Effects of hollow cathode and Ar/H₂ ratio on plasma cleaning of Cu leadframe

Oxidized copper leadframe was cleaned using Ar/H₂ plasma in a conventional RF-plasma cleaner. It was found that the etching (cleaning) rate of oxide increased with the decrease of Ar/H₂ ratio, and reached maximum at Ar/H₂ = 0.25, under which the cleaning rate was 12.6 nm/min. The result showed that chemical effect was more significant than the physical sputtering effect. However, the cleaning rate then decreased a little when 100% of hydrogen was used. This could be due to the decrease of plasma density. In order to increase further the etching rate, oxidized samples were placed inside a rectangular hollow cathode. The results showed that the smaller the height of the hollow cathode was, the faster the etching rate would be. This is due to the increase of plasma density. In addition, it is also found that surface micro-roughness decreased with the increase of H₂ concentration.