3. Conclusion and further remarks

The low-pressure radio frequency ICP source is characterized as non-equilibrium, weakly ionized and bounded plasma and finds wide applications in many fields. It holds many interesting physical phenomena and mechanisms. One is the mode transition and hysteresis that happen at two operating modes, that is, inductive and capacitive modes. In this chapter, the characteristics of plasma parameters and neutrals during mode transition are presented by a hybrid model. Moreover, the discontinuity feature of mode transition and hysteresis excited by adjusting the matching network are predicted by a fluid model that couples an external equivalent circuit module. Still, the role of metastables on triggering hysteresis is discussed and the interesting hysteresis loop formed by plasma-transferred impedance is analyzed. The present chapter indicates that the mutual interaction of plasma with circuit is the reason which excites the hysteresis.

Note that the mode transitions and hysteresis of ICP sources are very complicated. Besides the above representative features, it still exhibits research values in the topics of reactive gas mixtures, such as O2 [30], CF4/Ar [31], SO2 [32], ammonia [33] and so on and double hysteresis loop [29], inverse hysteresis [34], spatial characteristics [35], optical emission [36], electrical diagnostics [37], instability of electronegative plasma source [38] and so on. To the author, the exploration of precursors that triggers hysteresis, for instance, metastables and multistep ionizations [13, 21], electron energy distribution function [39], power coupling efficiency [40], sheath [24, 41], external circuit [26, 27] and nonlinear mechanisms [13] and so on, is the most attractive topic. The investigations greatly advance the improvements of analytical theory, numerical modeling, and experimental diagnostics of low-temperature plasma physics.
