The effect of oxygen on the interfacial reactions of Cu/TaN_x/Si multilayers

Interfacial reactions of Cu/TaN_x/Si and silicon nitride/Cu/TaN_x/Si multilayers after thermal treatment at 500 and 700°C under an ambient with residual oxygen were investigated using an energy-filtered TEM (EFTEM). The Cu and TaN_x films were deposited onto the Si (0 0 1) wafer by ionized metal plasma (IMP) technique. An interlayer of TaO_xN_y was observed between Cu and TaN_x diffusion barrier in the Cu/TaN_x/Si sample after 500°C annealing. It is evident that oxygen diffused through the Cu grain boundaries and promotes the oxidation of the Ta nitride barrier layer to form the TaO_xN_y. It is also found that the as-deposited TaN_x (x∼0.5) film with nano-crystalline microstructure would transform into Ta₂N structure with large grain character after 500°C heat treatment. After 700°C annealing, not only the TaN_x barrier layer transformed into Ta₂N but the silicidation of Cu to Cu₃Si and TaN_x to Ta₅Si₃ occurred. However, no TaO_xN_y interlayer was observed. This may result from the preferable oxidation of Cu₃Si that may suppress the oxidation of TaN_x. Nevertheless, in the silicon nitride capped (silicon nitride/Cu/TaN_x/Si) case, there was no TaO_xN_y interlayer observed in the 500°C annealed specimen. And the interfacial reaction in the silicon nitride/Cu/TaN_x/Si annealed specimen at 700°C also showed much less severe extent than the sample without capping. Experiments show that the oxygen in the ambient enhances the oxidation at 500°C and silicidation at 700°C. © 2001 Elsevier Science B.V.