Scanning interference evanescent wave lithography for sub-22 nm generations

In this paper, we report progress in developing a scanning evanescent wave lithography (EWL) imaging head with a twostage gap control system including a DC noise canceling carrying air bearing that floats at a constant air gap with regulated air pressure, and an AC noise canceling piezoelectric transducer with real-time closed-loop feedback from gap detection. Various design aspects of the system including gap detection, prism design and alignment, software integration, feedback actuation and scanning scheme have been carefully considered to ensure sub-100 nm gapping. To validate the design concepts, a prototyped scanning EWL imaging head is integrated into a two-beam interferometer platform for gapping tests and imaging evaluation. Experimental results show successful gap gauging at sub-100 nm with gap noise root-mean-square around 1.38 nm in static gapping and 4.64 nm in linear scanning gapping. We also demonstrate scanning imaging results with NA comparable to previously reported static imaging using both fused silica prism and sapphire prism. Our gapping and imaging results confirmed the promise of scanning EWL to extend optical lithography to sub-22 nm generations.