Ion-induced tracks in amorphous Si_3N_4 films

摘要

Silicon nitride layers of 140 nm thickness were deposited on silicon wafers by low pressure chemical vapour deposition (LPCVD). The samples were irradiated in the electronic slowing-down regime, with either Pb ions of 110 MeV (S_e = 19.3 keV nm~(-1)) or Xe ions of 710 MeV (S_e = 22.1 keV nm~(-1)). Using infrared absorption spectroscopy, the radiation-induced disorder in Si_3N_4 was analysed as a function of the ion fluence (up to 4 x 10~(13) cm~(-2)). Some targets irradiated at low fluences (~10~9 cm~(-2)) were etched at room temperature in aqueous HF solution (10 vol.%) for various durations. The processed surfaces were probed using atomic force microscopy (AFM) in order to evidence etched tracks and to measure their mean surface diameter. The non-simultaneous emergences of the nanopores at the Si_3N_4/Si interface and the limited etching efficiency allow to conclude that the tracks are probably discontinuous in the present irradiation conditions.