Distribution Of Material Removal Rate Research Articles

Experimental investigation and analytical modelling of the tool influence function of the ultra-precision numerical control polishing method based on the water dissolution principle for KDP crystals

A single crystal of potassium dihydrogen phosphate (KH2PO4, KDP), which possesses unique excellent non-linear electro-optical properties, is currently the only material suitable for electro-optic switches and high power laser-frequency conversion applications in laser-induced inertial confinement fusion. However, KDP crystals are difficult to produce because of their inherent softness, brittleness, and water-solubility, as well as their strong anisotropy and temperature sensitivity. Obtaining high-quality near-lossless KDP elements is an issue that should be solved urgently. In this study, an ultra-precision numerical control polishing method based on the water dissolution principle was introduced to achieve a controllable material removal. A small polishing tool was used to process a large KDP surface, and an accurate tool influence functions is required for deterministic fabrication of KDP surface. In order to quantify the influence of critical parameters (e.g., polishing speed, polishing pressure, water content, and directions of revolution and rotation) on material removal rate distribution, a tool influence function model was established based on the Preston equation. The model was then modified based on experiments, and its accuracy was verified. This modified model lays the foundation for ultra-precision water dissolution polishing of large KDP crystals. A very smoothed surface with high surface accuracy (peak-to-valley value below 0.4 λ) and low surface roughness (Ra 1.598 nm) could indeed be obtained by using the model. This research is also applicable to the polishing of other water-soluble materials.

High precision material removal of copper surface by jet electrochemical machining

High-precision machining technology has attracted increasing attention with the rapid development of modern industry. Jet electrochemical machining is a promising method for forming complex 3D shape surface by controlling the path and dwelling time of electrode nozzle moving over workpiece surface. The machining accuracy mainly relies on the stability of the material removal rate and the smoothness of the machined surface. In this paper, a new jet electrochemical machining method, which is based on a newly developed acid electrolyte, is proposed to improve its machining performance. The effects of voltage, interelectrode gap, electrolyte temperature and flow rate are discussed in this work. Stable machining can be achieved by selecting the optimum process parameters, and the surface roughness (Ra) can be reduced to 14.8 nm. Moreover, the obtained material removal rate distribution agrees well with the Gaussian function, which is recognized to have high capability to form complex 3D surface through controlling the movement of the tools.

A Global Correction Process for Flat Optics With Patterned Polishing Pad

To improve the efficiency of flat optics fabrication, a global correction method with the patterned polishing pad is developed in this paper. Through creating grooves on a polishing pad, the contact pressure distribution on the optics surface can be adjusted to change the material removal rate (MRR) distribution during polishing. Using the patterned pad, the selective removal ability of the polishing process is greatly enhanced. The predictability and stability of the MRR distribution are the preconditions to efficiently implement the proposed global correction method. Relying on the MRR distribution prediction method proposed and validated in this paper, the pad pattern can be designed based on the original surface figure of the workpieces. The designed groove pattern is created on the polishing pad using the custom-developed equipment. Then, the optical glass is polished on the designed pad with the optimized polishing time. A flat optical glass sample (Φ 100 mm) is polished with the global correction method to show its feasibility and advantage. The correction instance shows that the peak-to-valley (PV) value of the surface profile (with 3 mm edge exclusion) dropped from 1.17 µm to 0.2 µm in 14 min using a polyurethane pad with two ring grooves. Comparing with the conventional polishing process, which usually takes hours or days, the global correction method proposed in this paper can improve the efficiency of the optics manufacturing significantly.

Development an identification method of friction coefficient between wafer and carrier in double-sided lapping

Behavior of a wafer is one of the most significant concerns in double-sided lapping since it depends on the distribution of material removal rate. Though the wafer behavior is affected by the friction coefficient between the wafer and a carrier, the coefficient has hardly been discussed. In this study, an identification method of the friction coefficient based on variation of wafer rotational speed with wafer position in the carrier during single-sided lapping operation on double-sided lapping machine is developed for accurate estimation of the wafer behavior. The friction coefficient is identified by comparing experimental and theoretical variation of the rotational speed of the wafer. The experiment is carried out under the condition where lubrication condition between the wafer and the carrier is similar to that in double-sided lapping, and the variation is measured by image processing of the wafer behavior. The theoretical variation is calculated based on the equilibrium of force and moment applied to the wafer. It is confirmed that the theoretical rotational speed of the wafer under a friction coefficient condition agrees well with the measured one in terms of not only the highest and the lowest speed but also the variation with the wafer position in the carrier. Thus, it is assumed that the practical coefficient is identified by utilizing this method. In addition, the behavior of the wafer in double-sided lapping is calculated using the identified friction coefficient, and it is suggested that precise consideration of the contact status between the wafer and the carrier, i.e., non-slip, slip, and non-contact is essential for practical estimation.

Estimation of material removal rate distribution in double-sided polishing of thick square workpiece considering workpiece attitude

Estimation of material removal rate distribution in double-sided polishing of thick square workpiece considering workpiece attitude

Development of Accurate Prediction Technology of Material Removal Rate Distribution in Planarization CMP

Development of Accurate Prediction Technology of Material Removal Rate Distribution in Planarization CMP

Quantitative low-energy ion beam characterization by beam profiling and imaging via scintillation screens.

This study presents the imaging and characterization of low-current ion beams in the neutralized state monitored via single crystal YAG:Ce (Y3Al5O12) scintillators. To validate the presented beam diagnostic tool, Faraday cup measurements and test etchings were performed. Argon ions with a typical energy of 1.0 keV were emitted from an inductively coupled radio-frequency (13.56 MHz) ion beam source with total currents of some mA. Different beam properties, such as, lateral ion current density, beam divergence angle, and current density in pulsed ion beams have been studied to obtain information about the spatial beam profile and the material removal rate distribution. We observed excellent imaging properties with the scintillation screen and achieved a detailed characterization of the neutralized ion beam. A strong correlation between the scintillator light output, the ion current density, and the material removal rate could be observed.

Effects of the Profile of Workpiece Surface on Material Removal Rate Distribution in Polishing Process

Accurate prediction of the material removal rate (MRR) distribution is very important for the control of the polishing process. However, the widely used prediction method of MRR based on the Preston equation is still incapable of predicting the roll-off phenomenon in polishing process. One of the reasons is that many of the researchers’ neglected the effect of the surface profile of the workpiece on the MRR. In this paper, the evolutionary process of MRR distribution with the change of surface profile using two different polishing pad is studied, it is found that MRR varies gradually with the change of surface profile and tends to be uniform finally. Based on the analysis of contact pressure considering the actual surface profile of workpiece and modified Preston equation, the distribution of MRR is analyzed. It is found that the Preston coefficient distribution on workpiece surface is stable when the surface profile variation is small and shows obvious differences from the center to the edge of the workpiece. Through the comparison it is found that correlation between the regularities of Preston coefficient distribution and the type of polishing pad is significant. The research results in this paper will play an important guiding role in the quantitative prediction method research of polishing process.

Effect of Surface Profile on the Material Removal Rate Distribution in CMP Process

Material removal rate (MRR) distribution is a major concern in CMP process. In the published literatures, both experimental and theoretical research, MRR distribution is given without considering the surface profile of wafer. In this paper, the effect of surface profile on the MRR is analyzed based on the Preston equation and the contact pressure distribution calculated by the mixed lubrication model. It is found that the MRR distribution is dramatically affected by the profile of wafer surface, and whatever the polishing pad is conditioned in situ, the MRR distribution will be uniform at last. In addition, the wear of the pad surface induces a decrease of MRR.

Effects of pressure and shear stress on material removal rate in ultra-fine polishing of optical glass with magnetic compound fluid slurry

Optical glasses used in a range of industrially important optoelectronic devices must be polished to nano-level roughness for proper device operation. Polishing process with magnetic compound fluid slurry (MCF polishing) under a rotary magnetic field is an influential candidate for the method to precisely polish optical glass. MCF slurry has been successfully utilized to polish a variety of materials, ranging from soft optical polymers to hard optical glasses. MCF was developed by mixing a magnetic fluid and a magnetorheological fluid with the same base solvent, and hence includes not only μm-sized iron particles but also nm-sized magnetite particles. To elucidate the behaviour of material removal in MCF polishing, this study measured the normal and shear forces generated in the polishing zone during polishing. From these measurements, the distributions of pressure P and shear stress τ were obtained. The distribution of material removal rate (MRR) was investigated through spot polishing of borosilicate glass. The effects of three process parameters, namely magnet revolution speed, MCF carrier rotational speed and working gap, on pressure P, shear stress τ and the MRR were also investigated. The results revealed that P is higher near the centre of the interacting area (i.e. the polishing spot centre) and the point of maximum shear stress τ appears at about 5mm from the polishing spot centre. All of P, τ and MRR are sensitive to MCF carrier rotational speed and working gap but insensitive to magnet revolution speed. Shear stress is more sensitive to these process parameters than the pressure. Cross-sectional profiles of the polishing spots exhibit a characteristic symmetric W-shape; material removals are minimal at the spot centre and maximal at approximately 8.2–10.2mm from the spot centre depending on the process parameters. MRR is proportional to the MCF carrier rotational speed and is negatively correlated with working gap. An MRR model involving both the pressure and shear stress in MCF polishing is proposed. In the model, MRR is more dominated by shear stress than by pressure.

Semi-empirical material removal rate distribution model for SiO2 chemical mechanical polishing (CMP) processes

► We propose a material removal rate (MRR) distribution model for SiO 2 CMP. ► Contact mechanics are used for modeling the average MRR of SiO 2 film. ► A spatial parameter for MRR distribution is obtained from semi-empirical study. ► The MRR distribution model consists of the average MRR and spatial parameter. ► The proposed model includes the newly proposed line density of particles. A novel semi-empirical model was developed for predicting the material removal rate (MRR) during chemical mechanical polishing (CMP) based on the following assumptions: plastic contact at the wafer–particle interface, elastic contact at the pad–particle interface, a particle size distribution, and a randomly distributed surface roughness of the polishing pad. The proposed model incorporates the effects of particle size, concentration, and distribution, as well as the slurry flow rate, pad surface topography, material properties, and chemical reactions during the silicon dioxide (SiO 2 ) CMP. To obtain the unknown parameters and ensure the validity of the model, a SiO 2 CMP experiment was conducted by using various-sized CMP slurries. The spatial distribution of the MRRs is expressed with respect to the normal contact stress distribution and the relative velocity distribution. The proposed MRR model can be used for the development of a CMP simulator, the optimization of CMP process parameters, and the design of next-generation CMP machines.