Projection optics for extreme ultraviolet lithography (EUVL) micro-field exposure tools (METs) with a numerical aperture of 0.5

In support of the Extreme Ultraviolet Lithography (EUVL) roadmap, a SEMATECH/CNSE joint program is under way to develop 13.5 mn R and D photolithography tools with small fields (micro-field exposure tools [METs]) and numerical apertures (NAs) of 0.5. The transmitted wavefront error of the two-mirror optical projection module (projection optics box [FOB]) is specified to less than 1 mn root mean square (RMS) over its 30 μm x 200 μm image field. Not accounting for scatter and flare losses, its Strehl ratio computes to 82%. Previously reported lithography modeling on this system [1] predicted a resolution of 11 mn with a k-factor of 0.41 and a resolution of 8 mn with extreme dipole illumination. The FOB's magnification (5X), track length, and mechanical interfaces match the currently installed 0.3 NA FOBs [2] [3] [6], so that significant changes to the current tool platforms and other adjacent modules will not be necessary. The distance between the reticle stage and the secondary mirror had to be significantly increased to make space available for the upgraded 0.5 NA illumination modules [1].