Status of bonding technology for hybrid integration - A review of the surface activated bonding (SAB)

Direct wafer bonding is a key technique to realize III-V/Si optical devices such as hybrid laser and optical amplifier on silicon platform. The conventional method of semiconductor wafer bonding has been developed mainly as fusion bonding technique that is based on adhesion phenomena between hydrophilic surfaces of oxides. However to achieve a permanent bonding, hydroxyl group at the interface must be dissolved by post annealing in elevated temperature. It, however, may cause high residual stresses or brittle reaction products at the bonded interfaces, leading to degradation of the bond quality. In the contrary, the Surface Activated Bonding (SAB) is a unique method for room temperature bonding which is capable to bond various dissimilar materials at room temperature without any adhesives. Various semiconductor wafers are bonded directly at room temperature on the atomically clean surfaces created by ion beam bombardment or plasma activation. The present paper describes the current status of development of direct wafer bonding techniques for hybrid integration at low temperatures. The methods include a modification of the conventional fusion bonding technique using plasma activation and the surface activated bonding method with a certain modification using nano-adhesion layer at the interface.