Bilayer resist used in e-beam lithography for deep narrow structures

A bilayer resist system developed by Olin Microelectronic Materials, consisting of a UV curable polystyrene bottom coat and a silicon loaded UV sensitive positive tone top coat ('bamboo resist'), has been investigated for its sensitivity and resolution in electron beam lithography, and its etch selectivity during subsequent use in Reactive Ion Etching of silicon. The ultimate resolution obtainable with the top coat appears to be around 80 nm, with a Dose-to-Clear of 28 mu C/cm(2) and a contrast value above 25. The mechanical and chemical stability of the bottom coat and its adhesion on silicon are excellent, allowing the fabrication of 30 nm thick free standing resist 'fences'. The best resolution obtained here in e-beam lithography, indicates that the resolution of this system will most probably not be limited by the resist performance down to at least 80 nm in optical lithography as well.