SYMMETRIC AND ASYMMETRIC DOUBLE LANGMUIR PROBES CHARACTERIZATION OF RADIO FREQUENCY INDUCTIVLEY COUPLED NITROGEN PLASMA

The symmetric and asymmetric double Langmuir probe systems with their necessary driving circuits are developed for characterization of low pressure inductively coupled nitrogen plasma, generated and sustained with 13.56 MHz RF source and an automatic impedance matching network. First of all the plasma parameters such as ion saturation current, electron temperature and electron number density are determined with symmetric double probe system at different input RF powers, filling gas pressures and radial distance from the plasma chamber wall. Then the electron temperature and electron energy probability function are determined with asymmetric double probe system at the centre of the discharge plasma chamber by changing the filling gas pressure and input RF power. It is observed that the electron temperature and electron number density increase with the increase in input RF power and radial distance but decreases with the increase in filling gas pressure. The electron energy probability function determined with asymmetric probe system evidently deviates from the Maxwellian, particularly at low filling gas pressures.