Enhancing effect of substrate bias on nanotwin formation of sputtered Ag thin films

In this study, a novel method for producing high-density 〈111〉-oriented nanotwinned Ag film is proposed so as to improve the performance of backside metallization for power devices. Negative bias voltages were applied during sputtering to facilitate the formation of densely stacked nanotwinned columnar structures. In addition, the effects of substrate bias on the properties of Ag films were observed in the lower transition layer thickness, stronger 〈111〉 texture, and higher indentation hardness. The optimal indentation hardness, 1.71 GPa, was found in the nanotwinned Ag film sputtered with a bias voltage of − 150 V; it was about twice that of the normal-grained Ag film sputtered without substrate bias, 0.85 GPa. In addition, the results showed that the Ag film sputtered with a bias voltage of − 150 V possessed the strongest (111) intensity, and its surface (111) ratio was 98%, much higher than the 77% of the Ag film sputtered without substrate bias. It is concluded that the Ag nanotwinned film sputtered with a bias voltage of − 150 V has the potential for application as an interlayer in low-temperature direct bonding.