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Nano-Fabrication on GaAs Surface by Resist Process with Scanning Tunneling Microscope Lithography

Recently scanning tunneling microscopes (STMs) have become important tools for nanometer scale fabrication. In order to make a nanoscale structure on a semiconductor surface, we attempted to lithograph very fine lines (possibly less than 10 nm) by using a resist process with an STM as an electron beam source. A diluted positive electron beam resist, poly-methyl methacrylate (PMMA), was first coated on a S-doped GaAs substrate. Using the STM in air, we approached a W-tip to the surface at a bias voltage of 10 V and a tunneling current of 0.5 nA, and made a line using by scanning the tip with various scan times. We then analyzed those lines made by the STM tip using an atomic force microscope (AFM) in air. After these processes, we deposited a Ti membrane on the sample surface by vacuum evaporation, then lifted it off. As a result, we confirmed that it was possible to make fine Ti lines as narrow as 50 nm by this process.