pISSN 0374-4914 eISSN 2289-0041

## Research Paper

New Phys.: Sae Mulli 2020; 70: 715-721

Published online September 29, 2020 https://doi.org/10.3938/NPSM.70.715

## Projection Photolithography for Microscale Patterning and 2D Field-effect Transistor Demonstration

So Jeong SHIN, Hyun Seok LEE*

Department of Physics, Research Institute for Nanoscale Science and Technology, Chungbuk National University, Cheongju 28644, Korea

Correspondence to:hsl@chungbuk.ac.kr

Received: July 16, 2020; Revised: July 31, 2020; Accepted: August 11, 2020

### Abstract

In this paper, we introduce a method to realize microscale patterning at arbitrary positions via a projector-based photolithography technique even without a hard photomask. For applying this technique to micro/nano device fabrications, we equip an optical microscope with a digital micromirror device module and a UV light source with a 405-nm wavelength. A bilayer photoresist (PR) and a lift-off processes are used for fabricating versatile micropatterns implemented by using this equipment, where the PMGI (polymethylglutarimide) PR and the AZ 5214 PR used for the bilayer allow the construction of undercut structures for a post-lift-off process. Through process optimization, we realize a line pattern width of $\sim$ 560 nm without a side-wall effect, nearly approaching the theoretical optical diffraction limits of the given optics. Using the optimization process, we demonstrated field-effect-transistors with a channel length of a few $\mu$m for randomly oriented triangular-MoS$_{2}$ monolayers synthesized by using chemical vapor deposition. Our demonstration visualizes that the projection photolithography technique partially replaces an expensive electron-beam lithography for microdevice fabrication at a laboratory level.

Keywords: Projection photolithography, Micropattern, Field effect transistor, 2D semiconductors, Image photomask