POWER DISSIPATION MEASUREMENTS IN A LOW-PRESSURE N(2) RADIOFREQUENCY DISCHARGE

Energy-flux density measurements using silicon substrates were perform ed on various parts of a parallel-plate etch reactor in contact with a low-pressure nitrogen radio-frequency discharge. The energy flux cons ists of contributions of ions, electrons, atoms, photons, and excited particles. Experimental results on the reaction kinetics of N2+ and at omic oxygen, and some additional model calculations of the excitation rates of molecular nitrogen (N2 X 1SIGMA(g)+) to excited electronic st ates were used to determine the rates of ionization and dissociation, and of vibrational, rotational, translational, and electronic excitati on of molecular nitrogen. On the basis of these rates the contribution of various particles to the measured energy flux density on the power ed and grounded electrode is discussed. It is shown that for a nitroge n 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 en ergetic neutrals formed by charge-exchange and elastic collisions in t he sheath, accounts for 93% of the measured energy flux on the powered electrode. The remaining energy flux density is caused by recombinati on of atomic nitrogen and fluxes of thermal electrons, photons and exc ited particles. The contributions of thermal electrons in the plasma a nd the acceleration of secondary electrons and ions in the sheaths to the power dissipation of the rf discharge were determined from experim ental results and some additional model calculations.