Density functional theory study on the selective capping of cobalt on copper interconnect

The selective Co capping is essential for improving the electromigration resistance of the copper interconnects. We studied the mechanism of selective Co deposition using CpCo(CO)(2) on Cu over SiO2 by density functional theory calculation. We also investigated the role of H-2 co-reactant and the impact of the silylation treatment of SiO2. The calculation results show that H-2 plays a critical role on the Cu substrate but acts as a spectator on the SiO2 & nbsp;substrates. The chemisorption was exothermic on Cu by forming H2CO or CO, and H-2 lowered the activation energy from +1.09 eV to +0.62 eV. Contrarily, the reaction was endothermic on the -OH terminated SiO2 , releasing CO. However, the low activation energy of +1.35 eV was not desirable. The silylation of the SiO2 surface increased the activation energy to +1.74 eV. Therefore, the silylation can effectively improve the selectivity of CpCo(CO)(2) chemisorption on Cu over SiO2, especially at high temperatures. Our DFT simulation successfully explains the mechanism of experimental observations on CVD Co in literature.