Electron power absorption in symmetric and asymmetric CCRF discharges

Capacitively coupled radio frequency (CCRF) discharges play a crucial role in various etching processes within the semiconductor industry. These discharges operate at low pressures, around a few Pascals, and require voltages in the range of hundreds of volts, facilitating the anisotropic ion bombardment essential for precision etching. This study employs one-dimensional Particle-in-Cell/Monte Carlo collisions (PIC/MCC) simulations in the low-pressure regime at 1.0 Pa, using both spherical and Cartesian geometries. In CCRF discharges, the mechanisms of power absorption significantly differ between asymmetric and symmetric configurations. Our investigation reveals that in asymmetric discharges, electron density initially increases with the enlargement of the electrode gap size but subsequently declines, a behavior not observed in symmetric discharges. This phenomenon is linked to the sheath dynamics at the grounded electrode. Analysis of cumulative power density shows that in asymmetric discharges, power absorption predominantly occurs in a stepwise manner during the expanding sheath phase. We examine spatiotemporal information on electron power gain and loss to gain a deeper understanding of the nonlocal and nonlinear power absorption dynamics. The findings suggest that the control and efficiency of plasma applications can be significantly enhanced by understanding power absorption dynamics by manipulating the geometry.