Radio frequency magnetron sputter deposition of CaF2 films

Calcium fluoride films have been deposited onto unheated (<100 °C) substrates by low power rf magnetron sputtering of CaF2 targets using Ar and Ne process gases at pressures of 0.5–2.7 Pa, biased and floating substrate potentials, and various geometries of the substrate with respect to the source. The thickness and composition of the films are very sensitive to resputtering of the growing film. Uniform and stoichiometric films were most readily obtained on off-axis substrates using two sputter sources oriented with the targets facing each other. The films were found to be crystalline, have a fine textured microstructure, and to be transparent and highly resistive.