Secondary ion emission enhancement assisted by electron beam in secondary ion mass spectrometry

Secondary ion emission was enhanced by electron beam in a typical secondary ion mass spectrometry (SIMS) operation, which was demonstrated using the shallow p/n junction implanted with BF2+ ions of a dosage of 2.3 × 1015 cm−2 at 20 keV. In the SIMS mass spectra measurements, the 19F+ signal is enhanced by 39 times at an electron beam current of 100 μA. In contrast, the 11B+ signal is slightly enhanced by a factor of ∼50%. In order to characterize the spatial distribution of secondary ions along the surface normal direction, the energy spectra of 19F+, 11B+ and 30Si+ ions were measured by altering the sample potential by ±50 V (relative the original sample bias 2 kV). The energy spectra reveal that most 19F+ ion signal is generated by electron beam stimulated desorption on the sample surface and some by the electron induced post-ionization in the gas phase above the sample surface. In contrast, only small enhancements of 11B+ and 30Si+ occur on the sample surface. No 11B+ and 30Si+ ions are generated in the gas phase above the sample surface. The enhancement of 11B+ increases linearly with electron beam current based on the depth profile data of 11B+. This supports the occurrence of Penning ionization for 11B+ on the sample surface. The ionization enhancement of 11B+ is dominated by oxygen radicals O2*.