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 chemical-vapor-deposited silicon oxides is identified in this study. As a higher SiH4N2O gas flow rate ratio is employed during the deposition process, the silicon-to-oxygen atomic ratio and the dangling bond density both increase. 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≡O3 bonds (E′ centers) to ⋅Si≡Si3 bonds, which eventually cluster together and precipitate out from the oxide network to form the Si nanocrystals. The size of these Si nanocrystals falls within the range of 30–50 nm, as observed by high-resolution transmission electron microscopy. The formation of these nanocrystals inside the silicon-rich oxides results in a lower film density, a tensile stress component, and a higher wet etching rate, even under the ion bombardment provided by the rf bias power during deposition. The underlying mechanisms for the formation of these Si nanocrystals from the silicon oxide will be proposed.