Silica Slurry Research Articles

Fabrication of transparent silica glass and evaluation of silica particle dispersibility in silica slurries based on the solubility parameters of the slurry components

Silica particles were dispersed in 11 acrylic monomers at various concentrations. The dispersibility of the silica particles was evaluated based on the viscosity of the slurry. Furthermore, the relationship between the viscosity of the slurry and the solubility parameters (SPs) of the silica particles and acrylic monomers was investigated. When the SPs of the silica particles and acrylic monomers were close, the viscosity of the silica slurry decreased and high concentrations of the silica particles could be dispersed in the acrylic monomers. Therefore, SP can be used for predicting the dispersibility of silica particles. The prepared slurry was then used to fabricate sintered silica glass. Silica slurry was cured through photopolymerization to obtain a green body, which was then heat-treated at 850°C in air atmosphere and sintered at 1710°C under vacuum to obtain sintered silica glass. Transparent sintered silica glass with no cracks was obtained using 4-hydroxybutyl acrylate, which has a similar SP to that of silica particles, as a solvent. The obtained sintered silica glass exhibited a transmittance of 92% at a wavelength of 400 nm. In the ultraviolet region, light absorption originated from two-coordinated Si in the glass. The absorption spectrum in the infrared region showed an extremely low peak of the SiOH group, indicating that low-OH silica glass was obtained. Thus, this study provides a new method for fabricating silica glass and provides a method of selecting solvents for the slurries used in powder sintering.

Development of a manufacturing process for fine ceramic components using the composite of silica slurry: an evaluation of its mechanical durability

Development of a manufacturing process for fine ceramic components using the composite of silica slurry: an evaluation of its mechanical durability

Incorporating boron carbide into fused silica imparts multiple mechanisms to facilitate vat photopolymerization

Rapid manufacturing of complex-shaped ceramic components has long been a pressing issue in the aerospace industry. Recent progress in this direction takes advantage of additive manufacturing, by employing vat photopolymerization (VPP) followed by sintering. Here we demonstrate a new recipe/protocol that enables the VPP route to deliver silica products of high relative density as well as high strength. This is achieved by incorporating 2.5 wt% of boron carbide (B4C) into the fused silica slurry, which offers beneficial effects in multiple fronts. During the VPP process, the added black B4C, together with the refractive index difference between the two components in the mixture, effectively increased the light absorbance. Upon sintering, the boron oxide produced by the oxidation of B4C played the role of a sintering aid. The boron oxide also helped to suppress the crystallization of the amorphous silica and therefore the formation of cracks. As a result, the overall quality (forming precision, density, strength and dielectric constant) of the product surpasses by far those prepared previously via VPP-sintering. In particular, the flexural strength reached 60.7 MPa, a factor of 2.5 better than the previously reported highest value. Extending the success above further, we have manufactured a complex-structured silica radome, as a demonstration of the high-quality products achievable for practical applications.

Understanding and mitigating temperature-induced agglomeration in silica-based chemical mechanical planarization (CMP) slurry storage

This study explores the impact of temperature on silica particle agglomeration in Chemical Mechanical Planarization (CMP) slurries during storage. Slurries were stored at 15 °C, room temperature, and 45 °C, and analyzed. ATR-FTIR, RAMAN, SEM, zeta potential, and LPC were employed providing qualitative and quantitative data on slurry stability and agglomeration tendencies. Elevated temperature storage significantly increased agglomeration and large particle counts with particle counts value of ∼1.2×107 Part./ml, likely due to water molecule dehydration leading to destabilization. Low-temperature storage also induced agglomeration but to a lesser extent with particle counts the value of ∼4.0×106 Part./ml compared with the RT (∼2.0×106 Part./ml). Short-term storage yielded soft agglomerates with LPC of ∼(2.0–4.0)×106 Part./ml, while long-term high-temperature storage led to hard agglomerates with LPC of ∼3.0×107 Part./ml. The ATR-FTIR and Raman analysis indicate that the spectroscopic features of the original slurry exhibited changes upon variation of storage temperature from RT to 15 and 45 °C. The study also explored the reversibility of agglomeration post-treatment, indicating a potential mitigation pathway. The results demonstrated an inverse relationship between temperature and dissolved oxygen (DO) in silica slurries. For example. the curves depict a decrease in oxygen content from ∼10 ppm at RT to 7 ppm at 45 °C with increasing aging time. A mechanism outlining the temperature and aging-induced agglomeration was proposed, linking temperature fluctuations and thermodynamic aspects to colloidal stability. These findings offer a robust understanding of temperature-induced agglomeration in silica-based CMP slurry storage, paving the way for developing strategies to alleviate these issues and ensuring consistent CMP performance in semiconductor manufacturing.

An efficient polishing process for silicon carbide using ion implantation method

We have developed an efficient polishing process for silicon carbide (SiC) using the ion implantation method. An embrittlement layer is generated by an argon ion beam with 50 kV acceleration voltage. Although colloidal silica slurry without oxidant cannot remove the SiC substrate at all, the embrittlement layer is removed by the slurry. The polishing area is defined through patterning with a resin mask during implantation. Such patterning step is expected to compatible with the damascene process on SiC substrates. Raman spectra suggest that the crystal structure of the SiC substrate is not changed after surface polishing because of the E1 and A1 characteristics.

Analysis of Experience in the Use of Micro- and Nanoadditives from Silicon Production Waste in Concrete Technologies

The integration of nanotechnology across various industries has significantly enhanced product quality and manufacturing technologies for diverse materials. Within the construction sector, the adoption of nanomaterials has sparked the advent of innovative construction methods. Extensive studies have been conducted on various nanomaterials, particularly micro- and nanosilica, exploring their use as partial substitutes for cement in concrete formulations. This study aimed to furnish a comprehensive overview of silica’s impact on concrete properties in civil engineering and road construction. Environmental concerns and potential hazards necessitate the development of strategies for managing industrial by-products. Metallurgical processes generate several such by-products, among which is silica fume—a residue from smelting in the silicon and ferrosilicon industries. Waste silica dust and slurries have proven highly effective in creating high-strength, high-performance concrete. The study presents a literature review focusing on micro- and nanosilica derived from production waste at ferroalloy and silicon plants. It includes a comparative analysis of the primary characteristics of microsilica from various sources and examines the extensive use of microsilica as a modifying additive in building materials. Analyzing different concrete compositions with and without fumed silica determined the ranges of results for each indicator. The incorporation of micro- and nanosilica into the concrete mix demonstrated its efficacy. The morphology of waste silica particles, characterized by the smooth and spherical surfaces of micro- and nanosilica particles, significantly influences the workability properties of the concrete.

Effect of solid loading on phase composition, microstructure, mechanical and dielectric properties of fused silica ceramics by gecasting

In this study, the fused silica slurries with an ultra-high solid loading of 85 vol%, low viscosity of 0.34 Pa s at 99.4 s−1, and good suspension stability were successfully prepared using two-gradation fused silica raw powders by optimizing the preparation processes. Owing to the inherent characteristics of gelcasting and good dispersion stability of resulting fused silica slurries, all the fused silica ceramics prepared with various solid loadings exhibited a homogeneous bimodal size distribution microstructure after pressureless sintering at 1250 °C for 4 h. Furthermore, a small amount of nanoscale cristobalite was precipitated from fused silica, and solid loading had no significant effect on the crystallization kinetics of cristobalite. A significant increase in solid loading effectively facilitated the densification of fused silica ceramics, enhanced bulk density, decreased sintering shrinkage, and strengthened mechanical properties. However, the increase in solid loading deteriorated dielectric properties within the range of 2–18 GHz. When the solid loading was 85 vol%, the bulk density, linear shrinkage, flexural strength, dielectric constant, and dielectric loss tangent were 2.12 g/cm3, 1.1 %, 72.3 MPa, 3.91–4.36, 0.0081–0.0171, respectively. These properties were favorable making the materials potential applications in the field of microwave transmission.

Room-Temperature Molding of Complex-Shaped Transparent Fused Silica Lenses.

The high hardness, brittleness, and thermal resistance impose significant challenges in the scalable manufacturing of fused silica lenses, which are widely used in numerous applications. Taking advantage of the nanocomposites by stirring silica nanopowders with photocurable resins, the newly emerged low-temperature pre-shaping technique provides a paradigm shift in fabricating transparent fused silica components. However, preparing the silica slurry and carefully evaporating the organics may significantly increase the process complexity and decrease the manufacturing efficiency for the nanocomposite-based technique. By directly pressing pure silica nanopowders against the complex-shaped metal molds in minutes, this work reports an entirely different room-temperature molding method capable of mass replication of complex-shaped silica lenses without organic additives. After sintering the replicated lenses, fully transparent fused silica lenses with spherical, arrayed, and freeform patterns are generated with nanometric surface roughness and well-reserved mold shapes, demonstrating a scalable and cost-effective route surpassing the current techniques for the manufacturing of high-quality fused silica lenses.

Parametric Studies on Particle Removal and Erosion in Nozzle Injection Megasonic Cleaning

The process of quickly removing abrasive particles of silica and ceria slurries is important in the use of CMP equipment. Megasonic cleaning of nozzle injection type is one of a variety of post-CMP cleaning methods and its performance including cleaning efficiency and erosion was explored experimentally with parametric studies. In the cleaning process, it is favorable to achieve both high efficiency and low damage. The cleaning efficiency was defined by particle removal efficiency (PRE) with a glass sample spin-coated with small silica particles; the damage was detected from mass loss of aluminum foils after the cleaning. The cleaning tests show that the performance of nozzle injection megasonic cleaning depends significantly on ultrasound frequency and water temperature. Toward more efficient and less erosive cleaning, the nozzle injection angle is also expected to play a key role.

Improving the performance of alkali-activated slag mortar with electro/chemically treated carbon fiber textile

Alkali-activated slag is a widely used low-carbon binder. Incorporation of textile can mitigate the brittle weakness of alkali-activated composites. The bonding between fibers and matrix is critical for the performance of textile reinforced mortar. This paper is focused on the effect of different treatment methods on the bonding properties of carbon fiber in alkali-activated slag. The interfacial shear strength of fiber bundles in matrix was determined by the pull-out test. The flexural strength of the reinforced mortar was evaluated by a repeated bending. A scanning electron microscopy test was performed to characterize the interfacial properties of the fiber bundles. The results show that the interfacial shear strength of carbon fibers in matrix is improved by the electroplating with calcium silica slurry (CSS), impregnation in different solutions, and plasma treatments. An electroplating in CSS has the best improvement in the bonding strength with an increase by 620%. The CSS treatment increases the maximum flexural strength of CFT reinforced mortar with 22.5% and 30% at 7 and 28 d respectively, and it significantly inhibits the crack growth under the cyclic loading. This effect becomes more significant after a longer curing age. The electroplating treatment eliminates the cracks in the interface of fiber yarns. Slag reacts with the plated portlandite to strengthen the bonding between mortar and fiber bundles, so it has a better inhibiting effect on the crack growth after a longer curing.

Evaluation of chemical mechanical planarization slurry dispersion using a combined scanning mobility particle sizer-optical particle sizer system

A combined scanning mobility particle sizer-optical particle sizer (SMPS-OPS) system was evaluated for measuring the dispersion of a chemical mechanical planarization (CMP) slurry. The dilution rate of one particle per droplet was confirmed to minimize agglomeration. The SMPS and OPS measurements showed similar particle size distributions of 400 nm polystyrene latex particles. The particle size distributions of settled ceria and silica slurries were measured using the SMPS-OPS system. The settled commercial ceria slurry showed a decrease in the number concentration in the top layer. In the bottom layer, increases in the concentration of active particles and in the number of large particles were observed. This indicates that large particles were formed during settling of the slurry. In the silica slurry, there was a change in concentration with depth and little change in number of large particles with settling time. The SMPS-OPS system was able to analyze CMP slurries across a wide range of particle diameters for both active and large particles. Therefore, this system can be helpful for analysis of CMP slurry size.

Infiltration of silica slurry into silica-based ceramic cores prepared by selective laser sintering based on pre-sintering

The silica-based ceramic core is an important mold for manufacturing hollow blades. The preparation of silica-based ceramic cores by combining selective laser sintering (SLS) and vacuum infiltration (VI) technologies is a promising approach. To enhance infiltration effect, pre-sintering was introduced to obtain the bodies with high porosity and hydrophilicity. The infiltrated silica content increased from 29.58 wt% for samples infiltrated once to 68.91 wt% for samples infiltrated three times. The increase of silica content in the matrix reduced the porosity of final ceramics, thus improving the room-temperature flexural strength. The infiltrated silica gradually transformed into cristobalite during the high-temperature test, which improved the high-temperature flexural strength and creep resistance. When the final-sintering temperature was 1225 °C, room-temperature and high-temperature flexural strength reached 21.17 MPa and 21.21 MPa, respectively, due to the enhanced sintering necks and low porosity. These results indicate that our work provides a promising route to fabricate silica-based ceramic cores by SLS technology.

Fumed Silica-Derived, Ambient Dried, and Low-Cost Nanoporous Aerogel-like Monoliths for Thermal Insulation

Nanoporous silica aerogels have great potential in the application of thermal insulation. However, the commonly used supercritical drying technology of nanoporous silica aerogels has disadvantages such as high cost, high complexity, and harsh drying conditions. Herein, a template orientation strategy has been proposed for fabricating nanoporous aerogel-like silica monoliths (ASMs) based on the low-cost, rapid ambient drying technology without additional treatments of surface modification and solvent exchanging. The successful implementation of the template orientation strategy depends on the silica slurry, which is composed of commercial fumed silica, hydrolyzed methyltrimethoxysilane (MTMS), and sole water solvent. The solidification of silica slurry has been achieved by a controlled polycondensation reaction catalyzed by ammonia originating from the thermolysis of urea. Owing to the skeleton enhancement of fumed silica powders and the hydrophobic effect of methyl groups, ASMs maintain well monolithic formability during ambient drying. Meanwhile, low-cost fumed silica powders have been seen as template orientation agents for inducing MTMS molecules to generate nanoparticle-based network skeletons, endowing ASMs with typical nanopore features (specific surface area as high as 113 m2/g and pore diameter distribution concentrated at ∼40 nm). The resulting ASMs exhibit low density (0.36 g/cm3), high compressive strength (0.92 MPa), and low thermal conductivity [0.056 W/(m·K)]. This work would provide significant guidelines for the fabrication and thermal insulation applications of nanoporous ASMs derived from ceramic powders. This simple and low-cost preparation strategy would promote the large-scale applications and industrial production of nanoporous silica for thermal insulation materials.

Effects of carbides on abrasion-corrosion performance of carbide reinforced composites in saline silica slurries

The abrasion-corrosion resistance of bonding matrix materials for impregnated diamond bits reinforced individually with WC, TiC, Cr3C2, and B4C particles was investigated in an alkalic saline silica slurry. Potentiodynamic polarization and electrochemical impedance spectroscopy were used to investigate their corrosion behaviors. The worn surfaces’ morphology and the compositions of corrosion products were characterized. The results show that the weight loss of WC or TiC reinforced composite during tribocorrosion test was much lower than that of Cr3C2 or B4C-based composite; compared with WC-based composite, TiC- and Cr3C2-based composites had better corrosion resistance, consequently decreasing their synergistic effect of abrasion and corrosion. Therefore, TiC could be a potential substitute for WC as reinforcing phase in the bonding matrix for impregnated diamond bits.

A new chemo-mechanical slurry for close-to-atomic scale polishing of LiNbO3 crystal

A new graphite oxide (GO) nanosheet added KOH-based silica slurry was developed for close-to-atomic polishing of LiNbO3. Except synthesis method of the slurry, both polishing experiments and nanocharacterisation analyses were conducted to reveal the chemo-mechanical mechanism that dominates the material removal of LiNbO3 in nanoscale. Results indicate that the GO nanosheet additive can significantly improve the dispersibility and stability of KOH-based silica slurry. The accumulation of KOH-deprotonated GO/SiO2 nanosheets provide an effective tribo-lubricating-film at local polishing area. Ultra-smooth surface finish (Sa ≤ 0.15 nm) has been achieved at a material removal rate of 170.0 nm/min for two tested case studies.

Development of a vibration sensor-based tool for online detection of roping in small-diameter hydrocyclones

ABSTRACT An attempt has been made to develop a non-intrusive and robust technique for online detection of roping in hydrocyclones using commercially available vibration-based sensors. A 50.8 mm diameter hydrocyclone was operated with two different silica slurry size distributions till roping was achieved in the underflow. Vibration signals were captured simultaneously at the spigot region for various operating conditions. Empirical Mode Decomposition (EMD) was applied to the raw vibration signal for extracting Intrinsic Mode Function (IMF) within the frequency range of the natural frequency of the hydrocyclone. Subsequently, Power Spectral Density (PSD) and frequency spectrum were computed along the axial direction. The Grms (square root of the area under PSD) and peak frequency values were found to be different for the spray and rope discharge which were used for detecting roping conditions. The differences were considered to be associated with the changes in the axial velocity fluctuations of the air core at the spigot region. Further, a flowchart has been proposed based on the methodology suggested in this work, which has the potential for online detection of roping in the hydrocyclone.

Chemical Mechanical Polishing of MgO Substrate and Its Effect on Fabrication of Atomic Step-Terrace Structures on MgO Surface by Subsequent High-Temperature Annealing

Single-crystalline MgO is used as a substrate for the deposition of various functional thin films. The present study focused on the development of a complete sequence of fabricating atomic step-terrace structures on the MgO substrate via a method that includes grinding, precise mechanical polishing, chemical mechanical polishing (CMP), and high-temperature annealing. The effect of a damage-free surface pretreatment on the subsequent high-temperature annealing was investigated. An atomically smooth and damage-free MgO substrate surface with an average surface roughness of 0.05 nm was obtained via a CMP process using a colloidal silica slurry. Atomic step-terrace structures were formed on the substrate after the high-temperature annealing process at 1000 °C for 20 h under atmospheric air. The obtained step height was 0.20 nm, which corresponds to one-half the unit cell of an MgO crystal (0.21 nm). By contrast, when a mechanically damaged MgO substrate was subjected to the annealing process, Ca segregation was observed on the annealed surface, without the formation of an atomic step-terrace structure. CMP was found to be necessary prior to high-temperature annealing to attain atomic step-terrace structures and to avoid the out-diffusion of impurities in the MgO bulk crystals.

Development of novel multi-selective slurry with mechanically driven etching for through silicon via chemical mechanical polishing

As a new generation of semiconductor chips such as 3D integration has been developed, the circuit becomes diverse and fine with the composition of various materials. In this study, the novel multi-selective slurry was developed to control each material removal of SiO2, Si3N4, and Cu films respectively. The material removal rate (MRR) of SiO2 was chemically controlled using tetrabutylammonium fluoride (TBAF), in which the addition of 0.5 mM of TBAF increases the MRR of only SiO2 film by 16 times larger than pristine silica slurry without any side effect on the MRR of other materials. The MRR of the Si3N4 wafer was mostly influenced by mechanical abrasion owing to the solid contents. The MRR of the Cu wafer was adjusted by varying the amount of benzotriazole added as an inhibitor. Because each additive affected the material removal only for the target film, the MRR for various materials could be selectively adjusted. Finally, the dishing or protrusion of Cu pad in through-silicon via (TSV) could be controlled in a nanometer scale by using a fabricated multi-selective slurry. In addition, a completely flat surface was obtained when TSV wafer was polished by the selectivity of 1:1:1 on Si3N4, SiO2, and Cu films.

Effect of slurry particles on PVA brush contamination during post-CMP cleaning

PVA (polyvinyl acetal) brush scrubbing is a widely used post-CMP cleaning process due to its low cost and high cleaning efficiency. However, during these processes, the PVA brush gets contaminated with abrasive particles that result in wafer cross-contamination and reduced cleaning efficiency. This study investigated the effects of abrasive types such as silica and ceria, the slurry pH, and the scrubbing process parameters on brush contamination. Ceria slurries showed significantly more contamination of brushes compared to silica slurries. The brush contamination increased with a decrease in pH from 7 to 4 due to increased electrostatic attractive forces between the ceria particles and the brush surfaces, although very low brush contamination was observed by the ceria slurries at pH 10 due to a strong electrostatic repulsion. Conversely, very low brush contamination was observed for the silica slurries at all pH values due to the reduced interaction between the particles and the brush surface (electrostatic repulsion). Furthermore, there was no significant effect of gap distance and brush rotation speed on brush contamination. The abrasive concentration and the contamination process time showed a linear relationship as the contamination was significantly increased by increasing the abrasive concentration in slurry and process time. These results indicate that brush contamination is more sensitive to the abrasive nature and concentration, the slurry pH, and the process time than to other parameters.

Controlling Galvanic Corrosion with Oxalic Acid and Imidazole for Chemical Mechanical Planarization of Cobalt-Copper Interface

The work focuses on the investigation of Co/Cu removal rate (RR) selectivity and reduction of galvanic corrosion associated with Co and Cu by using oxalic acid (weak acid) as the complexing agent and imidazole as an inhibitor in hydrogen peroxide (H2O2) and fumed silica-based slurry. The results obtained from dissolution study, polishing experiments and potentiodynamic polarization measurements revealed that the proposed chemistry can achieve a desirable Co/Cu RR selectivity and a significant decrease in corrosion potential of Co and Cu (pH 9) to be used in the semiconductor industry. The corrosion potential difference (CuEcorr - CoEcorr) was reduced to 12 mV by using 0.1 wt% H2O2 + 0.02 M oxalic acid + 5 ppm imidazole solution at pH 9. Meanwhile, a removal rate of ∼147 nm min−1 for Co and ∼140 nm min−1 for Cu was achieved using the same composition in a fumed silica slurry which resulted in Co/Cu selectivity ratio of 1.05:1, which is acceptable for cobalt barrier and copper interconnect CMP. Based on FTIR and UV spectra, the dissolution mechanism in the proposed chemistry is also discussed.