Abrasive-free Polishing Research Articles

Abrasive-free polishing of hard disk substrate with H2O2-C4H10O2-Na2S2O5 slurry

Abstract The effect of tert-butyl hydroperoxide-sodium pyrosulfite ((CH3)3COOH-Na2S2O5) as an initiator system in H2O2-based slurry was investigated for the abrasive-free polishing (AFP) of a hard disk substrate. The polishing results show that the H2O2-C4H10O2-Na2S2O5 slurry exhibits a material removal rate (MRR) that is nearly 5 times higher than that of the H2O2 slurry in the AFP of the hard disk substrate. In addition, the surface polished by the slurry containing the initiator exhibits a lower surface roughness and has fewer nano-asperity peaks than that of the H2O2 slurry. Further, we investigate the polishing mechanism of H2O2-C4H10O2-Na2S2O5 slurry. Electron spin-resonance spectroscopy and auger electron spectrometer analyses show that the oxidizing ability of the H2O2-C4H10O2-Na2S2O5 slurry is much greater than that of the H2O2 slurry. The results of potentiodynamic polarization measurements show that the hard disk substrate in the H2O2-C4H10O2-Na2S2O5 slurry can be rapidly etched, and electrochemical impedance spectroscopy analysis indicates that the oxide film of the hard disk substrate formed in the H2O2-C4H10O2-Na2S2O5 slurry may be loose, and can be removed easily during polishing. The better oxidizing and etching ability of H2O2-C4H10O2-Na2S2O5 slurry leads to a higher MRR in AFP for hard disk substrates.

Abrasive-Free Polishing of SiC Wafer Utilizing Catalyst Surface Reaction

not Available.

Abrasive-Free Polishing of SiC Wafer Utilizing Catalyst Surface Reaction

Catalyst-referred etching (CARE) is an abrasive-free chemical polishing method that utilizes a catalytic chemical reaction at the contact points of a wafer and a catalyst plate surface. Using a platinum plate catalyst and hydrogen fluoride aqueous solution, an atomically flat 4H–SiC (0001) wafer was obtained. The removal rate was found to be proportional to the rotational velocity and processing pressure, and it reached approximately 500 nm/h, which is comparable to chemical mechanical polishing methods. Furthermore, it was found that an atomically flat SiC surface can be obtained by CARE using only deionized water and a platinum catalyst, which is significant from the viewpoint of the widespread use of CARE.

Effect of Cu (II) Ion on Abrasive-Free Polishing of Hard Disk Substrate with Peroxyacetic Acid System Slurry

Recently, abrasive-free polishing (AFP) has attracted a great deal of attention due to its gentler polishing process and lower particle residue than traditional chemical mechanical polishing (CMP). Our present work investigates the effectiveness of Cu (II) ion on AFP of hard disk substrate in peroxyacetic acid (PAA) system slurry. The polishing experimental results show that the PAA/Cu (II) system slurry has higher material removal rate (MRR) and lower roughness (Ra) than PAA system. Further, the reaction mechanism of Cu (II) ion in PAA/Cu (II) system AFP of hard disk substrate was investigated preliminarily by electrochemical analysis.

Cu (II) as a Catalyst for Hydrogen Peroxide System Abrasive-Free Polishing on Hard Disk Substrate

With the continuous increase of the hard disk drive capacity, higher requirements are set for hard disk substrate to minimize roughness and defects of the polished surface. Recently, abrasive-free polishing (AFP) has attracted a great deal of attention due to AFP has fewer micro scratches and better cleaning ability than traditional chemical mechanical polishing (CMP). Our present work investigates the effectiveness of Cu (Ⅱ) as a catalyst for hard disk substrate AFP with H2O2 employed as an oxidizer. Polishing slurries used in AFP on hard disk substrate include deionized water, dispersant and oxidizer. The polishing experimental results show that the slurry of H2O2/Cu(Ⅱ) system has higher material removal rate (MRR) than H2O2 system in abrasive-free polishing on hard disk substrate. Further, the catalytic reaction mechanism of Cu (Ⅱ) in AFP of hard disk substrate was investigated. Compared with the H2O2 system, electron spin-resonance spectroscopy (EPR) analysis shows that the H2O2/Cu(Ⅱ) system provides higher concentration of hydroxyl radical. Potentiodynamic polarization measurements shows that corrosion currents (icorr) of disk substrate in the H2O2/Cu(Ⅱ) system is larger than that in the H2O2 system. The results imply that Cu (Ⅱ) as a catalyst for hydrogen peroxide system possesses promising prospects in abrasive-free polishing.

Abrasive-Free Polishing of Hard Disk Substrate with H<sub>2</sub>O<sub>2</sub>-K<sub>2</sub>S<sub>2</sub>O<sub>8</sub>-NaHSO<sub>3</sub> Slurry

The effect of potassium peroxydisulfate-sodium hydrogensulfite (K2S2O8- NaHSO3) as an initiator system in H2O2 –based slurry for the abrasive-free polishing (AFP) of hard disk substrate was investigated. The polishing experimental results showed that the H2O2-K2S2O8-NaHSO3 slurry had ten times higher material removal rate (MRR) than the H2O2 slurry in AFP of the hard disk. Further, the polishing mechanism of H2O2-K2S2O8-NaHSO3 slurry was investigated. Compared with the H2O2 slurry, electron spin-resonance spectroscopy (EPR) analysis showed that the H2O2-K2S2O8-NaHSO3 slurry provides twenty times higher concentration of hydroxyl free radical. Potentiodynamic polarization measurement showed that the corrosion current of disk substrate in the H2O2-K2S2O8-NaHSO3 slurry is larger than that in the H2O2 slurry. The results imply that K2S2O8-NaHSO3 as an initiator system for H2O2–based slurry has application prospects in abrasive-free polishing.

Effect of K<sub>2</sub>S<sub>2</sub>O<sub>8</sub> on Material Removal Rate in Abrasive-Free Polishing of Hard Disk Substrate

The role of K2S2O8 (KPS) initiator on the material removal rate (MRR) of hard disk substrate in the H2O2-based slurry was investigated. Experiment results indicate that the MRR of slurry containing KPS and H2O2 is higher than that of slurry containing only H2O2 under the same testing conditions. The electrochemical test shows that KPS can increase the corrosion rate of hard disk substrate in the H2O2-based slurry. The electron spin-resonance spectroscopy (EPR) analysis shows that KPS, as an initiator, can increase the number of OH• free radical. Further, the reaction mechanism of KPS in abrasive-free polishing of hard disk substrate is discussed.

Study on Reactive Species in Catalyst-Referred Etching of 4H–SiC using Platinum and Hydrofluoric Acid

In this study, we developed aA novel abrasive-free polishing method called the catalyst-referred etching (CARE) has been developed. CARE can chemically remove SiC chemically with using an etching agent activated by a catalyst. Platinum and hydrofluoric (HF) acid are used for the planarization of SiC substrates as a catalyst and etchant, respectively. CARE can produce an atomically flat surface of 4H–SiC (0001) with a root-mean-square roughness of less than <0.1 nm, regardless of the cut-off angle. However, the mechanism of CARE has hasis not yet been clarified to date. In this study, to clarify the mechanism, KF and NH4F are added to the etchant to clarify the mechanism. The An investigation of removal rate revealeds that the removal rate is proportional to [HF]×([F^- ]+[〖HF_2〗^- ]), and it is shown that both the HF molecule and fluorine ions (F− and HF2−) arethe reactive species of the CARE process are both HF molecule and fluorine ions (F- and HF2-).

Abrasive-Free Polishing for Extreme Ultraviolet Lithography Mask Substrates

In the development of photo-masks for extreme ultraviolet (EUV) lithography, it is a formidable task to achieve the stringent requirements of angstrom-scale surface roughness, sub-30 nm peak-valley flatness and defectivity in single digits. The majority of the defects present on the substrate arise from the polishing/cleaning processes. Here we describe the effectiveness of depositing an amorphous silicon (a-silicon) thin film to cover the existing defects (e.g. pits, scratches, bumps, embedded and adhered particles) on the surface of EUV substrates followed by polishing the a-silicon film using abrasive-free liquids to help meet the EUV substrate requirements of surface roughness and defectivity (ideally zero pits or bumps greater than 1 nm in depth or height). Chemical mechanical planarization (CMP) using an abrasive-free poly (ethyleneimine) solution showed that both the final surface roughness and removal rate are strongly dependent on polishing pressure. We developed a hybrid two-step CMP process consisting of polishing first at 1 psi to remove sufficient material to eliminate the underlying defects, followed by polishing at 0.5 psi to achieve low surface roughness. Under these polishing conditions, CMP of a-silicon films deposited on EUV mask substrates resulted in a root mean square (RMS) surface roughness of ∼0.09 nm.

Structural and chemical characteristics of atomically smooth GaN surfaces prepared by abrasive-free polishing with Pt catalyst

This paper reports the structural and chemical characteristics of atomically flat gallium nitride (GaN) surfaces prepared by abrasive-free polishing with platinum (Pt) catalyst. Atomic force microscopy revealed regularly alternating wide and narrow terraces with a step height equivalent to that of a single bilayer on the flattened GaN surfaces, which originate from the differences in etching rate of two neighboring terraces. The material removal characteristics of the method for GaN surfaces were investigated in detail. We confirmed that an atomically smooth GaN surface with an extremely small number of surface defects, including pits and scratches, can be achieved, regardless of the growth method, surface polarity, and doping concentration. X-ray photoelectron spectroscopy showed that the flattening method produces clean GaN surfaces with only trace impurities such as Ga oxide and metallic Ga. Contamination with the Pt catalyst was also evaluated using total-reflection X-ray fluorescence analysis. A wet cleaning method with aqua regia is proposed, which markedly eliminates this Pt contamination without affecting the surface morphology.

Ultra-flat and ultra-smooth Cu surfaces produced by abrasive-free chemical–mechanical planarization/polishing using vacuum ultraviolet light

Abstract The new bonding technologies utilizing intermolecular bonding forces have been developed and attracting attention recently. Cu is known to be a suitable material for the bonding substrate due to its excellent physical properties. And an ultra flatness and an ultra smoothness over a relatively large area are strongly required for the Cu substrate surface. Chemical–mechanical planarization/polishing (CMP) with abrasives is widely adopted for planarizing and smoothing Cu surfaces. But this method has serious problems resulting from abrasives in CMP slurry. Hence, we have developed an abrasive-free polishing (AFP) method that utilizes vacuum ultraviolet (VUV) light in the previous study and an ultra-smooth Cu surface was achieved. However, the problems about a low removal rate and a small finished area remained. To overcome the problem, a new manufacturing process, namely, the process of combining CMP with abrasives and the AFP method was newly developed. First, an ultra-flat surface is achieved using CMP with abrasives. Next, the AFP method is applied for the final polishing step in order to achieve an ultra-smooth surface. As a result, utilizing VUV in situ irradiation and electrolyzed reduced water in the AFP process, the ultra-flat and the ultra-smooth surface produced has a roughness average of

Chemical-Mechanical Polishing for III-V Wafer Bonding Applications: Polishing, Roughness, and an Abrasive-Free Polishing Model

Chemical mechanical polishing (CMP) of III-V (and other materials) is an important component of subsequent wafer bonding or epitaxial growth. For example, transferred exfoliated layers possess roughness on the order of tens of nanometers and epitaxial layers may possess surface roughness that prevents subsequent bonding. Standard polishing processes are too aggressive and remove material at rates on the order of microns per minute. This paper develops a more controlled CMP process for Indium Phosphide (InP), which removes the RMS roughness to below 1 nm with a removal rate of 5 nm per minute. The technique is characterized at different time intervals and roughness values. A model for abrasive-free CMP is also developed to expand upon current models.

Experimental Investigation on Effects of Passivants in the Abrasive-Free Polishing of Copper Film

Abrasive Free Polishing (AFP) is a polishing technology without abrasives and widely employed in copper-base semiconductor fabrications. This paper investigates the effect of passivants, added to the slurry, on the material removal rate (MRR) and the non-uniformity (NU) via experiments. Two kinds of passivants, Benzotriazole (BTA) and citric acid (CA) are added to the slurry for the experiments. Experimental results showed that the MRR increases when polishing pressure increases while NU decreases at the same time. Both MRR and NU tends to increase when rotational speed increases, though MRR and NU at 40 rpm are lower than that at 30 and 50 rpm in the slurry with CA. Experimental data also showed that AFP using the slurry with CA performs better than that with BTA.

Experimental Study on Abrasive-Free Polishing for KDP Crystal

Abrasive-free polishing (AFP) has been developed for processing of soft, hygroscopic (KDP) crystal according to its deliquescence property. A new nonaqueous abrasive-free slurry, composed of water, dodecanol, and Triton X-100, is designed for the AFP process. In this slurry, the function of water, which is enveloped into surfactant micelles and has no direct contact with KDP crystal in the absence of polishing pressure, is to dissolve KDP surface material in the AFP. The experiments show that the material removal rate (MRR) is nonlinearly dependent on polishing pressure and platen speed; MRR as high as at certain polishing condition and a scratch-free polished KDP surface with root-mean-square roughness lower than 2 nm are achieved by the AFP process. Moreover, the repeat utilization times of the slurry are experimentally determined in KDP AFP with a relatively high removal rate and a smooth surface.

Chemical-Mechanical Polishing for III-V Wafer Bonding Applications: Polishing, Roughness, and an Abrasive-Free Polishing Model

not Available.

Effect of the Cd0.96Zn0.04Te substrate polishing procedure on Cd x Hg1 − x Te liquid phase epitaxy

This paper examines the effect of polishing procedure on the surface quality of Cd0.96Zn0.04Te substrates for Cd x Hg1 − x Te liquid phase epitaxy. Two polishing procedures are tested: stepwise polishing involving abrasive, chemomechanical, and chemical steps with the use of various abrasives, and abrasive-free polishing. The optimal procedure is chemomechanical polishing with no abrasives. The type of substrate surface can be identified using the Nakagawa etchant, which produces etch patterns in the form of triangles on the A(111) surface and circles on the B(111) surface.

Effect of pH on Material Removal Rate of Cu in Abrasive-Free Polishing

The effect of pH on the material removal rate (MRR) of Cu in an organic phosphonic acid system abrasive-free slurry was investigated by thermodynamics, X-ray photoelectron spectroscopy analysis, and electrochemical measurements. The pH range can be divided into three chemical regions according to the evolution of the polishing MRR, which relies on the effect of pH on the chelating effect of the chelating ligand, diethylene triamine penta methylene phosphonic acid. The higher the pH is, the more efficient the chelating ligand is. In the alkaline pH region, because of the enhanced chelating effect and precipitation of the chelate complex on the surface, both the MRR and friction coefficient during polishing process increase significantly, and the corrosion current acquired from the potentiodynamic polarization measurement decreases.

Development of Abrasive-Free Copper CMP Process

Abrasive free polishing (AFP) for copper interconnects was improved. A chemical mechanical polishing (CMP) process using in two-step Cu AFP conditions eliminates copper residue. The process has a higher short-yield margin than the conventional AFP process. It uses both a high selective barrier metal slurry and a randomly foamed polyurethane pad to achieve the same Cu wiring sheet resistance as a conventional polishing process. However, this method allows for increased depressions of less than 20% on a 20-μm Cu line of 98% density after Cu-AFP. We demonstrate that the process can meet the planarity target without any extra intermediate oxide polishes. Moreover, it is the compatible with low-k films and the Cu AFP process, and this prevents delamination and fractures in low-k materials during CMP. Therefore, this process should meet the requirements for Cu interconnects.

Development of Abrasive-Free Polishing Method for Cu Utilizing Vacuum Ultra-Violet Light

In recent years, it is strongly required to improve the Chemical Mechanical Polishing (CMP) technology for Cu. The conventional Cu-CMP slurries, however, have serious problems relating to detrimental impact on environment, because it includes a lot of organic compounds and abrasives. In this study, a new Cu-CMP method, that is, the polishing method utilizing vacuum ultra-violet (VUV) light irradiation and an electrolyzed water was proposed and developed in order to overcome the above-mentioned problem. In the newly-proposed method, the Xe excimer lamp was adopted as the VUV light source. The lamp has a sharp peek of the wave length at 172 nm, and can generate an ozone gas from decomposition of oxygen. The effects of the VUV light irradiation for Cu-CMP are thought to be as follows; 1) an oxidation effect by generated ozone, 2) a photoelectric effect for Cu substrate. Then the polishing experiments for Cu substrate were carried out with in-situ VUV light irradiation. The experimental results revealed that the developed method was effective for obtaining precise smooth surface, namely, the mirror-finished surface under 1 nm Ra was achieved. From the result, it was found that the developed polishing method has an electrochemical effect for polishing, namely, the amount of OH- groups and the density of oxygen or pH of polishing fluid have a strong influence on Cu polishing process.

Inhibitors for organic phosphonic acid system abrasive free polishing of Cu

Organic phosphonic acid system abrasive free slurry for copper polishing is developed in our earlier work. Since material removal rate is too high to be applied as precision polishing slurry for copper, inhibitors are needed. Experiment results also show us that the most commonly used inhibitor benzotriazole is unsuitable for this abrasive free slurry, and then another kind of compound inhibitors for this organic phosphonic acid system abrasive free slurry are developed. The compound inhibitors, consisting of ascorbic acid and ethylene thiourea, can control the material removal rate and also reduce surface roughness. XPS results show that, in the compound inhibitors, ascorbic acid participates in the surface chemical reaction, forms passivating layer on copper surface and helps to control the material removal rate. Corrosion current calculated from polarization curve is consistent with material removal rate. Ethylene thiourea contributes to the reduction of surface roughness, which can be indicated by the peak shape change of S 2p in XPS results.