Effect of flash copper on Cu diffusion

This paper reports the effect of a flash copper layer, sandwiched between a copper film deposited by metal-organic chemical vapour deposition (MOCVD) and a TaN barrier metal, on copper diffusion through TaN barrier to Si substrate. The structures studied include a Cu film deposited by MOCVD, a thin layer of flash Cu and a TaN barrier layer deposited by ionised metal plasma (IMP), and SiO₂ grown on Si substrate. It is found that for the structure of CVD Cu/TaN/SiO₂/Si, which has no flash Cu layer, the Cu could diffuse through the 25-nm thick barrier layer at an annealing temperature of 600°C. However, by depositing a flash Cu layer between the CVD Cu film and the TaN barrier, the Cu diffusion can be significantly reduced. In addition to Cu, the diffusion of Ta and oxygen, and the interaction between them at different temperatures are also examined. Our observations provide useful information on Cu moralization for deep sub-micron integrated circuits.