Lattice destruction during micro-channeling measurements

The degree of postimplantation damage in various semiconductor crystals depends on the dose rate applied. In particular strong effects have been observed at dose rates up to 10¹⁹ cm^-2s^-1 which are typical for focused ion beam (FIB) devices with sub-µm beam diameters. For a systematic study of such damages a nuclear microprobe must be employed for RBS/channeling measurements. But the fluence of the analysing beam of light ions is here orders of degree higher than usually in RBS/C experiments. Therefore the damage generation by the analysing beam must be considered.
We have studied the near-surface damage accumulation at room temperature in 6H-SiC by H, He and Li ions of various energies both for channeling and random incidence.
The fluence dependence of the regular damage, observed with beams in the MeV region, is much smaller than that with low and medium energies. The damage level observed by RBS/C seems to saturate at a cmin value far below unity. The calculated ratios of Rutherford cross section to deposited nuclear energy [SRIM 2000] for H, He, and Li ions predict lowest damage per backscattering yield for H ions at the lower energy end. But in the case of µm beam dimensions the lattice damage by the proton beam due to swelling, bubble formation, precipitation etc. exceeds by far the regular ballistic disorder and is higher than in the case of He or Li ions of the same energy.