Depth resolution studies in SiGe delta-doped multilayers using ultralow-energy O2+ secondary-ion-mass spectrometry

Improvements in depth resolution using low primary ion energy secondary-ion-mass spectrometry have been demonstrated. This comprehensive study is done using a wide range of impact angles at ultralow energies. In this work, using Ge delta-doped Si samples, we confirm that depth resolution can be improved by lowering the primary ion impact energy at ultralow energy. By varying the angle of incidence from 0 degrees to 70 degrees, we noted that a better depth resolution is achievable not only at normal incidence but over a wider range of impact angles as the probe energy is reduced. The best depth resolution was observed using E-p similar to 250 eV and theta similar to 0 degrees-40 degrees with full width at half maximum (FWHM) similar to 1.5 nm and lambda(d) < 1 nm throughout the depth profiled (120 nm). Using E-p similar to 500 eV, we observed a good depth resolution of FWHM similar to 2.2 nm and lambda(d) similar to 1.2 nm throughout the depth evaluated at theta similar to 0 degrees-30 degrees. Using E-p similar to 1 keV, a good depth resolution of FWHM similar to 3.5 nm and Xd similar to 1.8 nm was observed at theta similar to 0 degrees-20 degrees. The dynamic range was also evaluated, the best being achieved at theta similar to 50 degrees for E-P similar to 250 eV, theta similar to 40 degrees for E-p similar to 500 eV, and at theta similar to 30 degrees for E-p similar to 1 keV. Contributions from roughening and atomic mixing to the depth resolution of delta layers are discussed using the mixing-roughness-information depth model. (c) 2006 American Vacuum Society.