THE INTERACTION BETWEEN DIFFERENT BARRIER METALS AND THE COPPER SURFACE DURING THE CHEMICAL-MECHANICAL POLISHING

The copper polishing rate in a weak acid slurry with H2O2 as a oxidizi ng agent is determined by a two-step process of the formation of coppe r oxides followed by its mechanical abrasion. The electrochemical pote ntial is a criterion for the driving force of oxidation-reduction reac tions that occur during the Cu dissolution process. Using the experime nt a corrosion potential (E-corr) was determined. It depends on the po tential of the cathodic reaction, the Tafel slopes of each reaction an d the control of the reaction by Tafel kinetics pr concentration polar isation. Potentiodynamic measurements were performed with different H2 O2 contents in the slurry. The dissolution current density (i(corr)) i s correlated to the oxidation-reduction reaction rate. In the presence of a barrier metal, such as WTi, the dissolution rates were influence d by galvanic effects. W and Ti and their compounds were dissolved in the slurry by the complexing ability of H2O2. There is an increase in the barrier wet etch rate when copper is present. In the case of polis hing both Ti-W and Cu simultaneously a dramatic increase of the barrie r polish rate was observed. The acceleration of the W or Ti polish rat e can be explained by the galvanic coupling between Cu and the barrier metal. By the use of TiN as a barrier metal no galvanic interaction h as been observed. The removal rates of TIN have not been influenced by the presence of Cu.