Application Of Chemical Mechanical Polishing Research Articles

Characterization of Ceria Nanoparticles as Abrasives Applied with Defoaming Polymers for CMP (Chemical Mechanical Polishing) Applications.

Chemical mechanical polishing/planarization (CMP) is an essential manufacturing process in semiconductor technologies. This method combines chemical and mechanical forces to smooth the surfaces of wafers. The effectiveness of CMP relies on a carefully chosen slurry, demanding a sophisticated manufacturing technology. This technology must seamlessly integrate both chemical composition and mechanical elements, highlighting the intricate synergy required for successful semiconductor fabrication. Particularly in milling processes, if agglomerated particles due to slurry particle corrosion are present during polishing, uneven polishing, numerous fine scratches occur, leading to an increase in roughness and a deterioration in the quality of the finished surface. In this study, to overcome the issue of particle agglomeration and uneven polishing in commonly used ceria nanoparticle slurries during CMP processes, we investigated the ceria nanoparticle behavior based on styrene-maleic acid (SMA) dispersant polymer applied with three types of defoaming polymers. The investigations are expected to open up the possibility of utilizing ceria nanoparticles with applied defoaming polymer as an abrasive for advanced CMP applications. All samples were characterized by DLS (dynamic light scattering), SEM-EDX (scanning electron microscopy-energy dispersive X-ray spectroscopy), pH, conductivity, viscosity, a 10-day stability test at 60 °C, the AF4 test, and the polishing rate efficiency test. Our research demonstrates a significant improvement achieved through the use of SMA dispersant polymer, resulting in a polishing selection ratio exceeding 80 for oxide and nitride films. The G-336 defoaming polymer utilized here is expected to serve as a viable alternative in CMP processes by providing stable uniformity.

Surface acidity of colloidal silica and its correlation with sapphire surface polishing

Colloidal silica occupies the field of polishing solution application of chemical mechanical polishing (CMP). Si-OH groups dominate the surface of colloidal silica nanoparticles, and their chemical nature, acidity, is a determining factor for CMP. However, due to the delicate nature, very vulnerable to self-condensation at elevated temperatures, of colloidal silica nanoparticles, traditional techniques used for characterizing powder samples are limited to gaining true insights into the chemical reactivity of these Si-OH groups without disturbing the surface chemistry, which hinders the deep exploration of the essential mechanism of CMP on silica. In this manuscript, low-field nuclear magnetic resonance (LF NMR) and freeze-drying-programmed temperature desorption (TPD) techniques were, for the first time, combined to investigate the true acidity of the surface Si-OH groups in colloidal silica with minimized perturbance from sample preparations. The results from both characterization methodologies complemented each other, and are in good agreement about the surface structure and acidity of the surface Si-OH groups on colloidal silica. The results demonstrate that the acidity of Si-OH hydroxyl groups on the surface of silica-soluble nanoparticles spreads in a very broad range from very weak, medium-strong, to very strong. CMP performance of sapphire substrates by using colloidal silica strongly correlates with the acidic nature of surface Si-OH groups at the acidic polishing condition. The stronger acidity of surface Si-OH groups, the higher material removal rates in sapphire polishing through the chemical bonding of deprotonated Si-O- functional surface of colloidal silica with hydrolyzed sapphire Al-OH surface. Therefore, when a large number of Si-O- active centers in the basic environment attack the sapphire Al-OH sites, the rate of the chemical reaction is accelerated.

Tunable synthesis, characterization, and CMP performance of dendritic mesoporous silica nanospheres as functionalized abrasives

The type, morphology, structure, size and distribution, surface chemistry, and mechanical behavior of particle abrasives play a key role in advanced chemical mechanical polishing (CMP) applications. In this work, dendritic mesoporous silica (D-mSiO2) nanospheres with tunable structures were synthesized via a modified n-hexane/water biliquid system coupled with a shearing assisted interfacial coassembly method. The resulting samples were characterized in terms of transmission electron microscopy, scanning electron microscopy, thermogravimetric analysis, Fourier transform infrared spectroscopy, powder X-ray diffraction, and nitrogen adsorption-desorption measurements. The spherical D-mSiO2 products presented three-dimensional and center-radial structures with particle size of 30–140 nm, pore diameter of 3–9 nm, surface area of ~780 m2/g, and pore volume of ~1.5 cm3/g. The elastic property and compressive elastic modulus of D-mSiO2 nanospheres were investigated by atomic force microscopy (AFM) nanoindentation. Oxide-CMP performances of the series of D-mSiO2 nanospheres as functionalized abrasives were tracked via high-resolution AFM and interferometric microscopy. The subtle differences of surface characteristics were systematically compared in terms of roughness, topographical variation, and image surface area difference (SAD). Sub-100 nm D-mSiO2 nanospheres achieved superior CMP qualities with the decreased surface roughness (less than 0.2 nm Rq and 0.3 nm Rz, within 5.0 × 5.0 µm2), the reduced maximum peak height/minimum valley depth (less than 0.5 nm), as well as the low image SAD (less than 0.009%). Furthermore, the interfacial contact behavior, water-involved tribochemical wear, and material removal mechanism of D-mSiO2 nanoabrasives were also discussed. The investigations are expected to open up the possibility of utilizing D-mSiO2 nanospheres as novel abrasives for advanced CMP applications.

Approaches to Sustainability in Chemical Mechanical Polishing (CMP): A Review

Chemical mechanical polishing (CMP) is an essential planarization process for semiconductor manufacturing. The application of CMP has been increasing in semiconductor fabrication for highly integrated devices. Recently, environmental burden caused by the CMP process was assessed because of interest in the global environment. In this study, the previously reported impacts of CMP on the environment and studies conducted on developing various methods to reduce environmental burden are reviewed. In addition to analyzing the impacts of CMP, this paper introduces a method for treating CMP wastewater and improving the material removal efficiency through the improvement of CMP consumables. Finally, the authors review research on hybridization of the CMP process and discuss the direction in which CMP technology will progress to improve sustainability in the future.

Engineered Ceria Slurries for Electronic Glass Substrate CMP Application

Glass substrates have gradually gained more attention as the media platters in hard disk drives (HDD) used in laptops, data centers, and cloud storage due to its advantageous properties. Particularly, advanced technologies like Heat Assisted Magnetic Recording (HAMR) in HDD and Through-Glass-Via (TGV) in 3D packaging applications all require the use of glass substrates with precisely controlled surface properties. Glass substrate’s advantages include lower weight, improved flatness, less flutter at high RPM’s and lower thermal expansion as compared to aluminum / NiP substrates. This lower expansion when exposed to heat makes it ideal for HAMR technology, which will be the key to creating hard disk drives with growing storage capacity. Chemical mechanical polishing (CMP) is a method to eliminate surface defects induced by grinding & lapping to meet final requirements of HAMR or TGV for glass substrates with surface finishes down to a few angstrom level or less. Key performance targets include removal rate, surface roughness, TTV, FSW, ceria residue / particle content (cleanability) on glass disks as well as recyclability. In this study, slurries for CMP are investigated utilizing engineered ultra-pure ceria particles which are known to have high material removal rate (MRR) on glass substrates. Various particle sizes, morphology, and chemical additives were evaluated. Results of systematic CMP tests including MRR, surface roughness, recyclability, and most importantly, ease of ceria residue removal from the glass substrate will be reported. Morphology of ceria particles was found to play a critical role in MRR. An optimized combination of ceria morphology and additive chemistries enables high MRR together with improved Ceria residue / cleanability performance. Figure 1

Soft Chemical Mechanical Polishing Pad for Oxide CMP Applications

Chemical mechanical polishing (CMP) is widely accepted as the best planarization technique for fabricating nanoscale devices. A soft CMP pad that can enable higher oxide removal rates (RRs) and good planarity has been proposed for oxide CMP applications. In this study, three pads namely, Pad-1 (hard), Pad-2 (soft), and a commercial pad (hard) were used to polish blanket oxide, and STI patterned wafers. The Pad-2 demonstrated significantly higher RRs and better planarization than the hard pads. Post-polish pad texture analysis on Pad-2 showed a uniform surface asperity distribution. This is due to the novel method of pad manufacturing, which enables precise material placement and consistent pore construction.

Preliminary Study on Polishing SLA 3D-Printed ABS-Like Resins for Surface Roughness and Glossiness Reduction.

After the development of 3D printing, the post-processing of the 3D-printed materials has been continuously studied, and with the recent expansion of the application of 3D printing, interest in it is increasing. Among various surface-machining processes, chemical mechanical polishing (CMP) is a technology that can effectively provide a fine surface via chemical reactions and mechanical material removal. In this study, two polishing methods were evaluated for the reduction of surface roughness and glossiness of a stereolithography apparatus (SLA) 3D-printed ABS (acrylonitrile butadiene styrene)-like resin. Experiments were conducted on the application of CMP directly to the 3D-printed ABS-like resin (one-step polishing), and on the application of sanding (#2000) and CMP sequentially (two-step polishing). The one-step polishing experiments showed that it took a considerable period of time to remove waviness on the surface of the as-3D printed specimen using CMP. However, in the case of two-step polishing, surface roughness was reduced, and glossiness was increased faster than in the case of one-step polishing via sanding and CMP. Consequently, the experimental results show that the two-step polishing method reduced roughness more efficiently than the one-step polishing method.

Measurement and Error Analysis of Cu Film Thickness With Ta Barrier Layer on Wafer for CMP Application

Accurate thickness measurement of copper (Cu) film on silicon (Si)-based wafers is very important in the chemical mechanical polishing (CMP) process. For thickness measurement of Cu film, the eddy current method is widely adopted due to noncontact, high-efficiency, and high-accuracy characteristics. However, existing thickness measurements of Cu film ignore the effect of tantalum (Ta) barrier layer between Cu film and Si substrate, which makes the measurement result inaccurate. Therefore, it is necessary to investigate the effect of Ta barrier layer on thickness measurement of Cu film. In this article, an improved eddy current sensor system with a nanoscale resolution is proposed. It is based on the inductance–capacitance resonance principle and theoretical analysis is conducted. Several Si-based specimens with pure Cu film, pure Ta film, and Cu–Ta multilayer structure are prepared and measured. Experimental results show that there exists a balance thickness of Ta barrier layer as a threshold in Cu–Ta multilayer structure. When the thickness of Ta barrier layer is larger than the threshold, the measured thickness of Cu film increases with the increase of Ta barrier layer thickness. Conversely, the measured thickness of Cu film decreases when Ta barrier layer is thinner than the threshold. Then, a compensation method is presented, and the error of thickness measurement of Cu film is reduced to less than 6 nm.

Review on modeling and application of chemical mechanical polishing

Abstract With the development of integrated circuit technology, especially after entering the sub-micron process, the reduction of critical dimensions and the realization of high-density devices, the flatness between integrated circuit material layers is becoming more and more critical. Because conventional mechanical polishing methods inevitably produce scratches of the same size as the device in metal or even dielectric layers, resulting in depth of field and focus problems in lithography. The first planarization technique to achieve application is spin on glass (SOG) technology. However, this technology will not only introduce new material layers, but will also fail to achieve the global flattening required by VLSI and ULSI technologies. Moreover, the process instability and uniformity during spin coating do not meet the high flatness requirements of the wafer surface. Also, while some techniques such as reverse etching and glass reflow can achieve submicron level regional planarization. After the critical dimension reaches 0.35 microns (sub-micron process), the above methods cannot meet the requirements of lithography and interconnect fabrication. In the 1980s, IBM first introduced the chemical mechanical polishing (CMP) technology used to manufacture precision optical instruments into its DRAM manufacturing [1]. With the development of technology nodes and critical dimensions, CMP technology has been widely used in the Front End Of Line (FEOL) and Back End Of Line (BEOL) processes [2]. Since the invention of chemical mechanical polishing, scientists have not stopped studying its internal mechanism. From the earliest Preston Formula (1927) to today’s wafer scale, chip scale, polishing pad contact, polishing pad - abrasive - wafer contact and material removal models, there are five different scale models from macro to the micro [3]. Many research methods, such as contact mechanics, multiphase flow kinetics, chemical reaction kinetics, molecular dynamics, etc., have been applied to explain the principles of chemical mechanical polishing to establish models. This paper mainly introduces and summarizes the different models of chemical mechanical polishing technology. The various application scenarios and advantages and dis-advantages of the model are discussed, and the development of modeling technology is introduced.

Preparation of Surface Modified Ceria Nanoparticles as Abrasives for the Application of Chemical Mechanical Polishing (CMP)

In this study, a method to improve the chemical mechanical polishing (CMP) performance of ceria as abrasive particles was proposed. Surface doping of ceria nanoparticles was realized by incipient impregnation method, in order to improve its valance change properties (Ce3+/Ce4+). This study presents detailed characterization of the lanthanide-doped CeO2 by both experimental methods and density functional theory (DFT) calculation. The dispersion stability of the doped ceria nanoparticles in CMP slurries are investigated. Results show that the doped CeO2 nanoparticles exhibit more oxygen vacancies and higher content of Ce3+ compared with the pristine CeO2. Good dispersion stability of the doped CeO2 nanoparticles could be achieved by adding dispersants in the CMP slurries.

Chemical Mechanical Polishing Implementation for Corrosion Prevention of Titanium Bio-Implants

Corrosion and surface film dissolution are two mechanisms for titanium-based bioimplants to release ions into the human body and hence degrading the biocompatibility. Electrochemical methods are commonly practiced in testing metallic biomaterials in-vitro measurements[1] (Kuhn, Neufeld and Rae, 1988). In an attempt to prevent the in-vivo corrosion of the titanium implants, we have introduced a new approach by utilizing chemical mechanical polishing (CMP) as a synergistic approach to form a protective surface film and as a tool to control the surface nanostructure [2] to promote or demote cell attachment. In this paper, application of CMP on titanium implant surfaces is studied through electrochemical analyses in the absence and presence of an oxidizer. Corrosion rates are extrapolated from anodic polarization of the potentiodynamic curves (Figure 1) with and without CMP implementation to compare the affect of surface engineering. It was observed that the higher corrosion (Table 1) rates correlated to the higher material removal during polishing, which can be controlled through oxidizer concentration that affects the surface TiO2 film growth. Furthermore, potentiostatic measurements showed that the addition of oxidizer increased the rate of oxide growth and decreased the surface current density levels indicating that the surface self-passivation took place. Post CMP contact angle (wettability) and AFM measurements confirmed an improved surface topography and surface homogeneity by CMP treatment as better surface smoothness and wettability control was achieved. [1] Kuhn, A., Neufeld, P. and Rae, T. (n.d.). Synthetic Environments for the Testing of Metallic Biomaterials. The Use of Synthetic Environments for Corrosion Testing, 1988, pp.79-79-19. [2] Ozdemir, Z., Ozdemir, A. and Basim, G. (2016). Application of chemical mechanical polishing process on titanium based implants. Materials Science and Engineering: C, 68, pp.383-396. Figure 1

Germanium electrochemical study and its CMP application

When the feature size of ultra-large scale integrated(ULSI) circuit shrinks to sub–10nm, germanium(Ge) as a novel material with high hole mobility is needed for further development. Chemical mechanical polishing(CMP) is an important process for the integration of channel materials into silicon wafer. In this paper, starting with electrochemical studies of Ge, different types and concentrations of oxidants for Ge corrosion were investigated; then the effect of NaCl and Dodecylamine for Ge activation and inhibition were studied. After that, corresponding CMP experiments were conducted, which confirmed the results of electrochemical experiments. Moreover the polish selectivity of Ge/SiO2 in H2O2-based slurry was also investigated. Atomic force microscope(AFM) was used to test the surface morphology of wafers after polish. Finally the slurry with 5wt% SiO2 abrasive and 1 vol.% H2O2 at pH 9 were chosen to polish Ge/SiO2 wafers, and it has a high polish selectivity of Ge to SiO2 while high Ge removal rate and good quality surface were obtained.

Application of chemical mechanical polishing process on titanium based implants

Modification of the implantable biomaterial surfaces is known to improve the biocompatibility of metallic implants. Particularly, treatments such as etching, sand-blasting or laser treatment are commonly studied to understand the impact of nano/micro roughness on cell attachment. Although, the currently utilized surface modification techniques are known to improve the amount of cell attachment, it is critical to control the level of attachment due to the fact that promotion of bioactivity is needed for prosthetic implants while the cardiac valves, which are also made of titanium, need demotion of cells attachment to be able to function. In this study, a new alternative is proposed to treat the implantable titanium surfaces by chemical mechanical polishing (CMP) technique. It is demonstrated that the application of CMP on the titanium surface helps in modifying the surface roughness of the implant in a controlled manner (inducing nano-scale smoothness or controlled nano/micro roughness). Simultaneously, it is observed that the application of CMP limits the bacteria growth by forming a protective thin surface oxide layer on titanium implants. It is further shown that there is an optimal level of surface roughness where the cell attachment reaches a maximum and the level of roughness is controllable through CMP.

Effects of non-spherical colloidal silica slurry on Al-NiP hard disk substrate CMP application

Spherical and non-spherical colloidal silica size and shape were characterized and its effects on aluminum alloy nickel plated (Al-NiP) hard disk substrate during chemical mechanical polishing (CMP) was investigated. Non-spherical colloidal silica slurry shows significantly higher material removal rate (MRR) with higher coefficient of friction (CoF) when compared to spherical colloidal silica of similar size. CMP evaluations on non-spherical colloidal silica slurry particle size distribution (PSD) reveal that MRR can be further increased by using wider PSD. Conventional slurry for Al-NiP hard disk substrates which use alumina–silica composite slurry induces embedded alumina thermal asperities (TA) defects which can cause reliability failure at product level. CMP comparison between conventional alumina–silica slurry and non-spherical colloidal silica slurry shows substrates polished by using non-spherical colloidal silica slurry have no embedded TA defects, lower surface roughness and lower surface defects.

A novel kind of TSV slurry with guanidine hydrochloride**Project supported by the Major National Science and Technology Special Projects (No. 2009ZX02308), the Fund Project of Hebei Provincial Department of Education, China (No. QN2014208), the Natural Science Foundation of Hebei Province, China (No. E2013202247), and Colleges and Universities Scientific research project of Hebei Province, China (No. Z2014088).

The effect of a novel alkaline TSV (through-silicon-via) slurry with guanidine hydrochloride (GH) on CMP (chemical mechanical polishing) was investigated. The novel alkaline TSV slurry was free of any inhibitors. During the polishing process, the guanidine hydrochloride serves as an effective surface-complexing agent for TSV CMP applications, the removal rate of barrier (Ti) can be chemically controlled through tuned selectivity with respect to the removal rate of copper and dielectric, which is helpful to modifying the dishing and gaining an excellent topography performance in TSV manufacturing. In this paper, we mainly studied the working mechanism of the components of slurry and the skillful application guanidine hydrochloride in the TSV slurry.

A Contact Mechanics Formulation for Predicting Dishing and Erosion CMP Defects in Integrated Circuits

A three-dimensional contact mechanics formulation is presented for chemical mechanical polishing applications. The formulation is coupled with the Preston material removal equation in order to simulate the evolution of pressure and wafer height. The physics-based formulation allows the pressure and height to evolve such that dishing and erosion appear seamlessly. Results are compared against another feature-scale model and experiment. The methodology and model offer physics-based results that further the understanding of chemical mechanical polishing for a given layout.

Non-spherical colloidal silica particles—Preparation, application and model

Non-spherical colloidal particles have shown their great potential in the field of chemical mechanical polishing (CMP) due to their high polishing rate. A new method named “cation induced method” has been developed and used to produce non-spherical colloidal silica particles. We have tested this kind of novel shape particles in the application of SiO2's CMP. The material removal rate of this kind of abrasive particles has been tested and verified to be much faster than traditional spherical silica particles. In addition, both the particles’ morphology and properties have been characterized by the scanning electron microscope (SEM), transmission electron microscope (TEM) and dynamic light scattering (DLS). Finally, a semiquantitative model is built to show the relationship between the shape of particles and the amount of inducing agents.

Development of 3-D Chemical Mechanical Polishing Process for Nanostructuring of Bioimplant Surfaces

This study focuses on the development of a three dimensional chemical mechanical polishing (CMP) process to induce smoothness or controlled nano-structures on the bio-implant material surfaces, particularly for an application on the dental implants. CMP helps produce implant surfaces that are cleaned from potentially contaminated surface layers by removing a nano-scale top layer during the process. Simultaneously, it creates a protective oxide film on the surface to limit any further contamination to minimize risk of infection [1]. Furthermore, the process can induce controlled surface topography. Therefore, we propose CMP as a synergistic method for nano-structuring of implant surfaces. In our earlier work, we have demonstrated that the CMP induced controlled surface roughness on the titanium based bio-materials helped control the infection resistance through formation of a self-protective titanium oxide film on the implant surfaces [2]. Yet, it is critical to be able to extent these findings to a 3-D platform to make the dental implants processed by CMP application.The 3-D CMP process is established through use of robotics and control systems by integrating a robotic arm to the sample to be polished through a force-torque sensor. This technique, once programmed, can induce the same force on the various regions of the bio-implant sample and effectively smoothen or nano-structure the alternative surfaces on the implant. Considering the wide applications [3] of the implants as dental implants, orthopedic devices, cardiac pacemakers and catheters, this new application of CMP is believed to help create a new market for the process.

A study of material removal amount of sapphire wafer in application of chemical mechanical polishing with different polishing pads

The study mainly explores the fabrication mechanism for fabricating sapphire wafer substrate, by using chemical mechanical polishing (CMP) method. A slurry containing the abrasive particles of SiO2 is used to contact with the sapphire substrate polish and to produce chemical reaction for removal of sapphire wafer substrate when CMP method is used. The study observes the changes of the removal amount of sapphire wafer substrate when the pattern-free polishing pad and hole-pattern polishing pad are used under different down forces, polishing velocities, abrasive particle sizes and slurry concentrations. Employing regression analysis theory, the study makes improvement of the equation of material removal rate (MRR) to be the material removal height per 30 minutes (MRRh), and develops a compensation parameter Crv of the error caused by the volume concentration of slurry. The results of experimental analysis show that under a certain down force, if the polishing velocity is greater, the material removal amount will be greater. Generally speaking, the material removal amount of hole-pattern polishing pad is greater than that of pattern-free polishing pad. As to the relationship between abrasive particle size and slurry concentration, when particle size is smaller, the volume concentration of slurry will be higher, and the number of abrasives for polishing wafer will be greater. As a result, a better material removal depth can be acquired. Through the above analytical results, considerable help is offered to the polishing of sapphire wafer.

Cerium-incorporated SBA-15-type materials for CMP: synthesis, characterisation, and CMP application on hard disk substrate

Cerium-incorporated SBA-15-type abrasives were synthesised by a two-step synthesis method in order to improve the performance of chemical mechanical polishing (CMP). An analysis using transmission electron microscope (TEM) and nitrogen adsorption showed that this new type of abrasives exhibited highly ordered mesostructures with nanoscale pore diameter, large pore volume and uniform porous size distribution. The performances of CMP on hard disk substrates using the new abrasives were then investigated. The polishing results showed that cerium-incorporated SBA-15-type composite abrasives with larger pore diameter were more likely to get higher material removal rate (MRR), while the surfaces of hard disk polished by this type of abrasives were associated with lower topographical variations and lower surface roughness as compared with those polished by sing pure SBA-15 abrasives.