Hybrid plasma bonding for void-free strong bonded interface of silicon/glass at 200°C
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A novel hybrid plasma bonding (HPB) that combines sequential plasma activation (reactive ion etching followed by microwave radicals) with anodic bonding has been developed to achieve void-free and strong silicon/glass bonding at low temperature. The interfacial voids were observed at the silicon/glass interface both in the anodic bonding and in the plasma activated anodic bonding, but the voids were completely disappeared in the HPB method at 200 degrees C. The bonding strength of the silicon/glass in the HPB was as high as 30 MPa at 200 degrees C, which was higher than that in the individual treatment of anodic and plasma activated bonding methods. The improved characteristic behavior of the interface in the HPB is attributed to the higher hydrophilicity and smooth surfaces of silicon and glass after sequential plasma activation. These highly reactive and clean surfaces enhance the mobility of alkaline cations from the glass surface across the interface toward the bulk of glass in the HPB. This transportation resulted in a approximately 353 nm thick alkaline depletion layer in the glass and enlarged the amorphous SiO(2) across the interface. The void-free strong bonding is attributed to the clean hydrophilic surfaces and the amorphous SiO(2) layer across the interface.
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