IRON SOLUBILITY IN HIGHLY BORON-DOPED SILICON

We have directly measured the solubility of iron in high and low boron -doped silicon using instrumental neutron activation analysis. Iron so lubilities were measured at 800, 900, 1000, and 1100 degrees C in sili con doped with either 1.5 x 10(19) or 6.5 x 10(14) boron atoms/cm(3). We have measured a greater iron solubility in high boron-doped silicon as compared to low boron-doped silicon, however, the degree of enhanc ement is lower than anticipated at temperatures >800 degrees C. The de creased enhancement is explained by a shift in the iron donor energy l evel towards the valence band at elevated temperatures. Based on this data, we have calculated the position of the iron donor level in the s ilicon band gap at elevated temperatures. We incorporate the iron ener gy level shift in calculations of iron solubility in silicon over a wi de range of temperatures and boron-doping levels, providing a means to accurately predict iron segregation between high and low boron-doped silicon. (C) 1998 American Institute of Physics. [S0003-6951(98)01936- 6].