Analyses of Reactive Plasma Dynamics by Particle Simulations

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Plasma processing, such as thin-film formation and surface modification technologies based on reactive plasmas, is one of the most important technologies for the advanced electronics, including semiconductor chips and liquid-crystal displays. In the present research, we have employed particle simulations based on the Particle-in-Cell (PIC) and Monte-Carlo Collision (MCC) methods to analyze plasma-processing tools used in semiconductor manufacturing. The PIC and MCC methods are ideal for reactive plasma simulations as the former can resolve electron velocity distribution functions and the latter can determine chemical reaction rates using fundamental physical data such as reaction collision cross sections. In 1999, we have developed a PIC/MCC code to simulate capacitively coupled parallel-plate Ar discharges in 2D cylindrical geometry. As to collisions, we have included ionization, excitation, and elastic collisions for electron-neutral collisions, and charge exchange and elastic collisions for ion-neutral collisions. Currently the neutral gas is assumed to be uniform with the room temperature. In 2000, we have extended the simulation code to handle dual-frequency capacitively coupled discharges and also introduced external electrical circuits for realistic plasma processing tools. Furthermore, we have employed an acceleration scheme for ion dynamics calculations to increase efficiency of the simulation code. In our simulations we have observed that, in both single- and dual-frequency capacitively coupled discharges, as the gas pressure decreases, the electron heating mechanism changes from ohmic heating to collisionless heating, and the electron energy distribution function exhibits a bi-Maxwellian distribution due to the Ramsauer minimum of the elastic collision cross section for Ar.