UNIST Develops 'Next-Generation Wide-Field Photolithography' Using Femtosecond Laser

A research team at Ulsan National Institute of Science and Technology (UNIST) has developed a next-generation wide-field photolithography technique using lasers with a pulse duration of one quadrillionth of a second.

The research team led by Professor Oh-Hoon Kwon from the Department of Chemistry at UNIST succeeded in forming nanoscale patterns with nanometer-level precision and creating various forms of nanostructures on black phosphorus, a semiconductor material, by utilizing femtosecond (10 to the power of -15 seconds) lasers.

They also directly observed the entire process in real space and time using transmission electron microscopy, providing a theoretical background that explains the physical reasons for the formation of the nanopatterns and the strong light-matter interactions underlying them.

The team instantaneously irradiated black phosphorus samples with light of 515 nm wavelength, corresponding to visible light, producing arrays of nanoribbons with widths one-tenth of the light wavelength and spacings one-hundredth of it.

This resolution matches the minimum linewidth achievable by extreme ultraviolet lithography equipment. Notably, regardless of the crystal structure of the black phosphorus samples, the direction of the ribbons can be changed according to the polarization of the irradiated light, and various nanostructures such as cubes and rings can be freely fabricated.

Black phosphorus (BP) nanoribbon formed by irradiating with a femtosecond laser.

This differs from synthesis methods that can only produce nanostructures with specific crystal orientations.

Currently, electron-beam lithography, which is most widely used in device microfabrication, offers high resolution and precise processing capabilities.

However, it requires multiple processing steps, resulting in significant time and cost. Additionally, during the scanning of the electron beam over the substrate, there is a drawback that resolution and information processing capacity are inversely proportional.

In contrast, the wide-field photolithography technique developed by the research team does not require pre-processing steps and can process an area 1000 times larger than the resolution at once.

The team demonstrated that the reason they could form fine nanopatterns on black phosphorus using light was due to the formation of ‘solitons’ caused by modulation instability of the light.

When light undergoes perturbation in nonlinear media such as black phosphorus, it can form a unique wave that maintains its waveform and velocity without energy loss; this is called a soliton.

In other words, black phosphorus interacted with the irradiated laser light to generate solitons, and patterns were formed as phosphorus atoms were released along the crests of waves where energy was locally increased.

Various forms of black phosphorus nanostructures created by altering the polarization of femtosecond lasers.

Dr. Yejin Kim, the first author, said, “Existing lithography technologies for fabricating nanostructures have been top-down, and chemical synthesis methods have been bottom-up. This study is unique in that it created nanostructures by inducing the distinctive properties of black phosphorus using light, thus approaching nanostructure fabrication from both top-down and bottom-up directions simultaneously.”

Professor Oh-Hoon Kwon of the Department of Chemistry stated, “This is the first time that wide-field photolithography was implemented using transmission electron microscopy to observe the pattern formation process in real time and simultaneously realize precise patterns with high resolution on two-dimensional semiconductor materials. This research broadens the understanding of nonlinear light-matter interactions and confirms the potential for developing next-generation semiconductor device fabrication technologies based on optical phenomena.”

The theoretical and computational analyses of this study were conducted jointly with Professor Kyuhwan Park from the Department of Physics at Korea University, and Professor Kwanpyo Kim’s research team from the Department of Physics at Yonsei University also participated.

The research was supported by the Samsung Future Technology Development Fund and was published on March 6 in Nano Letters, a world-renowned journal in the field of nanochemistry and materials.

This content was produced with the assistance of AI translation services.