Power dissipation measurements in a low-pressure N2 radio-frequency discharge

Abstract

Energy-flux density measurements using silicon substrates were performed on various parts of a parallel-plate etch reactor in contact with a low-pressure nitrogen radio-frequency discharge. The energy flux consists of contributions of ions, electrons, atoms, photons, and excited particles. Experimental results on the reaction kinetics of N+2 and atomic oxygen, and some additional model calculations of the excitation rates of molecular nitrogen (N2 X 1Σ+g) to excited electronic states were used to determine the rates of ionization and dissociation, and of vibrational, rotational, translational, and electronic excitation of molecular nitrogen. On the basis of these rates the contribution of various particles to the measured energy flux density on the powered and grounded electrode is discussed. It is shown that for a nitrogen discharge at a pressure of 30 Pa and a rf power setting of 300 W the energy flux density of the energetic particles, which are ions and energetic neutrals formed by charge-exchange and elastic collisions in the sheath, accounts for 93% of the measured energy flux on the powered electrode. The remaining energy flux density is caused by recombination of atomic nitrogen and fluxes of thermal electrons, photons and excited particles. The contributions of thermal electrons in the plasma and the acceleration of secondary electrons and ions in the sheaths to the power dissipation of the rf discharge were determined from experimental results and some additional model calculations.