In electron beam lithography (EBL), after developing, the cross section of the resist has a parabolic undercut with a linewidth determined by the exposure in the top resist layer resulting in a typical linewidth of 100nm.
Researchers at UC Irvine have developed a double-dose exposure process which easily achieves both higher linewidth resolution and a large undercut. Using this process, a top linewidth of 40 nm and undercut of more than 400nm can be achieved. This technique is important for electronic device applications such as the fabrication of single electron transistors.
Single electron transistor fabrication
Large undercut and fine linewidth