Polycrystalline silicon films were transient preannealed, As implanted, and transient post-annealed at peak temperatures up to 1250 degree C for times up to 17. 5 seconds. Structural changes occurring during post-annealing were examined by transmission electron microscopy. These results were correlated to Rutherford Backscattering and sheet resistance results. The grain size, which increased from 5-20 to 150-300 nm during preannealing, did not increase during post-annealing. During early stages of post-annealing, As diffused along grain boundaries and generated dislocation sources at grain boundary surfaces. Subsequently, as annealing progressed, a fine, As-rich cellular network structure propagated into the grains until the structure of an entire grain was transformed into a fine cellular network at the longest annealing times. Residual stresses in the film were relieved during formation of the network structure.