| Abstract [eng] |
These days most optical components are deposited using physical vapor deposition (PVD). However, the improvement of laser technologies rises a demand for more complex, three dimensional (3D) substrates or more specific optical coatings that PVD is not capable to the deposit. Therefore, the search for methods to maintain thin film uniformity and conformality throughout the whole 3D substrate has started. One of such ways is atomic layer deposition (ALD) technique. Since ALD was started to be used to deposit optical coatings rather recently, the optimization of deposition parameters is a necessity. The investigation of low (SiO2) and high (Al2O3, HfO2, TiO2 and Ta2O5) refractive indices materials as well as in situ investigation of thin film growth dynamics are presented in this study. Different levels of optical losses in UV range were observed for SiO2 thin films which were higher compared to bare fused silica substrate. To find out possible causes of absorption the investigation of chemical composition and appropriate stoichiometry of thin films using X-ray photoelectron spectroscopy (XPS) was made. Al2O3, HfO2, TiO2 and Ta2O5 were deposited using two different oxygen sources – water and oxygen plasma. Al2O3 and Ta2O5 deposited using both oxygen sources resulted in amorphous structure thin films with optical characteristics comparable to conventional electron beam evaporation and ion beam sputtering deposited coatings. The HfO2 depositions resulted in crystalline thin films, however nanolaminate structure investigation is yet to be done. However, TiO2 thin film deposition resulted in poor optical quality thin films. A thorough investigation of causes of high optical losses is needed to be done. The experimental in situ investigation of thin film growth dynamics led to conclusions, that in some cases the initial growth rate can be more than twice lower compared to the stable growth of thin film. On the contrary, when Ta2O5 is being deposited on Al2O3 sublayer, the sublayer barely influences the initial growth rate. Also, it has been observed that in most cases linear growth of thin films begins after 10 – 15 cycles. Finally, optimized parameters were used to deposit antireflection coating on sphere lenses. The target of < 0,6 % reflectance at 450 nm, 520 nm and 645 nm wavelengths was successfully achieved. |
