Low-temperature plasma activated bonding for a variable optical attenuator

Low-temperature plasma activated bonding using the plasma etcher AMS200SE (Alcatel) has been investigated. Process parameters for obtaining strong bonds for SiSi, SiO2Si, and SiO2SiO2 surface material combinations are presented. A maximum average surface energy of 1.91 J/m2 and a maximum average bond strength of 4.6 MPa was obtained. Annealing, and activating one wafer only was found to increase the fracture surface energy. The same effects were not observed in the bond strengths. Increasing the source power of the plasma reactor increased both the fracture surface energy and the bond strength. Voids were observed at the interface of SiSi bonds after a 2 h anneal at 400 °C, and after 6 months of storage at room temperature. Successful film transfer for the fabrication of variable optical attenuators has been demonstrated.