Low Temperature Direct Bonding of Ge Chips with DBC Alumina Substrates using Ag Nanotwinned Films

Abstract

Epitaxial Ag nanotwinned films with highly (111)preferred orientation were deposited by magnetron sputtering onto germanium substrates, some with the addition of a Ti layer and application of negative substrate bias. A high density of Ag nanotwins with an average twin spacing of 2.18 nm formed in the Ag columnar structures. Twin boundaries formed along the direction perpendicular to the growth direction of the film. The influences of the Ti interlayer and negative substrate bias on the formation of Ag nanotwins were also examined. The highly (111)-textured thin films had an impressive film surface roughness, as low as 11.2 nm. The (111)-oriented nanotwins provided higher surface diffusivity than did other orientations. The electrical resistivity decreased significantly as more ( 111)oriented nanotwinned structures formed. The bonding experiment was also performed at 200 ℃ for 60 min at a bonding pressure of 20 MPa, and extremely rare voids appeared at the bonding interface. The combination of low surface roughness, rapid diffusivity on the (111)-planes, and lower electrical resistivity present a high possibility of reliable interconnections for future microelectronic technology via direct bonding.