Low Temperature Hybrid Bonding of Organic/Inorganic Substrates at Atmospheric Pressure

Homo- and heterogeneous bonding of Cu, SiO2, and polyimides, by using a single vapor-assisted surface activation method at 150 °C and atmospheric pressure, is highly feasible and will be of practical use in three-dimensional hetero-integration of thin, flat interconnection layers where the surfaces of electrodes and insulation layer appear on the same plane. Since it is necessary to achieve good bondability to diverse materials in a single process in order to obtain such a “bumpless” hybrid structure, 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 activated 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 based on the diffusion distance of Cu atoms. 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. Because of the well-controlled layer thickness, a low electrical resistivity of ∼ 4 × 10−8 Ω·m was obtained at the Cu-Cu interface. Furthermore, the preliminary study on the surface treatment using ultraviolet irradiation was carried out to Cu and transparent resin substrate to eliminate the vacuum process.