Deposition of nanocrystalline silicon films at room temperature

Bond rearrangements, facilitated by H insertion into strained Si-Si bonds have been shown to result in H-induced crystallization of amorphous silicon films. Whether such H-induced rearrangements can lead to synthesis of nanocrystalline films at room temperature has remained an open question. In this article, the authors demonstrate the deposition of thin films containing nanocrystals of silicon using inductively coupled SiH4/H-2 plasma at room temperature. Real time in situ spectroscopic ellipsometry and ex situ transmission electron microscopy revealed that the silicon nanocrystals nucleate below the surface, and grow beneath an amorphous silicon crust. This observation validates the hydrogen-induced crystallization model. Analysis of the crystal size distribution shows that the distribution depends on the growth duration rather than the substrate temperature. Observation of crystals as large as 100-150 nm at room temperature indicates that silicon nanocrystals not only nucleate but also grow substantially in the bulk even at room temperature.