Fluid Simulation For Charged Particle Transport In Capacitively Coupled Dual Radio-frequency Discharges

In the process of capacitively coupled plasma(CCP) etching, normally we put a radio-frequency (rf) source of 13.56MHz to the substrate. However, this single rf source discharge will not solve the confliction between generating high density plasma and etching rates. Recently, a dually rf driven CCP at widely different frequencies have been extensively studied. Comparing to single rf source CCP, ion flux and electron flux will be influenced by both of the sources in the dually rf driven CCP. Therefore, particles in plasma behave more complicated. It has been proved by experiments that the ion density and the ion energy bombarding in the substrate can be controlled in a better way through adjusting the rate between the frequencies of the two rf source. Furthermore, this dual rf CCP method broads the range of the ion energy on which grade we could control it, and it has a better performance that the single rf source one. But, studies on this area, especially the model that with two different rf sources rarely has been developed.In this work, we use a self-consistent sheath model to study the structure of a collisionless dual rf biased sheath. In the model, we include the time-dependent terms in ion fluid equations and an equivalent circuit equation which can self-consistently determine the relationship between the instantaneous sheath voltage and the thickness.In this work, we both study the situation of conductive substrate and insulating substrate, including the parameters in the sheath, such as, the spatio-temporal distribution of sheath voltage, the effect of frequency and power of the rf bias on voltage of the substrate, the thickness of the sheath and the ion energy distribution (IED). The numerical result shows that some parameters like frequency and power of the low frequency source are crucial for determining the parameters of dual rf biased-sheath and IED for both the conductive and insulating substrate;the thickness of the insulating layer also play a important role in the process of etching;the IED arriving at the substrate have multiple peak shapes.