Ion beam lithography

By analogy to E-beam lithography, focused ion beam lithography scans an ion beam across a surface to form a pattern. The ion beam may be used for directly sputtering the surface, or may induce chemical reactions in the exposed top layer (resist). In the case of direct sputtering, redeposition is a common occurrence, which will affect the final surface profile. In the case of resist exposure, the slowing down of secondary electrons is the basis for forming the final image, which therefore limit the resolution of acceptably printed features to about 30 nm, even though the beam spot size can be smaller. The ion beam may also either be focused through a (stencil) mask or directly on the surface without a mask. The masked approach is no longer popular, due to erosion of the openings by the ion beam through the inherent sputterning process.