Pad effects on material-removal rate in chemical-mechanical planarization

The role of a porous pad in controlling material-removal rate (MRR) during the chemical-mechanical planarization (CMP) process has been studied numerically. The numerical results are used to develop a phenomenological model that correlates the forces on each individual abrasive particle to the applied nominal pressure. The model provides a physical explanation for the experimentally observed domains of pressure-dependent MRR, where the pad deformation controls the load sharing between active-abrasive particles and direct pad-wafer contact. The predicted correlations between MRR and slurry characteristics, i.e., particle size and concentration, are in agreement with experimentally measured trends reported by Ouma¹ and Izumitani.²     

Elastic and elastic-perfectly plastic analysis of an axisymmetric sinusoidal surface asperity contact

ABSTRACT

Closed-form finite-element empirical models are available for elastic and elastic–plastic spherical and sinusoidal contact. However, some of these models do not consider the effect of interaction with adjacent asperities or require extensive numerical resources because they employ a full 3-D model. Therefore this work has analysed and quantified the behaviour of an elastic and elastic- perfectly plastic axisymmetric sinusoidal surface in contact with a rigid flat for a wide range of material properties and different values of the amplitude to wavelength ratio from initial to complete contact (high load). The numerical results agreed well with the Hertz model and the Jackson–Green elastic–plastic spherical contact model at low loads. Empirical equations for elastic and also elastic-perfectly plastic cases are formulated for the contact pressure, contact area and surface separation. From the current analysis, it is found that it is not any single parameter, but different combinations of material properties and surface roughness that govern the whole contact behaviour. The critical value of the amplitude of the sinusoidal asperity below which it will deform completely elastically from initial to complete contact is established. At low values of amplitude normalized by the critical amplitude, it was found that the contact behaved similar to a spherical contact, with the average pressure (hardness) always remaining lower than three times the yield strength. However, at higher values the average pressure increased toward a value as high as six times the yield strength at complete contact. All of these equations should be useful in rough surface contact modelling, lubrication analysis, electrical contact modelling and in many other applications.     

Optimizing tape‐burnishing/wiping process of magnetic recording media through Taguchi method

For the ever‐increasing recording density in hard disk drives, ultra‐low gliding height media are required. It is an immense challenge for the tape‐burnishing/wiping process of media to reduce the asperities effectively and efficiently while no scratches occur. The purpose of this paper is to characterize and then optimize the tape‐burnishing/wiping process as so to minimize the asperities without leaving any scratches on the media surface. A Taguchi experiment design method is adopted to analyze the data and acquire an optimal level combination of process parameters. The resulting optimal combination is practically implemented in tape‐burnishing/wiping the several magnetic recording media, which reveals that the average pass ratio of 5 nm glide avalanche testing increases nearly doubly to a level of 96%. Copyright © 2008 John Wiley & Sons, Ltd.     

渗氮钢粗糙表面的弹塑性接触研究

利用弹塑性有限元和单纯形法求解弹塑性接触模型，分别模拟了屈服强度呈梯度变化的渗氮钢、未经处理的匀质材料和硬涂层材料粗糙表面的弹塑性接触行为。与未经处理的匀质材料相比，渗氮钢可承受更大接触载荷。在相同载荷作用下，渗氮钢表面粗糙峰接触面积较小，平均间距较大，接触体内材料不易发生屈服，从而显著提高接触性能。和硬涂层材料相比，渗氮钢接触体内等效von Mises应力分布平缓，没有应力突变。最后讨论了渗氮层和硬涂层的厚度对粗糙表面接触特性的影响。     

齿形节理渐进破坏直剪试验研究

通过对由两个齿形凸体组合构成的双齿节理进行直剪试验,分析了两个齿形凸体的起伏角相等时和不等时双齿节理的剪切特性;观察和分析含两种不同起伏角凸起体的双齿节理的渐进破坏过程与机理,以及两个齿形凸起体的排列顺序对此类双齿节理的剪切强度和变形特性的影响.     

结合面切向接触刚度的概率统计模型

该文考虑结合面上微凸体接触为椭圆形接触, 运用弹性力学空间半无限体受载荷变形理论, 并根据椭圆形接触面上压力分布的Hertz理论, 推导出椭圆形接触面的长、短半轴计算式和单个微凸体接触时的切向接触刚度表达式. 建立了结合面上微凸体椭圆形接触面的长、短半轴呈二维正态分布、高度呈正态分布情况下的宏观切向接触刚度模型, 得到了相应的宏观切向接触刚度表达式. 通过数值计算给出了切向接触刚度随结合面的法向载荷、切向载荷、椭圆微凸体的离心率、微凸体分布的相关系数、微凸体测量高度和微凸体分布的标准方差等各影响因素的变化情况, 增大法向载荷可以提高结合面的切向接触刚度, 而切向载荷的增大会导致切向接触刚度的 减小.     

Metallic sliding friction under boundary lubricated conditions: Investigation of the influence of lubricant at the start of sliding

Experiments are described in which a hard half-wedge, representing a scaled up model asperity, was indented into the horizontal surface of a relatively soft specimen with the specimen then moved in a direction parallel to its surface and normal to the wedge edge. Forces measured at the wedge-specimen interface are used to investigate the state of lubrication at the interface at all stages of the experiment, i.e. from initial indentation to final steady-state wave formation. The results are used to offer possible explanations for the nature of boundary lubrication and of stick-slip motion.     

表面横向粗糙峰对点接触热弹流润滑的影响

通过数值解研究丁固体表面的横向粗糙峰对钢球与玻璃盘形成的热弹流润滑接触区压力、膜厚以及温度分布的影响。计算中假设钢球是静止的．即滚滑比为2。结果表明在粗糙峰出现的位置上，压力、温度均有急剧的增加，并且固体表面的凹陷现象也变得更加复杂。     

An analysis of three-dimensional elasto-plastic sinusoidal contact

Researchers have developed many models to simulate the elasto-plastic contact of spheres. However, there does not appear to exist a closed-form analytical model for elasto-plastic three-dimensional sinusoidal contact. This work uses a finite element model (FEM) to characterize elasto-plastic sinusoidal contact. Although at initial contact the sphere and sinusoidal case are very similar and can both be described by the classic elastic Hertz contact case, once the contact is pressed past a certain range of deformation the two cases are very different. The model produces equations which can be used to approximately relate the area of contact to the contact pressure for elasto-plastic sinusoidal contact. The equations are fit to the FEM results and existing elastic solutions of sinusoidal contact. An empirical expression for the average pressure which causes complete contact between elasto-plastic sinusoidal contacts is also provided.     

Computational model of asperity contact for the prediction of UHMWPE mechanical and wear behaviour in total hip joint replacements

The effect of sliding friction on the size of yielding region in the ultra high molecular weight polyethylene asperity in contact with metal was investigated. The main objective of this work was to gain an understanding of wear particle generation mechanism from the two-dimensional finite element model. To assess the influence of the parameters of interest, different friction coefficients and loading conditions were used in the numerical simulations. Results from the finite element analysis show that the increase of the yielding region is strongly influenced by the friction coefficient and the rise in the tangential force, which is related to the generation of wear particles. Finite element wear particle generation model, based on strain discontinuities, was therefore proposed. The results obtained in this study can lead to the development of an accurate finite element particle generation model that would be of use in the assessment of an artificial implant performance and their development.