The objective of this study is to test the feasibility of RuMoC films for its application in seedless Cu diffusion barriers of damascene structure. The compatibility with IC fabrication and thermal stability of RuMoC barriers were investigated. The RuMoC barriers were amorphous at temperatures up to 500 ℃, showing great thermal stability. This is because the Ru-C bonds were well preserved at those temperatures, as revealed by XPS results, which hindered the Ru from crystallizing. A Cu plug of good quality was successfully electroplated on RuMoC barriers and filled the trench without seed layer, and the barrier effectively blocked the diffusion of Cu atom at temperatures up to 500 ℃. The results indicated a great prospect of RuMoC film as seedless Cu diffusion barrier in damascene structure for Cu interconnect.