Influence of adhesion of silica and ceria abrasive nanoparticles on Chemical-Mechanical Planarization of silica surfaces

We report on a direct measurement of adhesion between abrasive nanoparticles of irregular shape, which are used in semiconductor industry in the process of Chemical-Mechanical Planarization (CMP), and silica surface. The adhesion of ceria and silica nanoparticles to silica surface is measured in multiple chemistries of different CMP slurries using a specially developed atomic force microscopy (AFM) method. Using this method, we study the influence of adhesion on the main parameters of CMP, removal rate and defectivity, scratches. While being plausible to expect correlation between these parameters and adhesion, it has not been systematically studied as of yet. We observed direct correlation between adhesion and removal rate. Comparing the measured defectivity and adhesion, we observe the presence of some correlation between these parameters. We conclude that both adhesion and shape of abrasive particles influence defectivity, micro-scratches. Direct measurements of the adhesion between abrasive nano-particles and surface can be used in the screening of new slurries as well as various modeling related to wearing of the surfaces.     

Preparation of alumina/silica core-shell abrasives and their CMP behavior

Abrasive is one of key influencing factors on the surface quality during the chemical mechanic polishing (CMP). α-Alumina particles, as a kind of widely used abrasive in CMP slurries, often cause to surface defects because of its high hardness. In the present paper, a series of novel alumina/silica core-shell abrasives in slurries were described. The CMP performances of the alumina/silica core-shell abrasives on hard disk substrate were investigated by using a SPEEDFAM-16B-4M CMP equipment. Experimental results indicate that the CMP performances are strong dependent on the coated SiO₂ content of the alumina/silica composite abrasives. Slurries containing the alumina/silica composite abrasives exhibited lower surface roughness and waviness as well as lower topographical variations and less scratch than that containing pure alumina abrasive under the same testing conditions.     

Biocompatibilities of sapphire and borosilicate glass as cortical neuroprostheses

The in vivo biocompatibility of pure sapphire and borosilicate glass (BSG) implanted onto the cerebral cortex was studied via magnetic resonance imaging (MRI) and histopathology. Each implant was embedded onto the cortical surface of an adult rat brain for a total of 28 days. Rats underwent surgery with and without implants, and rats with purposely damaged cortical implant sites were also studied. Each animal was imaged via MRI before surgery as well as 10 and 28 days after the surgery. Histopathological results of animals were obtained on the 28th day to determine the specific effect on neurons. Despite the fact that sapphire has been widely used in a variety of medical implants, both MRI and histopathological results indicate that pure sapphire is not biocompatible with the cerebral cortex. On the contrary, BSG implants appear to be biocompatible with the cortical surface.     

Effects of the ultrasonic flexural vibration on the interaction between the abrasive particles; pad and sapphire substrate during chemical mechanical polishing (CMP)

In this paper, the technique of ultrasonic flexural vibration assisted chemical mechanical polishing (UFV-CMP) was used for sapphire substrate CMP. The functions of the polishing pad, the silica abrasive particles, and the chemical additives of the slurry such as pH value regulator and dispersant during the sapphire's UFV-CMP were investigated. The results showed that the actions of the ultrasonic and silica abrasive particles were the main factors in the sapphire material removal rate (MMR) and the chemical additives were helpful to decrease the roughness of sapphire. Then the effects of the flexural vibration on the interaction between the silica abrasive particles, pad and sapphire substrate from the kinematics and dynamics were investigated to explain why the MRR of UFV-CMP was bigger than that of the traditional CMP. It indicated that such functions improved the sapphire's MRR: the increasing of the contact silica particles’ motion path lengths on the sapphire's surface, the enhancement of the contact force between the contact silica particles and the sapphire's surface, and the impaction of the suspending silica particles to the sapphire's surface.     

Synthesis and characterization of silica microspheres functionalized with porphyrin monolayer

A new type of inorganic and organic composite (SiO₂-MPS-TAPPI), oppositely charged meso-tetra-(4-trimethylaminophenyl)porphyrin iodide (TAPPI) bonded on the surface of silica microspheres coated with mercaptopropyltrimethoxysilane (MPS), was prepared by self-assembly method. The composite was tested by TEM, XRD and TG. The TEM images show that SiO₂-MPS microspheres in the composite are uniform. There are linkages among some different SiO₂-MPS microspheres. The XRD measurement bears out that the composite structure is the same with SiO₂-MPS. TG curves show that thermal stability of TAPPI assembled onto SiO₂-MPS microspheres is higher than that of TAPPI. Solid UV diffusion reflection spectra and fluorescence spectra are used to investigate the photophysical properties of the SiO₂-MPS-TAPPI composite. It is showed that the spectra of the composite exhibit significant enhancement of the spectra range. The strong interaction between TAPPI and SiO₂-MPS in the composite is responsible for the different spectra.     

Luminescence property of Ce-doped silica decorated with S and Cl anions

Ce³⁺-doped silica was synthesized by sol-gel technique and was further decorated with S²⁻ and Cl⁻ anions through chemical exchange in controlled ambient at elevated temperature. The structure and optical property of samples were examined by X-ray diffraction spectrum, XPS pattern, reflection pattern, and photoluminescence patterns. There is a broad luminescence band at 445 nm under the excitation at 320 nm in the Ce³⁺-doped silica heat-treated in air at 1000 °C. The heat-treatment of the sample in vacuum at 800 °C can increase the intensity of luminescence but have no effect on the wavelength of luminescence. The decoration of S²⁻ and Cl⁻ anions cannot only increase the luminescent intensity but also shift the luminescent wavelength to shorter wavelength.     

Subsurface defect characterization and laser-induced damage performance of fused silica optics polished with colloidal silica and ceria

This paper mainly focuses on the influence of colloidal silica polishing on the damage performance of fused silica optics. In this paper, nanometer sized colloidal silica and micron sized ceria are used to polish fused silica optics. The colloidal silica polished samples and ceria polished samples exhibit that the root-mean-squared(RMS) average surface roughness values are 0.7 nm and 1.0 nm, respectively. The subsurface defects and damage performance of the polished optics are analyzed and discussed. It is revealed that colloidal silica polishing will introduce much fewer absorptive contaminant elements and subsurface damages especially no trailing indentation fracture. The 355-nm laser damage test reveals that each of the fused silica samples polished with colloidal silica has a much higher damage threshold and lower damage density than ceria polished samples. Colloidal silica polishing is potential in manufacturing high power laser optics.     

Synthesis and characterization of multifunctional silica core-shell nanocomposites with magnetic and fluorescent functionalities

Multifunctional core-shell nanocomposites with a magnetic core and a silica shell doped with lanthanide chelate have been prepared by a simple method. First, citric acid-modified magnetite nanoparticles were synthesized by a chemical coprecipitation method. Then the magnetite nanoparticles were coated with silica shells doped with terbium (Tb³⁺) complex by a modified Stöber method based on hydrolyzing and condensation of tetraethyl orthosilicate (TEOS) and a silane precursor. These multifunctional nanocomposites are potentially useful in a variety of biological areas such as bio-imaging, bio-labeling and bioassays because they can be simultaneously manipulated with an external magnetic field and exhibit unique phosphorescence properties.     

Effect of sintering temperature on mechanical behaviour and bioactivity of sol-gel synthesized bioglass-ceramics using rice husk ash as a silica source

Bioglass-ceramics with SiO₂-Na₂O-CaO composition was prepared by sol-gel method using rice husk ash as a silica source. Material was sintered at different temperatures ranging from 900 to 1050 °C for 2 h. Phase-formation behaviour, densification characteristics, and mechanical strength of glass-ceramics were investigated. The material sintered at 1000 °C showed a good mechanical strength. Mechanical properties were correlated with microstructural features. Both in vitro bioactivity and biodegradability of sintered material were investigated by incubating in simulated body fluid and Tris buffer solution, respectively. Scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction were used to investigate the surface deposition during body fluid incubation. Both bioactivity and degradability decreased with increase in sintering temperature.     

Function of liquid and tool wear in ultrasonic bound-abrasive polishing of fused silica with different polishing tools

The recently proposed fixed-abrasive polishing process was revisited, but this paper focuses mainly on the potential influence of various liquids and the different kinds of pellets on the polishing process as well as the wear of pellet in ultrasonic assisted and conventional processes. The results show that using liquids is helpful in improving surface quality and lowering surface roughness. In particular, the surface roughness is improved sharply for pore-free pellet, from >80 nm to <1 nm (avg.) and the polishing process smoothly proceed that otherwise will hardly progress without liquids. However, the liquids do not necessarily always improve polishing process. There is an optimal volume for a specific polishing process. Moreover, the wear of pellet was also evaluated as well. The results suggest that applying ultrasonics can effectively alleviate the wear loss of pellet and increase the “G-ratio” of polishing process.     

Environmentally superior cleaning of diatom frustules using sono-Fenton process: Facile fabrication of nanoporous silica with homogeneous morphology and controlled size

Existing techniques for the preparation of silica structures from diatom cells include cleaning of frustules through baking at high temperature and oxidant cleaning using concentrated sulfuric acid, hydrogen peroxide, nitric acid, or sodium dodecyl sulfate (SDS)/ethylenediaminetetraacetic acid (EDTA). In this study, sono-Fenton (SF) process was examined to prepare nanoporous silica through cleaning diatom frustules, while preserving their structural features. Single colonies of Cyclotella sp. were cultivated in batch mode f/2-enriched seawater. Combination of Fenton process with ultrasonication was found to be more efficient than the sum of individual processes in the removal of organic compounds from Cyclotella sp. structure. The optimized amounts of operational parameters were determined as suspension pH of 3, diatom cell density of 4.8 × 10⁵ cell mL⁻¹, H₂O₂ concentration of 60 mM, Fe²⁺ concentration of 15 mM, ultrasound irradiation power of 400 W and the temperature of 45 °C. The results of energy-dispersive X-ray spectroscopy (EDX) and thermal gravimetry (TG) analyses proved that organic materials covering the cell wall were significantly removed from the frustules through SF process. Scanning electron microscopy (SEM) images showed that after SF treatment, silica nanostructures were produced having uniform pores less than 15 nm in diameter. N₂ adsorption–desorption isotherms demonstrated that almost non-porous structure of diatom frustules became mesoporous during removing the organic matrix. Lipids, amino acids, carbohydrates and organic acids or their oxidized products were identified using GC–MS analysis as the main organic compounds released from diatom cells to the solution after SF treatment. Treated frustules exhibited adsorption capability of 91.2 mg/g for Methylene Blue, which was almost 2.5 times higher than that of untreated frustules (34.8 mg/g).     

Influencing factors and kinetics analysis on the leaching of iron from boron carbide waste-scrap with ultrasound-assisted method

In this paper, the ultrasound-assisted leaching of iron from boron carbide waste-scrap was investigated and the optimization of different influencing factors had also been performed. The factors investigated were acid concentration, liquid-solid ratio, leaching temperature, ultrasonic power and frequency. The leaching of iron with conventional method at various temperatures was also performed. The results show the maximum iron leaching ratios are 87.4%, 94.5% for 80 min-leaching with conventional method and 50 min-leaching with ultrasound assistance, respectively. The leaching of waste-scrap with conventional method fits the chemical reaction-controlled model. The leaching with ultrasound assistance fits chemical reaction-controlled model, diffusion-controlled model for the first stage and second stage, respectively. The assistance of ultrasound can greatly improve the iron leaching ratio, accelerate the leaching rate, shorten leaching time and lower the residual iron, comparing with conventional method. The advantages of ultrasound-assisted leaching were also confirmed by the SEM-EDS analysis and elemental analysis of the raw material and leached solid samples.