Impurity Measurement in Specialty Gases Using an Atmospheric Pressure Ionization Mass Spectrometer with a Two-Compartment Ion Source

Abstract

Using an atmospheric pressure ionization mass spectrometer (APIMS) with a two-compartment ion source, impurity in specialty gases (CH4, SiH4, GeH4) is measured due to a stable ionization reaction with a detection limit of approximately 0.1 to 1 parts per billion (ppb). The form in which the impurity exists in these gases has been clarified. In the case of SiH4, the main impurity is disiloxane (SiH3–O–SiH3). We have also established a method for obtaining the SiH3–O–SiH3 calibration curve standardized for a known concentration of SiH3–O–SiH3 generated from the reaction of SiH4 with H2O. In the case of CH4 and GeH4, the main impurity is moisture (H2O) and it is quantified from the plotted H2O calibration curve.