p-CVD For Nano-Powders Formation of Silicon Carbide

Abstract

In order to obtain a large amount of highly pure, and nano-size ultra fine powders (UFP) of silicon carbide, much kind of trials have been performed. The presentation is a summery of molar ratio effects on product SiC manufactured via the plasma CVD method. Synthetic conditions are summarized as follows; frequency=4 MHz, maximum out-put power=15 kW, reactants=monosilane+methane/ethane, plasma working gas=argon, and sheath gas=argon. Powders were characterized to be ultra fine (UHP, 5∼100 nm), ultra pure (each cation impurity: ppb level), and spherical shape with a very narrow particle size distribution. Silicon carbide UFP were covered their surfaces with amorphous carbon, when UFP were prepared under excess carbon condition. Temperature and reaction during the formation of silicon carbide were monitored in-situ by measuring the emission spectra from plasma flame using an optical analyzer. The present experimental conditions established local thermodynamic equilibrium (LTE). Temperature distribution in the plasma flame and near the flame was consisted with that expected from plasma reactor design. In the region of 200∼550 nm, optical emission spectra of neutral Si, C, Ar, H, H₂, and C₂ were observed. As C/Si molar ratio of the reactant gases was increased, both of Si and C spectra became weak. Radial distributions of spectral intensities of Ar, Si, and C after Abel inversion showed that Si and C atoms were mainly excited at center of the plasma while Ar atoms were mainly excited at off-axis position. These obtained results were attributed to plasma reactor design.