Experimental investigations of the Electrical Asymmetry Effect

In 2008 a method to generate a variable DC self bias even in geometrically symmetric capacitively coupled radio frequency (CCRF) discharges was proposed theoretically [1]. If the discharge is operated at a fundamental frequency and its second harmonic, it has been predicted that the resulting DC self bias can be adjusted by the phase angle between the applied voltage harmonics. A PIC simulation demonstrated that this Electrical Asymmetry Effect (EAE) allows separate control of the energy and flux of ions at the electrode surfaces. Here the EAE and the related separate control of ion energy and flux is investigated experimentally in a geometrically symmetric CCRF discharge operated at 13.56 MHz and 27.12 MHz with variable phase shift between the harmonics in argon at different pressures. The DC self bias, the energy as well as the flux of ions at the grounded electrode are measured. The experimental results verify the theoretical predictions and show that ion energy and flux can be controlled separately. The EAE is optimized by choosing low and high frequency voltage amplitudes that yield the strongest relative DC self bias. \\[4pt] [1] Heil B G et al. 2008 J. Phys. D 41 165202