Materials Processing: KABRA laser-based SiC wafer slicing quadruples productivity
A key amorphous-black repetitive absorption technique can quadruple the productivity of silicon carbide wafer production.
Using a patented and patent-pending laser materials processing technique called key amorphous-black repetitive absorption (KABRA), scientists at DISCO Corporation (Tokyo, Japan) can quadruple the productivity of silicon carbide (SiC) wafer production, as well as increase yield by reducing material loss.1 The technique is applicable to both single-crystal and multicrystalline ingots, regardless of the orientation of the crystal layers.
Currently, penetration of SiC power devices is slow within the marketplace, primarily because of small yields and high production costs. The KABRA method, however, dramatically improves production yields, and should enable SiC devices to gain more traction as power devices, space-based mirrors, ultra-stable optical molds, and bolometers and other detectors.
To produce 350-μm-thick SiC wafers from a 20-mm-thick, 4-in.-diameter ingot, the conventional process using a diamond wire saw requires 1.6 to 2.4 hours per wafer for cutting alone, followed by a double-sided lapping process and a final polishing process—producing 30 wafers from one ingot and taking anywhere from 2.5 to 3.5 days total.
While many polishing processes are being developed, SiC is still a very hard, brittle material that must be carefully ground because of deep undulation grooves that form in the mechanical cutting process.
KABRA wafer separation
Implied by its name, the KABRA process essentially focuses a laser in the interior of a SiC wafer that, through repetitive passes or "amorphous-black repetitive absorption," decomposes SiC into amorphous silicon and amorphous carbon, and forms a layer that acts as the base point for wafer separation—that is, the black amorphous layer absorbs more light and allows the wafer to be separated easily in a proprietary process (see figure).
|To separate a silicon carbide (SiC) ingot into thin wafers (a), scientists have developed a laser-based key amorphous-black repetitive absorption (KABRA) method (b) that roughly quadruples production capacity and increases wafer yield per ingot. (Image credit: DISCO)|
Taking only 25 minutes to separate each wafer compared to 1.6–2.4 hours in the conventional process, the KABRA process also produces no material loss during separation compared to 200 μm of material loss per wafer using the conventional slicing process. Furthermore, the diamond-saw-sliced wafers require 16 hours of final lapping time that is not needed in the KABRA process.
Overall, a 2.5- to 3.5-day conventional process to produce 30 wafers from one ingot is reduced in the KABRA process to just 18 hours for a total of 44 wafers in one ingot—a three- to fivefold capacity improvement range (or roughly, a quadrupling of capacity).