Study of Cu diffusion in Cu/Tan/SiO₂/Si multilayer structures

This paper reports the effect of a flash copper layer, sandwiched between a copper film deposited by metal-organic chemical vapor deposition (MOCVD) and a TaN barrier metal, on copper diffusion through TaN barrier to Si substrate after rapid thermal annealing at different temperatures. It is found that for the structure of CVD Cu/TaN/SiO₂/Si, which has no flash Cu layer, Cu could diffuse through the 25-nm-thick TaN barrier layer at an annealing temperature of 600°C for 180 s. However, by incorporating a flash Cu layer between the CVD Cu film and the TaN barrier, Cu diffusion can be significantly reduced. In addition to Cu, the out-diffusion of Si and oxygen, and the interaction between them can also be reduced by the incorporated flash Cu layer, due likely to the change of the crystallographic orientation of the CVD Cu films.