Cold plasma cleaning of copper and aluminum tested by SIMS depth profile analysis

The study tests cold plasma purifying as an efficient and economic alternative to wet methods of cleaning metal surfaces. Aluminum and copper substrates, intentionally covered by machine tool coolant, are treated in plasma. The cold plasma is generated in electric discharge which occurs under atmospheric pressure between cleaned surface of metal and electrode covered by ferroelectric ceramics of high (1000) electric permittivity. The process is conducted in argon, air and also in the mixtures of argon and air with water vapor. The film of hydrocarbons is eliminated most effectively when the process of purification takes place in the air or in the mixture of air with water vapor. Fourier transformation infrared (FTIR) spectroscopy is used to monitor efficiency of purification. SIMS depth profile analysis is applied to characterize the residual organic layer effectiveness of purification process and estimate layer thickness in the nanometric scale. This analysis shows that the remaining film consists of metal oxides, oxidized hydrocarbons and hydrocarbons at metal surface. Assuming 15 nm/min sputtering rate of the organic film, the thickness of this film at the copper substrate is equivalent to 120-160 nm, and the remaining film at aluminum is equivalent to 250-500 nm, depending on the plasma working gas composition. Copyright (C) 2010 John Wiley & Sons, Ltd.