High-pressure effects in miniature arrays of quadrupole analyzers for residual gas analysis from 10(-9) to 10(-2) Torr

The design, construction, and characterization of a miniature array of 16 rods forming nine quadrupole mass analyzers for residual gas analysis are presented. The novel design takes advantage of the reduction of the dimensions and hence the mean free path to broaden the dynamic range by extending the operating pressure range up to 10 mTorr at the high end while maintaining the low-end sensitivity and mass resolution. The small size, low weight, low power consumption, and low cost of this mass analyzer enable many new applications such as ia situ process control in high pressure processes. Applications which take advantage of the capability of operating the source pressure two orders of magnitude higher than conventional devices such as high-pressure contaminant monitoring are discussed. Data on high-pressure effects on the ionizer lifetime in various atmospheres and nonlinearities of the signal are presented and correlated with theoretical analysis. Ray tracing simulations and Monte Carlo statistical calculations are used to provide an understanding of the sensitivity reduction at pressures-substantially higher than 10 m Torr. These calculations take into account the ion charge density in the source and the dissociation, charge exchange, and energy loss by the ions when colliding with residual molecules along the length of the rods. (C) 1996 American Vacuum Society.