Ultrahigh depth resolution secondary ion mass spectrometry with sub-keV grazing O2+ beams

Compositional analysis of interfaces in semiconductor materials grown with the most modern equipment requires a substantial improvement of the depth resolution of secondary ion mass spectrometry (SIMS). The lowering of the impact energy to improve depth resolution is limited on most magnetic-sector instruments to ∼1.5 keV. In this work it is shown that in the VG IX70S magnetic-sector instrument a reduction of the impact energy to 600 eV is possible. The reduction is achieved by use of a deceleration electrode in the primary beam line, allowing for independent variation of the energy and the incidence angle θ (50°<θ<80°). The best depth resolution obtained—for a shallow Ge δ layer with a 600 eV θ=80° O2+ beam—was 1.6 nm full width at half-maximum and an exponential decay length of 0.65 nm; about three times better than achievable on any other magnetic-sector SIMS instrument. In addition, a very shallow (∼3–4 nm) Ge δ layer has been analyzed by high-resolution Rutherford backscattering and SIMS. There is good agreement between both techniques.