ULTRALOW ENERGY SECONDARY-ION MASS-SPECTROMETRY AND TRANSIENT YIELDS AT THE SILICON SURFACE

The use of a normal incidence sub-kev O-2(+) beam in secondary ion mas s spectrometry (SIMS) depth profiling minimizes the widths of the tran sient regions at the surface of a shallow profile in addition to provi ding a very high depth resolution, At 300 eV we show that the transien t width in silicon is <1 nm, and that the ion yields are relatively in sensitive to the presence of native oxide. This suggests that ideal co nditions for the profiling of very shallow implants are available at 3 00 eV and below. Nevertheless, the transient signals reflect differenc es in the thickness of native oxide, as well as differences in primary beam energy, and could, in principle, be used to measure process and wafer age related differences in the top few nm. We present one of the earliest attempts to accurately calibrate the depth in the pre-equili brium region of a SIMS profile, taking account of the variation in ero sion rate. (C) 1998 American Vacuum Society.