Oxide Powders for Chemical Mechanical Polishing Produced by Chemical Vapor Synthesis
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Oxide Powders for Chemical Mechanical Polishing Produced by Chemical Vapor Synthesis H. Sieger*, M. Winterer*, U. Keiderling*# and H. Hahn* *Thin Films Division, Institute of Materials Science, Darmstadt University of Technology, Petersenstr. 23, D-64287 Darmstadt, Germany, #permanent address: Hahn-Meitner-Institut, Glienicker Str. 100, D-14103 Berlin, Germany. Abstract Ultrafine silica, alumina and doped alumina/silica powders have been produced by Chemical Vapor Synthesis (CVS). Primary particle sizes from 3.5 to 12.4 nm have been achieved. Agglomerate sizes ranging from approx. 10 to 150 nm have been achieved in aqueous dispersions.
Introduction Ultrafine oxide powders (1-100 nm) have a great potential for applications in Chemical Mechanical Polishing (CMP). Recently, we developed a gas phase process called Chemical Vapor Synthesis [1,2]. In this process volatile metalorganic precursors are decomposed in a hot wall reactor at reduced pressures forming nanoscaled particles. The process is scaleable and has a well defined reaction zone in which temperature, pressure and mass flows are controlled and reproducible. The modular design of the reactor enables the production of doped and coated powders. The dispersability, which is critical for CMP application, of nanoscaled zirconia could be improved by coating the individual nanoparticles with alumina [3]. This work focuses on the synthesis and characterisation of ultrafine silica, alumina and doped alumina/silica powders and dispersions. It is a starting point for further investigations on polishing performances of these synthesized powders.
Experimental The modular CVS-Reactor consists of a precursor delivery system, a hot wall tubular reactor and a thermophoretic collection zone (Figure 1). The main process steps are: evaporation of the metalorganic precursors, thermal decomposition, formation of ultrafine particles in the hot reaction zone and thermophoretic collection of the particles. The silica precursor tetraethylorthosilicate (TEOS) was evaporated at 100 °C and mixed with a He gas flow in a Liquid Precursor Delivery System (MKS), that controls both the liquid precursor flow rate and the evaporation temperature. The alumina precursor was evaporated by bubbling a controlled He gas flow through liquid aluminiumtrisecbutylate (ASB) which was held at a constant temperature. An additional O2 flow was mixed with the precursor vapor prior to the hot reaction zone assuring complete oxidation to stochiometric silica and alumina. For the production of doped alumina/silica both vapors were mixed prior to the entry of the hot wall reactor.
M2.5.1
T He
MFC
ASB alumina tube
controller
p O2
MFC
He
MFC
valve vakuum pump
reaction zone
LPDS TEOS
thermophoretic collector resistance furnace heating
T
Figure 1: CVS reactor used for synthesis of alumina, silica and doped alumina/silica nanoparticles. The mixed flow of precursor vapor, He and O2 was then delivered to the hot reaction zone consisting of an alumina tube with an inner diameter of 20 mm heated by a resi
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