Deep-UV scribing "boosts LED production yield"
by Marie Freebody
Front-side wafer scribing using a 266 nm source rather than a conventional 355 nm laser could allow manufacturers to produce up to one-fifth more LEDs per wafer.
According to laser system vendor JPSA Laser, its deep-UV laser, which is based on a frequency-quadrupled source, achieves an industry-leading kerf width of 2.5 µm at a cut speed of 100 mm/s.
"Typically you can design a wafer to get up to 20 percent more LEDs by front scribing using a 266 nm laser, compared with scribing from the back using a 355 nm laser," said Adrian Baughan, international sales manager at JPSA.
"The shorter wavelength couples well into a larger variety of materials and can be focused to a smaller spot to get very high quality ablation with a minimal heat-effected zone," added Baughan, who detailed the technology at last month's Association of Laser Users (AILU) meeting in Cardiff, UK.
Until now, using a 266 nm laser in industrial applications has been limited by the source's relatively low power. "The laser operates at around 2 W, which is limiting in overall material removal rates for many applications," explained Baughan. "We have not increased the power, it is advanced optical design and the higher absorption of a shorter wavelength in sapphire that has resulted in faster scribing."
According to Baughan, careful design and choice of application means that high-speed scribing in LED die singulation is feasible. "We can now achieve high quality and very narrow kerf scribing of exotic materials," he said.
"In difficult materials such as sapphire or GaN for example, the improved coupling of the radiation to the substrate can result in faster scribing speed at lower power when compared to using a 355 nm laser."
The front scribing method is key to achieving yields of over 99 percent, reckons Baughan: "Front scribing means you can position the laser very accurately to the street that appears on the wafer, and using a narrow kerf of 2.5 µm enables utilization of more of the wafer."
"It also has the advantages of easier set up and alignment and better light output from the final packaged LED device."
Having demonstrated the potential of the deep-UV approach, the next steps for the JPSA team is to work towards using larger wafers, higher power and achieving faster processing.
Author
Marie Freebody is a reporter for optics.org, a sister publication of compoundsemiconductor.net
