Measurements of rf bias effect in a dual electron cyclotron resonance-rf methane plasma using the Langmuir probe method

Low-pressure (0.35 Pa) methane (CH4) plasma was generated by a dual microwa ve electron cyclotron resonance (ECR)-radio frequency (rf) discharge. The p lasma parameters and electron energy distribution functions (EEDFs) were me asured using an automated cylindrical Langmuir probe. Optical emission spec troscopy was achieved as a complementary measurement to the probe results. The measured electron and ion densities increase from 10(9) to 10(10) cm(-3 ) as a function of the applied rf power. Plasma parameters obtained from bo th orbital motion limited theory and EEDF integrals show a consistent trend on the applied rf biasing. The EEDFs measured are well represented by Maxw ellian distribution functions and show a significant increase in the electr on temperature when rf biasing is applied. This contribution of hot electro ns observed above 10 eV in the presence of rf biasing may lead to enhanceme nt of the ionization and dissociation processes of CH4 in our dual ECR-rf d ischarge. (C) 2000 American Vacuum Society. [S0734-2101(00)05502-0].