Polishing Pressure Research Articles

Experimental study of key factors on super smooth surface fabrication upon single crystal silicon based on mechanochemical synergy

Due to rapid advancements in fields of modern optics and opto-electronics, the need for the production of super-smooth surfaces on single crystal silicon has become increasingly pressing. Although previous research has elucidated the mechanism of material removal and defect evolution in chemical mechanical polishing, brittle characteristic of the vulnerable silicon material makes it rather challenging to catch up with the extreme requirements of high performance and highly efficient manufacture. Nevertheless the critical polishing pressure for scratch free super-smooth surface in pragmatic machining remains undiscovered, which greatly hinders improvement in related fields. Consequently, this paper presents a series of analyses and experiments focused on the material removal process at the micro scale. A micron-sized SiO2 ball tip is utilized to simulate the scratching on surface of a single crystal silicon substrate. Experimental results reveal that appropriate pH conditions and a maximal contact pressure of 0.97 GPa (at a scratching speed of 2 µm/s) between the particle and substrate are crucial for achieving a super-smooth surface. Based on these findings, a defect-free chemical mechanical polishing method is proposed, which involves controlling contact pressure for practical fabrication. Further verification using the KDOSP 650γ machining system and ion beam figuring has demonstrated that a defect-free surface with a roughness of 0.209 nm RMS (Root Mean Square) can be achieved at an average removal rate of 316 nm/min. These insights provide new understandings in the fabrication of super-smooth surfaces on single crystal silicon, offering significant benefits for enhancing the performance of brittle single crystal silicon-based devices and the corresponding machining capabilities.

Investigation of the removal mechanism in amorphous carbon chemical mechanical polishing for achieving an atomic-scale roughness

Amorphous carbon is replacing conventional hard masks in semiconductor fabrication due to its exceptional etching selectivity towards silicate. After amorphous carbon deposition, a chemical mechanical polishing (CMP) is essential for planarizing the surface locally and globally. This study investigated the chemical oxidation and mechanical abrasion of amorphous carbon based on several factors, including pH, polishing pressure, and oxidants. Oxidants promoted the formation of C-O, C=O, and –COOH. Mechanical abrasion accelerates carbon surface oxidation and the removal of oxidized film. In addition, slurries containing three potent oxidants were evaluated: ferric nitrate with hydrogen peroxide, potassium permanganate, and cerium ammonium nitrate (CAN). These oxidants accelerated C–C breakage and increased the removal rate. In comparison, the slurry containing 1 wt% CAN exhibited a maximum removal rate of 480 Å/min and an atomic-scale roughness of 0.056 nm.

Experimental Investigation on Chemical Mechanical Polishing of ZA27 Alloy Considering Galvanic Corrosion at Zn/Al Interface

To improve the surface integrity of ZA27 alloy, a method of chemical mechanical polishing (CMP) considering the galvanic corrosion at the Zn/Al interface is proposed to treat the surface of ZA27 alloy. Firstly, the electrochemical experiment is carried out to study the influence of the pH, H2O2 concentration, and glycine concentration on corrosion potential between zinc and aluminum. Then the Taguchi method integrated with grey relation analysis and fuzzy inference are used to optimize the CMP parameters of ZA27 alloy. Finally, the prediction model of the MRR and surface roughness Ra is established using the mathematical regression analysis method. The experimental results showed that the minimum zinc-aluminum corrosion potential difference is 14 mV when the pH is 10, H2O2 concentration is 1 wt%, and glycine concentration is 0.4 wt%. The optimum CMP parameter is the polishing pressure of 34 kPa, the polishing plate’s rotational speed of 70 rpm, and the abrasive particle concentration of 15 wt%. After polishing with the optimum CMP parameter, the MRR is 242 nm min−1, and the surface roughness Ra is 13.91 nm. This study demonstrates that the CMP considering the galvanic corrosion at the Zn/Al interface is an effective method for treating ZA27 alloy surface.

Deep ensemble learning for material removal rate prediction in chemical mechanical planarization with pad surface topography

Chemical mechanical planarization (CMP) stands as a critical process in semiconductor manufacturing, necessitating precise prediction of material removal rate (MRR) to achieve optimal global planarization of material surface step heights. A notable hurdle in MRR prediction lies in the nonlinear pad-wafer interaction stemming from variations in the polishing pad surface. Despite numerous extant studies examining the asperity of the pad surface and the wafer-pad contact, aspects such as slurry lubrication and micro-topographical structure of the pad surface remain unaddressed. This study firstly proposes a deep ensemble learning-based approach for MRR prediction, leveraging the intricate interactions between the overall features of the pad surface and the polishing pressure. We experimentally generated diverse pad surfaces by controlling the process variables governing pad surface topography. The Multi-TabNet model, constructed by independently training multiple TabNet instances with distinct initialization and hyperparameters, furnishes a framework for MRR prediction across a broad spectrum of pad surface features, encompassing pores and cores. The results demonstrate a root mean square error of 80 Å/min, with the error margin reduced by up to 70 % compared to predictions utilizing a single parameter of the pad surface. Furthermore, it exhibits an error improvement exceeding 17 % relative to the existing method solely considering asperity. This study not only imparts insights for addressing MRR variations contingent on pad condition but also facilitates dependable material removal even on variable pad surfaces due to conditioner wear.

Material removal rate model for chemical–mechanical polishing of single-crystal SiC substrates using agglomerated diamond abrasive

Material removal mechanisms are essential for the selection of polishing slurries and parameter optimization of chemical–mechanical polishing (CMP) processes. This study established a material removal rate (MRR) model for CMP of single-crystal SiC substrates using a fixed agglomerated diamond (AD) abrasive pad (FADAP). The distribution of the polishing pressure between the AD abrasive and FADAP matrix was examined, and the influence of the abrasive and polishing parameters on the MRR was revealed. Furthermore, single-factor experiments were conducted to validate the rationality of the MRR model. The experiments demonstrated that when the thickness of the surface-affected layer of the single-crystal SiC substrate in the MRR model was set to 5 nm, the error between the calculated and experimental values of the model could be controlled to within 20%. This result experimentally verified the validity of the MRR model and its associated assumptions. Moreover, the MRR of the CMP process of a single-crystal SiC substrate reached 36.26 μm/h with a polishing pressure of 27.6 kPa and an AD abrasive primary particle size range of 7–10 μm. Therefore, the feasibility of efficiently processing single-crystal SiC substrates using an FADAP was theoretically confirmed.

Improving monocrystalline silicon surface quality with chemical mechanical polishing using the slurry with the additive of isopropanol

Enhancing the silicon surface smoothness with chemical mechanical polishing (CMP) is crucial to achieve better beam quality in X-ray systems. The additive in CMP slurry is the key factor in determining the resulting surface morphology. This paper exploits the effect of isopropanol (IPA) additive on regulating the material removal process and resulting microscopical surface morphology through varying the IPA concentration and polishing pressure. The improvement of surface quality and a dropping material removal rate (MRR) are obtained by increasing the IPA concentration from 0.1 to 2.5 mol/L. When the polishing pressure increases from 0.25 to 0.48 psi, a better surface quality and enhanced MRR are observed. By using the optimal polishing pressure of 0.48 psi and IPA concentration of 2.5 mol/L, the root-mean-square roughness can be reduced to 0.10 nm under a measurement area of 1 µm × 1 µm with atomic force microscopy, more than 58.3% lower compared to surfaces polished without IPA. This work suggests an approach to obtain the ultra-smooth silicon mirrors, which has promising applications in the field of X-ray, aerospace, and photovoltaics.

Molecular dynamics and experiment on ultraviolet-thermal curing abrasive tools for polishing microstructures

To achieve efficient polishing of the microstructure array, a preparation method of the UV-thermal curing abrasive tools with diamond was proposed. The properties of the UV-thermal curing system were studied using molecular dynamics (MD) and experiments. The time, frequency, and pressure parameters of the UV-thermal curing abrasive tool were optimized by polishing the copper plate. MD simulation results show that increasing the temperature to 340 K can improve the blending compatibility. With the increase of the bisphenol A acrylate, the tensile property enhances from 16.38 MPa to 42.98 MPa, and the size shrinkage and mass loss weaken. The addition of diamond particles improves the anti-friction coefficient. Finally, the microstructure is polished twice under the polishing pressure of 300 N and 200 N, resulting in a roughness of Ra61nm on the upper surface and Ra105nm on the lower surface. This study can be used to guide the preparation and application of UV-thermal curing abrasive tools for polishing microstructure.

Simulation and experimental study of ultrasonic-assisted shear thickening polishing of cemented carbide

In order to obtain a good surface quality of carbide inserts, an ultrasonic-assisted shear thickening polishing (UASTP) method is proposed in this paper. Using the shear thickening property of non-Newtonian fluids and combining with the principle of ultrasonic vibration, the abrasive grains wrapped by the polishing slurry carry out both flexible micro-cutting and high-frequency micro-collision on the material surface. This enables more efficient polishing of the microscopic surface of the material. In this paper, the polishing principle of this method is analyzed. The rheological characteristics of shear thickening polishing slurry are studied, and a continuity model that can adapt to nonlinear rheological behavior is proposed based on the Gross constitutive equation. The effects of fluid velocity, ultrasonic amplitude and ultrasonic frequency on polishing speed and polishing pressure in the Preston equation are studied by COMSOL Multiphysics simulation software. This method's material removal rate model is established based on the high-frequency periodic characteristics of ultrasonic action, combining the simulation results with polishing experiments, which accurately describe the variation law of material removal rate with polishing time. After polishing the carbide insert for 60 min with this method, a smooth surface is obtained with continuous surface ripple measurements and small floating values; the surface roughness is reduced from 195 nm to 16.1 nm with an improvement rate of 91.7 %, and the material removal rate reached 0.71 μm/h, which improved the surface roughness improvement rate and material removal rate by 27.6 % and 44.9 %, respectively, compared with the STP method. The experimental results show that the UASTP method is an efficient composite polishing technology to enhance the cemented carbide's surface quality further.

Mechanism elucidation of Sn-Bi alloy lapping plate surface instability

Sn-Bi alloys are currently employed as lapping plate material in the magnetic slider manufacturing process of Hard Disk Drives. However, it was observed that the Sn alloy lapping plate has surface roughness instability issues leading to poor productivity. Such plate surface instability is considered due to the metallic structure changing of Sn alloy. To elucidate the underlying mechanism, samples made from Sn-1.0 wt%Bi alloys were mounted and then subjected to polishing process at room temperature employing different polishing pressures ranging from 5 kPa to 122 kPa. The applied pressure is regarded as one factor imparting variable levels of energy onto the Sn alloy sample. The recrystallization and grain growth processes were confirmed by grain size distribution and misorientation study using Electron Backscattered Diffraction (EBSD). Furthermore, the developments of residual stress were investigated by using X-ray Diffraction (XRD). Finally, the surface roughness instabilities were confirmed in the involved Sn alloys samples via a Laser Scanning Microscope (LSM). It is recommended that a small level of pressure should be applied to the Sn-1.0 wt%Bi lapping plate to maintain the surface stable.

Modeling of material removal rate considering the chemical mechanical effects of lubricant, oxidant, and abrasive particles for aluminum chemical mechanical polishing at low pressure

Lubricants are widely used for aluminum (Al) chemical mechanical polishing (CMP) to eliminate surface scratch damage. Understanding of the fundamental of CMP material removal mechanisms including lubrication is crucial to offer insights into the control and optimization of the polishing process. This paper proposes a novel material removal rate (MRR) model based upon molecular-scaled removal mechanism, micro-contact force equilibrium theory, chemical reaction kinetics and diffusion effects, with further considering the lubricant effect on the removal rate at low polishing pressure. Moreover, the presented model also clarifies the nonlinear dependence of removal rate on lubricant concentration, oxidizer concentration, and abrasive concentration. The model prediction results could provide qualitative insights into the influence of lubricant concentration, oxidizer concentration, and abrasive concentration on MRR, thus providing theoretical foundation and support for delineating the Al-CMP process at low pressure. Finally, it is found that the theoretical predictions possess qualitative agreement with the experimental results.

Influences of process parameters on chemical mechanical polishing effect of ZnGeP2 crystal

To obtain the ultra-smooth surface of ZnGeP2 crystal (ZGP), the workpiece-abrasive-polishing pad contact model during polishing was established to calculate the load Fw and the cutting depth hw of a single abrasive. The influences of polishing methods, abrasive hardness, abrasive size, polishing pressure, polishing time and other factors on the polishing effect were studied, and the mechanism underpinning the formation of surface morphology after polishing was revealed, and the mathematical model between material removal rate (MRR) and surface roughness (Ra) was established. The results show that the critical cutting depth hc of ZnGeP2 crystal is 95.21 nm, when the polishing load is 5 N, the material removal under mechanical polishing and chemical mechanical polishing entails plastic removal. Compared with mechanical polishing, the MRR of chemical mechanical polishing is increased by 23.4% and Ra is decreased by 26.5%. The increases of abrasive hardness, abrasive size and polishing load will increase the cutting depth hw of the abrasive, resulting in the increases of MRR and Ra, but the influence forms of various factors are different. After optimizing the process parameters, the minimum Ra of ZnGeP2 crystal is 0.76 nm. MRR and Ra will decrease significantly with the increase of polishing time, and there is a significant correlation between them.

Experimental Study on Shear Rheological Polishing of Si Surface of 4H-SiC Wafer

In this study, shear rheological polishing was used to polish the Si surface of six-inch 4H-SiC wafers to improve polishing efficiency. The surface roughness of the Si surface was the main evaluation index, and the material removal rate was the secondary evaluation index. An experiment was designed using the Taguchi method to analyze the effects of four critical parameters (abrasive particle size, abrasive particle concentration, polishing speed, and polishing pressure) on the Si surface polishing of SiC wafers. By evaluating the experimental results for the signal-to-noise ratio, the weight of each factor was calculated using the analysis of variance method. The optimal combination of the process parameters was obtained. Below are the weightings for the influence of each process on the polishing result. A higher value for the percentage means that the process has a greater influence on the polishing result. The wear particle size (85.98%) had the most significant influence on the surface roughness, followed by the polishing pressure (9.45%) and abrasive concentration (3.25%). The polishing speed had the least significant effect on the surface roughness (1.32%). Polishing was conducted under optimized process conditions of a 1.5 μm abrasive particle size, 3% abrasive particle concentration, 80 r/min polishing speed, and 20 kg polishing pressure. After polishing for 60 min, the surface roughness, Ra, decreased from 114.8 to 0.9 nm, with a change rate of 99.2%. After further polishing for 60 min, an ultrasmooth surface with an Ra of 0.5 nm and MRR of 20.83 nm/min was obtained. Machining the Si surface of 4H-SiC wafers under optimal polishing conditions can effectively remove scratches on the Si surface of 4H-SiC wafers and improve the surface quality.

Research on Spherical Self-rotating Polishing Technology

Polishing technology is widely used in the polishing process of aspheric optical elements, complex curved surface molds, and so on because of its high machining accuracy, good flexibility, and other advantages. Based on the Preston equation, this paper deduces the material removal function of spherical self-rotating polishing by applying the kinematics principle, obtains the removal function with approximate Gaussian distribution by using computer simulation method, conducts processing technology experiments through the spherical self-rotating polishing device, analyzes the influence of polishing pressure and polishing speed on the polishing removal characteristics of ceramic materials by simulation, and verifies the stability of the removal function through experiments. The results show that the removal function graph is Gaussian distribution, which is conducive to the surface shape convergence of airbag machining. The influence of process parameters on material removal rate is in good agreement with the theory and practice and has a good linear relationship. It is a controllable and deterministic processing mode.

Research on Chemical Mechanical Polishing Technology for Zirconium-Based Amorphous Alloys

Crystallization often occurs in the processing of amorphous alloys, causing the materials lose their excellent properties. The study adopts chemical mechanical polishing of amorphous alloys, presenting the effect of the rotational speed of the polishing turntable, size of abrasive, polishing pressure, and oxidant concentration. The Taguchi method is used to find the best processing parameters, and AFM is used to characterize the machined material surface. At the same time, XPS is used to detect the change of oxide film composition with the addition of oxidant. The results indicate the optimum process parameters: rotational speed of the polishing turntable is 75 r/min, polishing pressure is 28.3 kPa, the size of abrasive is 0.5 μm, and the size of abrasive is a significant factor affecting surface roughness Sa. In addition, as the size of abrasive increases, the material removal rate increases while the surface roughness Sa increases. At pH 10, with an abrasive particle size of 0.5 μm, as the H2O2 concentration increases, the MRR first rapidly decreases at 0.21 wt.% H2O2, and then gradually increases, while the Sa decreases. Furthermore, with the addition of oxidant, the main composition of the surface oxide film changes from oxide to hydroxide, and the contents of Zr4+ and Cu0/Cu1+ elements increase. The findings can provide a feasible chemical mechanical polishing process for zirconium-based amorphous alloys to obtain a satisfactory polishing effect.

Material removal mechanism in magnetorheological foam plane finishing

The material removal process of magnetorheological foam plane finishing (MRFPF) method which considers various processing conditions was studied in this paper. A material removal rate (MRR) model based on the updating type of workpiece moving trajectory, magnetic field distribution, and polishing speed in the polishing area was established for MRFPF. In this model, MRR is generated by integrating the polishing pressure and speed over the time that polishing pressure on workpiece updating for 1 cycle with the relative error between theoretical and experimental results less than 11.63 %. Moreover, MRFPF can achieve much higher MRR and surface flatness improvement rate than that of magnetorheological finishing (MRF) under different processing conditions, which further indicates the effectiveness of MRFPF in planar finishing.

The Poles in Ireland Against Martial Law in Poland 1981-1983

Aid for Poland during the period of martial law in Poland was organised predominantly by members of the Irish Polish Society, the Irish Catholic Church with the help of the Charitable Commission of the Episcopate of Poland, Polish merchant ships, Irish shipping agents, Irish pharmaceutical and food firms, and generous Irish people. A small Polish community in a short period of time managed to collect in Ireland unbelievable amounts of money and goods. During the 18 months of fundraising, £250,000 in cash and £300,000 worth of food and medicines was shipped to Poland in 20 containers. £50,000 was donated separately by the Irish Government to the Irish Red Cross and the charitable organisation Trocaire. A huge political effort was made to influence the Irish Government to condemn the imposing of martial law in Poland. The Irish Polish Society became a strong and solidified Polish organisation, a united voice for Poles in Ireland and an effective Polish pressure group , supportive for their country of origin and knowing their identity and potentials.

Ultra-smooth surface with 0.4 Å roughness on fused silica

Ultra-smooth surface with sub-nanometer roughness is of great significance in various fields, including Ring Laser Gyro (RLG), high-power laser apparatus, ultraviolet optical systems, and the semiconductor industry. However, the mechanism of the ultra-smooth polishing process remains to be studied, which is of great value for understanding and optimizing optical-fabrication methods. This paper establishes a relationship between surface densification characteristics and surface roughness in conventional polishing. Moreover, we conclude that the densification process created by the longitudinal pressure, which avoids non-uniformity, is beneficial to forming super-smooth surfaces in the conventional polishing methods. Under this guidance, we can stably fabricate ultra-smooth surfaces on fused silica with 0.4 Å roughness. This result overturns the mainstream view that the longitudinal pressure in polishing should be minimized. This conclusion is meaningful for the understanding of the ultra-smooth surface formation not only in conventional polishing but also in other optical-fabrication technologies.

Finishing of micro-aspheric tungsten carbide mold using small viscoelastic tool

Tungsten carbide is widely used as the material of replication mold to produce small aspheric optics, and the polishing process determines the precision of these molds. However, for micro-aspheric tungsten carbide mold, the existing polishing methods are difficult to realize the form error modification during a polishing process due to the polishing tool is always larger than small mold. Therefore, a polishing tool using polyester fiber cloth to wrap small-size rigid ball is used in this paper. In order to predict the tool influence function (TIF) of this polishing tool, a series of theoretical analysis and experimental verification are carried out in this paper. Firstly, by analyzing the structural and viscoelastic characteristics of the fiber cloth, the pressure distribution in the polishing contact area is determined. And the polishing speed distribution is obtained by analyzing the kinematic movement of polishing tool; Then, combined with Preston equation, the TIF is derived; Afterward, through a series of single point polishing experiments, it is verified that the volume error between the theoretical removal model and the experimental removal is less than 6.9% when the polishing pressure is low; Finally, the TIF is applied to the form error corrective polishing of small size symmetric aspheric tungsten carbide mold. After a form error corrective polishing test, the PV value (peak to valley) of form error is decreased from 0.268 to 0.083 μm, which verifies the effectiveness of this polishing method for small size tungsten carbide mold in form error correction.

Study on rheological properties and polishing performance of viscoelastic material for dilatancy pad

Shear dilatancy polishing (SDP) is an emerging flat polishing method for hard and brittle materials, which can achieve high-efficiency and high-precision polishing of workpieces under high-pressure and high-speed conditions. In our research, a novel viscoelastic material (VM) with non-Newtonian fluid properties was prepared. The dilatancy pad was subsequently obtained based on VM, abrasives, and a polyurethane pad. The effects of abrasive size and abrasive concentration on the rheological properties of VM were analyzed. The mechanism of abrasives in VM was investigated, and the principle of SDP was revealed. VM-30 wt%Diamond (0.5 μm) with excellent shear hardening performance was selected in the polishing experiment to study the effects of polishing time, polishing speed, and polishing pressure on polishing performance, and the optimal polishing parameters of SDP for tungsten were determined. Compared with traditional abrasive free polishing (AFP), SDP can realize a higher material removal rate (MRR increased by 33.4%) and better surface quality (Sa reduced by 32.2%) due to the shear dilatancy effect under high-pressure and high-speed conditions. After 90 min of SDP, the surface roughness (Sa) of tungsten workpiece was reduced from 307.9 nm to 12.1 nm. Results show that SDP is a promising and feasible polishing method for hard and brittle materials.

Highest Quality and Repeatability for Single Wafer 150mm SiC CMP Designed for High Volume Manufacturing

Silicon Carbide (SiC) provides excellent characteristics such as superior thermal conductivity, high carrier mobility and extreme chemical stability in comparison with those of Silicon (Si). SiC is already showing significant device performance benefits in power devices, high performance communication, and LED lighting. However, SiC presents many challenges for wafer surface treatment because of its high hardness and remarkable chemical inertness. Today, mechanical polishing techniques on industrial batch CMP tools are the predominant methods for SiC wafer surface treatment, but material removal rate (MRR), surface defects and wafer flatness control are reaching fundamental limits with increasing wafer diameter. Batch processing typically results in a higher amount of surface scratches and defects, higher wafer to wafer variability, and higher wafer breakage rates. A unique single wafer chemical mechanical polishing (CMP) technique on 150mm n-doped, 4° off-axis, single crystal, 4H-SiC wafers was developed to create a virtually defect-free surface. A polishing head has been designed to manipulate polishing pressures at various zones of the wafer. This capability can modulate the removal thickness at each region on the wafer surface, resulting in a highly uniform wafer profile. Additionally, a CMP slurry has been formulated to maximize MRR from 2μm/hr to over 8.5μm/hr. Potassium permanganate has been selected as an oxidant and aluminum oxide particles as the abrasive. The oxidant concentration and abrasive content along with slurry pH level have also been optimized for ideal chemical and mechanical activity. Scratch-free wafer surfaces are observed with atomic force microscopy (AFM) and bright field (BF) and dark field (DF) inspection techniques. Roughness on the Si face is reduced to below 0.08nm. Total length of surface scratches was reduced to 10mm or less. Industrial metrics of wafer flatness, including total thickness variation (TTV) and local thickness variation (LTV) are modulated and improved. A test run completed on 25-wafers shows an overall 31% improvement of TTV post CMP process.