Design of illumination system for ArF excimer laser step-and-scanner

In a lithography tool, illumination uniformity on the wafer surface is important, because the variance of intensity on the wafer surface makes it hard to control the line width of the pattern. An illuminating system for ArF excimer laser step- and-scanner has been designed and assessed. The system showed good illumination homogeneity in both of the reticle and pupil plane with a reasonable light transmission efficiency. The goal of design is the uniformity within plus or minus 1% on the reticle surface. In order to achieve the goal, the output beam of the excimer laser with nonuniform intensity distribution was re-shaped by using a beam expander which is composed of 4 cylindrical lenses, and the zoom lens varying the beam size according to the aperture of fly's eye lens integrator. The fly's eye lens integrator consists of 208 lenses and generates the good homogeneity in the reticle plane. The effective light sources, i.e. the images made by fly's eye lenses, were projected onto the entrance pupil of the combined system of projection and relay lenses. The exposure field at reticle plane is 104 X 20 mm², and is defined as the image of reticle blinder by the 1x relay optics. The designed illumination system showed good performance by simulation and it will be adequate to the ArF excimer laser step-and-scanner under development.