Korean researchers, atomic layer-level copper thin film growth “The worlds first clarification on the principle of oxidation” Can it make copper that does not rust? If that happens, gold used for semiconductor nanocircuits can be replaced with copper with high conductivity and low price, greatly improving performance and price competitiveness.
Korean researchers have elucidated the principle of copper oxidation at the atomic level. Based on this, a method to prevent oxidation of copper was also found.
The Ministry of Science and ICT announced on the 15th that a research team led by Pusan National University Professor Jeong Se-young, Sungkyunkwan University Professor Kim Young-min, and Mississippi State University Professor Kim Seong-gon used an ultra-flat copper thin film with a monoatomic layer roughness to investigate the principle of copper oxidation in theory and experiment for the first time in the world. .
The results of this research were published on the 17th in the academic journal ‘Nature’.
Schematic model for copper oxidation. It shows that oxygen does not permeate in the ultra-planar surface of one layer of atomic steps, and oxygen can permeate in two or more layers of atomic steps.
■ Creating a thin layer of copper at an atomic level
The research team first implemented an ultra-flat copper thin film at the level of one atom with the ASE, a thin-film growth device developed by the research team. Since it is empirically known that oxidation proceeds from the rough part of copper, thin film growth with the best possible surface condition was a priority.
Until now, it was considered almost impossible to grow an ultra-planar copper thin film into a single crystal. This is because, when a thin film is grown, defects or rough surfaces of ‘grain boundaries, which are boundaries where different crystals meet in polycrystals, are formed. The oxidation of copper is not controlled because it occurs randomly at grain boundaries and rough surfaces, which are more than a trillion in polycrystalline copper.
The researchers removed these defects and grew the thin film into a single crystal. At the same time, the surface roughness was controlled to 0.2 nm level. Roughness refers to the jagged height of the thin film surface, and so far, 1.5 nm has been the highest level of roughness control.
As a result of observing the ultra-flat copper thin film made in this way with a high-resolution transmission electron microscope, etc., after being exposed to air for one year, neither the natural oxide film normally observed on the copper surface nor even oxidation at the level of an atom was observed.
■ Copper oxidation, finding the cause can prevent it
The researchers calculated the energy change for oxygen to enter the copper interior. As a result, when the surface roughness is two or more atomic layers, oxygen easily penetrates into the copper, whereas when the surface is perfectly flat or monoatomic, oxidation does not occur at room temperature because very high energy is required for oxygen penetration.
Changes in Oxygen Penetration Energy According to Surface Roughness and Transmission Electron Microscopy Surface Analysis
It was also revealed that oxygen sitting on the surface of the ultra-smooth thin film has a self-regulating function that suppresses oxidation by pushing out other oxygen from access when 50% of the sites where oxygen can exist are filled.
This study is meaningful in that it not only revealed the exact cause of copper oxidation, but also provided an opportunity to replace gold used in nanocircuits with a thin copper film. The development of technology to grow an atom-level thin film is also noteworthy. It is expected to be able to replace expensive semiconductor deposition equipment such as MBE, PLD, and ALD.
Professor Sei-Young Jeong said, “This research result is the worlds first case in which the origin of copper oxidation is identified at the atomic level,” and “opens the possibility of manufacturing unchanging copper.”
This research was carried out with support from the Ministry of Science and ICTs individual basic research and group research support project.