Characterization of self-assembled monolayers for CuCu bonding technology

Abstract Cu Cu bonding process is intensively investigated nowadays because of the possibility of obtaining fine-pitch interconnects in 3D stacks for efficient electronic and sensing applications. These interconnects possess high shear strength, as well as excellent electrical and thermal conductivity compared to commonly used solder joints. The bottleneck of Cu Cu bonding technology is the rapid oxidation of Cu and adsorption of a contamination layer upon exposure to air. This effect can be strongly reduced by using self-assembled monolayers (SAMs) as temporary protective coatings on Cu substrates. The results of X-ray photoelectron spectroscopy (XPS) yielded a drastic decrease in oxidation rate of both sputtered and electroplated Cu surfaces during storage of passivated samples at −40 °C for 7 days. The results of infrared spectroscopic ellipsometry (IRSE) showed that after 10 days of air exposure at room temperature the long-chain 1-hexadecanethiol (C16) SAMs appear to still remain on the Cu surface and to have much slower oxidation rate in comparison to the short-chain 1-hexanethiol (C6) SAMs. Therefore, we can make a conclusion that the application of long-chain alkanethiols or storage of passivated samples at low temperature can provide a long-term oxidation protection for Cu surfaces stored in air.