Formation and characteristics of silicon nanocrystals in plasma-enhanced chemical-vapor-deposited silicon-rich oxide

The formation of nanosized Si crystals in dual-frequency plasma-enhanced ch emical-vapor-deposited silicon oxides is identified in this study. As a hig her SiH4N2O gas flow rate ratio is employed during the deposition process, the silicon-to-oxygen atomic ratio and the dangling bond density both incre ase. The resulting oxide films contain more Si-H bonds and less Si-O and Si -O-H bonds, as determined from the Fourier-transform infrared spectra. The main type of charge defects in these oxides change from . Si=O-3 bonds (E' centers) to . Si=Si-3 bonds, which eventually cluster together and precipit ate out from the oxide network to form the Si nanocrystals. The size of the se Si nanocrystals falls within the range of 30-50 nm, as observed by high- resolution transmission electron microscopy. The formation of these nanocry stals inside the silicon-rich oxides results in a lower film density, a ten sile stress component, and a higher wet etching rate, even under the ion bo mbardment provided by the rf bias power during deposition. The underlying m echanisms for the formation of these Si nanocrystals from the silicon oxide will be proposed. (C) 2000 American Institute of Physics. [S0021-8979(00)0 8905-2].