Vacuum Spectroscopy
Assessment of the chemical composition of gases remaining in a sealed system or vacuum chamber identifies contaminants and leaks. Residual gas analysis rga determines the partial pressures of different gas species by ionizing the molecules and separating them by their mass-to-charge ratio. This process is essential for verifying the cleanliness of ultra-high vacuum systems before high-temperature processing begins.
It detects trace amounts of water, hydrocarbons, and helium.
Analysis Process
Gas molecules from the vacuum chamber are drawn into the ionizer where they are bombarded by electrons to create positive ions. These ions are then accelerated into a quadrupole mass filter, which uses variable radio-frequency and direct-current voltages to allow only ions of a specific mass-to-charge ratio to reach the detector. The resulting ion current is proportional to the partial pressure of that gas species in the vacuum chamber.
This spectrum is compared against reference spectra to identify the chemical compounds present. Because each compound has a unique fragmentation pattern, this analysis can distinguish between similar masses, such as nitrogen and carbon monoxide.
Calibration Check
Calibration of the mass spectrometer requires the introduction of a known reference gas mixture at a controlled pressure. Metrologists use this reference to adjust the gain of the detector and to verify the mass scale of the instrument. Drift in the ion source or multiplier requires regular adjustment to maintain accuracy.
This calibration ensures that the residual gas analysis rga results are traceable and reproducible over long testing cycles.
Leak Detection
Identification of atmospheric gases in the spectrum indicates the presence of a physical leak in the vacuum enclosure. A high level of helium or nitrogen confirms that ambient air is entering the system. These findings allow technicians to locate and seal the leak before starting the process.
