Design Of Extreme Ultraviolet Lithography Illumination Syteme For Sub-11nm Node

The Illumination system is a key part of the extreme ultraviolet lithography(EUVL)exposure system.It has to illuminate the mask plane uniformly and realize a lot of off-axis illumination sources.Mainstream EUV illumination systems use double flys eye to uniformize the illumination and realize the illumination source change by tilting the flys eye facet mirrors.As the technology node moves down,EUVL under 11 nm node requires the illumination system to realize more kinds of off-axis illumination sources or even freeform illumination sources prescribed by source mask optimization(SMO)technology.The increase and complication of illumination modes raise higher requirements on the illumination system and make the facets mapping problem more prominante.Thus it is desirable to have a facets mapping method which can get the facets mapping relation quickly and accurately.In recent years,the lithography industry has accepted the anamorphic imaging projector,which has different imaging magnification in the X and Y directions respectively,for EUVL with numerical apeture(NA)higher than 0.5.But the illumination system suitable for the anamorphic projector still needs to be researched.Currently available relay system design method for the EUV illumination system needs to adjust the design parameters repeatedly to get a satisfactory relay system,and in some cases the method will fail to get a satisfactory relay system.Such design methods are apparently not efficient and suitble for only limited cases.Thus,an efficient relay system design method suitable for more types of projectors is also desirable.Due to the above mentioned problems,this thesis conducted some research works on the relay system design method,the facets mapping method and the design of the illumination system suitable for the anamorphic projector.The thesis established a relay system design method of the EUV illumination system.The method designs the relay system in a reverse ray path(ray path from the mask and exit pupil to the relay system)based on the ABCD matrix analysis method in the paraxial optics.By analysing the object-image conjugate matrix,the structure parameters of the relay system can be directly calculated using some constraits related to the imaging property of the relay system.The tedious parameter adjusting process is avoided by this direct calculation method.The design examples of two relay systems suitable for two projectors with NA0.33 and NA0.5 respectively show the correctness of this design method.A facets mapping relationship optimization method is proposed in this thesis.The method considers the illumination spot tilt induced by the facets tilt and construcs a merit function of the net tilt of the illumination spots on the mask plane.The facets mapping problem is converted into an assignment problem,a kind of combinatory optimization problem,and some combinatory optimization algorithms can be used to solve this assignment problem.Due to the merit function is composed of the illumination spots tilt,the facets mapping method can make the facets tilt have least influence on the illumination uniformity.The method can be used to get the facets mapping relation and the facets tilt angle under a given illumination mode effectively.An illumination system suitable for the projector with NA0.33 and another one suitable for the anamorphic projector with NA0.5 are designed using the relay system design method proposed in this thesis.The facets mapping relation under different illumination modes is calculated using the proposed facets mapping relation optimization method.The peformance analysis of the two systems show that the EUV illumination system suitable for the projector with NA0.33 can illuminate the mask plane with a high uniformity under many different illumination modes.The illumination system suitable for the anamorphic projector with NA0.5 will illuminate the mask with a lower uniformity,but the system can still realize many different illumination modes using the facets mapping relation optimization method proposed in this thesis.