A CONDENSATION NUCLEUS COUNTER FOR CHEMICALLY REACTIVE GASES

A condensation nucleus counter (CNC) capable of detecting sub-20nm contaminant particles in chemically reactive gases has been developed. The new instrument was constructed from corrosion-resistant materials, and uses a chemically inert working fluid. A test apparatus was also constructed to check the counting efficiency of the CNC. The tests confirmed the sensitivity of the new instrument in 13 different gases. The CNCs lower size sensitivity varied with the physical properties of the gas. The measured lower size sensitivity among the gases ranged from 19nm to <7nm. Theoretical predictions of the CNC performance were also obtained using a calculation of working fluid saturation ratio and droplet formation in the CNCs condenser. The predicted CNC performance corresponded approximately to the test results for each gas. The new instrument can monitor the level of particulate contamination in reactive semiconductor process gases to the 20nm level or lower.