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It was experimentally demonstrated that bonding strength strongly depends on the total SiO 2 thickness near the bonding interface for a given O 2 plasma surface activation. Systematic experiments of Si/ SiO 2 and SiO 2 /SiO 2 wafer bonding are performed for analyzing the evolution of the bonding surface energy with the interfacial oxide thickness. Optimum plasma exposure time increases with the interfacial SiO 2 thickness to achieve the maximum bonding strength in SiO 2 / SiO 2 or SiO 2 /Si. An optimal process option for plasma activated SiO 2 /SiO 2 wafer bonding is proposed.

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This work demonstrates that the insertion of thin dissipative interlayers can substantially increase the resistance to fracture of interfaces obtained by wafer bonding. A multiscale numerical modelling strategy has been developed in order to quantify the protective effect resulting from the presence of a plastically deforming interlayer. The concept has been applied, for experimental demonstration, to a system known to be difficult to bond, i.e. PECVD SiO2/PECVD SiO2 interface. The introduction of a 1 micrometer thick aluminium interlayer next to the interface has lead, on average, to an increase by 67% of the overall interface fracture toughness. Proper combinations of interlayer thicknesses and mechanical properties can theoretically lead to improvement of the fracture energy by a factor of up to 10.