Influence of impurities on ion beam induced TiSi2 formation

In this study, the influence of oxygen and arsenic which both have a high affinity to form compounds with titanium on ion beam induced TiSi2 formation was investigated. For this purpose, titanium layers with different oxygen contents were prepared by sputter deposition at various base pressures. Then, highly contaminated Ti films with an oxygen content of about 50 % were ion beam mixed with arsenic and germanium ions, respectively, at energies ranging from 15 to 150 keV; the dose used was 5 x 10 high15 cm high-2. For mixing of Ti layers with an oxygen amount below 30 %, 15 to 150 keV arsenic ions at doses of 5 x 10 high14 and 1 x 10 high16 cm high-2, respectively, were implanted. Subsequently, a two-step annealing process was performed with all implanted and unimplanted samples which were fabricated for comparison. By RBS and XRD analyses, it was shown that arsenic mixing of highly contaminated Ti films resulted in complete silicidation for mixing energies at or above 60 keV. TEM inves tigations, however, revealed also for these energies inhomogeneous silicide films consisting of large TiSi2 grains in a TiSi matrix. In thermally treated samples or in samples mixed with energies below 60 keV, only TiSi and TiN could be detected but not TiSi2. Germanium mixing of highly contaminated films led to complete silicidation for all energies used; homogeneous films with abrupt TiSi2/Si interface, however, were achieved only in case of energies at or above 100 keV. Ion beam induced silicidation of pure Ti films using arsenic ions led to inhomogeneous formation of high-resistivity TiSi2 films when arsenic ions were implanted with energies above 15 keV whereas thermal treatment resulted in smooth films with a resistivity of 20 myOhm cm which agrees well with literature values. By these investigations, it could be demonstrated that in case of highly oxygen contaminated Ti films, ion beam induced silicidation is only superior to thermal silicidation when elements like germanium wh i ch have no tendency for compound formation with titanium were implanted. To achieve homogeneous film formation, the maximal implanted concentration should be located in the substrate. In contrast to thermal silicidation, arsenic ion beam mixing of pure titanium films leads to formation of inhomogeneous, high-resistivity films because of concurrent compound formation. Therefore, it could be concluded that oxygen and arsenic which both have an affinity to form Ti-O and Ti-As compounds, respectively, can strongly affect ion beam induced silicidation.