A model of the chemical processes occurring in CF4/O2 discharges used in plasma etching

Abstract

A model has been developed in an attempt to explain the chemistry which occurs in plasmas produced in mixtures of CF4 and O2. Emphasis is placed on gas-phase free radical reactions, and the predictions of the model are compared with experimental results. Dissociation rates following electron impact are deduced mainly from experimental observations although relative dissociation rates have been calculated. An important assumption of the model is that CF2 can be produced as a primary dissociation product following electron impact. Furthermore, this process is favored over that producing CF3 by more than a factor of 2. Experimental evidence is presented to support this assumption. Although the model agrees well with experiment on the total amount of fluorine produced, some discrepancy exists between the predicted and measured values of [F2]. It is suggested that the higher concentrations detected in the experiments resulted from recombination of F atoms in the sampling region. The agreement for concentrations of CO2, CO, and COF2 is generally better than a factor of 2 over a wide range of experimental conditions.