A fundamental analysis of abrasive slurry hydrodynamics in Chemical-Mechanical Polishing (CMP)

化学机械抛光广泛应用于微电子和半导体行业。表面薄膜(通常只有纳米厚)通过将芯片或晶片暴露在流动的浆液中来去除，浆料由悬浮在化学反应溶液中的惰性磨粒组成。化学成分和磨粒协同作用去除材料的表层。化学机械抛光的两个考虑因素是材料去除速率(或MRR)和表面质量(即粗糙度、划痕、沟槽、凹坑、不均匀的材料去除必须最小化)。MRR和表面质量之间的平衡必须通过控制操作条件来实现，例如磨粒类型、抛光液化学成分、抛光压力和速度。发展化学机械抛光过程的机理模型的最大障碍之一是没有很好地了解将晶片与衬垫分开的薄膜中的浆料流动。剪切作用下磨粒聚集体的形成可能会导致非牛顿浆料行为，这将显著改变浆料的流动模式、衬垫和晶片之间的压力分布、晶片所经历的剪切应力以及与表面接触的颗粒的速度和浓度。拟议的研究计划将建立在首席研究员在实验多相流和机械磨损方面的专业知识的基础上。拟议的研究计划的主要目标是对化学机械抛光过程中的浆料流动流体动力学有一个新的、更严格的理解，并展示流体动力学、磨料颗粒特性、浆料流变学、垫块压力之间的相互联系以及它们对材料去除速度和表面质量等力学方面的综合影响。为了直接研究速度场和颗粒聚集之间的关系，将在一种新的定制设计的测试装置中同时进行微观PIV(粒子图像速度计)和浆体流变学测量。此外，还将使用小型化学机械抛光机进行额外的微型PIV实验，以便确定抛光事件期间衬垫粗糙度和磨粒聚集对速度场和剪切场的影响。最后，将测试为特定流体动力条件设计的聚合物复合颗粒，并将其设计为最大限度地减少剪切引起的聚集。该项目的结果将对所有化学机械抛光研究人员和从业者来说是无价的，因为浆液流动流体动力学确实是化学抛光动力学和机械磨损之间的纽带。微电子行业将能够使用这些结果来预测化学机械抛光性能并优化其操作，而无需使用当前的试错方法。**

Chemical-mechanical polishing (CMP) is widely used in the microelectronics and semiconductor industries. Surface films (often just nanometers thick) are removed by exposing the chip, or wafer, to a flowing slurry consisting of inert abrasive particles suspended in a chemically reactive solution. The chemical components and the abrasive particles work synergistically to remove a surface layer of material. The two considerations for CMP are material removal rate (or MRR) and surface quality (i.e. roughness, scratches, gouges, pits, nonuniform material removal must be minimized). A balance between MRR and surface quality must be attained by manipulating operating conditions, e.g. abrasive particle type, slurry chemistry, polishing pressure and velocity. One of the greatest impediments to the development of a mechanistic model of the CMP process is that the flow of the slurry within the thin film separating the wafer from the pad is not well understood. Formation of abrasive particle aggregates under shear can cause non-Newtonian slurry behavior, which will substantially alter the flow pattern of the slurry, the pressure distribution between the pad and the wafer, the shear stresses experienced by the wafer, and the velocity and concentration of particles coming into contact with the surface. The proposed research program will build upon the expertise of the principal investigator in experimental multiphase flows and mechanical abrasion. The main objective of the proposed research program is to develop a new and more rigorous understanding of the slurry flow hydrodynamics in a CMP process and to show the interconnectivity among hydrodynamics, abrasive particle properties, slurry rheology, pad pressure and their combined effect on the mechanical aspects of material removal rate and surface quality. Micro-PIV (particle image velicometry) and slurry rheology measurements will be made simultaneously in a novel, custom-designed test apparatus to study directly the relationship between velocity field and particle aggregation. Additional micro-PIV experiments will be done using a bench-scale CMP machine so that the effects of pad asperities and abrasive particle aggregation on the velocity and shear fields during a polishing event can be determined. Finally, polymer composite particles designed for specific hydrodynamic conditions, and designed to minimize shear-induced aggregation, will be tested. The results of this program will be invaluable to all CMP researchers and practitioners because the slurry flow hydrodynamics really are the link between the kinetics of chemical-based polishing and mechanical abrasion. The microelectronics industry will be able to use these results to predict CMP performance and optimize their operations without using the current trial-and-error approach.**