Two-dimensional fluid simulations for the inductively coupled acetylene/hydrogen plasmas

Abstract

Summary form only given. Recently, due to the potential application of carbon nanotubes in field emission flat panel displays and nanoelectronics, the inductively coupled hydrocarbon plasmas such as acetylene plasma were used to grow carbon nanotubes directly on substrates. We developed a two-dimensional fluid simulation model to study the inductively coupled acetylene/hydrogen plasmas. The simulated plasma chamber has a cylindrical shape with a height of 18 cm. The upper part has a diameter of 8.5 cm, and three inductive coils surround the cylindrical quartz wall. The lower part has a diameter of 17 cm. Our model included 16 neutral species and 10 ionic species. Simulation was done for a gas pressure of 100 mtorr and a gas flow rate of 100 sccm for pure acetylene plasma, and 25 sccm C2H2 and 75 sccm H2 for C2H2/H2 plasma. The absorption power is set at 500 W Simulation results show that the plasma density is equal to 4.39times1017 l/m3 for the C2H2/H2 case. This plasma density is much smaller than the 5.94times1018 l/m3 for the pure acetylene plasma. Due to the addition of hydrogen gas, much energy is used to dissociate hydrogen molecules instead of ionization. In addition, electron temperature is higher for the case of C2H2/H2 plasma since the ionization rate constants of hydrogen atom and hydrogen molecule are lower and both hydrogen atom and hydrogen molecule are more abundant in the C2H2/H2 case than in the case of pure acetylene. For the C2H2/H2 plasma, H, CH, C2H, C4H, C6H and C8H are concentrated near the coil region. These species are, however, concentrated in the chamber center for the case of pure acetylene plasma. For C2H2/H2 plasma, it was found that the electron temperature is higher near the coil region and thus a higher production rate in that region. In the C2H2/H2 plasma, the concentrations of H, H2, CH, CH2, C2H, C4H, C6H and C8H are higher compared with the case of pure acetylene plasma. On the other hand, the concentrations of other neutral species are lower in the C2H2/H2 case. It was found that the addition of hydrogen gas would change the concentration distribution profile and electron temperature distribution as well as the concentration of neutral species. Simulation results can provide a better understanding of the complicated chemical kinetics in acetylene/hydrogen ICP discharges and help to elucidate the growth mechanism of carbon nanotubes.