Arsenic implantation into polycrystalline silicon and diffusion to silicon substrate

Abstract

Arsenic implantation into polycrystalline silicon and drive‐in diffusion to silicon substrate have been investigated by MeV He⁺ backscattering analysis and also by electrical measurements. The range distributions of arsenic implanted into polycrystalline silicon are well fitted to Gaussian distributions over the energy range 60–350 keV. The measured values of R_P and ΔR_P are about 10 and 20% larger than the theoretical predictions, respectively. The effective diffusion coefficient of arsenic implanted into polycrystalline silicon is expressed as D=0.63 exp[(−3.22 eV/kT)] and is independent of the arsenic concentration. The drive‐in diffusion of arsenic from the implanted polycrystalline silicon layer into the silicon substrate is significantly affected by the diffusion atmosphere. In the N₂ atmosphere, a considerable amount of arsenic atoms diffuses outward to the ambient. The outdiffusion can be suppressed by encapsulation with Si₃N₄. In the oxidizing atmosphere, arsenic atoms are driven inward by growing SiO₂ due to the segregation between SiO₂ and polycrystalline silicon, and consequently the drive‐in diffusion of arsenic is enhanced. At the interface between the polycrystalline silicon layer and the silicon substrate, arsenic atoms are likely to segregate at the polycrystalline silicon side.