Control of Ion Species and Energy in High-Flux Helicon-Wave-Excited Plasma Using Ar/N2 Gas Mixtures

Abstract

The atomic nitrogen (N) ion flux and impacting ion energy are the two important parameters, which influence the performance of production of plasma nitridation applications such as N-doped graphene. In this paper, a novel method is described to control the flux and ion energy of atomic N ion (N+) and molecular N2 ion (N2+) using a helicon-wave-excited plasma (HWP) with Ar/N2 gas mixtures. It shows that by varying the flow-rate ratio of N2/(N2+Ar) ( $\alpha$ ), the ratio of [N+]/[N2+] ( $\beta$ ) can be controlled obviously, and $\beta $ could be increased up to 1.2 at $\alpha = 0.5$ , which is much higher than that in pure N2 HWP discharge ( $\beta \sim 0.2$ ). The maximum density and flux of atomic N+ are obtained, which are $2.5\times 10^{18}\,\,\text {m}^{-3}$ and $8.6\times 10^{21}\,\,\text {m}^{-2}\text {s}^{-1}$ , respectively. The results show that the addition of Ar into N2 plasma can be employed to remarkably increase the [N+]/[N2+] due to electron-impact ionization involving the metastable state of Ar. The N+ ion beams are formed with a speed near to Mach 3, and the ion-beam energy is increased from 30 to 50 eV with increasing $\alpha $ to 0.75.