Photoresist-Free and Large-Area Patterning Method for van der Waals Materials via Direct Optical Lithography

Van der Waals (vdW) materials have attracted significant interest as new research platforms of next-era research since they exhibit novel properties with surface-dominant geometry. However, the properties of vdW materials are highly affected by the surface state of the materials owing to the geometrical feature of the materials and, therefore, the conventional photolithography technique accompanying undesired photoresist residues and solution process has negative effects on vdW materials. Several alternative patterning techniques have been reported to avoid the issue, but they suffer from low resolution, scalability, and low throughput.<br/>In this work, we report a new patterning technique, the direct optical lithography technique, specialized for vdW materials. The direct optical lithography uses highly intensive photo illumination in a short pulse with a special photomask to follow the advantage of conventional photolithography without photoresists and solvents. We patterned various vdW materials (monolayer MoS₂, bilayer MoS₂, monolayer graphene, monolayer WSe₂, and two-dimensional metal-organic framework) in multiscale and desired shapes. Morphological characterization revealed that direct optical lithography did not cause photoresist residues unlike conventional photolithography and optical characterization exhibited critical differences between direct optical lithography and conventional photolithography. The finite element method (FEM) simulation results demonstrated that the photo source used in this work, the highly intensive light with a short pulse, was suitable for high-resolution patterning of vdW materials without degradation of patterned materials.