Axial uniformity diagnosis of coaxial surface wave linear plasma by optical emission spectroscopy

The coaxial surface wave linear plasma with preeminent axial uniformity is developed with the 2.45 GHz microwave generator. By optical emission spectroscopy, parameters of the argon linear plasma with a length over 600 mm are diagnosed under gas pressure of 30 and 50 Pa and different microwave powers. The spectral lines of argon and H_β (486.1 nm) atoms in excited state are observed for estimating electron excitation temperature and electron density. Spectrum bands in 305–310 nm of diatomic OH (${\mathrm{A}}^2{\mathrm{\sum }}^{+}-{\mathrm{X}}^2{\mathrm{\prod }}_{\mathrm{i}}$) radicals are used to determine the molecule rotational temperature. Finally, the axial uniformity of electron density and electron excitation temperature are analyzed emphatically under various conditions. The results prove the distinct optimization of compensation from dual powers input, which can narrow the uniform coefficient of electron density and electron excitation temperature by around 40% and 22% respectively. With the microwave power increasing, the axial uniformity of both electron density and electron excitation temperature performs better. Nevertheless, the fluctuation of electron density along the axial direction appeared with higher gas pressure. The axial uniformity of coaxial surface wave linear plasma could be controlled by pressure and power for a better utilization in material processing.