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 SIM S spectra from insulators. For static SIMS using a quadrupole mass spe ctrometer, the problem is exacerbated by the narrow spread of ion ener gies passed by the quadrupole system. Here, for a positive ion beam we study three methods of electron beam surface charge neutralization an d compare their effectiveness for large-area static SIMS analysis. The se methods are: a traditional low-energy flood source aimed at the sam ple; a 500 eV electron beam aimed at the sample; and a low-energy sour ce 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 pote ntial are considerably reduced but small variations still show an effe ct leading to variable intensities in different peaks. This variation is reduced a further order of magnitude so that, in the static mode, f inal scatters for poly(tetrafluoroethene) have standard deviations bel ow 2%. This final reduction is achieved by the application of a triang ular waveform potential of 32 V peak-to-peak amplitude at 6.5 kHz freq uency, to the sample holder and the sample environment. The mass spect ra are then equivalent to the results for a mass spectrometer with a 3 2 eV wide energy acceptance window.