Pupil plane analysis on AIMS 45-193i for advanced photomasks

Hyper-NA lithography with polarized light illumination is introduced as the solution of 45nm or 32nm node technology. In that case, consideration of new characteristics of mask materials and pellicle films has been required. In order to analyze the influence of mask material's optical characteristics, we have proposed to use the AIMS TM system measuring diffraction intensity balance in previous work. That was enabled by acquiring pupil plane images using the Bertrand lens in the AIMS TM system to measure selected area's diffracted light. In this study of mask material evaluation, we used same functionality of AIMS TM system, MonoPole illumination and Bertrand lens, as previous work but other direction's pole is also used on the illumination aperture to cover total diffraction orders of Cross-quad illumination because this illumination is more flexible for x and y patterns. In order to get diffracted light of 45nm half-pitch, hyper-NA e.g. NA=1.35 was applied and the AIMS TM 45-193i Alpha system was used for this evaluation. The examinations were performed with binary and half tone PSM with half pitch 40 to 150nm on a 1x scale and fixed half pitch 45nm with various mask bias. We confirmed the relation between diffractions' intensity balance and wafer printing performance for each material and we compared them to 3D simulation results. Moreover, by using the same functionality of AIMS TM system, the transmission change by pellicle film was also examined. We have prepared two different thickness pellicles to compare transmission change and printed CD on the wafer. Intensity profile at pupil plane on the clear region of the mask was acquired with Bertrand lens and conventional large sigma setting for both with and without pellicle film on the mask. By comparing transmission distribution change between with and without pellicle, we could calculate transmission loss by pellicle at large incident angles. For this experiment, NA=1.40 was applied and the AIMS TM 45-193i Alpha system was also used. The examinations were performed with half tone PSM at half pitch 45nm and 65nm on a 1x scale on linear polarized DiPole illumination. As a result, we have confirmed good agreement between AIMS TM measurement data and optical 3D simulations. In conclusion, the AIMS TM system is a valuable tool for analyzing diffraction efficiency or intensity distribution on the pupil plane and comparison to wafer printing performance.