Effects of defect evolution during rapid thermal annealing (RTA) on the anomalous diffusion of ion implanted boron have been studied by implanting silicon ions prior to boron implantation with doses ranging from 1 × 1014cm−2 to 1 × 1016cm−2 at energies ranging from 20 to 150 KeV into silicon wafers. Diffusion of boron atoms implanted into a Si preamorphized layer during RTA is found to be anomalous in nature, and the magnitude of boron displacement depends on the RTA temperature. While RTA of preamorphized samples at 1150°C shows an enhanced boron displacement compared to that in crystalline samples, a reduced displacement is observed in preamorphized samples annealed by RTA at 1000°C. In addition, low dose pre-silicon implantation enhances the anomalous displacement significantly, especially at high RTA temperatures (1 150°C). Finally, the anomalous diffusion is found to depend strongly on the defect evolution during RTA.