• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.281-281
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• 2010

Very low refractive index (<1.4) materials have been proved to be the key factor improving the performance of various optical components, such as reflectors, filters, photonic crystals, LEDs, and solar cell. Highly porous SiO2 are logically designed for ultralow refractive index materials because of the direct relation between porosity and index of refraction. Among them, ordered macroporous SiO2 is of potential material since their theoretically low refractive index ~1.10. However, in the conventional synthesis of ordered macroporous SiO2, the time required for the crystallization of organic nanoparticles, such as polystyrene (PS), from colloidal solution into well ordered template is typical long (several days for 1 cm substrate) due to the low interaction between particles and particle - substrate. In this study, polystyrene - polyacrylic acid (PS-AA) nanoparticles synthesized by miniemulsion polymerization method have hydrophilic polyacrylic acid tails on the surface of particles which increase the interaction between particle and with substrate giving rise to the formation of PS-AA film by simply spin - coating method. Less ordered with controlled thickness films of PS-AA on silicon wafer were successfully fabricated by changing the spinning speed or concentration of colloidal solution, as confirmed by FE-SEM. Based on these template films, a series of macroporous SiO2 films whose thicknesses varied from 300nm to ~1000nm were fabricated either by conventional sol - gel infiltration or gas phase deposition followed by thermal removal of organic template. Formations of SiO2 films consist of interconnected air balls with size ~100 nm were confirmed by FE-SEM and TEM. These highly porous SiO2 show very low refractive indices (<1.18) over a wide range of wavelength (from 200 to 1000nm) as shown by SE measurement. Refraction indices of SiO2 films at 633nm reported here are of ~1.10 which, to our best knowledge, are among the lowest values having been announced.

• Korean Chemical Engineering Research
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• 제46권1호
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• pp.1-6
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• 2008

블록공중합체(block copolymer)는 각 고분자 블록의 상대적인 조성비와 분자량에 따라 구, 실린더, 라멜라 등의 다양한 자기조립 나노구조를 형성하는 것으로 알려져 있다. 최근에는 블록공중합체의 자기조립 나노구조를 이용하여 나노복합재료, 포토닉 크리스탈, 나노선, 자기저장매체, 플래시 메모리 소자 등에 적용하려는 연구들이 활발히 진행되고 있다. 그러나 자연적으로 형성되는 블록공중합체 나노구조는 수많은 결함구조들을 포함하고 있어 실제 소자 적용에 큰 걸림돌이 되고 있다. 블록공중합체 나노구조의 실제적인 응용을 위해서는 박막상태의 시료 내에서 나노구조의 배향과 배열을 원하는 형태로 조절할 수 있는 공정의 확립이 선행되어야 한다. 즉, 블록공중합체의 자기조립을 나노기술분야에 적용하기 위해서는 대면적으로 완벽히 제어된 블록공중합체 나노구조를 구현하는 것이 필요하다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.526-528
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• 2005

파장 분할 다중화 방식 (WDM)의 광통신은 중앙 기지국에서 각 가입자에게 서로 다른 파장을 할당하여 동시에 데이터를 전송하는 방식으로서 각 가입자는 할당된 파장을 이용하여 항상 데이터를 송/수신할 수 있고 각 가입자에게 대용량의 데이터를 전송할 수 있을 뿐만 아니라 통신의 보안성이 뛰어나고 성능 향상이 용이하다 따라서 상, 하향(양방향, bidirectional) 3 파장 WDM-필터 소자(Flat band-path filter)는 광 가입자망 구축에서 통신 방송을 융합한 양방향 고화질 멀티미디어 서비스 사업에 반드시 필요로 하는 원천 부품이다. 본 연구에서는 1차원 광자결정을 이용한 저 손실 양방향 3 파장 WDM-필터를 얻을 수 있는 이론적 모델을 설계하고 그에 따라 2-cavity $Ta_2O_5/SiO_2$ 1차원 광자결정체를 제작하고 그 특성을 고찰 하였다. 파장에 따른 투과도 측정 결과 1550nm파장에서 투과되고 1310nm 및 1490nm파장에 대한 차단이 이론값과 일치하였다. 1550nm 파장 대에서 손실이 매우 낮은 flat-투과 밴드가 생성되었다. 특히 입사각도에 따라 flat-band 중심 파장의 변화를 이용하므로 새로운 개념의 WDM 소자로의 응용이 가능하다.

• Korean Chemical Engineering Research
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• 제45권2호
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• pp.149-154
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• 2007

나노임프린트 공정기술은 나노구조물이 패턴된 스템프(혹은 몰드)를 이용하여 적절한 기판 위에 나노구조물을 복제하여 패턴을 전사하는 기술이다. 효과적인 나노임프린트 공정을 위해서는 몰드의 이형처리뿐 아니라 반대쪽의 기질과 레지스트 사이에 접착력 증가(adhesion promoter) 처리가 매우 중요한 역할을 한다. 본 연구에서는 자기조립 실란커플링제의 기상증착을 이용하여 나노임프린트 공정에서 사용되는 접착 증가막 및 표면처리 방법을 비교 분석 하였다. 이를 위해서 평탄화층(DUV-30J), 산소 플라즈마 처리, 실란커플링제 자기조립막이 비교되었다. 실란커플링제 자기조립막이 형성된 실리콘 표면은 전체적으로 나노 두께의 균일한 막이 형성되며 임프린트시 구조물들을 정밀하게 전사하였으며 3-acryloxypropyl methyl dichlorosilane(APMDS)을 이용한 자기조립막(SAMs) 처리가 평탄화층과 산소 플라즈마 처리보다 강한 접착력을 가지고 있어 나노임프린트 공정에 적합함을 알 수 있었다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.418-418
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• 2008

The electrochemical etching of silicon in HF-based solutions is known to form various types of porous structures. Porous structures are generally classified into three categories according to pore sizes: micropore (below 2 nm in size), mesopore (2 ~ 50 nm), and macropore (above 50 nm). Recently, the formation of macropores has attracted increasing interest because of their promising characteristics for an wide scope of applications such as microelectromechanical systems (MEMS), chemical sensors, biotechnology, photonic crystals, and photovoltaic application. One of the promising applications of macropores is in the field of MEMS. Anisotropic etching is essential step for fabrication of MEMS. Conventional wet etching has advantages such as low processing cost and high throughput, but it is unsuitable to fabricate high-aspect-ratio structures with vertical sidewalls due to its inherent etching characteristics along certain crystal orientations. Reactive ion dry etching is another technique of anisotropic etching. This has excellent ability to fabricate high-aspect-ratio structures with vertical sidewalls and high accuracy. However, its high processing cost is one of the bottlenecks for widely successful commercialization of MEMS. In contrast, by using electrochemical etching method together with pre-patterning by lithographic step, regular macropore arrays with very high-aspect-ratio up to 250 can be obtained. The formed macropores have very smooth surface and side, unlike deep reactive ion etching where surfaces are damaged and wavy. Especially, to make vertical microwire or nanowire arrays (aspect ratio = over 1:100) on silicon wafer with top-down photolithography, it is very difficult to fabricate them with conventional dry etching. The electrochemical etching is the most proper candidate to do it. The pillar structures are demonstrated for n-type silicon and the formation mechanism is well explained, while such a experimental results are few for p-type silicon. In this report, In order to understand the roles played by the kinds of etching solution and mask patterns in the formation of microwire arrays, we have undertaken a systematic study of the solvent effects in mixtures of HF, dimethyl sulfoxide (DMSO), iso-propanol, and mixtures of HF with water on the structure formation on monocrystalline p-type silicon with a resistivity with 10 ~ 20 $\Omega{\cdot}cm$. The different morphological results are presented according to mask patterns and etching solutions.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 하계학술대회 논문집 Vol.9
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• pp.241-241
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• 2008

Macrofore formation in silicon and other semiconductors using electrochemical etching processes has been, in the last years, a subject of great attention of both theory and practice. Its first reason of concern is new areas of macropore silicone applications arising from microelectromechanical systems processing (MEMS), membrane techniques, solar cells, sensors, photonic crystals, and new technologies like a silicon-on-nothing (SON) technology. Its formation mechanism with a rich variety of controllable microstructures and their many potential applications have been studied extensively recently. Porous silicon is formed by anodic etching of crystalline silicon in hydrofluoric acid. During the etching process holes are required to enable the dissolution of the silicon anode. For p-type silicon, holes are the majority charge carriers, therefore porous silicon can be formed under the action of a positive bias on the silicon anode. For n-type silicon, holes to dissolve silicon is supplied by illuminating n-type silicon with above-band-gap light which allows sufficient generation of holes. To make a desired three-dimensional nano- or micro-structures, pre-structuring the masked surface in KOH solution to form a periodic array of etch pits before electrochemical etching. Due to enhanced electric field, the holes are efficiently collected at the pore tips for etching. The depletion of holes in the space charge region prevents silicon dissolution at the sidewalls, enabling anisotropic etching for the trenches. This is correct theoretical explanation for n-type Si etching. However, there are a few experimental repors in p-type silicon, while a number of theoretical models have been worked out to explain experimental dependence observed. To perform ordered macrofore formaion for p-type silicon, various kinds of mask patterns to make initial KOH etch pits were used. In order to understand the roles played by the kinds of etching solution in the formation of pillar arrays, we have undertaken a systematic study of the solvent effects in mixtures of HF, N-dimethylformamide (DMF), iso-propanol, and mixtures of HF with water on the macrofore structure formation on monocrystalline p-type silicon with a resistivity varying between 10 ~ 0.01 $\Omega$ cm. The etching solution including the iso-propanol produced a best three dimensional pillar structures. The experimental results are discussed on the base of Lehmann's comprehensive model based on SCR width.