Illuminator design for the printing of regular contact patterns

Diffraction patterns of two different contact arrays of 0.32 μm pitch are investigated using the AIMS TM tool and analyzed using Fourier analysis. We introduce a simple method to analytically predict the pupil pattern for an arbitrary periodic mask feature. A circular illuminator is split up into components that produce varying amount of interference at the wafer plane and it is shown that contrast can be enhanced by excluding certain parts of this illuminator. The optimized illuminator depends only on stepper parameters and mask geometry.