High-resolution Rutherford backscattering spectroscopy (HRBS) is a powerful technique to measure elemental depth profiles with depth resolution of atomic level. Application of HRBS to microelectronics, in particular the issues of ultra-low energy ion implantation, is discussed in this paper. Boron profiles in silicon wafers implanted with 0.5-keV B+ ions are measured. The observed profile agrees with TRIM simulation very well. Molecular effect in ion implantation is investigated for 6-keV As-2(+). It is shown that the radiation damage created by 6-keV As-2(+) ion implantation is almost twice larger than that by 3-keV As+ ion implantation. It is also found that the projected range of 6-keV As-2(+) is several % larger than that of 3-keV As+.