German foundry X-Fab Silicon Foundries is moving its fab in Lubbock, Texas, entirely to silicon carbide (SiC), and says it is the first to add an in-house epitaxial process to improve yields.
The automotive-qualified fab has a capacity of 26,000 6in wafers per year that it expects to be moved over to SiC wafers from silicon. The fab also has the ability to add one or two layers of epitaxy on top of these SiC wafers depending on the application to improve the yield.
“SiC is a unique, discrete product and there are two or three different ‘care abouts’ in the performance: breakdown voltage, leakage of a diode and forward voltage drop,” said Chris Toelle, SiC business director. “All of our customers will be defining a certain application and that will determine the sweet spot and then what we will be able to do is tune the parametric sweet spots and at the same time driving yield,” he said. “If you use a standard epi wafer on different projects you don’t necessarily hit the sweet spot for either and you might see lower yield.”
The epi process has been added for SiC wafers to improve the quality and yield. “SiC substrate production at 6in is still in its infancy,” said Ed Pascasio, CFO at X-FAB Texas
“You need to start with a good substrate so having access to those substrate suppliers and assess the market on where those suppliers are on their quality is critical,” he said. “The SiC wafers have many, many defects so you have to put the epi on top of it to provide a higher quality layer. You still have to start with a good quality wafer substrate to get the yield.”
Next: Improving SiC yields
“The market is very concerned about the supply and we are working with the major suppliers on the quality feedback loop and also making sure that the supply they need in the future is available,” said Pascasio. “The total available substrates for SiC are being eaten up years in advanced.”
“For our foundry offering we are continuously evaluating new entrants – we have good relationships with existing suppliers.”
This is for 6in for the foreseeable future.
“Our strategy is to be the leading SiC foundry at 6in and as it moves to 8in we want to remain the SiC foundry – if and when this moves to 8in we want to move with it. We are in constant communication with suppliers on when they can sample 8in and when we go out to buy tools we try to buy 8in tools and retro fit to run 6in wafer so we have that capability,” he said.
This would not be for at least two years. “The supply times that we get vary so much from different suppliers so we don’t believe it will be in the next couple of years. There are people that have made them and you can see one but you can’t get enough samples for a line. We also don’t know what the specifications are for an 8in wafer.”
“When we look at capabilities, it ends at dicing,” said Pascasio. “We have no plans to get into modules and packaging, but we do have some interest in the backend processing if our customers ask for it.”
The fab has numerous high-volume projects for diodes, MOSFETs and JFETs all currently running for mass market adoption, he says.
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