Research On Deep Ultraviolet Coatings With Low Polarization Properties

Deep ultraviolet (DUV) coatings play very important roles in excimer laser systems and lithographies. The qualities of DUV coatings are critical to guarantee the optical properties and longlife stabilities of these systems.With the development of semiconductors, the integration of the micro-circuits has been raised to an unprecedented level, which promotes the improvement of the resolution of lithographies.A straightforward approach resulted in a higher resolution is shortening the wavelength of the exposure light. Presently, the dominant exposure wavelength steps into DUV spectrum, which makes it difficult to design appropriate coatings due to the lack of options of materials. Most of general materials are directly omitted because of the high absorption, whereas only the ones with a large band gap can be considered. In addition, immersion techniques with polarized illumination are also widely applied in lithography to further enhance the resolution by introducing a larger numerical aperture (NA). In this situation, coating induced polarization aberrations may inevitably influence the final imaging quality, thereby being strictly concerned in recent designs. Hence, it is essential to research on the design and fabrication of DUV coating with low polarization properties. This dissertation focuses on the design and fabrication of DUV coating, including the experiments on material properties in DUV sperctrum, analysis and reduction of coating induced polarization aberrations, fabrication and laser induced damage threshold (LIDT) test of DUV coating, as well as application of ALD in DUV coating fabrication.The detailed contents of this thesis are followed:1. The mechanism of coating induced polarization state variation is analysed. The relationship between coating induced polarization state variation and polarization aberrations is established. Based on this relationship, an approach to reduce the coating induced polarization aberrations through control of the coating induced polarization state variation is proposed. After numerical simulation of polarization state variations by the Jones matrix and calculation of coating induced polarization aberrations by polarization ray tracing, the proposed method is validated very well. Accordingly, polarization state variation induced by different coatings can be compensated by appropriate design.2. To eventually optimize the deposition parameters for multilayer DUV coating but simplify the model, single layer of DUV coating material is explicitly fabricated and characterized in priority. The influence of deposition parameters on optical properties> surface morphology and microstructure of MgF2and LaF3are analysed.3. DUV multilayer coating is fabricated and tested. The Low Polarization Anti-reflection (LPAR) at248nm is designed and deposited. Its differential transmittances at various incident angles are compared with those of the common Anti-reflection (AR) coating. At mean time, the profile of the LPAR is measured to verify that the deposition parameters we adoped is efficient to control the residual stress induced birefringence.The Laser Induced Damage Thresholds (LIDT) of MgF2/LaF3HR coating and MgF2/AlO3HR coating are measured, and the results show that the LIDT of fluoride is higher than that of oxide in DUV spectrum.4. The precision and stability of optical coating fabricated by ALD are investigated. The interface characteristics of coating are discussed, and the pre-deposited layer is carried forward to avoid the thickness error caused by unstable growth rate. With this manner, the experimental performance of Broad-band Anti-reflection (BBAR) coating is much better than that in previous works. Furthermore, to validate the deposited stability, Rugate filter is deposited by ALD using the method of equivalent refractive index.5. The experiments on DUV coating deposited by ALD are carried out. With the hot sources in ALD, the optical properties、surface morphology and microstructure of oxide single-layer coating are characterized,On this basis, the multilayer coatings are designed and fabricated. Furthermore, the exploratory research on fluoride is carried out.