Copper-filled anodized aluminum oxide a potential material for low temperature bonding for 3D packaging

Copper-filled anodized aluminum oxide (Cu-filled AAO) will be presented as a potential base material for bonding between the small pads of IC chips. This paper presents a potential material for low temperature bonding for 3D packaging. The material was prepared by filling metal Cu into isolated nano-holes of anodized aluminum oxide (AAO), which were formed by the anodic oxidation treatment of aluminum. The tips of nano-Cu filaments were exposed from AAO surface (Cu nano-nail) so as to bond to Cu pads. In 3D packaging, upper and lower chips can be connected using anisotropic conductive materials. In Cu-filled AAO, the electric conductivity appears only in the vertical direction along filled metal, and insulation property by AAO appears in the horizontal direction. As a result, the anisotropic conductivity ratio (vertical vs. horizontal) is 10¹⁷. Thermal anisotropy is also demonstrated, because the filled metal conducts heat in the vertical direction. The anisotropic thermal conductivity ratio is about 34. Thermal conductivity of Cu-filled AAO is 20 times higher than that of the conventional resin, used for under-fill materials. Cu-filled AAO is promising bonding material for the thermal management in 3D integration. The low-temperature-sintering technology using the metallic Nano particle is known already well. The exposed Cu nano-nail can be sintered similar to the metallic nano-particles. We demonstrate the low temperature Cu-Cu bonding capability by using the Cu nano-nail. The direct bonding of Cu was achieved at 523K on this Cu nano-nail on Cu- filled AAO.