Dose rate dependence and time constant of the ion-beam-induced crystallization mechanism in silicon

The influence of dose rate on the ion-beam-induced crystallization of amorphous layers in silicon has been investigated. The amorphous layers were produced by self-ion implantation both in bulk silicon and in silicon on sapphire. Subsequent recrystallization was induced at 200 to 400 °C by Ne, Si, Ar, and Kr ion beams of 300 keV energy passing through the amorphous layers. Rutherford backscattering/channeling measurements showed that the regrowth rate decreased with increasing dose rate. This behavior was more pronounced for heavy ions where high dose rates and/or low temperatures could reverse the recrystallization and induce further amorphous growth of the layer. In this new solid-phase growth regime, the amorphous/crystalline interface moved inwards into the crystal in a manner similar to an epitaxial process. An intermittent beam experiment yielded a time constant for the ion beam induced crystallization mechanism of the order of 0.3 s. The time constant and a scaling law for different ions support a model where the planar growth is caused by the accumulation of divacancies in the interface region.