Minimizing radiation damage in silicon structured with low energy focused ion beams

Monocrystalline silicon has been irradiated with ion beams of different energies (60 keV down to 100 eV) with fluences from 10(10)/cm(2) to 10(16)/cm(2). Ga, Si, Pr and Au ion beams have been used with a spot size between 0.1 and 1 mu m Reflectivity at normal incidence at a wavelength of 785 nm and laser induced, modulated reflectivity have been applied for the characterisation of the optical and surface properties of the samples after irradiation. Sputtering and deposition have been studied by Atomic Force Microscopy (AFM). For keV energies an abrupt increase in reflectivity and modulated reflectivity has been found with the onset of the amorphisation process at fluences around 10(14) to 10(15) atoms/cm(2). Irradiation with silicon ions shows a smaller increase in reflectivity, since there is no enhanced optical absorption due to implantation of metallic ions. Irradiation at energies below 1 keV results in a three orders of magnitude lower defect production in comparison to higher energies. While AFM measurements of silicon irradiated with Au to fluences of 5 x 10(17)/cm(2) still showed removal of material down to an energy of 500 eV, irradiation with Si ions produced no significant removal at any investigated energy. A minimum of crystal damage per removed substrate atom has been found for sputtering with Au and Ga at energies around 1 keV.