Determination of micro amounts of oxygen in silicon by inert-gas fusion

Abstract

A chromatographic inert-gas fusion method using an Ni-Sn fusion bath and helium as carrier gas has been developed for determining micro amounts of oxygen in silicon. With the Ni-Sn bath, the oxygen determination can be done at lower temperatures (1650–1700°) in a heated graphite crucible than in an empty crucible (with no molten metal bath) in which the sample is directly in contact with the carbon. Four samples can be analysed in succession in a single crucible with a relatively short time for oxygen extraction (5 min). Careful control of experimental conditions, and the use of a water-cooled quartz tube and a small unshielded graphite crucible have resulted in a lower blank (0.1 μg of oxygen), and better reproducibility, enabling oxygen in silicon to be determined down to 1 ppm. A calibration curve for determining oxygen in single crystals of silicon by measuring the infrared absorption at 9 μm has been constructed and gives results agreeing with those obtained by α-particle activation analysis.