Copper Dissolution in Aqueous Ammonia-Containing Media during Chemical Mechanical Polishing

Copper dissolution in ammonia-containing media during chemical-mechanical polishing (CMP) was investigated. Both a stationary and a rotating disk electrode (RDE) were used for electrochemical characterization. Ammonia can etch copper in the presence of oxidizers by dissolving the oxide film on the copper surface and the dissolution rate varied from about 8 to 30 nm/min, depending on the hydrodynamic conditions. The copper dissolution rate in NH 4 NO 3 or (NH 4 ) 2 SO 4 solution does not vary significantly with solution pH. Ammonium nitrate results in a higher dissolution rate, due to the extra oxidizing power of the nitrate ion. The addition of an inhibitor, benzotriazole (BTA), reduces the copper dissolution rate significantly, even though the dissolution rate can be increased by rotating the copper disk. The dissolution of copper in stagnant aqueous ammonia solutions is controlled by oxygen diffusion at high NH 4 OH concentrations and by mixed kinetics at low NH 4 OH concentrations (≤0.3 wt %).