How does a Residual Gas Analyzer (RGA) work?
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A residual gas analyzer (RGA) is a type of mass spectrometer used primarily to identify and quantify the gases present in a vacuum system. It allows for the analysis of gas species in the low-pressure environments often required in high-tech industries such as semiconductor manufacturing and surface science. Here is a simplified description of how an RGA works:
Ionization of Gas Molecules: Gas molecules within the RGA’s sampling volume are ionized, usually by electron impact. This means that electrons are fired at the gas molecules by an electron gun, knocking off an electron and creating positively charged ions.
Mass Analysis: The ions are then directed into a mass filter, which is often a quadrupole mass filter. A quadrupole consists of four parallel metal rods, with each opposing rod pair connected to a radio frequency (RF) voltage with a direct current (DC) offset. The RF and DC fields are applied to the rods in such a way that only ions of a specific mass-to-charge ratio (m/z) can pass through the filter at any one time, with other ions being deflected and lost. By scanning through a range of RF and DC settings, ions of different m/z can be selectively filtered through the quadrupole, allowing the RGA to scan across a range of masses and thus detect multiple gas species.
Detection of Ions: The ions that pass through the mass filter reach a detector, which is often a Faraday cup or a secondary electron multiplier (SEM). These devices generate a signal proportional to the number of ions hitting them. The detector’s output is then processed and read out as a mass spectrum. Peaks on the spectrum correspond to the m/z of the ions, which can be used to identify the gas species. The height or area of the peak is proportional to the concentration of that species in the gas mixture.
Data Interpretation: The resulting data are interpreted to determine the types and quantities of gases present in the vacuum system. RGAs are crucial for quality control and system maintenance in vacuum systems, as they help identify contaminants, leaks, and outgassing sources which may compromise the integrity of the vacuum environment or the processes occurring within it.
For a more detailed explanation visit: Residual Gas Analysers – VAC AERO International