Chemical Mechanical Polishing Performance Research Articles

Chemical mechanical polishing of sapphire elucidated by densely discrete phase model and verified using atomic force microscopy

The chemical mechanical polishing (CMP) is extensively applied in sapphire substrate processing. However, the mechanism is unclear because of the challenging in the dynamic characterization. In this paper, effects of the polishing speeds, slurry concentrations, and abrasive sizes on the removal action of granular flow in sapphire CMP are investigated using the discrete particle model (DPM) and densely discrete phase model (DDPM). Contours of the residence time, concentration, and abrasive velocity present that rotation speeds of the wafer and pad (30 and 80 rpm respectively) are beneficial to improving sapphire CMP performance. When the SiO2 slurry concentration is higher than 1 wt%, DDPM is more suitable for the fluid-solid flow in sapphire CMP compared to DPM. As the slurry concentration increases, the growth trend of material removal rate (MRR) slows down because of the reduction of the integral particle erosion ratio (PER). The 100 nm SiO2 abrasive can obtain the maximum MRR (10.90×10−9 nm/s), although its PER is 2 × 10−5 of 5 µm particles’ PER. The in-situ atomic force microscopy experiments prove the MRR function of granular flow owing to the hydro-dynamic contact. In addition, the removal ability will be improved by enhancing the interactive force between the abrasive and sapphire. It provides a novel idea to boost the efficiency of sapphire CMP.

Improvement of chemical mechanical polishing performance by introducing N–Si bond via external coating of cerium oxide with ZIF-8

Cerium oxide (CeO2) nanoparticles are widely used as abrasives in chemical mechanical polishing (CMP), an essential process for obtaining Si wafers with excellent surface quality. While CeO2 nanoparticles form Ce–O–Si bonds, which exhibit good CMP performance, their low activity results in a low removal rate. To address this issue, a two-step ultrasonic dispersion method was employed to prepare a uniform nuclear@shell CeO2@ZIF-8. The process of chemical bond generation in CMP was studied using spherical aberration-corrected transmission electron microscopy and X-ray photoelectron spectroscopy. In comparison to pure cerium oxide, the formation of Ce–O–Si bond was observed, and notably, the emergence of N–Si bond originating from the N of the ZIF-8 shell was identified. Coupled with the increased Ce3+ content, these developments enhanced CMP performance. The material removal rate (MRR) of the CeO2@ZIF-8 abrasives was 151.507 nm/min, which is 89.72 % higher than that of the pure CeO2 abrasives. Moreover, the surface roughness, as determined via AFM testing, was reduced to 0.231 nm within the confines of a 5.0 × 5.0 μm² region. Therefore, this study introduces a novel concept for CMP research by developing a CeO2@ZIF-8 compound abrasive to create a new N–Si bond.

Effect of Polyoxyethylene-Based Nonionic Surfactants on Chemical–Mechanical Polishing Performance of Monocrystalline Silicon Wafers

Effect of Polyoxyethylene-Based Nonionic Surfactants on Chemical–Mechanical Polishing Performance of Monocrystalline Silicon Wafers

Chemical-mechanical synergies effects of multi-purpose pH regulators on C-, A-, and R-plane sapphire polishing

The development of sapphire slurry follows the requirements of environmental friendliness, low cost and high efficiency. Therefore, the effects of KOH, aminomethyl propanol (AMP) and arginine (ARG) as pH regulators on the chemical mechanical polishing (CMP) performance of C-, A- and R-plane sapphire were investigated. The results showed that ARG was the most effective, which could increase the removal rates of C-, A- and R-plane sapphire to 5.65 µm/h, 2.80 µm/h and 3.59 µm/h, and reduce the surface roughness Sq to 0.194 nm, 0.161 nm and 0.173 nm, respectively. Mechanical action analysis, XPS, UV-Vis, and theoretical calculations revealed that ARG could improve the mechanical action of CMP and chemical action by acting as a complexing agent to complex with AlOH4−.

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.

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.

Synergistic effect of abrasive friction and glycine on improving chemical mechanical polishing performance of single-crystal GaN substrate

With the rapid development of the third-generation semiconductor materials, the chemical mechanical polishing rate and surface quality of single-crystal gallium nitride (GaN) substrates have been a research hot-spot. In this work, the synergistic effect of abrasive friction and glycine (Gly) on improving the chemical mechanical polishing (CMP) performance of single-crystal GaN substrate is proposed and studied systematically. The results indicated that the polishing solutions with Gly have a 2.3-fold improvement in material removal rate (MRR) as well as scratch-free surface than that without Gly. The maximum MRR of the single-crystal GaN substrate is 129.4 nm/h with surface roughness (Ra) of 0.64 nm attained by using the polishing solutions containing only 3 wt% potassium persulfate (K2S2O8). In contrast, when Gly is added as a reaction reagent, which can be activated by abrasive friction, the maximum MRR is increased to 304.2 nm/h with Ra of 0.42 nm. Meanwhile, the epitaxial evaluation indicates that two-dimensional (2D) MoS2 grown on processed single-crystal GaN substrate has superior crystalline quality and optical properties. Finally, the polishing mechanism of the single-crystal GaN substrate using the mixed solutions of K2S2O8 and Gly is discussed. The proposed CMP method has potential applications in the semiconductor and microelectronics industries.

Effect of amino acid complexing agents on chemical mechanical polishing performance and action mechanism of C-plane sapphire: Combining experiments and theoretical calculations

Chemical mechanical polishing (CMP) of sapphire faces greater challenges as the performance and processing requirements of sapphire devices continue to improve. Amino acids are often used as complexing agents on CMP because of their high water solubility, environmental friendliness and strong complexing ability. In this study, a combination of experimental techniques and theoretical calculations were used to investigate the effects of glycine (Gly), serine (Ser) and lysine (Lys) as complexing agents on the CMP properties of C-plane sapphire. The existence forms of three amino acid molecules under alkaline conditions were analyzed, and their possible binding modes to sapphire were discovered. Experimentally, it can be found that all three amino acids can improve the performance of C-plane sapphire CMP in different degrees. The measure results of X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) show that the three amino acids can be complexed with the Al(OH)4‒ ions produced by the sapphire to form soluble substance, thus speeding up the removal of sapphire. By calculation, it can be shown that the process of complexation is that the –NH2 and –OH groups in amino acids form covalent bonds with Al atom in Al(OH)4‒. Finally, the complexation capacity of the three amino acids is in the following order: Gly < Ser < Lys. Therefore, this study can confirm that amino acids as complexing agent have a good complexing effect on sapphire CMP, and the addition of –NH2 and –OH groups can help to enhance the complexing ability of the complexing agent, which has a certain good guiding significant for the selection of sapphire CMP complexing agent.

Triple Synergism Effect of Ammonium Nitrilotriacetate on the Chemical Mechanical Polishing Performance of Ruthenium Barrier Layers.

As the feature size of integrated circuits continues to decrease, ruthenium (Ru) has been suggested as the successor to traditional Ta/TaN bilayers for barrier layer materials due to its unique properties. This research delves into the effects of ammonium nitrilotriacetate (NTA(NH4)3) on the chemical mechanical polishing (CMP) performance of Ru in H2O2-based slurry. The removal rate (RR) of Ru surged from 47 to 890Åmin-1, marking an increase of about 17 times. The essence of this mechanism lies in the triple synergistic effects of NTA(NH4)3 in promoting ruthenium (Ru) removal: 1) The interaction between from NTA(NH4)3 and SiO2 abrasives; 2) The chelating action of [(NH4)N(CH2COO)3]2- from NTA(NH4)3 on Ru and its oxides; 3) The ammoniation and chelation of Ru and its oxides by from NTA(NH4)3, which enhance the dissolution and corrosion of oxidized Ru, making its removal during the barrier layer CMP process more efficient through mechanical means. This research introduces a synergistic approach for the effective removal of Ru, shedding light on potential applications of CMP in the field of the integrated circuits.

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.

Virtual metrology of material removal rate using a one-dimensional convolutional neural network-based bidirectional long short-term memory network with attention

Material removal rate (MRR) is a key parameter for chemical mechanical polishing (CMP). It can affect the polished product quality, and has often been used as an indicator of CMP performance. Virtual Metrology (VM) is an technique for estimating the target value without physical measurement. It can reduce measurement time and save the cost of measurement tools. In this paper, we propose a VM framework, One-Dimensional Convolutional Neural Network-based Bidirectional Long Short-term Memory Network with Attention (1DCNN_BiLSTMwA), for monitoring the condition of components in a wafer chemical mechanical polishing system, to solve the complex data pre-process and feature extraction issue of traditional VM, and to achieve high accuracy of prediction. To evaluate the effectiveness of the proposed method, an empirical dataset from a semiconductor CMP process was used. According to the results of comparison, the proposed 1DCNN_BiLSTMwA has the lowest prediction error and outperforms 1DCNN, LSTM, BiLSTM models and the other machine learning techniques with statistical features and hand-designed features. A weighted, deep learning model was also used to improve performance. The experimental results demonstrate the practical viability of the proposed approach.

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.

Electrochemical corrosion behavior and theoretical simulation of cobalt in chemical mechanical polishing process

The chemical mechanical polishing (CMP) process for cobalt (Co) interconnects is essential for the fabrication of integrated circuits with feature sizes below 10 nm. However, achieving high removal rates coupled with low dissolution rates remains a significant challenge. In this work, we have developed a dual-functional polishing slurry, which integrates ethylenediamine tetramethylphosphonic acid (EDTMPA) as a complexing agent, and octahydroxamic acid (OHA) as a corrosion inhibitor. The novel slurry-derived Co CMP meets ideal situation, delivering a removal rate (RR) of 246 nm/min, a dissolution rate (DR) of 0.8 nm/min, and a root mean square (RMS) roughness (Sq) of 2.31 nm. Experimental data and theoretical calculations reveal that the improved CMP performance results from the effective complexation of EDTMPA with Co ions. Furthermore, the adsorption of OHA as a corrosion inhibitor on the Co surface effectively counteracts the corrosion induced by EDTMPA. The development of this novel polishing slurry presents a strategy that harmoniously combines reduced process time with enhanced surface quality, holding the potential to significantly influence the CMP field.

Effects of Surfactants on the Chemical Mechanical Polishing Performance of a-Plane Sapphire Substrates

The effects of four different types of surfactants, cetyltrimethylammonium bromide (CTAB, cationic type), sodium dodecyl benzene sulfonate (SDBS, anion type), N-Laurylaminoacetic acid (NL, amphoteric type) and primary alcohol ethoxylate (AEO, non-ionic type), on the chemical mechanical polishing (CMP) performance of a-plane sapphire substrates in the range of pH 6–12 were investigated using colloidal silica as abrasive particles. The results demonstrated that cationic surfactants promoted the material removal of the sapphire substrate in the range of pH 9–12, while anionic, amphoteric, and non-ionic surfactants inhibited the material removal of the sapphire substrate in the range of pH 6–10. The mechanism of material removal in sapphire CMP was discussed through AFM observations, zeta potential measurements, particle size distribution tests, and friction behavior analysis.

Monodispersion of SiO2/CeO2 Binary Nano-Abrasives with Adjustable Size in Chemical Mechanical Polishing Performance of Copper

Chemical mechanical polishing (CMP) is an efficient methodology to achieve atomic-level roughness and global planarization. The selection and structural design of the abrasive particles in the polishing slurries play an essential role in the CMP process. In this work, silica (SiO2) microspheres with adjustable size and structure were prepared by a modified Stöber template approach, and ceria (CeO2) nano-shell layers were coated via in situ chemical precipitation on the core surfaces forming core/shell composite particles. The SiO2/CeO2 composites were characterized by XRD, SEM, TEM, XPS, and BET. The polishing performance of SiO2/CeO2 abrasives in copper (Cu) CMP was investigated by AFM. The small-sized (ca. 98 nm), large-sized (ca. 296 nm), and mesoporous (ca. 277 nm) composite abrasives were named as SiO2/CeO2-1, SiO2/CeO2-2, and mSiO2/CeO2, respectively. The best average surface roughness (Ra) and root-mean-square roughness (Rq) were obtained using SiO2/CeO2-1 abrasives, which decreased from 1.485 and 1.832 to 0.363 and 0.511 nm, respectively. The material removal rate (MRR) of the composite abrasives was improved to 279 nm min−1 by SiO2/CeO2-2 abrasives. The mSiO2/CeO2 composites were not manifested with evident superiority in terms of polishing characterization, which was attributed to the coating of CeO2 nanolayers. Finally, the material removal of Cu-CMP mechanisms was discussed.

Defect-Engineered MnO2 as Catalyst for the Chemical Mechanical Polishing of Silicon Carbide Wafer

Chemical mechanical polishing (CMP) of SiC wafer is challenging due to its extreme hardness and inertness. Catalyst assisted CMP is a cost-effective approach to increase material removal rate (MRR) without sacrificing surface quality. Herein, oxygen-deficient α-MnO2 was prepared by mechanochemical synthesis and the effect of catalyst physiochemical structure on the CMP performance of Si-face SiC wafer was systematically studied. The addition of 1% α-MnO2 catalyst increased MRR by 38.8% to 1.11 μm h−1, much higher than commercial γ-MnO2. The synergy of phase structure, oxygen vacancy and surface area & porosity contributed to the high catalytic activity. α-MnO2 is an outstanding oxidation catalyst due to its stable framework, large tunnel size, rich surface area and porosity, which can facilitate the adsorption, activation and transfer of guest species and intermediates and therefore affects the reaction pathway and reaction kinetics. Mechanochemical synthesis generates nano MnO2 particles with rich oxygen vacancies. The presence of more surface oxygen vacancies can improve oxidizing activity of MnO2 catalyst, facilitating the oxidation of C species on wafer surface. The use of defect-engineered α-MnO2 catalyst is promising for overcoming the present bottlenecks of long processing time and high cost of current CMP of SiC wafer.

Effect of the carboxyl group number of the complexing agent on polishing performance of alumina slurry in sapphire CMP

Alumina abrasive has a high polishing rate in the polishing process, but there are issues that need to be addressed with poor dispersion and poor post-polishing surface quality. This study used complexing agents with various numbers of carboxyl groups to prepare a series of alumina slurries. Scanning electron microscope images and zeta potential analysis demonstrated that the complexing agents could effectively increase the absolute value of alumina particles’ zeta potential and significantly enhance their dispersibility. Additionally, utilizing the UNIPOL-1502 polishing machine, the chemical mechanical polishing (CMP) performance of polishing slurries with complexing agents on sapphire substrates was investigated. According to the findings, as the carboxyl group count rises, material removal initially increases and subsequently declines. The material removal rate using alumina slurry added with complexing agent disodium ethylenediaminetetraacetic acid (the number of carboxyl groups is 4) can reach up to about 4.0 μm/h, which is 52% higher than that without complexing agents, while the average surface roughness of 0.96 nm can be obtained, which is 51% less than that without complexing agents. The X-ray photoelectron spectroscopy results showed that the complexing agents can react with the abrasive particles and sapphire substrates. The friction coefficient test and contact angle test revealed that slurries with complexing agents demonstrated excellent wettability and mechanical action. The sapphire surface becomes smoother as a result of the synergistic effect of chemical etching and mechanical removal.

Chemical–Mechanical Polishing of 4H Silicon Carbide Wafers

Abstract4H silicon carbide (4H‐SiC) holds great promise for high‐power and high‐frequency electronics, in which high‐quality 4H‐SiC wafers with both global and local planarization are cornerstones. Chemical–mechanical polishing (CMP) is the key processing technology in the planarization of 4H‐SiC wafers. Enhancing the performance of CMP is critical to improving the surface quality and reducing the processing cost of 4H‐SiC wafers. In this review, the superior properties of 4H‐SiC and the processing of 4H‐SiC wafers are introduced. The development of CMP with chemical, mechanical, and chemical–mechanical synergistic approaches to improve the performance of CMP is systematically reviewed. The basic principle and processing system of each improvement approach are presented. By comparing the material removal rate of CMP and the surface roughness of CMP‐treated 4H‐SiC wafers, the prospect on the chemical, mechanical, and chemical–mechanical synergistic improvement approaches is finally provided.

Structure-Performance Relationships of Complexing Agents on the Chemical Mechanical Polishing of 6063 Aluminum Alloy

Aluminum alloy has wide applications in many industries due to its unique properties. Chemical mechanical polishing (CMP) is commonly used to treat aluminum alloy to generate mirror-finish surface. In this study, the effects of pH and H2O2 concentration on the CMP of 6063 aluminum alloy were studied. Better CMP performance was obtained in basic media with 1.0 wt% H2O2. Moreover, complexing agents with different structures and functional groups were evaluated for the CMP of Al-alloy, and their structure-performance relationship was systematically studied. It was found that complexing power, steric hindrance and electrostatic repulsion of complexing agents were important factors determining material removal rate and surface roughness. The complexing agent with high complexing power can favor the dissolution and Al substrate. The complexing agent with large steric hindrance and high charge density can form a stable boundary layer on the surface of substrate and improve its dispersion ability, thereby improving MRR and surface quality. In addition, the amino functional groups of complexing agents exist in the form of neutral molecules at pH 10, which is inferior to carboxyl complexing agents due to their poor static repulsion. XPS analysis confirmed the anchoring of carboxylate anions on the sample surface.

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).