Comparative annealing effect on bonded wafers in air and ultrahigh vacuum for microelectromechanical systems/microfluidics packaging

摘要

The fundamentals of room temperature bonding methods—nsurface activated bonding (SAB) and sequentially plasma-activatednbonding (SPAB)—are reviewed with applications for packaging of micro-nelectromechanical systems (MEMS) and microfluidic devices. The roomntemperature bonding strength of the silicon/silicon interface in the SABnand SPAB is as high as that of the hydrophilic bonding method, whichnrequires annealing as high as 1000◦nC to achieve covalent bonding. Afternheating, voids are not observed and bonding strengths are not changednin the SAB. In the SPAB, interfacial voids are increased and decreasednthe bonding strength. Water rearrangement such as absorption and des-norption across the bonded interface is found below 225◦nC. While voidsnare not significant up to 400◦nC, a considerable amount of thermal voidsnabove 600◦nC is found due to viscous flow of oxides. Before heating, inter-nfacial amorphous layers are observed both in the SAB (8.3 nm) and SPABn(4.8 nm), but after heating these disappear and enlarge in the SAB andnSPAB, respectively. This enlarged amorphous layer is SiO2, which is duento the oxidation of silicon/silicon interface after sequential heating. Thenbonding strength, sealing, and chemical performances of the interfacesnmeet the requirements for MEMS and microfluidics applications