Electroless Deposition of Cu-Mn Alloy

Interconnect scaling in semiconductor devices presents numerous challenges to the current dual-damascene process flow. One issue is the deteriorated Cu electromigration resistance, which shortens the device life. To address this problem, one approach is to dope the Cu interconnects with small amounts of manganese (Mn). The Mn segregates at the interface between Cu and the dielectric substrate and forms a barrier layer, thereby suppressing Cu diffusion. It was found that incorporation of ~2 at.% Mn increases the lifetime of Cu interconnects four-fold [1]. Currently, the state-of-the-art method for depositing Cu-Mn alloys is sputter deposition with Mn content generally above a few atomic percent [2,3]. Compared to sputter deposition, electroless deposition has numerous advantages such as simplicity, low cost and faster deposition rate. Therefore, it is of great interest to develop an electroless process for depositing Cu-Mn alloy. In this study, we report electroless deposition of Cu-Mn. The Mn incorporated was found to be ‘mobile’, a prerequisite for its application in interconnect metallization. It was also observed that Mn was incorporated during electroless Cu-Mn deposition at potentials that are much more anodic to its standard reduction potential (-1.18 V vs. SHE). To further our understanding of the electroless Cu-Mn deposition, a combination of voltammetry and quartz crystal microbalance were used to unravel the Mn deposition mechanism. References [1] J. P. Gambino, “Improved Reliability of Copper Interconnects Using Alloying”, Proc.17th IEEE IPFA, 1-7 (2010). [2] J. Koike and M. Wada, Applied Physics Letters, 87, 041911 (2005). [3] J. Koike, M. Haneda, J. Iijima, Y. Otsuka, H. Sako and K. Neishi, Journal of Applied Physics, 102, 043527 (2007).