Donald Lee Black

Phase Transformations Induced by Arsenic Implants into Silicon

Micro-Raman spectroscopic investigations of arsenic-implanted silicon show lines characteristic of silicon crystallites even at implant doses above the amorphization threshold. The intensity and frequency of occurrence of the lines increase with the implanted dose. Polarization/orientation Raman studies indicate the crystallites are silicon in the hexagonal phase (Si-IV) and silicon in the diamond phase (Si-I). The latter are oriented differently than the substrate silicon. Monte Carlo simulations of the arsenic ion energy loss and published molecular dynamics studies suggest that each arsenic ion deposits sufficient energy to locally melt the silicon lattice. This is taken as the basis of the present attempt to explain the origin of the crystallites. A one-dimensional numerical model is developed to determine the time scale for the liquid silicon to solidify. The effect of amorphous silicon on the solidification is also investigated.

Phosphorus Diffusion in Polycrystalline Silicon: Monte Carlo Simulation of Experimental Diffusion Profiles

Phosphorus ions were implanted into silicon layers deposited by low pressure chemical vapor deposition onto thermally oxidized silicon substrates. Thermal anneals diffused the phosphorus and the resulting depth profiles were determined by secondary-ion mass spectrometry (SIMS). Transmission electron microscopy shows that the polysilicon layers have a multi-layer pattern of grains. The phosphorus profiles are fit by a Monte Carlo simulation technique that includes both grain and grain-boundary diffusion. The grain-boundary diffusion coefficient is found to be thermally activated with an activation energy of 3.3 eV.