Optical Design And Aberration Control For Immersion ArF Lithographic Lens

With the application of several new resolution enhancement technologies(RET), hyper numerical aperture(NA) ArF immersion lithographic exposure tool can achieve 45nm-14 nm lithographic node. The illumination system and projection lens must achieve the corresponding structure and performance predicted by RET. The immersion exposure tools have been realized industrialization abroad, but behind abroad several generations in our country. Facing the foreign strict technology blockade, this thesis is meeting the demand of National Program for Key Science & Technology Projects of China for the lithography equipment development and designed the immersion projection lens for immersion lithography. The immersion projection lens is one of the most complex and precision optical systems, included 20 optical elements. The number of structure parameters is so large that the traditional design and optimization methods are difficult to realize the high imaging performance. Moreover, because the polarization illumination is applied in immersion lithography, not only scalar aberration(one subset of polarization aberration) but also polarization aberration(PA) should be controlled. The previous studies are focused on the representations of PA and the impact of PA on image performance. There is no comprehensive and detailed study on PA control at design phase for lithographic optics. In addition, the manufacturing and measuring precision of immersion projection lens is extremely high. Therefore, the aberration control and compensation method in each stage from optical manufacture to system integration need be developed simultaneously.Firstly, three optical structure of immersion projection lens are designed, and a multi-dimension-parameters optimization method is presented in this thesis. The catadioptric structure with two mirrors is chosen as the design starting point. The design features and engineering constraint conditions are studied, which are the optical design basis of immersion projection lens. The multi-dimension-parameters optimization method solves the hard optimization problem of immersion projection lens with a large number of parameters. The process of the method is as follows: based on CODE V, the optical structure is modified by manual intervention, the different constraint conditions are set in different optimization stages, and the final structure is obtained with high efficiency and stability. Three immersion projection lenses are obtained using the method, and the NA is respectively 1.2, 1.25 and 1.35. For NA1.2 lens with telecentricity, the monochrome wavefront error RMS is below 1nm, and the distortion is below 0.5nm. The wavefront error can only cause critical dimension(CD) error of 0.1nm and pattern placement error(PE) of 0.5nm for different pattern pitches at 45 nm CD.Secondly, the influence of PA on imaging performance is studied, and the control method of PA in design stage is built. The polarization effects of coating and intrinsic birefringence are respectively studied, which is benefit for polarization aberration control. For NA1.2 lens, the influence of different subsets of polarization aberration on imaging performance is analyzed in design stage for the first time. The results indicate that the scalar transmission and diattenuation mainly cause CD error(CDE), and the scalar phase and retardance mainly cause PE. The results also show the diattenuation is the main controlled object in the process of PA control. Furthermore, a cooperative design strategy for PA control is proposed, which is to cooperate between custom coating design and the optimization of crystal orientation based on optical structure design. Through the cooperative design, the diattenuation can be reduced by 90% and the retardance can be reduced by 26%. The simulation results of the final system reveal that the dynamic range of CD error for NA1.2 lens is suppressed from-12.7nm ~ +4.3nm to-0.1nm ~ +0.9nm after PA control, while keeping PE below 3.4nm. According the need of this research, five programs are design as follows: acquiring the subsets of PA program, acquiring the PA caused by each surface program, acquiring the PA caused by CaF2 program, analysis the range of incidence of each surface program, and the cooperative optimization between custom coating and crystal orientation program. These programs enrich the function of commercial optical design software and play important roles in our study.Thirdly, the tolerances of NA1.2 lens are analysed and the optimal combination of compensators is selected. For the figure-error compensation, two effective methods are further developed, the automatic figure-errors balancing method and the fine surface figuring method on compensation lens. For figure-errors balancing method, a global and general optimization method based on analyzing the precise relationships between the figure errors and the wavefront error is proposed. Using the footprint data of each optical surface, the resulting wavefront error is calculated. Direct map operation is used for intercepting and rotating the figure-error maps. The simulated annealing algorithm is used to seek the optimal combination of rotation angles for the optical elements. For the fine surface figuring method, the calculation method for the figure error of compensation lens is described. The simulation results in NA1.2 lens show the high effectiveness of the two methods. The two methods have considerable engineering potential.Finally, the experimental Ar F lithography lens is designed and manufactured. We designed an experimental ArF lithography lens using a novel catadioptric Schwarzschild structure with NA of 0.75 and wavelength band of 100 pm. The aberration compensation techniques are studied and applied in practical manufacturing. The radius error and thickness error can be almost completely compensated by optimizing air space. For figure error compensation, the two methods developed in this thesis are applied in the experimental ArF lithography lens. By using figure-errors balancing method, the astigmatism and coma are reduced significantly, and the wavefront error RMS is reduced to 0.11λ from 0.35λ(λ=193.29nm). By using the fine surface figuring method on compensation lens, the wavefront error RMS is reduced to 0.04λ, and the performance is improved by 84%.