DUV/MEMS based stencils for full-wafer scale, resistless, patterning of mesoscopic structures

Photoresist-based lithography has major limitations if applied to MEMS with mechanically fragile and chemically functionalized surfaces. As remedy, new alternative and complementary nanopatterning methods have been developed, such as thermo-mechanical indentation (nanoimprint lithography), local deposition of molecular layers (soft-lithography), and shadow-mask deposition (nano-stenciling). Nano-stenciling is a resistless pattering method based on direct, local deposition of material through a solid-state silicon nitride (SiN) membrane applicable on arbitrary surfaces. Patterning of mesoscopic structures (10^-9 – 10^-5 m) through focused ion beam (FIB) fabricated stencils has been demonstrated within a limited area. In order to increase area size and throughput of the nanostencil method we developed a 4” wafer-scale DUV/MEMS fabrication process. The mesoscopic patterns were first defined by a 4x reduced projection exposure using an ASML wafer stepper and transferred into the SiN layer by means of reactive ion etching. The membranes were released by wafer-through etching using KOH. Nano-scale structuring using stencil masks allows a large choice of materials and surface to be nanopatterned, as no etch-steps need to be applied. We have studied nanopatterns of various materials such as Al, Au, Bi and Cr for various mesoscopic experiments, on various surfaces such as silicon, oxides, but also on freestanding cantilevers and self-assembled monolayers (SAM). In the presentation we will show details on the DUV/MEMS process and the application of the full-wafer stencil for specific applications such as templates for molecular electronics, nano-mechanical devices with 90 MHz resonance frequency, as well as nano-scale Hall-sensor devices.