Aberration's impact on sub-resolution contact hole process windows in ultra-thin Imaging resist

Sub-resolution, 130 nm, contact holes are exposed into thick (400 nm) and thin (160 nm) resists. Three types of resist, ESCAP, hybrid and bi-layer, are used in the experiment. The lens aberration is studied with respect to the effect it has individual on process windows and the resultant common latitude shared by similar features across the exposure field. Affected Bossung curves show behaviors of tilt and best focus offset. Additional behavior is seen at this dimension in that aberrations cause the process windows to be truncated in the thicker resist. The thin imaging, layer solves this problem and adds back the lost depth of focus to the common process latitude. A modified Strehl ratio, for out of focus images, is used to explain how process windows become reduced by larger aberrations.