Nitrogen-Oxygen defects in Silicon

  Nitrogen can be incorporated into Si in a variety of ways, although it only has a low solubility. Anneals in an ambient environment usually use N₂ gas. Si₃N₄ is used as a surface diffusion barrier or as a dielectric layer in metal insulator semiconductor systems. In addition, N doping in Cz-Si suppresses vacancy and interstitial defects and increases gate oxide integrity. It suppresses `swirl defects' and stops wafer bowing during processing, as well as suppressing thermal donor formation. Many of these properties are dependent on nitrogen-oxygen interactions.

In this chapter we study the interaction between nitrogen and oxygen in silicon. Previous calculations using AIMPRO have shown that N in Si exists primarily in the form of interstitial (N_i)₂ pairs [145]. Isolated N_i has been observed experimentally but only in small quantities, and it rapidly diffuses to form (N_i)₂. It is shown here that the primary N--O defect is (N_i)₂O, or NNO, consisting of O_i neighbouring a (N_i)₂ pair [103]. This is electrically inactive and can reversibly break down to give (N_i)₂ and O_i. We also examine a N_iO_i complex and show that small quantities of this are also present over similar temperature ranges. Electrically active N_iO_2i complexes are considered in Chapter 8.