**4. Conclusion**

We repaired NIL molds by FIB etching and CVD. In the case of a T-NIL mold, we used phenanthrene as a source gas to repair the hollow-defect by FIB-CVD. The deposited material was DLC containing gallium. However, the gallium evaporation from DLC did not occur during T-NIL because gallium's evaporation temperature is about 500 C. The protrusion- and hollow-defective SiO2/Si molds were successfully repaired by FIB etching and CVD and the lines were clearly imprinted by T-NIL using the repaired mold.

In UV-NIL, UV-curable resin is irradiated by UV through a UV-NIL mold. This means that phenanthrene cannot be used as a source gas in FIB-CVD because the deposited DLC is not transparent. We therefore used SiOx material deposited by FIB-CVD using tetraethoxysilane as the source gas. We measured the transmittance and hardness of the SiOx film deposited by FIB-CVD, and results demonstrated that the deposited SiOx material has sufficient transmittance and hardness to perform UV-NIL.

To repair the defective UV-NIL mold, we must consider the effect of electrical charge because the material of UV-NIL molds is usually quartz. We proposed the use of an antistatic agent to prevent electrical charge because the antistatic agent can be spin-coated on the UV-NIL mold and is easy to wash away with water after the repair. However, failure to use an optimum beam current in FIB-CVD resulted in the fabrication of thorns. This highlights the need for an optimum beam current if we want to achieve hollow defect repair by FIB-CVD.

We repaired the defective quartz mold by FIB etching and CVD and performed UV-NIL using the repaired mold. The repaired lines were clearly imprinted on the resin. Results demonstrated that the deposited SiOx material has a sufficient durability for repeated UV-NIL. In this work, we used gallium-FIB to repair the NIL molds. Recently, helium ion microscopy (HIM) with a subnanometer probe size has become commercially available. Apart from the obvious advantage of small probe sizes, HIM also boasts a narrow interaction volume in the substrate and the predominance of secondary electron emission. A helium ion microscope can also be used for nanofabrication. We expect the mold repair resolution to dramatically improve by using HIM.

## **5. References**

168 Recent Advances in Nanofabrication Techniques and Applications

The durability of a repaired mold is crucial for applying UV-NIL to mass production. Therefore, we tested the durability of the SiOx material deposited by FIB-CVD by observing over 200 repeated uses of the mold repaired by FIB-CVD. Figure 16(a) and (b) shows the SEM images of the 100th and 200th imprinted pattern. After nanoimprintings, the pattern was still clearly imprinted on the resin. This result indicates that the deposited SiOx material

(a) (b) Fig. 16. SEM images of (a) 100th and (b) 200th imprinted patterns on PAK-01 formed by UV-

We repaired NIL molds by FIB etching and CVD. In the case of a T-NIL mold, we used phenanthrene as a source gas to repair the hollow-defect by FIB-CVD. The deposited material was DLC containing gallium. However, the gallium evaporation from DLC did not occur during T-NIL because gallium's evaporation temperature is about 500 C. The protrusion- and hollow-defective SiO2/Si molds were successfully repaired by FIB etching

In UV-NIL, UV-curable resin is irradiated by UV through a UV-NIL mold. This means that phenanthrene cannot be used as a source gas in FIB-CVD because the deposited DLC is not transparent. We therefore used SiOx material deposited by FIB-CVD using tetraethoxysilane as the source gas. We measured the transmittance and hardness of the SiOx film deposited by FIB-CVD, and results demonstrated that the deposited SiOx material has sufficient

To repair the defective UV-NIL mold, we must consider the effect of electrical charge because the material of UV-NIL molds is usually quartz. We proposed the use of an antistatic agent to prevent electrical charge because the antistatic agent can be spin-coated on the UV-NIL mold and is easy to wash away with water after the repair. However, failure to use an optimum beam current in FIB-CVD resulted in the fabrication of thorns. This highlights the need for an

We repaired the defective quartz mold by FIB etching and CVD and performed UV-NIL using the repaired mold. The repaired lines were clearly imprinted on the resin. Results demonstrated that the deposited SiOx material has a sufficient durability for repeated UV-NIL.

and CVD and the lines were clearly imprinted by T-NIL using the repaired mold.

optimum beam current if we want to achieve hollow defect repair by FIB-CVD.

500 nm 500 nm

has sufficient durability for repeated UV-NIL.

NIL using quartz mold repaired by FIB-CVD.

transmittance and hardness to perform UV-NIL.

**4. Conclusion** 


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**9** 

**Improving the Light-Emitting Efficiency of GaN** 

A light-emitting diode (LED) is an electroluminescent device with a broad selection of emission wavelengths (colors). The unique properties of LEDs, such as compactness, low power consumption, long lifetime, and fast turn-on time have made LEDs an indispensable component in modern traffic lighting, display, car lighting, and cell phones applications. In recent years, LED usage has grown more rapidly due to the application of backlights in large-size flat panel displays, a market previously dominated by CCFL. In addition, wide speculation foresees that the next boom for LEDs could arise from the interior/exterior lighting market. As shown in U.S. energy consumption statistics conducted by the U.S. government, the energy consumption for interior/exterior lighting occupies 22%~25% of the total electrical energy produced in the U.S. Using LEDs to replace all traditional interior/exterior lighting used today can save at least an estimated amount of 20 billion U.S. dollars in annual energy costs while also significantly reducing carbon emission. Therefore, LEDs have attracted a large amount of investments from corporations in Asia, North America, and Europe, aiming to develop reliable processes to improve the production yield

The nanoimprint lithography is a nanoscale structural formation technique with highly reproducible patterns, and is therefore suitable for LED fabrication. The typical length scale of structures for applications of LEDs ranges from a few hundred nanometers to a few micrometers, which is roughly on par with the resolution limit of the traditional optical lithography technology. Though a higher resolution is attainable using the stepper projection lithography method, the corresponding higher process cost renders the fabricated LEDs less economical. Unlike the integrated circuit, the micro- and nanostructures of an LED are often simple 2D periodic patterns. Once an imprinting mold with a high accuracy and precision is made from techniques such as the stepper projection lithography (or alternatively the electron beam, the ion beam, and the interference lithography), the LED patterns can be massively reproduced. This article discusses the role of the precision

**2. Limits and enhancements of the light-extraction efficiency of GaN LEDs** 

No single semiconductor material alone is capable of emitting white light. A white light LED typically consists of an appropriate mixture of (a) red, blue, and green LEDs, or (b) blue

nanoimprint lithography for improving the optical efficiency of LEDs.

**1. Introduction** 

and optical efficiency of LEDs.

**LEDs Using Nanoimprint Lithography** 

*1Department of Mechanical Engineering, Chung Yuan Christian University* 

Yeeu-Chang Lee1 and Sheng-Han Tu2

*2Genesis Photonics Inc.* 

*Taiwan* 

