Sputtering of Ultra-thin Ag Nano-twinned Films on Si Wafers for the Applications in TSV Interconnection of 3D-IC Advanced Packages Copper Solvent Extraction

Abstract

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 as-deposited 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.