Atomic-scale redistribution of dopants in polycrystalline silicon layers

80 nm thick polycrystalline silicon (poly-Si) layers implanted with As, P, and C were subjected to spike heating (1000 °C, 1.5 s) or laser anneal (1300 °C, 0.25 ms) and analyzed by atom probe tomography. A strong interfacial segregation of dopants to the grain boundaries (GBs) was revealed in the spike annealed samples. The heterogeneous precipitation of C to the GBs was observed, as well as the clustering of C in the interior of the grains. Theses clusters are also rich in As and P. Their shapes (loop, rod) strongly suggest that these clusters are the result of dopant segregation to extended defects. Nanometer size oxygen clusters were also observed. They originate from the recoil of oxygen atoms during the implantation process through the oxide layer. Laser annealed samples showed a lower segregation excess of dopants to GBs. Consequently, the dopant concentration inside grains was found larger compared to the spike annealed sample. The lower segregation rate at GB is explained by the larger temperature in the laser annealing.