HIGH-DOSE, HEAVY-ION IMPLANTATION INTO METALS - THE USE OF A SACRIFICIAL CARBON SURFACE-LAYER FOR INCREASED DOSE RETENTION

Ion implantation into metals has the potential of producing metastable compounds and solutions that cannot be achieved using conventional processing methods. However, when high doses of heavy ions into metals are necessitated, the technique is often limited by sputtering effects which dictate a maximum achievable implanted ion concentration in the target. Sputtering of light materials (such as C) by heavy ions is much less significant, however. This study investigates the feasibility of "protecting" a metal target surface from sputtering during a heavy ion implant by using a thin "sacrificial" C layer deposited on the target surface. Uncoated and C-coated (approximately 1000-angstrom-thick C) Cu targets were bombarded with 600-1000 keV I- ions to a total dose of approximately 2 X 10(17) I/cm2. Uncoated samples displayed typical saturation behavior, retaining between 17% and 42% of the dose, depending on the energy. The maximum I concentration achieved in the uncoated samples was about 6 at. %. Excellent results were achieved with the C-coated samples, with retentions of 100% and peak I concentrations between 18 and 33 at. %. Significant mixing of C was found to occur at the C/Cu interface, however as the implantation energy was increased the I concentration profile shifted more deeply into the sample and away from the mixed C/Cu region. This suggested that higher energies and careful tailoring of the implant parameters can eliminate any problems with C mixing.