CMP Slurry Research Articles

Analysis, identification, and application of distribution of relaxation times in CMP slurry

This study delves into the mechanistic roles of oxidants, complexing agents, and inhibitors in slurries through of Distribution of Relaxation Times (DRT) analysis. The influence of varying concentrations of these chemicals on electrochemical processes is discussed. This article divides the spectrum obtained through DRT analysis into four different frequency regions and differentiate naming through electrode reaction process: the double-layer charging step, the charge transfer step, the mass transfer step, and the surface transformation step by adsorption or chemical alterations at the electrode surface. The results reveal that the peak observed in the low-frequency range at 10−2–10° Hz is associated with mass transfer step, while the relaxation peak at 10°–102 Hz corresponds to the charge transfer process, while the relaxation peak occurring at 102–104 Hz is linked to the surface transformation step, and the first peak emerging in the 104–106 Hz range is attributed to double-layer charging step.

(Invited) The Evolving SiC Market and Impact on CMP Supply Chain

Silicon carbide (SiC) is a wide bandgap semiconductor with physical and electrical properties that provide superior performance in high-voltage or high-power applications. Compared to the more established silicon devices, SiC provides better thermal conductivity, ~10x higher breakdown voltage, faster switching speeds and lower resistivity. Even with the performance advantages, the adoption rate of SiC is slowed by high cost and the inherent difficulty of processing this material. SiC is extremely hard (just below diamond on the hardness scale) and chemically inert which makes processing boules into wafers rather difficult. This presentation will contrast some of the basic differences between process methods developed for silicon and other semiconductor materials versus those required for SiC.Demand for high-quality single crystal SiC substrates continues to rise as the worldwide demand for electric vehicles, charging infrastructure, green energy production, and more efficient power devices in general requires more and more SiC devices. SiC wafer manufacturers are trying to ramp output as quickly as possible but technical difficulties of processing SiC are often a limiting factor. In spite of aggressive capital spending by many of the major players, the actual growth in substrate production has been constrained to around 15% CAGR even though demand would support a much faster ramp. As end use markets continue to evolve, ripple effects are also evident in the underlying supply chains, such as CMP pads and slurries.

SiC CMP Process Sensitivities

Single-crystal silicon carbide (SiC) is a wide bandgap semiconductor with physical and electrical properties that provide superior performance compared to silicon or almost any other semiconductor material in high-voltage and high-power applications. It is also extremely hard, second only to diamond, and chemically almost inert which makes the CMP process step quite challenging. In recent years, a great deal of effort has been expended on advancing this process, particularly with regard to slurry formulations that can provide reasonable removal rates and damage-free final surface finishes. In this presentation, we will review a number of these developments for SiC CMP slurries. We will present data highlighting their process responses to standard CMP parameters, interactions with pad conditioning, and describe some of the requirements for production process controls.

Controlling Diameter and Morphology of Colloidal-Silica-Abrasives Via Designing Surfactant Functional Group

As the design rule of logic semiconductor has been scaled down toward 5, 3, 2.1, 1.5, and 1.0 nm, the line width of Cu-film as interconnect line of logic semiconductor has been rapidly scaled down toward 36, 32, 24, 20 and 16 nm. The CMP of the Cu-lines is essential fabrication process, challenging an achievement of dishing and erosion during Cu-film CMP. In particular, the dishing and erosion of the Cu-film CMP has been principally affected by the diameter and morphology of colloidal-silica-abrasives in a CMP slurry. In a conventional synthesis method synthesis of colloidal-silica-abrasives, ethoxysilanol was formed via the hydrolysis reaction by Tetraethyl orthosilicate(TEOS) and H2O producing ethoxysilanol, following the condensation reaction between two ethoxysilanol. The diameter of colloidal-silica-abrasives could be obtained by adjusting the concentrations of TEOS, alcohol, and alkali catalyst, but the solid loading of colloidal-silica-abrasives could be varied. Thus, in our study, a novel synthesis method of the colloidal-silica-abrasives was designed by adding a charged functional group surfactant during the conventional colloidal-silica-abrasives synthesis method. The effect of the surfactant having negative charged carboxyl functional group (i.e. Ethylenediaminetetraacetic acid: EDTA) on the diameter and morphology of the colloidal-silica-abrasives were investigated as function of the EDTA concentration; i.e. when the concentration of EDTA increased from 0 to 0.03 wt%, the diameter of colloidal-silica-abrasives increased from 47.0 to 103.8 nm and the solid loading of colloidal-silica-abrasives increased from 2.0 to 2.36 wt%, as shown in Fig. 1. In addition, when the ETDA concentration increased above 0.0025 wt%, the morphology of colloidal-silica-abrasives was transformed from cocoon shape to spherical shape. Furthermore, the effect of the surfactant having the positive charged amine functional group (i.e. Triethanolamine: Tri-ETA, Ethylenediamine: EDA, Diethylenetriamine: DETA, Triethylenetetramine: TETA) were estimated as function of the number of amine functional group in the surfactant, as shown in Fig. 2. When the number of positive charged amine functional groups increased 0 to 4, the diameter of colloidal-silica-abrasives increased from 67.2 to 143.86 nm and the solid loading of colloidal-silica-abrasives increased from 2.0 to 2.2 wt%. In addition, the synthesis with positive charged amine functional group was transformed from cocoon shape to spherical shape. The synthesis mechanism, the enhanced polishing rate of Cu-film surface, dishing and erosion after Cu-film will be presented in detail. Acknowledgement This research was supported by the MOTIE(Ministry of Trade, Industry & Energy (1415180388) and KSRC(Korea Semiconductor Research Consortium) (20019474) support program for the development of the future semiconductor device. Figure 1

Unraveling the Slurry/Substrate Interfacial Reaction Mechanism for Wide Band Gap (WBG) Chemical Mechanical Planarization (CMP)

Wide band gap (WBG) semiconductors have become of great interest to extend Moore’s Law beyond the limitations of current Si IC technology. More specifically, WBG materials (i.e., Silicon Carbide and Gallium Nitride) have been shown to increase performance due to their intrinsic properties (i.e., high capacitance, thermal stability, and wear resistance) associated with these materials. Current CMP processing of these WBG materials utilizes aggressive chemical conditions (i.e., abrasive nanoparticles and harsh oxidizers) and increasing shear forces to obtain the desired material removal rates (MRR) and surface planarity. Unfortunately, these processing conditions can cause defectivity (i.e., organic residue, pad debris, scratches, etc.) during the polishing process, leading to increasingly complex post-CMP cleaning steps. This work focuses on the strategic design of chemically activated, peroxide-based CMP slurries for emergent materials that target redox activation at the slurry-substrate surface interface to achieve improved CMP performance (i.e., enhanced material removal rates, superior surface quality, and low defects). More specifically, the catalytic generation of reactive oxygen species (ROS) (i.e., hydroxyl radical (*OH) and singlet oxygen (1O2)) at the substrate interface via surface complexation during the polishing process is exploited. The generated ROS can weaken the Si-C bonds within the surface of the substrate, allowing the particles to remove the surface more readily. This work explored organometallic complexes and non-metal catalysts, such as boron-based additives, as surface-active redox modulators. Initial results show that lower-stability complexes result in equally low MRR ranges below 400 nm/hr, while highly stable complexes increase the MRR as high as 1600 nm/hr. This complex stability/MRR trend has been further correlated to changes in the electron-poor areas of the complexes and ROS generation via radical trapping. The surface roughness analysis has shown improved surface quality between 0.8-1.0 nm across the substrate; however, organic residues from the complexes remain. Transitioning to non-metal boron electrophiles has shown similar MRR results (1000-1400 nm/hr) but can alleviate surface contamination. This implementation of Araca. Inc.’s patent-pending Flucto-CMP® technology employs megasonic energy to promote enhanced ROS generation, thus accelerating removal and significantly improving surface defectivity.

Slurry Activation for Enhanced Surface Redox Reactions in CMP

A novel add-on hardware device is placed near the point of slurry dispense that can instantaneously activate slurry performance during polishing via megasonic irradiation. This new technology (Flucto-CMP® is able to overcome the inherent polisher-slurry weaknesses such as wafer-level defects, process vibrations, cost of ownership, slurry waste, remval rate (RR), and RR selectivity. Flucto-CMP® has been successfully applied to various types of CMP slurries resulting in significant increases in the removal rates of copper, SiC, borosilicate hard mask, ILD, TiN, and silicon carbide through chemical alteration of the passivation layer needed for material removal. Specifically, for copper CMP, using Flucto-CMP®, we see an up to 31% boost in RR which is well correlated with the amount of reactive oxidizing species generated through irradiation as well as the measured relative indentation depth of the passivation layer. In addition to boosts in RR, for copper, we see a 50X drop in the variance of shear force and a 5X drop in the variance of normal force when Flucto-CMP® is used. This dramatic reduction in process vibration for copper soft-landing processes ought to reduce wafer-level defects. Much greater rate improvements are observed when polishing SiC, and borosilicate hard masks.

Cetyltrimethylammonium bromide reformed ceria nanocomposites of chemical mechanical planarization for silica wafers

BackgroundChemical-mechanical planarization (CMP) is the most important process in the semiconductor industry, as it affects the product manufacturing yield. Of the several factors involved in planarization, the choice of abrasive slurries affects the extent to which impurities and roughness are removed. Cerium oxide (CeO2) is considered an outstanding polishing material because of its excellent hardness, well-controlled structure, and chemical force, and CMP requires well-dispersed slurry nanoparticles (NPs) with uniform structure, size, and shape. In this study, urea/alkaline-induced nanocubic MethodsCeO2 was synthesized in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB)-generated cubic CeO2 NPs, which were then used in a silica wafer polishing test. Dynamic laser scattering and transmission electron microscopy indicated that the cubic plate NP size distribution and zeta potential ranged from 18 to 30 nm when measured between –35 and –45 mV. Elemental composition via X-ray photoelectron spectroscopy was studied to demonstrate the mechanism of Ce3+/Ce4+ with crystal information, which matched the X-ray diffraction grain size calculation and finite element–scanning electron microscopy measurements. We also performed a simulation of cubic CeO2 NP formation and pillar CeO2 inhibition under an additional amount of structure-modifying agent (e.g., CTAB). Fourier transform infrared spectra indicated a successful CTAB reaction with CeO2. Small angle X-ray scattering spectra were used to obtain simulated NP shapes and parameters via the SasView model. A confocal laser scanning microscope was then used to measure the roughness and 2-D plane view of an 8-inch tetraethyl orthosilicate coated silica wafer. Significant findingsOur results showed that the bared silica wafer planarize with CTABx-CeO2 NPs reduced the ISO grade number from Level 9 to Level 7, which corresponds to a 70.7–74.5% roughness planarization of the raw material. This study presents a fast, uniform, low-roughness CMP slurry material synthesis and characterization method that can enhance the technique of slurry nanoparticle synthesis from stable materials.

Silicon Wafer CMP Slurry Using a Hydrolysis Reaction Accelerator with an Amine Functional Group Remarkably Enhances Polishing Rate.

Recently, as an alternative solution for overcoming the scaling-down limitations of logic devices with design length of less than 3 nm and enhancing DRAM operation performance, 3D heterogeneous packaging technology has been intensively researched, essentially requiring Si wafer polishing at a very high Si polishing rate (500 nm/min) by accelerating the degree of the hydrolysis reaction (i.e., Si-O-H) on the polished Si wafer surface during CMP. Unlike conventional hydrolysis reaction accelerators (i.e., sodium hydroxide and potassium hydroxide), a novel hydrolysis reaction accelerator with amine functional groups (i.e., 552.8 nm/min for ethylenediamine) surprisingly presented an Si wafer polishing rate >3 times higher than that of conventional hydrolysis reaction accelerators (177.1 nm/min for sodium hydroxide). This remarkable enhancement of the Si wafer polishing rate for ethylenediamine was principally the result of (i) the increased hydrolysis reaction, (ii) the enhanced degree of adsorption of the CMP slurry on the polished Si wafer surface during CMP, and (iii) the decreased electrostatic repulsive force between colloidal silica abrasives and the Si wafer surface. A higher ethylenediamine concentration in the Si wafer CMP slurry led to a higher extent of hydrolysis reaction and degree of adsorption for the slurry and a lower electrostatic repulsive force; thus, a higher ethylenediamine concentration resulted in a higher Si wafer polishing rate. With the aim of achieving further improvements to the Si wafer polishing rates using Si wafer CMP slurry including ethylenediamine, the Si wafer polishing rate increased remarkably and root-squarely with the increasing ethylenediamine concentration.

Corrosion Inhibition and the Synergistic Effect of Three Different Inhibitors on Copper Surface

Copper(Cu) has been an interconnect material widely used in giant-large scale integrated circuits (GLSI). Corrosion inhibitor is a key factor to ensure global planarization of Cu in the CMP slurry. In this paper, three selected inhibitors BTA(Benzotriazole), TAZ(1,2,4-triazole), and MBO( 2-Benzoxazolethione) were investigated inhibition behaviors and synergy on the Cu surface. The results show that they are all effective Cu inhibitors in alkaline solutions. MBO loses its ability in H2O2, but BTA and TAZ do not. The calculated synergistic parameters of BTA/TAZ is 0.1763, XPS and UV–Via experiments show that the antagonism between them is caused by two competitive reactions due to the similar adsorption mechanism: one is the competition for the adsorption site on the surface, and the other is the competition of copper ions that affects the formation of Cu(I)-BTA. The calculated synergistic parameter of BTA/MBO is 1.7763, the synergy between them is obvious.

Observation of Polymer Additive Absorption on Substrates for STI CMP Slurries

High SiO2 to SiN removal rate selectivity and SiN removal rate suppression are indispensable for the shallow trench isolation (STI) CMP slurry and those characteristics are achieved by the polymer additives such as poly-acrylic acid (PAA). Recently, it is reported that the polymers containing hydrophobic and hydrophilic moieties show high selectivity and SiN removal rate suppression [1, 2]. For further improvement of these characteristics, it is important to clarify the mechanisms of the effects of the polymer additives. Several studies have reported that polymer additives preferentially adsorbs on the SiN film resulting high rate selectivity [2, 3]. However, evaluation of adsorption properties of the polymer additives are limited to thermal or electrochemical analysis and few studies have been reported on the direct observation of adsorbed polymers on the SiO2 and SiN surfaces. In this study, we have investigated adsorption properties of the polymer additives by using surface enhanced Raman scattering (SERS) suitable for analysis of trace organic substance on surface in water.Figure 1 schematically illustrates the measurements of SERS spectra. The SiN/SiO2=30/70 m patterned wafer chip with 1% polymer solution is putted on the quartz glass with Ag nanoparticles, resulting high Raman scattering intensity. Figure 2 show the spectra measured on the SiO2 and SiN films in PAA solution. The peak of CH stretching mode of the PAA polymer chain was observed at approximately 2935 cm-1 on the SiO2 and SiN. This result implies that the polymer is adsorbed both on the SiO2 and SiN. Meanwhile, the case in the polymer containing hydrophobic moiety, the peak attributed to the hydrophobic group is observed at approximately 1000 cm-1. Its intensity is stronger on the SiO2 than SiN, indicating the preferential adsorption of polymer on the SiO2 surface.The ratio of peak intensity of polymer on the SiN to SiO2 (SiN/SiO2) for PAA (0.26) is higher than the polymer containing hydrophobic moiety (0.03), implying that the adsorption of polymer with hydrophobic moiety to the SiN film is lower than PAA. This suggests that the nitride removal suppression effect is not caused by the adsorption of the polymer on the SiN surface. The influence of other components, such as abrasive, dispersant, pH adjuster is under investigation.[1] T. Otsuki, US Pat. 2019/0136089 (2019).[2] N. K. Penta et. al, Appl. Surf. Sci., 283, 986(2013)[3] S. Kim et. al., J. Colloid Interface Sci., 319, 48 (2008). Figure 1

A Method of Chemical-Mechanical Polishing of a Thick Silver Layer on Patterned Silicon Wafer

Microfluidics-based biochips for biochemical analysis are receiving much attention nowadays. These composite microsystems, also known as lab-on-a-chip or bio-MEMS, offer a number of advantages over conventional laboratory procedures. They automate highly repetitive laboratory tasks by replacing cumbersome equipment with miniaturized and integrated systems, and they enable the handling of small amounts, e.g., micro- and nano-liters, of fluids. Thus they are able to provide ultra-sensitive detection at significantly lower costs per assay than traditional methods, and in a significantly smaller amount of laboratory space. Advances in microfluidics technology offer exciting possibilities in the realm of enzymatic analysis (e.g., glucose and lactate assays), DNA analysis (e.g., PCR and nucleic acid sequence analysis), proteomic analysis involving proteins and peptides, immuno-assays, and toxicity monitoring.Biochips can be used to detect molecules and/or sequence nucleic acid molecules with aid of an array of electrochemical detector cells containing one or more electrodes per cell where each cell being electrically isolated at a wafer level. For many applications it is beneficial to form a non-planar working electrode using a metal which will corrode during CMP steps.We’ve developed a novel Ag and Cu integration process which a) solves problems of metal corrosion over 3D topography during CMP step and b) prevents metal surface contamination with CMP residual slurry and polishing byproducts not usually removable by brush or megasonic cleaning.Electrochemical studies show corrosion behavior of thick Ag layers in different CMP slurries used in this process. SEM images of cross-sectioned metal lined electrochemical cells (vias) clearly demonstrate advantages of new process (right) without traces of corrosion vs conventional CMP process (left).This process can be used also for polishing of other metals and dielectrics over topography where aggressive cleaning post-CMP steps are not desirable. Figure 1

Barrier and Packaging Level CMP Optimization

The yield of chip packaging operations is a function of the surface finish that is solderable and wire-bondable. It has been shown that the use of palladium (Pd) plated lead-frame for packaging has improved the processing cost and reliability by simplifying the process integration [1]. Pd can also be used as a sacrificial layer to protect the copper (Cu) substrate material from oxidation and interdiffusion before the SnPb solder application. In packaging applications, Pd is advantageous in forming a Ni(Pd)Si allowing a lower sheet resistance at higher temperatures as compared to the NiSi in addition to much better surface morphology [2].The new integration schemes of Pd into the circuitry at the packaging level also require a CMP application where the Pd is deposited on the dielectric layer with bond-pad recess and polished to form a Pd based pad surrounded by Ni [3]. In combination with the applications of the 2.5 and 3-D microelectronics packaging technologies, the CMP electivity becomes critical where a competitive removal rate is desired between the Cu, Cu-barrier (TaN) and Ni filmsIt has been demonstrated on W-CMP in an earlier study that the 1:1:1 removal rate selectivity of the W/Ti/TiN layers can be achieved through adjusting CMP formulations in terms of the slurry chemistry and the particle concentrations. The systematic study has demonstrated a methodology for developing optimal CMP configurations for the newly introduced films to CMP applications based on electrochemical evaluations [5].In this paper, we study the removal rate selectivity for Pd integrated packaging level CMP applications through electrochemical and surface energy evaluations in commercial bulk and barrier CMP slurries. It can be seen that the thin film dissolution rates relate to the surface passivation as well as the surface energy measured by the contact angle evaluations on the Cu, Pd, TaN and Ni wafer coupons. Pd being a novel metal shows strong passivation that results in minimal dissolution in the slurry environment which requires alternative formulations for CMP slurries to promote the removal rate performance.

Novel rotary chemical mechanical polishing on an integral impeller

Abstract Traditional polishing on an integral impeller is labour intensive owing to its complicated curved surfaces. In this study, a novel rotary chemical mechanical polishing (R-CMP) for an integral impeller has been proposed using a developed polisher and a novel CMP slurry to improve efficiency and quality as compared to the traditional polishing method. The novel slurry consists of phosphoric acid (H3PO4), hydrogen peroxide (H2O2), nicotinic acid (NA) and silicon carbide (SiC). A model for predicting the surface roughness is established, according to the R-CMP process parameters during polishing an integral impeller, which is in good agreement with experimental results. It was found out that the polishing mechanism of R-CMP consists of four processing steps: oxidation, dissolution, chelating and removal. After R-CMP on an integral impeller, the surface roughness Ra of the blade root is reduced from 1.664 to 0.559 μm, and the thickness of the damage layer is decreased from 900 to 350 nm. The polishing time is 2 h, which is faster than the conventional manual polishing on an integral propeller by twenty times. The findings in this research open a new pathway to polish an integral high performance component with complicated curved surfaces using immersive CMP at high efficiency and high quality, without the need to exert external pressure.

Communication—A Novel Method to Improve Cleaning Performance by Removing Small Particles in CMP Slurry

In the present study, a separation system with a tangential flow filter (TFF) was applied to reduce the number of small ceria particles in chemical mechanical polishing slurry. The small ceria particles were reduced by 30.7% via the TFF system, and slurry properties of particle mean diameter, pH, zeta potential, and solids concentration were maintained. There was no significant difference in removal rate between original and TFF-treated slurry. In addition, the cleaning efficiency with the TFF system was improved by 34.7% compared to that without the TFF system.

Contact Vs. Non-Contact Cleaning: Correlating Interfacial Reaction Mechanisms to Processing Methodologies for Enhanced FEOL/BEOL Post-CMP Cleaning

Due to the emergence of sub-7 nm technologies, next generation CMP slurry formulations have continued to increase in additive (nanoparticle and chemistry) complexity to meet stringent device specifications. Therefore, it is essential to probe the molecular level interactions at the nanoparticle/slurry chemistry/substrate interface and in turn correlate them to key performance metrics such as removal rate, post CMP defects, and planarization efficiency. This work will address key interactions through a series of case studies focusing on the role of supramolecular structure and cleaning method (i.e. contact vs. non-contact) during STI post-CMP cleaning, probing the impact of supramolecular structure and mode of cleaning relevant to Cu post-CMP, and development of a biomimetic matrix with chemical activity to act as a brush in STI post-CMP cleaning processes. Results show in both BEOL and FEOL post-CMP cleaning there is a strong correlation to the delivery and “soft” nature of the chemistry to allow for effective particle removal at low mechanical force and prevent further defect formation. Furthermore, this work shows a clear correlation between supramolecular structure and particle removal efficiency under both contact and non-contact post-CMP processes.

A New Permanganate-Free Slurry for GaN-SiC CMP Applications

Single crystal SiC wafers are known to be extremely difficult to polish by conventional CMP slurries because of their high hardness and chemical resistance. Previously only those manganese-containing CMP slurries are capable of producing measurable and useful polishing rates with this versatile wide band-gap substrate. A new permanganate-free SiC polishing slurry containing a generic formula of MXO2 etchant, where M is an alkali metal, X is a halogen, O is oxygen is disclosed. When mixed with an abrasive powder in an aqueous slurry form, the tribochemical reactant that activates under pressure, etches SiC effectively, rendering an enhanced Material Removal Rate (MRR) when processing CMP SiC wafers. The MRR can sometimes go up to a few order of magnitudes, as compared to the abrasive slurry without these chemical etchants. The series of MXO2 compounds that can activate SiC polishing belong to the chemical family of halites. Sodium chlorite, NaClO2, the simplest and most available member of the halites family, is a good example. The accelerated polishing rates offer increased throughput of the slow SiC CMP process. The new slurry is particularly useful for non-oxide wafer polishing, which includes SiC, GaN and AlN wafers. An outstanding character of the new halite-based polishing formulation that is different from the current permanganate-based slurries is that the waste stream produced from the CMP process can be easily treated in the waste water treatment facilities because they do not contain toxic heavy metal ions such as manganese and permanganate in the polishing formulations. Continuous exhaustive CMP polishing test with 32 4” 4H-N SiC wafers using a production CMP tool containing 32L of the alumina-chlorite slurry has demonstrated an MRR of 1.7um/hr (Si-face) when the slurry is fresh, and a final MRR of 1.0um/hr after 16 hours polishing at 800mL/min slurry flow rate with pH buffer control without fresh oxidant addition. The resulting 32 polished 4H-SiC test wafers show overall excellent smooth surface roughness with the best Ra of 0.05nm by AFM after fine CMP polishing.

Citric acid/tartaric acid as complexing agent in sodium carbonate based CMP slurry for tantalum

Citric acid/tartaric acid as complexing agent in sodium carbonate based CMP slurry for tantalum

Study of the additives influence in the CMP slurry for the surfaces planarisation covered by selective transfer

Study of the additives influence in the CMP slurry for the surfaces planarisation covered by selective transfer

Material removal characteristics of precorroded Lu2O3 laser crystals and elastic deformation model during nanoscratch process

Abstract At present, CMP is the only ultra-precision machining technology that can achieve global flattening. Unfortunately, CMP processing efficiency is extremely unsatisfactory. Although the processing efficiency can be improved by increasing the alkaline concentration of CMP slurry, the surface quality will deteriorate rapidly due to excessive concentration. In this study, the removal characteristics of both uncorroded and precorroded Lu2O3 laser crystals were investigated based on nanoscratch tests with edge-forward Berkovich indenter. Further, the elastic deformation model considering both elastic extrusion and elastic recovery deformation was established. The origin of the microcracks was then discussed. The observed responses of surface quality were shown to depend greatly on the extent of elastic deformation prevalent during the nanoscratch and associated material removal processes.

Effect of surface hydroxylation on ultra-precision machining of quartz glass

Chemical mechanical polishing is a main technology to flatten the surface of quartz glass. However, the role of water in polishing slurry and the removal mechanism in the CMP process of quartz glass are still unclear. The simulation based on ReaxFF-MD method was utilized to explore the microphenomenon and the removal mechanism in the CMP process of quartz glass. The simulation results indicated that the H atoms dissociating from H2O in polishing slurry present a weakening effect on SiO bonds in quartz glass. Besides, the hydroxylation process when the pristine surface of quartz glass reacts with OH groups dissociating from H2O was elucidated explicitly in this simulation. To verify the correctness of this ReaxFF-MD simulation, a set of experiments including nanoindentation and nanoindentation were implemented on quartz glass modified in solutions with different concentrations of aqueous H2O2 and KOH. According to the results of experiments, surface modification of quartz glass contributes to the removal of surface materials and processability of quartz glass modified by 5% aqueous H2O2 is the best. This work combining simulations and experiments contribute to understand the chemical behavior of nanoparticles at the atomic scale and provide an effective method to choose the CMP slurry.