Local Removal Rate Research Articles

Numerical simulation and experimental study of normal force and particle speed in the robotic stream finishing process

Normal force and particle speed are the two most important parameters in determining the mass removal rate on the workpiece in the stream finishing process. However, quantifying them is still a big challenge due to the complexity of the interaction between media flow and the workpiece. In this study, a continuum-based (μ(I) rheology) numerical model was developed to simulate the granular media flow in a robotic stream finishing (RSF) system and validated with in-house experimental data. A novel frictional wall-slip model was developed to describe the media flow speed on the surface of a rectangular workpiece. The impact of three key process variables: (i) immersion depth (D), (ii) angle of attack (θ), and (iii) radial distance (r) on the resulting normal force and media flow speed was analyzed. The resulting normal force on the workpiece strongly depends on the immersion depth. A small increase in the hydrostatic pressure is amplified through elevated effective viscosity near the workpiece, resulting in a significant increase in the normal force. A critical θ for the dependency of normal force was identified. Below the critical θ, the normal force varies slightly with the increase in θ. Above the critical θ, the normal force decreases rapidly with the increase in θ. The normal force also increases linearly with the increase in radial distance. In general, the media flow speed increases rapidly with θ. However, the increase peaks at θ = 75° due to the wake effect behind the leading edge. As D increases, the media flow speed only changes marginally, given the same θ. The media flow speed increases with radial distance, and the relationship is quadratic. We have validated – through experiments – that the numerical model can reliably predict both normal force and media flow speed on the rectangular workpiece. As the local material removal rate has a direct correlation to the normal force and the media flow speed, this numerical model is capable of predicting material removal distribution on an actual polished component and, therefore, will be an indispensable tool for conducting in-process optimization and toolpath planning.

The ideal implant for Mayo 2A olecranon fractures? An economic evaluation

The ideal implant for stable, noncomminuted olecranon fractures is controversial. Tension band wiring (TBW) is associated with lower cost but higher implant removal rates.On the other hand, plate fixation (PF) is purported to be biomechanically superior, with lower failure and implant removal rates, although associated with higher cost. The primary aim of this study is to look at the clinical outcomes for all Mayo 2A olecranon between PF and TBW. The secondary aim is to perform an economic evaluation of PF vs. TBW. This is a retrospective study of all surgically treated Mayo 2A olecranon fractures in a tertiary hospital from 2005-2016. Demographic data, medical history, range of motion, and complications were collected. All inpatient and outpatient costs in a 1-year period postsurgery including the index surgical procedure were collected via the hospital administrative cost database (normalized to 2014). A total of 147 cases were identified (94 TBW, 53 PF). PF was associated with higher mean age (P < .01), higher American Society of Anesthesiologists score (P< .01), and higher proportion of hypertensives (P = .04). There was no difference in the range of motion achieved at 1 year for both groups. In terms of complications, TBW was associated with more symptomatic hardware (21.6% vs. 13.7%, P= .24) and implant failures (16.5% vs. none, P < .01), whereas the plate group had a higher wound complication (5.9% vs. none, P = .02) and infection rate (9.8% vs. 3.1%, P = .09). TBW had a higher implant removal rate of 30.9% compared with 22.7% for PF (P = .36). PF had a higher cost at all time points, from the index surgery ($10,313.64 vs. $5896.36, P < .01), 1-year cost excluding index surgery ($5069.61 vs. $3850.46, P = .46), and outpatient cost ($1667.80 vs. $1613.49, P = .27). Based on our study results, we have demonstrated that TBW is the ideal implant for Mayo 2A olecranon fractures from both a clinical and economic standpoint, with comparable clinical results, potentially similar implant removal rates as PF's, and a lower cost over a 1-year period. In choosing the ideal implant, the surgeon must take into account, first, the local TBW and PF removal rate, which can vary significantly because of the patient's profile and beliefs, and second, the PF implant cost.

A chemical mechanical planarization model for aluminum gate structures

In this work, we propose a new aluminum gate chemical mechanical planarization (CMP) model to describe the metal gate height variation in 32nm high-k metal gate (HKMG) process based on chemical kinetics and contact mechanics. The effects of mechanical abrasion, concentration of different types of chemical reagents and hydrogen ions, pattern geometry and pad elastic properties on surface profile are physically captured. In the process of constructing the model, the discrete convolution and fast Fourier transform (DC–FFT) technique is integrated with conjugated gradient method (CGM) for calculating the contact pressure between the wafer surface and the polishing pad. Then the computed pressure distribution is introduced into the new constructed chemical kinetics formula to determine the local removal rate of the underlying patterns and predict the evolution of the wafer surface topography. The detailed relationship between the metal gate dishing post-Al-CMP and the design pattern structures are systematically investigated. The model agrees reasonably well with the experimental data measured from the HKMG test structures. Therefore, it can be utilized for quantifying the effect of pattern geometry on dishing, predicting the wafer surface height evolution and optimizing some design rules for manufacturability to improve the surface planarization of HKMG structures.

A Feature-Scale Greenwood–Williamson Model for Metal Chemical Mechanical Planarization

In this work, a new feature-scale model is proposed for investigating the interaction between the wafer pattern and individual pad asperities in the process of chemical mechanical planarization (CMP). Based on the contact mechanics equation and the modified Greenwood–Williamson (GW) model which captures the evolution of feature curvature and the modification of the pad asperity height distribution, the discrete convolution and fast Fourier transform (DC-FFT) technique is adopted and combined with the Picard iteration method to calculate the direct contact pressure distribution between the wafer surface and the polishing pad. The computed pressure is then used to determine the local removal rate of the underlying patterns and predict the evolution of the wafer surface profile. Furthermore, the method is extended to capture the metal dishing as the feature size changes. It is shown that the present model can avoid the false simulated results produced by directly applying the original GW model for CMP when the feature size approaches zero. Otherwise, the calculated surface profile and dishing values of pattern geometries are in good agreement with the experimental data. Therefore, this model can not only be used to simulate the evolution of the wafer surface for global planarization at lower technology nodes, but can also be applied to provide some basic design rules for improving the process parameters and reducing the time and cost for developing new architectures.

Hepatic Galactose Metabolism Quantified in Humans Using 2-18F-Fluoro-2-Deoxy-d-Galactose PET/CT

Accurate quantification of regional liver function is needed, and PET of specific hepatic metabolic pathways offers a unique method for this purpose. Here, we quantify hepatic galactose elimination in humans using PET and the galactose analog 2-(18)F-fluoro-2-deoxy-d-galactose ((18)F-FDGal) as the PET tracer. Eight healthy human subjects underwent (18)F-FDGal PET/CT of the liver with and without a simultaneous infusion of galactose. Hepatic systemic clearance of (18)F-FDGal was determined from linear representation of the PET data. Hepatic galactose removal kinetics were determined using measurements of hepatic blood flow and arterial and liver vein galactose concentrations at increasing galactose infusions. The hepatic removal kinetics of (18)F-FDGal and galactose and the lumped constant (LC) were determined. The mean hepatic systemic clearance of (18)F-FDGal was significantly higher in the absence than in the presence of galactose (0.274 ± 0.001 vs. 0.019 ± 0.001 L blood/min/L liver tissue; P < 0.01), showing competitive substrate inhibition of galactokinase. The LC was 0.13 ± 0.01, and the (18)F-FDGal PET with galactose infusion provided an accurate measure of the local maximum removal rate of galactose (V(max)) in liver tissue compared with the V(max) estimated from arterio-liver venous (A-V) differences (1.41 ± 0.24 vs. 1.76 ± 0.08 mmol/min/L liver tissue; P = 0.60). The first-order hepatic systemic clearance of (18)F-FDGal was enzyme-determined and can thus be used as an indirect estimate of galactokinase capacity without the need for galactose infusion or knowledge of the LC. (18)F-FDGal PET/CT provides an accurate in vivo measurement of human galactose metabolism, which enables the quantification of regional hepatic metabolic function.

Observations of surface radon in Central Italy

Two years of in situ radon concentration measurements in the atmospheric surface layer have been collected in a central Italy town (L’Aquila), located in the Aterno river valley. These data have been analyzed in order to study the controlling mechanisms of surface radon abundance; observations of coincident meteorological parameters confirmed the role of dynamics on the local removal rate of this tracer. The relatively high negative correlation of hourly data of surface wind speed and radon activity concentration (R = −0.54, on annual scale) suggests that dynamical removal of radon is one of the most important controlling processes of the tracer accumulation in the atmospheric surface layer. An attempt is made to quantify the precipitation impact on radon soil fluxes. No anticorrelation of radon and precipitation comes out from the data (R = −0.15), as in previous studies. However, since the main physical parameter affecting the ground radon release is expected to be the soil accumulation of water, snow or ice, the emission flux has also been correlated with soil moisture; in this way a much clearer anticorrelation is found (R = −0.54).

Modeling and calculation of slurry-chemistry effects on chemical–mechanical planarization with a grooved pad

During chemical–mechanical planarization (CMP), a rotating wafer is pressed against a rotating pad, while a slurry is dragged into the pad–wafer interface. Here, taking into account the dependence of local material removal rate (MRR) on the slurry’s chemical activity, the effects of pad groove geometry and various other process parameters on the spatial average and non-uniformity of MRR are examined. Technically, the slurry flow is calculated by following an existing approach that integrates two-dimensional fluid-film lubrication theory and contact-mechanics models. A slurry impurity transport equation is then used to calculate the impurity concentration that determines the slurry’s chemical activity and hence the local MRR. The numerical results obtained here indicate that the presence of pad grooves generally decreases the average slurry impurity concentration, and increases the average contact stress on the pad–wafer interface. However, as a grooved pad has less contact area for effective interaction with the wafer surface, the average MRR may or may not be increased, depending upon the specific setting of process parameters. Meanwhile, it appears that the retaining ring generally used to keep the wafer in place also plays an important part in reducing the MRR non-uniformity.

ASPHERO5 – Simulation and Analysis of Aspherical Polishing Process

ASPHERO5 is a funded German research project (project prime: Schneider OpticalMachines) with the goal of economic fabrication of high precision aspheres. The research is concentrated on the classical process chain consisting of grinding and polishing. The characterization of the incoming and outgoing surface quality is one issue to characterize the improvements. The variation of the local removal rate related to local curvature is one of the limiting factors of the polishing process. In this paper we report on first results characterizing the surface quality with a PSD (Power Spectral Density) algorithm and analyzing the local removal rates for the polishing step. In our research, two types of aspheres with 30 and 60 mm diameter were polished with a spinning tool process. The final deviation between simulation and experiment was less than 10 percent. That’s the starting point for further investigations within the project.

Effects of Pad Grooves on Chemical Mechanical Planarization

Chemical mechanical planarization (CMP) has played an enabling role in producing near-perfect planarity of interconnection and metal layers in ultralarge scale integrated devices. For stable and high performance of CMP, it is important to ensure uniform slurry flow at the pad–wafer interface, hence necessitating the use of grooved pads that help discharge debris and prevent subsequent particle loading effects. Here, using two-dimensional lubrication theory and contact mechanics models, we examine the effects of pad groove designs (viz. their width, depth, and spacing) on slurry flow in CMP. It is found that the presence of pad grooves generally increases the slurry flow rate (which clearly facilitates debris discharge) and the magnitude of the subambient fluid pressure (i.e., suction) on the pad–wafer interface. The increased suction implies higher contact stress on the pad–wafer interface, and hence the local material removal rate is expected to increase as well. However, our numerical results suggest that, as a grooved pad has less contact area for effective interaction with the wafer, the overall material removal rate is expected to increase as well. However, our numerical results suggest that, as a grooved pad has less contact area for effective interaction with the wafer, the overall material removal rate is decreased by the presence of pad grooves. There is therefore a trade-off between slurry flow rate enhancement and material removal rate reduction in pad groove design.

Investigation of the material removal model for bonnet tool polishing with precession

Bonnet tool polishing is a novel aspherical polishing method. This paper describes a method to obtain the local removal rate for the polishing process by using bulbous flexible membrane covered with a polishing pad and pressurised by an internal fluid. During the polishing process the precession process, in which the bonnet tool cannot only spines itself but also precesses along the local normal on the specimen surface, was applied. The local removal rate model was established according to the Preston equation. The influence of the precession process on the material removal rate was analysed and also the polishing pressure distribution was obtained according to the experiment data. It is confirmed by the experiments that the dwelling time has a linear relation with the local removal depth. Preston coefficient can be calculated from the experimental data. Finally, the expression of the local removal rate in bonnet tool polishing was acquired experimentally.

Influence of Microstructure on Aggressive Chemical Mechanical Planarization Processes for Thick Copper Films

ABSTRACTNovel die-stacking schema using through-wafer vias may require thick electrodeposited copper and aggressive first-step chemical mechanical planarization (CMP). However, the effect of microstructural parameters, including surface orientation and grain size, on the CMP behavior of thick electrodeposited copper is not well understood. Here we explore the relationship be-tween the surface orientation of copper grains and local CMP removal parameters using electron backscatter diffraction and topography correlation techniques. In the present work, solid copper disks are studied which are annealed to produce samples with differing grain sizes. In addition, aggressive CMP is performed on copper films (30 μm) electrodeposited on silicon. At the bulk level, the slurry composition is found to have the greatest effect on the removal rate and surface roughness. At the microstructural level, the nature of the grain boundaries (e.g. coincidence site lattice (CSL) vs. non-CSL boundaries) is shown to impact the depth of grooving at the grain boundaries. A relationship between surface orientation and local removal rate is found.

Performance of a real-time local thermal management system for casting dies with multiple cooling channels

In high-pressure die casting processes, proper control of die temperature is essential for producing superior quality components and yielding high production rates. Very often it is impractical to control die temperature to a specific point during solidification stages. In this paper, a computerised Intelligent Real-Time Monitoring and Control System (IRMCS) is developed for die casting processes involving cooling of a die with multiple channels. A local temperature controller is designed to confine temperature fluctuations of a die within a desirable range. The performance of the system is evaluated through a laboratory die casting process simulator in terms of measurement accuracy, time delay and local heat removal rate. The experimental results indicate that the developed control system is capable of adjusting the desirable supply of cooling water into multiple cooling lines. Hence, the ideal thermal pattern of the die becomes achievable.

Study of Local Material Removal Model of Bonnet Tool Polishing

Bonnet tool polishing is a novel aspherical polishing method. This paper describes a method to obtain the local removal rate for the polishing process using bulbous flexible membrane covered with a polishing pad and pressurized by an internal fluid. According to the principle of bonnet polishing and Preston equation, the local removal rate model was established. It is confirmed by the experiments that the local removal depth has a linear relation with the dwell time. Preston coefficient can be calculated from the experimental data. Finally the expression of the local removal rate in bonnet tool polishing is acquired semi-empirically.

Modeling of chemical–mechanical polishing on patterned wafers as part of integrated topography process simulation

The simulation of chemical–mechanical polishing (CMP) is particularly important within integrated topography process simulation environments to allow for studying the interplay between etching, deposition, and CMP process steps. In this work, a feature-scale physical model based on contact-mechanics has been implemented in 2D. The model takes into account both the roughness and elastic deformation of the polishing pad for computing the pressure distribution. This pressure distribution is used to determine the local removal rate using the Preston equation. Our simulator allows for two-step polishing of multi-line structures with different pads, slurries and polishing parameters. The data format used is supported by a standard software environment (ISE TCAD) which therefore allows for coupling of our topography simulation modules with various tools such as process simulators and modules for electrical characterization. The integration of our simulator with the 3D simulation of barrier and copper deposition is demonstrated for two damascene processes.

Local material removal mechanism considering curvature effect in the polishing process of the small aspherical lens die

This paper describes a method to obtain the local removal rate for the polishing process of the small aspherical lens die using a spherical tool. When the small spherical polishing tool traverses an aspherical surface, non-uniform polishing area and local removal rate are locally generated around the contacting points according to the curvature change of an aspherical surface. Therefore, an aspherical surface is divided into multiple patches and the local removal rate on the patches is calculated semi-empirically from the Preston equation. Formation of the elliptical polishing area is confirmed experimentally and the Preston coefficient is calculated from the central removal depth and dwell time that has a linear relation with the local removal depth. Finally, using the equivalent radius of two contact bodies, the curvature effect of an aspherical surface on the polishing area is explained.

The evaluation of respiration rate in fixed‐film systems under various organic loading rates

Oxygen microprofiles were used to evaluate the relationship between organic loading and respiration rate. The oxygen fluxes into the biofilms represent the total aerobic reaction rate of the biofilm, and the total organic removals represent the total use rate of the biofilm. The ratios of respiration rate to total chemical oxygen demand (COD) removal rate were evaluated under various operational conditions. Results showed that an increase in oxygen supplied increased only the respiration rate and did not affect the overall COD use rate. Systems fed additionally with azo dyes (possible inhibitors) had lower organic removals. Azo dyes appeared to affect both the local respiration rate and the local COD removal rate inside the biofilm.

Use of satellite data to constrain the model‐calculated atmospheric lifetime for N2O: Implications for other trace gases

The source gases, such as nitrous oxide (N2O) and chlorofluorocarbons (CFCs), are released into the atmosphere at the Earth's surface and are removed mainly by photolysis in the stratosphere. The atmospheric abundance of a source gas is proportional to its emission rate and atmospheric lifetime. The lifetime is, in turn, determined by the local photochemical removal rate of the gas and the efficiency of transport that carries the gas from where it is emitted to the dominant photochemical removal region. The latter is particularly important for source gases for which the removal is restricted to the tropical stratosphere, a region where both the photolysis rates and concentrations are highest. We calculate that approximately 80% Of N2O is removed in the stratosphere between 30°N and 30°S. Using the data for N2O obtained from the stratospheric and mesospheric sounder (SAMS) instrument on the Nimbus 7 satellite to constrain the model‐calculated distributions, we concluded that previous models may have underestimated the magnitude of vertical transport over the tropics and that the calculated lifetimes for N2O and CFC source gases could be 30% shorter than previously reported values. The calculated lifetime for N2O of 110 years would imply a source strength of 13×106 tons (N) yr−1, compared to a source strength of 9.2×106 tons (N) per year for a lifetime of 160 years. A shorter lifetime for the CFCs (47 years for CFC‐11 and 95 years for CFC‐12) would imply a more rapid decrease in the atmospheric chlorine content once the CFC emissions are stopped, making it possible to reach the pre‐ozone hole value of 2 ppbv as early as 2045. Accurate determination of the lifetime of CFC‐11 is particularly important, since the lifetime is used in the definitions of the ozone depletion potentials (ODP), chlorine loading potentials (CLP), and greenhouse warming potentials (GWP) of the replacement chemicals for the CFCs. A shorter lifetime for CFC‐11 would elevate the magnitudes of ODP, CLP, and GWP for these chemicals.