ON THE COMPARISON OF REACTIVE-ION ETCHING MECHANISMS FOR SiO2 IN FLUORINE- AND CHLORINE-CONTAINING PLASMAS

This work investigated the influence of component ratio, input power and gas pressure on electro-physical plasma parameters, steady-state densities of active species and reactive-ion etching kinetics for SiO2 in CF4 + Ar and Cl2 + Ar plasmas. The combination of plasma diagnostics by Langmuir probes and plasma modeling indicated that the variation of processing conditions causes similar changes in physical and chemical factors influencing the reactive-ion etching (RIE) rate for SiO2. The only one exception is the opposite effect of gas pressure on densities of fluorine and chlorine atoms. The analysis of RIE kinetics was carried out using model-predicted data on fluxes of ions and chemically active species. It was found that the dominant etching mechanism in both gas mixtures is the heterogeneous chemical reaction while the reaction rate correlates with fluxes of fluorine or chlorine atoms. The effective probability for the Si + nF -SiFn reaction decreases with an increase in the ion bombardment intensity. Such situation reveals no ion-driven limiting stages while the negative effect of ion bombardment may result from desorption of F atoms under conditions of high adsorption degree and spontaneous interaction mechanism. The effective prob-ability for the Si + nCl -SiCln reaction exhibits much lower absolute values as well as always traces the change in the ion bombardment intensity. This allows one to assume the ion-assisted reaction regime which is activated by the formation and/or cleaning of adsorption sites for chlo-rine atoms.