Ultrasensitive non-chemically amplified low-contrast negative electron beam lithography resist with dual-tone behaviour

A non-chemically amplified negative-tone electron-beam resist with an extremely high sensitivity is presented in this work. The resist, poly(2-hydroxyethyl methacrylate-co-2-methacrylamidoethyl methacrylate) (P(HEMA-co-MAAEMA)), has been synthesized using free radical polymerization of 2-hydroxyethyl methacrylate and 2-aminoethyl methacrylate, and exhibits a crosslinking threshold dose as low as 0.5 mu C cm(-2). Exposed resist patterns show good adherence to silicon substrates without the assistance of adhesion promoters or thermal treatments and are shown to be adequate for use as a mask for both wet and dry etching of Si. A low contrast value of 1.2 has been measured, indicating that the synthesized polymeric mixture is particularly suitable for achieving grey (3D) lithography. Other relevant properties of the new e-beam resist are optical transparency, visible photoluminescence when crosslinked at low electronic doses, and dose-dependent dual-tone behaviour.