Wafer bonding techniques for hybrid silicon photonic devices based on surface modifications

The low-temperature bonding of lithium-niobate to silicon and of indium-phosphide to silicon is reported. The bonding technique is based on modifications to the surfaces of the substrates to-be-bonded, through the deposition of self-assembled, single layers of organic molecules. Chemical functionalization of the monolayers promotes the subsequent formation of bonds across the interface between the two substrates. The technique could be applicable to the fabrication of hybrid-silicon active photonic devices such as light sources, amplifiers and modulators, which are more difficult to implement solely in the silicon materials platform. Compared with direct molecular bonding methods that are currently being used in the fabrication of such devices, monolayers-assisted bonding provides numerous potential advantages: the functional groups at the monolayers termini can be chosen and adjusted to accommodate specific substrates; the process is carried out at a relatively low temperature of 120–150 °C; the outgassing of by-products may be avoided; lastly, while the bonding interface is only a few nm-thin and does not disrupt optical coupling, it may nevertheless provide a relaxation of the substrate flatness and micro-roughness requirements.