IRON DETECTION IN THE PART PER QUADRILLION RANGE IN SILICON USING SURFACE PHOTOVOLTAGE AND PHOTODISSOCIATION OF IRON-BORON PAIRS

The photodissociation of iron-boron pairs in p-type silicon produces l ifetime killing interstitial iron and may be combined with noncontact surface photovoltage (SPV) measurement of the minority carrier diffusi on length to achieve fast detection of iron. We found that, for iron c oncentrations ranging from 8 X 10(8) to 1 X 10(13) atoms/cm3, the pair dissociation using a white light (10 W/cm2) was completed within 15 s . Surface recombination was a major rate limiting factor. Passivation of the surface enhanced the rate by as much as a factor of 20. The pho todissociation rate increased with increasing temperature, however, th e increase was smaller than that of the thermal dissociation rate. The se characteristics are consistent with a previously proposed recombina tion enhanced dissociation mechanism. For practical iron detection, it is important that the detection limit of the approach is close to one part per quadrillion.