Reduction of Stress in Dual Ion Beam Sputtered Ta₂O₅ and SiO₂ Optical Interference Coatings

We studied the mechanical and optical properties of tantalum pentoxide (Ta₂O₅) and silicon dioxide (SiO₂) films prepared by dual ion beam sputtering with the goal to realize thin films with a stress below 0.3 GPa. It is shown that the use of a low energy assist beam consisting of oxygen and argon species results in a Ta₂O₅ film with a stress below 100 MPa and a SiO₂ film with a stress below 250 MPa. Using photothermal common path interferometry (PCI), spectrophotometry, and ellipsometry, it is shown that these films are suitable for use in interference coatings.