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Unformatted text preview: Journal of Nanoparticle Research 3: 455–467, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands . Describing hydrodynamic particle removal from surfaces using the particle Reynolds number G.M. Burdick, N.S. Berman and S.P. Beaudoin ∗ Department of Chemical and Materials Engineering, Arizona State University, Box 876006, Tempe, AZ 85287 6006, USA; ∗ Author for correspondence (Tel.: (480)965-7769; Fax: (480)965-0037; E-mail: firstname.lastname@example.org) Received 15 February 2001; accepted in revised form 19 May 2001 Key words: particle adhesion, hydrodynamic detachment, chemical–mechanical planarization (CMP), post-CMP cleaning, particle Reynolds number, van der Waals forces Abstract The fundamental processes related to the removal of fine particles from surfaces in a hydrodynamic flow field are not adequately understood. A critical particle Reynolds number approach is proposed to assess these mechanisms for fine particles when surface roughness is small compared to particle diameter. At and above the critical particle Reynolds number, particle removal occurs, while below the critical value, particles remain attached to a surface. The system under consideration consists of glass particles adhering to a glass surface in laminar channel flow. Our results indicate rolling is the removal mechanism, which is in agreement with the literature. Theoretical results of the critical particle Reynolds number model for rolling removal are in general agreement with experimental data when particle size distribution, particle and surface roughness, and system Hamaker constant are taken into account. Introduction Understanding particle adhesion and removal is important for many industrial processes, especially for semiconductor device fabrication. This is true for two reasons, (1) semiconductor devices and integrated cir- cuits must have uniform electrical characteristics and high reliability, which means particle contamination must be kept to a minimum, and (2) as feature size continues to decrease, methods to remove increas- ingly smaller particles will be required (Amick, 1976; Kern, 1990; Heroux et al., 1996). Though semicon- ductor device fabrication requires ultra-clean environ- ments and surfaces, particle-producing processes like chemical–mechanical planarization (CMP) are neces- sary at certain stages of device fabrication. CMP leaves tens of thousands of sub-micron and micron-size parti- cles on a wafer surface, which must be removed before further processing or they will cause defects in finished integrated circuits (Roy et al., 1995; Liu et al., 1996; de Larios et al., 1997; Murkami, 1997; Hymes et al., 1998). Post-CMP cleaning involves either the application of an external force to a particle to overcome its adhe- sion force or the application of a brief polish or etch to remove chemisorbed or partially embedded mate- rials. Efficient particle removal is extremely difficult because of the wide variety of particulate contaminants and strong adhesion forces. Studies indicate that a com-and strong adhesion forces....
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