Characteristics of Copper Nitride Nanolayer Used in 3D Cu Bonding Interconnects

Cu–Cu bonding is a key process in fine pitch Cu interconnect in 3-dimenssional Si integration. Despite the excellent electrical property and pattern ability of Cu material, the Cu–Cu bonding process is affected by the high bonding temperature and easy oxidation. Thus, the ability to protect the copper surface in a reactive air environment is very important in Cu–Cu bonding, especially for die–to–wafer Cu bonding applications. We studied Cu–Cu bonding using a copper nitride nanolayer as an antioxidant passivation layer and investigated the stability of the copper nitride nanolayer over 7 days and its decomposition capability across temperatures of up to 400 °C. We found that the copper nitride (Cu₄N) nanolayer formed by two-step Ar/N₂ plasma treatment protected the copper surface from further oxidation in the air, and that the energy required for thermal decomposition of the copper nitride nanolayer in this study was about 29.6 kJ/mol. It can be seen that the bonding temperature of Cu–Cu bonding can be sufficiently lowered by using a low–temperature decomposition property of copper nitride. Graphic Abstract: [Figure not available: see fulltext.]