Energy and mass‐resolved detection of neutral and ion species using modulated‐pole‐bias quadrupole mass spectroscopy

Abstract

An analyzer capable of determining the mass as well as the energy (5–200 eV) of neutral and ion species has been developed from a quadrupole mass spectrometer (QMS). The system, which is similar to a retarding grid energy analyzer (RGEA), functions by biasing the rods of a QMS and monitoring the analyzer signal as a function of bias potential. Modulation of the pole bias greatly increases the minimum detectable signal level. Experiments were performed using species generated in a single‐grid Kaufman ion gun operated with N2 or Ar. Results show that the pole bias techniques can provide energy resolution of 1–2 eV. Ion species from the gun were found to have an energy equal to the sum of the beam and the plasma potentials, with an energy spread between 1 and 3 eV. Fast N2 and Ar neutral species were measured as a function of discharge voltage (30–80 V), beam acceleration voltage (50–100 V), grid voltage (−20 to +5 V), and pressure (0.5 and 1.5 mTorr). The energy of the fast neutral species was always less than that of the ions. This was consistent with the fast neutrals being formed by a charge‐exchange process.