Fluoride thin film formation with low optical absorption by gas cluster ion beam assisted deposition

Gas cluster ion beam (GCIB) shows characteristics of low-energy irradiation effect and dense energy deposition. GCIB-assisted deposition is expected to be used for high-quality fluoride film formation, although these films are sensitive to damage by ion irradiation. In this study, LaF3 and MgF2 films were deposited by SF6-GCIB-assisted deposition. When the acceleration voltage was 3-7 kV, the deposited LaF3 film had a high packing density, small columnar structure, and very flat surface. The average roughness of the LaF3 film surface was 0.25 nm by the surface smoothing effect of the GCIB. The LaF3 film density showed 5.90 g/cm(3), which was very close to the theoretical density of crystalline LaF3. The refractive index (n) of the LaF3 film increased from 1.62 to 1.72 with an increase in the ion current density. The extinction coefficient (k) was 1 X 10(-3) at a wavelength of 193 nm. By the deposition of a thin layer of Al2O3(extinction coefficient: 5 x 10(-3)) on the quartz substrate as an interfacial film, a strong adhesive fluoride film was obtained. (c) 2007 Published by Elsevier B.V.