Assessing the impact of atomic oxygen in the damage threshold and stress of Hafnia films grown by ion beam sputter deposition

D. Patel; Y. Wang; M. Larotonda; J. Lovewell; J. Jensen; K. J. Hsiao; E. Krous; J. J. Rocca; C. S. Menoni; F. Tomasel; S. Kholi; P. McCurdy

doi:10.1117/12.696080

15 January 2007 Assessing the impact of atomic oxygen in the damage threshold and stress of Hafnia films grown by ion beam sputter deposition

D. Patel, Y. Wang, M. Larotonda, J. Lovewell, J. Jensen, K. J. Hsiao, E. Krous, J. J. Rocca, C. S. Menoni, F. Tomasel, S. Kholi, P. McCurdy

Author Affiliations +

Proceedings Volume 6403, Laser-Induced Damage in Optical Materials: 2006; 640314 (2007) https://doi.org/10.1117/12.696080
Event: Boulder Damage Symposium XXXVIII: Annual Symposium on Optical Materials for High Power Lasers, 2006, Boulder, Colorado, United States

Abstract

Hafnium oxide (HfO₂) is undoubtedly one of the most desirable high-index optical coatings for high power laser applications. One of the key goals in the fabrication of oxide films with high Laser Induced Damage Threshold (LIDT) is to minimize the number of film imperfections, in particular stoichiometric defects. For HfO₂ films deposited by ion beam (reactive) sputtering (IBS) of a hafnium metal target, stoichiometry is controlled by the injection of molecular oxygen, either close to the substrate or mixed with the sputtering gas or some other combination. Good stoichiometry is important to reduce the density of unoxidized particles buried in the coatings, which affect the LIDT. This work evaluates the potential advantages of using pre-activation of oxygen in the IBS of HfO₂, with special emphasis on its impact on LIDT and film stress. For the experiments, oxygen was activated by an independent plasma source and then introduced into a commercial IBS chamber. The optical properties of the films were characterized using spectrophotometry and ellipsometry. Their structural quality and composition were determined from x-ray diffraction and x-ray photoelectron emission spectroscopy. The stress was determined from interferometer measurements. For optimized conditions, 2.5 J/cm² LIDT was measured on HfO₂ films at λ=800 nm with 1 ps and 25 mJ pulses from a chirped amplification Ti:Sapphire laser. In the range of oxygen variations under consideration the effects on LIDT are shown to be minimal.

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D. Patel, Y. Wang, M. Larotonda, J. Lovewell, J. Jensen, K. J. Hsiao, E. Krous, J. J. Rocca, C. S. Menoni, F. Tomasel, S. Kholi, and P. McCurdy "Assessing the impact of atomic oxygen in the damage threshold and stress of Hafnia films grown by ion beam sputter deposition", Proc. SPIE 6403, Laser-Induced Damage in Optical Materials: 2006, 640314 (15 January 2007); https://doi.org/10.1117/12.696080

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