Plasma parameters in very high frequency argon plasmas mixed with nitrogen at atmospheric pressure Available to Purchase

A recently reported procedure [Yoshida et al., J. Appl. Phys. 128, 133303 (2020)] for estimating plasma parameters in atmospheric-pressure (AP) Ar plasma has been extended to be applicable for Ar-N₂ AP plasma. Amplitudes of current density and voltage between the electrodes and power absorbed in the plasma have been obtained by three-dimensional computer simulation of the whole system. The only needed input parameters for the simulation are input power and capacitance gaps in the matching unit. Using an inhomogeneous plasma model and a power balance relation, the central electron density (n₀) and the collisional energy loss per electron–ion pair created (ɛ_c) have been estimated. In this study, to estimate the average electron temperature (T_e), ɛ_c as a function of T_e has been calculated from the cross-sectional data set on electron impact reactions in the range applicable for the present plasma condition. In the low T_e range (<1 eV) where ɛ_c has not been well reported, we have calculated ɛ_c(T_e) as a function of N₂ concentration in Ar taking the vibrational and rotational excitations of N₂ molecules into account. From the experiments and analyses of Ar-N₂ AP plasma generation, it is found that n₀ decreases drastically with increasing N₂ concentration while T_e increases slightly. Also, it is found that n₀ increases with increasing input power (P) such as $n0∝P1.9$ while T_e increases gradually. Based on the N₂ concentration and input power dependences of T_e and n₀, some guidelines for selecting effective AP plasma nitridation conditions have been discussed.