Resistivity of Heavily Doped Polycrystalline Silicon Subjected to Furnace Annealing

Abstract

We investigated the dependence of the resistivity of heavily doped polycrystalline silicon (poly-Si) on the doping concentration and annealing conditions. The resistivity of As-doped poly-Si with equal sized grains depends on the annealing temperature when the doping concentration is less than 5×1020 cm-3. This dependence is related to As segregation to the grain boundaries; that is, more As segregates to the grain boundaries as the temperature decreases. When the doping concentration exceeds 5×1020 cm-3, the As concentration in the grain reaches saturation and remains almost constant with increasing temperature. This means that the solid solubility limit is insensitive to the annealing temperature, and the resistivity remains almost constant with increasing annealing temperature. The resistivity of B-doped poly-Si does not depend on the annealing temperature when the doping concentration is less than the solid solubility limit. This indicates that B does not segregate significantly at the grain boundaries. When the doping concentration exceeds the solid solubility limit, the resistivity depends on the annealing temperature, because the solid solubility limit of B depends significantly on the annealing temperature. The solubility limit of B in poly-Si increases from 6×1019 cm-3 at 800° C to 1.5×1020 cm-3 at 1100° C. We proposed an empirical model that explains the experimental data.