Fabrication of the electroless NiMoB films as a diffusion barrier layer on the low-k substrate

Fabrication of electroless NiMoB thin films as a diffusion barrier layer and capping layer for Cu interconnects in ULSI (ultra large scale integrated circuits) with low-printer level dielectrics were developed. The films containing the Mo were expected to improve the barrier property for Cu diffusion and thermal stability of the films. This study included the novel wet formation process, i.e. we use self-assembled monolayer (SAM) and catalyzing process to obtain the uniform catalyzed surface to initiate the electroless deposition reaction. The deposition rate was strongly dependent on the MoO₃ concentration in the solution. Low concentration (< 0.003 M) of MoO ₃ acted as an accelerator. On the other hand, high concentration of MoO₃ inhibited the deposition reaction. Moreover, the addition of Mo beyond 0.01 M completely suppressed the electroless deposition reaction. The content of Mo in the deposit increased as the concentration of MoO₃ in the solution increased. The Mo composition in the film saturated when the MoO₃ concentration was 0.003 M. The resistance of the layer was significantly affected by Mo, Ni and B contents in the film and deposition rate and film morphology. The surface morphology was evaluated by FE-SEM and AFM. Surface roughness depended on the deposition rate. The selective deposition was attained on the Cu line substrate without catalysis process. Thermal stability of the NiMoB film for Cu diffusion was evaluated. The obtained films (Mo concentration = 20 to 25at %) was stable against vacuum annealing under 400°C. copyright The Electrochemical Society.