SCIVAX uses nanoimprint technology to process sapphire surface and improve light extraction efficiency of LED chips

January 05, 2024

Japan's SCIVAX recently exhibited the sapphire surface processing technology used in the processing of LED substrates using nanoimprint technology at the "3rd New Generation Lighting Technology Exhibition". According to this technique, by providing epitaxial grooves of a pitch of several hundred nm, for example, from 100 nm to 250 nm, on the surface of the sapphire substrate, the GaN-based semiconductor crystal is epitaxially grown, whereby the light extraction efficiency of a GaN-based LED chip such as a blue LED can be improved. This is because when light emitted from the GaN-based semiconductor layer is extracted outside the chip, light reflection at the interface between the layer and the sapphire substrate can be reduced. Since the pitch of the concavities and convexities is about half of the emission wavelength of the LED chip, it can function as a photonic crystal.  

SCIVAX said it is currently introducing the technology to LED chip makers. The technique of providing hundreds of nm-level bumps on the surface of a sapphire substrate "will be applied to products in the next 1-2 years, and may become the mainstream technology for producing LED chips in three years" (SCIVAX Vice President Okuda Tak). Okuda believes that by using nanoimprint technology, these fine concavities and convexities can be formed at a lower price.  

According to the technical proposal proposed by SCIVAX, a silicon mold which forms fine irregularities is used as a master, fine irregularities are transferred onto a resin, and the resin is used as a die for transferring a fine pattern (imprint) on a sapphire substrate. Regarding the reason why the die was changed to resin, the company talked about the fact that the surface of the sapphire substrate can be bent after switching to resin. With the resin, even if the surface of the sapphire substrate is curved, the die can be well adhered to the surface of the sapphire substrate, and the fine pattern can be transferred with high precision. In addition to selling nanoimprinting devices and silicon molds, the company is also engaged in trial production and other businesses.  

In the past, LED manufacturers have used a manufacturing process in which epitaxial growth of GaN-based semiconductor crystals is performed after unevenness is formed on the surface of a sapphire substrate. However, the size of the concavities and convexities is several μm, and its main purpose is to reduce crystal defects in the GaN-based semiconductor crystal. Since the size of the concavities and convexities is much larger than the emission wavelength of the LED chip, it cannot be used as a photonic crystal.

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