Effect of oxide thickness on the low temperature (≤400 deg. C) growth of cone-shaped silicon nanowires

Au-catalyzed cone-shaped silicon nanowires (CSiNWs) were grown at low temperature (≤400 deg. C) using plasma-enhanced chemical vapor deposition (PECVD). Thin (≤3 nm) Au films were evaporated and annealed on a thermally oxidized (0-80 nm) silicon substrate so as to form Au silicides, which, under a supply of SiH4, catalyzed the growth of CSiNWs. We have found that the thickness of thermally grown SiO2 and silicidation annealing critically affect the growth behavior of CSiNWs based on an analysis of areal CSiNW densities. X-ray photoelectron spectroscopy (XPS) and real-time in situ ellipsometry were used to characterize the silicidation behavior of a thin Au film annealed with different oxide thicknesses. Interestingly, the optimal condition (10-nm-thick oxide), which showed a maximum areal density of CSiNWs, revealed the highest integration intensity of Au-Si-O (or Au-O-Si) bonding units rather than the Au-Si bonding, as generally expected. The Au-Si-O (or Au-O-Si) bonding is believed to transform into an Au-Si bonding unit during the dissociation of SiH4 for nanowire growth