• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.11
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• pp.1464-1469
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• 2000

The effects of SiCl$_4$addition on flame structures have been studied in flame hydrolysis deposition (FHD) processes using Coherent anti-Stokes Raman spectroscopy (CARS) and planar laser induced fluorescence (PLIF) to measure temperatures and OH concentrations, respectively. The results demonstrate that even a small amount of SiCl$_4$ addition can change thermal and chemical structures of H$_2$/O$_2$ diffusion flames. When SiCl$_4$ is added to a flame temperature decreases in non-reacting zone due to the increases in both specific heat and density of the gas mixture, while flame temperature increase in particle formation zone due to the heat release through hydrolysis and oxidation reactions of SiCl$_4$. It is also found that OH concentration decreases dramatically in particle formation zone where temperatures increase. This can be attributed to consumption of oxidative species and generation of HCl during silica formation.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.428-433
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• 2000

The consolidation behavior of multicomponent particles prepared by the flame hydrolysis deposition process is examined to identify the effects of Si substrate temperature. To fabricate multi-component particles, a vapor-phase ternary mixture of $SiCl_4(100 cc/min),\;BCl_3(30cc/min)\;and\;POCl_3,(5cc/min)$ was fed into a coflow diffusion oxy-hydrogen flame burner. The doped silica soot bodies were deposited on silicon substrates under various deposition conditions. The surface temperature of the substrate was measured by an infrared thermometer. Changes in the chemical states of the doped silica soot bodies were examined by FT-IR(Fourier-transformed infrared spectroscopy). The deposited particles on the substrate were heated at $1300^{\circ}C$ for 3h in a furnace at a heating rate of 10K/min. Si-O-B bending peak has been found when surface temperature exceeds $720^{\circ}C$. Correspondingly, the case with substrate temperatures above loot produced good consolidation result.

• Journal of the Korean Ceramic Society
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• v.38 no.1
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• pp.74-83
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• 2001

FHD(Flame Hydrolysis Deposition) 공정은 광통신에서 사용되는 수동형 집적광학소자를 제작하는 공정으로서, SiCl$_4$를 형성하는 방법이다. 이 FHD 공정은 화염 형성에 관여하는 장비의 조건에 따른 매우 다양한 공정인자에 의하여 박막의 조성이 결정되므로, 박막의 조성을 예측하는 것이 용이하지 않았다. 본 연구에서는 FHD 공정에서 첨가가스의 유량을 제어하여 박막의 조성 및 광학적 특성을 예측할 수 있는 공정 분석의 기초자료를 제공하기 위하여 FTIR과 ICP-AES를 이용하여 실리카 soot의 조성분석에 대한 연구를 수행하였다. FTIR 흡수스펙트럼을 통해 실리카 soot에 존재하는 Si-O, B-O, OH($H_2O$) 농도의 변화를 관찰할 수 있었으며, ICP-AES를 통해 B-O의 흡수스펙트럼의 변화를 B의 농도와 정량적으로 연관지을 수 있었다.

• Journal of the Korean Ceramic Society
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• v.37 no.6
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• pp.524-529
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• 2000

Silica slab wavegudie was fabricated on Si substrates by FHD for planar optical passive devices. The slab waveguide consists of lower clad and core layers, where core layer index is controlled by GeO2 addition. Doping of GeO2 in silica is difficult because of the low deposition density due to nonspherical particle generation in FHD process. Silica core particles deposited at various conditions such as flame temperature and substrate scanning were analyzed by SEM and TEM. As the flame temperature increased, the surface roughness of the core layer was decreased up to 3.6 nm after consolidation. Index difference and thickness of core of slab waveguide were 0.3%, 8$\mu\textrm{m}$ respectively. Measured optical loss at TE mode was <0.04 dB/cm at 1.3$\mu\textrm{m}$ and <0.06 dB/cm at 1.55$\mu\textrm{m}$.

• Journal of the Korean Ceramic Society
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• v.35 no.4
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• pp.364-370
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• 1998

Boron-phoshor-silicate glass was fabricated on Si substrates by FHD(Flame Hydrolysis Deposition) The microstructrue of silica soot deposited at various conditon such as composition and substrate temperature was analysed by SEM. After consolidation the refractive index and composition of the silica layer were in-vestigated. For refractive index control B, P and Ge were used as additive elements while B and Ge oxides are easily mixed into $SiO_2$, P oxide($B_2O_3$) doping is difficult because of the volatile property due to low melt-ing point. Boron-phosphorous-silicate glass (BPSG) layer were fabricated using bertical torch and optimized flame temperature substrate temperature and distance of torch and substrate. P concentration of BPSG lay-er measured 3.3 Wt% and the consolidation temperature was lower than $1180^{\circ}C$. The measured refractive index of BPSG silica layer in $1.55\;\mu\textrm{m}$ wavelength was $1.4480{\pm}1{\times}10^{-1}$ and the thickness was $22{\pm}1\;\mu\textrm{m}$.

• Journal of the Korean Ceramic Society
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• v.39 no.3
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• pp.278-285
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• 2002

For planar optical devices, silica film deposited by FHD was fabricated at low temperature. To prepare silica film at low temperature, we have changed B, P amounts and investigated consolidation effect with varying consolidation temperature and atmosphere on microstructural change, and also observed optical property. The optimum consolidation temperature in He was lower than that of other atmosphere, its temperature could be lowered to 1050$^{\circ}C$. As a result, the roughness of flat silica film prepared at 1050$^{\circ}C$ showed 5, 6nm.

• Journal of the Korean Ceramic Society
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• v.34 no.8
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• pp.811-816
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• 1997

SiO2-P2O5-B2O3 glass soot was fabricated by flame hydrolysis deposition and their properties by SEM, XRD, TGA-DSC were investigated., The mechanism of consolidation process of a glass soot as a function of consolidation temperature was analyzed by SEM observations. In the XRD patterns, the crystalline peaks which seem to be generated from B2O3 and BPO4 were observed. When the temperature of heat treatment exceeded 105$0^{\circ}C$, the non-crystalline state of SiO2-P2O5-B2O3 glass was observed. In the TGA-DSC curves, the evaporation of water molecule by a sudden endothermic reaction was observed at 128$^{\circ}C$ and a broad endothermic peak was seen in the temperature range of 40$0^{\circ}C$-95$0^{\circ}C$, without any weight loss. Finally, this peak was began to recover its baseline at 953$^{\circ}C$. This point is equal to the temperature at which the densification begins. Furthermore, we observed that the addition of dopants such as P2O5 and B2O3 decrease the onset of consolidation temperature till 95$0^{\circ}C$.

• Journal of the Korean Ceramic Society
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• v.39 no.9
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• pp.896-901
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• 2002

Since many process parameters of FHD(Flame Hydrolysis Deposition) are involved in forming multi-component amorphous silica film ($SiO_2-B_2O_3-P_2O_5-GeO_2$), it has not been easy to predict the optical, mechanical and thermal properties of deposited film from the simple process parameters, such as source flow rate. Furthermore, the prediction of final composition of film becomes even more difficult after sintering at high temperature due to the evaporation of volatile dopants. The motivation of the study was to clarify the quantitative relationship between simple process parameters such as the flow rate of source gases and resulting chemical composition of sintered film. Hence, the compositional analysis of silica soot by FTIR(Fourier Transformation Infrared Spectroscopy) and ICP-AES(Inductively Coupled Plasma-Atomic Emission Spectrometry) under the control of the amount of dopant was carried out to obtain the quantitative composition. By measuring spectrum of absorbance from FTIR, the compositional change of B-O, Si-O, OH($H_2O$) in silica film was measured. The concentrations of these dopants were also measured by ICP-AES, which were compared with the FTIR result. The final quantitative relationship between simple process parameters and composition was deduced from the comparison between two results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.9
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• pp.1151-1162
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• 1999

The effects of radial heat and $H_2O$ diffusion on the evolution of silica particles in coflow diffusion flames have been studied experimentally. The evolution of silica aggregate particles in coflow diffusion flames has been measured experimentally using light scattering and thermophoretic sampling techniques. The measurements of scattering cross section from $90^{\circ}$ light scattering have been utilized to calculate the aggregate number density and volume fraction using with combination of measuring the particle size and morphology through the localized sampling and a TEM image analysis. Aggregate or particle number densities and volume fractions were calculated using Rayleigh-Debye-Gans and Mie theory for fractal aggregates and spherical particles, respectively. Flame temperatures and volumetric differential scattering cross sections have been measured for different flame conditions such as inert gas species, $H_2$ flow rates, and burner injection configurations to examine the relation between the formation of particles and radial $H_2O$ diffusion. The comparisons of oxidation and flame hydrolysis have also been made for various $H_2$ flow rates using $N_2$ or $O_2$ as a carrier gas. Results indicate that the role of oxidation becomes dominant as both carrier gas($O_2$) and $H_2$ flow rates increases since the radial heat diffusion precedes $H_2O$ diffusion in coflow flames used in this study. The effect of carrier gas flow rates on the evolution of silica particles have also been studied. When using $N_2$ as a carrier gas, the particle volume fraction has a maximum at a certain carrier gas flow rate and as the flow rate is further increased, the hydrolysis reaction Is delayed and the spherical particles finally evolves into fractal aggregates due to decreased flame temperature and residence time.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.5
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• pp.1671-1678
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• 1996

In external chemical vapor deposition processes including VAD and OVD the distribution of flame-synthesized silica particles is determined by heat and mass transfer limitations to particle formation. Combustion gas flow velocities are such that the particle diffusion time scale is longer than that of gas flow convection in the zone of particle formation. The consequence of these effects is that the particles formed tend to remain along straight smooth flow stream lines. Silica particles are formed due to oxidation and hydrolysis. In the hydrolysis, the particles are formed in diffuse bands and particle formation thus requires the diffusion of SiCl$\_$4/ toward CH$\_$4//O$\_$2/ combustion zone to react with H$\_$2/O diffusing away from these same zones on the torch face. The conversion kinetics of hydrolysis is fast compared to diffusion and the rate of conversion is thus diffusion-limited. In the language of combustion, the hydrolysis occurs as a Burke-Schumann process. In selected conditions, reaction zone shape and temperature distributions predicted by the Burke-Schumann analysis are introduced and compared with experimental data available. The calculated centerline temperatures inside the reaction zone agree well with the data, but the calculated values outside the reaction zone are a little higher than the data since the analysis does not consider diffusion in the axial direction and mixing of the combustion products with ambient air. The temperatures along the radial direction agree with the data near the centerline, but gradually diverge from the data as the distance is away from the centerline. This is caused by the convection in the radial direction, which is not considered in the analysis. Spatial distribution of silica particles are affected by convection and diffusion, resulting in a Gaussian form in the radial direction.