Collision Impact On The Physical Properties Of Asymmetric Rf Plasma Sheath

Low pressure plasmas have been widely used for processes in the microelectronics industry, such as plasma etching and film deposition. It is well known that surface reactions and etching rates are strongly affected by the energy and angle distributions of ions incident on the substrate surfaces. Generally, it is often required to set independently a radio-frequency (rf) bias voltage on a substrate in a plasma process, so that a rf sheath will be formed near the substrate surface.For most reactive rf plasma etching processing, plasma sheaths near two electrodes are asymmetric due to the powered electrode area being smaller than the grounded electrode area. Taking account into collisional effects of ions with neutrals in the sheaths, a self-consistent dynamic model is proposed here to describe characteristics of radio-frequency sheaths. Numerical results show the collisional effects on some physics quantities, such as instantaneous voltages on the electrodes, instantaneous thicknesses of the electron sheathes, spatial distributions of the ion density and the electric field in the sheaths, and instantaneous voltage difference between two electrodes.It has been shown form numerical results that as increasing the discharge pressure, ion kinetic energy, the instantaneous sheath voltage drop, the electron sheath thickness are decrease, and ion density isincrease. We have also found that the instantaneous voltage in the powered electrode is larger than it in the grounded electrode. As increasing the rate of two electrode area, the rate of the time-average sheath voltages in two electrodes is increase.