Effects of crystalline regrowth on dopant profiles in preamorphized silicon

The phenomenon of dopants migrating towards the surface against the concentration gradient may be useful to control junction depth for ultra-shallow profiles. We apply high-resolution SIMS - in combination with channelling Rutherford backscattering spectroscopy (RBS) - to reveal these subtle, yet highly significant changes in dopant profiles during or after solid phase epitaxial regrowth (SPER) in germanium-preamorphized silicon. We observe redistribution for shallow implantations of arsenic in preamorphized Si towards the surface during SPER. This is caused by segregation of As in front of the amorphous/crystalline (a/c) Si interface. Also for boron anomalous behavior has recently been reported, showing preferential migration towards the surface after crystalline regrowth at high concentrations for shallow implantation of BF ₂ ⁺ in crystalline Si or B ⁺ in Ge-preamorphized Si. Here, we investigate the time- and temperature-dependence of this phenomenon to clear up the mechanism for redistribution during crystalline regrowth. Redistribution of B is shown to occur only partly during SPER, most likely caused by segregation. Still, significant changes take place after completion of SPER during prolonged annealing. We propose that this is provoked by the locally steep concentration gradient of interstitials close to the surface after restoration of the crystalline structure.