Optical coatings deposited by the dual ion beam sputtering (DIBS) method usually show high compressive stress, which results in severe wavefront deformation of optical elements. Annealing post-treatment has been widely used to control the residual stress of optical coatings. However, the effect of annealing on the stress of Ta 2 O 5 films deposited by the IBS method has not been reported in detail. In this study, different thicknesses of Ta 2 O 5 films were deposited by IBS and annealed at different temperatures from 473 to 973 K in air, and the effect of annealing on the stress of Ta 2 O 5 films was investigated. The as-deposited Ta 2 O 5 films deposited by IBS show high compressive stress, which are about 160 MPa. The compressive stress decreases linearly with the increasing temperature, and the wavefront deformation of Ta 2 O 5 films increases linearly with film thickness (within 20 µm) at the same annealing temperature. When the temperature rises to 591 K, Ta 2 O 5 films with zero-stress can be obtained. Ta 2 O 5 films show tensile stress instead of compressive stress with further increasing annealing temperature, and the tensile stress increases with increasing temperature. Meanwhile, with the increasing annealing temperature, the refractive index of Ta 2 O 5 film decreases, indicating the decreasing packing density. The atomic force microscope (AFM) test results show that surface roughness of Ta 2 O 5 films slowly increases with the increasing of annealing temperature. Moreover, X-ray photoelectron spectroscopy (XPS) analysis shows that the Ta in Ta 2 O 5 films can be further oxidized with increasing annealing temperature, namely, the absorption of Ta 2 O 5 film can be reduced. X-ray diffraction (XRD) analysis shows that the annealing temperature should be below 923 K to maintain the amorphous structure of the Ta 2 O 5 film.

No abstract

No abstract