Experimental investigation on optimal plasma generation in inductively coupled plasma

Abstract

Total energy loss per ion-electron pair lost (ϵ T) 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 ϵ T at the plasma-sheath edge. At a fixed RF power, the obtained ϵ T 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 ϵ T 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 ϵ T is compared with the calculated result from the global model that includes multistep ionization, and these are consistent with each other.