A single crystal silicon layer on an insulator is a desirable structure for applications in electronics. One of the leading processes for achieving such a structure is the formation of a buried oxide layer in silicon by heavy dose oxygen implantation. Characteristics of this material have been reported for implantation by beam scanning. In this work we report on material prepared by wafer scanning at rates such that significant temperature cycling occurs during implantation, and we use TEM and Auger analysis to investigate the differences between these samples and others prepared by the conventional technique of beam scanning. For the implantation and annealing conditions used here, we find more oxygen in the top silicon layer in the case of wafer scanning, and the oxygen concentration increases after annealing at 1150°C for 2 hours, leading to a structure of precipitates throughout the single crystal top silicon layer. For beam scanning, the oxygen concentration decreases after annealing and achieves background levels near the surface, leading to a zone which is free of precipitates.