PIC-MCC Simulations of Capacitive RF Discharges for Plasma Etching

A numerical study of parallel-plate rf discharges in Ar has been performed including the transport of ions and electrons in the sheath on the substrate. We employ a two-dimensional particle-in-cell with Monte Carlo collisions (PIC/MCC) method for an asymmetric capacitive discharge with an external electrical circuit containing a blocking capacitor and an rf power supply. The model gives self-consistently the dc self-bias voltages that usually occur on the rfpowered electrode, along with the energy and angular distribution of ion and electron fluxes incident on substrate surfaces. The peak electron density obtained in the discharge is 5.0×10 cm at the Ar gas pressure of 20 mTorr, rf frequency of 13.56 MHz, and rf voltage of 100 V, where the dc self-bias voltage is determined to be −60 V. For the range of rf voltage (50− 400 V) and frequency (13.56−40.68 MHz) examined, the peak electron density increases linearly with rf voltage and frequency squared. Higher rf frequency leads to larger distribution at lower incident angle of ions (more normal to the substrate surface), so that more desirable angular distribution is obtained.