Collisional ion dynamics in capacitively coupled rf discharges

Based on a one-dimensional fluid model, the collision-dominated ion dynamics in capacitively coupled rf discharges are studied theoretically as well as numerically in the low rf frequency regime ω≤V_B/l (here ω is the rf frequency, V_B is the Bohm velocity, and l is the plasma length). It is found that the ion current entering the sheath varies with time as we have shown in the collisionless sheath [N. Xiang and F. L. Waelbroeck, J. Appl. Phys. 93, 5034 (2003)]. The mechanisms for the ion current modulation in the collision-dominated and collisionless sheaths, however, are different. It is also shown that the sheath dynamics and ion energy distribution are affected significantly by this time-varying ion current.