Composite Nanoparticles for Defectivity Reduction during CMP

The synthesis and characterization of nanoparticles comprising a polymer core and a silica shell, with and without a silane-coupling agent between the core and the shell, is presented in this paper. The first step in the nanoparticle synthesis is a “surfactant free” radical suspension polymerization in water of monomeric units of methylmethacrylate in the presence of methoxypolyethilene glycol methacrylate, as a comonomer, and 4-vynilpyridine. Vynilpyridine provides electrostatic stabilization in the form of functional basic amino groups located at the polymer surface, as confirmed by FTIR analysis. In the second step of the procedure, the Polymethyl Methacrylate (PMMA) spheres were mixed with silica spheres. Dynamic Light Scattering (DLS) measurements were used to correlate particle size to pH or ionic strength, while Electrophoretic Light Scattering (ELS) measurements revealed the dependency of the zeta potential on pH or ionic strength (I). Since the interaction between the abrasives and the wafer surface in the CMP process is expected to be dependent also on the particle morphology and structure of the polymer core, N2 adsorption isotherms on PMMA were taken to evaluate porosity and total surface area using the Brunauer-Emmett-Teller (BET) method.