Low-Temperature Die Bonding of SiC Chips with DBC Ceramic Substrates Using High-Density Ag (111) Nanotwinned Films

Silicon carbide (SiC) has long been known for its potential to replace Si and has rapidly emerged as a new power device material that provides opportunities to extend the power, temperature, or frequency capabilities of power modules. In this study, an innovative method for the die bonding of SiC chips with DBC alumina substrates has been performed at 250 & DEG;C using (111) preferentially oriented Ag nanotwinned films. For this purpose, the optimized conditions for the deposition of such Ag nanotwins using magnetron sputtering and electron beam evaporation techniques were investigated. The results indicated amounts of 36.4 and 3.5% for the proportions of & sigma;3 and & sigma;9 coincident twin boundaries to the total grain boundaries, respectively. AFM measurements revealed that the Ag nanotwinned films were quite uniform, with an average surface roughness of 10.5 nm, which is beneficial for the direct bonding of SiC power modulus. The hardness increased from 0.7 & PLUSMN; 0.2 to 1.57 & PLUSMN; 0.3 GPa when the substrate bias was increased from 0 to - 150 V, while the electrical resistivity was reduced from 2.71 to 2.02 & mu;& omega;& BULL;cm. It is obvious that applying an appropriate substrate bias can improve both the mechanical and electrical properties of Ag nanotwinned films on SiC chips. Finally, a satisfactory bonding strength of 39.4 & PLUSMN; 3.1 MPa without obvious voids at the interface has been achieved.