Chemical Mechanical Polishing of Glass Substrate with α-Alumina-g-Polystyrene Sulfonic Acid Composite Abrasive

Abrasive is the one of key influencing factors during chemical mechanical polishing（CMP） process. Currently, α-Alumina （α-Al2O3） particle, as a kind of abrasive, has been widely used in CMP slurries, but their high hardness and poor dispersion stability often lead to more surface defects. After being polished with composite particles, the surface defects of work pieces decrease obviously. So the composite particles as abrasives in slurry have been paid more attention. In order to reduce defect caused by pure α-Al2O3 abrasive, α-alumina-g-polystyrene sulfonic acid （α-Al2O3-g-PSS） composite abrasive was prepared by surface graft polymerization. The composition, structure and morphology of the product were characterized by Fourier transform infrared spectroscopy（FTIR）, X-ray photoelectron spectroscopy（XPS）, time-of-flight secondary ion mass spectroscopy（TOF-SIMS）, and scanning electron microscopy（SEM）, respectively. The results show that polystyrene sulfonic acid grafts onto α-Al2O3, and has well dispersibility. Then, the chemical mechanical polishing performances of the composite abrasive on glass substrate were investigated with a SPEEDFAM-16B-4M CMP machine. Atomic force microscopy（AFM） images indicate that the average roughness of the polished glass substrate surface can be decreased from 0.835 nm for pure α-Al2O3 abrasive to 0.583 nm for prepared α-Al2O3-g-PSS core-shell abrasive. The research provides a new and effect way to improve the surface qualities during CMP.

Research on Abrasives in the Chemical Mechanical Polishing Process for Silicon Nitride Balls

Silicon nitride (Si 3N 4) has been the main material for balls in ceramic ball bearings, for its lower density, high strength, high hardness, fine thermal stability and anticorrosive, and is widely used in various fields, such as high speed and high temperature areojet engines, precision machine tools and chemical engineer machines. Silicon nitride ceramics is a kind of brittle and hard material that is difficult to machining. In the traditional finishing process of silicon nitride balls, balls are lapped by expensive diamond abrasive. The machining is inefficiency and the cost is high, but also lots of pits, scratch subsurface micro crazes and dislocations will be caused on the surface of the balls, the performance of the ball bearings would be declined seriously. In these year, a kind of new technology known as chemical mechanical polishing is introduced in the ultraprecision machining process of ceramic balls. In this technology, abrasives such as ZrO 2, CeO 2 whose hardness is close to or lower than the work material (Si 3N 4) are used to polishing the balls. In special slurry, these abrasives can chemo-mechanically react with the work material and environment (air or water) to generate softer material (SiO 2). And the resultants will be removed easily at 0.1 nm level. So the surface defects can be minimized, very smooth surface (Ra=4 nm) and fine sphericity (0.15～0.25 μm ) can be obtained, and the machining efficiency is also improved. The action mechanism of the abrasives in the chemical mechanical polishing process in finishing of silicon nitride ball will be introduced in this paper.

A nano-scale mirror-like surface of Ti–6Al–4V attained by chemical mechanical polishing

Metal Ti and its alloys have been widely utilized in the fields of aviation, medical science, and micro-electromechanical systems, for its excellent specific strength, resistance to corrosion, and biological compatibility. As the application of Ti moves to the micro or nano scale, however, traditional methods of planarization have shown their short slabs.Thus, we introduce the method of chemical mechanical polishing（CMP） to provide a new way for the nano-scale planarization method of Ti alloys. We obtain a mirror-like surface, whose flatness is of nano-scale, via the CMP method. We test the basic mechanical behavior of Ti–6Al–4V（Ti64） in the CMP process, and optimize the composition of CMP slurry.Furthermore, the possible reactions that may take place in the CMP process have been studied by electrochemical methods combined with x-ray photoelectron spectroscopy（XPS）. An equivalent circuit has been built to interpret the dynamic of oxidation. Finally, a model has been established to explain the synergy of chemical and mechanical effects in the CMP of Ti–6Al–4V.

Effect of Abrasive Concentration on Chemical Mechanical Polishing of Sapphire

Effects of abrasive concentration on material removal rate CMRR） and surtace quality m the chemical mecnamcal polishing （CMP） of light-emitting diode sapphire substrates are investigated. Experimental results show that the MRR increases linearly with the abrasive concentration, while the rms roughness decreases with the increasing abrasive concentration. In addition, the in situ coefficient of friction （COF） is also conducted during the sapphire polishing process. The results present that COF increases sharply with the abrasive concentration up to 20 wt% and then shows a slight decrease from 20wt% to 40wt%. Temperature is a product of the friction force that is proportional to COF, which is an indicator for the mechanism of the sapphire CMP.

Theoretical and experimental investigation of chemical mechanical polishing of W–Ni–Fe alloy

Fine finishing of tungsten alloy is required to improve the surface quality of molds and precision instruments. Nevertheless, it is difficult to obtain high-quality surfaces as a result of grain boundary steps attributed to differences in properties of two-phase microstructures. This paper presents a theoretical and experimental investigation on chemical mechanical polishing of W–Ni–Fe alloy. The mechanism of the boundary step generation is illustrated and a model of grain boundary step formation is proposed. The mechanism reveals the effects of mechanical and chemical actions in both surface roughness and material removal. The model was verified by the experiments and the results show that appropriately balancing the mechanical and chemical effects restrains the generation of boundary steps and leads to a fine surface quality with a high removal rate by citric acid-based slurry.

Iron trichloride as oxidizer in acid slurry for chemical mechanical polishing of Ge_2Sb_2Te_5

The effect of iron trichloride （FeC13） on chemical mechanical polishing （CMP） of Ge2Sb2Te5 （GST） film is inves- tigated in this paper. The polishing rate of GST increases from 38 nm/min to 144 nm/min when the FeC13 concentration changes from 0.01 wt% to 0.15 wt%, which is much faster than 20 nm/min for the 1 wt% H2O2-based slurry. This polish- ing rate trends are inversely correlated with the contact angle data of FeCl3-based slurry on the GST film surface. Thus, it is hypothesized that the hydrophilicity of the GST film surface is associated with the polishing rate during CMP. Atomic force microscope （AFM） and optical microscope （OM） are used to characterize the surface quality after CMP. The chemical mechanism is studied by potentiodynamic measurements such as Ecorr and Icorr to analyze chemical reaction between FeCl3 and GST surface. Finally, it is verified that slurry with FeCl3 has no influence on the electrical property of the post-CMP GST film by the resistivity-temperature （RT） tests.

Mechanism of titanium-nitride chemical mechanical polishing

During the preparation of the phase change memory,the deposition and chemical mechanical polishing(CMP)of titanium nitride(TiN)are indispensable.A new acidic slurry added with sodium hypochlorite(NaClO)as an oxidizer is developed for the CMP of TiN film.It has achieved a material removal rate of 76 nm/min,a high selectivity between TiN film and silica(SiO_(2))films of 128:1,a selectivity between TiN film and tungsten film of 84:1 and a high surface quality.To understand the mechanism of TiN CMP process,x-ray photoelectron(XPS)spectroscope and potentiodynamic polarization measurement are performed.It is found that the mechanism of TiN CMP process is cyclic reaction polishing mechanism.In addition,both static corrosion rate and the inductively coupled plasma results indicate TiN would not be dissolved,which means that the mechanical removal process of oxide layer plays a decisive role in the material removal rate.Finally,the mechanism of TiN polishing process is given based on the analysis of surface potential and the description of blocking function.

Atomistic understanding of rough surface on the interfacial friction behavior during the chemical mechanical polishing process of diamond

The roughness of the contact surface exerts a vital role in rubbing.It is still a significant challenge to understand the microscopic contact of the rough surface at the atomic level.Herein,the rough surface with a special root mean square(RMS)value is constructed by multivariate Weierstrass–Mandelbrot(W–M)function and the rubbing process during that the chemical mechanical polishing(CMP)process of diamond is mimicked utilizing the reactive force field molecular dynamics(ReaxFF MD)simulation.It is found that the contact area A/A0 is positively related with the load,and the friction force F depends on the number of interfacial bridge bonds.Increasing the surface roughness will increase the friction force and friction coefficient.The model with low roughness and high lubrication has less friction force,and the presence of polishing liquid molecules can decrease the friction force and friction coefficient.The RMS value and the degree of damage show a functional relationship with the applied load and lubrication,i.e.,the RMS value decreases more under larger load and higher lubrication,and the diamond substrate occurs severer damage under larger load and lower lubrication.This work will generate fresh insight into the understanding of the microscopic contact of the rough surface at the atomic level.

Chemically-induced active micro-nano bubbles assisting chemical mechanical polishing:Modeling and experiments

The material loss caused by bubble collapse during the micro-nano bubbles auxiliary chemical mechanical polishing(CMP)process cannot be ignored.In this study,the material removal mechanism of cavitation in the polishing process was investigated in detail.Based on the mixed lubrication or thin film lubrication,bubble-wafer plastic deformation,spherical indentation theory,Johnson-Cook(J-C)constitutive model,and the assumption of periodic distribution of pad asperities,a new model suitable for micro-nano bubble auxiliary material removal in CMP was developed.The model integrates many parameters,including the reactant concentration,wafer hardness,polishing pad roughness,strain hardening,strain rate,micro-jet radius,and bubble radius.The model reflects the influence of active bubbles on material removal.A new and simple chemical reaction method was used to form a controllable number of micro-nano bubbles during the polishing process to assist in polishing silicon oxide wafers.The experimental results show that micro-nano bubbles can greatly increase the material removal rate(MRR)by about 400%and result in a lower surface roughness of 0.17 nm.The experimental results are consistent with the established model.In the process of verifying the model,a better understanding of the material removal mechanism involved in micro-nano bubbles in CMP was obtained.

Novel model of material removal rate on ultrasonic-assisted chemical mechanical polishing for sapphire

Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still unclear.This paper proposed a novel model of material removal rate(MRR)to explore the mechanism of sapphire UA-CMP.It contains two modes,namely two-body wear and abrasive-impact.Furthermore,the atomic force microscopy(AFM)in-situ study,computational fluid dynamics(CFD)simulation,and polishing experiments were conducted to verify the model and reveal the polishing mechanism.In the AFM in-situ studies,the tip scratched the reaction layer on the sapphire surface.The pit with a 0.22 nm depth is the evidence of two-body wear.The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies.The maximum total velocity and the air volume fraction(AVF)in the central area increased from 0.26 to 0.55 m/s and 20%to 49%,respectively,with the rising amplitudes of 1–3μm.However,the maximum total velocity rose slightly from 0.33 to 0.42 m/s,and the AVF was nearly unchanged under 40–80 r/min.It indicated that the ultrasonic energy has great effects on the abrasive-impact mode.The UA-CMP experimental results exhibited that there was 63.7%improvement in MRR when the polishing velocities rose from 40 to 80 r/min.The roughness of the polished sapphire surface was R_(a)=0.07 nm.It identified that the higher speed achieved greater MRR mainly through the two-body wear mode.This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.

Preparation of CeO_(2) abrasives by reducing atmosphere-assisted molten salt method for enhancing their chemical mechanical polishing performance on SiO_(2)substrates

Ce^(3+)as the active site on the CeO_(2)abrasive surface is the key to enhancing the material removal rate(MRR).The CeO_(2)abrasives with high chemical activity were prepared by the molten salt method under a reducing atmosphere.The crystal structure and morphology of CeO_(2)abrasive s were characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),Fourier transform infrared spectroscopy(FT-IR),ultraviolet—visible diffuse reflectance spectroscopy(UV-Vis DRS),and X-ray photoelectron spectroscopy(XPS).The CeO_(2)abrasives were obtained under different atmospheres(Air,Ar,and Ar/H_(2)).With the enhancement of the reducing atmosphere,the morphology of the abrasives transforms from spherical to octahedral,while more oxygen vacancies and Ce^(3+)are generated on the surface of CeO_(2)abrasives.The CMP experiments show that the MRRs of the CeO_(2)-Air,CeO_(2)-Ar,and CeO_(2)-Ar/H_(2)abrasives on SiO_(2)substrates are 337.60,578.74,and 691.28 nm/min,respectively.Moreover,as confirmed by atomic force microscopy(AFM),the substrate surfaces exhibit low roughness(20.5 nm)after being polished using all of the prepared samples.Especially,the MRR of CeO_(2)-Ar/H_(2)abrasives is increased by 104.76%compared with CeO_(2)-air abrasives.The improved CMP performance is attributed to the increased Ce^(3+)concentration and the octahedral morphology of the abrasives enhancing the chemical reaction and mechanical removal at the abrasive-substrate interface.

Chemical mechanical polishing: Theory and experiment

For several decades,chemical mechanical polishing(CMP)has been the most widely used planarization method in integrated circuits manufacturing.The final polishing results are affected by many factors related to the carrier structure,the polishing pad,the slurry,and the process parameters.As both chemical and mechanical actions affect the effectiveness of CMP,and these actions are themselves affected by many factors,the CMP mechanism is complex and has been a hot research area for many years.This review provides a basic description of the development,challenges,and key technologies associated with CMP.We summarize theoretical CMP models from the perspectives of kinematics,empirical,its mechanism(from the viewpoint of the atomic scale,particle scale,and wafer scale),and its chemical-mechanical synergy.Experimental approaches to the CMP mechanism of material removal and planarization are further discussed from the viewpoint of the particle wear effect,chemical-mechanical synergy,and wafer-pad interfacial interaction.

Modeling Chemical Mechanical Polishing with Couple Stress Fluids

Chemical mechanical polishing (CMP) is a manufacturing process used to achieve high levels of global and local planarity. Currently, the slurries used in CMP usually contain nanoscale particles to accel-erate the removal ratio and to optimize the planarity, whose rheological properties can no longer be accu-rately modeled with Newtonian fluids. The Reynolds equation, including the couple stress effects, was de-rived in this paper. The equation describes the mechanism to solve the CMP lubrication equation with the couple stress effects. The effects on load and moments resulting from the various parameters, such as pivot height, roll angle, and pitch angle, were subsequently simulated. The results show that the couple stress can provide higher load and angular moments. This study sheds some lights into the mechanism of the CMP process.

Effect of FA/O complexing agents and H_2O_2 on chemical mechanical polishing of ruthenium in weakly alkaline slurry

This paper investigated the effect of FA/O and hydrogen peroxide （H2O2） on ruthenium （Ru） removal rate （RR） and static etching rate （SER）. It was revealed that Ru RR and SER first linearly increased then slowly decreaseed with the increasing H2O2 probably due to the formation of uniform Ru oxides on the surface during polishing. Their corrosion behaviors and states of surface oxidation were analyzed. In addition, FA/O could chelate Ru oxides （such as （RuO4）2- and RUO4- changed into soluble amine salts [R（NH3）4] （RuO4）2） and enhance Ru RR. The non-ionic surfactant AD was used to improve the Ru CMP performance. In particular, the addition of AD can lead to significant improvement of the surface roughness.

Flatness maintenance and roughness reduction of silicon mirror in chemical mechanical polishing process

As an important optical component in laser system,silicon mirror surface is required to have micron-level flatness and subnanometer-level roughness.The research concentrates on how to improve roughness as far as possible while maintaining flatness of silicon mirror surface during chemical mechanical polishing(CMP)process.A polishing edge effect model is established to explain the reason of flatness deterioration,and a roughness theoretical model is set up to get the limit of perfect surface roughness.Based on the models above,a polishing device is designed to maintain the surface flatness,and the optimized polishing process parameters are obtained by orthogonal tests to get a near-perfect surface roughness.Finally the maintenance of flatness and the improvement of roughness can be achieved at the same time in one step of CMP process.This work can be a guide for silicon mirror manufacture to improve optical reflection performance significantly.

Chemical mechanical polishing of freestanding GaN substrates

Chemical mechanical polishing （CMP） has been used to produce smooth and scratch-free surfaces for GaN. In the aqueous solution of KOH, GaN is subjected to etching. At the same time, all surface irregularities, including etch pyramids, roughness after mechanical polishing and so on will be removed by a polishing pad. The experiments had been performed under the condition of different abrasive particle sizes of the polishing pad. Also the polishing results for different polishing times are analyzed, and chemical mechanical polishing resulted in an average root mean square （RMS） surface roughness of 0.565 nm, as measured by atomic force microscopy.

Scratch-concerned yield modeling for IC manufacturing involved with a chemical mechanical polishing process

In existing integrated circuit (IC) fabrication methods,the yield is typically limited by defects generated in the manufacturing process.In fact,the yield often shows a good correlation with the type and density of the defect.As a result,an accurate defect limited yield model is essential for accurate correlation analysis and yield prediction.Since real defects exhibit a great variety of shapes,to ensure the accuracy of yield prediction,it is necessary to select the most appropriate defect model and to extract the critical area based on the defect model.Considering the realistic outline of scratches introduced by the chemical mechanical polishing (CMP) process,we propose a novel scratch-concerned yield model.A linear model is introduced to model scratches.Based on the linear model,the related critical area extraction algorithm and defect density distribution are discussed.Owing to higher correspondence with the realistic outline of scratches,the linear defect model enables a more accurate yield prediction caused by scratches and results in a more accurate total product yield prediction as compared to the traditional circular model.

Exploring the role of --NH2 functional groups of ethylenediamine in chemical mechanical polishing of GCr15 bearing steel

Ethylenediamine with two-NH2 functional groups was used as a critical complexing agent in chemical mechanical polishing(CMP)slurries for a high carbon chromium GCr15 bearing steel(equivalent to AISI 52100).The polishing performance and corresponding mechanism of-NH2 functional groups were thoroughly investigated as a function of pH.It is revealed that,when polished with ethylenediamine and H2O2-based slurries,the material removal rate(MRR)and surface roughness Ra of GCr15 steel gradually decrease as pH increases.Compared with acidic pH of 4.0,at alkaline pH of 10.0,the surface film of GCr15 steel has much higher corrosion resistance and wear resistance,and thus the material removal caused by the pure corrosion and corrosion-enhanced wear are greatly inhibited,resulting in much lower MRR and Ra.Moreover,it is confirmed that a more protective composite film,consisting of more Fe3+hydroxides/oxyhydroxides and complex compounds with-NH2 functional groups of ethylenediamine,can be formed at pH of 10.0.Additionally,the polishing performance of pure iron and a medium carbon 45 steel exhibits a similar trend as GCr15 steel.The findings suggest that acidic pH could be feasible for amine groups-based complexing agents to achieve efficient CMP of iron-based metals.

Modeling and experimental research on a removal mechanism during chemical mechanical polishing at the molecular scale

In order to understand the fundamentals of the chemical mechanical polishing（CMP） material removal mechanism,the indentation depth of a slurry particle into a wafer surface is determined using the in situ nanomechan-ical testing system tribo-indenter by Hysitron.It was found that the removal mechanism in CMP is most probably a molecular scale removal theory.Furthermore,a comprehensive mathematical model was modified and used to pinpoint the effects of wafer/pad relative velocity,which has not been modeled previously.The predicted results based on the current model are shown to be consistent with the published experimental data.Results and analysis may lead to further understanding of the microscopic removal mechanism at the molecular scale in addition to its underlying theoretical foundation.

Effect of ammonium molybdate concentration on chemical mechanical polishing of glass substrate

The effect of the ammonium molybdate concentration on the material removal rate（MRR） and surface quality in the preliminary chemical mechanical polishing（CMP） of a rough glass substrate was investigated using a silica-based slurry.Experimental results reveal that the ammonium molybdate concentration has a strong influence on the CMP behaviors of glass substrates.When the ammonium molybdate was added to the baseline slurry,polishing rates increased,and then decreased with a transition at 2 wt.%,and the root mean square（RMS） roughness decreased with increasing ammonium molybdate concentration up to 2 wt.%,after which it increased linearly up to 4 wt.%.The improvement in MRR and RMS roughness may be attributed to the complexation of hydrolysis products of the glass substrate with the ammonium molybdate so as to prevent their redeposition onto the substrate surface.It was found that there exists an optimal ammonium molybdate concentration at 2 wt.%for obtaining the highest MRR and the lowest RMS roughness within a particular polishing time.