HIGH-DOSE, HEAVY-ION IMPLANTATION INTO METALS - THE USE OF SACRIFICIAL SURFACE-LAYERS TO ENHANCE RETENTION

While of considerable interest for the production of metallic alloys, high dose, heavy ion implantation is highly problematical, since the p rocess is limited by sputtering effects. Sputtering is less significan t, however, for light target materials, such as C and Al. This paper s ummarizes studies involving the use of light materials (such as C and Al) which act as slowly sputtering ''sacrificial layers'' when deposit ed on metallic targets prior to heavy ion implantation. The use of C a nd Al sacrificial coatings has enabled implanted ion retentions of 100 % to be obtained in a number of ion-metal target systems, where the re tentions in uncoated samples were as low as 20%. Ion implantation inva riably leads to mixing at the sacrificial layer-metal target interface . This mixing may be detrimental in certain systems, so it is useful t o be able to minimize or remove this mixed region. To achieve this, a number of techniques have been investigated: (1) removal of the mixed region in the latter stages of the implant; (2) using a barrier layer or chemical effects to minimize mixing at the sacrificial layer-metal interface, (3) choosing a sacrificial layer material which forms a mix ed region which has desirable properties. The results of these investi gations, for a number of different ion-target systems, are outlined in this paper.