Kinetic aspects of solid-phase epitaxial growth of amorphous Si

We have studied solid-phase transport phenomena in the thin-film system which consists of a Pd₂Si layer sandwiched between an underlying Si single crystal substrate and a top layer of amorphous Si. After a 475°C annealing, the Pd-silicide layer moves toward the surface on the sample as the single crystal substrate grows with a corresponding consumption of the amorphous Si layer. Using MeV ⁴He⁺ backscattering spectrometry, we find that the time dependence of the transport process has rather different rates for samples prepared at different times, varying by up to three orders of magnitude. By monitoring the rate under various modified experimental conditions, we have established that the transport rate depends on the vacuum deposition of the amorphous Si layer during sample preparations. Specifically, the rate was found to correlate with the carbon contamination (≲3 at.%) which was detected in the amorphous Si layers by Auger electron spectroscopy (AES) and secondary ion mass spectroscopy (SIMS). Relatively "carbon-free" depositions were carried out and unique features were indeed observed on these samples.