Chemical Mechanical Polishing Experiments Research Articles

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.

Chemical Mechanical Polishing for Monocrystal SiC Assisted by the Heterogeneous Sono-Fenton Oxidation

The efficient chemical mechanical polishing (CMP) ability of monocrystal SiC determines the development of advanced semiconductor device. In order to improve the ultra-precision polishing efficiency for SiC, a CMP method based on the heterogeneous sono-Fenton oxidation was proposed. The effects of heterogeneous sono-Fenton on SiC surface softening and polishing based on hydroxyl radical oxidation were studied by means of the corrosion and CMP experiments. Utilizing the indentation tester, the ultra depth of field microscope and optical profilometer, the synergistic effects of heterogeneous sono-Fenton method on the improvement of SiC surface softening and polishing performance were revealed. The research results showed that the change rates of SiC hardness and elastic modulus after heterogeneous sono-Fenton corrosion were the highest, which were 0.12 and 0.6, respectively. The depth variation of indentation on SiC after heterogeneous sono-Fenton corrosion was the highest, which was 1.741 μm. Correspondingly, the improvement degree of SiC surface quality after polishing based on the heterogeneous sono-Fenton corrosion was the greatest and the material removal rate was the highest, which were Sa2.94 nm and 0.469 μm h−1, respectively.

Mechanism Exploration of the Effect of Polyamines on the Polishing Rate of Silicon Chemical Mechanical Polishing: A Study Combining Simulations and Experiments.

Polyamines have become important chemical components used in several integrated circuit manufacturing processes, such as etching, chemical mechanical polishing (CMP), and cleaning. Recently, researchers pointed out that polyamines can be excellent enhancers in promoting the material removal rate (MRR) of Si CMP, but the interaction mechanism between the polyamines and the silicon surface has not been clarified. Here, the micro-interaction mechanisms of polyamines, including ethylenediamine (EDA), diethylenetriamine (DETA), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and pentaethylenehexamine (PEHA), with the Si(1, 0, 0) surface were investigated through molecular dynamics (MD) simulations using the ReaxFF reactive force field. Polyamines can adsorb onto the Si(1, 0, 0) surface, and the adsorption rate first accelerates and then tends to stabilize with the increase in the quantity of -CH2CH2NH-. The close connection between the adsorption properties of polyamines and the polishing rate has been confirmed by CMP experiments on silicon wafers. A comprehensive bond analysis indicates that the adsorption of polyamines can stretch surface Si-Si bonds, which facilitates subsequent material removal by abrasive mechanical wear. This work reveals the adsorption mechanism of polyamines onto the silicon substrate and the understanding of the MRR enhancement in silicon CMP, which provides guidance for the design of CMP slurry.

Optimization and Mechanism of SiO2-Based Slurry Components for Atomically Smooth Gallium Nitride Surface Obtained Using Chemical Mechanical Polishing Technique

With the ongoing progress of mobile communication and new energy technologies, the market interest in high-frequency and high-power semiconductor devices has risen. Gallium nitride (GaN), a wide bandgap semiconductor material, has become a popular area of research in relevant fields. A sufficiently flat material surface can significantly enhance the device’s performance. Therefore, this paper explores the effect of oxidants on the quality of GaN surface during chemical mechanical polishing (CMP). Atomic force microscopy (AFM) was employed to examine the surface morphology of GaN after each CMP experiment. The aim was to evaluate the effect of specific slurry components on GaN surface quality. The results revealed that the introduction of oxidizers, particularly the potent oxidizer potassium persulfate (K2S2O8), was advantageous in reducing the surface roughness Sq and thus, enhancing the surface quality of GaN. The surface roughness (Sq) of GaN was reduced from 7.7 nm to 0.78 nm after the CMP process with the optimal components. AFM tests were conducted on different areas of the GaN surface within a range of 1 μm2, which revealed that clear images of the GaN atomic steps can be obtained, and the Sq can reach as low as 0.26 nm.

Atomic surface achieved through a novel cross-scale model from macroscale to nanoscale.

Chemical mechanical polishing (CMP) is widely used to achieve an atomic surface globally, yet its cross-scale polishing mechanisms are elusive. Moreover, traditional CMP normally employs toxic and corrosive slurries, resulting in potential pollution to the environment. To overcome these challenges, a novel cross-scale model from the millimeter to nanometer scale is proposed, which was confirmed by a newly developed green CMP process. The developed CMP slurry consisted of hydrogen peroxide, sodium carbonate, sodium hydroxycellulose, and silica. Prior to CMP, fused silica was polished by a ceria slurry. After CMP, the surface roughness (Sa) was 0.126 nm, the material-removal rate was 88.3 nm min-1, and the thickness of the damaged layer was 8.8 nm. The proposed model was built by fibers, through integrating Eulerian and Lagrangian models and reactive force field-molecular dynamics. The results predicted by the model were in good agreement with those of CMP experimentally. A model for large-sized fibers revealed that a direct contact area of 11.12% was obtained for a non-woven polishing pad during the CMP experiments. Another model constructed via combining Eulerian and Lagrangian functions showed that the stress at the intersections of the fibers varied mainly from 0.1 to 0.01 MPa and was higher than the stress at other parts. An increase in viscosity led to a decrease in the areas with low stress, demonstrating that viscosity enhanced the stress and facilitated the removal of material. At the microscale and nanoscale, the stress of the abrasive surface exposed to the workpiece changed from 2.21 to 6.43 GPa. Stress at the interface contributed to the formation of bridging bonds, further promoting the removal of material. With increasing the compressive stress, the material-removal form was transformed from a single atom to molecular chains. The proposed model and developed green CMP offer new insights to understand the cross-scale polishing mechanism, as well as for designing and manufacturing novel polishing slurries, pads, and setups.

Real-time prediction of material removal rate for advanced process control of chemical mechanical polishing

Polishing torque holds significance in monitoring the chemical mechanical polishing (CMP) process due to its close correlation with material removal. This study introduces a new model-based technique for estimating the material removal rate (MRR) using in-process data from CMP machines. The proposed method employs either the sequential least squares method or Kalman filter for real-time state estimation. Real-time estimation of MRR enables material removal control without relying on conventional endpoint detection (EDP) technologies. The accuracy of the proposed approach is validated through oxide CMP experiments, demonstrating precise estimation of the center-slowed MRR profile towards the end of the pad life.

Improvement of dispersion stability and polishing performance of chemical mechanical polishing slurry for cemented carbide inserts

Aiming at defects such as small pits and scratches on the surface caused by the aggregation of alumina particles during the chemical mechanical polishing (CMP) process of the cemented carbide inserts, the effect of the dispersant types, pH and dispersant concentration on the dispersion stability of the alumina suspension is investigated. It is found that sodium dodecyl sulfate (SDS) is the best dispersant of the six different dispersants, and the suspension has good dispersion stability when the pH value is 11 and the SDS concentration is 3 wt%. Furthermore, based on the DLVO theory, SDS is verified to improve suspension stability at the micro-scale. Finally, the insert CMP experiments are carried out using the polishing slurry with SDS and without dispersant. CMP experiments show that using the polishing slurry with SDS to polish the insert can achieve a better material removal rate (MRR) and lower surface roughness.

Effect of EDTA-modified alumina composite abrasive on the CMP performance of sapphire substrate

Sapphire is one of the most widely used substrate materials for semiconductor lighting. With the improvement of chemical mechanical polishing (CMP) processing technology for sapphire substrate, mass production, and cost control requires faster polishing efficiency and better surface quality. In CMP, alumina abrasive is widely used for its high polishing rate, but it also has the disadvantages of easy agglomeration and poor polishing quality. Therefore, ethylenediamine tetraacetic acid (EDTA)-grafted alumina composite abrasives were produced by a two-step process for the sapphire substrate CMP. As demonstrated by time of flight secondary ion mass spectrometry and fourier transform infrared spectroscopy, EDTA has been successfully grafted onto the surface of alumina particles. As shown by the scanning electron microscope, particle size distribution, and zeta potential analyses, the modified alumina composite abrasives exhibit superior dispersion properties than pure alumina particles. CMP experiment results show that the material removal rate (MRR) of the alumina composite abrasives can reach up to 2.6 μm/h, and the surface roughness (Sa) of the sapphire substrate can be reduced to 0.89 nm, which is 53 % higher and 66 % lower than pure alumina, respectively. According to X-ray photoelectron spectroscopy, the chemical etch of modified abrasive particles was strengthened, and the complex reaction occurred throughout the CMP process to generate the C–O–Al structural compound. Meanwhile, the friction coefficient test and contact angle test were combined to create the contact wear model. It shows that the addition of EDTA expands the contact area between the composite abrasives and the surface of substrates, improving the mechanical interaction during CMP. The chemical reaction and mechanical action combine and promote each other to enhance the CMP performance.

An ethylenediaminetetraacetic acid (EDTA) surface-functionalized CeO2 composite abrasives with the effective improvement of the removal rate on glass CMP

With the increasing demand for surface processing, there has been a growing interest in enhancing the performance of cerium oxide (CeO2) abrasives for glass chemical mechanical polishing (CMP). To enhance the CeO2 abrasives’ CMP performance, we use the surface modification method to combine inorganic CeO2 with organic ethylenediaminetetraacetic acid (EDTA) molecules, thus utilizing the chemical reaction activity of organic substances to raise the chemical reaction between CeO2 and glass. A series of ethylenediaminetetraacetic acid grafted cerium oxide (CeO2-EDTA) composite abrasives were synthesized and characterized. The CMP experiment indicates that CeO2-EDTA with the EDTA content of 8.33 wt%, called CeO2-EDTA(8.33 %), had a splendid polishing performance. Compared with CeO2, the material removal rate of CeO2-EDTA(8.33 %) could be increased by about 40 % while the surface quality concurrently ameliorated. X-ray photoelectron spectroscopy analysis, dynamic friction test, and contact angle test were further used to probe the removal mechanism of composite abrasives. As a result, the correlation between MRR value and the concentration of cerium trivalent ion, particle size, dynamic friction coefficient, and contact angle was found. This provides a reference for the modification of cerium oxide in the future.

Improving the Dispersion Stability and Chemical Mechanical Polishing Performance of CeO2 Slurries

The dispersion stability of CeO2 suspensions limits their widespread use in IC manufacturing because unstable slurries can be very damaging to the chemical mechanical polishing (CMP) flattening process. Therefore, this study is based on the use of wet ball milling in synergy with chemical agents to improve the dispersion stability of CeO2 slurry. Different organic acids were used as adjusting agents, including acetic acid, propionic acid, lactic acid, and phytic acid. The characterization of the dispersion stability showed that, compared to other organic acids, the CeO2 suspensions using acetic acid as a modest particle size distribution, good stability (zeta potential > 50 mV), monodispersity (polydispersity index < 0.1) and higher chemical activity (higher content of Ce3+). Moreover, CMP experiments showed that the CeO2 slurry using acetic acid as the adjusting agent had a higher removal rate (4139 Å min−1).

Analyzing the effects of pad asperity on chemical mechanical polishing of copper thin film wafer

Copper thin film has been identified as a promising material for multi-level interconnecting materials in IC fabrication due to its unique electrical properties and high electrical conductivity. However, it is very challenging to manufacture a superior planar surface with low dishing and minimal erosion of copper thin film in the chemical mechanical polishing (CMP) process. In this study, the micro-topography model of a soft polishing pad is performed using an X-ray micro-computed tomography scan combined with finite element method simulation to evaluate the contact area between the CMP pad and wafer during the CMP process. Additionally, the material removal rate (MRR) model for the copper wafer is calibrated based on the wear of the material between abrasive particles and the wafer surface. The results of this study not only investigate the effect of CMP pad asperities during the CMP process but also provide a new method for fully calibrating MRR in comparison with CMP experiments for the verification of model parameters.

Improvement in dispersion stability of alumina suspensions and corresponding chemical mechanical polishing performance

The dispersion stability of alumina suspensions is an obstacle to its large-scale application for chemical mechanical polishing (CMP) since the aggregation of particles will cause scratches on the wafer surface during polishing. Therefore, this study was devoted to improving the physicochemical properties of alumina suspensions using different polymeric dispersants, including polyethylene glycol (PEG) with nonionic properties, sodium polyacrylate (PAAS) with anionic properties, and their triblock copolymer poly(acrylic acid)-b-PEG-b-poly(acrylic acid) (PAEG). The characterization results of dispersion stability showed that, compared with PEG and PAAS, the suspensions containing a suitable dosage of PAEG exhibited the advantages of low-viscosity (Viscosity < 3 mPa·s), good-stability (Zeta potential < -50 mV), and monodisperse (Polydispersity index < 0.1). The adsorption isotherm indicated that the adsorption of dispersants on alumina particles was consistent with Langmuir model. Furthermore, the total potential energy between particles in suspension was calculated for theoretical analysis of the inter-particle interactions. Besides, the dispersion mechanisms of PEG, PAAS, and PAEG were proposed as steric stabilization, electrostatic stabilization and electrosteric stabilization, respectively. Finally, CMP experiments showed that the suspension prepared by using PAEG as a dispersant to polish SiC substrates resulted in better removal rates (382 nm/h) and lower surface roughness (Ra: 1.85 nm).

Analytical Modelling of Material Removal in Copper Chemical Mechanical Polishing Incorporating the Scratch Hardness of the Passivated Layer on Copper Thin Film Wafer

Chemical mechanical polishing (CMP) is the most crucial process for semiconductor fabrication and the scale of its application is broadening year by year. And understanding the varied mechanical interaction at pad-wafer contact as well as chemical alteration of the wafer surface is essential to comprehend the mechanism of material removal in the CMP process. In this study, an analytical material removal model is established as a function of polishing pad properties and scratch hardness of copper thin film wafer in CMP slurry environment. The model incorporates both, the mechanical material wear of chemically altered surface and, the chemical dissolution of copper based on corrosion theory. The contact between the polishing pad, wafer and abrasive is analysed and, in addition, the effect of the polishing pad and wafer properties on material removal is simulated. The model predicted MRR is compared to the copper CMP experiment MRR. This study establishes a strong correlation between the experimentally measured polishing pad and wafer properties and the material removal within the nanoscale contact model assumptions. The model provides a theoretical and experimental framework for optimizing the CMP process parameters, which can be employed to develop a simulator to analyze the advanced node copper CMP process

Study on Electrochemical Corrosion and CMP of GaN in Different Oxidation Systems

With the rapid development of the third generation semiconductor materials, the chemical mechanical polishing rate and surface quality of GaN have been a research hot-spot. By changing the concentration of oxidant and the pH of the solution, the corrosion characteristics of gallium nitride material were studied. The oxidant used in the experiment were hydrogen peroxide, sodium hypochlorite and potassium permanganate. Next, according to the results of electrochemical experiments, chemical mechanical polishing experiments were designed and accomplished with colloidal silica based slurry. Finally, the surface morphology of gallium nitride wafer was measured. The experimental results showed that MRR of GaN was as high as 404.6 nm h−1 by using the sodium hypochlorite as the oxidant under UV, with surface roughness (Ra) of 1.61 nm; MRR of GaN was 380.3 nm h−1 by using H2O2 as the oxidant under UV, with surface roughness (Ra) of 0.065 nm.

Synergistic Effect of Photocatalysis and Fenton on Improving the Removal Rate of 4H-SiC during CMP

To improve the material removal rate (MRR) of single-crystal silicon carbide (SiC) by chemical mechanical polishing (CMP), an ultraviolet (UV) photocatalysis–Fenton (UV + TiO2 + Fenton) composite reaction is used to increase the hydroxyl radical (·OH) concentration. In this study, the effects of UV photocatalysis, the Fenton reaction, and their composite reaction on ·OH concentration are experimentally investigated by the chemical degradation of methyl orange. Subsequently, the oxidation–reduction potential (ORP) during the reaction is measured to characterize the oxidisability of the chemical reaction. Finally, a CMP experiment is conducted to verify the synergistic effect of the UV + TiO2 + Fenton composite reaction. The ·OH test results show that the ·OH concentration in the UV + TiO2 + Fenton composite reaction is relatively significantly improved. They are 6 and 1.38 times those obtained in the Fenton and UV + TiO2 + H2O2 systems, respectively, and 11.4% higher than the summations of these properties achieved in both the systems. The CMP experiment results show that the MRR reaches 387.2 nm h−1 when the single-crystal 4H-SiC is polished by the UV + TiO2 + Fenton system, which is 44.1% and 22.4% higher than those of the Fenton and UV + TiO2 + H2O2 systems, respectively. The synergistic mechanism of the UV + TiO2 + Fenton composite reaction system for CMP is discussed.

Tribological behavior of 6H–SiC wafers in different chemical mechanical polishing slurries

The chemical mechanical polishing (CMP) slurry has a significant impact on the processing effects. However, the evaluation methods of processing effects, such as surface roughness, surface morphology and material removal rate (MRR), are affected by the instruments' accuracy and inspectors’ behaviors, which cannot reflect the change process of the wafer surface intuitively and accurately. This study evaluated the effect of different polishing slurries (H2O2, KMnO4 and Fenton reagent) on single crystal 6H–SiC in the form of friction and wear. Using a ball-on-disk tribotester, the friction and wear effects of these slurries on 6H–SiC were experimentally assessed, and then four polishing different slurries were employed for CMP experiments. The friction experiments showed that the SiC surface had obvious scratches and larger COF value only the silica sol abrasive existed. The SiC surface formed a loose and porous chemical reaction layer only the oxidant presented, which made the SiC surface rough and the COF curve fluctuate. When the chemical reaction worked in combination with the abrasive mechanical removal, the COF curve tended to stabilize but wear rate increased. The CMP experiments results were consistent with the friction test results.

Synergetic Effect of 5-Methyl-1H-Benzotriazole and Sodium Dodecyl Benzene Sulfonate on CMP Performance of Ruthenium Barrier Layer in KIO4-Based Slurry

The chemical mechanical polishing (CMP) of ruthenium barrier layer of copper interconnection for 14 nm and below technology node has been connected with more challenges, among which the corrosion of copper and ruthenium and the selectivity of removal rate between ruthenium and copper has attracted more attention. This paper mainly focus on the influence of 5-methyl-1H-benzotriazole(MBTA) and sodium dodecyl benzene sulfonate (SDBS) on the polishing properties of copper and ruthenium during ruthenium barrier CMP in the KIO4-based solutions. The results show that the removal rate and corrosion current density of ruthenium decrease with the increase of MBTA concentration. Subsequently, it is demonstrated that the formation of passivating film on ruthenium surface is due to the physisorption of MBTA, which occupies the reaction sites between ruthenium and KIO4 and inhibits the corrosion of ruthenium. SDBS was introduced to KIO4-based solution to compensate for the deficiency of MBTA in inhibiting copper corrosion. It has been proved that the coordinated use of MBTA and SDBS can reduce the copper removal rate to about 326 Å min−1 and obtain acceptable surface morphology. The synergistic inhibition mechanism of MBTA and SDBS on copper corrosion can be elucidated as: under the action of KIO4 and mixed inhibitors, a dense and integrated passivating film is generated on the copper surface to inhibit the excessive corrosion of copper. The passivating film is comprised of Cu–MBTA complex, adsorbed SDBS, copper oxides, Cu(IO4)2 and Cu(IO3)2. The results of CMP and ZRA experiments represent that the combination of MBTA and SDBS can adjust the removal rate selectivity of copper, ruthenium and low-κ dielectrics to 1.56:1:1.01 and evidently alleviate the galvanic corrosion of copper.

CHEMICAL MECHANICAL POLISHING AND ITS MECHANISM ON YTTERBIUM-DOPED MIXED SESQUIOXIDES (Yb:LuScO3)

In this paper, Yb:LuScO3 crystal was processed by chemical mechanical polishing (CMP), and the surface roughness of 0.18[Formula: see text]nm was obtained. The atomic step structures of these sesquioxide crystals are successfully characterized by AFM scanning probe technology. Through several CMP experiments, the basic material removal mechanism of a ytterbium-doped LuScO3 crystal during CMP is studied. Based on the findings, a material removal model is established. The results of this study provide ideas for the study of CMP, crystal growth and epitaxy.

Effect of photocatalysts on electrochemical properties and chemical mechanical polishing rate of GaN

The improvement of polishing rate during chemical mechanical polishing of GaN materials has been a research hotspot. Efficient and inexpensive catalysts are important for large-scale industrial production. In this paper, the effects of ZnO, TiO2 and ZrO2 catalysts on the polishing rate in photocatalytic oxidation polishing were studied, and the mechanism of UV photocatalytic oxidation of GaN was analyzed. In combination with ultraviolet light irradiation, three different kinds of catalysts were used in both electrochemical and chemical mechanical polishing experiments with varying pH values in both H2O2 and K2S2O8 systems. The experimental results show that ZrO2 can effectively improve the chemical mechanical polishing rate of GaN wafers. A slurry containing 0.15 M K2S2O8 and 0.05 wt% ZrO2 had a polishing rate of 487.9 nm/h at pH 10.

The synergistic inhibitory effect and density functional theory study of 2,2’-[[(Methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol and potassium oleate on copper in H2O2 based alkaline slurries

Copper (Cu), during the chemical mechanical polishing (CMP) of barrier layer, was associated with several challenges, one of which is to screen slurries required to address the corrosion of Cu. A large number of CMP studies have proved the effectiveness of inhibitors on Cu, but the passivation mechanism is not clear from the perspective of atoms, which needs further confirmation by computational chemistry. In this study, 2,2’-[[(Methyl-1H-benzotriazol-1-yl)methyl]imino]bisethanol (TT-LYK) and potassium oleate (PO) as inhibitors for Cu were widely investigated by experimental and density functional theory (DFT) methods. The CMP experiments and potentiodynamic polarization data showed that both of them were mixed - type corrosion inhibitors with significant corrosion inhibition ability on Cu. Besides, the combination of TT-LYK and PO exhibited excellent performance in suppressing the Cu corrosion, which were well prove by the surface morphology, single frequency electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) measurements. In addition, DFT calculation show that TT-LYK and PO were adsorbed on the Cu surface by the Cu-N bonds and Cu-O bonds at the bridge site, respectively, thereby obtaining the most stable configuration. This work is conducive to elucidate the role of corrosion inhibitors from a micro level.