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

High-resolution X-ray diffractometry, absolute integrated intensity ( ) measurements, diffuse X-ray scattering (DXS) and infrared (IR) absorption techniques were used to investigate the in ̄uence of oxygen on the structural perfection of high purity (resistivity of the order of 4 k cm) ̄oat zone (FZ) grown (111) silicon single crystals. A multicrystal diffractometer set in …‡;ÿ;ÿ;‡† geometry, with Mo K 1 radiation, was employed. From the infrared measurements, the oxygen concentration in the sample was determined to be 1.3 10 atoms cmÿ3. High-resolution X-ray diffraction curves of the asgrown crystal had half-widths of 11 arcsec; the value was 3.5 10ÿ5 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 signi®cant improvements in the degree of perfection. For example, as the level of oxygen increased from 1.3 10 to 3.6 10 atoms cmÿ3 for AT ˆ 873 K, the values of half-widths and decreased to 7 arcsec and 2.4 10ÿ5 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 in AT. Up to AT ˆ 973 K, the defects were predominantly vacancy clusters. However, with AT in the range 1073±1273 K, the predominent defects were isolated interstitials. Further increase in AT led to interstitial cluster formation, which deteriorated the lattice perfection. This study clearly demonstrates that oxygen concentration in the range 3 10 to 13 10 atoms cmÿ3 leads to signi®cant improvement in structural perfection of silicon single crystals.