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

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 (ɛc) have been estimated. In this study, to estimate the average electron temperature (Te), ɛc as a function of Te 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 Te range (<1 eV) where ɛc has not been well reported, we have calculated ɛc(Te) 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 Te increases slightly. Also, it is found that n0 increases with increasing input power (P) such as n 0 ∝ P 1.9 while Te increases gradually. Based on the N2 concentration and input power dependences of Te and n0, some guidelines for selecting effective AP plasma nitridation conditions have been discussed.