Improvement of Ag films with highly (111) surface orientation for metal direct bonding technique: Nanotwinned structure and ion bombardment effect

High-density nanotwinned structure are introduced into Ag films with over 95% of (111) surface orientation. Different substrate biases were applied to the nanotwinned Ag films during the deposition process in order to optimize the nanostructure and properties of nanotwinned Ag films, while maintain the strong (111) surface orientation. The formation of undesirable transition region, which is consisted of random-oriented nanocrystalline structure, can be sufficiently depressed by increasing applied substrate bias. The effect of Ar+ ion bombardment on the nanostructure and properties of nanotwinned (111) Ag films was discussed in this study. With moderate applied substrate bias, the nanotwinned (111) Ag film reveals very low resistivity of 1.84 μΩ cm and high hardness over 2 GPa. This study provides a concept to optimize both the nanostructure and properties of sputtered Ag film with strong (111) surface orientation for metal direct bonding applications. [Display omitted] •Nanotwinned Ag films with over 95% of (111) surface orientation are fabricated.•High-density nanotwinned structure with the twin thickness of only ~ 6 nm.•The Ag films exhibit ultrahigh hardness >2 GPa and low resistivity of 1.84 μΩ cm•Transition region can be effectively reduced due to Ar + ion bombardment effect.•Potential structure for the applications of direct bonding in electronic devices.