Continuous hydrothermal processing of nano-crystalline particulates for chemical-mechanical planarization

A wide range of nano-crystalline, single and multi-component oxide/oxyhydroxide particulates, which may be potentially useful as abrasives for chemical-mechanical planarization (CMP) processes, have been produced using a novel, flow-through hydrothermal technology previously developed at the Pacific Northwest National Laboratory. The process, termed rapid thermal decomposition of precursors in solution (RTDS), converts aqueous feed stock solutions containing metal salts and other thermally activated reactants into suspensions or slurries of nano-crystals (with diameters of generally less than 30 nm) by continuous flow through a heated, high pressure reaction pipe (typically, 200-400 degrees C, 6000-8000 psi). Flow at pressure is maintained using a nozzle at the down-stream end of the reaction tube. Crystallite formation occurs during the solution's brief residence time (<30 a) in the reaction pipe. Control over crystalline phase and, in some cases, particle morphology call be tailored by selecting the appropriate feed chemistry and processing conditions. Using bench-scale equipment, RTDS is capable of producing nano-crystalline particulate material at rates of up to approximate to 500 gm of solids per hour. The RTDS processing and characterization of nanocrystalline zirconium-, titanium-, and iron-based oxide and oxyhydroxide particulates are reviewed.