Pressure dependence of dissociation fraction and optical emission characteristics in low-pressure inductively coupled N2-Ar plasmas

A diagnostics study of low-pressure inductively coupled N2-Ar plasmas was performed by using optical emission spectroscopy (OES) and an rf-compensated Langmuir probe under the conditions of pressures of 1 - 30 mTorr and powers of 300 - 600 W. In the OES experiments, the argon was used as an actinometer and as an adding gas. The effect of the argon content in the gas mixture was examined in the range of 5 - 30%. The investigation of the effects of pressure on the dissociation fraction of nitrogen molecules and on the optical emission characteristics were carried out. The correction factors for estimating the dissociation fraction by OES actinometry accounting for argon effect were formulated and calculated. It was found that the dissociation fraction increased with increasing power and Ar content, while it decreased with increasing pressure. In addition, the electron energy probability function (EEPF), the electron density, and the electron temperature were obtained by using a Langmuir probe to investigate the effects of the plasma parameters on the optical emission characteristics and the dissociation fraction.