iLED iLED, October issue : 10
OCT OBER 2011 ISSUE N°2 COMP ANY INSIGHT Laser dicing brings LED manufacturing to the cutting edge Overcapacity is slowing demand for standard dicing technologies in GaN-on-sapphire LED manufacturing, but alternative substrate material systems are still growing, explains Rene Hendriks, Dutch tool maker ALSI's director of commerce. A Rene Hendriks, Director of commerce, Advanced Laser Separation International row of laser beams, lined up together much like train carriages, dashes from one side of a circular disc to another and back at speeds up to half a metre per second. The Advanced Laser Separation International (A.L.S.I.) method of dicing an LED epitaxial wafer is a truly 21st century process. Moreover, as its fellow 21st century technology – solid state lighting – seeks improved brightness levels and manufacturing yields, that laser dicing method is helping deliver them. That's according to Rene Hendriks, director of commerce at the Beuningen, Netherlands, based company. in between. Then of course you have parameters like the power and the pulse duration.” Iterating through these variables, it takes A.L.S.I. less than one month to tailor equipment for each individual LED manufacturer's production line. Though this tailoring helps minimise kerf width, and in turn raises yields, conventional laser dicing methods do confer undesirable properties to the LEDs they singulate. These methods are ablation, where die are completely separated from each other, and scribing, where lines are etched into the wafer so they can be easily broken apart later. “When you use an ablation or a scribe on the surface, you modify the layers,” Hendriks explained. “You get a sort of debris or solidi fi ed material called recast on the side of the die that absorbs rather than re fl ects the light. As a result the emission is reduced.” Now, in standard GaN-on-sapphire LED epiwafers, A.L.S.I.'s customers are showing a preference for alternative dicing methods like subsurface separation and “stealth dicing”. “The lasers modify the inner layers on the wafer,” said Hendriks. “You can then break the wafer apart. Although it is one of the most expensive dicing technologies it gives the product more light output, and it apparently pays off.” How much this approach grows further could be limited by a shift by LED producers away from standard GaN-on-sapphire towards alternative processes. In particular, A.L.S.I. has been extensively developing dicing tools for LEDs made after removing the sapphire substrate and bonding “We have seen clearly that the LED industry has overcapacity installed and that has an impact,” said Rene Hendriks, A.L.S.I “Our customers want to have extremely high dicing speed and the narrowest kerf possible,” Hendriks explained. “Smaller scribe lanes enable more dies on a wafer and the smaller the die gets, the more attractive this is. Say you have die of 250 μ m pitch, and lanes of 50 μ m pitch. If you can reduce that to 30 μ m then you can get 15-20% more output from your wafer fab.” While laser dicing's cutting generally provides narrower kerf than blade dicing methods, Hendriks' company strives to help its customers fully exploit this advantage. A.L.S.I., which was founded in 2001 as a spin-off from Philips Semiconductors, achieves this by optimising the dicing process parameters. That begins with its key beam-splitting technology, which distributes laser power between several beams, avoiding thermal wafer damage that can occur with the same power concentrated in a single beam. “The variables are: the wavelength of the laser and the number of beams we apply,” Hendriks said. “It can be two to 48 beams, and anything Role of the dice: Ablation, or full cut, dicing and scribing both leave recast debris on LED wafers that absorbs rather than re fl ects light, while subsurface separation, or stealth dicing, doesn't. (Courtesy of A.L.S.I.) 10 i LED
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