Hybrid bonding of organic/inorganic substrates in ambient air for eco-friendly 3D integration of microelectronics

Hybrid bonding of Cu, SiO₂, and polyimides, by using a single vapor-assisted method at 150°C and atmospheric pressure, is highly feasible and will be of practical use in 3D hetero-integration of flat layer structures with reduced process complexity and toxicity. Since it is necessary to achieve good bondability to diverse materials simultaneously, we have to create a compatible bridging layer at low temperature. Bridging layers, based on Cu hydroxide hydrate and silanol and hydroxyl groups formed from SiO₂ and a polyimide, respectively, were prepared by introducing water onto the clean surfaces at atmospheric pressure. The growth rate of the bridging layers was tunable via absolute humidity, and an exposure of 8 g/m³ was chosen. Heating at 150 °C, after exposure to humidity, caused tight adhesion between the mating surfaces for all combinations of starting materials with voidless amorphous interfacial (bridging) layers. At the Cu-Cu interface, a low electrical resistivity of ~ 4 × 10^-8 Ω·m was obtained. Furthermore, the preliminary study on the ultraviolet surface treatment was carried out to Cu and transparent resin substrate. In order to eliminate the use of vacuum and the ozone formation in the process, the surface treatment was carried out in nitrogen atmosphere.