A new way to shape SiC semiconductor crystals?
SiC is capable of handling enormous voltages, but shaping the raw ingots into mirror-smooth wafers can shatters the surface with microscopic cracks that can cause microchips to fail.
In the International Journal of Extreme Manufacturing, Shuiquan Huang at Yanshan University, Han Huang at Sun Yat-Sen University and colleagues claim to have have flipped this manufacturing curse on its head, using the destructive friction heat of high-speed cutting to trigger a chemical reaction that lets diamond tools carve brittle crystals as smoothly as butter.
Grinding discs embedded with diamond grit can flatten SiC quickly, but the violent impacts leave behind deep sub-surface fractures. To buff out those cracks, manufacturers must rely on sluggish chemical slurries that take days to smooth away a single millimeter of material. Earlier strategies tried softening the crystal first using high-power lasers, which risk warping the wafer with excessive heat, or corrosive chemical oxidisers that gradually destroy the precision grinding machines themselves.
Huang’s team have tackled the problem by turning to a clever chemical additive borrowed from 3D printing: a non-toxic azo compound called ACVA dissolved in an everyday liquid polymer coolant. This is described the paper 'Atomic-scale damage control via thermochemical mechanical grinding induced amorphisation of single crystal SiC'.
Under resting conditions, the mixture behaves like standard industrial lubricant. But the moment a diamond grit strikes the wafer, the intense micro-contact friction instantly spikes the localised temperature exceeding 45°C. This brief flash of heat causes the additive to split into fleeting free radicals, which immediately attack the top layer of silicon atoms.
Atomic simulations and electron microscopy reveal that this targeted reaction temporarily rewires the crystal surface, creating a pliable and 10nm-thick skin of amorphous silicon oxycarbide. Instead of splintering under mechanical force, this glassy top layer behaves like a sacrificial molecular cushion, deforming smoothly under the diamond grit and nearly doubling the crystal’s crack-free cutting depth from 29nm to 51nm.
The resulting process slashes subsurface crystal defects to a depth of only 70nm while entirely preventing hidden microcracks. The researchers say that allowing chipmakers to bypass laborious intermediate polishing stages and jump straight from fast grinding to final finishing, promises to streamline SiC manufacturing.
The researchers note that the immediate next step is scaling the chemistry to run on commercial 8-inch wafer processing equipment and engineering closed-loop fluid recycling systems for large-scale industrial foundries.
