Front scribing using a 266 nm source rather than a conventional 355 nm laser is helping researchers at JPSA in the US to produce more LEDs per wafer. What's more, the company believes that its UV diode-pumped solid-state (DPSS) laser achieves an industry-leading cut width of 2.5 µm at a cut speed of 100 mm/s.
"Typically you can design a wafer to get up to 20 % more LEDs by front scribing using a 266 nm laser compared with scribing from the back using a 355 nm laser," Adrian Baughan, international sales manager at JPSA, told optics.org. "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."
Until now, using a 266 nm laser for industrial applications has been limited by its shorter wavelength and lower 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 high-speed scribing for die singulation for the manufacture of LEDs 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," continued Baughan.
The front scribing method is key to achieving yields of over 99 %. "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," explained Baughan. "It also has the advantages of easier set up and alignment and better light output from the final packaged LED device."
The next steps for Baughan and his colleagues is to work towards using larger wafers, higher power and achieving faster processing. They will also be looking into new applications and materials that can utilize the specific advantages of the 266 nm wavelength in industry.
