Study On The Thickness Gradient Control And Anti-thermal Damage For EUV Multilayers

Multilayer optics is the key component of Extreme Ultraviolet Lithography(EUVL) system. The EUVL system requires multilayers with high-quality attributes, such as high reflectivity, low stress, high uniformity and anti-damage. To solve the last two problems, this thesis is focusing on the study of following issues:1. To meet the requirements of wavelength matching and figure preservation for EUV multilayer optics, study of precise control of the lateral thickness gradients of multilayers was performed. The distribution of the magnetron sputtering source was derived by fitting the coating thickness profiles of flat substrates sweeping across the source with contant velocity at different heights using genetic algorithm. Then, genetic lgorithm was also used in finding the proper speed profile for the desired thickness profile. By the method mentioned above, extremely precise control of the lateral thickness gradients of multilayers on curved substrates was realized.2. To meet the wide angular bandpass requirement of small-size mirrors in condenser EUVL optics, the study of depth graded EUV multilayer stack was performed. The effective thickness method was used to deal with the influence of interdiffusion in the Mo/Si multilayers on the spectral performance of broadband multilayers. At first, the relations between effective thickness of molybdenum as well as effective thickness of silicon layers and velocities, were calibrated. Then, the depth graded multilayer stack was designed utilizing Levenberg-Marquardt algorithm. Finally, the designed stack was deposited by magnetron sputtering. The measured EUV reflectance of broadband Mo/Si multilayer stack was very close to the designed one.3. To meet the requirement of EUV source collector using in high temperature environment, the preliminary study of anti-thermal damage for EUV multilaeyrs was performed. By inserting a Boron Nitride barrer between Mo layer and Si layer, the anti-thermal damage performance of new forming Mo/BN/Si/BN multilayer was increased significantly. The characterization results by x-ray diffraction and HRTEM showed that the multilayer could work at a temperature of 500℃.These discussions provide theoretical bases and technical supports for the research of high performance multilayers in EUVL system. They lay the foundation for developing multilayer optics in the commercial EUVL system in future.