We have studied the process of buried oxide formation as a function of implantation and annealing conditions. Concentrating on substoichiometric implants (<1×1018O/cm2), we varied the implantation energies from 100 keV to 1 MeV. Some apparent precipitation of SiO2similar to that observed in Czochralski‐grown silicon occurs on implantation. This means that formation of the buried oxide layer and perfection of the overlying crystalline Si layer depend more strongly on the substrate temperature during the implant than on the annealing temperature.