Dose-rate dependence of negative copper ion implantation into silica glasses and effects on colloid formation

Although high-current implantation of negative ions, which alleviates charging, is potentially capable of efficient surface modification of insulators, the beam-solid interactions and material kinetics have not been well understood. We have studied the implantation of 60 keV negative Cu ions into silica glasses, at various current densities up to 260 mu A/cm(2), at a fixed fluence of 3.0 x 10(16) ions/cm(2). A masking method was developed to dissipate the beam loading, and multi- or single-hole masks were alternatively applied to change the boundary condition. Optical properties were determined in the range of 1.4-6.2 eV and the microstructures were examined by TEM. A significant dose-rate effect occurred for optical absorption and reflection. There was an optimum dose-rate to obtain a certain absorbance. Changes in the mask shape resulted in different dose-rate dependence, which indicated that beam-solid interactions near the surface affected the implantation. At high dose rates, spherical Cu colloids with a pronounced bimodal distribution were produced. The surface morphology also changed and suggested significant atomic migration. (C) 1998 Elsevier Science B.V. All rights reserved.