Highly Dispersed Fe3+-Substituted Colloidal Silica Nanoparticles for Defect-Free Tungsten Chemical Mechanical Planarization

Abstract

Silica nanoparticles (NPs) are used as abrasives for tungsten chemical mechanical planarization (CMP) at acidic pH. However, the use of silica NPs at pH near their isoelectric point remains a problem because agglomeration due to low surface charge leads to defects on the tungsten surface during CMP. Herein, we report a simple strategy to increase the surface charge of silica NPs at acidic pH for defect-free tungsten CMP. The isomorphic substitution of Si4+ by Fe3+ ions on the surface of silica NPs by hydrothermal reaction led to a pH-independent permanent negative surface charge, which increased as the concentration of substituted Fe3+ ions increased. At acidic pH, the increased negative surface charge of Fe3+-substituted silica (Fe-silica) NPs resulted in a reduction in the number of agglomerated large particles relative to that of pure silica NPs. As a result, highly negatively-charged Fe-silica NPs showed high performance in the reduction of defect count on the tungsten surface after CMP.