Abstract
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 x N 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 x N y . It is also found that the as-deposited TaN x (x∼0.5) film with nano-crystalline microstructure would transform into Ta 2 N structure with large grain character after 500°C heat treatment. After 700°C annealing, not only the TaN x barrier layer transformed into Ta 2 N but the silicidation of Cu to Cu 3 Si and TaN x to Ta 5 Si 3 occurred. However, no TaO x N y interlayer was observed. This may result from the preferable oxidation of Cu 3 Si 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 x N 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.