Fabrication of open stencil masks with asymmetric void ratio for the ion projection lithography space charge experiment

Abstract

For the ion projection lithography space charge experiment [P.W.H. de Jager et al., J. Vac. Sci. Technol. B 17, 3098 (1999)] a suitable stencil test mask has been realized and used. This article addresses the stress engineering and fabrication process of this specific test mask with openings in the range of some few 100 nm up to some 100 μm. This large difference in stencil pattern dimensions causes reactive ion etching (RIE) lag (dependence of the etch rate on feature size and pattern density) during the fabrication process and considerable stress variations across the membrane field. The solution to these problems was by (i) implementing novel doping technologies to create variable thickness areas on the membrane serving as reinforcement and stress relief structures, and (ii) adjusting the design to feature sizes and pattern densities to the same order of magnitude for the e-beam lithography and RIE processing steps. The etching of the openings through the 3 μm thick Si membrane was done by inductively coupled plasma etching with gas chopping techniques. These methods as devoloped for this specific test mask can be used to improve the stencil mask technology in general.