Function Of Polishing Time Research Articles

Surface characteristics of maraging steel during electropolishing as a function of polishing time

ABSTRACT Thermal-based machining process like EDM, Laser-assisted additive manufacturing process degrades the surface integrity of the component. Therefore, a post-polishing method is required to improve the surface integrity as well as the performance of the component. A gyroscope, made of maraging steel, fabricated by EDM, is utilised in space industry and has poor surface integrity, which affects its performance. Thus, electropolishing (EP), a non-conventional polishing process, is used for the above said problem as it possesses several advantages over other polishing methods. There are very few literatures available for EP of maraging steel. The present manuscript is the preliminary analysis for the electrolyte (Ortho-phosphoric acid, sulphuric acid and hydrochloric acid) and its effect on maraging steel with respect to time. The surface characteristics such as surface roughness and surface reflectivity, along with surface elemental composition, have been evaluated. With increase in time, maximum improvement in surface roughness and surface reflectivity is 61.23% and 70%, respectively. It can be concluded that the selected electrolyte gives a promising improvement in the surface characteristics of maraging steel.

Electrochemical Analysis of Film Forming Mechanisms Relevant to Data Storage Chemical Mechanical Planarization

With the rapid increase of data storage density, the operation distance between read/write head and media has fallen into the nanometer regime. This requires an atomic level planarization to avoid defects on the surface and “crashes” of the read/write head media. Chemical mechanical polishing (CMP) has been selected to produce high quality surface finish on a Nickel Phosphorous (NiP) plated substrate, through the removal of a metal complex film formed on the surface. CMP is a process that balances the kinetic/ thermodynamic reactions between the formation of a chemically modified layer and its interaction with the slurry. In order to understand the mechanistic CMP film forming process, electrochemical techniques were developed to probe the impact of organic additives on the surface redox and film forming mechanisms. More specifically, through monitoring the OCP (under abrasive and nonabrasive conditions) versus time, the film removal rate and passivation film formation kinetics can be determined as a function of slurry additives. Using OCP, the film passivation of the metal slurry complex on the surface of a nickel electrode can be monitored as a function of polishing time and related to the film forming mechanism of the CMP process.

Control of adhesion force between ceria particles and polishing pad in shallow trench isolation chemical mechanical planarization.

The adhesion force between ceria and polyurethane (PU) pad was controlled to remove the step height from cell region to peripheral region during Shallow Trench Isolation Chemical Mechanical Planarization (STI-CMP) for NAND flash. Picolinic acid was found to be adsorbed on ceria particles at pH 4.5 following a Langmuir isotherm with the maximum adsorbed amount of 0.36 mg/m2. The ceria suspension with full surface coverage of picolinic acid showed a threefold increase in the number of adhered ceria particles on the PU pad over non-coated ceria particles. It was shown that the coverage percent of picolinic acid on ceria corresponds well with the amount percent of adsorbed ceria on PU pad. The change in adsorbed particles was directly reflected in the CMP polishing process where significant improvements were achieved. Particularly, convex areas on the chip experienced higher friction force from the attached abrasives on the PU pad than concave areas. As a result, the convex areas have increased removal rate of step height compared to the ceria suspension without picolinic acid. The changing profiles of convex areas are reported during the step height reduction as a function of polishing time.

Chemical mechanical planarization of barrier layers by using a weakly alkaline slurry

A weakly alkaline barrier slurry (pH = 8.0) was proposed, which was free of unstable H2O2 and inhibitor such as benzotriazole (BTA). The polishing results of Cu, Ta and oxide blanket wafers show that the slurry has a high removal rate on oxide, while Ta has a low removal rate on Cu. The evaluation of the slurry was implemented in a way that the process conditions of Cu CMP and consumables on platen 1 and platen 2 were fixed. Copper dishing and oxide erosion have been characterized as a function of polishing time. The experiment results reveal that the barrier slurry without inhibitors has an obvious effect on the correction of dishing and erosion, and it also suggests that the slurry has a high selectivity of Ta and oxide to Cu. The sheet resistance does not exhibit any difference as polishing time increased, which indicates substantially lower copper loss.

Impact of Pad Conditioning on Thickness Profile Control in Chemical Mechanical Planarization

Chemical mechanical planarization (CMP) has been proven to be the best method to achieve within-wafer and within-die uniformity for multilevel metallization. Decreasing device dimensions and increasing wafer sizes continuously demand better planarization, which necessitates better understanding of all the variables of the CMP process. A recently highlighted critical factor, pad conditioning, affects the pad surface profile and consequently the wafer profile; in addition, it reduces defects by refreshing the pad surface during polishing. This work demonstrates the changes in the postpolish wafer profile as a function of pad wear. It also introduces a wafer material removal rate profile model based on the locally relevant Preston equation by estimating the pad thickness profile as a function of polishing time. The result is a dynamic predictor of how the wafer removal rate profile shifts as the pad ages. The model helps fine-tune the pad conditioner operating characteristics without the requirement for costly and lengthy experiments. The accuracy of the model is demonstrated by experiments as well as data from a real production line. Both experimental data and simulations indicate that the smaller conditioning disk size and extended conditioning sweep range help improve the post-CMP wafer planarization. However, the defectivity tends to increase when the conditioning disk sweeps out of the pad radius; hence, the pad conditioning needs to be designed by considering the specific requirements of the CMP process conducted. The presented model predicts the process outcomes without requiring detailed experimentation.

Analysis of Local Planarization with Polishing Time, Film Thickness, Chemical Non-Uniformity, Line Density, Line Width, and Pad Relaxation Property

AbstractTheoretical chemical mechanical polishing local planarization models as a function of polishing time and film removal are reviewed, and re-derived in a systematic and correlative way. The derived models employ pad viscoelastic and relaxation properties to explain the experimental phenomena that step height local planarization is an exponential function of line width at the same line density, and also account for the affect of pattern density and polishing of two different materials at the same time on step height planarization.

Evaluation of polishing damage in alumina

Abstract Grazing incidence X-ray scattering and line focus acoustic microscopy have been applied to the study of grinding, lapping and polishing processes on alumina. Changes as a function of polishing time in the near-surface density, measured from the critical angle for total external reflection of X-rays, were related to changes in the bearing area and surface morphology. No relation was found between the micrometre-scale roughness measured by a stylus instrument and the integrated diffuse scatter, the latter being related to the nanometre-scale roughness on the top of the polished mesas remaining after grain pull-out during the grinding and lapping process. The surface acoustic wave velocity was also found to vary with polishing time. These changes cannot be ascribed to changes in roughness and are believed to measure changes in the residual crack density.