Chemical Mechanical Polishing Slurry Research Articles

Effect of Novel pH Regulators on Copper film Chemical Mechanical Polishing for Ruthenium-Based Copper Interconnect under Weak Alkalinity Conditions

For Ruthenium (Ru)-based copper (Cu) interconnects Cu film chemical mechanical polishing (CMP), it is crucial to select appropriate pH regulators in the slurry to ensure the chemical reactions and maintain the stability of the polishing chemical environment. In this study, the effects of inorganic pH regulator KOH, organic pH regulator diethanolamine (DEA), and 2-amino-2-methyl-1-propanol (AMP) on CMP and slurry properties of Cu film were compared. It was found when using AMP as a pH regulator, the Cu/Ru removal rate selectivity (RRS) can reach 598:1, the surface roughness of Cu film decreased to 0.76 nm, and the slurry can remain stable for at least 7 d. The performance order of the three pH regulators is AMP＞KOH＞DEA. Meanwhile, through experimental results and test analysis, it has been confirmed that AMP can also play a multifunctional role as a complexing agent, dispersant, and surfactant. Therefore, AMP can replace KOH as a new pH regulator in weak alkaline slurries. This result plays an important role in guiding the selection of organic pH regulators in the optimization of Cu film CMP slurry.

Green chemical mechanical polishing of copper with 2,5-dihydroxy-1,4-dithianeas as the inhibitor: Experimental and theoretical studies

It is a great challenge to develop green chemical mechanical polishing (CMP) technique owing to the limited inhibitory performance of green inhibitors. In this study, 2,5-dihydroxy-1,4-dithiane (DHD) was found and utilized as a superior inhibitor in CMP slurry, which realized nanometer-scale smoothness for copper surface. The strong inhibition effect of DHD, in both static and dynamic situations, was demonstrated by microscopic observations and electrochemical characterizations. The effectiveness of DHD was achieved mainly through its chemisorption onto copper surface, determined by Langmuir adsorption isotherm. X-ray photoelectron spectroscopy and density-functional-theory calculations proved that the chemisorption occurred between the S atom of DHD and Cu. Overall, DHD as an efficient and eco-friendly inhibitor with low-cost exhibits immense potential for applications in chip fabrication, particularly at a low technology node.

First-principles insight into the pH-dependency of the corrosion inhibition ability of benzotriazole and 1,2,4-triazole for copper in chemical mechanical polishing slurry

A comprehensive set of first-principles calculations was conducted to elucidate the disparity and pH-dependency of the corrosion inhibition performance of benzotriazole and 1,2,4-triazole in copper chemical mechanical polishing (CMP) slurry. Unlike previous calculations adopted the simplified and rigid model with neutral molecules adsorbed on metallic copper surface, the models, including Cu and Cu2O surfaces covered with O or -OH species, as well as neutral and deprotonated forms of inhibitor molecules, were constructed to simulate the adsorption interface based on the experimental results. The calculated adsorption energy successfully explained the pH-dependency of the inhibition ability of the two inhibitors.

Improving monocrystalline silicon surface quality with chemical mechanical polishing using the slurry with the additive of isopropanol

Enhancing the silicon surface smoothness with chemical mechanical polishing (CMP) is crucial to achieve better beam quality in X-ray systems. The additive in CMP slurry is the key factor in determining the resulting surface morphology. This paper exploits the effect of isopropanol (IPA) additive on regulating the material removal process and resulting microscopical surface morphology through varying the IPA concentration and polishing pressure. The improvement of surface quality and a dropping material removal rate (MRR) are obtained by increasing the IPA concentration from 0.1 to 2.5 mol/L. When the polishing pressure increases from 0.25 to 0.48 psi, a better surface quality and enhanced MRR are observed. By using the optimal polishing pressure of 0.48 psi and IPA concentration of 2.5 mol/L, the root-mean-square roughness can be reduced to 0.10 nm under a measurement area of 1 µm × 1 µm with atomic force microscopy, more than 58.3% lower compared to surfaces polished without IPA. This work suggests an approach to obtain the ultra-smooth silicon mirrors, which has promising applications in the field of X-ray, aerospace, and photovoltaics.

Polishing performance and mechanism of a novel Fe-based slurry for chemical mechanical polishing

The planarization of silicon carbide (SiC) achieved through chemical mechanical polishing (CMP) poses a significant challenge. In this work, the CMP performance of a novel slurry containing Fe, Al2O3, and graphene oxide (GO) on SiC substrate was systematically investigated. Morphological characterization revealed a significant enhancement in the dispersion of Fe due to the presence of GO. Furthermore, CMP results demonstrated that the material removal rate (MMR) using the novel slurry could reach 700 nm/h, resulting in an average surface roughness (Sa) reduction to 0.6175 nm. Through the measurement of hydroxyl radical (·OH) concentration, the novel slurry was found to generate sufficient ·OH for the oxidation of SiC surface. This study proposes a viable processing method for CMP of hard materials.

Atomic-scale planarization surface of quartz glass induced by novel green chemical mechanical polishing using three ingredients

Traditional chemical mechanical polishing (CMP) usually employs more than three kinds of toxic or corrosive ingredients for its slurry. Quartz glass is a hard-brittle solid, and it is extremely difficult to achieve its atomic-scale planarization surface. In these respects, it is a challenge to obtain atomic surface of quartz glass using green CMP slurry with three ingredients. To solve this challenge, a novel green CMP was developed, containing three green ingredients, such as ceria, sodium alginate and aminobutyric acid. After CMP, atomic surface is acquired with surface roughness Ra of 0.093 nm and material removal rate of 12.47 μm/h. Transmission electron microscopy confirms the thickness of damaged layer is 8.57 nm. X-ray photoelectron spectroscopy shows that –OH, C–N and –COOH groups adsorbed on the surface of quartz glass after immersion in CMP slurry, which agrees well with the simulated results of molecular dynamics. Density functional theory calculations reveal that electron transfer groups of aminobutyric acid and sodium alginate were predominantly located on –NH2 and –COOH, forming the covalent bonds between them. Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy indicate that new complexes were generated between aminobutyric acid and sodium alginate, increasing the viscosity of CMP slurry. Furthermore, the breakage of C–N and O–H bonds after CMP suggests that the complexes play a pivotal role in the CMP process. The developed novel green CMP with three ingredients provides new viewpoints to obtain atomic-scale planarization surface for a hard-brittle solid.

Investigation on chemical mechanical polishing of Ga-faced GaN crystal with weak alkaline slurry

A remarkable improvement in the chemical–mechanical polishing (CMP) of GaN using a weakly alkaline ZrO2–SiO2 based slurry is described in detail, and an almost complete atomic step-platform structure with a surface roughness (Ra) of 0.059 nm is obtained. ZrO2 nanoparticles were added to the CMP slurry to replace part of the SiO2 to obtain a higher removal rate. When the content of ZrO2 reaches 0.5 wt%, the material removal rate of GaN is increased by 47.5 % compared with that of SiO2 with equal content, which significantly improves the material removal rate (MRR) of GaN, and does not destroy the atomic ladder-platform structure. In addition, we also investigate the causes of the formation of atomic ladder-terrace morphology on Ga-face, and describe the removal mechanism of materials in CMP process.

Development of core–shell SiO2@A-TiO2 abrasives and novel photocatalytic chemical machinal polishing for atomic surface of fused silica

It is extremely hard to achieve atomic surface on fused silica with a high material removal rate (MRR). Furthermore, in traditional chemical mechanical polishing (CMP), toxic and corrosive slurries are widely employed. To address these challenges, core–shell SiO2@A-TiO2 abrasives were prepared, and novel photocatalytic CMP was developed. The developed CMP slurry consists of sodium carbonate, hydrogen peroxide, sodium carboxymethylcellulose and deionized water. After CMP, atomic surface with surface roughness Sa of 0.181 nm was achieved at a scanning area of 50 × 50 μm2 and a high MRR of 10.727 μm/h. X-ray diffraction, X-ray photoelectron spectroscopy and Fourier transform infrared were used to elucidate the photocatalytic CMP mechanisms. The developed SiO2@A-TiO2 abrasives could generate electrons and holes irradiated by simulated solar light, producing free radicals (OH–). As a result, OH– combined with Si atoms on the surface of fused silica, forming Si-OH-Si bonds. This constructed interlinkage of slurry and surface of fused silica via SiO2@A-TiO2 abrasives improved synergistic effect between chemical and mechanical functions. The developed core–shell abrasives and photocatalytic CMP suggest new findings to achieve atomic surface for a hard-brittle solid with a high MRR.

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.

A novel atomic removal model for chemical mechanical polishing using developed mesoporous shell/core abrasives based on molecular dynamics.

To improve polishing performance and reduce the environmental pollution of chemical mechanical polishing (CMP) tests, mesoporous shell/core silica abrasives were prepared, and a novel green CMP slurry was developed, including sorbitol, hydrogen peroxide and sodium carbonate. Prior to CMP, fused silica was roughly polished with ceria slurry. Using developed mesoporous abrasives, surface roughness Sa is reduced from 0.347 to 0.253 nm for a scanning area of 200 × 200 μm2, and the material removal rate (MRR) is increased from 70 to 127 nm min-1, compared with traditional solid abrasives. Based on molecular dynamics (MD) simulations, a novel atomic removal model is proposed for mesoporous abrasives through the immediate elastic recovery of atoms. MD simulations suggest that the formation of convex peaks and pits was inhibited by the mesoporous structure, promoting uniform distribution of surface atoms and atomic removal. This is different from a conventional simple increase of polishing times. In addition, more bridge bonds of Si-O-Si and a lower average Si-O bond order are produced in fused silica samples due to their mesoporous structure, contributing to a higher MRR.

The damage mechanism in copper studied using in situ TEM nanoindentation.

Copper (Cu) has a soft-plastic nature, which makes it susceptible to damages from scratching or abrasive machining, such as lapping and polishing. It is a challenge to control these damages as the damage mechanism is elusive. Nonetheless, controlling damages is essential, especially on the atomic surfaces of Cu. To interpret the damage mechanism, in situ transmission electron microscopy (TEM) nanoindentation was performed using a cube-corner indenter with a radius of 57 nm at a loading speed of 5 nm s-1. Experimental results showed that damages originate from dislocations, evolve to stack faults, and then form broken crystallites. When the indentation depth was 45 nm at a load of 20 μN, damages comprised dislocations and stacking faults. After increasing the depth to 67 nm and load to 30 μN, the formation of broken crystallites initiated; and the critical depth was 67 nm. To validate the damage mechanism, fixed-abrasive lapping, mechanical polishing, and chemical mechanical polishing (CMP) were conducted. Firstly, a novel green CMP slurry containing silica, hydrogen peroxide, and aspartic acid was developed. After CMP, a surface roughness Ra of 0.2 nm was achieved with a scanning area of 50 μm × 50 μm; and the thickness of the damaged layer was 3.1 nm, which included a few micro-stacking faults. Lapping and mechanical polishing were carried out using a silicon carbide plate and cerium slurry, with surface roughness Ra values of 16.42 and 1.74 nm, respectively. The damaged layer of the former with a thickness of 300 nm comprised broken crystallites, dislocations, and stacking faults and that of the latter with a thickness of 33 nm involved several stacking faults. This verifies that the damage mechanism derived from in situ TEM nanoindentation is in agreement with lapping and polishing. These outcomes propose new insights into understanding the origin of damages and controlling them, as well as obtaining atomic surfaces using a novel green CMP technique for soft-plastic metals.

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.

Atomic surface of quartz glass induced by photocatalytic green chemical mechanical polishing using the developed SiO2@TiO2 core-shell slurry.

High-performance devices of quartz glass demand an atomic surface, which induces a challenge for chemical mechanical polishing (CMP) with a high material removal rate (MRR). Moreover, traditional CMP usually employs toxic and corrosive slurries, leading to the pollution of the environment. To overcome these challenges, a novel green photocatalytic CMP is proposed. In the CMP, SiO2@TiO2 core-shell abrasives were developed, and the CMP slurry included the developed abrasives, sodium carbonate, hydrogen peroxide and sorbitol. After photocatalytic CMP, the surface roughness Sa of quartz glass is 0.185 nm, with a scanning area of 50 × 50 μm2, and the MRR is 8.64 μm h-1. To the best of our knowledge, the MRR is the highest on such a big area of atomic surface for quartz glass. X-ray photoelectron spectroscopy reveals that SiO2@TiO2 core-shell abrasives were used as photocatalysts motivated by simulated solar light, generating electrons and holes and producing hydroxyl radicals through hydrogen peroxide. As a result, OH- could combine with Si atoms on the surface of quartz glass, forming Si-OH-Si bonds. Then the formed bonds were removed based on the balance between chemical and mechanical functions. The proposed CMP, developed SiO2@TiO2 abrasives and slurry provide new insights to achieve an atomic surface of quartz glass with a high MRR.

Investigation of CMP Process of Silica Substrate by Ceria Abrasive: Insights from Molecular Dynamics Simulation with Neural Network Potential

Chemical mechanical polishing (CMP) is a process of surface planarization by chemical and mechanical driving forces. CMP is expected to solve various problems, including the surface roughness on semiconductor devices. An aqueous slurry, including abrasive grains and chemical components, is used in the CMP process. Development of slurries with high polishing rate, excellent planarity, and superior processability is not only a key challenge, but also a significant opportunity for the future of our industry. In order to achieve the development, it is necessary to understand the detailed mechanism of CMP, which involves complex phenomena accompanied by interfacial chemical reactions and mechanical friction. Computational scientific approaches, such as density functional theory (DFT) and molecular dynamics (MD) simulations, are powerful tools for understanding complex tribochemical phenomena at the atomic scale. However, these methods require much computation time and present difficulties for large-scale simulations. To overcome this limitation, a computational method called Neural Network Potential (NNP) is a powerful tool because it achieves a good balance between accuracy and computational efficiency by constructing potential energy surfaces based on a neural network-based method. We performed NNP-MD simulations of the ceria/silica interface with the development of CMP slurry including ceria abrasive grains, which is typically used on the surfaces of silicon layered devices. As a result, we succeeded in observing polishing phenomena at the interface at the atomic scale, namely Ce-O-Si bond formation between ceria abrasive grains and silica substrate, hydrolysis reaction of Si-O bond, and associated mono-silica dissociation from the substrate. We also performed simulations of systems containing chemical compounds added to the slurry for the purpose of controlling the polishing rate and observed the role of additives on the CMP process. In this presentation, we will show simulation results and discuss the mechanism of CMP of silica substrates with ceria abrasive grains in terms of dependence on surface morphology at the atomic scale and the role of additives. Reference [1] Tran*, R., Lan*, J., Shuaibi*, M., Wood*, B., Goyal*, S., Das, A., Heras-Domingo, J., Kolluru, A., Rizvi, A., Shoghi, N., Sriram, A., Ulissi, Z., & Zitnick, C. (2022). The Open Catalyst 2022 (OC22) Dataset and Challenges for Oxide Electrocatalysis. arXiv preprint arXiv:2206.08917.

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.

Contamination reduction for 150 mm SiC substrates by integrating CMP and Post-CMP cleaning

The quality of silicon carbide (SiC) substrates has great influence on the quality of the epitaxial layers atop. During the epitaxial growth, crystallographic defects and substrate contaminations may transform to various surface defects, such as carrots, polytype inclusions and scratches, which are detrimental to the performance and reliability of SiC devices. In general, chemical mechanical polishing (CMP) and post-CMP cleaning are the last two steps before the epitaxial growth, playing critical roles in controlling the scratch and contamination levels on the SiC substrates. In this article, the methods for reducing the aluminum (Al) and manganese (Mn) metal contaminations as well as other surface particle contaminations are investigated. We found that different commercial CMP slurries may lead to different contamination levels. Most importantly, by adding a scrubber cleaning step prior to the conventional RCA cleaning process, the contamination levels can be greatly reduced, achieving the quality for mass production.

Insight into Polishing Slurry and Material Removal Mechanism of Photoassisted Chemical Mechanical Polishing of YAG Crystals.

Yttrium aluminum garnet (YAG) crystals are an important gain medium in thin-sheet solid-state lasers, and their processing quality directly affects the performance of solid-state lasers. But it is difficult to achieve high efficiency and high quality of YAG crystals by traditional chemical mechanical polishing (CMP). In this study, we developed a new polishing slurry for photoassisted chemical mechanical polishing (PCMP) of YAG crystals. The polishing slurry is composed of peroxymonosulfate (PMS), manganese ferrite (MnFe2O4), alumina (Al2O3) abrasives, and deionized water. PCMP is conducted in an ultraviolet (UV) light environment. When employing this polishing slurry for PCMP processing of YAG crystals, the material removal rate (MRR) achieved 250 nm/min and the surface roughness achieved 0.35 nm Sa. The experiments verified that both UV light and MnFe2O4 can effectively activate PMS to produce active free radicals and further enhance the chemical action of the polishing slurry. X-ray photoelectron spectroscopy (XPS) analysis results indicated that active radicals reacted with the surface structure of the crystal and removed the aluminum-oxygen octahedron in large quantities from it. The structural defects reduced the surface hardness of the crystal, which means that active free radicals can modify the crystal surface materials.

Analysis of cavitation and shear in bellows pump: transient CFD modelling and high-speed visualization

Pneumatic drive bellows pumps (PDBPs) are a crucial fluid control component in the semiconductor industry. However, when dealing with specific chemical mechanical polishing (CMP) slurries, agglomeration of particles can occur, leading to scratches, particle residues, pits, and other defects on the wafer surface. The leading cause of agglomeration has been proposed to be cavitation and excessive shear in PDBPs. A high-fidelity multiphase computational fluid dynamics (CFD) model, which fully resolves the response of check valves under hydrodynamic and other external loads, was established to evaluate cavitation behaviour and shear distribution in PDBPs. Moreover, a test rig was built to visualize cavitating flow patterns in PDBPs and verify the accuracy of the CFD model. Among different cavitation regions captured by high-speed visualization, the region near the inner leading edge of the end-ring of the inlet valve is dominant, with high intensity, long duration, and complex morphology evolution. Detailed initiation and development process of cavities in the dominant region are analysed numerically. The shear rate in different domains of PDBPs is estimated, and the inlet valve domain stands out from the other. The strongest shear rate is observed near the leading edge of the end-ring. Furthermore, an analysis of the relationship between cavitation and shear indicates that the high-intensity vortices generated owing to strong shear account for the inception of cavitation. This study contributes to understanding inner flow details in PDBPs and provides a guideline for further optimization of similar pumps.

Atomic surface of fused silica and polishing mechanism interpreted by molecular dynamics and density functional theory

For fused silica, it is difficult to obtain an atomic surface with a high material removal rate (MRR), and the polishing mechanism is still a challenge. Chemical mechanical polishing (CMP) has historically used toxic and polluted ingredients. To meet these demanding constraints, it is extremely difficult to produce green CMP for fused silica. In this work, we report on the development of a novel green CMP slurry containing ceria, nicotinic acid, sodium alginate, and deionized water. After CMP, an atomic surface is achieved with a surface roughness Sa of 0.098 nm using a scanning area of 20 × 20 μm2, and the MRR is 7.65 μm/h. According to density functional theory and molecular dynamics simulations, nicotinic acid and fused silica generated a novel complex during CMP that could be peeled by active ceria by creating coordinating bonds. These findings offer an intuitive understanding of the CMP mechanism and suggest a novel method for fabricating fused silica atomic surfaces for possible usage in high-performance optical devices.

Novel green chemical mechanical polishing of fused silica through designing synergistic CeO2/h-BN abrasives with lubricity

It is a challenge to produce an atomic-scale surface of fused silica with a high material removal rate (MRR) using green chemical mechanical polishing (CMP). In traditional CMP, a slurry usually contains four or more components and is normally toxic and corrosive, causing environmental degradation. To address this problem, a novel green CMP slurry for fused silica was developed using ceria/hexagonal boron nitride (CeO2/h-BN) abrasives, potassium oleate, and deionized water. Due to the two-dimensional nanosheet structure of h-BN, it is simple to generate a sheared layer, which lowers friction at the contact area. Ceria abrasives realized a new function for superlubricity during CMP through this design, preventing damages and reaching atomic-scale surface. This is confirmed by research showing that a damaged layer’s thickness following CMP, as determined by high-resolution transmission electron microscopy, is only 2.7 nm. The MRR of fused silica is 31.92 µm•h−1 during CMP, and surface roughness Sa is 0.124 nm after CMP. The MRR is currently at its highest with such a low surface roughness. These findings provide a new pathway to achieve an atomic-scale surface for a hard-brittle material with a high MRR using the synergistic effect of abrasives.