Transmission electron microscopy and Rutherford backscattering were used with polycrystalline Si films implanted at 100 keV with 3×1016arsenic ions/cm2. During annealing, grain growth occurred first in the implanted portion, then arsenic diffused into the unimplanted poly‐Si, and finally grain growth occurred in this region. We believe that arsenic in the implanted region accumulates on grain boundaries during grain growth and subsequently diffuses along grain boundaries into the unimplanted region where grain growth occurs when arsenic can diffuse into the interior of the polycrystalline Si grains.