Feasibility of SAB using nano-adhesion layer for low temperature GaN wafer bonding

GaN wafer bonding has been developed using conventional fusion techniques at high temperature. However, the future integration of complex 3D or photonic devices, a low temperature bonding technique, should be developed. Using the surface activated bonding (SAB) method, we demonstrated that surface activation by Ar fast atom beam irradiation is effective for room temperature bonding of GaN to Al, Si, and GaN. Because Ar atom irradiation of the GaN surface induces a modified layer revealing a Ga-Ga bond over an approximately 0.6 nm thickness, and an exposure of the surface to residual gases longer than 1.7×10 ^-4 Pa s leads to re-oxidation of the activated surface which results in a drastic decrease of the bond strength, it is concluded that a nano-layer enriched by Ga on the GaN surface may contribute to the formation of direct GaN wafer bonding at room temperature.