Silica Abrasive Particles Research Articles

Micro-scratches generation mechanism by copper oxides adhered on silica abrasive in copper chemical mechanical polishing

Chemical mechanical polishing (CMP) may introduce micro-scratches on the copper surface, posing a substantial challenge for developing advanced technology nodes. This study used macroscopic CMP and microscopic atomic force microscopy to investigate the micro-scratches generation mechanism in copper CMP from the perspective of abrasive particles. In the near-neutral slurry containing a low concentration of H2O2, copper can be oxidized to cuprous oxide and/or cupric oxide, forming a fragile oxide layer that can be removed by silica abrasive particles. The removed copper oxides can be adhered on the silica abrasive particles through electrostatic attraction, modifying the surface state. The adhered copper oxides possess irregularities and high hardness, likely inducing high contact stress locally and resulting in micro-scratches on the copper surface.

Preparation and Performance Testing of Green Non-toxic Polishing Solution for Medical Titanium Alloy

To obtain the lower toxic residue on the medical titanium alloy surface in chemical mechanical polishing process, a new green polishing solution was proposed and evaluated in this study. The humoral fluid was selected as the basic solution in which the silica abrasive particles were used for the grinding particles, and the H2O2 was added as the oxidant. A chemical mechanical polishing test was carried out for its performance investigation with titanium alloy material. Then the surface roughness and material remove ratio of test samples were analyzed and compared with that of existed polishing solution condition. At last, the toxic residue of the titanium alloy samples was obtained by scanning electron microscopy technology. The experimental results indicated that the better material removal rate and surface roughness of medical titanium alloy with humoral polishing solution are obtained comparing with existed polishing solution condition. More importantly, the content of toxic elements on the sample surface was significantly reduced due to the more aluminum and vanadium ions dissolved in polishing solution, which is more beneficial for its application in the medical prosthetics field. This study provides a new reference for the toxic residue reduction on the material surface of medical titanium alloy in chemical mechanical polishing process.

Influence of the ball material on friction and wear in microabrasion tests

This work aims to contribute to the understanding of the complex relationship between ball material, friction, particle dynamics and wear during microabrasion tests. For that, five different balls (Ø 25.4 mm) were used: one ceramic (Si3N4), one metal (AISI 52100 steel) and three thermoplastic polymers (polypropylene, polyacetal, and polyamide 6.6). The tests used a fixed ball micro-abrasion test rig, AISI 304 austenitic stainless steel specimens, silica abrasive particles (10 %wt. slurry concentration), rotational speed of 150 rpm and total test time of 90 min. The harder balls induced higher friction but resulted in lower wear rates than the softer polymeric balls. The wear craters showed that particle entrainment was favoured for the low friction, softer balls (polypropylene and polyamide 6.6), leading to sliding of the abrasives and thus grooving. The craters produced with the harder balls (AISI 52100 steel and Si3N4) presented a few, sparsely spaced deep grooves, but with significant amount of microindentations between the grooves, characterizing the mechanism of microrolling. The polyacetal ball resulted in intermediate results between the other two groups. It was hypothesised that for the lower friction materials the larger difference in friction between the abrasive and the ball (μab) and between the abrasive and the specimen (μas) favoured particle entrainment and increased wear rates. For the harder balls this difference should be smaller, leading to fewer particles entraining into the contact, but fragmentation of the abrasives could induce microrolling between the grooves.

Chemical Mechanical Polishing of Mo Using H2O2 as Oxidizer in Colloidal Silica Based Slurries

Chemical mechanical polishing (CMP) of molybdenum (Mo) using H2O2 based slurry with colloidal silica as abrasives has been systematically investigated. Effects of pH values, abrasives and additive of the slurry on CMP of Mo were investigated respectively. Results show that by adding ammonium sulfate (AS) in the alkaline H2O2 based slurry, both static etch rate (SER) and removal rate (RR) of Mo became much greater than without adding AS because of formation of a highly soluble (NH4)2MoO4. It is found that colloidal silica abrasive particles could adsorb on the Mo surface and have inhibitory effect on corrosion and polishing of Mo, and the higher concentration of colloidal silica particles, the lower SER and RR. AS addition in the slurry would enhance this phenomenon. Raman measurement results show that, silicomolybdic acid could form on the Mo surface in the slurry because of reaction between Moly oxide and silica particles, which causes the adsorption and inhibition of Mo etching and polishing.

Application of Fluorescence Correlation Spectroscopy in the Characterization of Particle Size Distributions of Colloidal Silica Abrasives Used in Chemical-Mechanical Planarization

Recent studies have demonstrated that fluorescence correlation spectroscopy (FCS) can be used to analyze the adsorption of dissolved chemical compounds onto the dispersed abrasive particles in a CMP slurry (1, 2). The technique exploits competitive adsorption at the particle’s surface between a fluorophore and CMP-relevant, dissolved chemical compounds. As chemical compounds in a slurry adsorb to a fluorescent abrasive particle and de-sorb the fluorophore from the particle, FCS-measured diffusion coefficients of the fluorophores will indicate increasing concentration of the free fluorophore in solution as the concentration of adsorbed chemical compounds increases.In the present study, the FCS method is extended for the analysis of particle size distributions of smaller-sized colloidal silica CMP abrasives. This new application of the FCS technique is motivated by the commercial need to further reduce wafer defect formation in conjunction with increased removal of slurry and wafer particulates produced during CMP processes. A key analytical capability gating this processing requirement is the necessity to analyze, quantitatively, the smallest abrasive particles in a CMP slurry which are present at extreme dilution. Established methods for particle size analysis, such as disc centrifugation and dynamic light scattering, typically lack the sensitivity required to analyze a minute fraction of abrasive particles, such as colloidal silica, with hydrodynamic diameters less than 20 nm in a CMP slurry. Because FCS has sizing capability for small molecules equivalent in hydrodynamic diameter (d h) to fluorescent dyes (d h = 1.0 to 1.5 nm) coupled with its analytical sensitivity in the nanomolar range, particle size distribution analysis of silica abrasive particles with mean diameters less than 10 nm, is potentially accessible via FCS.Representative particle size distributions determined by FCS are shown in Figure 1 for a pair of related fluorescently-labeled silica dispersions. The data overlay in the figure compares the particle size distributions of a parent silica dispersion (solid line, mean hydrodynamic diameter = 45 nm) and that of the isolated supernatant of the dispersion obtained by ultracentrifugation of the parent dispersion in order to isolate the smallest particles (dashed line, mean hydrodynamic diameter = 11 nm) in the dispersion. These data demonstrate the ability of the FCS technique to detect and quantity the fraction of smallest particles in abrasive colloidal silica dispersions. Additional examples illustrating the range and applicability of the technique in the quantitative analysis of particle size distributions for representative silica particles used commonly in CMP abrasives are discussed in this presentation.1. Moinpour, M.; Wayman, A.; Rawat, R.; Carver, C. T.; Remsen, E. E. Surface Adsorption of CMP Slurry Additives on Abrasive Particles. Electrochem. Soc. Trans. 2013, 52,489-494.2. England, A.N.; Rawat, A.; Moinpour, M.; Remsen, E.E. Additive/Abrasive Interactions in Solution: Investigation of the Surface Chemistry and Adsorption Behaviour of CMP Abrasives. Proc. Int. Conf. Planar. Tech. 2012, 1-6.

Effect of Modified Silica Abrasive Particles on Nanosized Particle Deposition in Final Polishing of Silicon Wafers

The silane coupling agent γ-aminopropyl triethoxysilane (APTS) and polyethylene oxide (PEO) are proposed to modify the SiO2 abrasive particles for final polishing of silicon wafers. The effects of the modified silica abrasive particles on nanosized particle deposition, roughness, and removal rate of the silicon wafer are explored in detail. PEO is proved to be a potential modifying agent for controlling deposition of large particles (∼410 nm diameter), leading to low roughness (Ra = 0.097 nm), and APTS is found to be effective in controlling deposition of both large and small particles (∼410 and ∼200 nm diameter, respectively), resulting in lower roughness (Ra = 0.054 nm).

(Invited) Surface Adsorption of CMP Slurry Additives on Abrasive Particles

Fluorescence correlation spectroscopy (FCS) is used to study additive-abrasive particle interactions in chemical-mechanical planarization (CMP) slurries. FCS provides quantitative determinations of the binding between additives and abrasive particles by characterizing the competitive adsorption of the additive and a fluorescent probe molecule, Alexa fluor 546 (A546) at the surface of a silica abrasive particle. Analysis of the adsorption of benzotriazole (BTA) on colloidal silica confirms the displacement of A546 by added BTA. However, glycine enhances the adsorption of A546 by colloidal silica. FCS is also shown to be a sensitive technique for detecting differences in the surface chemistry between different types of colloidal silica abrasive particles used in CMP processes.

ILD CMP with Silica Abrasive Particles: Effect of Pore Size of CMP Pad on Removal Rate Profiles

The influence of pad intrinsic properties on the removal rate profiles of ILD CMP with fumed silica abrasive slurry was studied by changing pad's polymer hardness, porosity, and pore size. Of these intrinsic properties, pore size is found to be most critical to removal rate profiles. By systematically changing the pore size from <1 μm to >100 μm, with porosity from 5% to 50%, of pad made of thermal-plastic urethane (TPU), removal rate profile of oxide polishing was studied. A flat removal rate profile cross wafer is desired for ILD CMP. It was found that when the pore size was larger than a certain threshold, flat removal rate profiles could be achieved. Below the threshold, severe edge-fast/center-slow removal rate profiles were observed and such profiles cannot be remedied by changing pad's other properties like porosity or polishing process conditions. A model is proposed to explain the non-flat removal rate profiles associated with the small pore size (<20 μm).

Erosive wear of advanced composites based on WC

WC based and yttria stabilized zirconia doped (13 vol%) cermets with different metal binders (Co, Ni or Fe) have been successfully produced and tested for performance in erosive media (silica abrasive particles; particle velocity of 80 ms −1 and impact angles of 30° and 90°). An increase in fracture toughness and erosion resistance was shown to be influenced by tetragonal zirconia transformability. Wear performance of the newly developed cermets is found to be highly dependent on sintering conditions.

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.

ILD CMP with Silica Abrasive Particles: Interfacial Removal Kinetics and Effect of Pad Surface Textures

The removal mechanism for interlevel dielectric (ILD) chemical mechanical polishing (CMP) with fumed silica abrasive slurry was studied by measuring silicon dioxide wafer removal rates as a function of abrasive concentration and pH and also by examining the surface charges of the abrasive particles at different pH’s. The interfacial removal kinetics indicates that the wafer removal rate is consistent with a first-order reaction and is proportional to the concentration of surface silanolates on the abrasive particles. The actual removal is proposed to be achieved by a direct nucleophillic attack of the silica particle silanolates on the wafer Si–O bond. Pad surface texture provides the means to transport the slurry to the contact zone and the effective concentration of abrasive particles doing actual removal is greatly influenced by the pad surface macrotexture by grooving design and the microtexture by conditioning. The observed correlation between the pad surface parameters that are used to characterize the pad microtexture and the removal rate highlights the importance of the pad surface texture to ILD CMP.

Chemical mechanical planarization of copper using abrasive-free solutions of oxalic acid and hydrogen peroxide

In this work we study aqueous solutions of oxalic acid and hydrogen peroxide as possible abrasive-free slurries for chemical mechanical planarization (CMP) of Cu. We show that the addition of (3 wt%) colloidal silica abrasive particles has no measurable effects on the already relatively high polish rates of Cu. These results suggest that chemical rather than mechanical effects dominate removal of Cu surface layers in this system. The Cu removal efficiency of this slurry can be controlled by adjusting its acidity and H 2O 2 content. By combining measurements of Cu polish and dissolution rates with electrochemical experiments, we propose a reaction scheme that describes the mechanism of Cu removal in abrasive-free solutions of H 2O 2 and oxalic acid as a function of pH and H 2O 2 concentrations.

Mechanical properties and features of erosion of cermets

The erosive wear resistance of cermets with different composition, structure and properties has been investigated. It has been shown that cermets erosive wear resistance cannot be estimated only by hardness, characterised by resistance to penetration. The differences in wear resistance between cermet materials with equal hardness level can be attributed to differences in their resistance to fracture. The present paper discusses some features of the material removal process during the particle–wall collision. Solid particle erosion tests on eight materials have been performed using silicon carbide and silica abrasive particles within a range of erodent size of 0.1–0.3mm, impact angles from 30 to 90° and particle velocity from 30 to 80ms−1. In order to clarify the details of the impact, the process of interaction of solid particles with cermet targets was studied using a laser Doppler anemometer (LDA) measuring technique. Systematic studies of the influence of the impact variables on the collision process have been carried out.

Chemical–mechanical polishing of copper and tantalum with silica abrasives

Chemical mechanical polishing of copper and tantalum was performed using fumed amorphous silica abrasive particles dispersed in H2O2, Fe(NO3)3, and glycine solutions. Results showed that in DI water silica did not polish Cu but Ta had a relatively high polish rate. Cu polish rate decreased with increasing particle concentration in Fe(NO3)3-based slurries due to the adsorption of Fe3+ on the silica surface. Addition of H2O2 enhanced Cu polish rate but reduced Ta polish rate. The specific surface area of the particles played an important role in the removal of Ta and Cu, presumably due to some chemical bonding between the materials being polished and the silica particles.

Effect of abrasive contaminants on scuffing

Four-ball machine tests have been performed to study the effect on scuffing of fine silica abrasive particles contained in the lubricant. The boundary lubrication zone that sets in after seizure recovery has been utilized in the study. The particles are found to increase abrasive wear but reduce adhesive wear and to cause scuffing at less severe conditions that with clean oil by contributing to frictional heating. When the heat generated cannot be dissipated from the contact zone the contact temperature is found to increase and lubricant desorption causes scuffing.