Effect of Particle Interaction on Agglomeration of Silica-Based CMP Slurries
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Effect of Particle Interaction on Agglomeration of Silica-Based CMP Slurries. A. Sorooshian*, R. Ashwani, H.K. Choi, M. Moinpour, A. Oehler, A. Tregub# Intel Corporation, FMO-IMED # - corresponding author * - FMO technical intern; currently, a PhD student at California Institute of Technology Abstract Chemical Mechanical Planarization has become a method of choice for planarization of metal and oxide layers in microelectronics industry. A CMP process includes up to 16 variables that need to be controlled to achieve a stable CMP process [1]. One of the major variables in CMP is related to slurry compositions. In particularly, a uniform distribution of the sizes of the abrasive particle in slurry is crucial for a stable CMP performance. The agglomerates can be unstable, since their size depends on addition of chemical additives and shearing during the CMP process. In this work, the authors studied agglomeration of the fumed and colloidal silica-based slurries using dynamic rheometry, zeta potential tests, and an accusizer. Slurry viscosity, determined using a steady state rheometry, was correlated to the particle charge, characterized by zeta potential, and to the particle sizes obtained using the particle size analyzer. Additionally, rheometer was used for slurry shearing to study effect of shear on slurry characteristics. Particle agglomeration due to slurry shearing and storage was observed and corroborated using rheometry, zeta potential, and particle size measurements. 1. Introduction: Chemical Mechanical Polishing (CMP) has emerged as the premier technique for achieving both local and global planarization in silicon integrated circuit manufacturing. CMP is a complex chemical and mechanical process that depends heavily on numerous consumable parameters, such as slurry chemicals, slurry concentration, solution pH, abrasive type, charge, and size, percent of solid fraction, concentration of oxidizer, surfactants, corrosion inhibitor, buffering agents, etc.[1]. In this paper, we concentrated on study of the interactions between the slurry particles. Depending on this interaction, slurry particle may form agglomerates. Agglomeration of the abrasive particles during polishing (due to fluctuations in local particle, or concentration under dynamic processing conditions) may alter the slurry stability [2, 3] and polishing performance. It is known that, for a silica-based slurry, particle agglomerates of above 1 micron are the major cause of the wafer defects [1]. It was also shown [2] that even particle agglomerates, or, in other words, "soft" particle, adversely affect polishing performance. Normally, agglomerates in slurry are held together by the weak Van-der-Waals forces; due to mechanical shearing during a CMP process, the agglomerates can be destroyed. Generally, particle agglomeration in slurry should be avoided since they interfere with slurry filtering and blending in slurry-delivery systems, and cause large defects during polishing. In this paper, particle size agglomeration was studied for different ab
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