Microwave Discharge Modeling with Resonance Power Absorption

Microwave discharges have become increasingly popular to produce reactive neutral and charged species at low electron temperature. For example, atmospheric-pressure micro-discharges have been extensively studied for electrical and biomedical applications. In semiconductor manufacturing, large-area microwave discharges can provide both high plasma density and low ion energy leading to high process throughput with low wafer damage in a wide process parameter space [1]. Theoretically, resonance power absorption has been proposed by Aliev et al for the efficient microwave heating mechanism [2]. The mode transition from under-dense to over-dense has been confirmed experimentally by Sugai et al [3]. In this study, microwave discharges at 2.45 GHz were investigated numerically in a cylindrical reactor with an azimuthal slot antenna. A fluid-based plasma model was coupled with the microwave power deposition from a frequency-domain electromagnetic solver. The under-dense to over-dense transition has been explored in Ar discharges at various power levels. The over-dense discharge shows high plasma density and low electron temperature because of the resonance power absorption near the critical density. Effect of the effective collision frequency was discussed in terms of plasma physics and numerical stability. The study provides a feasible model to design and control microwave discharges for large-area semiconductor processing.

1. Tian et al, J. Vac. Sci. Technol. A 24, 1421 (2006);

2. Aliev et al, Plasma Sources Sci. Technol. 1, 126 (1992);

3. Sugai et al, Appl. Phys. Lett. 77, 22 (2000);