Contamination by sputtering in mirror field electron cyclotron resonance microwave plasma sources

Langmuir probe measurements, visual observation, and Rutherford backscattering spectrometry have been used to investigate source chamber sputtering for electron cyclotron resonance plasma systems operated with Ar, N2, and Cl2. Potentials in the source ≳20 eV combined with high plasma densities (≳1012 cm−3) led to source chamber sputtering and coating of the microwave entrance window. The microwave entrance window coating caused significant absorption of incident microwave power and decreased source efficiency by as much as 50% within 5 min. Operation of the source with an anodized aluminum liner was effective in reducing microwave entrance window coating but resulted in some heavy metal contamination due to sputtering of impurities in the liner itself. Also, checks with secondary ion mass spectrometry indicated some Al contamination from sputtering of the anodized aluminum liner material. Finally, a technique for in situ cleaning of the microwave entrance window was developed and is described in detail.