Sputtering of Ag (111) nanotwinned films on Si (100) wafers for backside metallization of power devices

Abstract

For improving the performance of backside metallization for power electronic devices, an innovative Ag film with ultra-high twin density is proposed in this study. Experimentally, nanotwinned Ag films with thicknesses ranging from 2 to 8 µm and a strong (111) preferred orientation were sputtered on Si (100) wafers with and without a Ti thin film. The results indicated that the coincident Σ3 twin and Σ9 near-twin boundaries in proportion to the total grain boundaries in this Ag nanotwinned film on Ti pre-coated Si (100) wafer were 50.8 % and 13.5 %, respectively. These Ag nanotwins had spacing of 2 to 50 nm, with an average spacing of about 12 nm, and were contained in columnar Ag grains grown normal to the Si wafer. The employment of a Ti interlayer of 0.1 µm thickness clearly improved the adhesion at the Ag/Si interface under peeling tests, resulting in a bonding strength of 1.7 MPa and a maximal indentation hardness of 2 GPa.