Optical Design For The Hyper Numerial Aperture Lithographic Lens

Exposure tool lies in the core of the large-scale integrated circuit manufacturing devices, and the kernel of the exposure tool is lithographic lens which duplicate the pattern from the mask to the wafer. This paper devotes to optical design and simulation of high numerical aperture(NA) immersion lithographic lens, which is aimed for equipping deep ultra-violet(DUV) scanner with 45 nm critical dimension. The lens is specified by NA≥1.30, and working wavelength at 193 nm. In order to meet the preceding target, the necessary considerations for works include illumination light, optical material, optical fabrication, optical test and mechanical structure scheme. Meanwhile, we also develop methods on imaging performance compensation and polarization aberrations analysis strategies.The most advanced 193 nm projection lenses are almost all of catadiopric type, which usually contains more than 25 components(several aspheric elements included), with a field of view(FOV) of 26 mm×5.5 mm and wavefront error RMS less than 1nm. Research on lithographic lens involves cutting edges in a variety of subjects, including optics, mechanics, compute science and electronics, etc. It is impossible to design a modern lithographic lens just simply rely on brain power and experience. It is necessary to use of modern commercial optical design software to aid the optical design for 193 nm exposure system.In accordance with the destination of designing qualified projection lens and related research, a great of energy is focused on the following contents.1. Optical design: First of all, determine system specifications and input parameters and doing research on methods for evaluating the performance of the lens. Secondly, among the general configurations existed, select 2 suited types as starting point to optimizing, and after contrasting the two optimizing results, select more promised one to continue on detailed analysis works. Finally, come up with an aberration auto-balancing algorithm to reduce the maximum wavefront errors of the high NA lithographic lens.2. Imaging performance compensation: Firstly, conduct analysis on tolerance sensitivity based on Zernike coefficients decomposition, and categorize the compensation methods in according with low-order and high-order aberrations. Secondly, innovate on optical recomputation and element clocking compensation algorithm, promote techniques of computer aided assembly adjustment, including how to choose the compensators wisely and to find out compensation rate. Lastly, simulate optical recomputation and computer aided assembly adjustment based on the completed lens design.3. Research on polarization aberrations: At the beginning, discuss the differences and connections between vectorial and scalar theorems of imaging, and draw the conclusion that the former is necessary when aiming at high NA lithographic lens. Then, into commonly used math for describing the polarization characteristics of various optical components, which including Jones matrix and Muller matrix specifically, we will analyze their respective con and pro when it comes to describe polarization aberrations. The method of singular value decomposition(SVD) for Jones matrix is emphasized during the process, so as to simplify the Jones pupil and make it more physically intuitive. At last, we analyze the polarization aberrations of full FOV of the lithographic lens.The final results and simulation analysis show that, the lens design form, methods of imaging performance compensation and analytical methods regarding polarization aberrations have provided advantageous theoretical guidance and basis for research and development of 45 nm critical dimension lithographic lens.