A photoemission investigation of surface processes affecting the reactive ion etching of TiSi₂ in CF₄

Abstract

Photoemission was used to probe the surface modifications which occur while etching TiSi2 in CF4 plasmas. Fluorination of the silicide leads to the depletion of Si from the surface region and the formation of a relatively thick (∼15-20 Å) overlayer with an average stoichiometry of TiF3. An identical overlayer also forms on pure Ti. The overlayer is primarily composed of a single fluorinated species and apparently does not contain a distribution of different species as in the case of fluorinated Si. This observation strongly suggests that the limiting factor in the etching of these materials is the further reaction/sputtering of this stable, nonvolatile fluoride. Also, as in the case of Si etching in halocarbon plasmas, CFx films were found to form with increasing addition of H2. Significant differences in the quantity and composition of the films were found compared to those formed on Si substrates, with Si exhibiting a higher tendency to promote CFx film growth.