Diagnostic study of capacitively coupled neon rf plasma with traces of O2/H2 at intermediate pressure

Abstract

In this work, we have performed the non-invasive diagnostic study of capacitively coupled Ne–O2/H2 mixture plasma through the optical emission spectroscopy (OES) coupled with a suitable collisional radiative (CR) model. Capacitively coupled neon radio-frequency (rf) discharge (flowing downstream) with small admixture of O2/H2 have been generated in a vacuum chamber using 13.56 MHz rf signal and 120 W power supply. Keeping O2 and H2 flow rates fixed at 0.01 and 0.015 LPM respectively, the neon flow rate has been varied as 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8 LPM to obtain different mixture concentration of Ne–O2 and Ne–H2 discharge. The pressure in the chamber has been observed in intermediate range (∼500–25 000 Pa) for different mixture concentrations. OES measurements are recorded at various operating conditions in the wavelength range from 200 to 1200 nm. To extract the information of plasma parameters from the OES measurements, a comprehensive fine-structure resolved CR model has been developed. In the diagnostic process, five intense Ne–I emission lines at 594.48, 607.43, 633.44, 638.30, 703.24 nm are used. The CR model considers all the important processes i.e. electron impact excitation, electron impact de-excitation, radiative decay, ionization, two–three body recombination, and diffusion. The quenching process of 1s (1s5,1s4,1s3) levels of neon by the O2/H2 molecule has been included in the model. The radiative transitions from the upper levels to the ground state (1S0) as well as to the 1s levels of neon are corrected for self-absorption. The electron temperature (T e) and electron density (n e) of the plasma have been extracted for all the mixture concentrations of Ne–O2 and Ne–H2. Also, with the different mixture concentrations of O2/H2 in neon discharge, the variation of population of metastable levels (1s5, 1s3) of neon as well as intensities of 656.28 nm of hydrogen and 777.4 nm of oxygen lines have been reported and discussed.