Study of the influence of oxygen on structural perfection of silicon single crystals by high-resolution X-ray diffraction and infrared absorption measurements

Abstract

High-resolution X-ray diffractometry, absolute integrated intensity (ρ) measurements, diffuse X-ray scattering (DXS) and infrared (IR) absorption techniques were used to investigate the influence of oxygen on the structural perfection of high purity (resistivity of the order of 4 kΩ cm) float zone (FZ) grown (111) silicon single crystals. A multicrystal diffractometer set in (+,-,-,+) geometry, with Mo Kα1radiation, was employed. From the infrared measurements, the oxygen concentration in the sample was determined to be 1.3 × 1017 atoms cm^{-3}. High-resolution X-ray diffraction curves of the as-grown crystal had half-widths of ∼11 arcsec; the ρ value was 3.5 × 10^{-5} rad. To incorporate oxygen in a controlled manner into the specimens, they were annealed under dry oxygen ambient for 8 h in the temperature range 573–1373 K (in eight steps). Up to 723 K there was no appreciable change in oxygen content or in the degree of perfection. Annealing at temperatures (AT) > 873 K resulted in considerable increases in the oxygen content, as well as significant improvements in the degree of perfection. For example, as the level of oxygen increased from 1.3 × 1017to 3.6 × 1017 atoms cm^{-3} for A_T=873 K, the values of half-widths and ρ decreased to ∼7 arcsec and 2.4 × 10^{-5} rad, respectively. However, annealing above 1273 K produced deterioration in lattice perfection. DXS measurements showed remarkable changes in the nature of point defects and their clusters with change inAT. Up to A_T=973 K, the defects were predominantly vacancy clusters. However, withATin the range 1073–1273 K, the predominent defects were isolated interstitials. Further increase inATled to interstitial cluster formation, which deteriorated the lattice perfection. This study clearly demonstrates that oxygen concentration in the range ∼3 × 1017to 13 × 1017atoms cm^{-3} leads to significant improvement in structural perfection of silicon single crystals.