Concepts for creating ultra-deep trenches using deep X-ray lithography

This work presents an approach relevant to deep X-ray lithography (DXL) for manufacturing much deeper and more precise microstructures than those produced by the conventional LIGA process. The approach using successive exposure or multiple exposure scheme is designed to alleviate major difficulty encountered in ultra-DXL, such as development of high-aspect-ratio trench, induced photoelectrons and mask preparation. The dosages with successive exposure can be elevated after the second exposure over the normal constrains. High exposure dosage leads to a high developing rate, making it possible to create deeper trenches with higher aspect ratios. More significantly, the existing sidewall profile is virtually uninfluenced by the dosage elevation. The structure walls generated by the first segment of lithography process serves as fiberglass-like waveguides. The total reflection of X-rays on the sidewalls inhibits further dosage deposition during the second exposure. No stepwise disconnection on the wall between exposures is observed when a conformal mask is applied. Very thick microstructures (2 mm deep and 100 mu m wide) are made using X-rays with a characteristic wavelength of 3 Angstrom. The X-rays are generated from the Taiwan Light Source at SRRC, which is a medium energy 1.5 GeV light source. (C) 2000 Elsevier Science S.A. All rights reserved.