J. J. McNally

Ion assisted deposition of optical and protective coatings for heavy metal fluoride glass

Heavy metal fluoride glass materials are attractive for optical applications in the near UV through IR wavelength regions. However, many compositions are relatively soft and hygroscopic and possess low softening temperature (250–300°C). We have applied ion assisted deposition (IAD) techniques to deposit MgF2, SiO2, and A12O3/SiO2 thin filmstructures on fluorideglass substrates at ambient substrate temperature (~100°C). The coatings deposited using IAD improve the environmental durability of the fluoride glass and appear to have reasonably good optical characteristics; without application of IAD, the deposited coatingsare not durable and have poor adhesion.

Influence of metal films on the optical scatter and related microstructure of coated surfaces.

Deposition of 0.1–1.0-μm thick metal on a CaF2 coated Si wafer causes a reduction in optical scatter and related microroughness. This effect is not observed when the coated surfaces are examined using a surface profilometer (Talystep). Scanning electron micrographs indicate that coated surfaces are smoother than uncoated surfaces.

Ion Beam Assisted Deposition Of Optical Thin Films - Recent Results

We have examined the properties of dielectric (Ti02, Si02, -Al203, Ta205 and Hf02) films deposited using ion-assisted deposition (IAD). The films were characterized using an angularly resolved scatterometer, spectrophotometer and Raman spectroscopy. A reduction in optical scatter, especially that due to low spatial frequencies, is observed for films deposited with simultaneous ion bombardment. Higher values of refractive index are obtained for films deposited using IAD. Raman spectra indicate a crystalline phase change in TiO2 films is induced by bombardment of samples with 02 ions during deposition. Other experimental data and the effects of the induced phase transition on the optical properties of TiO2 will be discussed.

Ion Beam Deposition

Publisher Summary This chapter provides a general description and two specific applications of ion beam for thin film coating. The typical ion source consists of an enclosure containing electrodes, magnetic fields, ion accelerating grids, and emitters suitably arranged to sustain electron-bombardment ionization of a working gas. Two general arrangements are most popular for application of the ion source to thin film coating. First, ions from the source can be directed at a target, which is sputtered, and the sputtered material is deposited as a thin film. This is termed ion beam sputter deposition (IBS). Second, ions from the source can be directed to the substrate, which is being coated with material generated by some independent technique. A common advantage of ion beam techniques is the degree of flexibility and control provided compared to other techniques that incorporate a gas discharge. Ion beam sources will continue to be incorporated into deposition arrangements and applied to other materials to provide films with improved properties.

Ion Beam Processing of Optical Materials

We have deposited thin films of optical materials using ion beam sputtering and ion assisted deposition techniques. It is possible to obtain good quality film material deposited on substrates at temperatures lower than normally required. Ion assisted deposition influences film stoichiometry and packing density, which in turn determine optical and mechanical properties of the film material. We discuss two general indicators which appear helpful in predicting the degree to which these occur.

Ion Beam Reduction Of Optical Scatter From Coated Metal Surfaces

Deposition of thin (0.2 - 2.0 μm) metal film on a polished metal substrate changes its scatter characteristic. The light scatter due to high spatial frequency structure is reduced by as much as a factor of ten; total integrated scatter is reduced by as much as a factor of four. The effect is strongly influenced by the deposition mechanism employed, film and substrate materials and film thickness. The effect is most apparent when using simultaneous Ar+ bombardment during film deposition (i.e., ion assisted deposition).