TRACE MOISTURE MEASUREMENT IN SEMICONDUCTOR GASES

There are quite a few methods for measuring moisture in gases, roughly into two categories: a direct measurement using an alternation amount of gaseous property. We have established a technology for trace moist ure measurement in gases by optimizing a dew point method, one of the direct categories of measurement. Dew points are defined as the surfac e temperature at which dew or frost starts to form on a mirror during cooling of the mirror. To obtain moisture concentrations from measured dew points, calculations should be carried out based on a saturation vapor pressure curve for moisture. However equilibrium must be reached . That is, temperatures should be measured when moisture coexists in g as and liquid or solid phase and their partial pressure is equal to ea ch other. Using this principle, measuring the phase changes of moistur e in the equilibrium state enables us to measure trace moisture in gas es more accurately.