Nanocrystalline silicon thin films prepared by low pressure planar inductively coupled plasma

The present work deals with the optimization of nano-crystalline silicon films at a low substrate temperature, using planar inductively coupled low pressure plasma CVD. The films have been produced at 300 °C using 1.5 sccm SiH4 diluted by 50.0 sccm H2 in the rf glow discharge reactor. By varying the gas pressure in the plasma from a very low (15 mTorr) to moderate value (200 mTorr), nC-Si films with high crystalline volume fraction, φc = 86%, could be prepared. The preferred crystallographic orientation of the silicon crystallites gradually changes from 〈1 1 1〉 towards 〈2 2 0〉 at an optimum pressure of 50 mTorr. At higher pressure, the material quality is deteriorated in terms of crystalline volume fraction, network density and surface roughness, due to intense etching by atomic hydrogen on the growing surface. While at very low pressure the precise development of the material is hampered due to very low density of the available precursors as well as low H+ and atomic H density. The nC-Si films with grain size down to 4-5 nm, having crystalline volume fraction φc ~36%, are produced by varying the rf-power applied to the substrate at an optimum gas pressure. The nC-Si films exhibit photoluminescence in the visible region. The blue shift of PL peak position with the decrease in grain size during lowering of rf power identifies the quantum confinement phenomena occurring in the silicon grains within nano dimension.