A slippery discovery could help polish next-generation computer chips
New study suggests layered materials may follow a different polishing pathway during semiconductor manufacturing
image: Scientists propose shear slipping as a third material-removal mode — in addition to chemical bonding and mechanical plowing — in chemical mechanical polishing. A thin oxide layer formed on bismuth slips relative to the underlying material under shear forces from the polishing pad, enabling rapid material removal.
Credit: Friction, Tsinghua University Press
The materials behind tomorrow’s computer chips may not wear away in the way engineers expect. Southwest Jiaotong University researchers have discovered an unusually fast and previously unknown polishing mechanism in bismuth, a promising material for future microchips. Their study offers new insight into how layered materials behave during semiconductor manufacturing.
The study was published in Friction on March 19.
Integrated circuits, better known as microchips or simply chips, power smartphones, computers, televisions and many other consumer or industrial technologies. These devices rely on precisely engineered materials to process and transmit electrical signals. As conventional materials approach their limits, researchers are exploring layered materials, solids made of stacked, ultra-thin sheets, as candidates for next-generation electronics.
“Layered materials are increasingly important for future integrated circuits, yet their chemical mechanical polishing behavior and mechanisms are not fully understood,” said Liang Jiang, professor at Southwest Jiaotong University and lead author of the study.
Chemical mechanical polishing (CMP) is a key manufacturing process used to smooth and flatten surfaces during chip fabrication.
To better understand how these materials are removed during CMP, the researchers selected bismuth as a representative layered material and studied what happens at its surface during polishing from the viewpoint of tribology — the science of friction, wear and surface interactions.
“Our investigation shows that bismuth does not follow either of the previously discovered modes of material removal: chemical bonding and mechanical plowing,” Jiang said.
In the chemical bonding mode, oxidation activates the material surface, allowing chemically active abrasive particles to bond with it. As the abrasives move, weakened bonds beneath the surface break, pulling material away. In mechanical plowing, chemical reactions soften and weaken the surface, enabling hard abrasive particles to scrape material off mechanically.
But bismuth behaved differently.
The team found that bismuth could be removed rapidly, using only a chemically inert polishing pad and without chemically active abrasives, at rates exceeding 10 micrometers per minute, far faster than the less than 1 micrometer per minute typical of conventional CMP.
“This challenged the idea that chemical bonding was responsible,” Jiang said. “At the same time, experiments showed that hydrogen peroxide, a common polishing chemical, actually hardened the bismuth surface instead of softening it, contradicting the mechanical plowing mode.”
“We therefore proposed a third material-removal mode in CMP from a tribological perspective: shear slipping.”
In this model, hydrogen peroxide oxidizes bismuth to form a thin surface layer of bismuth oxide that interacts only weakly with the material underneath. As microscopic roughness on the polishing pad moves across the surface, this loosely attached layer slips sideways rather than being scratched or chemically pulled away, removing material as micron-sized debris. Sliding layers apart takes less energy than breaking strong bonds directly, which may explain why bismuth polishes so quickly.
The team look forward to determining whether this slipping behavior extends beyond bismuth to other layered materials being explored for use in advanced electronics. If confirmed, the finding could help engineers improve polishing precision and better control manufacturing processes for future semiconductor devices.
“Ultimately, we hope to develop reliable polishing strategies capable not only of removing layered materials efficiently, but also of producing atomically smooth, defect-free surfaces, a critical requirement for manufacturing next-generation integrated circuits,” Jiang said.
Funding
- National Natural Science Foundation of China (Nos. 51991373 and 52235004),
- National Key R&D Program of China (No. 2020YFA0711001),
- Fundamental Research Funds for the Central Universities (Nos. 2682025CG001 and 2682024CG007).
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