Three-dimensional fluid simulation of a planar coil inductively coupled argon plasma source for semiconductor processes

Abstract

In this paper, the effect of the coil structure, as well as the gas pressure, on the spatial distribution of an inductively coupled argon plasma is numerically investigated based on a self-developed three-dimensional fluid model. The model is based on a modified ambipolar diffusion model, in which the electron density is solved by quasi-neutral condition, the ion density and neutral particle density are obtained by solving continuity equations, and the ion flux is achieved by solving the full momentum balance equation. In addition, the inductive electric field is governed by the Maxwell equations, which are solved in the frequency domain. The results show that the electron density is nonuniform along the azimuthal direction due to the asymmetry of the coil structure, and the uniformity becomes better as gas pressure decreases. Besides, the plasma azimuthal uniformity can also be improved by reducing the opening of the coil. As the coil radius enlarges, the plasma density decreases, while the plasma radial uniformity becomes better, and the azimuthal uniformity becomes worse. In addition, the effect of the current amplitude ratio of the inner and outer coils on the plasma uniformity is also investigated in dual-coil discharges. It is found that the plasma radial uniformity becomes better by decreasing the inter-to-outer coil current amplitude ratio. The results obtained in this work demonstrate that the plasma uniformity can be improved by optimizing the coil structure and adjusting the discharge parameters, which is of significant importance for etching and deposition processes.