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Low Temperature Hybrid Bonding of Organic/Inorganic Substrates at Atmospheric Pressure
Keywords: hybrid bonding, low temperature, atmospheric pressure
Homo- and heterogeneous bonding of electrode metal, oxides, glass insulators, and polymer substrates is highly feasible at the temperatures lower than 150 C and at atmospheric pressure, by using a single vapor-assisted surface activation method. This will be of practical use when we consider a 3D hetero integration including organic materials through bumpless structures. In order to achieve good bondability to diverse materials and to maintain good electric conduction at the metal interconnection simultaneously at a low temperature, a compatible bridging layer has to be created. In addition, the fabrication process has to be simple, thickness-tunable, and nontoxic. One of the simplest and most feasible ways is to take advantage of attractive force acting between the surfaces with hydrophilic group property. For interconnection metal, glass materials, and polymers, such surfaces are available by forming hydroxide hydrate, silanol and hydroxyl groups, respectively. Taking Cu, SiO2, and polyimide as the examples of typical materials for the hybrid bumpless structures, we created those groups by introducing atomized water onto the clean surfaces at room temperature and atmospheric pressure. Results of XPS analyses showed that the hydrophilic groups were successfully created at the targeted sites on the surfaces of testing materials, and that the growth rate of the bridging layers was tunable via absolute humidity, or more specifically, the number of water molecules colliding with the surface. And based on the previous bonding results, 8 g/m3 was used as the optimum vapor exposure condition. Heating at 150 C, after the surface touchdown, 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 considerably low resistivity of ~ 4E-8 ohm*m was obtained.
Akitsu Shigetou, Senior researcher
National Institute for Materials Science
Tsukuba, Ibaraki

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