Effect of interfacial SiO2 thickness for low temperature O2 plasma activated wafer bonding

It was experimentally demonstrated that bonding strength strongly depends on the total SiO2 thickness near the bonding interface for a given O-2 plasma surface activation. Systematic experiments of Si/SiO2 and SiO2/SiO2 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 SiO2 thickness to achieve the maximum bonding strength in SiO2/SiO2 or SiO2/Si. An optimal process option for plasma activated SiO2/SiO2 wafer bonding is proposed.