Nanofabrication on 2D and 3D Topography via Positive-Tone Direct-Write Laser Lithography

Direct laser writing (DLW) lithography using two-photon absorption is a powerful technique mostly used for the fabrication of complex structures in micro- and nanoscale, by photopolymerizing a negative-tone resist. In contrast, herein, it is demonstrated that DLW is also well suited for fabricating nano- to microscale metallic structures using liftoff and a positive-tone photoresist. It is shown first that versatile, fast, and large-area fabrication is possible on flat 2D insulating substrates, and an expression for how the line width varies with the scanning speed is derived, with excellent agreement with the experiments. Even more interestingly, a unique application for the DLW lift-off process is demonstrated, by fabricating submicron scale metallic wiring on uneven substrates with sloping elevation changes as high as 20 mu m. Such fabrication is practically impossible with more standard lithographic techniques.