder.