A technology has been developed to remove defects in semiconductor materials, enabling the creation of smaller, faster, lower-power chips.

Professor Kwon Ji-min's research team from the Department of Electrical and Electronic Engineering at UNIST, in collaboration with Professor Noh Yong-young's research team from the Department of Chemical Engineering at POSTECH, announced on the 25th that they have developed a technology to remove defects in molybdenum disulfide, a next-generation semiconductor material, at 200℃.

A single semiconductor chip the size of a fingernail contains at least several billion elements. Molybdenum disulfide is a semiconductor material that is attracting attention from the industry because it is expected to increase the integration of chips and create low-power semiconductor chips that do not generate heat by controlling leakage current.

The technology to remove defects that occur during the process of integrating molybdenum disulfide into actual chips at low temperatures is a key task for commercialization. Since molybdenum disulfide is used by depositing it on a silicon device, the already completed silicon device must not be damaged by heat.

The research team filled the defects at 200℃ with a material called PFBT, restoring the atomic ratio of molybdenum to sulfur in molybdenum disulfide (MoS2) to 1:1.98, which is close to the theoretical ratio of 1:2.

During the process of depositing molybdenum disulfide in the form of a thin film, defects occur where sulfur atoms are scattered in the places where they should originally be, so in reality, the ratio of sulfur to molybdenum is synthesized at approximately 1:1.68.

Since defects impede the flow of electrons, these defects must be filled and restored to a state close to the theoretical atomic ratio to secure semiconductor performance and durability.

“The biggest advantage is that it is compatible with existing silicon semiconductor BEOL processes because defect repair occurs below 200℃,” explained first author Dr. Jeonghak Soon.

The BEOL process is a process of connecting devices already deposited on a substrate to each other, and is performed at temperatures below 350℃ to prevent damage to the devices.

PFBT (Pentafluorobenzenethiol) used in the recovery step has a structure in which a thiol functional group (-SH) and fluorine (F) are attached to a hexagonal benzene ring.

The sulfur contained in the thiol functional group directly fills the defect, and the fluorine induces this substance into the sulfur defect, and then plays a role in easily separating the remaining portion of the substance excluding sulfur.

The research team confirmed that this chemical reaction was possible through molecular dynamics simulations. In addition, X-ray spectroscopy analysis results showed that the actual sulfur vacancy was filled at low temperatures.

When transistor elements were made with defect-filled molybdenum disulfide, the charge mobility was improved by 2.5 times compared to when the defect was present. The faster the charge transfer, the faster the operating speed. The 'subthreshold swing value', which is an indicator of power consumption, has also been reduced by about 40%.

Professor Kwon Ji-min said, “Sulfur defects that occur during the process are a big problem for semiconductor devices targeting advanced nanoscale nodes,” and “We plan to further expand our research on defect recovery and interface characteristic improvement of not only molybdenum disulfide but also various next-generation semiconductor materials through the low-temperature sulfur defect recovery technology using the developed organic molecules.”

This study was conducted with the participation of Dr. Jeong-Hak Soon from UNIST and Researcher Min-Kyu Kim from the Department of Chemical Engineering at POSTECH as the first authors, and was supported by the National Research Foundation of Korea (NRF) through the Ministry of Science and ICT (MSIT), the Institute of IT Planning and Evaluation (IITP), and Ulsan National Institute of Science and Technology (ULST).

The research results were officially published on February 18 in ACS Nano, an authoritative international academic journal in the field of nanoscience and technology.