RGA

RGA stands for residual gas analyzer, a type of mass spectrometer used to monitor the composition of gases in high and ultrahigh vacuum systems. RGAs are commonly built around a quadrupole mass filter and a sensitive ion detector, enabling continuous online analysis of gas species present in the chamber.

In operation, a small sample of the chamber air is admitted through a capillary or orifice into the ionization region, where gas molecules are ionized by an electron beam. The resulting ions are separated by mass-to-charge ratio and detected, producing a mass spectrum that reflects the relative partial pressures of species such as hydrogen, water, carbon monoxide, carbon dioxide, and hydrocarbons. Although the instrument yields relative partial pressures, with calibration it can provide quantitative estimates of gas concentrations.

RGA measurements are used to diagnose vacuum quality during coating and etching processes, monitor outgassing of vacuum chambers, detect leaks, and study surface reactions in vacuum systems. They are common in semiconductor fabrication, thin-film deposition, and surface science laboratories.

Limitations include fragmentation of molecules in the ionization process, mass spectral overlap between species with similar mass, and varying ionization cross-sections that affect sensitivity. Calibrations, background subtraction, and regular maintenance of the filament and inlet are required for reliable data. RGAs operate in high to ultra-high vacuum environments and are often paired with turbomolecular pumps.

Other uses of the acronym RGA exist, including as an abbreviation for organizations such as the Reinsurance Group of America. This article focuses on the instrumental use of RGA in vacuum technology.