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Infineon Tackles SiC Supply Shortages


Will Infineon's acquisition of Siltectra secure SiC wafer supply for the German semiconductor manufacturer, asks Rebecca Pool.

In a bid to guarantee materials supply, Infineon bought Dresden-based start-up, Siltectra, for €124 million, last month.

At a time when shortages in SiC wafer supplies rumble on, Siltectra has developed a novel technology - 'cold splitting' - to process crystals with minimal materials loss.

The technology is used to split SiC wafers and double the number of chips produced from one wafer. Importantly, Infineon now hopes to industrialise this process.

As Peter Friedrichs, Infineon's senior director of wide band gap semiconductors, puts it; "A huge motivation for this acquisition is security of supply and production ramp capability."

"Given the silicon carbide shortage of supply, especially with 150 mm wafers, we just want to make sure that if this continues, we are able to still deliver to customers," he adds.

Founded in 2010, Siltectra has spent the last eight years developing its wafer-splitting process and building a solid patent base. The spalling process uses externally applied stresses to separate crystalline materials along crystal planes with a well-defined thickness.

A laser defines a layer within the crystal to a predefined depth, with a custom polymer foil then deposited onto the top of the material. This materials system is then rapidly quenched to around -160ºC to induce enough stress to mechanically split the material along its laser-defined layer, separating a wafer from the rest of the boule.

The polymer foil can then be removed from the new wafer by standard wet-chemical cleaning. And, importantly, the remaining crystal boule can then be prepared for the next 'bonus' wafer, vastly reducing manufacturing costs.

Materials gains aside, cold-splitting promises other benefits. As Friedrichs highlights, the mechanical stresses from traditional wire-saw processes far outweigh those imposed by cold-splitting, so the new process yields wafers with fewer defects.

What's more, the process can also be used on GaN, GaAs and sapphire wafers, although Infineon intends to focus on SiC in the next few years.

But crucially, results to date indicate that the process can thin wafer materials to 100μm and below in minutes with high precision and virtually no material loss, a feat that Infineon now intends to repeat at production scale.

"Right now we have a proof-of-concept, laboratory scale process so we now need to scale up and automate the process to run with high throughput, twenty four hours a day, seven days a week," says Friedrichs. "As part of this, we need to define the equipment for a mass manufacturing process from scratch, as there is nothing else this out there."

"You know, the company in Dresden is a start-up, has used demonstrator tools and sometimes even home-made equipment," he adds. "The challenge for us is that there is nowhere to order new equipment for scale, so we are now partnering with companies that can manufacture the necessary production equipment that can be implemented into an automated manufacturing set-up."

All in all, the company estimates that the transfer to volume production will be completed within the next five years. Industrialisation is set to take place at Siltectra's existing Dresden site as well as Infineon's SiC manufacturing site and headquarters in Villach, Austria.

According to Friedrichs, final SiC chip production will take place at Villach, and Infineon will not create an additional manufacturing site at Dresden. "As in intermediate situation, we might also use Dresden for some initial pre-production trials," he says. "But the plan is to use the Dresden facility for alternative development in other directions."

Proving the process

Earlier this year, Siltectra revealed it had produced GaN on SiC HEMT devices on split-off wafers, with Friedrichs confirming Infineon has also fabricated practical devices. And with question marks still hanging over the supply of SiC wafers - only a few months ago industry analyst firm Yole Développement confirmed the supply bottleneck remained - Infineon's latest acquisition looks set to ease the ramp-up of SiC devices.

"The biggest motivation for this has been to increase the availability of SiC material," emphasises Friedrichs. "With cold-splitting we can simply double the number of wafers that we have allocated to our long-term agreements with suppliers."

"This is our first counter-measure to tackle the materials shortage problem and is part of our long-term strategy to roll out technologies relating to silicon carbide," he adds.

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