High-rate reactive magnetron sputtering of zirconia films for laser optics applications

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2014, Vol.116 (3), p.1229-1240
• Main Authors: Juškevičius, K., Audronis, M., Subačius, A., Drazdys, R., Juškėnas, R., Matthews, A., Leyland, A.
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Machines; Manufacturing; Nanotechnology; Optical and Electronic Materials; Physics; Physics and Astronomy; Processes; Surfaces and Interfaces; Thin Films
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-013-8214-1

ZrO 2 exhibits low optical absorption in the near-UV range and is one of the highest laser-induced damage threshold (LIDT) materials; it is, therefore, very attractive for laser optics applications. This paper reports explorations of reactive sputtering technology for deposition of ZrO 2 films with low extinction coefficient k values in the UV spectrum region at low substrate temperature. A high deposition rate (64 % of the pure metal rate) process is obtained by employing active feedback reactive gas control which creates a stable and repeatable deposition processes in the transition region. Substrate heating at 200 °C was found to have no significant effect on the optical ZrO 2 film properties. The addition of nitrogen to a closed-loop controlled process was found to have mostly negative effects in terms of deposition rate and optical properties. Open-loop O 2 gas-regulated ZrO 2 film deposition is slow and requires elevated (200 °C) substrate temperature or post-deposition annealing to reduce absorption losses. Refractive indices of the films were distributed in the range n  = 2.05–2.20 at 1,000 nm and extinction coefficients were in the range k  = 0.6 × 10 −4 and 4.8 × 10 −3 at 350 nm. X-ray diffraction analysis showed crystalline ZrO 2 films consisted of monoclinic + tetragonal phases when produced in Ar/O 2 atmosphere and monoclinic + rhombohedral or a single rhombohedral phase when produced in Ar/O 2  + N 2 . Optical and physical properties of the ZrO 2 layers produced in this study are suitable for high-power laser applications in the near-UV range.