Predoping effects of boron and phosphorous on arsenic diffusion along grain boundaries in polycrystalline silicon investigated by atom probe tomography

Abstract

The effect of P or B predoping on As diffusion in polycrystalline Si was investigated by atom probe tomography. In all samples, a high concentration of As was found at grain boundaries, indicating that such boundaries are the main diffusion path. However, As grain-boundary diffusion was suppressed in the B-doped sample and enhanced in the P-doped sample. In a sample codoped with both P and B, As diffusion was somewhat enhanced, indicating competition between the effects of the two dopants. The results suggest that As grain-boundary diffusion can be controlled by varying the local concentration of P or B.

Segregation mechanism of arsenic dopants at grain boundaries in silicon

“…Arsenic (As) atoms, as important n-type dopants in Si, are frequently used for Si nano-devices due to their excellent physical properties such as high solubility (1.8 x 10 21 cm -3 ) needed for low resistivity [16], low diffusivity (about 1/10 in comparison with the other important n-type dopants of phosphorus atoms) used for diffused junctions and buried layers that can resist annealing processes [17], and the atomic radius similar to Si that do not induce large strains by doping [18]. Meanwhile, they can diffuse in GBs with a diffusivity four orders of magnitude higher than the single-crystal value [19], and therefore they preferentially segregate at GBs, rather than distribute homogeneously in grains, as visualized in polycrystalline Si by scanning transmission electron microscopy (STEM) [20] and atom probe tomography (APT) [8][9][10][11][21][22][23].…”