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

2001 Fiscal Year Final Research Report Summary

• Project/Area Number: 11450288
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: 化学工学一般
• Research Institution: Tohoku University
• Principal Investigator: HOZAWA Mitsunori Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Professor, 多元物質科学研究所, 教授 (70005338)
• Co-Investigator(Kenkyū-buntansha): KUBO Masaki Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Research Associate, 大学院・工学研究科, 助手 (50323069) ; TSUKADA Takao Tohoku University, Institute of Multidisciplinary Research for Advanced Materials, Associate Professor, 多元物質科学研究所, 助教授 (10171969)
• Project Period (FY): 1999 – 2001
• Keywords: CMP / Particle Dynamics / Polystyrene particles / Numerical Simulation / DEM / In-situ Observation / Laser Microscope

Research Abstract

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 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.