Electrodeposition of CoMoP thin film as diffusion barrier layer for ULSI applications

CoMoP thin films were fabricated by electrodeposition technique from citrate based bath onto Cu sheets for the application as diffusion barriers and metal capping layers in the copper interconnect technology. The study focused on the effect of (NH4)6Mo7O24·4H2O concentrations in the plating solution on the plating rate and chemical composition of the deposited layer. It was found that the Mo wt.% in the deposited layer increased from 13 to 22 wt.% with increasing (NH4)6Mo7O24·4H2O concentration. The influence of deposition current density, solution pH and deposition temperature at certain (NH4)6Mo7O24·4H2O concentration in the plating bath on the plating rate and chemical composition was studied. Polarization behavior of induced co-deposition of CoMoP at various electrolyte pH values was studied using cyclic voltammetry and chronoamperometry to estimate the current efficiency (CE%) of the plating solutions and the optimum pH for the plating process. Scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) techniques have been applied to characterize the morphology and chemical composition of the deposited layer. CoMoP alloys of high P wt.% as-deposited films showed irregular microcracks amorphous structure and of low P wt.% showed amorphous/nanocrystalline structure while, after annealing at 400 °C for 1 h, the films deposited with low and high P wt.% converted into polycrystalline structure. The results of oxidation property showed that, the Co–13.2 wt.% Mo–10.3 wt.% P alloy has highest stability against oxidation and lowest electrical resistance values (100–150 µΩ). The ferromagnetism nature of coated materials has been studied by hysteresis loop measurements. The electrochemical corrosion results were calculated from polarization studies for as-plated and annealed CoMoP coatings in 3.5% NaCl solution.