STATIC SIMS - SURFACE-CHARGE STABILIZATION OF INSULATORS FOR HIGHLY REPEATABLE SPECTRA WHEN USING A QUADRUPOLE MASS-SPECTROMETER

Surface charge stabilization is important to achieve stable static SIMS spectra from insulators. For static SIMS using a quadrupole mass spectrometer, the problem is exacerbated by the narrow spread of ion energies passed by the quadrupole system. Here, for a positive ion beam we study three methods of electron beam surface charge neutralization and compare their effectiveness for large-area static SIMS analysis. These methods are: a traditional low-energy flood source aimed at the sample; a 500 eV electron beam aimed at the sample; and a low-energy source of scattered electrons placed between the sample and the quadrupole-based static SIMS entrance ion optics. The latter method is shown to be efficient, easy to use and reliable. Variations in the surface potential are considerably reduced but small variations still show an effect leading to variable intensities in different peaks. This variation is reduced a further order of magnitude so that, in the static mode, final scatters for poly(tetrafluoroethene) have standard deviations below 2%. This final reduction is achieved by the application of a triangular waveform potential of 32 V peak-to-peak amplitude at 6.5 kHz frequency, to the sample holder and the sample environment. The mass spectra are then equivalent to the results for a mass spectrometer with a 32 eV wide energy acceptance window.