Optical Emission Spectroscopy Based Diagnosis in He/N2 RF Plasmas under Different Gas Pressures and Powers

He/N2 discharge characteristics were investigated through optical emission spectroscopy (OES) in a capacitively coupled radio frequency discharge plasma. The evolution processes of characterized spectral line intensities, electron temperature, electron energy distribution function (EEDF), electron density and the density of N2+ as gas pressure and RF power were analyzed. The results show that increasing gas pressure leads to enhanced collisional cooling, which results in the decrease of electron temperature, and the subsequent reduction in the population of helium metastable states. Consequently, the Penning ionization of N2 is inhibited, leading to a decrease in electron density. While increasing rf power significantly enhances N2+ production through both direct ionization and helium metastable-assisted Penning ionization. The bi-Maxwellian model with a low-energy bulk group and a high-energy tail group was employed to express the overall EEDF characteristics. Compared with typical molecular plasmas, the He/N2 system demonstrates the superior energetic electron sustainability and stronger generation of reactive nitrogen ions. These findings provide valuable guidance for the optimization of plasma-assisted nitriding, dry etching, and other nitrogen-related surface engineering processes.