On Advanced Large-Field Photolithography

The information age we live in today relies on highly integrated devices. They are fabricated with the help of photolithography, the patterning technique at the heart of their production. With the continuous demand for higher integration density to achieve ever growing performance levels, not only the front-end-of-line lithography, responsible for realizing the smallest structures, is under constant pressure for improvements. At the back-end-of-line, where ICs are interfaced, and elements like display panels are structured, this drive can be felt as well. The development here goes towards the processing of substrates of increasing size surpassing the wafer-level to increase throughput, thus becoming large-field photolithography. The current resolution requirements here are typically in the 1 &mto 2 &mfor minimumfeature size. An investigation in phase-space identifies two possibilities for advanced photolithographic systems relying on different exposure mechanics. We combine a novel semiconductor laser light source emitting in the deep ultra-violet at 193 nmwith a beam-shaping system to enable proximity printing with sub-2 &mresolution with a proximity gap of 20 &m. The integration of this approach with optical exposure gapmetrology and a high-precision substrate positioning stage demonstrates the possibility for large-field exposure. In a second approach we realize a highly integrated micro-optical multi-aperture projection lens to pattern an exposure field of 100mmby 100mm. A mechanical scanner to mount the projection lens, required to achieve uniform exposure of the entire field, is realized as well. Projection lens and scanner are integrated with a high-precision substrate positioning stage and a mask aligner illumination system to demonstrate the ability for large-field photolithographic printing. The optical design is validated by demonstrating printedminimumfeature sizes of 2 &m. Practical shortcomings of the system are investigated and strategies to overcome these issues are presented and discussed.