Elon Terrell

Hydrodynamics of Slurry Flow in Chemical Mechanical Polishing A Review

Chemical mechanical polishing (CMP) is a process that is commonly used to planarize wafer surfaces during fabrication. Although the complex interactions between the wafer, pad, and slurry make the CMP process difficult to predict, it has been postulated that the motion of the slurry fluid at the wafer-pad interface has an important effect on the wafer surface wear distribution. This paper thus serves as a review of past studies of the hydrodynamics of slurry flow during chemical mechanical polishing. The reviewed studies include theoretical and numerical models as well as experimental measurements.

A Particle-Augmented Mixed Lubrication Modeling Approach to Predicting Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) is a manufacturing process that is commonly used to planarize integrated circuits and other small-scale devices during fabrication. Although a number of models have been formulated, which focus on specific aspects of the CMP process, these models typically do not integrate all of the predominant mechanical aspects of CMP into a single framework. Additionally, the use of empirical fitting parameters decreases the generality of existing predictive CMP models. Therefore, the focus of this study is to develop an integrated computational modeling approach that incorporates the key physics behind CMP without using empirical fitting parameters. CMP consists of the interplay of four key tribological phenomena—fluid mechanics, particle dynamics, contact mechanics, and resulting wear. When these physical phenomena are all actively engaged in a sliding contact, the authors call this particle-augmented mixed lubrication (PAML). By considering all of the PAML phenomena in modeling particle-induced wear (or material removal), this model was able to predict wear-in silico from a measured surface topography during CMP. The predicted material removal rate (MRR) was compared with experimental measurements of copper CMP. A series of parametric studies were also conducted in order to predict the effects of varying slurry properties such as solid fraction and abrasive particle size. The results from the model are promising and suggest that a tribological framework is in place for developing a generalized first-principle PAML modeling approach for predicting CMP.

It's Not Easy Being Green: Supporting Collaborative Green Design Learning

We present the results of a study in which we contrast alternative forms of collaborative learning support in the midst of a collaborative design task in which students negotiate between increasing power and increasing environmental friendliness. In this context, we evaluated the instructional effectiveness of four alternative support conditions as well as a goal manipulation. Both manipulations yield surprising findings, which we are continuing to investigate.

A Modeling Approach for Predicting the Abrasive Particle Motion During Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) is a manufacturing process in which a wafer surface is polished by pressing it against a rotating pad that is flooded with slurry. The slurry itself is a fluid containing abrasive particles. Past experimentation has shown that the distribution of suspended particles in the slurry is significantly related to the distribution of material removal on the wafer during CMP. Therefore, this study involves the development and simulation of a model that predicts the kinematics and trajectory of the abrasive particles. The simulation results compare well to data from shear cell experiments data conducted by other researchers.

Application of Smoothed Particle Hydrodynamics to Full-Film Lubrication

An in-house solver was created in order to simulate hydrodynamic lubrication utilizing smoothed particle hydrodynamics (SPH). SPH is a meshfree, Lagrangian, particle-based method that can be used to solve continuum problems. In this study, transient hydrodynamic lubrication in a pad bearing geometry was modeled utilizing the SPH method. The results were validated by comparison to computational fluid dynamics (CFD) and an analytical solution provided by lubrication theory. Results for the pressure distribution between SPH and CFD were agreeable while lubrication theory failed to capture any inertial effects of the fluid. Velocity profile comparisons differed slightly between all three methods. However, since smoothed particle methods have been shown to have the advantage of being able to model large deformations, as well as allowing easy definitions of fluid-solid interfaces, they can be useful tools for complex problems in tribology.

Modeling the Motion of Slurry Nanoparticles During Chemical Mechanical Polishing

Chemical mechanical polishing (CMP) has emerged as a commonly used method for achieving global surface planarization of micro-/nano-scale systems during fabrication. During CMP, the wafer to be polished is pressed against a rotating polymeric pad that is flooded with slurry. The motion of the wafer surface against the asperities of the pad and the abrasive nanoscale particles in the slurry causes the surface of the wafer to be polished to an atomically smooth level. Past studies have shown that the wear distribution is a function of the distribution of slurry particles in the wafer/pad interface, and thus it is desirable to model the migration of particles in order to predict the wear of the wafer surface. The current study involves the creation and simulation of a mathematical model which predicts the paths of slurry particles in a Lagrangian reference frame. The model predicts the effects of the various forces on each particle to determine its motion. The model also accounts for interparticle collisions and wafer/particle and pad/particle collisions. It is expected that the particle motion that is predicted from this model will allow for a more accurate correlation of the wafer surface wear distribution.© 2005 ASME

THE EFFECT OF MICROSTRUCTURE ON CHEMICAL MECHANICAL POLISHING PROCESS OF THIN-FILM METALS

Chemical mechanical polishing (CMP) is a critical nanomanufacturing process used to remove or planarize ultrathin metallic, dielectric, or barrier layers on silicon wafers. The CMP process is a vital interim fabrication step for integrated circuits and data storage devices. One of the major shortcomings of existing CMP models is that they do not account for crystallographic effects of the thin film metal materials when predicting material removal rates. This work investigates the effect of the microstructure on the CMP of copper and metal thin films on silicon wafer. Nanoindentation tests were conducted to measure the hardness variations across a wafer surface due to the crystallography of the metal films. Spatial variation of mechanical properties was also input into an existing multi-scale CMP model. Nano-characterization and CMP experimental results are presented and compared to an existing CMP wear model.Copyright

Contact Stress Analysis of Thin Film Compression: Modeling, Simulation, and Experiment

Two different elastic contact stress modeling approaches were compared to results from a flat punch compression experiment. The two approaches, which employed the Greenwood and Williamson contact stress model and the Volume Pixel (“Voxel”) asperity modeling simulation, were used to analyze the force-displacement response of a sample surface when pressed down by a smooth, rigid, flat plane to a prescribed load. The results of the model and simulation are compared to experimental measurements from the flat punch compression performed using a nanoindenter.Copyright

A Model for Studying the Hydrodynamic Slurry Behavior in CMP: Discrete and Continuous Phases

Chemical mechanical polishing (CMP) is a manufacturing process in which a wafer surface is polished by pressing it against a rotating pad that is flooded with slurry. The slurry itself is a fluid containing abrasive particles. Past experimentation has shown that the distribution of suspended particles in the slurry is significantly related to the distribution of material removal on the wafer during CMP. Therefore, this study involves the development and simulation of a model that predicts the kinematics and trajectory of the abrasive particles. The simulation results compare well with data from shear cell experiments data conducted by other researchers.Copyright

TWO-PHASE HYDRODYNAMIC MODELING OF PARTICULATE FLUIDS IN SLIDING CONTACTS

Chemical mechanical polishing (CMP) is a manufacturing process that uses controlled wear to planarize dielectric and metallic layers on silicon wafers. The wafer is polished by pressing it against a rotating pad that is flooded with slurry. The slurry itself is a fluid containing abrasive particles. Material removal rate (MRR) results have shown that the distribution of suspended particles in the slurry is significantly related to the wafer surface wear distribution during CMP. In this study, a simple model has been developed and solved as a preliminary step in analyzing the migration of the particles.Copyright