A study of oxygen precipitation in silicon using high-resolution transmission electron microscopy, small-angle neutron scattering and infrared absorption

Abstract

Czochralski silicon samples have been heated at 750°C for periods of 48,96 and 431 h under clean conditions appropriate to device fabrication. The loss of oxygen from solution was measured from the strength of the 9 pm absorption band with the samples at 4·2 K; detailed information about the SiO₂ precipitates was obtained by measurements on many foils using transmission electron microscopy, and by small-angle neutron scattering. The three techniques were applied to common samples. The measurements show excellent overall self-consistency and some new features have been found in the transmission electron microscopy analysis. In general, platelets are observed with length increasing from 12 to 26 nm, and with thicknesses of about 2 nm. The number density of particles drops from 2 × 10¹³ to 7 × 10¹² cm⁻³ as the heating time is increased. We deduce a value of the oxide density to be 2·6 g cm⁻³, which is somewhat higher than the normally quoted value of 2·3 g cm⁻³ for amorphous silica.