• Journal of the Korean Ceramic Society
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• v.34 no.1
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• pp.70-78
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• 1997

3Y-TZP/SUS316 Functionally Graded Material (FGM) was fabricated by slip casting method. Alumina mold was used to overcome problems of gypsum mold in slip casting process, and the optimal dispersion con-ditions of 3Y-TZP/SUS316 binary slurries was determined using electrokinetic sonic amplitude and a viscometer, and observing sedimentation behavior. The properties of the specimens casted by gypsum mold and alumina mold were compared in terms of changes in shrinkage rate, drying and sintering conditions, and microstructure. It was found that the specimens obtaine from the alumina mold showed a clean surface, easier thickness control of each layer, and higher productivity. Especially, no degradation was observed in the SUS316 prepared using alumina mold. Thus it is desirable to use porous alumina mold rather than gyp-sum mold for the slip casting of 3Y-TZP/SUS316-FGM.

• Journal of the Korean Ceramic Society
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• v.40 no.12
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• pp.1183-1188
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• 2003

LCP (Liquid Crystal Polymer)/BT(BaTiO$_3$) composite was prepared by mixing LCP varnish and BT slurry. And the effect of the composition of LCP/BT composites and the size of BT powder on dielectric properties of LCP/BT composite were investigated. The dispersion properties of BT slurries were also studied as a function of volume fraction of dispersant, GLYMO (3-glycidyloxypropyltrimethoxysilane) added to various sized BT powders. The quantity of optimum dispersant in BT slurry decreased with an increase of BT powder size because of the decrease of specific surface area of BT powder. LCP/BT composite sheet was prepared by tape-casting method with mixing BT slurry and LCP varnish. The dielectric constant of the composites increased from 34.3 to 44.1 and their dielectric loss increased from 0.05 to 0.063 as the size of BT powder increased from 100 nm to 500 nm.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.04b
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• pp.38-41
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• 2004

The oxidizer plays an important role in the metal chemical mechanical polishing(CMP) slurry. Currently, the oxidizer used in CMP slurry is nearly divided into several kinds such as $Fe(NO_3)_3$, $H_2O_2$, $KIO_3$, and $H_5IO_6$. It is generally known that oxidizer character of $H_2O_2$ is more effective than other oxidizers. In this work, we have been studied the characteristics for the $H_2O_2$ concentration of copper slurry, which can applicable in the recent semiconductor manufacturing process. Also, it plays an important role in the planarization of copper films using copper slurries during micro-electronic device fabrication. In this work, we confirmed that removal rate of Cu/TaN changed by $H_2O_2$ concentration on copper slurry. And we used $KMnO_4$ in the measurement method of $H_2O_2$. In analysis results, we confirmed that the difference of results is large. We thought that the difference was due to organic component existence. So in titration method of $H_2O_2$ concentration, we used $Na_2S_2O_3$ instead of $KMnO_4$ as solution. Consequently, using the titration method, we could calculate correct data reduced error. And $H_2O_2$ concentration has been adjusted to the target concentration of 0.1 wt%.

• Korean Journal of Materials Research
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• v.21 no.9
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• pp.520-524
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• 2011

Porous W with controlled pore characteristics was fabricated by a freeze-drying process. $WO_3$ powder and camphene were used as the source materials of W and sublimable vehicles, respectively. Camphene slurries with $WO_3$ contents of 10 and 15 vol% were prepared by milling at $50^{\circ}C$ with a small amount of oligomeric polyester dispersant. Freezing of a slurry was done in a Teflon cylinder attached to a copper bottom plate cooled at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green body was hydrogen-reduced at $800^{\circ}C$ for 30 min and sintered in a furnace at $900^{\circ}C$ for 1 h under a hydrogen atmosphere. Microstructural observation revealed that all of the sintered samples were composed of only W phase and showed large pores which were aligned parallel to the camphene growth direction. The porosity and pore size increased with increasing camphene content. The difference in the pore characteristics depending on the slurry concentration may be explained by the degree of powder rearrangement in the slurry. The results strongly suggest that a porous metal with the required pore characteristics can be successfully fabricated by a freeze-drying process using metal oxide powders.

• Korean Journal of Materials Research
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• v.23 no.4
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• pp.246-249
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• 2013

Nano-sized ${\beta}$-SiC nanoparticles were synthesized combined with a sol-gel process and a carbothermal process. TEOS and carbon black were used as starting materials for the silicon source and carbon source, respectively. $SiO_2$ nanoparticles were synthesized using a sol-gel technique (Stober process) combined with hydrolysis and condensation. The size of the particles could be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The average particle size and morphology of synthesized silicon dioxide was about 100nm and spherical, respectively. The average particles size and morphology of the used carbon black powders was about 20nm and spherical, respectively. The molar ratio of silicon dioxide and carbon black was fixed to 1:3 in the preparation of each combination. $SiO_2$ and carbon black powders were mixed in ethanol and ball-milled for 12 h. After mixing, the slurries were dried at $80^{\circ}C$ in an oven. The dried powder mixtures were placed in alumina crucibles and synthesized in a tube furnace at $1400{\sim}1500^{\circ}C$ for 4 h with a heating rate of $10^{\circ}C$/min under flowing Ar gas (160 cc/min) and furnace cooling down to room temperature. SiC nanoparticles were characterized by XRD, TEM, and SAED. The XRD results showed that high purity beta silicon carbide with excellent crystallinity was synthesized. TEM revealed that the powders are spherical shape nanoparticles with diameters ranging from 15 to 30 nm with a narrow distribution.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2005.11a
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• pp.68-69
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• 2005

BTO ($BaTiO_3$) thin film is one of the high dielectric materials for high-density dynamic random access memories (DRAMs) due to its relatively high dielectric constant. It is generally known that BTO film is difficult to be etched by plasma etching, but high etch rate with good selectivity to pattern mask was required. The problem of sidewall angle also still remained to be solved in plasma etching of BTO thin film. In this study, we first examined the patterning possibility of BTO film by chemical mechanical polishing (CMP) process instead of plasma etching. The sputtered BTO film on TEOS film as a stopper layer was polished by CMP process with the self-developed $BaTiO_3$- and $TiO_2$-mixed abrasives slurries (MAS), respectively. The removal rate of BTO thin film using the$ BaTiO_3$-mixed abrasive slurry ($BaTiO_3$-MAS) was higher than that using the $TiO_2$-mixed abrasive slurry ($TiO_2$-MAS) in the same concentrations. The maximum removal rate of BTO thin film was 848 nm/min with an addition of $BaTiO_3$ abrasive at the concentration of 3 wt%. The sufficient within-wafer non-uniformity (WIWNU%)below 5% was obtained in each abrasive at all concentrations. The surface morphology of polished BTO thin film was investigated by atomic force microscopy (AFM).

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.46-49
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• 2003

Chemical mechanical polishing (CMP) is an essential dielectric planarization in multilayer microelectronic device fabrication. In the CMP process it is necessary to minimize the extent of surface defect formation while maintaining good planarity and optimal material removal rates. The polishing mechanism of W-CMP process has been reported as the repeated process of passive layer formation by oxidizer and abrasion action by slurry abrasives. Thus, it is important to understand the effect of oxidizer on W passivation layer, in order to obtain higher removal rate (RR) and very low non-uniformity (NU%) during W-CMP process. In this paper, we compared the effects of oxidizer or W-CMP process with three different kind of oxidizers with 5% hydrogen peroxide such as $Fe(NO_3)_3$, $H_2O_2$, and $KIO_3$. The difference in removal rate and roughness of W in stable and unstable slurries are believed to caused by modification in the mechanical behavior of $Al_3O_3$ particles in presence of surfactant stabilizing the slurry.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2003.07a
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• pp.50-53
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• 2003

CMP (chemical mechanical polishing) process remained to solve several problems in deep sub-micron integrated circuit manufacturing process. especially consumables (polishing pad, backing film, slurry, pad conditioner), one of the most important components in the CMP system is the slurry. Among the composition of slurries (buffer solution, bulk solution, abrasive particle, oxidizer, inhibitor, suspension, antifoaming agent, dispersion agent), the abrasive particles are important in determining polish rate and planarization ability of a CMP process. However, the cost of abrasives is still very high. So, in order to reduce the high COO (cost of ownership) and COC (cost of consumables) in this paper, we have collected the silica abrasive powders by filtering after subsequent CMP process for the purpose of abrasive particle recycling. And then, we have studied the possibility of recycle of reused silica abrasive through the analysis of particle size and hardness. Also, we annealed the collected abrasive powders to promote the mechanical strength of reduced abrasion force. Finally, we compared the CMP characteristics between self-developed KOH-based silica abrasive slurry and original slurry. As our experimental results, we obtained the comparable removal rate and good planarity with commercial products. Consequently, we can expect the saving of high cost slurry.

• Korean Journal of Materials Research
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• v.23 no.12
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• pp.722-726
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• 2013

Freeze drying of a porous Cu-Sn alloy with unidirectionally aligned pore channels was accomplished by using a composite powder of CuO-$SnO_2$ and camphene. Camphene slurries with CuO-$SnO_2$ content of 3, 5 and 10 vol% were prepared by mixing with a small amount of dispersant at $50^{\circ}C$. Freezing of a slurry was done at $-25^{\circ}C$ while the growth direction of the camphene was unidirectionally controlled. Pores were generated subsequently by sublimation of the camphene during drying in air for 48 h. The green bodies were hydrogen-reduced at $650^{\circ}C$ and then were sintered at $650^{\circ}C$ and $750^{\circ}C$ for 1 h. XRD analysis revealed that the CuO-$SnO_2$ powder was completely converted to Cu-Sn alloy without any reaction phases. The sintered samples showed large pores with an average size of above $100{\mu}m$ which were aligned parallel to the camphene growth direction. Also, the internal walls of the large pores had relatively small pores. The size of the large pores decreased with increasing CuO-$SnO_2$ content due to the change of the degree of powder rearrangement in the slurry. The size of the small pores decreased with increase of the sintering temperature from $650^{\circ}C$ to $750^{\circ}C$, while that of the large pores was unchanged. These results suggest that a porous alloy body with aligned large pores can be fabricated by a freeze-drying and hydrogen reduction process using oxide powders.

• Journal of Korean Society of Water and Wastewater
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• v.23 no.4
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• pp.471-479
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• 2009

A Nanoscale Zero-Valent Iron(NZVI) was modified to build a reactor system to treat nitrate. Shell layer of the NZVI was modified by slow exposure of the iron surface to air flow, which produced NZVI particles that are resistant to aerial oxidation. A XANES (X-ray Absorption Near-Edge Structure) analysis revealed that the shell consists of magnetite ($Fe_3O_4$) dominantly. The shell-modified NZVI(0.5 g NZVI/ 120 mL) was able to degrade more than 95% of 30 mg/L of nitrate within $30 hr^{-1}$ ( pseudo first-order rate constant($k_{SA}$) normalzed to NZVI surface area ($17.96m^2/g$) : $0.0050L{\cdot}m^{-2}{\cdot}hr^{-1}$). Ammonia occupied about 90% of degradation products of nitrate. Nitrate degradation efficiencies increased with the increase of NZVI dose generally. Initial pH values of the reactor systems at 4, 7, and 10 did not affect nitrate removal rate and final pH values of all experiments were near 12. Nitrate removal experiments by using the shell-modified NZVI immobilized on a cellulose acetate (CA) membrane were also conducted. The nitrate removal efficiency of the CA membrane supported NZVI ($k_{SA}=0.0036L{\cdot}m^{-2}{\cdot}hr^{-1}$) was less than that of the NZVI slurries($k_{SA}=0.0050L{\cdot}m^{-2}{\cdot}hr^{-1}$), which is probably due to less surface area available for reduction and to kinetic retardation by nitrate transport through the CA membrane. The detachment of the NZVI from the CA membrane was minimal and impregnation of up to 1 g of NZVI onto 1 g of the CA membrane was found feasible.