End-of-range disorder influenced by inherent oxygen in silicon

Abstract

Enhanced end-of-range disorder elimination was achieved by decreasing the inherent oxygen impurities in (100) silicon wafers implanted with 5 × 1015 phosphorus ions/cm2 at 40 keV after germanium preimplantation at 80 keV with 2 × 1014 cm−2. Before heat treatment the implanted silicon layers were shown to be amorphous by Rutherford backscattering and single-wavelength ellipsometry. Czochralski-grown silicon with oxygen impurity concentrations of 7.3 ± 0.2 × 1017 cm−3 was chosen as a reference material. For 550°C, 30 min, and then 800°C, 30 min annealing in an Ar ambient, plan-view transmission electron microscopy showed that the concentration of atoms bound by the extrinsic end-of-range dislocation loops (trapped interstitials) decreased from 14.3 ± 1.4 × 1013 atoms/cm2 (Czochralski-grown silicon) to 11.5 ± 1.7 × 1013 atoms/cm2 in intrinsic gettered silicon and to 4.3 ± 0.3 × 1013 atoms/cm2 in float-zone silicon containing more than two orders of magnitude less oxygen that the Czochralski-grown one. For 550°C, 30 min and then 900°C, 3.5 h annealing the number of trapped of interstitials in the gettered silicon was less than 50% of that found for the former annealing and did not reduce remarkably for Czochralski-grown and float-zone silicon. Chemical analyses by secondary ion mass spectroscopy and cross-sectional transmission electron microscopy revealed that there might be a correlation between the little peaks found on the oxygen depth profiles and the locations of end-of-range dislocation loops in Czochralski-grown and float-zone samples after 550°C, 30 min, and then 900°C, 30 min annealing.