(a) Field of the Invention
The present invention is concerned with a process and a device for determining the quantity of impurities in a gas by chromatography in gas phase and the utilization of such a process for measuring the quantity of doping impurities found in traces in silane.
(b) Description of Prior Art
The technology of chromatography, under normal conditions, does not permit detection to reach thresholds lower than about 2.10.sup.-2 ppm.volume and it may be necessary to determine the quantity of impurities which are found in a gas as traces, in lower quantities. This is particularly the case during the utilisation of silane in the manufacture of semi-conductors. This gas should indeed contain so called doping gas impurities, such as phosphine (PH.sub.3), arsine (AsH.sub.3) or hydrogen sulfide (H.sub.2 S). The effect of these impurities once incorporated into the semi-conductor should be controlled and maintained at a very specific level of concentration, which is very low, is exceeded. For example, it may be necessary to detect in silane traces of phosphine and arsine which are not in excess of 10.sup.-5 ppm.volume in order to be able to guarantee the quality of the silane used in the manufacture of semi-conductors.