Graded Multilayer Coating Design For Sub 11nm Resolution EUV Lithographic Projection Lens

Extreme ultraviolet(EUV)lithography is the most promising lithography technology for the large scale integrated circuit manufacture at 11 nm node and beyond.EUV lithography projection systems use reflective optics,and multilayer coating must be designed to achieve high reflectivity.However,the optical design of the EUV lithographic projector for sub 11 nm resolution,is progressed to the direction of high numerical aperture(NA)and anamorphic magnification,which results in the sharp increase of incident angle and angle range in the projection lens.The normalized multilayer and laterally graded multilayers design scheme is difficult to meet the objective lens system's reflectivity and image quality requirements at the same time.Meanwhile,international lithography enterprises keep the technology lock-in all the time,multilayer design method for large field and high NA EUV lithographic projection lens has been rare reported.In order to further support China's independent development of high NA EUV lithography,multilayer design method used in EUV lithographic projection lens for sub 11 nm resolution is deeply studied in this thesis.To ensure the high reflectivity and good imaging quality,the multilayer design method combining laterally graded multilayer with depth graded multilayer is presented,which has important engineering significance in high NA EUV lithographic projection lens manufacture.With the support of the national science and technology major project,this thesis mainly studies the following aspects:The thesis presents the multilayer design method combining laterally graded multilayer with depth graded multilayer.Based on the analysis of the optical characteristics of the EUV multilayers and the development trend of the EUV lithography projection lens,a method combining laterally graded multilayer with depth graded multilayer is proposed,in which the laterally graded multilayer is used to improve the reflectivity,and the depth graded multilayer is used to improve the reflectivity uniformity and reduce aberrations introduced by multilayer.The method is suitable for reflection systems with large incident angle and angle range.In this thesis,the graded multilayer coating design for the noval NA0.50 anamorphic magnification EUV lithography projection lens for sub 7nm node is accomplished for the first time.Through the objective system analysis,taking the requirements of high reflectivity and high image quality into account,a reasonable multilayer design is determined and the analysis of the objective with multilayer is completed,which strongly support the practical application of the anamorphic magnification EUV lithography projection lens in the future EUV lithography.Besides,the graded multilayer coating design for two sets of coaxial EUV lithography projection lens with NA0.30 and NA0.33 which are suitable for 11?8nm nodes are designed.The effective multilayer coating design is finished and the analysis of objective with multilayer is completed,which improve the application value of EUV lithography projection lens.At last,the direct construction freeform surface design method is explored to be used in the anamorphic magnification EUV lithography projection lens design.The design scheme is proposed.Through the optimized design of the simplified anamorphic magnification system,the feasibility of the direct construction method in the design of anamorphic magnification EUV lithography projection lens is verified.