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We present a systematic study on redistribution of B, P, and As in silicon-on-insulator (SOI) during RTA as the top silicon layer is scaled down to /spl sim/0.05 um. New observations are reported on dopant diffusion in the thin SOI layers compared with bulk Si and its dependence on silicon thickness, initial doping distribution, and anneal conditions. It is shown, for the first time, that pile-up of boron occurs in the thinner SOI near the buried oxide (BOX) interface during inert RTA, while phosphorus is depleted. We show that the amount of each dopant inside the SOI layers changes due to interface transport as Si layer thickness is reduced. Theoretical models of the BOX effects are tested experimentally by using high resolution X-ray diffraction and direct-contact rapid thermal heating.