50 nm lines patterned into silicon using water developable chitosan bioresist and electron beam lithography
Résumé
Electron beam (EB) lithography enables reaching very high resolution1. However, current chemicals used in EB lithography (resists, solvents and developers) not only generate safety and waste management issues but are also oil-based chemicals. With the issue of peak oil and with the regulations as REACH in Europe and Polluting Act in USA, finding a safer and synthetic free chemicals process is a key issue for eco-friendly EB lithography. In the recent years, researches have been undertaken to replace the current synthetic resists as polymethyl methacrylate (PMMA) by water soluble, water developable and biosourced resists. For instance, Takei et al2,3 used natural polysaccharides (dextrin and glucose from plants). But these polymers are chemically modified generally to enhance electrosensitivity. In addition, their low etching resistance requires a three layers process instead of the classical two layers. In this work, chitosan (figure 1), a natural and abundant polymer soluble in aqueous solutions4, was assessed as a positive and water developable resist for a two-layer EB lithography and transfer process. 50 nm lines patterns were successfully obtained in a chitosan film by EB lithography at doses between 140 μC.cm-2 and 200 μC.cm-2. The resulting features were, then, transferred into a silica layer by CHF3 plasma reactive ion etching (figure 2). Finally, they were transferred into the silicon substrate with respect to the size and without line edge roughness. References 1 H.J. Levinson, in Princ. Lithogr. Third Ed., edited by H.J. Levinson (Society of Photo-Optical Instrumentation Engineers (SPIE), Bellingham, Washington USA, 2010). 2 S. Takei, A. Oshima, A. Sekiguchi, N. Yanamori, M. Kashiwakura, T. Kozawa, and S. Tagawa, Appl. Phys. Express 4, 106502 (2011). 3 S. Takei, A. Oshima, T. Ichikawa, A. Sekiguchi, M. Kashiwakura, T. Kozawa, S. Tagawa, T.G. Oyama, S. Ito, and H. Miyasaka, Microelectron. Eng. 122, 70 (2014). 4 M. Rinaudo, Prog. Polym. Sci. 31, 603 (2006).