Polishing Removal Rate Research Articles

Simulation of chemical reactions with methanol and oxalic acid on 4H-SiC surfaces before and after nanoabrasion

Previous work by our team has shown that not only can oxalic acid added to a reactive methanol polishing solution significantly further improve SiC polishing removal rate but also surface quality. However, due to the lack of fundamental information on the nature of the interfacial reaction, the reaction mechanism involved in continuously improving SiC polishing performance remains unresolved. This study explores the chemical interactions of pristine and nano-scratched surfaces with the reaction medium using a molecular dynamics (MD) model combined with the ReaxFF reaction force field. The results show that –OH and –CHn, methanol can effectively break the Si-C bond on the surface of silicon carbide and the high amount of OH and C=O in oxalic acid favors the formation of surface silicon oxides and the softening of the silicon carbide surface. The synergistic effect of oxalic acid and methanol in the pre-scratch system indirectly supports the notion that nanoabrasion caused by nano-abrasives enhances the chemical reactivity of polishing fluid components. In conjunction with the experimental data, a proposed reaction mechanism for organic acid-containing alcohol fluids with SiC based on non-aqueous solvent systems is presented. This may stimulate ideas for better developing and applying novel non-aqueous-based polishing fluids.

Effect of Structures with Structured Surface Pad on Material Removal Rate in Chemical Mechanical Polishing

We investigated the impact of the designed contact area (DCA) and designed contact length (DCL) on material removal rates (MRR) when using a pad with a structured surface in chemical mechanical polishing. The structure of the structured surface pad (SSP) was precisely defined, and an examination was conducted to assess the influence of variations in the shape, size, and spacing of the unit figure (UF) on the MRR. The results revealed that maintaining the DCA constant while altering the UF shape to extend the DCL led to a 203% increase in the MRR. Furthermore, modifications in the UF size enhanced the MRR by approximately 630%. The relationship between the DCL and MRR was dependent on the DCA. The characteristics of the SSP, particularly the concentrated pressure and involvement of slurry particles at the edges of the contact area, indicated that an increase in the DCL could augment the active slurry particles. This study offers valuable insights into the pad figure structure, simultaneously advancing our understanding of the pad surface topography and its influence on material removal. By focusing on both structural engineering and practical applications, this study paves the way for future research and enables further exploration in this field.

Application of the Fenton reaction in silicon carbide polishing and its oxidative active center

The Fenton reaction is known for generating highly reactive hydroxyl radicals that are applied to accelerate the polishing removal rate of chemically inert SiC substrates. However, previous research primarily focuses on the polishing removal rate acceleration on the C surfaces of SiC substrates, and very limited studies have been conducted to investigate whether the hydroxyl radicals produced by the Fenton reaction serve as the primary agents of oxidative activity. Furthermore, the oxidation ability of hydroxyl radicals on the C surface and its relationship with their concentration are still not well-established. Therefore, more extensive research is needed to gain comprehensive understanding on the role of hydroxyl radicals in the oxidative activity on the C surface and their concentration-dependent effects. In this study, the polishing results of alumina, cerium oxide, and silica containing polishing slurries with and without Fenton reaction were compared and analyzed. The material removal rate (MRR) of the C surfaces of SiC substrates was significantly improved after the introduction of the Fenton reaction in alumina-containing slurry at pH 4, resulting in a smoother surface. Low-field nuclear magnetism, atomic force microscopy (AFM), ultraviolet spectrophotometry, and X-ray photoelectron spectroscopy (XPS) were employed to gain insights on inter-particle interactions and oxidation mechanisms of C face of SiC in presence of Fenton reaction. The results revealed that while hydroxyl radicals demonstrated potent oxidation ability, they alone were incapable of oxidizing C face of SiC.

Electrolyte Effect on Photoetching of Gallium Nitride

The limited material removal rate of conventional chemical mechanical polishing (CMP) significantly hinders the fabrication efficiency and surface quality, thereby preventing the development of gallium nitride (GaN)-based devices. Moreover, the incorporation of photoelectrochemistry in CMP has garnered increasing attention because of its potential to enhance the quality and efficiency of the GaN process. However, a considerable gap still exists in the comprehensive understanding of the specific photoelectrochemical (PEC) behavior of GaN. Here, we report the influence of the electrolyte on the PEC etching of GaN. Various acids and bases were tested, with their pH being carefully adjusted. The concentrations of the cations and anions were also examined. The results showed that photocorrosion/photoetching was more pronounced in sulfuric acid, phosphoric acid, and nitric acid environments than in alkaline environments, but it was less pronounced in hydrochloric acid. Furthermore, the effects of pH and anion concentration on photoetching were investigated, and the results revealed that photoetching in acidic environments weakened with increasing pH levels and diminished with increasing sulfate concentration. The underlying reasons contributing to this observation were explored. These findings provide ideas for improving the photoetching efficiency of GaN, thereby enriching the photoelectrochemical mechanical polishing (PECMP) technology of GaN.

Material removal model for magnetorheological polishing considering shear thinning and experimental verification

To establish a more accurate magnetorheological polishing material removal model, the shear thinning effect of magnetorheological polishing solution under high shear rate conditions was analyzed based on magnetic dipole theory, and the two-particle chain junction model was used to analyze the force of magnetic particles in magnetorheological polishing solution, and the shear yield stress of magnetic chain under tilted condition was obtained, and the magnetorheological polishing material removal model considering shear thinning was established by combining the modified Preston equation. The effect of shear thinning on the magnetorheological polishing material removal model was analyzed. The calculated results of the model are compared with the experimental data of magnetorheological polishing material removal, and the results show that the material removal model considering shear thinning can accurately predict the material removal rate of magnetorheological polishing, especially the trend of decreasing material removal rate of magnetorheological polishing at high shear rate is effectively predicted.

Fabrication of self-standing large (111) single crystal diamond using bulk growth of (100) CVD diamond and lift-off process

Diamond (111) plane is superior in impurity doping and quantum spin control to (100) plane, however, there are many technical issues in mass production of the substrate, such as a smaller seed substrate size, low removal rate of polishing, and low growth rate. In this study, a large (111) single crystal diamond substrate of 7 mm × 6 mm was fabricated by growing and processing bulk (100) CVD single crystal. Furthermore, using this as a seed substrate, a (111) self-standing plate was fabricated using the lift-off method. The FWHM of the X-ray rocking curve was 46 arcsec and that of the Raman peak was 2 cm−1. This method can be applied to fabrication of any high index plane such as (113) and can be utilized to fabrication of substrate for electronic and quantum devices, device processing to fabricate vertical structure.

MD simulation of chemically enhanced polishing of 6H-SiC in aqueous H2O2

Chemical enhanced polishing (CEP) is a widely employed final process for achieving precise surface shaping and planarization of semiconductor wafers. However, determining the chemical effect involved in material removal through experimental means is extremely challenging. In this study, we conducted reactive force field (ReaxFF) molecular dynamics (MD) simulations to gain insight into the chemical effects of CEP using an aqueous hydrogen peroxide (H2O2) diamond suspension as a polishing medium for 6H-SiC single crystals. The inclusion of aqueous H2O2 resulted in the formation of SiOH and COH species, which are comparatively easier to remove through mechanical abrasion. Furthermore, an increase in H2O2 concentration was found to enhance the material removal. The MD simulations also revealed that the chemical effects on the Si-face of 6H-SiC were more pronounced than those on the C-face due to the generation of a greater number of SiO species and the favourable atomic structure of the Si-face for chemical removal. The results showed that the material remove rate on the Si-face is greater than that on the C-face during polishing, aligning with the findings from MD simulation. Furthermore, a systematic experimental study was carried out to examine the influence of various conditions on material removal rate and surface quality in both polishing and lapping processes.

Polymer Nanoparticles Applied in the CMP (Chemical Mechanical Polishing) Process of Chip Wafers for Defect Improvement and Polishing Removal Rate Response.

Chemical mechanical planarization (CMP) is a wafer-surface-polishing planarization technique based on a wet procedure that combines chemical and mechanical forces to fully flatten materials for semiconductors to be mounted on the wafer surface. The achievement of devices of a small nano-size with few defects and good wafer yields is essential in enabling IC chip manufacturers to enhance their profits and become more competitive. The CMP process is applied to produce many IC generations of nanometer node, or those of even narrower line widths, for a better performance and manufacturing feasibility. Slurry is a necessary supply for CMP. The most critical component in slurry is an abrasive particle which affects the removal rates, uniformity, defects, and removal selectivity for the materials on the wafer surface. The polishing abrasive is the source of mechanical force. Conventional CMP abrasives consist of colloidal silica, fume silica or other inorganic polishing particles in the slurries. We were the first to systematically study nanoparticles of the polymer type applied in CMP, and to compare traditional inorganic and polymer nanoparticles in terms of polishing performance. In particular, the polymer nanoparticle size, shape, solid content dosing ratio, and molecular types were examined. The polishing performance was measured for the polishing removal rates, total defect counts, and uniformity. We found that the polymer nanoparticles significantly improved the total defect counts and uniformity, although the removal rates were lower than the rates obtained using inorganic nanoparticles. However, the lower removal rates of the polymer nanoparticles are acceptable due to the thinner film materials used for smaller IC device nodes, which may be below 10 nm. We also found that the physical properties of polymer nanoparticles, in terms of their size, shape, and different types of copolymer molecules, cause differences in the polishing performance. Meanwhile, we used statistical analysis software to analyze the data on the polishing removal rates and defect counts. This method helps to determine the most suitable polymer nanoparticle for use as a slurry abrasive, and improves the reliability trends for defect counts.

Catalyst enhancement approach for improving the removal rate and stability of silica glass polishing via catalyzed chemical etching in pure water

Precision polishing using transition metal catalysts such as Pt and Ru, called catalyst-refereed etching, is employed to fabricate atomically smooth surfaces on optical devices, realizing the designed device performance. However, the catalyst surface is covered with post-processing products during processing, drastically decreasing the removal rate. To address this issue, this paper proposes using an Ru-based alloy catalyst. Density functional theory calculation results show that doping Ti to Ru significantly reduces the adsorption energy of post-processing products, suggesting that the active site of the catalyst is easily recovered. When polishing silica glass, the Ru2Ti catalyst significantly improves the removal rate stability and enables the fabrication of an atomically well-ordered smooth surface, similar to that polished using a Pt or Ru catalyst.

Quantitative-regulated material removal rate in solid dielectric electrochemical polishing (QRR-SDEP) for smoothing high roughness surface of additively manufactured 316L stainless steel components

Quantitative-regulated material removal rate in solid dielectric electrochemical polishing (QRR-SDEP) for smoothing high roughness surface of additively manufactured 316L stainless steel components

Influences of Nonaqueous Slurry Components on Polishing 4H-SiC Substrate with a Fixed Abrasive Pad

4H-SiC wafers are more likely to sustain a lower material removal rate (MRR) and severe subsurface damage in conventional chemical mechanical polishing (CMP) methods. To overcome the material removal bottleneck imposed by aqueous chemistry, a high-efficiency polishing of 4H-SiC wafers method by applying reactive nonaqueous fluids to self-sharpening fixed abrasive pads has been proposed in our former research works. Furthermore, to improve the material removal rate and reduce the surface roughness Sa value of 4H-SiC substrates of the Si face, the effect of organic acid, H2O2, and Triton X-100 in nonaqueous slurry on 4H-SiC polishing was investigated. The MRR of 12.83 μm/h and the Sa of 1.45 nm can be obtained by the orthogonally optimized slurry consisting of 3 wt% H2O2, 0.5 wt% Triton X-100 at pH = 3. It is also found that the addition of different levels of oxidant H2O2 and surfactant Triton X-100 components not only increased the MRR of the 4H-SiC substrates of the Si face but also achieved a lower Sa value; in that, the polishing efficiency of the Si side of the 4H-SiC wafers and the surface quality of the 4H-SiC wafers could be effectively improved by the optimization of the polishing slurry.

A novel method of water bath heating assisted small ball-end magnetorheological polishing for hemispherical shell resonators

Hemispherical shell resonator (HSR) is the core component of hemispherical resonator gyro. It is a ψ-shaped small-bore complex component with minimum curvature radius less than 3 mm. Thus, traditional polishing methods are difficult to polish it. Small ball-end magnetorheological polishing method can polish the small components with complicated three-dimensional surface and obtain non-destructive surface. Therefore, this method is suitable for polishing HSR. However, the material removal rate of the ordinary small ball-end magnetorheological polishing is low, leading to long polishing time and low output of HSR. To solve this problem, a water bath heating assisted small ball-end magnetorheological polishing method is proposed in this research. The influence rule of processing parameters on the material removal rate is studied experimentally. A set of optimal processing parameters is obtained to maximize the material removal rate. Compared with the ordinary method, the material removal rate of the new method can be improved by 143%. Subsequently, an HSR is polished by the new method. The results show that the polishing time can be reduced by 55%, and the polished surface roughness can reach 7.7 nm. The new method has the great potential to be used in actual production to improve the polishing efficiency of HSR.

A Physics-Based Chip-Scale Surface Profile Model for Tungsten Chemical Mechanical Planarization

In this work, a new physics-based chip-scale surface profile model is proposed to focus on investigating the influence of the design pattern effects on the tungsten surface topography in the chemical mechanical planarization (CMP) process. Due to its significance of the contact pressure on CMP planarity simulation, a two-scale contact pressure computation method is constructed to obtain an accurate pressure distribution between the wafer surface and the polishing pad. First, chip-scale contact mechanics-based global pressure has been introduced to capture the long range height variation of W CMP caused by deposition and polishing processes. Then feature-scale pattern dependent effect is considered to accurately calculate the local contact pressure in constructing the final removal rate formula and achieving chip surface profile simulation. The calculated local contact pressure is further integrated with the fundamental of steady-state oxidation reaction to construct a new material removal rate model, which systematically captures the effects of mechanical abrasion and concentration of chemical reagent on the polishing rate. The model prediction results are consistent with the collected experimental data in predicting the dishing effect at different slurry conditions. The simulated surface topography and polishing removal rate characteristics post tungsten CMP indicate prominent design pattern-dependent effects. Therefore, the present W CMP model can be utilized to assist in analyzing the influence of the design pattern effects on the wafer surface topography and performing sensitivity analysis of design parameters on the surface planarity. It can also be readily incorporated into a design for manufacturability flow to form a chip-scale planarity simulator to detect the hotspots of the entire design layout.

Real-Time Prediction of Removal Rate and Friction Coefficient During Chemical Mechanical Polishing Using Motor Load Currents with a Polisher

Herein, a method for predicting real-time removal rate and friction coefficient between the pad and substrate during chemical mechanical polishing was investigated using only the load currents of two motors of a polisher. Polishers for semiconductor devices are equipped with various sensors, enabling a real-time prediction of the removal amount. The polishers used to polish substrates are not usually equipped with sensors, and the polishing time is fine-tuned by skilled-technicians to achieve the desired substrate thickness. However, since every polisher has some motors, predicting the removal rate and friction coefficient using only the real-time data produced by these motors would be beneficial. This study attempts to predict the removal rate and friction coefficient in long-time polishing using a training dataset obtained from short-time polishing. Results showed that by performing extremely low-pressure, long-time polishing to understand the polisher characteristics and then subtracting the polisher characteristics from the motor information during long-time polishing, highly accurate predictions of the removal rate and friction coefficient within ∼94% in percent match (prediction accuracy) between the experimental and predicted values can be obtained. Furthermore, slurry degradation during CMP can be monitored using this prediction method.

A quantitative study of removal mechanism of copper polishing based on a single pad-asperity polishing test

Continuous requirement for the improvement of chip performance caused an increasing attention on the copper polishing precision. To predict the copper removal rate, it is critical to understand the copper removal mechanism and quantitatively decouple the chemical and mechanical interactions. In this paper, the copper removal mechanism was investigated by a single pad-asperity polishing test with an in situ measurement device, which minimized the effects of random pad-asperity contact states and slurry distribution differences encountered in conventional experiments. Several electrochemical methods were used to monitor the chemical reaction rate and passivation processes, including the chrono-current method, electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS). The results reveal that mechanical action can hardly remove the unreacted copper. The complexing agent can only dissolve the mechanically removed passivation layer rather than dissolve the passivation layer directly. The copper is removed in an alternating process of generation and removal of passivation layers. A model is developed to predict the copper removal depth within 10% error. This research provides a quantitative analysis method for material removal rate of metal polishing. It can answer whether chemical reaction or mechanical action limits the improvement of removal rate or causes the change of removal rate.

A general strategy for polishing SiC wafers to atomic smoothness with arbitrary facets

SiC is essential for epitaxial growth of graphene and promises to be an ideal material for next generation high-power electronics. The electronic properties of graphene are highly dependent on the facet on which it is grown. Therefore, the selection of facet provides an extra tuning parameter to obtain its desired characteristics. As one of the key factors of growing pristine graphene on SiC wafers, their roughness requires to be atomically smooth. In this work, we present a data-driven study of the grinding, mechanical polishing and chemical mechanical polishing (CMP) procedures applied to a SiC wafer with arbitrary facets. The phenomena and principles in the polishing steps are discussed. As specific facets of SiC have unique atomic arrangements, different recipes are required for the C and Si faces and their performances are investigated. The interesting, but rarely studied (1 1‾ 05) facet is taken as an example of a non-polar case to apply the procedures. It is found that the material removal rate (MRR) in mechanical polishing is directly related to the facet hardness. Hence, the MRR of the (1 1‾ 05) facet is the slowest in that process, however, during CMP its MRR is 18 times faster than the Si-face, hints the different chemical and physical polishing mechanism. Accordingly, polishing recipes are proposed that can be adjusted to create atomically smooth wafers of arbitrary facets of SiC.

An optimized passivation mechanism at the copper film recess for achieving efficient planarization of copper chemical mechanical polishing

This article proposed an improvement plan for the slurry to reduce the dishing caused during copper chemical mechanical polishing (CMP) of the interconnect structure. According to the difference in the pressure between the concave and convex parts of the copper film in the high-hardness polishing pad, polishing slurries were designed with a distinct difference in the polishing removal rate under high and low platen pressures to improve their planarization efficiency. 2 wt% GLY (glycine) and 1 wt% H2O2 can provide a chemical dissolution effect, adding 0.1% TAZ (1,2,4-triazole) to slow down the corrosion mainly for the recession, by adjusting the slurry pH to 7. The polishing results showed that the slurry had a high copper removal rate (6772 Å/min) at high pressure (3.0 psi) and a much lower removal rate (3273 Å/min) at low pressure (1.2 psi). The pattern wafer polished with this slurry obtained relatively low dishing. The other comparison groups showed slight differences in copper removal rate at high and low pressure and a deeper dishing of the polished pattern wafer. In this paper, based on the analysis of static dissolution experiments, electrochemical experiments, and XPS experiments of copper films in different slurries, the chemical reaction mechanism of copper films in the solution system of GLY and H2O2 was studied at different pH values. In addition, the inhibition mechanism of TAZ on the copper surface at different slurry pH values was proposed, including the properties of the TAZ molecule adsorption film on the copper surface, the uniformity of the surface coverage, and the thickness of the passivation layer. The results can reflect the polishing results to a certain extent despite some deviations, but it can also be used as a more reasonable argument to explain the optimization scheme of the slurry proposed in this article.

Modeling of forces and material removal rate in ultrasound assisted magnetorheological polishing (UAMP) of sapphire

In order to fully investigate the polishing performance of the Fe 3 O 4 /SiO 2 core-shell abrasive for sapphire material, it is necessary to conduct a comprehensive study into polishing forces and establish corresponding mathematical models. In this paper, based on the bonding strength of core-shell abrasive chains and the motion analysis of ultrasonic vibration in UAMP process, the mathematical models of shear force F τ and normal force F N generated on sapphire surface are established. Experiments were implemented to verify the reliability of the F τ and F N models under varying parameters, including the volume concentration of core-shell abrasives, excitation gap and working gap. The values and the variation trends of theoretical results are well in agreement with those of experimental results. Then, on the basis of the F τ and F N models and Preston equation, we proposed a modified material removal rate (MRR) model, in which the contributions of F N and F τ are all taken into consideration. Through the comparative analysis with the experimental results, the modified MRR model exhibits higher prediction accuracy than those models involving only F τ or F N . The high-precision MRR model will facilitate the deterministic removal of sapphire surface material in UAMP process. • Mathematical models of shear force and normal force in sapphire UAMP are established. • The reliability of the force models is verified by targeted experiments. • A modified MRR model based on the synergy of shear and normal force is developed. • The modified MRR model exhibits higher prediction accuracy than general MRR models.

Material removal rate of double-faced mechanical polishing of 4H-SiC substrate

Silicon carbide (SiC) has been a promising the third-generation semiconductor power device material for high-power, high-temperature, and substrate applications. However, under certain surface quality requirement, its current processing efficiency is the bottleneck. Therefore, it aims to improve the material removal rate (MRR), on the premise of ensuring the surface roughness requirements. To obtain the relationship between any point on SiC substrate and polishing pads, the model about double-faced mechanical polishing has been established, and the kinematics equations have been created. Best optimized material removal rate parameters were obtained. MRR reached the maximum when speed rate of the outside ring gear to the inside sun gear m = − 1, speed rate of lower plate to the inside sun gear n = 5, and SiC substrate distribution radius RB = 75. The primary and secondary order of MRR (n>m>RB) was obtained. An accurate mathematical model of orthogonal rotary regression test of Tri-factor quadratic of MRR was established, and the regression model was significant. Surface quality of SiC substrate was observed and characterized with SEM and AFM. It greatly provides a key guarantee for the next process of CMP, confirms the importance of MRR to ultra-smooth polishing, and provides a guarantee for its application in semiconductor equipment and technology.

Rapid Estimation of Removal Rate of Chemical Mechanical Polishing of Gallium Nitride Substrate by Quantitative Diagnosis of Cathodoluminescence Images

Rapid estimation of the removal rate of the chemical mechanical polishing (CMP) process of a gallium nitride (GaN) substrate contributes to the quick diagnosis of CMP progressing, leading to accelerated process development. The present study discusses the feasibility of using cathodoluminescence (CL) imaging for a rapid diagnosis of the removal rate of the CMP process. Mechanically induced subsurface damage was detected as black lines in the CL images due to nonradiative recombination. To quantitatively understand the CL images from the GaN substrate, the CL images was analyzed for the mean image brightness. We developed an advanced theory interpreting CL image brightness as a logistical function with the CMP processing time by assuming that the mechanically induced damages at and near the surface exponentially decrease with depth from the surface. Therefore, the CMP progress was successfully characterized by analyzing CL images in CMP process with the logistic functions, which provided a rapid estimation of the CMP removal rate.