This paper summarises current understanding of phosphorus diffusion gettering (PDG) of metal impurities in silicon. One mechanism that is generally operative is the enhanced solubility of substitutionally dissolved metal species at high P-doping levels due to the Fermi-level effect and pair formation with electrically active phosphorus. For those impurities which are predominantly dissolved on substitutional sites also in intrinsic silicon, an additional gettering effect results from the self-interstitial super-saturation in the intrinsic bulk with respect to the highly P-doped area. Experimental results for cobalt and platinum in silicon lead to the conclusion that silicide formation in the highly P-doped area close to SiP precipitates or directly at the interface to the phosphor-us silica glass (PSG) is a very effective mechanism beyond segregation. The role of electrically inactive phosphorus, self-interstitial injection and PSG growth in this regime is highlighted.

Analytical, high-resolution and scanning transmission electron microscopy as well as secondary ion mass spectroscopy has been used to study phosphorus diffusion gettering of platinum in silicon at 1100 degreesC. These techniques consistently show that a thin layer of PtSi islands forms directly beneath the interface between the phosphorus silica glas and the silicon which accounts for about 50% of the gettered platinum atoms.

Various techniques of transmission electron microscopy as well as secondary ion mass spectroscopy have been used to study phosphorus diffusion gettering of platinum in silicon under conditions of high phosphorus concentrations. PtSi precipitates have been observed directly beneath the interface between silicon and the phosphorus silica glass formed on top of the wafers. Gettering at 920 °C leads to the formation of isolated PtSi particles adjacent to SiP precipitates whereas an almost closed silicide film is observed at 1100 °C in the absence of SiP precipitates. For the latter conditions we observe a broad band of extrinsic faulted loops which establish a supersaturation of silicon self-interstitials in the highly phosphorus doped layer. The results support previous modeling of the precipitation mode of phosphorus diffusion gettering which assumes that local currents of silicon self-interstitials may lead to silicide precipitate formation.

We report recent experimental results on impurity gettering in silicon obtained by combining macroscopic techniques like tracer measurements or SIMS and microscopic investigations using Mossbauer spectroscopy or analytical and high-resolution electron microscopy. The latter provide insight into structural properties of gettering sites while the former allow to measure the redistribution kinetics of metal impurities during gettering which provides indispensible informations for quantitative simulations of gettering processes.