Theoretical and experimental study of ion flux formation in an asymmetric radio-frequency capacitive discharge

Ion flux formation in a capacitively coupled radio-frequency discharge in argon in axially symmetric chambers of different geometries is studied in experiments and by means of two-dimensional kinetic modeling by the particle-in-cell Monte-Carlo collisions method. A scaling exponent that relates the ratio of voltage drops within sheaths and the ratio of areas of driven and grounded electrodes delta S = A(rf)/A(0) is calculated for several types of geometrical discharge asymmetry. It is found that the scaling exponent has a maximum at delta S = 2.4. The dc self-bias voltage rises linearly at delta S < 2.4 and then becomes saturated. It is demonstrated that a change in dS can substantially increase the ion energy on the electrode practically without disturbing the plasma parameters. The results of self-consistent calculations are in good agreement with experimental data.