A Novel Bonding Method for Ionic Wafers

A novel method for bonding sapphire, ${\hbox{LiNbO}}_{3}$, quartz, and glass wafers with silicon using the modified surface activated bonding (SAB) method is described. In this method, the mating surfaces were cleaned and simultaneously coated with nano-adhesion Fe layers using a low energy argon ion beam. The optical images show that the entire area of the 4-in wafers of ${\hbox{LiNbO}}_{3}$/Si was bonded. Such images for other samples show particle induced voids across the interface. The average tensile strength for all of the mating pairs was much higher than 10 MPa. Prolonged irradiation reduced polarization in ${\hbox{LiNbO}}_{3}$, sapphire, quartz, and Al-silicate glasses. Fe and Ar ion-induced charge deposition result in the formation of an electric field, which was responsible for the depolarization. The lattice mismatch induced local strain was found in ${\hbox{LiNbO}}_{3}$/Si. No such strain was observed in the Al-silicate glass/Si interface probably because of annealing at 300°C for 8 h. The Al-silicate glass/Si interface showed an interfacial layer of 2 nm thick. A 5-nm-thick amorphous layer was observed with the other layer across the ${\hbox{LiNbO}}_{3}$/Si interface. The EELS spectra confirmed the presence of nano-adhesion Fe layers across the interface. These Fe layers associated with the electric field induced by ion beam irradiation for prolonged period of time, particularly in ${\hbox{LiNbO}}_{3}$/Si, might be responsible for the high bonding strength between Si/ionic wafers at low temperatures.