The effect of beam current and dose on the formation of buried silicon nitride layers by nitrogen implantation with a stationary beam

The effect of beam current and dose on the formation of buried silicon nitride layers produced by 150 keV N⁺ implantation into silicon with a stationary beam have been studied by infrared transmission and glancing angle X-ray diffraction experiments. It is found that both alpha-Si₃N₄ and beta-Si₃N₄ can be formed in the buried nitride layers, and that while alpha-Si₃N₄ is mainly formed during post-implantation annealing, beta-Si₃N₄ is mainly formed by in situ crystallization during implantation. When the beam current is low, or when the beam current is high but the dose is low, the buried nitride layers produced are amorphous as-implanted and crystallized in the alpha-phase after annealing in N₂ at 1200°C for 2 h. At sufficiently high dose and beam currents, and therefore sufficiently high implant temperature due to ion beam heating, in situ crystallization of the buried nitride layers mainly in the beta-phase occurs and the crystallinity increases with beam current and dose. Postimplantation annealing of these partially crystallized samples leads to further crystallization of the buried nitride layers in both phases.