Diagnostic studies of species concentrations in a capacitively coupled RF plasma containing CH4-H-2-Ar

Three plasma diagnostic methods, tunable infrared diode laser absorption sp ectroscopy, optical emission spectroscopy and microwave interferometry have been used to monitor concentrations of transient and stable molecules, CH3 , CH4, C2H2, C2H6, and of electrons in capacitively coupled CH4-H-2-Ar radi ofrequency (RF) plasmas (f(RF) = 13.56 MHz, p = 100 Pa, phi (total)= 66 scc m) for various discharge power values (P = 10-100 W) and gas mixtures. The degree of dissociation of the methane precursor varied between 3% and 60%. The methyl radical concentration was found to be in the order of 10(12) mol ecules cm(-3) and the electron concentration in the order of loll cm(-3). T he methyl radical concentration and the concentrations of the stable C-2 hy drocarbons, C2H2 and C2H6, produced in the plasma, increased with discharge power. The fragmentation rates of the methane precursor and conversion rat es to the measured C-2 hydrocarbons were estimated in dependence on dischar ge power. Radial distributions of the electron and methyl radical concentra tions, and of the gas temperature were measured for the first time simultan eously in the plasma region between the discharge electrodes. The measureme nts allow us to draw qualitative conclusions on the main chemical processes and the plasma chemical reaction paths.