Polishing Experiments Research Articles

Ultra-Precision Shaping and Polishing Experiments in Nanoparticle Colloid Jet Machining

In this paper, ultra-precision shaping and polishing experiments have been done to research the shaping and polishing characters of nanoparticle colloid jet machining. A high-purity quartz glass sample with aspheric surface profile was employed as workpiece and polished by nanoparticle colloid jet machining. We utilized surface profilometer to measure the surface profiles of workpiece before and after shaping by nanoparticle colloid jet machining. The measurement results indicate that the nanoparticle colloid jet machining has good shaping ability to satisfy the demands for surface shape correction in ultra-precision machining. Atomic force microscopy (AFM) was utilized to observe the surface microscopic morphological characteristics of the workpiece surface polished by nanoparticle colloid jet machining. The observation results show that the roughness of the workpiece surface has been reduced from 1.919 nm RMS to 0.784 nm RMS by nanoparticle colloid jet machining. Based on the atomic force microscopy observation results, power spectral density analyses have been done to evaluate the polishing performance of the nanoparticle colloid jet machining.

Development of a Two-Dimensional Ultrasonic Vibration Assisted Machining Technology with Tool Vibration

As the reliable technology, ultrasonic assisted machining is widely used for brittle materials. This paper provides a two-dimensional(2D) ultrasonic vibration assisted machining technology with tool vibration using elliptical vibrator with longitudinal mode and bending mode, and set up the experiment device. Si wafer is taken as the workpiece, and single point cutting experiments for micro groove are investigated. For the further application, the ultrasonic assisted polishing experiment with wheel block is executed. Experimental results indicate that ultrasonic assisted cutting with tool vibration can improve the cutting performance and enhance the ductile removal. And the ultrasonic assisted polishing with whetstone piece makes the better surface roughness and higher material removal rate.

NC polishing of aspheric surfaces under control of constant pressure using a magnetorheological torque servo

In this paper, a method of maintaining a constant polishing pressure is proposed for a NC polishing system by controlling the polishing force during the polishing process. First, the NC polishing system is developed to resolve the force–position coupling problem encountered in common polishing processes. It mainly consists of a force control subsystem based on a magnetorheological torque servo to provide a controllable torque to polishing tool to generate the polishing force and a position control subsystem based on a general CNC lathe to control the position of the polishing tool. Second, a constant polishing pressure model is established by controlling the polishing force according to the variation of the curvature of the aspheric surfaces, and the polishing parameters for model are planned. Then, the control model of the polishing system is proposed, and a PID controller is designed for torque tracking with the actual torque feedback from a torque sensor. Finally, polishing experiments are conducted with constant force and constant pressure, respectively. Experimental results show that the surface roughness is greatly improved, the aspheric surfaces can be polished more uniformly with constant pressure than with constant force, and the PID controller can meet the requirements for the polishing force control.

A Polishing Method of Single-Incentive Ultrasonic Elliptical Vibration for Tungsten Carbide Mould

The basic principles of ultrasonic transducer and ultrasonic elliptical vibration polishing are investigated. A new kind of single-incentive ultrasonic transducer is designed, and the finite element simulation is conducted, a polishing device is developed based on the ultrasonic elliptical vibration. The polishing experiment is adopted to polish a tungsten carbide mold with the diameter 5cm. The experimental result shows that the tungsten carbide mould surface roughness changes from the original 0.026μm to 0.017μm.

Selective layer chemical mechanical planarization process mimicked with atomic force microscope

To understand the mechanisms of chemical mechanical planarization (CMP), an atomic force microscope (AFM) was used to characterize polished layer surfaces formed by selective transfer after a series of polishing experiments. The AFM allows one to examine the effects of applying highly localized stress to a surface. In the presence of solutions, tribochemical friction and wear can be investigated. We present the results of fundamental studies of the simultaneous application of chemical agents and mechanical stress using a single asperity model and a solid surface. At the same time, we show the consequences of combining highly localized mechanical stress (due to contact with AFM tip) and exposure to aqueous solutions of known pH. The experiment simulates several features of a single particle–substrate–slurry interaction in CMP. To optimize the CMP process, one needs to obtain information on the interaction between the slurry abrasive particles and the polished surface. To study such interactions, we used AFM. An AFM tip of radius of about 50 nm was used to mimic a single abrasive particle, typical of those found in CMP slurry. Surface analysis of selective layer using the AFM revealed detailed surface characteristics obtained by CMP. Studying the selective layer CMP, of which the predominant one is copper (in proportion of over 85 per cent), we found that the AFM scanning removes the surface oxide layer in different rates depending on the depth of removal and the pH of the solution. It was found that removal mechanisms depend also on the slurry chemistry, potential, percentage of oxidizer, and the applied load. We show that linear scans and raster scans display significantly different material removal rates. Oxide removal happens considerably faster than the copper CMP removal from the selective layer. This is in agreement with generally accepted models of copper CMP. Both long-range and the friction forces acting between the AFM tip and surface during the polishing process were measured. The correlation between those forces and removal rate is discussed. At the same time, this article complements recent observations of tip-induced friction and wear and growth in a number of inorganic surfaces in aqueous solutions.

Modelling and simulation of structure surface generation using computer controlled ultra-precision polishing

Abstract The applications of structured surfaces have been more widespread. However, research on the fabrication of these surfaces is still far from complete. The paper presents a theoretical and experimental investigation of the generation of structured surfaces by using Computer Controlled Ultra-precision Polishing (CCUP). A surface topography simulation model and hence a model-based simulation system for the modelling and simulation of the generation of structure surfaces by using CCUP have been established and verified through a series of simulation and practical polishing experiments. The results of experiments demonstrate the capability of the model-based simulation system in predicting the form error and the pattern of the 3D-texture generated by using CCUP.

Study of Inhibition effects on Copper CMP Slurry Performance

With the development of the products with more advanced technology nodes, new challenges continue to emerge in CMP processes. For example, there is a strong need to use lower down force in polishing process while maintaining a high removal rate to avoid low-k/ultra-low k dielectric film damage. The requirements for dishing, overpolish window, Cu residue clearance capability and surface defectivity, especially corrosion related defects become more stringent as copper lines become narrower and narrower. In this paper, we share our research efforts and results in developing a novel copper CMP slurry to overcome these performance challenges in Cu CMP process. In short, a well designed inhibitor system was applied in this slurry. The impacts of these inhibitors on the slurry performance including blanket removal rate/profile, static etch rate, dishing, Cu residue clearance capability and corrosion were evaluated through polishing experiments, electrochemistry evaluations, and laboratory tests simulating CMP aggressive conditions. With a synergetic effect of these inhibition systems, the slurry shows the excellent CMP performance

Study on Machinability and Polishing Performance of 1CrMn2MoVTiB Non-Quenched and Tempered Plastic Mould Steel

Based on the cutting and polishing comparison experiments, the machinability and polishing performance of 1CrMn2MoVTiB non-quenched and tempered plastic mould steel were studied. The cutting comparison experiment showed that the plastic mould steel that had developed recently was better than P20 both in surface roughness and cutter wear; and the polishing experiment indicated that the surface roughness of the two plastic mould steels reached uniformity under the conditions that TriDent polishing fabrics and W0.5 polishing compound were adopted.

KDP晶体新型磁流变抛光研究

A new process of magnetorheological figuring (MRF) based on the deliquescence theory is proposed to finish KDP crystals. A novel, non-aqueous, and abrasive-free magnetorheological (MR) fluid is explored, and polishing experiments are performed on a self-developed MRF machine. The removal mechanism is reckoned to be the result of a combination of dominant chemical etching and accessorial mechanical drag. The results indicate that the surface roughness of I plate KDP of 80×80 (mm) polished by MRF is 1.2 nm (root mean square (RMS)), and the tool marks are completely removed. The surface accuracy by MRF is 0.035\lambda (RMS), and the low/middle-frequency errors are significantly corrected after MRF.

Laser Beam Polishing of Quartz Glass Surfaces

The laser beam is a small, flexible and fast polishing tool. With laser radiation it is possible to finish many outlines or geometries on quartz glass surfaces in the shortest possible time. It's a fact that the temperature developing while polishing determines the reachable surface smoothing and, as a negative result, causes material tensions.To find out which parameters are important for the laser polishing process and the surface roughness respectively and to estimate material tensions, temperature simulations and extensive polishing experiments took place. During these experiments starting and machining parameters were changed and temperatures were measured contact-free.

Improvement of Finishing Efficiency Considering Contact Behavior of Polishing Pad with Workpiece Surface

Recently, the achievement of further high-efficiency and high-quality polishing of glass disks as substrates of hard disk drives has been strongly required for reducing the production cost, increasing the storage capacity and downsizing the drive. In order to meet the requirements, it is very important to clarify and improve the polishing properties of suede polishing pads widely used in polishing glass disks and however, a very few researches concerning the pads have been conducted. Thus to overcome the problem, we performed the polishing experiments for glass disks in actual and found that the surface structure of the suede pads is key factor for improving the polishing efficiency. Based on the findings, we proposed a new polishing method that the polishing pad / workpiece contact zone is made intermittent and abrasives are uniformly supplied on the contact zone. As a result, it was found that high-efficiency and high-quality finishing were achieved by the method, as compared with the conventional polishing method.

Development of a circular-type integrated electrode tool for ER fluid-assisted polishing

This paper develops a newly-designed circular-type integrated electrode tool to make the abrasive particles in the electrorheological (ER) fluid concentrate around the tool end when the electric field is applied and it is suitable to polish not only the conductive material but also the non-conductive material in ER fluid-assisted polishing. The electric field of the integrated electrode tool is analysed. The polishing experiments for curved surfaces of tungsten carbide and optical glass with the developed integrated electrode tool are conducted to confirm the validity and suitability of the tool and to reveal the influence of the process parameters on the workpiece surface roughness.

On-Line Prediction Model of Ultrasonic Polishing Surface Roughness

In order to solve the difficulty of on-line measuring the surface roughness of workpiece under ultrasonic polishing, the artificial neural networks and fuzzy logic systems are introduced into the on-line prediction model of surface roughness. The surface roughness identification method based on fuzzy-neural networks is put forward and used to the process of plane polishing. In the end, the on-line prediction model of surface roughness is established. The actual ultrasonic polishing experiments show that the accuracy of this prediction model is up to 96.58%, which further evidence the feasibility of the on-line prediction model.

Polishing experiments on surface quality of building stone tiles

Polishing experiments were carried out on eight different carbonate stones with a machine designed for simulating industrial scale tile polishing process. Polishing was performed at 0.8, 1.3, 1.8 and 2.3 m/min belt speeds under fixed rotational speed and pressure of a polishing head. During the tests, calibrated stone tiles were sequentially polished with 60, 80, 120, 220, 320, 400 and 600 grit SiC abrasive stones at each belt speed. After polishing of each abrasive size, the quality of surfaces was assessed by measuring the surface roughness and gloss. As abrasive grit size gradually reduced to 320 grit, the roughness on the stone surfaces decreased greatly while gloss readings did not change significantly. But after 320 grit, gloss values increased greatly while change in roughness values was not significant. Reducing the belt speed resulted with a significant decrease in roughness for each grit size of abrasive, but after polishing with abrasive size larger than 320 grit, the influence of belt speed on the reduction in roughness values became less. Among the carbonate stones, micritic limestone tiles, which were homogenous in mineral composition with strong and hard structure, resulted with good surface finish. But clay minerals existing in other limestone and heterogeneous porous structure of travertines had an adverse effect on surface quality of tiles. Results from polishing tests suggest that belt speed value of 1.3 m/min provide optimum polishing quality conditions since optimum consistency in roughness and gloss of tile surfaces was reached at this belt speed. This findings were very valuable information for operating factories in which polishing is carried out. The gloss reading on stone surfaces was found to increase exponentially with decrease in surface roughness. Good correlation was found between surface roughness and gloss quality of micritic limestones and marbles compared to travertines.

Study on the Effect of Nonionic Surfactant in Copper CMP Slurry

The effect of surfactant in alkaline slurry for copper chemical mechanical polishing (CMP) was studied through polishing experiments with slurries containing different weight percentage of four nonionic surfactants respectively. The results indicate that properly chosen nonionic surfactants with proper weight percentage could result in little negative influence on the material removal rate, but can help to improve copper wafer surface quality significantly. Alkylphenol ethoxylates was found to be an excellent surfactant for alkaline slurry and a surface roughness of Ra 0.89nm and a material removal rate of 526 nm/min were obtained when polishing with the slurry containing 0.25 wt% alkylphenol ethoxylates, while the surface roughness and the material removal rate were Ra 1.34nm and 525 nm/min respectively when polishing with the origin slurry. The density of polishing defects such as scratches and etch pits decreased significantly. The action mechanism of surfactant was further analyzed based on the experiment results.

The Contact Pressure Distribution and its Effects on the Magnetic Disc Substrate Surface Profiles in Chemical Mechanical Polishing

In order to obtain the contact pressure distribution between the hard disc substrate and the polishing pad and its effects on the profile of polished substrate surface, the elastic contact mechanical model and mathematical equations on the chemical mechanical polishing of the hard magnetic disc substrate are established, and also the relevant boundary conditions are put forward. The contact pressure distribution is calculated with FEM, the polishing experiments are carried out and the surface profiles of polished substrates are obtained. The study results show that the contact pressure distribution on the substrate surface is non-uniformity and the contact pressure in the substrate edge present biggish undulation. Choosing properly the Young’s modulus of the polishing pads and decreasing its Poisson’s ratios can make the uniform area of the contact pressure distribution enlarging and improve the flatness of polished substrate.

Achieving High Flatness of Workpiece Edge Shape by Considering Polishing Pressure

In recent years, the achievement of further high flatness of workpiece edge shape is strongly required in mirror finishing. Especially, the edge roll off of silicon wafers as the substrates of semiconductor devices is demanded to decrease in the polishing process for raising the yield of IC chips. Many theoretical and experimental analyses for the edge roll off generation have been already done to meet the demand. The analyses, however, cannot fully account for the obtained edge shape in actual polishing. Concretely, the influence of the polishing pressure as one of the key polishing conditions on the edge roll off has not been clarified. In this study, the influence of the polishing pressure on the edge shape was investigated by the polishing experiments and the edge roll off generation analyses using the model based on the viscoelasticity of the polishing pad, which was proposed in the previous study. And it was revealed that an appropriate polishing pressure is needed to be set for achieving high flatness of workpiece edge shape with the consideration of the properties of applied polishing pads.

Development of an alternating magnetic-field-assisted finishing process for microelectromechanical systems micropore x-ray optics

X-ray astronomy research is often limited by the size, weight, complexity, and cost of functioning x-ray optics. Micropore optics promises an economical alternative to traditional (e.g., glass or foil) x-ray optics; however, many manufacturing difficulties prevent micropore optics from being a viable solution. Ezoe et al. introduced microelectromechanical systems (MEMS) micropore optics having curvilinear micropores in 2008. Made by either deep reactive ion etching or x-ray lithography, electroforming, and molding (LIGA), MEMS micropore optics suffer from high micropore sidewall roughness (10-30nmrms) which, by current standards, cannot be improved. In this research, a new alternating magnetic-field-assisted finishing process was developed using a mixture of ferrofluid and microscale abrasive slurry. A machine was built, and a set of working process parameters including alternating frequency, abrasive size, and polishing time was selected. A polishing experiment on a LIGA-fabricated MEMS micropore optic was performed, and a change in micropore sidewall roughness of 9.3+/-2.5nmrms to 5.7+/-0.7nmrms was measured. An improvement in x-ray reflectance was also seen. This research shows the feasibility and confirms the effects of this new polishing process on MEMS micropore optics.

An integrated tool for five-axis electrorheological fluid-assisted polishing

A five-axis electrorheological fluid-assisted polishing equipment is presented for the finishing of curved surfaces in this paper. An integrated electrode tool is specially designed to make the abrasive particles in the electrorheological fluid concentrate around the tool end when the electric field is applied and it is suitable to polish not only the conductive material such as tungsten carbide but also the non-conductive material such as optical glass. The polishing experiments for curved surfaces of tungsten carbide and optical glass are conducted to confirm the validity and suitability of the developed five-axis equipment with the designed integrated electrode tool and to reveal the influence of the process parameters on the workpiece surface roughness in electrorheological fluid-assisted polishing.

Tailoring Silica Nanotribology for CMP Slurry Optimization: Ca2+ Cation Competition in C12TAB Mediated Lubrication

Self-assembled surfactant structures at the solid/liquid interface have been shown to act as nanoparticulate dispersants and are capable of providing a highly effective, self-healing boundary lubrication layer in aqueous environments. However, in some cases in particular, chemical mechanical planarization (CMP) applications the lubrication imparted by self-assembled surfactant dispersants can be too strong, resulting in undesirably low levels of wear or friction disabling material removal. In the present investigation, the influence of calcium cation (Ca(2+)) addition on dodecyl trimethylammonium bromide (C(12)TAB) mediated lubrication of silica surfaces is examined via normal and lateral atomic force microscopy (AFM/LFM), benchtop polishing experiments and surface adsorption characterization methods. It is demonstrated that the introduction of competitively adsorbing cations that modulate the surfactant headgroup surface affinity can be used to tune friction and wear without compromising dispersion stability. These self-healing, reversible, and tunable tribological systems are expected to lead to the development of smart surfactant-based aqueous lubrication schemes, which include designer polishing slurries and devices that take advantage of pressure-gated friction response phenomena.