Miniature Quadrupole Arrays for Residual and Process Gas Analysis

Abstract

This paper includes computer simulations based on ray tracing to aid in the design of miniature quadrupoles. These quadrupoles are then assembled in a matrix-like pattern to operate in parallel. The tradeoffs between sensitivity and resolution for different mechanical and electrical configurations are examined using real-time trajectories of ions. The dependence of resolution versus sensitivity is computed and compared with experimental results. The pressure dependence of the sensitivity is simulated near the upper limit (mtorr range) of the operating pressure. Space charge effects at the inlet of the mass filter are evaluated to properly design electrode apertures and spacing. Using the results of ray tracing, miniature quadrupole arrays were designed and constructed. Performance parameters were derived from recorded spectra and compared with the computations. Since they are able to operate at higher pressures, these sensor-type devices are used as residual gas analyzers (RGAs) and as process gas analyzers (PGAs) in many semiconductor applications. Networking multiple sensors to monitor the state of the semiconductor manufacturing tool and the wafers at different stages of the process enables real-time, wafer-to-wafer control using preset fault detection schemes.

A Parallel Miniature Cylindrical Ion Trap Array

“…This experiment is novel when quadrupole ion traps are used, but not with mass analyzers in general. Two groups have already used the idea with miniature linear quadrupoles and designed 4 × 4 arrays of quadrupoles ,, to increase sensitivity lost as a result of miniaturization of the quadrupole rods. Here, we demonstrate that multiple cylindrical quadrupole ion traps, operated in parallel, show a comparable advantage.…”

Miniature mass analyzers

“…Ferran and Boumselleck have built a 4 ð 4 array of rods, forming nine quadrupole analyzers (weighing ¾25 g) and operated the device using an EI source. 24,29 The rods are 0.5 mm in radius, 10 mm long and mounted in a glass base. The array gives a linear response to argon over six decades of pressure (up to 10 mTorr) and can analyze ions up to 100 Th with 50 V d.c. and 300 V r.f.…”

“…24 A mass range of ¾300 Th was demonstrated with ndocosane (CH 3 (CH 2 ) 20 CH 3 ); air monitoring at 3 mTorr showed peak widths (FWHM) of 0.5 Th and the ability to detect Ne at concentrations down to 9 ppm. 29 A similar device has been built at the Jet Propulsion Laboratory, also consisting of a 4 ð 4 array of 1 mm radius, 25 mm long rods forming nine mass analyzers [Fig. 4(a)].…”

Handheld Rectilinear Ion Trap Mass Spectrometer

“…The complex interplay of factors that affect mass spectrometer performance as a function of the size of the mass analyzer and other components has seldom been systematically explored. Exceptions include (i) the work of Ferran on the quadrupole mass filter and (ii) that on ion traps in this lab; these studies led to the multiplexing of individual small analyzers , to achieve high system performance in a small package. Other exceptions are (iii) the work of Cotter and co-workers on short drift field time-of-flight mass analyzers, and (iv) recent investigations of the performance of micrometer-sized cylindrical ion traps by the Purdue/Sandia group and that of Pau, Ramsey, and co-workers …”