Optical Design Of Extreme Ultra-violet Lithography(EUVL) Objective System

Extreme Ultraviolet Lithography(EUVL) is one of the most promising techniques of the Next Generation Lithography(NGL), and being widely and deeply discussed.As the core component of lithography equipments, the EUVL objective system almost covers the most high-end techniques including applied optics, optical fabrication and testing, multilayer, etc. There are many practical issues which should be emphasized in design and estimation. Therefore, this thesis is focusing on the study of these practical issues in objective system optimization and design:An equivalent working surface model named EWSE based on the energy conservation is proposed for the multilayer analysis in EUVL system. With the basic theory of rigorous electromagnetic field, the EWSE model turns a multilayer with multi-interface into a single equivalent working surface(EWS) based on the energy conservation in terms of energy modulation of the film, building an equivalent system. Via the assess of the performance of the equivalent system, the compatibility between multilayer and objective is presented.The flare in EUVL objectives will degrade the imaging performance. With the aid of lithography simulations, a model for flare analysis in EUVL objectives is developed based on the basic definition and measurement method of flare. The model can get the accurate flare-related band of the extended middle spatial frequency roughness,providing a universal and self-consistent method for flare estimation.Through the analysis of reported EUVL objectives, the grouping and analyticalmethods are adopted to reduce the amount of variables. The visual construction which is intuitive and e?cient of initial configurations for NA 0.3, arc field, non-obscuration6-mirror EUVL objectives is presented. Then the optimization and simulation of EUVL objective are presented, also the effects of Fringe Zernike aberrations are analyzed for the future design based on lithography simulations.The image calculation based on the principle of Abbe’s imaging is presented,achieving the optimization of dipolar off-axis illumination for 16 nm HP dense line and space with NA 0.32 objective. In consideration of the illumination condition, the method based on genetic algorithm for structure and phase shifter material optimization of attenuated phase shift mask is put forward and realized.A binary mask structure for high NA EUVL objectives is raised theoretically. The pattern is located in a plane by etching the multilayer and implanting the absorber,and the 3D effect of mask is dismissed. Meanwhile, the etching depth of multilayer is minimized by the implantation of absorber. Therefore, the pattern is strengthened, and the lifetime of the mask is extended.These discussions provide theoretical bases and technical supports for some practical issues during the design and optimization of EUVL objectives. They lay the foundation of the co-design of higher NA, non-obscuration EUVL objectives for production,performance optimization of lithography integrations, and the promotion of computational lithography technique etc.