• 한국진공학회지
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• 제22권4호
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• pp.188-192
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• 2013

반도체 소자의 소형화, 고집적화로 박막의 다층화 및 선폭 감소로 인한 실리콘 웨이퍼와 금속 박막 사이의 확산을 방지하기 위한 많은 연구가 이루어지고 있다. 본 연구는 tungsten (W)을 주 물질로 증착시 nitrogen (N)의 유량을 2.5~10 sccm으로 변화시키며 증착된 확산방지막의 nano-mechanics 특성에 대해 연구하였다. 증착률, 비저항 및 결정학적 특성을 ${\beta}$-ray backscattering spectroscopy, 4-point probe, X-ray diffraction (XRD)을 이용하여 측정한 후 Nano-indenter를 사용하여 nano-mechanics 특성을 조사하였다. 그 결과 질소 가스 유량이 5 sccm 포함된 박막에서 표면 경도(surface hardness)는 10.07 에서 15.55 GPa로 급격하게 증가하였다. 이후 질소가스의 유량이 7.5 및 10 sccm에서는 표면 경도가 각각 12.65와 12.77 GPa로 질소 가스 유량이 5 sccm인 박막보다 표면경도가 상대적으로 감소하였다. 이는 박막 내 결정질과 비정질의 W과 N의 결합 비율의 차이에 의한 영향으로 생각되며, 또한 압축응력에 기인한 스트레스 증가가 원인으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제43회 하계 정기 학술대회 초록집
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• pp.154-155
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• 2012

The promise of nano-crystalites (nc) as a technological material, for applications including display backplane, and solar cells, may ultimately depend on tailoring their behavior through doping and crystallinity. Impurities can strongly modify electronic and optical properties of bulk and nc semiconductors. Highly doped dopant also effect structural properties (both grain size, crystal fraction) of nc-Si thin film. As discussed in several literatures, P atoms or radicals have the tendency to reside on the surface of nc. The P-radical segregation on the nano-grain surfaces that called self-purification may reduce the possibility of new nucleation because of the five-coordination of P. In addition, the P doping levels of ${\sim}2{\times}10^{21}\;at/cm^3$ is the solubility limitation of P in Si; the solubility of nc thin film should be smaller. Therefore, the non-activated P tends to segregate on the grain boundaries and the surface of nc. These mechanisms could prevent new nucleation on the existing grain surface. Therefore, most researches shown that highly doped nc-thin film by using conventional PECVD deposition system tended to have low crystallinity, where the formation energy of nucleation should be higher than the nc surface in the intrinsic materials. If the deposition technology that can make highly doped and simultaneously highly crystallized nc at low temperature, it can lead processes of next generation flexible devices. Recently, we are developing a novel CVD technology with a neutral particle beam (NPB) source, named as neutral beam assisted CVD (NBaCVD), which controls the energy of incident neutral particles in the range of 1~300eV in order to enhance the atomic activation and crystalline of thin films at low temperatures. During the formation of the nc-/pm-Si thin films by the NBaCVD with various process conditions, NPB energy directly controlled by the reflector bias and effectively increased crystal fraction (~80%) by uniformly distributed nc grains with 3~10 nm size. In the case of phosphorous doped Si thin films, the doping efficiency also increased as increasing the reflector bias (i.e. increasing NPB energy). At 330V of reflector bias, activation energy of the doped nc-Si thin film reduced as low as 0.001 eV. This means dopants are fully occupied as substitutional site, even though the Si thin film has nano-sized grain structure. And activated dopant concentration is recorded as high as up to 1020 #/$cm^3$ at very low process temperature (＜ $80^{\circ}C$) process without any post annealing. Theoretical solubility for the higher dopant concentration in Si thin film for order of 1020 #/$cm^3$ can be done only high temperature process or post annealing over $650^{\circ}C$. In general, as decreasing the grain size, the dopant binding energy increases as ratio of 1 of diameter of grain and the dopant hardly be activated. The highly doped nc-Si thin film by low-temperature NBaCVD process had smaller average grain size under 10 nm (measured by GIWAXS, GISAXS and TEM analysis), but achieved very higher activation of phosphorous dopant; NB energy sufficiently transports its energy to doping and crystallization even though without supplying additional thermal energy. TEM image shows that incubation layer does not formed between nc-Si film and SiO2 under later and highly crystallized nc-Si film is constructed with uniformly distributed nano-grains in polymorphous tissues. The nucleation should be start at the first layer on the SiO2 later, but it hardly growth to be cone-shaped micro-size grains. The nc-grain evenly embedded pm-Si thin film can be formatted by competition of the nucleation and the crystal growing, which depend on the NPB energies. In the evaluation of the light soaking degradation of photoconductivity, while conventional intrinsic and n-type doped a-Si thin films appeared typical degradation of photoconductivity, all of the nc-Si thin films processed by the NBaCVD show only a few % of degradation of it. From FTIR and RAMAN spectra, the energetic hydrogen NB atoms passivate nano-grain boundaries during the NBaCVD process because of the high diffusivity and chemical potential of hydrogen atoms.

• Advances in nano research
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• 제5권3호
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• pp.261-279
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• 2017

Spectroscopic investigation of Si quantum dots (Si-QDs) embedded in silicon nitride was performed over a broad stoichiometry range to optimize light emission. Plasma-enhanced chemical vapor deposition was used to grow the $SiN_x$ films on Si (001) substrates. The film composition was controlled via the flow ratio of silane ($SiH_4$) and ammonia ($NH_3$) in the range of R = 0.45-1.0 allowed to vary the Si excess in the range of 21-62 at.%. The films were submitted to annealing at $1100^{\circ}C$ for 30 min in nitrogen to form the Si-QDs. The properties of as-deposited and annealed films were investigated using spectroscopic ellipsometry, Fourier transform infrared spectroscopy, Raman scattering and photoluminescence (PL) methods. Si-QDs were detected in $SiN_x$ films demonstrating the increase of sizes with Si excess. The residual amorphous Si clusters were found to be present in the films grown with Si excess higher than 50 at.%. Multi-component PL spectra at 300 K in the range of 1.5-3.5 eV were detected and nonmonotonous varying total PL peak versus Si excess was revealed. To identify the different PL components, the temperature dependence of PL spectra was investigated in the range of 20-300 K. The analysis allowed concluding that the "blue-orange" emission is due to the radiative defects in a $SiN_x$ matrix, whereas the "red" and "infrared" PL bands are caused by the exciton recombination in crystalline Si-QDs and amorphous Si clusters. The nature of radiative and no radiative defects in $SiN_x$ films is discussed. The ways to control the dominant PL emission mechanisms are proposed.

• Advances in nano research
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• 제2권1호
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• pp.1-14
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• 2014

Dislocations are basic crystal defects and represent one-dimensional native nanostructures embedded in a perfect crystalline matrix. Their structure is predefined by crystal symmetry. Two-dimensional, self-organized arrays of such nanostructures are realized reproducibly using specific preparation conditions (semiconductor wafer direct bonding). This technique allows separating dislocations up to a few hundred nanometers which enables electrical measurements of only a few, or, in the ideal case, of an individual dislocation. Electrical properties of dislocations in silicon were measured using MOSFETs as test structures. It is shown that an increase of the drain current results for nMOSFETs which is caused by a high concentration of electrons on dislocations in p-type material. The number of electrons on a dislocation is estimated from device simulations. This leads to the conclusion that metallic-like conduction exists along dislocations in this material caused by a one-dimensional carrier confinement. On the other hand, measurements of pMOSFETs prepared in n-type silicon proved the dominant transport of holes along dislocations. The experimentally measured increase of the drain current, however, is here not only caused by an higher hole concentration on these defects but also by an increasing hole mobility along dislocations. All the data proved for the first time the ambipolar behavior of dislocations in silicon. Dislocations in p-type Si form efficient one-dimensional channels for electrons, while dislocations in n-type material cause one-dimensional channels for holes.

• 대한금속재료학회지
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• 제46권11호
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• pp.762-769
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• 2008

Hydrogenated amorphous silicon(a-Si : H) layers, 120 nm and 50 nm in thickness, were deposited on 200 $nm-SiO_2$/single-Si substrates by inductively coupled plasma chemical vapor deposition(ICP-CVD). Subsequently, 30 nm-Ni layers were deposited by E-beam evaporation. Finally, 30 nm-Ni/120 nm a-Si : H/200 $nm-SiO_2$/single-Si and 30 nm-Ni/50 nm a-Si:H/200 $nm-SiO_2$/single-Si were prepared. The prepared samples were annealed by rapid thermal annealing(RTA) from $200^{\circ}C$ to $500^{\circ}C$ in $50^{\circ}C$ increments for 30 minute. A four-point tester, high resolution X-ray diffraction(HRXRD), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and scanning probe microscopy(SPM) were used to examine the sheet resistance, phase transformation, in-plane microstructure, cross-sectional microstructure, and surface roughness, respectively. The nickel silicide on the 120 nm a-Si:H substrate showed high sheet resistance($470{\Omega}/{\Box}$) at T(temperature) < $450^{\circ}C$ and low sheet resistance ($70{\Omega}/{\Box}$) at T > $450^{\circ}C$. The high and low resistive regions contained ${\zeta}-Ni_2Si$ and NiSi, respectively. In case of microstructure showed mixed phase of nickel silicide and a-Si:H on the residual a-Si:H layer at T < $450^{\circ}C$ but no mixed phase and a residual a-Si:H layer at T > $450^{\circ}C$. The surface roughness matched the phase transformation according to the silicidation temperature. The nickel silicide on the 50 nm a-Si:H substrate had high sheet resistance(${\sim}1k{\Omega}/{\Box}$) at T < $400^{\circ}C$ and low sheet resistance ($100{\Omega}/{\Box}$) at T > $400^{\circ}C$. This was attributed to the formation of ${\delta}-Ni_2Si$ at T > $400^{\circ}C$ regardless of the siliciation temperature. An examination of the microstructure showed a region of nickel silicide at T < $400^{\circ}C$ that consisted of a mixed phase of nickel silicide and a-Si:H without a residual a-Si:H layer. The region at T > $400^{\circ}C$ showed crystalline nickel silicide without a mixed phase. The surface roughness remained constant regardless of the silicidation temperature. Our results suggest that a 50 nm a-Si:H nickel silicide layer is advantageous of the active layer of a thin film transistor(TFT) when applying a nano-thick layer with a constant sheet resistance, surface roughness, and ${\delta}-Ni_2Si$ temperatures > $400^{\circ}C$.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.41-41
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• 2003

비정질 실리콘 박막은 단결정 실리콘에 비해 저가이고 저온형성이 가능하여, 대면적/고효율의 실리콘 박막 태양전지 제작에 응용되고 있다. 태양전지에 적용하기 위해서는 우수한 암전류 및 광전류 특성을 나타내야 하고, 광학적 밴드 갭 특성 또한 중요하다. 본 연구에서는 HDP(High Density Plasma) PECVD 장비를 이용하여 나노결정립 및 비정질 실리콘 박막을 형성하고, 각 박막의 전기적, 광학적 특성을 측정, 평가하였다. 나노결정립 및 비정질 실리콘 박막의 전기적 특성은 Keithley 4200을 이용하여 암전류를 특성을 측정하였고, Solar Simulator를 이용하여 AM1.5, 100mW/$\textrm{cm}^2$ 조건에서 광전류 특성을 측정하였다. 또한, Spectrometer를 이용하여 박막의 투과율을 측정하여 Tauc Plot을 통해 광학적 밴드 갭을 계산하였다. 본 연구에서 형성된 비정질 실리콘 박막은 -$10^{6}$의 우수한 Photoresponse($\sigma$$_{ph}$ $\sigma$$_{d}$) 특성을 나타내었다. 또한, 비정질 실리콘 박막 내에 나노결정립이 형성됨에 따라 암전류는 증가하고, 광학적 밴드 갭도 증가하는 것을 알 수 있었다. 이렇게 밴드 갭이 증가된 나노결정립 실리콘 박막은 태양전지의 Window 층에 적용하면 효율 증가에 크게 기여할 것으로 판단된다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.306-306
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• 2010

A high density (> $10^{11}\;cm^{-3}$) and low electron temperature (< 2 eV) plasma is produced by using a conventional HF (13.56 MHz) plasma enhanced chemical vapor deposition (PECVD) with an additional ultra high frequency (UHF, 314 MHz) plasma source utilizing two parallel antenna assembly. It is applied for the high rate synthesis of high quality nanocrystalline silicon (nc-Si) films. A high deposition rate of 1.8 nm/s is achieved with a high crystallinity (< 70%), a low spin density (< $3{\times}10^{16}\;cm^{-3}$) and a high light soaking stability (< 1.5). Optical emission spectroscopy measurements reveal emission intensity of $Si^*$ and $SiH^*$, intensity ratio of $H{\alpha}/Si^*$ and $H{\alpha}/SiH^*$ which are closely related to film deposition rate and film crystallinity, respectively. A high flux of precursor and atomic hydrogen which are produced by an additional high excitation frequency is effective for the fast deposition of highly crystallized nc-Si films without additional defects.

• 한국해양공학회지
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• 제27권6호
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• pp.95-99
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• 2013

Lead zirconate titanate (PZT) thick films with a thickness of $10-20{\mu}m$ were fabricated on silicone substrates using an aerosol deposition method. The starting powder, which had diameters of $1-2{\mu}m$, was observed using SEM. The average diameter ($d_{50}$) was $1.1{\mu}m$. An XRD analysis showed a typical perovskite structure, a mixture of the tetragonal phase and rhombohedral phase. The as-deposited film with nano-sized grains had a fairly dense microstructure without any cracks. The deposited film showed a mixture of an amorphous phase and a very fine crystalline phase by diffraction pattern analysis using TEM. The as-deposited films on silicon were annealed at a temperature of $700^{\circ}C$. A 20-${\mu}m$ thick PZT film was torn out as a result of the high compressive stress between the PZT film and substrate.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2010년도 제39회 하계학술대회 초록집
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• pp.297-297
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• 2010

Precise control of the position and density of doping elements at the nanoscale is becoming a central issue for realizing state-of-the-art silicon-based optoelectronic devices. As dimensions are scaled down to take benefits from the quantum confinement effect, however, the presence of interfaces and the nature of materials adjacent to silicon turn out to be important and govern the physical properties. Utilization of visible light is a promising method to overcome the efficiency limit of the crystalline Si solar cells. Si quantum dots (QDs) have been proposed as an emission source of visible light, which is based on the quantum confinement effect. Light emission in the visible wavelength has been reported by controlling the size and density of Si QDs embedded within various types of insulating matrix. For the realization of all-Si QD solar cells with homojunctions, it is prerequisite not only to optimize the impurity doping for both p- and n-type Si QDs, but also to construct p-n homojunctions between them. In this study, XPS and SIMS were used for the development of p-type and n-type Si quantum dot solar cells. The stoichiometry of SiOx layers were controlled by in-situ XPS analysis and the concentration of B and P by SIMS for the activated doping in Si nano structures. Especially, it has been experimentally evidenced that boron atoms in silicon nanostructures confined in SiO2 matrix can segregate into the Si/$SiO_2$ interfaces and the Si bulk forming a distinct bimodal spatial distribution. By performing quantitative analysis and theoretical modelling, it has been found that boron incorporated into the four-fold Si crystal lattice can have electrical activity. Based on these findings, p-type Si quantum dot solar cell with the energy-conversion efficiency of 10.2% was realized from a [B-doped $SiO_{1.2}$(2 nm)/$SiO_2(2\;nm)]^{25}$ superlattice film with a B doping level of $4.0{\times}10^{20}\;atoms/cm^2$.

• 한국재료학회지
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• 제24권8호
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• pp.434-442
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• 2014

Serious environmental problems have been caused by the greenhouse effect due to carbon dioxide($CO_2$) or nitrogen oxides($NO_x$) generated by the use of fossil fuels, including oil and liquefied natural gas. Many countries, including our own, the United States, those of the European Union and other developed countries around the world; have shown growing interest in clean energy, and have been concentrating on the development of new energy-saving materials and devices. Typical non-fossil-fuel sources include solar cells, wind power, tidal power, nuclear power, and fuel cells. In particular, organic solar cells(OSCs) have relatively low power-conversion efficiency(PCE) in comparison with inorganic(silicon) based solar cells, compound semiconductor solar cells and the CIGS [$Cu(In_{1-x}Ga_x)Se_2$] thin film solar cells. Recently, organic cell efficiencies greater than 10 % have been obtained by means of the development of new organic semiconducting materials, which feature improvements in crystalline properties, as well as in the quantum-dot nano-structure of the active layers. In this paper, a brief overview of solar cells in general is presented. In particular, the current development status of the next-generation OSCs including their operation principle, device-manufacturing processes, and improvements in the PCE are described.