A study of the polycrystalline silicon depletion effect generated from the subsequent thermal process is undertaken. Although phosphorus out-diffusion, which causes the polycrystalline silicon depletion effect, is increased with an increase in the thermal process temperature, the polysilicon depletion effect is stronger when inducing rapid thermal annealing in lower temperatures of 600-800 degrees C than in 900 degrees C. This indicates that the major reason for the polysilicon depletion effect is not the out-diffusion of phosphorus but the electrical deactivation of phosphorus, which is segregated at the grain boundary. Therefore, by increasing the size of polycrystalline silicon grain, we can efficiently reduce the polysilicon depletion effect and enhance the tolerance to deactivation. (C) 2016 Elsevier Ltd. All rights reserved.