Dopant stabilization after high-temperature thermal spike annealing was investigated. 0.2 keV B implanted silicon wafers were thermally spike-annealed at 1100degreesC, followed by furnace annealing between 550 and 750degreesC to study their stabilities. We have observed the anomalous diffusion of boron during the post-spike furnace annealing in nitrogen ambient. It is indicated that p(+)/n junctions formed by ultralow energy B implant and spike annealing are not stable during subsequent thermal processes. By adding a megaelectronvolt (MeV) implantation after spike annealing, the B profile shows a negligible diffusion during the following furnace annealing at 750degreesC. The concept of MeV implantation can be used as a method to overcome instability of the shallow junction. (C) 2003 The Electrochemical Society.