Particles as Transport Carriers in CMP Slurries
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Particles as Transport Carriers in CMP Slurries Daniela White1, John Parker1, Shuyou Li2, and Vinayak Dravid2 1 Cabot Microelectronics, 870 N. Commons Dr., Aurora, IL, 60504 2 NUANCE, Northwestern University, Evanston, IL, 60208 ABSTRACT Nanoparticles provide multiple functionalities (chemical, mechanical) to the performance of CMP slurries. In this presentation we will highlight the significance of slurry abrasives as surface modified nanoparticles/chemical carriers, able to directly participate and control the metal oxidation/removal mechanism, removal rates and other polishing characteristics. We will discuss two relevant examples, both involving fumed silica as the carrier particle in two different low pH slurries of variable complexities in terms of design (with/without particles surface modifiers) and performance requirements for tungsten CMP. We will provide a complex variety of analytical evidence (TEMEELS, SEM, FT-IR, GPC, cyclic voltammetry, MS-TOF) in order to support the proposed mechanism of ìchemically activated fumed silicaî, in its natural (no interactions with organic additives in the slurry) and surface modified form (in-situ interactions with organic additives), as a carrier of selective slurry components with enhanced chemical activity, that ultimately controls the tungsten CMP mechanism and the ability of the slurry to efficiently and predictably remove the oxidized tungsten film formed at the wafer surface. INTRODUCTION Chemical Mechanical Planarization (CMP) of tungsten is commonly and practically accomplished using low pH, high solids aqueous slurries comprising different abrasives (colloidal and fumed silica, alumina, other inorganic oxides), organic and inorganic additives and at least one oxidizing reagent that is highly reactive in redox chemistry involving W(0) oxidation to W(IV) or W(VI) oxides/acids/salts. Several commercial tungsten slurries are based on fumed silica as the abrasive, Fe(III) and hydrogen peroxide (H2O2) as oxidizing reagents and/or a cationic polyelectrolyte which can function both as templating reagent for tailoring mesoporous precipitated WO3 during polishing [1], and as removal rates enhancer, as well as having a substantial contribution in reducing dishing and erosion at the wafer surface [2]. Since strong interactions between silica nanoparticles and metal cations (e.g. Fe3+) or organic polycations adsorbed at the particles surface seem to play an important role in W polishing, we decided to study, identify and describe the complex nature of these interactions in CMC slurries for a better understanding of how they ultimately affect the W oxidation kinetics, removal rates and other post-polishing important surface characteristics (dishing, erosion).
EXPERIMENTAL Fumed silica used in this study had a mean particle size of 120 nm (Horiba LA910). Cationic polyelectrolyte (CPE) used in this study was a high molecular weight water-soluble polymer with Mn = 7,311, Mw = 11,146, PDI = 1.52. Fe(NO3)3 (10% aqueos solution) and Fe3+ complexing reagent (CA, car
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