UV/vapor-assisted hybrid bonding technology as a tool for future nanopackaging

Hybrid bonding of electrode metal, glass insulator, and organic substrate, by using a single UV/vapor-assisted method at low temperature and atmospheric pressure, is highly feasible and will be of practical use in three-dimensional hetero-integration of nanosystems onto flex substrates where the surfaces of electrode and insulation layer appear on the same plane. Given Cu, SiO₂, polyimide, and polydimethylsiloxane as the typical materials for a hybrid integration, the vapor and UV-assisted surface modification method was used to create a compatible bridging layer to diverse materials in a single process. Bridging layers, which are based on Cu hydroxide hydrate, silanol and hydroxyl groups from SiO₂, polyimide and polydimethylsiloxane, respectively, could be prepared by introducing water molecules onto the clean surfaces created with Ar atom beam irradiation. The growth speed of the bridging layers on Cu, SiO₂, and polyimide was tunable via the absolute humidity only. Based on the diffusion distance of Cu, an exposure of 8 g/m³ was chosen as an optimum condition. Heating at 150 °C after exposure to humidity caused tight adhesion between the mating surfaces for all combinations of Cu, SiO₂, and polyimide. At the metal interface, a resistivity of around 4 × 10^-8Ω·m was obtained. Furthermore, the UV treatment in nitrogen gas, which was carried out to the initial surfaces of polydimethylsiloxane and Cu (with native oxide) films at atmospheric pressure, was found feasible in enhancing the generation of water adsorption sites without using vacuum processes.