The effect of point defects on copper precipitation in heavily boron-doped Czochralski silicon epitaxial wafer is systematically investigated by optical microscopy. The samples first experience the rapid thermal processing (RTP) in different atmospheres, and then are Cu-contaminated at different temperatures. It is found that RTP in O2 ambient leads to a low density of copper precipitation in the p+ substrate, however, high density of copper precipitation is observed in the sample subjected to RTP in Ar or N2 ambient. Additionally, in all of the samples, no defects are found in the epitaxial layer. On the basis of the experiments, it can be concluded that interstitial silicon will prevent the process of copper precipitation while vacancy has an opposite effect. Furthermore, p/p+ epitaxial structure could absorb copper impurities, thereby keeping the epitaxial layer free of defect.