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-N-2 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 (n(0)) and the collisional energy loss per electron-ion pair created (e(c)) have been estimated. In this study, to estimate the average electron temperature (T-e), e(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 e(c) has not been well reported, we have calculated e(c)(T-e) as a function of N-2 concentration in Ar taking the vibrational and rotational excitations of N-2 molecules into account. From the experiments and analyses of Ar-N-2 AP plasma generation, it is found that n(0) decreases drastically with increasing N-2 concentration while T-e increases slightly. Also, it is found that n(0) increases with increasing input power (P) such as n(0) proportional to P-1.9 while T-e increases gradually. Based on the N-2 concentration and input power dependences of T-e and n(0), some guidelines for selecting effective AP plasma nitridation conditions have been discussed. Published under an exclusive license by AIP Publishing.

Automated summary

A recently reported procedure for estimating plasma parameters in atmospheric-pressure Ar plasma has been extended to Ar-N-2 plasma. Through computer simulations and experiments, it was found that increasing N-2 concentration leads to a drastic decrease in electron density while electron temperature slightly increases. These results provide guidelines for selecting effective plasma nitridation conditions.