Low Temperature TSV Interconnection with Ultra-thin Ag Nano-twinned Films Sputtered on Si Wafers for 3D-IC Advanced Packages

Nanotwinned structure has been attracting a great deal of attention due to their excellent mechanical and electrical properties. In this study, ultra-thin nanotwinned Ag films can be fabricated by DC magnetron sputtering with moderate substrate bias. Within these nanotwinned films, only 100-400 nm thick equiaxed-grin transition layer was formed between the nanotwinned region and Si substrate observed by Focused ion Beam (FIB). For the analysis of nanotwinned films, the asdeposited films are shown to have a strong (111) preferred orientation. The roughness of the films was observed below 10 nm, which was smooth enough and acceptable for metal direct bonding. Ag-to-Ag direct bonding was then performed to satisfy the requirement of TSV interconnections. The ultra-thin nanotwinned Ag films with (111) preferred orientation will have many potential applications in interconnects and 3D IC packaging.