Discrete shape analysis of the energy distribution to discriminate non-atomic signal contributions in depth profiling with SNMS
✍ Scribed by Goschnick, J.; Natzeck, C.; Sommer, M.
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 308 KB
- Volume
- 28
- Category
- Article
- ISSN
- 0142-2421
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✦ Synopsis
Using a quadrupole mass spectrometer, a secondary neutral mass spectrometry (SNMS) instrument can be realized at relatively low cost. However, such a mass analyser is only suitable for nominal mass resolution, therefore sometimes intensities of mostly diatomic clusters or double-charged ions superimpose with elemental signals and result in quantification errors, especially for trace elements. A substantial improvement can be obtained with a shape analysis of the kinetic energy distribution (KED) of the mass of interest, because the KEDs of clusters and double-charged ions are considerably narrower than atomic KEDs. The improvement of the depth resolution and the dynamic range of concentration measurements in the interface region means that a very fast energy analysis is required to avoid a reduction of the depth resolution by the data acquisition rate. The discrete shape analysis of the KED was tested on a superposition of a nitrogen signal and a doublecharged silicon signal at mass 14 Da at the Si 3 N 4 /SiO 2 double layer on a silicon substrate. The intensity of the mass 14 Da was measured at only two discrete pass energies of the energy filter, with a narrow energy window. The latter data and the corresponding data of KCN as a reference for a true nitrogen signal were used to correct the 14 Da depth profile of the Si 3 N 4 /SiO 2 /Si sample. The dynamic range of the nitrogen determination was increased by more than an order of magnitude and the depth resolution was improved by nearly a factor of 3.