Scanning calorimetry measurements of the gas temperature in an RF-discharge fluorine-containing plasma

Abstract

The neutral-gas temperature in a low-pressure (50 Pa) capacitive RF discharge in a CF4+O2 mixture is determined from the heating kinetics of a gallium arsenide single crystal, which is chemically inert to any radicals in a fluorine-containing plasma. Experimental methods are discussed that make it possible to confirm the absence of heat sources capable of additional heating of the calorimeter in the discharge. The features and applicability limits of the method of non-steady-state gas thermometry in a weakly ionized nonequilibrium plasma are discussed. The method proposed is compared with conventional steady-state methods based on measurements of the established temperature of a thermal probe in the discharge. Temperature scanning makes it possible to study dependences that cannot be investigated by steady-state methods, in particular, the temperature dependence of the calorimeter heating power, which is very important for diagnosing the processes of plasma-surface heat transfer.