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What Makes LEDs Different?

Earlier this month, KLA-Tencor released their ICOS WI-2280 inspection tool for LEDs. Reading through all the things it does and the improvements in provides – things like enhanced recipe qualification and reduced setup time – well, for someone like me who doesn’t spend all his time in this world, you start to think… This sounds like a lot of other inspection tools. And there do seem to be a lot of different tools.

It makes you wonder, why can’t one tool simply do it all? Reading through what the 2280 does, it seems like it would be good stuff for any IC. So I asked that of them as one of those “OK, I feel really stupid asking this, but…” questions, and they clarified both why this is different from other IC inspection tools and what it is not intended to do.

First, and most fundamentally, LEDs use sapphire as a substrate, and it’s transparent. That means that different lighting is required as compared to a silicon wafer. I suppose you could argue that this should then just be a “setting” or adjustment on a more general-purpose tool. But that would fly up against a second concern: cost. The defects being detected on LEDs are in the 3-5-µm range, far larger than what you would look for on a 28-nm chip. No need to burden it with expensive micro-mote detection capabilities.

There’s also one other less obvious difference. LEDs are typically inspected again after dicing. It’s “relatively” easy to inspect dice on a wafer – once you align the wafer, you’re set. But with dice in trays, each die can shift around, so post-slicing inspection requires separate attention that’s not needed for standard ICs.

Meanwhile, the 2280 is intended for all in-line inspections of patterned wafers (or diced wafers). It’s not intended for sampling (which may use a slower, more detailed analysis) or for inspecting the blank substrate.

You can find out more in their release.

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