UV Roller-type Micro/Nanoimprint Lithography to Fabricate Patterned Sapphire Substrate
Date Issued
2014
Date
2014
Author(s)
Lin, Wei-Chun
Abstract
White LEDs have been widely used for light source and backlight in LCDs. It has been reported that micro-cone-pattern on sapphire substrates can improve GaN crystalline quality and the light scattering to enhance the output power of GaN-based LEDs. Therefore, LEDs are commonly grown on patterned sapphire substrates(PSS). To fabricate PSS, conventional photolithography and imprinting lithography are used to form high aspect ratio pillar array, which is served as the mask of subsequent ICP-RIE. Because a multi-layered sapphire substrate for LED is often warped, the imprinting methods with soft mold are attracted attention for their low cost and suitability. In this study, two continuous UV roller-type approaches to fabricate micro-pillar array on sapphire substrate have been developed. We expect that by using roller-imprinting, PSS can be fabricated with lower cost and higher throughput. There are three main topics are researched and discussed: fabrication of a soft roller mold, roller-type UV imprint and roller-type reverse imprint. To begin with the fabrication of the roller mold, by electroplating and hot embossing, we can replicate the pattern from flat resist master to a flexible circular mold with high fidelity. Then a roller with PSS cavity made of PDMS is fabricated by casting from the circular mold.The roller is integrally molded with simple process, high fidelity and low-cost. The second, with the conformal contact of the soft roller, we successfully form micro-pillar array on sapphire substrates by roller-type UV-imprinting at high feeding speed 1.25mm/s. The height of pattern in terms of applied pressure, feeding velocity and initial photoresist thickness were investigated. In the best condition, the average height can reach 2.01μm and 95.2% fidelity. Lastly, to enhance the uniformity of pattern and reduce the residual layer thickness (RLT), we develop another roller-type reverse imprinting process by the same soft roller mold. The pattern is formed on almost whole the 2-inch sapphire substrate at 1.68mm/s feeding speed with high uniformity. The height, top diameter and period are 2.07μm, 1.69μm and 3μm, respectively. In this study, two processes have been successfully developed to form micro-pillar array for the PSS mask by UV roller-type imprinting. These roller-type methods can be easily implemented and fabricate PSSs at high feeding speed. Therefore, they have a great potential in fabricating larger size PSS with low cost and high throughput in the future.
Subjects
patterned sapphire substrate
nanoimprint lithography
reversal imprinting lithography
roller-type micro/nanoimprint lithography
hot embossing
Type
thesis
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