Comparative study of polycrystalline Ti, amorphous Ti, and multiamorphous Ti as a barrier film for Cu interconnect

Ultrathin (10 nm) Ti films with various structures were deposited by physical vapor deposition (PVD) and chemical vapor deposition (CVD) processes. CVD-Ti films with low-temperature (<500 °C) plasma-enhanced chemical vapor deposition using Ti Cl4 and H2 as reactants is an amorphous structure. This result is different from PVD-Ti films deposited by magnetron sputtering, which have a columnar structure. Ammonia plasma was further employed to post-treat the CVD-Ti barrier layer to improve barrier properties. An amorphous Ti(N,H) layer was formed on the surface of the CVD-Ti layer after ammonia plasma post-treatment. The resultant films had a bilayered amorphous Ti (N,H) Ti structure. Furthermore, the effective resistivity of the resultant Ti (N,H) Ti film decreased to 122 μΩ cm. The thermal stability of CuPVD-TiSi and CuCVD-TiSi contact systems was evaluated by thermal stressing at various annealing temperatures. For the CuPVD-TiSi, the highly copper titanium compound was formed after 450 °C annealing. The PVD Ti barrier failed initially due to the reaction of Cu and the Ti barrier, in which Cu atoms penetrated into the Si substrate after annealing at high temperature. However, no copper-titanium and copper-silicide compounds were found for amorphous Ti and plasma-treated Ti [Ti (N,H) Ti] barriers, even after annealing at 500 and 600 °C, respectively. Improved barrier capability against Cu diffusion was found for the Ti (N,H) Ti barrier layer because the CuTi (N,H) Ti n+ -p junction diodes retained low leakage current densities even after annealing at 500 °C for 1 h. Ti (N,H) Ti barrier layers present lengthened grain structures to effectively impede Cu diffusion, thus acting as much more effective barriers than conventional Ti and TiN films.