Low pressure inductively coupled plasmas (ICPs) are investigated using theoretical modeling and experimental diagnostic methods. For various ICP discharges, time dependent global (volume averaged) models are developed and a number of diagnostic tools are used.
In a low pressure argon discharge, a new method is proposed to improve the precision of the pressure-dependent electron temperature calculated by the line ratio method. Using the electron energy distribution functions (EEDFs) and the electron density from Langmuir probe, the coefficient of the cascade cross-section are provided as a function of the pressure for argon 4p1 and 4p5. The effective electron temperature calculated by the corrected cascade cross-section is shown and compared with Langmuir probe results.
The production of argon excited states in the afterglow of pulse discharge is investigated. Experimentally time resolved optical emission spectroscopy (OES), optical absorption spectroscopy (OAS) and Langmuir probe are used to measure the emission of highly excited states, metastable atom density, electron density and electron temperature. From the time dependent global model, it is found that during the pulse-on time the electron impact excitation and the ionization from the ground state and Ar (3p54s) are the dominant population processes for all excited states. On the other hand, during the afterglow the main source of all excited states is the three body electron-ion recombination. As a consequence argon highly excited state can be populated more than during the pulse-on time.
The E-H mode transition and hysteresis in low pressure argon inductively coupled discharges are investigated using the previous global model and a transformer model. The total absorbed power by plasma electrons and coil current are calculated as a function of the electron density at fixed injected power. We found that the transition is due to the difference of the absorbed power between the two modes. Moreover the calculation results show that the existence of an inaccessible region between E and H mode, as well as a threshold coil current and a minimum absorbed power for the H mode.
The dissociation of the nitrogen molecule in an Ar-N2 ICP discharge is studied both experimentally and theoretically. Using the two-photon absorption laser-induced fluorescence (TALIF) an increase of the dissociation rate in highly Ar-diluted region is observed. A complete kinetic model is developed to understand the behavior of the Ar-N2 discharge. The calculated results are compared with the measured results, obtaining reasonably good agreement. In pure nitrogen discharge the N atoms are mainly created by electron impact dissociation at low pressure (20 mTorr) while it is due to metastable-metastable pooling dissociation at high pressure (200 mTorr). In Ar-N2 discharge, the N atom density increases despite less amount of N2 molecule in highly Ar-diluted region at 200 mTorr. From the model the charge transfer from Ar+ to N2 is an important source of nitrogen dissociation in Ar-N2 discharge.
The global kinetic models are developed in low pressure He, Ne, Ar and Xe discharges to calculate the electron temperature and the electron density. The calculated results are compared with experiments and the dominant creation sources and the routes of loss for electron and metastable atoms are discussed as function of pressure. Finally the transformer model is used to calculate the electrical properties of He, Ne, Ar and Xe discharges.