Coimplantation of heterogeneous dopants in materials can be used to control the principal dopant distribution. We used atom probe tomography (APT) and secondary ion mass spectrometry (SIMS) to investigate the impact of coimplanted carbon on boron diffusion in silicon. After annealing, three-dimensional APT analysis of dopant distributions revealed the presence of carbon-boron coclusters around the projection range of boron. In addition, SIMS depth profiles revealed enhanced boron concentration around the projection range of carbon. These results suggest that the carbon-boron interaction suppresses boron diffusion in silicon.