High density interconnect at 10µm pitch with mechanically keyed Cu/Sn-Cu and Cu-Cu bonding for 3-D integration

The results of bonding and stress testing of Cu/Sn-Cu bonded dice and Cu-Cu thermocompression bonded dice at 10µm and 15µm pitch in large area arrays are shown. The interconnect bonding process pressure and temperature required for the formation of low resistance (<100 mΩ), high yielding (99.99% individual bond yield), and reliable interconnects is described. In the case of Cu/Sn-Cu, use of a mechanical key was found to improve yield. A run of 23 consecutive bond pairs was made with mechanical key, resulting in 92% aggregate channel yield at 10µm pitch in area arrays containing 325,632 individual bonds per die to achieve an interconnect density of 10⁶ / cm². SEM cross sections of Cu/Sn-Cu and Cu-Cu bonded samples and EDS analysis of Cu/Sn intermetallic compounds both before and after stress testing are presented. The effects of thermal cycling on electrical yield and resistance are presented for Cu/Sn-Cu with underfill. Comparison of the electrical and shear test performance of Cu/Sn-Cu and Cu-Cu is made.