ATMOSPHERIC-PRESSURE IONIZATION MASS-SPECTROSCOPY FOR THE STUDY OF PERMEATION IN POLYMERIC TUBING

Polymeric tubes are used in the semiconductor manufacturing industry t o provide mechanical flexibility and electrical insulation. Since poly meric tubing has higher permeation rate compared to metal tubing, it c an easily become a source of contamination in ultrapure gas distributi on and delivery systems. In this study, an Atmospheric Pressure Ioniza tion Mass Spectrometer (APIMS) is used to determine the permeation coe fficients for two widely used polymeric tubing, PFA and Kel-F (PCTFE), at 25-degrees-C and 75-degrees-C. In the experiments, an ultra-high p urity N2 gas flow was maintained through the test tubing. The net impu rity uptake by nitrogen due to the permeation of O2, CO2, H2O, and CH4 from surrounding air into the polymeric tubing was measured by APIMS with sub-ppb sensitivities. CH4 had the highest and 02 had the lowest permeation coefficients. Results showed that Kel-F was a superior barr ier material for all impurities studied. The permeation coefficients f or these polymers increased with temperature but did not change signif icantly with the permeant partial pressure. Permeability of PFA showed a stronger temperature dependence than that of Kel-F.