Polymorphic States in the Electron-Beam Exposure-Induced CaSi2 Film Growth at the CaF2 Epitaxy on Si

The results of the study of the crystal structure of CaSi₂ films and their polymorphic transformations, depending on production conditions involving radiation-stimulated CaSi₂ formation during heat treatment of a CaF₂ layer, are presented in this contribution. CaSi₂ films with space group \(R\bar {3}m\) were obtained by exposing the CaF₂ layer to an electron beam, both directly during the epitaxial growth of CaF₂ and after the formation of CaF₂ films of various thicknesses. In both cases, at the initial stage of epitaxial growth with thin CaF₂ films (10 nm), the resulting CaSi₂ film is characterized by space group \(R\bar {3}m\) with a three-layer translational period of silicon substructures in the unit cell (tr3). As the CaF₂ film thickness increases, the CaSi₂ film formed via the radiation-stimulated process is characterized by space group \(R\bar {3}m\) with a six-layer translational period of silicon substructures in the unit cell (tr6). Analysis of the results obtained in this work, together with literature data, leads to the conclusion that the incorporation of F into the silicide lattice stabilizes the formation of CaSi₂ films with space group \(R\bar {3}m\) corresponding to a specific polytype.