Effect of epitaxial realignment on the leakage behavior of arsenic-implanted,as-deposited polycrystalline Si-on-single crystal Si diodes

When dopants are indiffused from a heavily implanted polycrystalline silicon film deposited on a silicon substrate, high thermal budget annealing can cause the interfacial “native” oxide at the polycrystalline silicon-single crystal silicon interface to break up into oxide clusters, causing epitaxial realignment of the polycrystalline silicon layer with respect to the silicon substrate. Anomalous transient enhanced diffusion occurs during epitaxial realignment and this has adverse effects on the leakage characteristics of the shallow junctions formed in the silicon substrate using this technique. The degradation in the leakage current is mainly due to increased generation-recombination in the depletion region because of defect injection from the interface.     

Ultra-Shallow junctions in silicon using amorphous and polycrystalline silicon solid diffusion sources

The inter-dependence of diffusion behavior and grain microstructure in amorphous silicon/polysilicon-on-single crystal silicon systems has been studied for rapid thermal and furnace annealing for P and BF₂ implants. It is found that the changes of microstructure during annealing play a major role in determining the diffusion profiles in the substrate as well as in the polysilicon layer. For P doping, a drive-in diffusion results in a much larger grain microstructure for as-deposited amorphous silicon than for as-deposited polysilicon, which leads to the formation of shallower junctions in the substrate for the first case. For B doping, there is little difference in the final microstructure and junction depth between the two cases. The P and B junctions formed in the substrate are found to be laterally very uniform in spite of expected doping inhomogeneities due to polysilicon grain boundaries both for as-deposited amorphous silicon diffusion sources and for as-deposited polysilicon diffusion sources.     

A physically based phenomenological model using boltzmann-matano analysis for boron diffusion from polycrystalline Si into single crystal Si

The diffusion of boron in single crystal Si from a BF₂-implanted polycrystalline Si film deposited on single crystal Si has been accurately modeled. The effective diffusivities of boron in the single crystal Si substrate have been extracted using Boltzmann-Matano analysis and the new phenomenological model for B diffusivity has been implemented in the PEPPER simulation program. The model has been implemented for a range of furnace anneal conditions (800 to 950°C, from 30 min to 6h) and implant conditions (BF₂ doses varied from 5×10¹⁵ to 2×10¹⁶ cm⁻² at 70 keV).