| Summary: | 博士 === 國立成功大學 === 材料科學及工程學系 === 102 === This dissertation has successfully demonstrated two different types of soft lithography techniques to fabrication pattern sapphire substrate (PSS), namely “metal embedded lithography” and “soft photo-mask contact lithography”. The metal embedded lithography is a novel nano/micro fabrication process combining nano-imprinting and photolithography. This method uses a metal transfer process to transfer the metal pattern defined by a soft mold to a PR layer deposited on a sapphire substrate surface. The transferred metal pattern will then act as a photo-mask for subsequent UV exposure. After development process, the PR microstructure is defined on the sapphire surface. This process inherits the advantages from metal contact transfer and photolithography, such as large patterning area, small line width, high throughput, and high aspect ratio.
The second proposed method is “soft photo-mask contact lithography”, which is based on traditional contact type photolithography process but using a soft photo-mask to replace the hard glass/quartz photo-mask. This soft photo-mask can overcome the non-flat surface problem of sapphire wafers and make a perfect contact with them for subsequent UV-light exposure. This process is especially suitable for PSS mass production since it can easily fabricate large-area pattern on non-flat sapphire wafers with high thought put and high reliability. Two different photo-masks have been proposed for their applications in soft photo-mask contact lithography, namely “PDMS/metal-film photo-mask” and “carbon-black/PDMS soft mask”. The PDMS/metal-film photo-mask is by using a metal evaporator system to deposit a metal film on a soft mold, and then removing part of the metal layer. The metal pattern defined by the mold's concave surface form a soft photo-mask. This process is becoming mature and stable, and ready for mass production test. The second type mask is the carbon-black/PDMS soft-mask. It is by using a carbon black PR to act as an opaque layer. The preparation of this carbon-black/PDMS soft-mask is based on spin-coating and contact transfer techniques, and has significantly simplified the fabrication process and reduced the cost.
In reviewing the progress of LED industry, 4” and 6” PSSs and sub-micrometer /nanometer scaled PSSs (NPSSs) are excepted to become the dominant products in the near future. However, projection type photolithography used in LED industry is not able to meet the challenges. In this dissertation, an automatically equipment based on the proposed soft photo-mask lithography is commercially built by a local equipment company, and is tested for mass production of 4 PSSs in a local epitaxy company. The test results show that there are still certain issues to be answered such as defect counts and lifetime of the soft photo-mask. However, outstanding performance on throughput, production stability, microstructures' homogeneousness, and large wafer size, ...etc. have shown great potential of this soft photo-mask contact lithography for the industrial mass production of 4” and 6” PSSs and NPSSs in the near future.
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