Ion-induced tracks in amorphous Si3N4 films

Silicon nitride layers of 140nm 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 110MeV (Se=19.3keVnm−1) or Xe ions of 710MeV (Se=22.1keVnm−1). Using infrared absorption spectroscopy, the radiation-induced disorder in Si3N4 was analysed as a function of the ion fluence (up to 4×1013cm−2). Some targets irradiated at low fluences (∼109cm−2) were etched at room temperature in aqueous HF solution (10vol.%) 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 Si3N4/Si interface and the limited etching efficiency allow to conclude that the tracks are probably discontinuous in the present irradiation conditions.