Experimental and Theoretical Studies on Particle Dynamics in Chemical Mechanical Polishing (CMP) Process

由于CMP过程中使用的浆料含有几种化学添加剂，在某些条件下，浆料中的颗粒可能在抛光过程之前和过程中聚集并粘附在晶圆和/或衬垫表面。这种聚集会导致晶圆表面出现划痕等缺陷。因此，为了获得良好的局部和全局平面性而不发生故障，确定无团聚的稳定浆料的最佳制备条件是很重要的。此外，在此过程中，如何正确地了解聚集体的大小和形状，即在晶圆和衬垫之间的有限剪切流动中，颗粒的聚集和破坏行为，也是一个关键问题。本文的目的是在实验和理论上研究两个平行壁面之间的简单剪切流中的粒子动力学。研制了一种激光共聚焦扫描显微镜实验装置，对平行圆盘间的剪切流进行了原位观察。实验中，将直径为2μm的聚苯乙烯颗粒悬浮在NaCl水溶液中。我们可以观察到聚集体在剪切流中的旋转行为。结果表明，剪切速率越低，骨料粒径越大。此外，随着两个圆盘之间距离的增加，聚集体的平均面积增加。建立了剪切流中颗粒聚集过程的数学模型。在该模型中，我们考虑了流体动力阻力、颗粒与颗粒、颗粒与壁面的相互作用以及胶体的相互作用。随着两平行墙间距的增大，骨料粒径增大，与墙接触的骨料数量减少。当颗粒与壁之间的胶体相互作用小于颗粒与壁之间的胶体相互作用时，团聚体的粒径增大，与壁接触的团聚体数量减少。少

Since the slurries used in the CMP process contain several chemical additives, under certain conditions, the particles in the slurries may aggregate and adhere to the wafer and/or pad surfaces before and during the polishing process. Such aggregations result in defects such as scratches on the wafer surface. Therefore, for performance of good local and global planarity without failures, it is important to determine the optimal conditions for preparation of stabilized slurries without aggregations. In addition, the acquirement of correct knowledge about the size and shape of aggregates during the process, i.e., the aggregation and breakage behaviors of particles in a confined shear flow between the wafer and the pad, is also a critical issue. The aim of the present work is to investigate experimentally and theoretically the particle dynamics in a simple shear flow confined between the two parallel walls.We developed an experimental apparatus with a confocal scanning laser microscope for … More in-situ observation of the particle dynamics in a shear flow between two parallel disks. In experiment, polystyrene particles of 2μm in diameter were suspended in a NaCl aqueous solution. We could observed the rotational behavior of aggregates in a shear flow. As a result, it was found that lower shear rate results in larger size of aggregates. In addition, as the distance between two disks increased, the average area of aggregates increased.We constructed a mathematical model for particle aggregation process in a shear flow. In this model, we considered the hydrodynamic drag, the interaction between particle and particle, and particle and wall, and colloidal interactions. As the distance between two parallel walls increased, the size of aggregates increased and the number of aggregates contacted with wall decreased. When the colloidal interaction between particle and wall was smaller than that between particle and particle, the size of aggregates increased and the number of aggregates contacted with wall decreased. Less