Nanoadhesion layer for enhanced Si–Si and Si–SiN wafer bonding

Direct wafer bonding of Si–Si and Si–SiN wafers was demonstrated using a nanoadhesion layer at room temperature. The two mating surfaces were cleaned by an Ar-ion beam and simultaneously deposited with ultrathin Fe layers (known as nanoadhesion layers). The ultrathin Fe layers imparted high bond strengths to Si–Si and Si–SiN bonds without heat treatment. Transmission electron microscopy revealed that the Si–Si and Si–SiN interfaces were tightly bonded and defect free. Moreover, the formation of crystalline iron silicide across the interface was found to enhance Si–Si wafer bonding. In addition to FeSi, an amorphous layer formed at the Si–SiN interface, resulting in a high bond strength at room temperature.