Ultrashallow depth profiling using SIMS and ion scattering spectroscopy

The accuracy of ultrashallow depth profiling was studied by secondary ion mass spectrometry (SIMS) and high-resolution Rutherford backscattering spectroscopy (FIRBS) to obtain reliable depth profiles of ultrathin gate dielectrics and ultrashallow dopant profiles, and to provide important information for the modeling and process control of advanced complimentary metal-oxide semiconductor (CMOS) design. An ultrathin Si3N4/SiO2 stacked layer (2.5 nm) and ultrashallow arsenic implantation distributions (3 keV, 1 X 1015 CM-2) were used to explorethe accuracy of near-surface depthprofiles measured by low-energy O-2(+) and C-s(+) bombardment (0.25 and 0.5 keV) at oblique incidence. The SIMS depth profiles were compared with those by FIRBS. Comparison between HRBS and SIMS nitrogen profiles in the stacked layer suggested that SIMS depth profiling with O-2(+) at low energy (0.25 keV) and an impact angle of 78 degrees provides accurate profiles. For the As'-implanted Si, the HRBS depth profiles clearly showed redistribution in the near-surf ace region. In contrast, those by the conventional SIMS measurement using Cs+ primary ions at oblique incidence were distorted at depths less than 5 nm. The distortion resulted from a long transient caused by the native oxide. To reduce the transient behavior and to obtain more accurate depth profiles in the near-surface region, the use Of O-2(+) primary ions was found to be effective, and 0.25 keV O-2(+) at normal incidence provided a more reliable result than C-s(+) in the near-surface region. Copyright (C) 2007 John Wiley & Sons, Ltd.