Mass Spectrometric Studies of Ions Produced in Halofluorocarbon Plasma Etching of Silicon and Silicon Dioxide

The distribution of ions present in halofluorocarbon (CF4, CF3Cl, CF3Br, CF2Cl2 ) plasmas has been studied by mass analysis of the ions extracted from the discharge. Silicon and silicon dioxide targets have been used to study the discharge chemistry in Reactive Ion Etching (RIE) conditions. In the case of silicon, both fluorine and chlorine participate in the etching; therefore, the discharge is enriched in halocarbon oligomers and etch products containing fluorine, chlorine and bromine. The higher reactivity of fluorine induces the formation of chlorine or bromine-enriched molecules and ions. Chlorine and bromine molecules are formed but their concentration in the discharge is not high due to consumption by etching. The situation is different with the silicon dioxide target. In this case, etching consumes both fluorine and fluorocarbon radicals, leading to the formation of silicon tetrafluoride and carbon oxides. The target, in this case, is “neutral”; the discharge is not enriched in oligomers as for silicon. The tendency to form chlorine and bromine-enriched species is still present and considerable amounts of molecular chlorine and bromine are present in the discharge because they do not participate efficiently in etching.