Micro-patterns were drawn on semiconductor materials with visible light


UNIST 권오훈 교수팀, 펨토초 레이저 활용한 차세대 광시야 포토리소그래피 개발
반도체 소재를 나노미터 수준에서 빠르고 자유자재로 조각


Recently, a number of semiconductor companies are focusing their efforts on superimposing extreme ultraviolet lithography equipment for ultra-precision circuit patterning processes. This is because using short wavelength light can draw more detailed circuits and patterns on semiconductor substrates and reduce device area, making it possible to produce high performance and low power semiconductors. However, due to the high scarcity of extreme ultraviolet lithography equipment, the demand for next-generation photolithography technology is also growing.

Professor Oh-Hoon Kwon’s team from the Department of Chemistry-15Second) a laser was used to form micropatterns with nanometer level accuracy on black phosphorus, a semiconductor material, and succeeded in creating different types of nanostructures. In addition, by directly observing the whole process in real time and space through a transmission electron microscope, the theoretical background that can explain the physical reason for the formation of nanopatterns and the strong interaction between light and matter which n basis is also presented.

Black phosphorus (BP) nanoribbon formed by femtosecond laser irradiation. (a) Schematic diagram of wide-field photolithography and formation of black phosphorus nanoribbons. (b) A black phosphorus nanoribbon formed with a width (50 nm) corresponding to one tenth of the wavelength of the irradiated light (515 nm). (c) A group of black phosphorus nanoribbons formed uniformly over an area of ​​several micrometers irradiated with a laser. Panel b is an enlargement of the area marked with a white box in the figure. Polarization is in the horizontal direction. Source: UNIST

The research team immediately irradiated a black phosphorus sample with light of a wavelength of 515 nm, which corresponds to visible light, to create a nanoribbon array with a width equal to one tenth of the light wavelength and a spacing equivalent to one hundredth. This is the resolution that reaches the smallest line width of a pattern that can be expressed with EUV exposure equipment. In particular, regardless of the crystal structure of the black phosphorus sample, it is possible to change the direction in which ribbons are formed according to the polarization of the irradiated light or make different types of nanostructures such as cubes and rings loose. It differs from synthetic methods that can only create nanostructures with a specific crystal orientation.

In the case of electron beam lithography, which is currently most widely used in device microprocessing, it shows the ability to process high resolution and precision. However, it takes a lot of time and money because it goes through many processes. In addition, there is a disadvantage that the resolution and amount of information processing is inversely proportional in the process of scanning the electron beam on the board. On the other hand, the research team’s wide-field photolithography technique has the advantage of being able to process an area of ​​1,000 times the solution immediately without the need for a pre-processing process.

Various types of black phosphorus nanostructures made by different polarizations of a femtosecond laser.  (a) Nanocubes (both vertical and horizontal polarization were used).  (b) Nano rings (ring polarized light was used).  (c) nano paver (clockwise and counter-clockwise circular polarizations were used).  Source: UNIST
Various types of black phosphorus nanostructures made by different polarizations of a femtosecond laser. (a) Nanocubes (both vertical and horizontal polarization were used). (b) Nano rings (ring polarized light was used). (c) nano paver (clockwise and counter-clockwise circular polarizations were used). Source: UNIST

The research team proved that the reason why they were able to form fine nanoparticles on black phosphorus using light was due to the formation of a ‘soliton’ due to the instability of light modulation. When light undergoes turbulent motion in a nonlinear medium such as black phosphorus, it can form a solitary wave that maintains its waveform and speed without losing energy, a soliton. In other words, black phosphorus interacted with the irradiated laser light to create a soliton, and a pattern was created as phosphorus atoms were ejected along the crest of the partially energized wave.

Dr said. Kim Ye-jin (currently a postdoctoral researcher at the California Institute of Technology (Caltech)), the first author, “Current lithography techniques have been performed in a top-down manner and chemical synthesis methods have u performed in bottom-up fabrication of nanostructures.” This study created a nanopattern by stimulating specific physical properties of black phosphorus using light, so this is the only research to create a nanostructure with a top-down and bottom-up approach.”

Professor Kwon Oh-hoon from 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, realizing accurate patterns with high resolution on at the same time. 2D semiconductor material.” It is a study that expands the understanding of nonlinear interactions between materials and confirms the possibility of developing next-generation semiconductor device manufacturing technology based on optical phenomena.”

The results of the research were published on March 6 (local time) in the journal ‘Nano Letters’ in the field of nano chemistry and nano materials.

Description: Tailoring Two-Dimensional Matter Using Strong Light-Matter Interactions

# Vocabulary

1. semiconductor

A semiconductor is a material that conducts electricity only under certain conditions and is used to control current as needed. It is a representative material used in semiconductor devices such as memory chips.

2. Black phosphorus

Black phosphorus is a typical anisotropic two-dimensional semiconductor material with a puckered honeycomb structure. It is attracting much attention as a major material for nano-electro-mechanical systems (NEMS). In addition, since the structural transformation of two-dimensional black phosphorus causes changes in its electronic structure, it is essential to observe the structural change of black phosphorus in response to light and understand its dynamics in controlling electrical properties including electrical conductivity.

3. Photolithography

It is a process used in microfabrication to pattern parts on thin films or substrates (wafers). It is done by using light to transfer a geometric pattern from a photomask to a photosensitive chemical photoresist on a substrate, etching the exposed pattern into the material through a series of chemical treatments, or depositing a new material of the desired pattern onto the material underneath. the photographer.

4. Electron beam lithography

It is a technique of forming a photoresist pattern on the surface of a sample by scanning and scanning an electron beam on a sample (wafer) coated with an electron beam photoresist to combine or break the polymer that forms the photoresist.

5. Transmission electron microscopy

It is an instrument that measures the shape, crystal structure, and chemical composition of a material at the atomic-nanometer level by transmitting a beam of electrons accelerated to high energy and with controlled properties through a series of electromagnetic lenses.

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