PREPARATION OF NANOSCALE AMORPHOUS-SILICON BASED POWDER IN A SQUARE-WAVE-MODULATED RF PLASMA REACTOR

Nanoscale amorphous silicon powder was prepared in a specially designed plasma reactor, operating with square-wave modulation (SQWM) of the rf power at low pressure and low temperature. We have observed that in order to increase the powder yield, the process temperature must be lower and the pressure must be higher than that normally used for thin film deposition of a-Si: H in plasma enhanced chemical vapour deposition (PECVD). The square-wave modulation (SQWM) of the rf generator at low frequencies also improves the generation of powder. The experimental set-up was equipped with a quadrupole mass spectrometer (QMS), which directly analyses the species present in the plasma, and with a time- and spatially-resolved optical-emission spectroscopy system (OES). The characterization of the amorphous silicon powders by electron microscopy (TEM) and thermal desorption spectroscopy (TDS) of hydrogen provides the nanoscale powder size, microstructure and chemical composition.