Cu-Cu Direct Bonding Through Highly Oriented Cu Grains for 3D-LSI Applications

The effect of an extremely large and relatively ordered Cu grains the yield of Cu-Cu direct bonding was investigated. Our modified electroplating process followed by post processing has resulted into the formation of 10 - 15 mu m large Cu grains before Cu-Cu direct bonding. The microstructural evaluation showed formation relatively (100) oriented Cu-grains. The less hard and strain-suppressed Cu-grains as inferred from respectively, Vickers hardness and tensile test highly facilitates the Cu diffusion across the oriented grains during the Cu-Cu direct/hybrid bonding.