The invention relates to the detection of trace amounts of condensible vapors in compressed gases, the measurement of their concentration and, further, their removal from the said compressed gases.
In many applications of gases, such as manufacture of VLSI chips, high purity gases are needed during the manufacturing process to avoid, among others, the creation of defects during the various masking steps of the process and thus enhance the manufacture output of said process as well as the reliability of the chips. There is also a need for high purity gases in the optical, aerospace and pharmaceutical industries.
Various impurities such as particles or vapors may be present in compressed gases stored in a container such as a cylinder. It is known from the article entitled "A gas filtration system for concentrations of 10.sup.-5 paticles/cm.sup.3 " from G. KASPER and H. Y. WEN; published in Aerosol Science and Technology 5: 167-185 (1986), to achieve "totally" particle-free process gases. Particle analysis has been also carefully studied by the same authors and the results of this study published in Proceedings--Institute of Environmental Sciences--May 6, 1987--in an article entitled "Particle Analysis in cylinder gases".
Trace quantities of condensible vapors such as hydrocarbons or fluorinated hydrocarbons in gases are commonly detected and quantified by a variety of means such as chromatography in the gas phase, IR absorption spectroscopy, mass spectrometry, total hydrocarbon detectors, etc.
However, detection limits of such techniques are about 100 ppb, while with a preconcentration step, such capabilities are about 1 ppb (part per billion). Such methods are time-consuming, especially when they comprise a pre-concentration step, costly and in some cases very costly and relatively insensitive to higher order hydrocarbons. Furthermore, such methods provide means for measuring the concentration of such vapors, with a limited accuracy but do not provide means for removing said vapors based on the same concept.
It is an object of the present invention to define a method to detect the presence of trace amounts up to part per trillion or less of condensible vapors in compressed gases.
It is a further object of the present invention to measure the concentration of trace amounts up to part per trillion or less of condensible vapors in compressed gases.
It is a further object of the present invention to remove trace amounts up to part per trillion or less of condensible vapors in compressed gases.