Iron gettering in silicon using doped layers and bulk defects

The removal of iron impurities to desired regions in silicon wafers has been studied using phosphorus and boron doped layers and bulk defects as gettering sites. Techniques to remove metal impurities, so-called gettering techniques, are needed for improving the performance of both the microelectronic and photovoltaic silicon devices, although the desired location of impurities may be different in various applications. In this work, both separate and simultaneous influences of the doped layers and bulk defects on the gettering behaviour of iron, e.g. the gettering efficiency and gettering mechanisms, were investigated. The phosphorus diffusion gettering studies at low temperatures enabled the determination of a more accurate segregation coefficient for iron between a phosphorus diffused layer and bulk silicon. Comparison between the phosphorus diffusion gettering experiments and similar experiments with boron showed that boron diffusion gettering can in some cases be nearly as effective as the phosphorus diffusion gettering. The gettering studies with implanted boron layers revealed that the gettering occurs also by precipitation, not only by segregation. Competitive gettering between an implanted boron layer and bulk defects was investigated using specially designed gettering anneals. It was found that depending on the desired location of iron in silicon wafers in different applications, iron can be collected either to the doped layers or the bulk defects. The gettering anneals were also applied to a microelectronic device process and their effect on the electronic device parameters was evaluated. These results contribute to the understanding of iron behaviour in silicon. Thus, they can help when designing the gettering anneals both for microelectronic and photovoltaic fabrication processes.