Density functional theory study on concentration of intrinsic point defects in growing N-doped Czochralski Si crystal

Abstract

In silicon (Si) crystal growth done using the Czochralski method, doping of nitrogen (N) atoms at a concentration of about 1014 atoms/cm3 reduces the size of void defects. Therefore, N-doping technology is commonly used to improve the quality of Si wafers. However, the mechanism behind the effect of N-doping on intrinsic point defects (vacancy V and self-interstitial Si I) during Si crystal growth remains unclear. Specifically, it is confusing that N-doping increases the total concentration of V to about 10% and yet also reduces the size of void defects. In this study, a density functional theory (DFT) study was performed to investigate the effect of N-doping on the concentration of V and I in Si crystal. We performed DFT calculations of the formation energy and formation (vibration) entropy of interstitial N (Nint) atoms, substitutional N (Nsub) atoms, Nint-Nint pairs, and V and I in the area influenced by the N atom in supercells composed of 64 and 216Si atoms, and we then obtained the concentration of point defects incorporated at the melt/solid interface on the basis of the results. Our main findings are as follows. (1) Nint atoms at the [161] dumbbell (D)-site were the most dominant at the melt/solid interface when the N concentration was less than about 3 × 1014/cm3. (2) The N impact on the V concentration was larger than that on the I concentration and became apparent when the N concentration was higher than about 5 × 1013/cm3. (3) The experimental finding of the N impact on the concentration of intrinsic point defects is explained quantitatively.