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A study of the influence of process parameter variations on the material properties and laser damage performance of ion beam sputtered Sc2O3 and HfO2 thin films




Langston, Peter F., author
Menoni, Carmen, advisor
Rocca, Jorge, committee member
Marconi, Mario, committee member
Yalin, Azer, committee member

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This work is a study of the influence of process parameter variations on the material properties and laser damage performance of ion beam sputtered Sc2O3 and HfO2 thin films using a Vecco Spector ion deposition system. These parameters were explored for the purpose of identifying optically sensitive defects in these high index materials after the deposition process. Using a host of optical metrology and materials analysis techniques we report on the relationship between oxygen partial pressure in the deposition chamber during film growth and optical absorption in the grown material at 1 μm. These materials were found to be prone to excess oxygen incorporation. Positive identification of this excess oxygen is made and exactly how this oxygen is bound in the different materials is discussed. The influence of this defect type on the optical and mechanical properties of the material is also given and discussed. Laser damage results for these single layers are presented. The influence of higher and lower deposition energy was also studied to determine the potential for defect creation both at the surface and in the bulk of the material grown. Optimized thin films of HfO2, Sc2O3 and Ta2O5 were grown and tested for laser damage with a 1030 nm laser having a pulse width of ~375 ps and a nominal spot size of ~100 um FWHM. The laser damage threshold ranking of these materials followed fairly well with the band gap of the material when tested in air. When these same materials were tested in vacuum Sc2O3 was found to be very susceptible to vacuum mediated laser induced surface defect creation resulting in a greatly reduced LIDT performance. Ta2O5 showed much the same trend in that its in vacuum performance was significantly reduced from its in air performance but there was not as great of a difference between the in air and in vacuum performance as there was for Sc2O3. HfO2 also showed a large reduction in its in vacuum LIDT results compared with its in air LIDT values however, this material showed the smallest decrease of the three high index materials tested. A second contribution of this work is in the investigation of the impact of capping layers on the in air and in vacuum LIDT performance of single layer films. Ultra thin capping layers composed of different metal oxides were applied to 100 nm thick single layers of the same high index materials already tested, HfO2, Sc2O3 and Ta2O5. These capped samples were then LIDT tested in air and in vacuum. These ultra thin capping layers were shown to greatly influence the in air and in vacuum damage performance of the uncapped single layers. Damage probability curves were analyzed to retrieve surface and bulk defect densities as a function of local fluence. Methods for maximizing the LIDT performance of metal oxides based on our studied materials for use in air and in vacuum are discussed.


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