Semiconductor manufacturers are a fastidious bunch. They have to be. Even micrometer-size contaminants can ruin a microcircuit. The vacuum chambers where microcircuits are made must be thoroughly cleaned at regular intervals. Molecules from gases used in these chambers gradually build up on the inside walls and on electrodes at the top and bottom of the chamber.
To remove this build up, chip makers use an ionized fluorocarbon gas called a plasma. Reactive molecules in the cleaning gas combine with silicon-containing deposits on the chamber surfaces and carry them out of the chamber. NIST researchers recently used a sheet of ultraviolet laser light to track the concentration of the reactive fluorocarbon molecules during the cleaning process. At low pressures, higher concentrations of the reactive gas were found closer to the walls of the chamber. At higher pressures, it was more concentrated nearer the electrodes. The researchers plan to correlate their findings with plasma monitoring systems used in industry to help manufacturers improve the efficiency of their operations and hopefully reduce their usage of fluorocarbon gases, which contribute to global warming.