26 February 2018
SILTECTRA validates twinned SiC wafer produced using COLD SPLIT laser-based wafer thinning technique
© Semiconductor Today Magazine / Juno PublishiPicture: Disco’s DAL7440 KABRA laser saw.
SILTECTRA GmbH of Dresden, Germany says that it has validated the first high-electron-mobility transistor (HEMT) structure fabricated on a twinned silicon carbide (SiC) wafer processed using its proprietary COLD SPLIT laser-based wafer thinning technology.
The firm says that, as a laser-based wafer-thinning technique for substrate materials like silicon carbide, gallium nitride, silicon and sapphire, COLD SPLIT outperforms traditional grinding methods by thinning wafers to 100μm and below in minutes, with virtually no material loss. Now, due to a novel ‘twinning’ adaptation, SILTECTRA has demonstrated that COLD SPLIT can reclaim substrate material generated (and previously wasted) during backside grinding, and create a second fully optimizable bonus wafer in the process.
The firm reckons that the development promises substantial benefits for manufacturers of SiC-based ICs for power electronics and RF applications. The firm reckons that the solution’s combined advantages - which include fewer process steps, potentially lower equipment costs, and efficient use of substrate material - could reduce total device production costs by as much as 30%.
SILTECTRA validated the process by producing a GaN-on-SiC HEMT power device on a split-off (twinned) wafer at its new facility in Dresden. The HEMT showed results that were said to be superior to a non-COLD-SPLIT-enabled HEMT when measured for CMP characterization, as well as GaN epitaxy, metal layer and gate layer outcomes.
New substrate materials demand manufacturing cost reductions
Until now, the traditional method to thin wafers to less than 20% of the original thickness was grinding, involving the use of expensive diamond grinding wheels. While valued as a reliable solution for silicon, certain challenges make it difficult for grinding to achieve the extreme level of thinness required for SiC-based devices, says SILTECTRA. Unlike silicon, which is relatively soft, SiC is very hard (second only to diamond), which makes cutting and grinding arduous and expensive. Also, grinding is not a fast process, and the cost of consumables for the grinding wheels can be substantial. Finally, grinding generates material loss, and the process lowers overall yield, further driving up cost.
SILTECTRA hence engineered COLD SPLIT as a faster, higher-yield, lower-cost alternative to grinding for substrates like SiC. The technique employs a chemical-physical process that uses thermal stress to generate a force that splits the material with precision along the desired plane. Thinning is hence accomplished in minutes instead of an hour for traditional grinding tools, and cuts material loss by as much as 90%, it is reckoned.
The twinning development extends COLD SPLIT’s capabilities. The adaptation provides a simple way for integrated device manufacturers (IDMs) to avoid expensive kerf loss when slicing ingots or boules into wafers, says SILTECTRA, effectively replacing backside grinding processes while producing an identical wafer primed for a second device run. “We were confident that we could not only produce a faster and cheaper thinning solution for substrates like SiC, but that we could double the value for customers by extending COLD SPLIT’s reach to create a twin wafer from material previously lost during backside grinding,” says CEO Dr Harald Binder.
Binder notes that the twinning development was achieved ahead of schedule on the company’s technology roadmap. IDMs are now evaluating the technology. SILTECTRA is qualifying the process on customers’ SiC material at its newly extended facility in Dresden, while preparing to apply the COLD SPLIT technique to additional substrate materials. The firm also provides wafering and thinning services at the same location.