Studying a low-pressure microwave coaxial discharge in hydrogen using a mixed 2D/3D fluid model

This work presents a numerical model of hydrogen plasma in a microwave coaxial discharge at low pressure (25-250 Pa). The model is a mixed two-dimensional (2D)/three-dimensional (3D) model in that it combines three-dimensional geometry for the electromagnetic field and two-dimensional geometry for the transport equations. The model is validated against experimental results available in the literature and, where possible, simulations of comparable discharges. The model shows reasonable agreement in the relevant pressure range. A parametric study with respect to pressure is carried out and it is observed that the plasma contracts towards the quartz tube with increasing pressure. Increasing the pressure also influences the abundance of H+ ions but on the other hand it has little impact on hydrogen dissociation degree and electron temperature. Furthermore, the uniformity of the plasma above the substrate holder is analyzed. It is observed that at pressures over 150 Pa, the plasma gets non-uniform in the direction parallel to the plasma lines. Finally, the uniformity of particle and energy fluxes to the substrate holder are analyzed. Knowing the fluxes is especially useful for the material applications of the device.