Illuminator design for small field ArF lithography system

Design and development of small field ArF lithography system can achieve the prospective studies and key technologies for industrial lithography with low cost. An illuminator has been designed for the ArF projection lens which has a specification of 0.75 numerical aperture (NA), 70μm×70μm image field and x40 reduction ratio. The illuminator consists of 3 parts: fly's eye, condenser lens and beam shaping unit. A design method based on the fly's eye, which is the core and starting point, has been proposed. At first, the basic structure of fly's eye has to be determined. Then the first order of the condenser, such as focal length and the diameter of the stop can be derived when both the field size and illumination NA are guaranteed. At last, the stop diameter is used as the goal of the beam profile exiting from the beam shaping unit. Thus the initial parameters and relationship between various units in the illuminator can be determined. This method can also be used in full field system design. The NA of the illuminator (NA _ILL) in the reticle space is 0.01875 and the illuminated area is 4mm×4mm. The telecentric degree is smaller than 6mrad, which guaranteed that the exit pupil of the illuminator match the entrance pupil of projection lens well. The illumination uniformity can reach 1.125% RMS (Root-Mean-Square) over the reticle with LightTools^TM. The results show that all the parameters meet the requirements of the small field ArF lithography system.