Evaluation of Monodispersed Silica Particles and Ceria Coated Silica Particles for Chemical Mechanical Polishing
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Evaluation of Monodispersed Silica Particles and Ceria Coated Silica Particles for Chemical Mechanical Polishing Zhenyu Lu, Seung-Ho Lee, Egon Matijević and S. V. Babu Departments of Chemistry and Chemical Engineering Center for Advanced Materials Processing Clarkson University, Potsdam, NY 13699 Abstract The properties of abrasive particles play a key role in chemical mechanical polishing (CMP). This study used well-defined dispersions of uniform particles, including spherical silica of varying diameters to polish Cu films and silica cores coated with nanosized ceria particles to polish oxide films. It was shown that the total surface area of the silica abrasives in the slurry controlled Cu material removal rate. However, pH, solid content, and particle size of ceria coated silica abrasives did not have a strong correlation to the removal rate of oxide films. 1. INTRODUCTION Historically, CMP slurries were developed using off-the shelf abrasives, because of their ease of availability, followed by optimization of the polish tool and pad designs and slurry chemistry to meet process needs [1–3]. For example, the abrasives used – alumina, silica, ceria, etc. – are generally polydispersed and usually consist of irregularly shaped particles. While several theories have been proposed to describe the interaction of the abrasive particles with the film surface that is being planarized [4], there is little experimental or theoretical information on the effects of the size, shape, and other parameters of abrasive particles. Depending on the size and structural properties of the abrasive particles, different mechanisms may be operational in the CMP process. It is, therefore, of interest to carry out planarization experiments using slurries consisting of uniform particles of different modal sizes and other properties. The purpose of this research has been to clarify some of these questions by carrying out CMP experiments with slurries consisting of monodispersed particles of different properties, including spherical silica of varying diameters and silica cores coated with nanosized ceria particles. Dispersions containing these abrasive particles were prepared at different weight concentrations in DI water in the presence of various slurry chemistries at different pH values and used to polish Cu discs and blanket films of Cu and of SiO2 on 4 inch silicon wafers. It was found that the total surface area of the silica particles in the slurry controlled the material removal rate in pure silica slurries for Cu. In contrast, the pH value, the solid content, and the particle size of ceria coated silica abrasives did not have a strong correlation to the removal rate of the oxide films. 2. EXPERIMENTAL 2.1. Silica Particles Five samples of monodispersed silica particles of different diameters (with a range from 50 nm to 400 nm) were supplied by the Nissan Company, illustrated in the I3.7.1 Downloaded from https://www.cambridge.org/core. Columbia University - Law Library, on 15 Jan 2020 at 23:43:03, subject to the Cambridge Core terms of
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