PRODUCTION OF NANOMETRIC PARTICLES IN RADIO-FREQUENCY GLOW-DISCHARGESIN MIXTURES OF SILANE AND METHANE

The formation of silicon particles in rf glow discharges has attracted attention due to their effect as a contaminant during film deposition or etching. However, silicon and silicon alloy powders produced by pl asma-enhanced chemical vapor deposition (PECVD) are promising new mate rials for sintering ceramics, for making nanoscale filters, or for sup porting catalytic surfaces. Common characteristics of these powders ar e their high purity and the easy control of their stoichiometry throug h the composition of the precursor gas mixture. Plasma parameters also influence their structure. Nanometric powders of silicon-carbon alloy s exhibiting microstructural properties such as large hydrogen content and high surface/volume ratio have been produced in a PECVD reactor u sing mixtures of silane and methane at low pressure (<1 Torr) and low frequency square-wave modulated rf power (13.56 MHz). The a-Si1-xCx:H powders were obtained from different precursor gas mixtures, from R=0. 05 to R=9, where R=[SiH4]/([SiH4]+[CH4]). The structure of the a-Si1-x Cx:H powder was analyzed by several techniques. The particles appeared agglomerated, with a wide size distribution between 5 and 100 nm. The silane/methane gas mixture determined the vibrational features of the se powders in the infrared. Silicon-hydrogen groups were present for e very gas composition, whereas carbon-hydrogen and silicon-carbon bonds appeared in methane-rich mixtures (R<0.6). The thermal desorption of hydrogen revealed two main evolutions at about 375 and 660 degrees C t hat were ascribed to hydrogen bonded to silicon and carbon, respective ly. The estimated hydrogen atom concentration in the sample was about 50%. (C) 1996 American Vacuum Society.