Polishing Performance Research Articles

Processing Optimization for Halbach Array Magnetic Field-Assisted Magnetic Abrasive Particles Polishing of Titanium Alloy.

To extend the working life of products made of titanium alloy, it is necessary to improve the polishing method to diminish the remaining defects on the workpiece surface. The Halbach array-assisted magnetic abrasive particle polishing method for titanium alloy was employed in this work. The distribution of magnetic field strength was simulated and verified at first to learn the characteristics of the Halbach array used in this work. Then, the polishing performance of the polishing tool was studied by conducting the polishing test, which aimed to display the relationship between shear force and surface roughness with polishing time, and the surface morphology during polishing was also analyzed. Following the establishment of the response surface model, a study on the optimal polishing parameters was conducted to obtain the suitable parameters for maximum shear force and minimum surface roughness. The results show that the maximum shear force 6.11 N and minimum surface roughness Sa 88 nm can be attained, respectively, under the conditions of (1) polishing tool speed of 724.254 r·min-1, working gap of 0.5 mm, and abrasive particle size of 200 μm; and (2) polishing tool speed of 897.87 r·min-1, working gap of 0.52 mm, and abrasive particle size of 160 μm.

Polishing performance and material removal mechanism in the solid-phase Fenton reaction based polishing process of SiC wafer using diamond gel disc

The use of SiC wafer is widespread in many fields, especially in aerospace, energy, 5 G communications, and microelectronics. Chemical-mechanical polishing (CMP) is the primary method used for achieving an ultra-smooth surface on SiC wafers. However, CMP suffers from low efficiency, leading to increased processing time and costs. To address this issue, we developed a novel diamond gel polishing disc that incorporates SiO2/Fe3O4 (S/F) powder. The disc enhances polishing efficiency through a solid-phase Fenton reaction between the disc and SiC. The research investigates the reaction mechanism and the material removal model of the polishing process using SEM, TEM, and XPS analysis. Experimental studies are conducted to assess the polishing performance and validate the effectiveness of the theoretical model. The findings indicate that SiC undergo a solid-phase Fenton reaction with polishing disc mixed S/F powder (SG-S/F disc) during polishing. The Fenton reaction generates hydroxyl radicals (·OH), which break the Si-C and Si-Si bonds in the crystal structure, leading to the formation of a softer nanoscale amorphous oxide layer on the SiC surface. The cyclic generation and removal of this oxide layer enable highly efficient polishing of SiC wafers. Compared to a gel disc without S/F (SG disc), SiC polished with the SG-S/F disc exhibits superior surface quality. Additionally, the material removal rate (MRR) of the SG-S/F disc reaches 1.42 μm/h, representing a 51.1 % improvement over that of the SG disc. These results clearly demonstrate that the solid-phase Fenton reaction significantly enhances the polishing performance of the gel polishing disc.

Efficient solid dielectric electrochemical polishing with minimal electrolyte consumption and reusable conductive media

Electrochemical polishing finds wide application across various industries, including manufacturing, biomedicine, and semiconductors. However, this technology requires substantial water usage and results in environmental pollution due to the generation of waste electrolytes containing highly corrosive acids and heavy metal ions. Herein, we propose an electrochemical polishing method (SDEP) that employs solid dielectrics consisting of macroreticular ion exchange resin (MIER) solid particles and phosphoric acid electrolyte as an alternative to traditional liquid conductive media. Maintaining a polishing current of 0.4–0.5 A requires only an electrolyte consumption of 10–20 mL/h, leading to a more than 65% reduction in electrolyte usage compared to liquid electrochemical polishing. Meanwhile, this method can be applied to polish additively manufactured metal parts with an initial roughness Ra>10 μm. The achievable surface finish features Ra = 0.778 ± 0.078 μm, Rq = 0.960 ± 0.121 μm, and Rz = 4.175 ± 1.111 μm after 1-h polishing, with a material removal rate of 0.15–0.19 mm3/min. The improvement of Ra, Rq, and Rz are 92.3%, 92.1%, and 92.0%, respectively. With the EDS and XPS analysis, rod-shaped by-products adhering to the surface of MIER particles generated during the SDEP process are confirmed as Fe3+, PO43−, and PO3−. Furthermore, the MIER particles can be reused after cleaning, exhibiting polishing performance comparable to fresh MIER. This method reduces the use of electrolytes at the source of electropolishing, and MIER particles can be recycled, pointing towards the development of eco-friendly electrochemical polishing.

Role of alumina particles in chemical-mechanical synergies in ruthenium polishing

Abrasive particles are usually considered to only play a "mechanical wear" role in the metal chemical mechanical polishing (CMP) process, neglecting their influence on chemical reactions. This study reveals the chemical role of Al2O3 particles in ruthenium (Ru) CMP by comparing the properties and polishing performance of Al2O3-SiO2 mixed slurry and pure SiO2 slurry. Several testing methods are used to investigate the mechanical and chemical actions of Al2O3 particles, including particle size distribution, Zeta potential, electrochemical reaction kinetics, oxide layer property and hydroxyl radical detection test. The results indicate that Al2O3 particles enhance the mechanical action by reducing the Zeta potential, and promote the chemical action by catalyzing hydrogen peroxide to produce hydroxyl radical (Fenton-like reaction) on Ru surface. These increase the material removal rate of Ru CMP with mixed slurry by nearly 5 times, while the surface roughness decreases by 60 %. The mechanism of chemical reaction promoted by increasing the hydroxyl radical concentration on Ru surface is confirmed from the aspects of increased corrosion current, oxide layer thickness and proportion of higher-valence Ru oxide (RuO2) in the oxide layer. Among them, the thickened oxide layer is a significant factor contributing to the substantial improvement in the material removal rate of Ru and the reduction in surface roughness. This study enhances the understanding of the chemical-mechanical synergistic mechanism of abrasive particles in metal polishing and elucidates the principle of this mechanism on promoting material removal and surface quality. It also provides new research ideas and theoretical guidance for efficient and high-quality metal polishing.

How low can you go? Short-read polishing of Oxford Nanopore bacterial genome assemblies.

It is now possible to assemble near-perfect bacterial genomes using Oxford Nanopore Technologies (ONT) long reads, but short-read polishing is usually required for perfection. However, the effect of short-read depth on polishing performance is not well understood. Here, we introduce Pypolca (with default and careful parameters) and Polypolish v0.6.0 (with a new careful parameter). We then show that: (1) all polishers other than Pypolca-careful, Polypolish-default and Polypolish-careful commonly introduce false-positive errors at low read depth; (2) most of the benefit of short-read polishing occurs by 25× depth; (3) Polypolish-careful almost never introduces false-positive errors at any depth; and (4) Pypolca-careful is the single most effective polisher. Overall, we recommend the following polishing strategies: Polypolish-careful alone when depth is very low (<5×), Polypolish-careful and Pypolca-careful when depth is low (5-25×), and Polypolish-default and Pypolca-careful when depth is sufficient (>25×).

Impact of sodium carboxymethyl cellulose on redispersibility and polishing performance of lanthanum-cerium-based slurry containing sodium hexametaphosphate

Impact of sodium carboxymethyl cellulose on redispersibility and polishing performance of lanthanum-cerium-based slurry containing sodium hexametaphosphate

Improvement of chemical mechanical polishing performance by introducing N–Si bond via external coating of cerium oxide with ZIF-8

Cerium oxide (CeO2) nanoparticles are widely used as abrasives in chemical mechanical polishing (CMP), an essential process for obtaining Si wafers with excellent surface quality. While CeO2 nanoparticles form Ce–O–Si bonds, which exhibit good CMP performance, their low activity results in a low removal rate. To address this issue, a two-step ultrasonic dispersion method was employed to prepare a uniform nuclear@shell CeO2@ZIF-8. The process of chemical bond generation in CMP was studied using spherical aberration-corrected transmission electron microscopy and X-ray photoelectron spectroscopy. In comparison to pure cerium oxide, the formation of Ce–O–Si bond was observed, and notably, the emergence of N–Si bond originating from the N of the ZIF-8 shell was identified. Coupled with the increased Ce3+ content, these developments enhanced CMP performance. The material removal rate (MRR) of the CeO2@ZIF-8 abrasives was 151.507 nm/min, which is 89.72 % higher than that of the pure CeO2 abrasives. Moreover, the surface roughness, as determined via AFM testing, was reduced to 0.231 nm within the confines of a 5.0 × 5.0 μm² region. Therefore, this study introduces a novel concept for CMP research by developing a CeO2@ZIF-8 compound abrasive to create a new N–Si bond.

Effect of Polyoxyethylene-Based Nonionic Surfactants on Chemical–Mechanical Polishing Performance of Monocrystalline Silicon Wafers

The use of surfactants is crucial in the chemical–mechanical polishing fluid system for silicon wafers. This paper examines the impact of the functional group structure of polyoxyethylene-based nonionic surfactants and the variation in the polyoxyethylene (EO) addition number on the polishing performance of monocrystalline silicon wafers, to achieve the appropriate material removal rate and surface quality. The results demonstrated that the straight-chain structure of fatty alcohol polyoxyethylene ether (AEO-9) exhibited superior performance in wafer polishing compared to octylphenol polyoxyethylene ether (OP-9) and isoprenol polyoxyethylene ether (TPEG) and polyethylene glycol (PEG). By varying the number of EO additions of AEO-type surfactants, this study demonstrated that the polishing performance of monocrystalline silicon wafers was affected by the number of EO additions. The best polishing effect was achieved when the number of EO additions was nine. The mechanism of the role of polyoxyethylene-type nonionic surfactants in silicon wafer polishing was derived through polishing experiments, the contact angle, abrasive particle size analysis, zeta potential measurement, XPS, and other means of characterization.

Preparation of CeO2 particles via ionothermal synthesis and its application to chemical mechanical polishing

CeO2 is a widely used abrasive for the chemical mechanical polishing of silicon during chip manufacturing. CeO2 can be synthesized via traditional coprecipitation, hydrothermal, and solvothermal methods; however, these methods have some issues, including high vapor pressure, flammability, toxicity, volatile solvents, and narrow heating temperature range. To overcome these issues, we developed a new ionothermal synthesis approach for high-quality CeO2 particles using 1-ethyl-3-methylimidazolium tetrafluoroborate as an imidazole ionic liquid without a template. Based on the scanning electron microscopy and particle size distribution, CeO2 particles synthesized at a reaction temperature of 210 °C for 16 h displayed sizes ranging between 0.1 and 0.3 μm. Additionally, the spherical shapes exhibited good crystallinity, regular morphology, and uniform dispersion. The results of CMP experiments indicated that the abrasives could reduce the surface roughness from 1.63 to 0.29 nm (scanning area is 5 μm × 5 μm). The obtained synthesized CeO2 particles demonstrated promising performance in Si polishing, achieving removal rates of up to 255.5 nm/min. It found that the removal rate of the abrasive prepared by ionic thermal synthesis in Si polishing was twice as much as other abrasives. Further, a possible mechanism was put forward to explain the formation of CeO2 structures with various morphologies. The proposed method presents a new approach for synthesizing CeO2 particles with uniform morphology and excellent polishing properties.

Parameters Optimization of Active Flexible Tool‐Assisted Shear Thickening Polishing Method for Concave Surface

An innovative approach, active flexible tool‐assisted shear thickening polishing (AFT‐STP), is introduced to overcome the limitations of low efficiency involved in the STP process of the concave surface. The principle and characteristics of AFT‐STP are presented, accompanied by the design of a flexible tool structure and the creation of an experimental setup. Utilizing the Taguchi method, experiments are planned and results are assessed via the signal‐to‐noise ratio to optimize process parameters. A variance analysis is then used to ascertain the relative influence of four key parameters—polishing speed, polishing gap, abrasive particle size, and abrasive concentration on the polishing performance of quartz glass in STP. Under the optimal parameters, a concave quartz glass workpiece with diameter Ø 20 mm and curvature radius 488 mm is polished, the average surface roughness Sa of the five measuring points on the surface decreases from 142.18 ± 8.63 (Avg. ± Std.) nm to 5.34 ± 1.16 nm in 45 min with MRR 57.3 nm min−1, and the surface defects of the processing area are completely removed, leaving only minor pits. The results show that the AFT‐STP is an effective method for high‐quality polishing of concave surfaces.

Enhancing dispersion stability and recyclability of ceria slurry with polyacrylic acid for improved glass polishing performance

This study aimed to enhance both the dispersion stability and recyclability of micron-sized ceria slurry in glass polishing by incorporating polyacrylic acid (PAA). PAA with a molecular weight of 240 k was very effective as a dispersant for ceria slurry due to its unique surface adsorption and its characteristics as an anionic polyelectrolyte. Using a 240 k-PAA concentration of 1.0 wt% led to significant improvements in polishing performances, as demonstrated by consistent glass removal rates across recycling cycles. Additionally, the study investigated the physico-chemical properties of polishing slurries, such as specific gravity, particle size, zeta potential, and pH. These properties were effectively maintained with the use of PAA as the dispersant, particularly when KOH was used as a pH adjuster. A 100 µm bag-type filtration system was also introduced for handling the micron-sized ceria slurry, highlighting its practical benefits in slurry management. In conclusion, employing 240 k-PAA as a dispersant in micron-sized ceria slurries for Gorilla glass polishing not only maintains quality and stability across recycling cycles but also provides notable economic advantages by enabling the recycling of the slurry.

Controlled Synthesis of Triangular Submicron-Sized CeO2 and Its Polishing Performance.

CeO2 is widely used in the field of chemical-mechanical polishing for integrated circuits. Morphology, particle size, crystallinity, and Ce3+ concentration are crucial factors that affect polishing performance. In this study, we successfully synthesized two novel triangular CeO2 abrasives with similar particle sizes (600 nm) but different morphologies and Ce3+ concentrations using a microwave-assisted hydrothermal method with high-concentration raw materials, and no surfactants or template agents were added. It is generally believed that CeO2 with a higher Ce3+ concentration leads to better polishing performance. However, the results of polishing indicate that CeO2 synthesized at 200 °C, despite its lower Ce3+ concentration, demonstrates outstanding polishing performance, achieving a polishing rate of 324 nm/min, and the Sa of Si wafers decreased by 3.6% after polishing. This suggests that, under similar particle size conditions, the morphology of CeO2 plays a dominant role in the mechanical effects during the polishing process. Additionally, compared to commercial polishing slurries, the synthesized samples demonstrated better polishing performance. This indicates that, in CMP, the pursuit of smaller spherical abrasives may not be necessary. Instead, the appropriate shape and particle size can better balance the material removal rate and surface roughness.

Influence of Microstructure on the Mechanical Properties and Polishing Performance of Large Prehardened Plastic Mold Steel Blocks

The microstructures throughout a 696 × 1360 mm cross-section of an ISO 1.2738 prehardened steel block for a plastic mold were characterized via optical and electron microscopy and electron backscatter diffraction. The hardness, strength, and polishing performance of the steel block were also tested. The results showed that the microstructure of the steel bloom from the edge to the core consisted of tempered sorbite, tempered bainite, and pearlite microstructures. Abnormal upper bainite and coarse carbides were also found. The bloom sections with hardness values of 37.4 to 39.3 HRC comprised tempered sorbite and bainite. The hardness of the core was approximately 36.5 HRC due to the presence of pearlite. The tensile and yield strengths were the same in the edge and middle areas mainly owing to tempered sorbite. The polishing performance was affected by the microstructure. Tempered sorbite produced the best polishing performance due to its fine and uniform microstructure, whereas that of tempered bainite and pearlite, which contained large carbide particles and mixed phases, was worse.

High precision polishing of aluminum alloy mirrors through a combination of magnetorheological finishing and chemical mechanical polishing

After the aluminum alloy mirror machined by single point diamond turning (SPDT), the residual tool marks and surface accuracy of the aluminum alloy mirror cannot meet the requirements of visible or ultraviolet light system. In this study, a processing method combining magnetorheological finishing (MRF) and chemical mechanical polishing (CMP) is proposed to realize the polishing of aluminum alloy mirrors with high efficiency, high precision and high-quality. Firstly, the properties and composition of passivation layer after MRF were analyzed and the polishing performance of acidic, neutral and alkaline alumina polishing fluid on passivation layer were investigated based on the computer numerical control (CNC) polishing equipment. Based on the experimental results, a new acidic nano-silica polishing fluid which is suitable for the efficient and high-quality removal of passivation layers on aluminum alloy surfaces was developed. Finally, a combined approach of MRF-CMP was used to the directly polishing of a rapidly solidified aluminum mirror (RSA-6061) with a diameter of 100 mm after SPDT. With two iterative of MRF-CMP polishing in 220 minutes, the surface accuracy of the aluminum alloy mirror was improved from 0.1λ (λ=632.8 nm) to 0.024λ, and the surface roughness (Ra) decreased from 3.6 nm to 1.38 nm. The experiment results manifest that high precision, and high-quality aluminum alloy mirror can be achieved by MRF-CMP method with the new developed acid nano-silica polishing fluid and suitable MR polishing fluid. The research results will provide a new strategy for ultra-precision direct polishing of aluminum alloy mirrors and will also give the important technical support for the extensive use of aluminum alloy mirror in visible light and ultraviolet optical systems.

Novel hybrid chemical magnetorheological fluid for polishing Ti–6Al–4V alloy

ABSTRACT This study presents a highly efficient chemical and magnetorheological fluid (C-MRF) hybrid polishing process established by using an eco-friendly slurry of malic acid, Fe3O4–SiO2 abrasive particles, and hydrogen peroxide (H2O2) as an oxidant, all mixed with purified water, highlighting its efficacy in a wide range of polishing applications. Herein, the polishing processes of Ti–6Al–4V alloy utilizing C-MRF with on Fe3O4–SiO2 abrasives are detailed, and the polishing performance is assessed by investigating the influence of oxidizing agent H2O2 and acid malic to the surface finish of the Ti–6Al–4V alloy. The linear variable magnetic field by improved Halbach array was proposed to improve the material removal rate and surface quality and create a polishing process with a highly efficient magnetic field source. Single-factor and orthogonal experimental analysis methods are applied to provide the technological parameters factors with varying influences on surface quality and material removal ability.

Center-injected Polishing for Efficient Slurry Utilization

Polishing is one of the most crucial finishing processes and usually consumes a sufficient slurry to achieve an ultra-fine surface. However, excess slurry consumption is environmentally costly, as it generates a large amount of wastewater. Given the growing environmental concerns, it is essential to improve the process efficiency and minimize the environmental burdens. Considering this, a novel polishing system, herein referred to as center-injected polishing, is proposed by injecting slurry into the center of the polishing pad. Here, it is aimed to utilize the centrifugal force of the rotating pad, with the aim of efficient slurry utilization. The slurry is directly introduced between the pad and the workpiece, then dispersed across the pad by centrifugal force. A simple experiment was conducted with computational analysis using the specially designed polishing tool to prove the concept; slurry was distributed more uniformly in center-injected polishing when compared to the conventional process. The polishing system was then constructed to evaluate polishing performances. Based on sets of experiments in the polishing of silicon carbide (SiC), slurry efficiencies and productivity were analyzed with respect to different rotational speeds and slurry supply rates. The material removal rate (MRR) was more than twice the rate achieved by conventional polishing at the same processing conditions; whereas the slurry consumption was approximately 60% less at the same MRR. The extended Preston equation was used to predict the MRR of the new process. It is expected that efficient slurry utilization will reduce the environmental footprint of abrasive processes.

Chemical-mechanical synergies effects of multi-purpose pH regulators on C-, A-, and R-plane sapphire polishing

The development of sapphire slurry follows the requirements of environmental friendliness, low cost and high efficiency. Therefore, the effects of KOH, aminomethyl propanol (AMP) and arginine (ARG) as pH regulators on the chemical mechanical polishing (CMP) performance of C-, A- and R-plane sapphire were investigated. The results showed that ARG was the most effective, which could increase the removal rates of C-, A- and R-plane sapphire to 5.65 µm/h, 2.80 µm/h and 3.59 µm/h, and reduce the surface roughness Sq to 0.194 nm, 0.161 nm and 0.173 nm, respectively. Mechanical action analysis, XPS, UV-Vis, and theoretical calculations revealed that ARG could improve the mechanical action of CMP and chemical action by acting as a complexing agent to complex with AlOH4−.

Synergistic effect of abrasive friction and glycine on improving chemical mechanical polishing performance of single-crystal GaN substrate

With the rapid development of the third-generation semiconductor materials, the chemical mechanical polishing rate and surface quality of single-crystal gallium nitride (GaN) substrates have been a research hot-spot. In this work, the synergistic effect of abrasive friction and glycine (Gly) on improving the chemical mechanical polishing (CMP) performance of single-crystal GaN substrate is proposed and studied systematically. The results indicated that the polishing solutions with Gly have a 2.3-fold improvement in material removal rate (MRR) as well as scratch-free surface than that without Gly. The maximum MRR of the single-crystal GaN substrate is 129.4 nm/h with surface roughness (Ra) of 0.64 nm attained by using the polishing solutions containing only 3 wt% potassium persulfate (K2S2O8). In contrast, when Gly is added as a reaction reagent, which can be activated by abrasive friction, the maximum MRR is increased to 304.2 nm/h with Ra of 0.42 nm. Meanwhile, the epitaxial evaluation indicates that two-dimensional (2D) MoS2 grown on processed single-crystal GaN substrate has superior crystalline quality and optical properties. Finally, the polishing mechanism of the single-crystal GaN substrate using the mixed solutions of K2S2O8 and Gly is discussed. The proposed CMP method has potential applications in the semiconductor and microelectronics industries.

Novel ceria/graphene oxide composite abrasives for chemical mechanical polishing

The structure and particle distribution of the abrasive used in chemical mechanical polishing (CMP) directly affect the performance of polishing and quality of the resulting surface. The ceria (CeO2) nanomaterial has been extensively employed in polishing abrasives. Increasing the Ce3+ content is known to improve removal efficiency and enable optimal surface quality. In this study, we increased the Ce3+ content on the CeO2 surface by growing CeO2 nanoparticles in situ on graphene oxide (GO; CeO2@GO) to develop novel composite abrasives for the high-performance CMP of silicon wafers. The designed composite abrasive fully utilized the special structure of GO and the effect on the charge-transfer between CeO2 and GO, which increase the Ce3+ content and number of chemical reaction sites available during the polishing process. This accelerates the generation rate of the oxide layer on the surface of the silicon wafer and increases the removal rate while improving surface quality. The removal rate of the composite abrasives reached 190.58 ± 13 nm/min, which is 50% higher than that of pure CeO2 abrasives. Moreover, the average surface roughness (Ra) of 0.278 ± 0.07 nm within the confines of a 5.0 × 5.0 μm2 region was achieved using the novel composite abrasives. This study offers a straightforward method to enhance the content of Ce3+ in materials and provides a novel route for obtaining efficient composite abrasives.

Synthesis of Al2O3@MnO2 composite abrasives and their chemical mechanical polishing performance on silicon carbide (SiC)

The effectiveness of silicon carbide (SiC) planarization mostly relies on the chemical and mechanical effects during chemical mechanical polishing (CMP). Nevertheless, the alumina (Al2O3) abrasive only provides a mechanical effect and is incapable of achieving a high-efficiency polishing of SiC. To address this issue, a series of novel Al2O3@MnO2 composite abrasives were prepared by encapsulating varying amounts of manganese dioxide (MnO2) on Al2O3 abrasive, and the polishing performance on SiC wafers was evaluated. The X-ray diffraction (XRD) and scanning electron microscope (SEM) images, along with the size and zeta potential data, show that MnO2 is successfully coated on the surface of Al2O3, and the dispersion of Al2O3@MnO2 composite abrasive is significantly improved when compared with the pure Al2O3. Furthermore, the CMP experiment and surface profile analysis demonstrate that the material removal rate (MRR) can reach a maximum value of 640.47 nm/h when using a 0.05 wt% MnO2-coated Al2O3 composite abrasive, which is 76 % higher than that of traditional Al2O3 abrasive. Furthermore, the average surface roughness (Sa, arithmetic mean height) of SiC is reduced to 0.73 nm. X-ray photoelectron spectroscopy results reveal that the surface of SiC is oxidized and forms a chemical bond known as Mn–O–Si after CMP. The results of the friction coefficient test and contact angle test indicate that slurries containing composite abrasive have exceptional wettability and a higher friction coefficient. Under the synergistic chemical and mechanical effects, SiC is oxidized to soft oxide and then removed circularly to reach excellent flatness.