Horizontal surface wave propagation in the sheath by the nonuniform electrode structure affecting plasma uniformity in RF capacitively coupled plasma

The effects of electrode holes and dielectric structures on low-pressure RF capacitively coupled plasmas have been investigated using a two-dimensional particle-in-cell simulation. Simulations were conducted with a driving voltage of 100 V at 50 MHz under gas pressures of 5 mTorr and 20 mTorr while varying the hole size between 5 mm and 10 mm. The presence of a hole induces a horizontal surface wave propagation of the electric field due to localized space charge, which results in the nonuniform electron density. Effective electron heating occurs near the hole, leading to a peak in electron density above the hole in all cases. The extension of electron heating with varying hole sizes is related to the sheath thickness. At 5 mTorr, the electron density above the hole is higher by 2.5% for a 5 mm hole and 4.2% for a 10 mm hole than at the center. At 20 mTorr, the increase is 11.9% for a 5 mm hole and 10.6% for a 10 mm hole. When a dielectric is added next to the hole, the local electric field near the dielectric is weakened, leading to a perturbation wave of electron density toward the dielectric side.