Identification of oxide precipitates in annealed silicon crystals

Abstract

Prolonged heat treatment of Czochralski-grown silicon crystals containing oxygen concentrations on the order of 1018 atoms/cm3 usually causes formation of precipitates (1-3). These precipitates are assumed to be a form of silicon oxide. This assumption is based on the fact that the oxygen concentration, as measured by IR spectroscopy, is reduced after annealing. The precipitates growth kinetics are diffusion-controlled and their size can be calculated with reasonable accuracy from the supersaturation and diffusion coefficient of oxygen in silicon at the annealing temperature (3). However, no direct evidence of the precipitates as a form of silicon oxide has been reported. The main difficulty arises from the fact that microanalysis of the precipitates requires an instrument with both a capability of detecting oxygen plus high spatial resolution and detection sensitivity. Techniques such as electron diffraction fail to reveal extra dots or rings from the precipitates (1-3).The Czochralski crystals used contained 1018 atoms/cm3 oxygen, were <100> oriented and doped with boron to 2 Ω-cm, annealed at 1100°C for 40 hours and then prepared for TEM analysis by chemical etching.