Influence of surfactant and salts on chemical mechanical planarisation of copper

Chemical mechanical planarisation (CMP) consist in polishing the surface of a wafer on a polyurethane pad with the addition of two abrasive slurries, the first one contains chemical active agents that passivate the copper superficial layer so that the abrasive particles of the second slurry can easily remove it. The input parameters are numerous and their relative influence is yet difficult to determine. Our study concerns the influence of surfactant and salts on dishing (a defect appearing during CMP) and on polishing speed. Results show that the decrease of surfactant concentration leads to a higher defect density and an increase of the polishing speed. This is possibly due to the fact that surfactant molecules adsorb on the copper surface and protect it from chemical and mechanical aggressions. It also may act as a lubricating agent. Results also show that defect density and polishing speed increase with salt concentration. This can be explained by the fact that the presence of salt leads to a decrease of the repulsive electrical double layer, which facilitates the removal of the passivated layer, created by the chemical reactants. (c) 2005 Elsevier B.V. All rights reserved.