Experimental investigation on optimal plasma generation in inductively coupled plasma

Abstract

Total energy loss per ion–electron pair lost (εT) is investigated to optimize the plasma generation at various RF powers and gas pressures in an argon inductively coupled plasma (ICP). The ion densities and electron temperatures are measured to obtain εT at the plasma–sheath edge. At a fixed RF power, the obtained εT has a minimum at a certain electron temperature, and at this condition, an optimal plasma generation is achieved according to a global model. Since the electron temperature is a function of the gas pressure, at that certain gas pressure the energy loss in the plasma is minimized and plasma is generated most efficiently. Interestingly, the electron temperature at which εT becomes the minimum decreases as the RF power increases. This is explained by multistep ionization and the electron density dependence of the density of the excited states. Measured εT is compared with the calculated result from the global model that includes multistep ionization, and these are consistent with each other.

Effect of electron energy distributions on the electron density in nitrogen inductively coupled plasmas

“…This is because the electron distribution of the calculated ε T and measured ε T is the same as the Maxwellian distribution. When the gas pressure is 1.33 Pa (10 mTorr) at 300 W, the measured ε T is slightly smaller than the calculated ε T because the population of the high-energy electron in the bi-Maxwellian distribution is larger than that in the Maxwellian distribution [78,79]. When compared to the measured ε T in the N 2 plasma, the measured ε T in the Ar plasma is significantly lower (see figure 6(b)) and did not considerably increase with gas pressure.…”