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Substrate Transfer for GaN-LED on Si (111) 4 Inch
Keywords: GaN LED, substrate transfer, Si (111)
With the increasing demand for energy saving, LED lighting market is booming as LEDs are the ideal light source due to their high efficiency and durable eco-friendly properties. GaN based LEDs already today can be found in a variety of applications including traffic lights, full color displays, back lighting in liquid-crystal displays and white light. In recent years, the fabrication of GaN-LEDs on Si substrate has gained a lot of attention of both research institutes and industry. GaN-LEDs on Si technology promises higher production volumes and lower cost compared to the existing LED technology on Sapphire or SiC substrate as it can be integrated with the standard IC manufacturing platforms. This paper focuses on the substrate transfer process which is applied after the fabrication of the LED on 4 inch Si(111) wafer comprising p- and n contact formation to the GaN layer. After applying a passivation layer, a bonding metal is deposited. The wafer is then bonded to a Si carrier substrate using metallic bonding. Next, the original substrate Si(111) is completely removed by grinding and wet etching. GaN-LEDs are thus transferred to a new carrier substrate. The last step is etching of transferred GaN layer from the back to open the contacts. A surface roughening technique on the backside of the transferred GaN layer to improve the light extraction efficiency of GaN-LEDs is also investigated. All the issues of the substrate transfer process steps such as permanent Cu/Sn bonding, thinning by grinding and wet etching will be discussed in detailed. A typical issue occuring during processing of GaN-LEDs on Si substrates is high stress and related large wafer bow originating from the GaN layer and the thick Cu/Sn metal bonding layer. Such a large wafer bow causes problems for some automatic handling tools and processes like lithography. Solutions to manage the stress and wafer bow have been investigated. Functional GaN-LEDs have been successfully fabricated on a 4 inch Si(111) substrate and transferred face down onto another Si 4 inch carrier substrate.
Nga P. Pham, Researcher
IMEC
Leuven 3001,
Belgium


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