Effects of Annealing on Residual Stress in Ta2O5 Films Deposited by Dual Ion Beam Sputtering

Abstract

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.

Synthesis of nanostructure Ta2O5 coatings using plasma reactive sputtering technique for optical filter application

“…2dsinθ=nλ ……. (6) Where d: the distance between levels, θ: diffraction angle, n: diffraction order, λ: X-ray wavelength. The parameters of the system are: source CuKα with radiation of wavelength λ=1.5406 Å.…”

“…An inert working gas, commonly Ar, is injected and acts as the medium for initiating and maintaining an electrical glow discharge [3]. In addition, prior research [Qipeng et al, 2018] has revealed that when deposited by magnetron sputtering at ambient temperature, the phase morphology of the as-deposited Tantalum films is amorphous. Hexagonal phases are unlikely to be representative of the crystalline phase obtained upon the application of a low thermal budget (<700ºC) and in the absence of a suitable substrate.…”

“…A study by Qipeng L. and coworkers et al in 2018 showed that annealing reduced the tension in Ta2O5 films deposited with the IBS technique. From 473 to 973 K in air, different thicknesses of Ta2O5 films were deposition using IBS, and the effects of annealing on Ta2O5 film stress were studied [6]. It was in 2013 when Bright and his colleagues at the University of Florida began to investigate a wide range of ghostly locations, ranging from the immediately apparent to the far-off infrared.…”

Effect of Nitrogen Doping on Tribological Properties of Ta2O5 Coatings Deposited by RF Magnetron Sputtering

“…Ta 2 O 5 coatings are often used as high-performance materials in optical devices [ 20 ] due to their good optical properties, thermal stability [ 21 ] and chemical stability [ 22 ] in the visible and near-infrared regions, and high refractive index [ 23 ]. Ta 2 O 5 also has good mechanical properties such as wear resistance [ 24 ] and high hardness [ 25 ], and can be used as a protective coating.…”

Laser-induced damage threshold in HfO2/SiO2) multilayer films irradiated byβ-ray

“…Postprocessing can effectively improve the resistance to laser damage. In general, the post-processing methods of optical films include surface processing, [3,5,6] heat treatment, [7][8][9] post hot isostatic pressing, [9,10] etc. Among these methods, surface processing can increase LIDT through improving surface quality.…”