High depth resolution medium energy ion scattering (MEIS) has been used to examine the influence of dynamic defect annealing on the damage formed in silicon substrates irradiated with ultralow energy ions (1 keV B+, 2.5 keV As+). Samples were implanted to doses ranging from 3 x 10(14) to 2 x 10(16) cm(-2) at sample temperatures -150/-120, 25, and 300 degreesC. For all doses examined, B implantation at 25 and 300 degreesC produced a near-surface disordered layer 3-4 nm thick. For doses above 1 x 10(15) cm(-2), a second, deeper damaged layer was resolved at a depth greater than the peak of the projected range (R-p) of the implanted ions. For irradiations at -150 degreesC, MEIS and transmission electron microscope studies indicated the formation of a continuous amorphous layer, extending from the deeper damage region to the surface. However, epitaxial regrowth of this layer was not complete after a 30 s anneal at 600 degreesC, being arrested near R-p by clusters containing B. The dependence of B transient enhanced diffusion on the implant temperature as observed in secondary ion mass spectrometry (SIMS) measurements is discussed in terms of different dynamic annealing conditions and the subsequent availability of interstitials that result from implantation at different temperatures. MEIS studies of the damage formation and rapid thermal annealing due to the heavier As implants, carried out at 2.5 keV to a dose of 1.5 x 10(15) cm(-2) at room temperature, confirmed that all the implanted As was trapped up to this dose. Following epitaxial regrowth at 600 degreesC for 20 s, approximately half of the As was observed to be in substitutional sites, consistent with the reported formation of AsnV clusters (n less than or equal to 4), while the remainder had segregated to and become trapped at the oxide interface. The damage produced by the As implant also displayed a strong dependence on the substrate temperature. Irradiation with 2.5 keV ions at -120 and 25 degreesC resulted in amorphous Si layers. In contrast, the damaged Si remained crystalline below the near-surface damage layer, when irradiated under the same conditions at 300 degreesC. Notably different As distributions were observed by SIMS in these samples following high temperature (900-1100 degreesC) annealing. The significant influence of complex defect agglomeration during ion bombardment on the subsequent annealing behavior is discussed.