Quantitative depth profile and bulk analysis with high dynamic range by electron gas sputtered neutral mass spectrometry

Abstract

The need for quantification in thin‐film and surface analysis has increased the interest in sputtered neutral mass spectrometry (SNMS) since this method is less affected by matrix effects than secondary ion mass spectrometry (SIMS) and in addition does not suffer from preferential sputtering like Auger electron spectroscopy and x‐ray photoelectron spectroscopy depth profiles, as it measures sputtered fluxes instead of surface concentrations. Among the different postionization techniques, electron gas SNMS [H. Oechsner and W. Gerhard, Z. Phys. B 221, 41 (1975)] using a hot and high‐density rf‐coupled plasma, is the one most established. Its field of applications has until recently been limited by two artifacts: mass resolved residual gas line interferences in SNMS spectra and structureless background induced by photons and electrons of the plasma. Both problems are overcome by a new ion optical arrangement which combines a three‐electrode retarding field configuration, adjusted to the maximum of plasma potential, with a simulated spherical deflection capacitor in front of a quadrupole mass filter. Theory, design, and analytical performance of this combined SNMS and SIMS spectrometer will be discussed and results of depth profiling of semiconductor layer structures and bulk trace analysis will be given. For these applications quantification is discussed in terms of plasma control (electron temperature and density) and particle emission process (energy and angular distribution, molecular emission, secondary ion yield) parameters.