As demand for next-generation photolithography technology grows due to the high scarcity of extreme ultraviolet exposure equipment in semiconductor ultra-fine circuit pattern processes, a technology that can quickly and freely engrave semiconductor materials at the nanometer level using optical phenomena has been developed, and expectations are high that it will be used in the production of next-generation semiconductor devices in the future.

UNIST (President Yong-Hoon Lee) Department of Chemistry Professor Oh-Hoon Kwon's research team announced on the 9th that they have successfully formed micro-patterns with nanometer-level accuracy on black phosphorus, a semiconductor material, using a femtosecond (10-15 seconds) laser and created various types of nanostructures.

In addition, by directly observing the entire process in real time and space using a transmission electron microscope, the theoretical background that can explain the physical reason for the formation of nano-patterns and the strong interaction between light and matter that is its basis was also presented.

The research team momentarily irradiated a black phosphorus sample with light of 515 nm wavelength, which corresponds to visible light, and created a nano ribbon array with a width corresponding to one-tenth of the light wavelength and a gap corresponding to one-hundredth. This is the resolution that reaches the minimum line width of a pattern that can be expressed by extreme ultraviolet exposure equipment.

In particular, the direction in which ribbons are formed can be changed depending on the polarization of the light shining on them, regardless of the crystal structure of the black phosphorus sample, and various nanostructures in the shape of cubes, rings, etc. can be freely produced. This differs from synthetic methods that can only produce nanostructures with a specific crystal orientation.

Electron-beam lithography, which is currently the most widely used in device microfabrication, has high resolution and precision processing capabilities.

On the other hand, it takes a lot of time and money because it goes through a lot of processes.

Additionally, there is a disadvantage in that the resolution and information processing volume are inversely proportional in the process of scanning the electron beam onto the substrate.

In contrast, the research team's wide-field photolithography technique has the advantage of not requiring a preprocess and being able to process an area a thousand times larger than the resolution at once.

The research team proved that the reason they were able to form fine nano patterns on black phosphorus using light was due to the formation of 'solitons' caused by modulation instability of light.

When light experiences disturbance in a nonlinear medium such as black phosphorus, it can form a singular wave that maintains its waveform and speed without energy loss; this is called a soliton.

That is, the black phosphorus interacted with the irradiated laser light to generate a soliton, and the pattern was created as phosphorus atoms were emitted along the crest of the partially energized wave.

“Existing lithography technologies have been performed top-down to create nanostructures, while chemical synthesis methods have been performed bottom-up,” said first author Dr. Ye-Jin Kim (currently a postdoctoral researcher at the California Institute of Technology (Caltech). “This study is the only study to create nanostructures using both top-down and bottom-up approaches, as it created nanopatterns by simultaneously using light and inducing the unique properties of black phosphorus.”

Professor Kwon Oh-hoon of the Department of Chemistry said, “This is the first time that a transmission electron microscope has been used to implement wide-field photolithography and observe the pattern formation process in real time while simultaneously implementing high-resolution and accurate patterns on a two-dimensional semiconductor material.” He added, “This research broadens the understanding of nonlinear interactions between light and matter and confirms the possibility of developing next-generation semiconductor device manufacturing technology based on optical phenomena.”

The theoretical and computational analysis of this study was conducted jointly with Professor Park Gyu-hwan of the Department of Physics at Korea University, and the research team of Professor Kim Kwan-pyo of the Department of Physics at Yonsei University also participated. The research was conducted with the support of the Samsung Future Technology Promotion Foundation, and was published on March 6 in Nano Letters, a world-renowned journal in the field of nanochemistry and nanomaterials.