Bulletin Autumn‧Winter 1997

HIGHLIGHTS OF RGC-FUNDED PROJECTS create a dense plasma from wh i ch an intense beam of metal ions of the cathode material is extracted. This new metal ion source operates in a pulse mode. A broad beam of high peak beam current of the order of about one ampere and a mean beam current of tens of milli-amperes can be obtained. Due to its high-current and broad-beam capabilities, the MEVVA ion sou r ce is emp l o y ed to so l ve t he throughput problem arising from the high imp l an t a t i on dose r equ i r ed to f o rm silicides. Forming CoSi 2 by MEVVA Implantation Prof. Wong and Prof. Wilson first chose to s t udy the f o r ma t i on and properties of CoSi 2 layers by MEVVA implantation under various conditions, using a number of analytical techniques including atomic force microscopy, cross- s e c t i onal t r a n sm i s s i on e l e c t r on microscopy, Rutherford backscattering s p e c t r ome t r y, X - r ay d i f f r a c t i o n, spectroscopic ellipsometry, electrical resistivity measurements, and Hall effect measurements. CoSi 2 is k n own to have the lowest electrical resistivity among all the silicides at room temperature. And w i th its small lattice mismatch of -1.2% w i th silicon, it can form a good-quality epitaxial layer in silicon. The researchers have shown that a continuous buried single-crystalline CoSi 2 layer i n silicon can be f o rmed w i t h appropriate thermal treatment. They have also studied in detail 3-7 the dependence of the structural and electrical properties of the b u r i ed CoSi 2 layers o n t he processing conditions. The use of MEVVA ion source in their project has enabled a detailed study of the ion beam synthesis of metal silicides. Prof. Wong said, 'Such a study is very difficult, if not impossible, by conventional ion implantation because of the high dose and long time required for the sample preparation.' Other Silicides and Their Application Possibilities In addition to CoSi 2 , Profs. Wong and W i l s on have started s t udy i ng other silicides formed by MEVVA implantation, including TiSi 2 and FeSi 2 . While TiSi 2 is similar to CoSi 2 and holds interest for metallization applications, b-FeSi 2 , a form Fig. 2 Typical atomic force micrographs showing the surface morphology of two as-implanted samples of Co implanted Si prepared at an extraction voltage of 70kV to a dose of 2 x 10 17 ions/cm 2 at substrate temperatures of (a) 210°C, and (b) 760°C Chinese University Bulletin Autumn . Winter 1 997 34