Titanium boride is known as a good diffusion barrier, in particular against copper, however outdiffusion of boron might deteriorate the semiconductor device. A TiSi2 sublayer prevents effectively boron penetration into the Si substrate. In this study the intention was to form a TiB2/TiSi2 bilayer film by silicidation of a titanium-rich titanium boride deposited by magnetron co-sputtering from elemental targets. The TiSi2 formation as well as the redistribution of titanium in the boride layer has been investigated by X-ray diffraction (XRD), Auger depth profiling and cross-sectional transmission electron microscopy (XTEM). Contact structure with Cu metallization was prepared to characterize this structure electrically.
The Ti-rich titanium boride film was completely amorphous by XRD up to 700 °C. Crystallization of Ti-rich silicides (Ti3Si, Ti5Si3) have started at 750 °C, but already at 800 °C crystallization of C54 TiSi2 was completed. TiB2 begins to crystallize at 800 °C. Sheet resistance measurements confirmed these results. The sheet resistance of the as-deposited film was about 16 ω/□ and no significant change was detected up to 700 °C. Then, a remarkable drop in the sheet resistance to ∼1 Ω/□ was obtained after 800 °C, and this value was actually unchanged up to 925 °C. Cross-sectional TEM revealed the formation of the C54 TiSi2 layer between TiB2 and Si and additionally, a second C54 TiSi2 layer was observed within the boride film. Current-voltage measurements of the prepared contact structure showed that it was a Schottky diode with very high leakage current.