Ion implantation of boron was substituted for the chemical deposition of boron in the manufacture of a bipolar integrated circuit. Then+p+test diodes were found to exhibit excessive reverse leakage while thep+ntest diodes behaved normally. This was attributed to the defect structures developed by the interaction of sequential diffusion with defect nuclei introduced by ion implantation. We have found that the low‐temperature annealing treatments which are used to return full electrical activity to the implanted atoms leave a high density of defect nuclei in the implanted area. When the silicon surface is subjected to wet oxidation, these defect nuclei expand to form stacking faults or dislocations loops of such size that they can be detected by chemical etching and optical microscopy. This technique has permitted us to determine the annealing temperatures necessary to eliminate these implantation‐induced defect nuclei. A model is presented to describe the manner in which defect nuclei are generated by ion implantation and the means by which these defects are expanded by subsequent oxidation.