$C_{60}$ 얇은 결정의 결정구조에 관한 투과형전자현미경 연구

송세안,김성훈,서영덕,김성근,Song, Se-Ahn,Kim, Sung-Hoon,Suh, Young-Doug,Kim, Seong-Keun 한국현미경학회 1991 Applied microscopy Vol.21 No.2

[ $C_{60}$ ] molecule, the Buckminsterfullerene, has generated great interest because of its unique molecular structure and of superconductivity exhibited in its alkali-doped solids. We have investigated the molecular stacking and crystal structure of $C_{60}$ thin crystals formed on amorphous carbon film. The $C_{60}$ powder which was chromatographically purified was dissolved in benzene. The thin crystals of $C_{60}$ were observed with a 300 keV transmission electron microscope. Electron diffraction analysis and direct imaging of its molecular stacking were carried out. It was found from this work that the molecules of $10.0{\AA}$ diameter are arrayed hexagonally on substrate surface and $8.7{\AA}$ lattice planes are quite often found in several types of ED patterns, which can never be explained with a fcc model. Therefore the structure of $C_{60}$ thin crystals is hcp, although we cannot fully exclude the possibility of co-existence of hcp and fcc.

투과전자현미경 조사에 의한 사파이어 $({\alpha}-Al_2O_3)$합성 결정내의 결함특성 분석

김황수,송세안,Kim, Hwang-Su,Song, Se-Ahn 한국현미경학회 2006 Applied microscopy Vol.36 No.3

합성 사파이어 기판 시료-GaN반도체의 성장기판으로 사용된-의 내재하는 결함 형태를 전통적인 투과식 전자현미경 조사기법 (TEM), LACBED, HAADF-STEM 방법으로 관찰 분석하였다. 이 시료에서 주로 발견된 결함들은 두께 ${\sim}2nm$에서 32nm를 가진(0001)면 미소 쌍정(basal microtwins), 모체 결정과의 계면 주위의 변형 결함, (0001)면 전위결함(basal dislocations), 그리고 {$2\bar{1}\bar{1}3$} 피라미드 미끄럼면 중 한 면에서 일어나는 복잡한 형태의 전위 결함들이다 이들(0001)면 및 {$2\bar{1}\bar{1}3$}면에 전위 결함들은 미소 쌍정과 강하게 관련되어 일어나는 것으로 보인다. 또한 전위결함 밀도는 매우 균일하지 않으며 수 ${\mu}m$의 크기의 결함 밀집 영역에서는 그 밀도가 ${\sim}10^{10}/cm^2정도만큼 높지만 시료 전체에서의 평균은 대체적으로 ${\sim}10^5/cm^2보다 작다. 이 값은 보통 합성되는 결정에서 평균적으로 예상되는 수치이다. The defects in a synthesized crystal of ${\alpha}-Al_2O_3$ used as substrate for growing of semi-conductor materials such as GaN were examined by the conventional transmission electron microscopy (TEM), Large Angle CBED and High-Angle Annular Dark Field (HAADF) STEM methods. The dominant defects found in the specimen are basal microtwins with the thickness of ${\sim}2\;to\;32 nm$ and the associated strong strain field at the interface of microtwin/matrix, basal dislocations and complex dislocations in the one of {$2\bar{1}\bar{1}3$} pyramidal slip plane. All these basal and pyramidal dislocations seem to be strong related to basal microtwins. It was also found that the density of defects is very uneven. In the certain area with the dimension of a few fm, the dislocation density is quite high as an order of ${/sim}10^{10}/cm^2, but the average density is roughly estimated to be less than ${\sim}10^5/cm^2, as is usually expected in general synthesized crystals.

마이크로파 플라즈마 화학기상증착법(PECVD)과 저압 화학기상증착법(LPCVD)을 이용한 실리콘 기판 위에서의 텅스텐 박막증착

김성훈(Sung Hoon Kim),송세안(Se Ahn Song),김성근(Seong Keun Kim) 한국진공학회(ASCT) 1992 Applied Science and Convergence Technology Vol.1 No.2

플라즈마 화학기상증착법과 저압 화학기상증착법을 사용하여 실리콘 기판 위에 텅스텐 박막을 증착하였다. 반응기체로 WF_6를 사용하였으며 환원기체로는 SiH₄를 사용하였다. 플라즈마 증착법에 의한 텅스텐 박막의 성장은 환원기체의 유무에 상관없이 주로 기상 반응에 의한 텅스텐 덩어리들의 증착에 의하여 이루어졌으며 비교적 균일도가 낮은 박막표면을 이루었다. 저압 화학증착법의 경우 환원기체를 사용하지 않았을 때에는 실리콘 기판에 의한 제한된 환원반응에 의해 텅스텐이 증착되었으나, 환원기체를 사용했을 때에는 초기의 실리콘 기판에 의한 환원반응과 이어 일어나는 SiH₄ 기체와의 불균일계 환원반응의 두 단계반응에 의하여 텅스텐 박막 증착이 이루어졌다. 저압 화학증착법의 경우 텅스텐 박막의 특성은 플라즈마 증착법에서 보다 우수하였으며 박막 성장은 island by island 양식을 따르는 것으로 추정되었다. 박막은 α-W의 체심입방 구조로 이루어졌으며 박막이 성장함에 따라 단결정 구조가 증가하였다. Tungsten films were deposited on silicon surfaces by Plasma Enhanced Chemical Vapor Deposition (PECVD) and Low Pressure Chemical Vapor Deposition (LPCVD) techniques. WF_6 was used as source gas along with SiH₄, as reducing gas. In PECVD, the films were grown by the deposition of tungsten grains produced in homogeneous reactions, irrespective of the presence of reducing gas. PECVD produced films of relatively low uniformity. In LPCVD, tungsten was deposited by limited reduction reaction by silicon substrate in the absence of reducing gas. With the reducing gas, however, the films were deposited by a two-step process: initial reduction reaction by silicon substrate and subsequent heterogeneous reduction reaction by SiH₄. Films of higher quality were obtained from LPCVD than from PECVD. The film growth mode was expected to be Volmer-Weber type (island-by-island mode), which eventually resulted in an α-W bcc structure.

Deposition Mechanism of Tungsten thin Film in LPCVD System

김성훈(Sung Hoon Kim),송세안(Se Ahn Song) 한국진공학회(ASCT) 1993 Applied Science and Convergence Technology Vol.2 No.3

텅스텐 박막 증착의 메카니즘을 밝히기 위하여 먼저 SiH₄와 WF_6의 열분해 반응에 관한 열역학적 결과들과 표면 촉매 반응에 대한 이론적인 결과들을 고찰하였다. 실험적으론 저압 화학기상 증착법을 이용하여 WF_6를 SiH₄로 환원시켜 텅스텐 박막을 Si(100) 기판위에 증착하였으며 증착 반응 중의 기판 표면의 변화를 in-situ로 측정하였다. 증착 메카니즘을 밝히기 위하여 반응기체를 WF_6, SiH₄, WF_6+ SiH₄, WF_6 → SiH₄ → WF_6+SiH₄로 달리하여 반응시켰으며 그 때의 박막 특성과 표면 및 단면 형상을 측정하였다. 이론적인 고찰과 실험적인 결과들로부터 텅스텐 박막은 먼저 Si기판에 의한 WF_6의 환원반응으로 인한 증착과 이어서 SiH₄에 의한 WF_6의 환원으로 증착됨을 밝혔다. As a first step to determine the deposition mechanism of tungsten thin film, we investigated the thermodynamics of SiH₄ and WF_6 thermal decomposition and the surface catalysis reaction. In experiment We deposited tungsten thin film on Si(100) substrate by using the LPCVD (low pressure chemical vapor deposition) technique. WF_6 was used as a source gas for tungsten and SiH₄ was used as a reducing gas for WF_6. Reduction of WF_6 by both Si substrate and SiH₄ was investigated. During the reaction, we monitored the variation of thin film surface. We also analyzed thin film morphology. From the theoretical considerations and obtained experimental results, we concluded that tungsten was deposited by Si substrate reduction of WF_6 and the subsequent SiH₄ reduction of WF_6.

ULSI용 Electroplating Cu 박막의 미세조직 연구

박윤창(Yun-Chang Park),송세안(Se Ahn Song),윤중림(Jung-Lim Yoon),김영욱(Young-Wug Kim) 한국진공학회(ASCT) 2000 Applied Science and Convergence Technology Vol.9 No.3

electroplating(EP)법을 이용하여 ULSI용 Cu 박막을 제조하였다. seed Cu는 sputtering으로 증착 하였으며, 확산방지막으로 TaN를 사용하였다. 제작된 EP Cu 박막은 seed Cu의 영향으로 열처리 조건에 관계없이 Cu(111) 방향으로 강하게 우선 배향 하였다. 열처리 온도와 시간이 증가함에 따라 Cu 박막의 미세조직이 non-columnar structure에서 약 2배 이상 결정립 성장하여 columnar structure로 바뀌었으며, 또한 as-deposit시 관찰되었던 stacking fault, twin, dislocation 들이 상당히 줄어드는 것이 관찰되었다. Cu의 확산에 의하여 생기는 copper-silicide는 관찰할 수 없었으며, 이것은 두께 45㎚의 TaN막이 450℃, 30분 열처리시 확산방지막으로 충분한 역할을 한 것으로 판단된다. Cu(111) 우선 배향과 열처리에 의한 결정립 성장 및 defect 감소는 Cu 박막의 결정립계에서 발생하는 electromigration 현상을 상당히 줄일 수 있을 것으로 판단된다. Electroplating Cu was deposited on Si(100) wafer after seed Cu was deposited by sputtering first. TaN was deposited as a diffusion barrier before depositing the seed Cu. Electroplating Cu thin films show highly (111)-oriented microstructure for both before and after annealing at 450℃ for 30min and no copper silicide was detected in the same samples, which indicates that TaN barrier layer blocks well the Cu diffusion into silicon substrate. After annealing the electroplating Cu film up to 450℃, the Cu film became columnar from non-columnar, its grain size became larger about two times, and also defects density of stacking faults, twins and dislocations decreased greatly. Thus the heat treatment will improve significantly electromigration property caused by the grain boundary in the Cu thin films.

초고진공 전자 사이클로트론 화학 기상 증착 장치에 의한 저온 실리콘 에피 성장에 기판 DC 바이어스가 미치는 영향

태흥식(Heung-Sik Tae),황석희(Seok-Hee Hwang),박상준(Sang-June Park),윤의준(Euijoon Joon),황기웅(Ki-Woong Whang),송세안(Se Ahn Song) 한국진공학회(ASCT) 1993 Applied Science and Convergence Technology Vol.2 No.4

Langmuir probe를 사용하여 UHV-ECRCVD 장치에서 기판에 가해진 DC 바이어스에 따른 플라즈마내의 공간적 전위 분포를 측정하였다. 양의 바이어스를 기판에 가하는 경우 플라즈마내의 공간적 전위 분포는 B-field를 따라 cavity로부터 기판으로 down-stream되는 이온의 flux 및 에너지를 감소시키는 오르막의 전위 분포를 갖게 되며 음의 바이어스를 가하는 경우는 down-stream되는 이온의 flux 및 에너지를 증가시키는 내리막의 전위 분포를 갖게 된다. DC 바이어스가 저온 실리콘 에피탁시(560℃ 이하)에 미치는 영향을 in situ reflection high energy electron diffraction(RHEED), cross-section transmission electron microscopy(XTEM), plan-view TEM 및 high resolution TEM(HRTEM)으로 고찰하였다. 음의 바이어스를 가한 기판에는 다결정 실리콘이 성장되고 양의 바이어스를 가한 기판에는 단결정 실리콘이 성장되며 다결정 실리콘의 성장 속도보다 단결정 실리콘의 성장속도가 낮은 것으로 관찰되었다. 플라즈마 증착 중 DC 바이어스에 의한 이온 에너지의 조절은 UHV-ECRCVD에 의한 저온 실리콘 에피탁시에 있어서 중요한 역할을 한다. The spatial potential distribution of electron cyclotron resonance plasma is measured as a function of the substrate DC bias by Langmuir probe method. It is observed that the substrate DC bias changes the slope of the plasma potential near the substrate, resulting in changes in flux and energy of the impinging ions across plasma/substrate boundary along the magnetic field. The effect of the substrate DC bias on the low-temperature silicon homoepitaxy (below 560℃) is examined by in situ reflection high energy electron diffraction (RHEED), cross-section transmission electron microscopy (XTEM), plan-view TEM and high resolution transmission electron microscopy (HRTEM). While the polycrystalline silicon layers are grown with negative substrate biases, the single crystalline silicon layers are grown with positive subatrate biases. As the substrate bias changes from negative to positive values, the growth rate decreases. It is concluded that the control of the ion energy during plasma deposition is very important in silicon epitaxy at low temperatures below 560℃ by UHV-ECRCVD.

Fe-25Cr-14Co-2Si-1.5 Ti 합금의 자기적 특성에 미치는 열처리 효과

김택기,김윤배,송세안 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.4

To study the effect s of heat treatment on the magnetic properties of ductile Fe-Cr-Co permanent magnets, a composition of Fe-25Cr-l4Co-2Si-1.5Ti alloy was prepared by induction melting, and the optimum heat treatment procedure and the microstructures of the alloy were investigated. After step aging treatments, it was concluded that aging at high temperature effects largely on the squareness of the demagnetization currve and aging at low temperature effects largely on the coercive force. The sample which was thermomagnetically treated for 10 minutes at 675℃ showed clearly the evidence of spinodal decomposition of the FeCo-rich phases from the Cr-rich matrix.

Alnico 5 의 열처리에 따른 2 상분리조직과 자기특성

김택기,김윤배,송세안,임동묵 대한금속재료학회(대한금속학회) 1986 대한금속·재료학회지 Vol.24 No.5

In order to study a relation between microstructures and magnetic properties in Alnico 5, Fe-24Co-14Ni-8Al-3Cu alloy was prepared by induction melting, and then optimum heat treatment procedures and microstructures of this alloy were investigated systematically. In Alnico 5, the cooling rate(c) in a magnetic field from 900℃ to 600℃ and the optimum aging time(t) at 600℃ have a relation of log(t)=0.417 log(c) + 0.884. However, the final magnetic properties are highly dependent on the cooling rate. Spinodally decomposed structures of this alloy show that the faster the cooling rate, the smaller the size of the FeCo-rich precipitates and the larger the aspect ratio. Length of the long axis of the FeCo-rich precipitates at a given cooling rate is not uniform due to the interconnection of sub sequent precipitates by magnetic field effect, and this tendency seems to be stronger when the cooling rate is slower. But the length of the short axis of the precipitates is almost same at a given cooling rate. The length of the short axis (ℓ) and cooling rate (c) in magnetic field have a relation of log (ℓ)=2.385-0.317 log(c) Optimum solution treatment temperature of the low temperature solution treatment method is 860℃. It is concluded that the low temperature solution treatment method is more desirable than the high temperature solution treatment method in improving the hard magnetic properties