Development of Self-Aligned Contact Using Negative Tone Lift-Off Process for Electron Beam Lithography On Phost/Pmgi Bilayer Resists

In this article, a simple, low cost self-aligned contact fabrication technique for metal line patterns is presented. The use of a new electron beam bilayer resists comprised of poly-(4-hydroxystyrene) (PHOST) as the top layer and poly-(dimethylglutarimide) (PMGI) as the bottom layer is demonstrated. The characterization of electron beam exposure on PHOST/PMGI has first been investigated, showing that deploying PMGI as underlayer has no significant influence on the exposure of PHOST. The well defined undercut configuration with 100nm undercut length in the PMGI layer was generated. An Ar ion milling etching on PHOST/PMGI was performed to remove unprotected Ta layer, showing that PHOST is an effective mask layer. A lift-off method using 2% TMAH aqueous solution was conducted after sputter deposition of 70nm thick Cu layer on the substrate, demonstrating good contact connection at both transverse sides of 400nm wide Ta line patterns. As a result, self-aligned contacts have been successfully obtained.