Title Optimization of intrinsic stress in sio₂ thin films deposited by dual ion beam sputtering and its impact on multilayer high-reflectance coatings
Translation of Title SiO₂ plonų sluoksnių, suformuotų dvigubo jonapluoščio dulkinimo metodu, vidinių įtempių optimizavimas ir jų įtaka daugiasluoksnėms didelio atspindžio koeficiento dangoms.
Authors Kandrotas, Dominykas
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Pages 46
Keywords [eng] Dual Ion Beam Sputtering, Flatness, Multilayer stress, Annealing
Abstract [eng] This master’s thesis investigates the optimization of intrinsic stress in SiO₂ thin films deposited by Dual Ion Beam Sputtering and evaluates its influence on multilayer high-reflectivity optical coatings. Residual mechanical stress is a major challenge in ion beam sputtered optical coatings because it can deform optical substrates, reduce surface flatness, and introduce wavefront distortions that negatively affect optical performance. These effects are especially critical in high-power laser optics and multilayer interference coatings. The main objective of this work was to investigate how assisting ion source parameters and ex-situ annealing influence the residual stress and optical properties of SiO₂ thin films and multilayer coatings. A series of SiO₂ monolayers were deposited while systematically varying assisting ion source conditions, including accelerating and collimating parameters as well as argon and oxygen gas flow ratios. The deposited films were characterized using spectrophotometric and interferometric methods, and residual stresses were evaluated using substrate deformation measurements. Additional thermal annealing experiments were performed to investigate stress relaxation behaviour after deposition. The results demonstrated that assisting ion source conditions strongly influence both the residual stress and optical properties of the deposited SiO₂ films. Higher ion source energies and optimized ion beam conditions reduced compressive stress and improved structural relaxation during film growth. Variations in gas flow ratios also affected stress development, where balanced argon and oxygen conditions produced the lowest residual stress. Optical characterization showed that films with lower residual stress generally exhibited lower refractive indices, indicating changes in film density and microstructure.Ex-situ annealing further reduced compressive stress in all investigated coatings due to structural relaxation of the amorphous film network. The lowest residual stress values were obtained for coatings deposited under optimized ion beam conditions and subsequently annealed at elevated temperatures. Based on the optimized deposition parameters, a multilayer high-reflectivity coating designed for near-infrared laser applications was fabricated and compared with coatings deposited without the assisting ion source.The optimized Dual Ion Beam Sputtering process demonstrated significantly improved substrate flatness and lower residual stress while preserving high optical reflectivity and good spectral performance. The results confirm that optimization of assisting ion source parameters combined with thermal annealing is an effective approach for reducing intrinsic stress in ion beam sputtered optical coatings and improving the mechanical stability of multilayer optical components.
Dissertation Institution Vilniaus universitetas.
Type Master thesis
Language English
Publication date 2026