Researchers in South Korea have developed a semiconductor manufacturing technique that has over 99% success in controlling where individual crystals form in 400 patterned growth regions, potentially helping manufacturers build vertically stacked computer chips.
The technique allows researchers to grow a single crystal of molybdenum disulfide (MoS₂), a semiconductor just a few atomic layers thick, at a predetermined position, rather than allowing multiple crystals to form randomly.
A team led by the Korea Advanced Institute of Science and Technology (KAIST), in collaboration with UNIST, Hanyang University and TDS Innovation, developed the method, which releases oxygen from an oxide barrier to control where crystal growth begins.
The researchers say the approach could remove a major obstacle in stacked chip manufacturing, which requires semiconductor layers to be precisely formed on existing circuits without creating defects that affect performance.
Oxygen controls crystal formation
Conventional semiconductor growth methods can define the general area in which a thin film forms, but precise control of the starting point of each crystal remains difficult.
When multiple crystals grow independently and come together, they form grain boundaries. These boundaries disrupt the regular arrangement of the atoms and can affect the movement of electrons through the semiconductor.
The researchers developed a process called etching-flux-mediated single-centered nucleation (EF-SCN). Nucleation is the initial stage of crystal formation when atoms begin to arrange themselves into an ordered structure.
The process uses an oxide barrier such as hafnium oxide (HfO₂) that surrounds the intended growth area. Oxygen released from the barrier acts as an etchant and suppresses unwanted crystal formation.
The effect of oxygen is strongest at the edges of the structured area and gradually weakens towards the center.
This creates conditions that favor crystal formation at a single central point. Once growth begins there, the process also prevents more crystals from forming nearby.
Using this method, the researchers were able to successfully grow individual MoS₂ crystals at specific central positions in more than 99% of 400 samples.
The team also demonstrated selective metal deposition using structures combining molybdenum disulfide and molybdenum diselenide (MoSe₂).
In these structures, a thin ruthenium metal film formed selectively on the MoSe₂ regions, providing another way to control material placement during semiconductor manufacturing.
Stacked chips get closer
Two-dimensional semiconductors are being investigated for future chips because they retain semiconductor properties despite being only a few atomic layers thick.
Their thinness could allow manufacturers to stack computing and storage components vertically, reducing the distance that data travels between them.
Moving data around within a chip consumes energy and contributes to processing delays. Placing components closer together could reduce these costs, particularly for systems that handle large computing workloads.
However, manufacturing such chips requires precise control of semiconductor growth on surfaces containing previously fabricated circuits.
The KAIST technique offers a way to grow high-quality 2D materials directly in specific locations without having to produce them separately and transfer them to a chip.
The researchers examined the mechanism through growth experiments and simulations, but were unable to demonstrate a fully stacked processor or measure improvements in computing speed or energy consumption.
The results demonstrate control over crystal nucleation rather than the performance of commercial chips. Further development would be required to determine whether the method can be integrated into semiconductor manufacturing on a large scale.
The study was published on October 8th Nature.
