Chemical Mechanical Polishing Mechanism Research Articles

Recent developments and applications of chemical mechanical polishing

This article discusses advanced developments and applications of chemical mechanical polishing (CMP) published recently in the selected papers indexed by Web of Science. The topics covered are advances in slurry and abrasives, pads and conditioning, CMP for semiconductor device manufacturing, CMP for other applications, modeling and simulations, and CMP with ultrasonic vibrations, lasers, photocatalysts, or UV lamps. Nonspherical abrasive particles have been developed for CMP, resulting in increased material removal rates (MRRs). Advanced conditioning methods have been proposed to uniformly generate pad surface shapes. Fixed abrasive CMP has advantages with higher MRRs. New models for designing the pad and conditioner have been proposed, and more uniform pad shapes can be obtained. Integrated advanced process control improves the wafer-to-wafer variation. Dental implants treated by CMP perform equally or better than the baseline-machined implants and the biphasic calcium phosphate-treated implants. The slurry distribution and the abrasive behavior can be simulated by means of multiphase modeling. Molecular dynamics simulations can explore the mechanism of CMP. CMP of wafers can be simulated using an atomic force microscope with its tapping mode. Theoretical models have been developed to calculate removal depths, study the chemical action in CMP, and explore the crystal orientation effects. CMP assisted by ultrasonic vibrations increases CMP MRRs and lowers the roughness of polished surfaces. CMP assisted by using UV lamp power, femtosecond lasers, or photocatalysts enhances CMP MRRs.

A New High Selectivity Acidic Slurry for Chemical Mechanical Planarization of Carbon-Doped Ge2Sb2Te5 Film

During the industrial application of the new phase change memory material carbon-doped Ge2Sb2Te5 (GSTC), it is necessary to perform planarization for the confined memory cell structure through the chemical mechanical polishing (CMP) process. The goal of CMP is to acquire a high material removal rate and selectivity while ensuring that the polished surface is free of scratches and corrosion pits. A new acidic slurry added with potassium persulfate (OXONE) as an oxidizer was developed. The acidic slurry added with 5000 ppm OXONE has a amorphous GSTC film material removal rate of 5200 Å min−1, a high selectivity between GSTC and Si3N4 films of 950:1, and no corrosion-induced pit. In order to clarify the mechanism of GSTC CMP with OXONE, the Energy Dispersive Spectrometer, potentiodynamic polarization curve and X-ray photoelectron spectroscope were adopted to analyze the surface of GSTC. It is found that the chemical reaction mechanism is significantly different from that of hydrogen peroxide (H2O2). Finally, the mechanism of GSTC during the CMP with OXONE in the acidic slurry is depicted.

Proposal of Intelligent Polishing System by Artificial Intelligence Using Neural Networks

With the background of spreading the small and high performance mobile computers and developing the electric vehicles, the establishment of various high performance devices is demanded. Since chemical mechanical polishing (CMP) process has played an important role for these development, there are several unclear points in the CMP mechanism. For example, the removal rate of CMP increases when the polishing pad which has large number of actual contact points between polishing pad and substrate was used. On the other hand, the excessive number of contact points adversely affects the removal rate, however, this mechanism has not been elucidated. Currently, development of artificial intelligence (AI) technologies remarkably makes progress, so that the introducing method of AI to the CMP apparatus is expected. In this paper, we propose the polishing system by neural networks as well as try to predict and operation among the desired removal rate, the pad surface asperities and conditioning parameters. As a result, we succeed in presenting the example of proposed system to the CMP apparatus. By using the proposed system, we can predict relationship between the removal rate and the polishing pad surface asperities precisely. Furthermore, the proposed system can achieve the desired removal rate within a few percent error by controlling the conditioning parameters.

Achieving ultralow surface roughness and high material removal rate in fused silica via a novel acid SiO2 slurry and its chemical-mechanical polishing mechanism

Fused silica is widely used as a substrate material in various optical precision devices, and its surface quality plays a significant role in determining the optical performance. However, it is difficult to achieve an ultra-smooth surface without obvious damage using traditional planarization techniques. In this work, we report on the simultaneous achievement of ultralow surface roughness of ~0.193 nm and high material removal rate of ~10.9 μm h−1 on a fused silica substrate via a novel acid SiO2 slurry. The results show an improvement of removal rate by ~900% compared to its alkaline counterpart. Comprehensive studies based on thermogravimetric analysis, infrared X-ray photoelectron spectroscopy, and nuclear magnetic resonance spectra reveal that phenolic hydroxyl in the acid SiO2 slurry plays a critical role in achieving high material removal rate during the chemical-mechanical polishing process, by well-distributing the SiO2 abrasives with an average size of only ~80 nm. This approach delivers the high surface quality. Evidence in support of this explanation has been obtained using advanced characterization techniques including scanning electron microscopy, atomic force microscopy, and optical interferometry profiling. This novel acid SiO2 slurry is also environmentally friendly with significantly higher durability and stability, which is especially suitable for industrial scale production.

Physically-based modeling of pad-asperity scale chemical-mechanical synergy in chemical mechanical polishing

Abstract The performance of chemical mechanical polishing (CMP) has been found highly dependent on the pad-workpiece contact status, which is far from theoretical understanding. To this end, a physically-based material removal rate (MRR) model is developed under pad-asperity scale. The theoretical predictions agree well with the experimental results no matter the contact spots distribution is dispersed or concentrated. It is found that the deterioration of MRR is attributed to the continuously reduced number of reacted atoms in each individual contact spot and the inadequate time for chemical reaction between successive contact spots. The present model is expected to facilitate the clarification of the effect of contact status on MRR, and further provide a strategy for CMP mechanisms investigation.

Insights into the atomistic behavior in diamond chemical mechanical polishing with [rad]OH environment using ReaxFF molecular dynamics simulation

Diamond has been utilized for various applications such as ultra-precision cutting tools and power semiconductor devices. Chemical mechanical polishing (CMP) is an effective processing method for the planarization of diamond, but the removal mechanism of the carbon atoms in diamond CMP is still under debate. Here, the atomic mechanism of removal in diamond CMP with OH environment was investigated using the molecular dynamics (MD) simulation method of reactive force field (ReaxFF). The simulation results show that with chemical action alone, the substrate surface adsorbs O, H or OH to form C–O, C–H, C–OH, etc., but no carbon atoms are removed from the diamond substrate. However, when the mechanical sliding is added, some carbon atoms are removed in form of CO or CO2, and the other carbon atoms are removed by the attachment to abrasive. The formation of C–C bonds between the diamond substrate and the abrasive or the formation of C–O bonds is a prerequisite for subsequent sliding removal. This work contributes to understanding the removal mechanism of diamond CMP at the atomic level.

Effect of multi-functional amines on SiGe surface finish during chemical mechanical polishing

SiGe is one of the most promising strain relaxed buffer at advanced technology nodes. In this paper, the effects of pentapotassium; 2-[bis[2-[bis(carboxylatomethyl)amino]ethyl] amino]acetate (DTPA-5K) and triethanolamine (TEA) on Si0.5Ge0.5 chemical mechanical polishing (CMP) under alkaline condition were investigated. The results show that, DTPA-5K is a corrosion and rate enhancer for Si0.5Ge0.5. GeO2 and the silicon sub-oxide are believed to be generated on Si0.5Ge0.5 surface in DTPA-5K solution. The Si0.5Ge0.5 removal rate and its selectivity to TEOS are both proportional to DTPA-5K concentration. However, DTPA-5K has an impact on the slurry stability. With proper DTPA-5K concentration to ensure colloidal stability, the surface roughness of Si0.5Ge0.5 can be improved by triethanolamine (TEA). An optimized slurry formulation in the presence of DTPA-5K and TEA yielded a high Si0.5Ge0.5 removal rate, an acceptable within-wafer non-uniformity (WIWNU), very low surface roughness and desirable selectivity to TEOS. A CMP mechanism for this system is also proposed.

Atomistic mechanisms of chemical mechanical polishing of diamond (1 0 0) in aqueous H2O2/pure H2O: Molecular dynamics simulations using reactive force field (ReaxFF)

Diamond CMP mechanisms have been widely investigated using the CMP experimental methods. However, the experiment could not observe the details of the removal process, it could not explain the mechanism of removal. The atom removal mechanism of chemical mechanical polishing (CMP) process on the diamond surface polished with a silica abrasive in aqueous H2O2/pure H2O was elucidated using ReaxFF molecular dynamics (MD) simulations. The research shows that the oxidation of diamond surface plays a dual role in the removal of C atoms. First, the diamond surface absorbs OH, O or H to form CO, COH or CH bonds. Then, the C atoms on the oxidized diamond surface are removed under the mechanical action of abrasive in aqueous H2O2. Three types of C atom removal pathway are detected in the CMP process: it can be removed in the form of CO, CO2 or C chain and C atom removal occurs on the first layer. However, no C atoms are removed in pure H2O. The friction in pure H2O is less than that in aqueous H2O2 due to the lubrication of pure H2O. In addition, comparing the different pressures applied to the abrasive, it is found that the greater the pressure applied, the more OH adsorbed on the diamond surface so that the more C atoms are removed. This work shows that the removal of C atoms is the result of the combination of chemical and mechanical effects, which helps understand the removal process of C atoms at the atomic scale in the CMP process and provide an effective method to choose the CMP slurry.

An in situ study of chemical-mechanical polishing behaviours on sapphire (0001) via simulating the chemical product-removal process by AFM-tapping mode in both liquid and air environments.

Chemical-mechanical polishing (CMP) has drawn significant attention as one of the most advanced techniques for achieving an atomic-level smooth surface. However, the mechanism of CMP is still unclear, and the in situ characterization of CMP behaviors at the nanoscale has been a challenge for decades. In this study, we, for the first time, report an in situ study of CMP behaviors on sapphire (0001) via simulating the chemical product-removal process by using atomic force microscopy (AFM) in tapping mode. Through a combination of intensive experimental measurements and detailed structural characterizations, it is shown that the AFM probe in tapping mode can act as a polishing abrasive to realize simultaneous imaging and chemical product removal on sapphire (0001), thus achieving successful in situ characterizations in both liquid and air environments. This work fills in gaps relating to fundamental CMP mechanisms, and provides a new perspective for the study of CMP behaviors on different materials.

研磨パッド・アスペリティ内のミクロなスラリー循環流れ

Chemical mechanical polishing (CMP) is used in a wide range of processes in semiconductor production. However, the polishing mechanism of CMP is not completely understood. The behavior of the abrasive particles and chemical species in the slurry is believed to play a critical role in the polishing mechanism. Therefore, in this study, we observed the slurry flow occurring in the polishing pad asperities experimentally. Because in situ observation of the slurry flow is exceptionally difficult, an enlarged visualization model of the pad asperities was made, based on the scaling laws of fluid dynamics. A refractive index matching technique and a particle suspension method were applied to visualize the scaled-up slurry flow. As a result, the circulation flows in the vertical direction to the wafer surface have been observed at the openings of the pad pores, and at the valleys of the undulations formed by the pad conditioning. The size of the biggest circulation flow observed in this study is approximately 200 μm. This result suggests that, similar to the pad pores, the valleys of undulations of the pad have the function of aiding the slurry transport to the entire wafer surface.

Change in Slurry/Glass Interfacial Resistance by Chemical Mechanical Polishing

ABSTRACTThe use of ceria abrasives in the chemical mechanical polishing (CMP) of glass allows us to prepare extremely smooth surfaces because it aides both the chemical and mechanical aspects of the polishing process. The mechanism of CMP has remained vague, but the redox of Ce4+/Ce3+ would play a major role for the formation of hydration layer by the chemical factors of CMP. This redox accompanies the process of the charge transfer at glass/slurry interface. Electron charge carrier would be important role in chemical polishing if the redox reaction occurs during polishing. We then prepared the polishing model that it is possible to estimate slurry resistivity and the interfacial area specific resistance (ASR). The effects of abrasive compositions and slurry solution on chemical factor of CMP were investigated to clarify CMP mechanism. The hydration layer forms as a result of the shear stress during polishing but is independent of polishing loads. The amount of hydration layer as well as removal rate was increasing with increasing lanthanum concentration dissolved in ceria lattice. Small amount addition of NH4NO3 increase electron charge carrier density in slurry and improves removal rate, but excess addition inhibited hydration reaction by steric hindrance.

Investigation into Chemical Mechanical Polishing Mechanism of Hard-to-Process Materials Using a Commercially Available Single-Sided Polisher

Chemical mechanical polishing (CMP) is one of the most important processes for fabricating highly planarized substrates such as sapphire for light emitting diodes (LEDs). However, sapphire is categorized as a hard-to-process material; therefore, a long processing time is required because of the low polishing efficiency (i.e., removal rate). This study investigates the CMP mechanism for hard-to-process materials using the following polishing evaluation parameters: (1) the velocity ratio, which is defined as the ratio of slurry flow velocity between the wafer and polishing pad during CMP to the pad tangential velocity, (2) the standard deviation of the velocity ratio distribution, and (3) the polisher vibration acceleration during CMP. Each parameter was measured at five rotational speeds and two polishing pressures for a total of ten conditions using a commercially available single-sided polisher. Moreover, the influence of each parameter on the removal rate was demonstrated via a multiple correlation analysis. As a result, we revealed that the velocity ratio and polisher vibration acceleration are strongly related with the removal rate.

Effect of Abrasive Concentration on Chemical Mechanical Polishing of Sapphire**Supported by the National Major Scientific and Technological Special Project during the Twelfth Five-year Plan Period under Grant No 2011ZX02704, the National Natural Science Foundation of China under Grant No 51205387, and the Science and Technology Commission of Shanghai under Grant Nos 11nm0500300 and 14XD1425300.

Effects of abrasive concentration on material removal rate (MRR) and surface quality in the chemical mechanical 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 20 wt% to 40 wt%. Temperature is a product of the friction force that is proportional to COF, which is an indicator for the mechanism of the sapphire CMP.

Investigation on S-136 steel surface planarization by chemical mechanical polishing

S-136 (STAVAX ESR) steel has been widely applied in the mold manufacturing industry. Commercially available S-136 steel possesses high surface roughness, which exerts negative effects on the device performance. In this paper, S-136 steel surface planarization using chemical mechanical polishing (CMP) was investigated and the process parameters included down pressure, platen speed, slurry pH and abrasive category. The results demonstrated that the relationship of material removal rate (MRR) with respect to the multiply of pressure and platen speed was in accordance with a modified Preston equation: MRR=(KP+B0) V+R0. With the variation of pH, the MRR changed rapidly. Compared with initial root mean square (RMS) roughness of 37.47nm, the ultra-smooth surface with RMS roughness 3.01nm was obtained under optimized condition with MRR as high as 187nm/min. Finally, optimized CMP process parameters for S-136 steel were proposed and its CMP mechanism was discussed in detail.

Mechanism of GaN CMP Based on H2O2 Slurry Combined with UV Light

Chemical mechanical polishing (CMP) of GaN(0001) with a H2O2-SiO2-based slurry is investigated in this paper. The result shows that an atomically flat surface with a roughness of 0.065 nm is obtained after polishing. Compared with a SiO2-based slurry, the H2O2-SiO2-based slurry can realize a higher material removal rate (MRR) and a better surface quality with less scratches. The pH value mainly affects the mean particle size of SiO2 and the chemical environment of the corrosion reaction with H2O2, resulting in different MRRs. An off-site auxiliary polishing method is employed along with the H2O2-SiO2-based polishing system using ultraviolet light to shine the outlet of slurry in order to catalyze the production of substance for oxidation, and it is proved to be efficient by improving the MRR to 103 nm/h. Physical and mathematic removal models are proposed to describe the removal mechanism of GaN CMP.

The Effect of pH on Sapphire Chemical Mechanical Polishing

In this paper, the effect of pH on sapphire chemical mechanical polishing (CMP) was investigated. The sapphire removal rate increased with ascending pH until 8. To investigate the electrostatic force between colloidal silica abrasive and sapphire surface, the zeta potential of sapphire surface and colloidal silica abrasive were studied. The sapphires immersed into the slurry containing 20 wt% colloidal silica were observed with scanning electron microscopy (SEM). For further insights into the mechanism of sapphire CMP with different pH values, particle size of the colloidal silica was used to analyze the mechanical function. Finally, the chemical actions between sapphire (Al2O3) and colloidal silica (SiO2) during sapphire CMP as a function of pH value were discussed.

Modeling and simulation for the distribution of slurry particles in chemical mechanical polishing

Slurry plays an important role in the material removal of chemical mechanical polishing (CMP). However, the behavior of abrasive particles of the slurry in the interface between the wafer and the pad during CMP is not fully understood. In this paper, a new computational fluid dynamic (CFD) model was developed. It was a combination of multiphase and discrete phase modeling. The abrasive particles behavior and the slurry distribution in the interface were simulated using this model. The total numbers of particles in the gap were quantified to characterize their mechanical effects under different operating parameters. The simulation results showed that when the gap thickness increased and speeds of the wafer and the pad decreased, the total number of particles in the gap increased. It also found that the particles were non-uniformly distributed below the wafer. The results have the capacity of providing a deeper insight understanding of the material removal of the CMP mechanism.

Chemical mechanical polishing of steel substrate using aluminum nanoparticles abrasive slurry

Purpose – Chemical mechanical polishing (CMP) has attracted much attention recently because of its importance as a nano-scale finishing process for high value-added large components that are used in the aerospace industry. The paper aims to discuss these issues. Design/methodology/approach – The characteristics of aluminum nanoparticles slurry including oxidizer, oxidizer contents, abrasive contents, slurry flow rate, and polishing time on aluminum nanoparticles CMP performance, including material removal amount and surface morphology were studied. Findings – Experimental results indicate that the CMP performance depends strongly on the oxidizer, oxidizer contents, and abrasive contents. Surface polished by slurries that contain nano-Al abrasives had a lower surface average roughness (Ra), lower topographical variations and less scratching. The material removal amount and the Ra were 124 and 7.61 nm with appropriate values of the process parameters of the oxidizer, oxidizer content, abrasive content, slurry flow rate and polishing time which were H2O2, 2 wt.%, 1 wt.%, 10 ml/min, 5 min, respectively. Originality/value – Based on SEM determinations of the process parameters for the polishing of the surfaces, the CMP mechanism was deduced preliminarily.

Synthesis and Characterization of SiO2Nanoparticles and Their Efficacy in Chemical Mechanical Polishing Steel Substrate

Chemical mechanical polishing (CMP) technology is extensively used in the global planarization of highly value-added and large components in the aerospace industry. A nanopowder of SiO2was prepared by the sol-gel method and was compounded into polishing slurry for the CMP of steel substrate. The size of the SiO2abrasives was controlled by varying the sol-gel reaction conditions. The polishing efficacy of nano-SiO2was studied, and the CMP mechanism with nanosized abrasives was further investigated. The proposed methods can produce SiO2abrasives whose size can be controlled by varying the sol-gel reaction conditions. The size of the SiO2abrasives was controlled in the range from 58 to 684 nm. The roughness of the steel substrate strongly depends on the size of the abrasive, and the surface roughness decreases as the abrasive size declines. A super-smooth surface with a roughness of 8.4 nm is obtained with nanosized SiO2. Ideal CMP slurry can be used to produce material surfaces with low roughness, excellent global planarization, high selectivity, an excellent finish, and a low-defected rate.

Chemical mechanical polishing: Theory and experiment

Abstract 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.