Generation and annihilation of point defects by doping impurities during FZ silicon crystal growth

摘要

The main purpose of this paper is to confirm the conclusion of a previous manuscript that the generation of silicon interstitials is the result of the relaxation of the lattice strain induced due to the thermal gradient. In this paper, we consider the relaxation of the lattice strain from a different point of view due to impurity doping during FZ crystal growth. Doping with nitrogen molecules annihilates both the A and D defects, which are the secondary defects of silicon interstitial and vacancy, respectively. The first half of this paper describes such peculiar behavior of nitrogen molecules in crystals doped with both a high concentration of vacancies and nitrogen molecules. The following four important values: the estimated vacancy concentrations, the deep levels at 0.44 eV under the conduction band for n-type and at 0.66 eV over the valence band for p-type for pure vacancies and the diffusion coefficient of the silicon interstitials D_I-FZ=1.3 exp(-4.5 eV/kT) are determined. The last half of the paper demonstrates how impurity doping is systematically correlated with the generation and annihilation of point defects. This phenomenon occurs in accordance with Vegard's law as tested with seven kinds of impurities, which have covalent bonding radii that are smaller or larger than that of silicon. Silicon interstitials are generated by doping with impurities that have smaller covalent bonding radii than silicon to maintain the essential lattice constant of silicon at around 1300 ℃, and vacancies are increased above the equilibrium concentration by doping with impurities that have larger covalent bonding radii than silicon.