Silicidation of Titanium-Rich Titanium Boride Deposited by Co-Sputtering on Si (100)
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SILICIDATION OF TITANIUM-RICH TITANIUM BORIDE DEPOSITED BY COSPUTTERING ON Si (100) G. SADE AND J. PELLEG Department of Materials Engineering, Ben-Gurion University of the Negev, Beer-Sheva, 84105, Israel ABSTRACT 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 oC. Crystallization of Ti-rich silicides (Ti3Si, Ti5Si3) have started at 750 oC, but already at 800 oC crystallization of C54 TiSi2 was completed. TiB2 begins to crystallize at 800 oC. Sheet resistance measurements confirmed these results. The sheet resistance of the as-deposited film was about 16 Ω/o and no significant change was detected up to 700 oC. Then, a remarkable drop in the sheet resistance to ~1 Ω/o was obtained after 800 oC, and this value was actually unchanged up to 925 oC. 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. Currentvoltage measurements of the prepared contact structure showed that it was a Schottky diode with very high leakage current. INTRODUCTION Recently, demands have been significantly increased to develop new interconnection materials in ultra large-scale integration (ULSI) devices. As a result, Cu is being considered as a potential substitute for Al because of its lower resistivity (1.67 µΩ cm) and higher resistance to electromigration [1, 2]. However, Cu diffuses easily into the Si substrate and SiO2 layers at elevated temperatures during device fabrication and it reacts with Si to form Cu3Si compounds at very low temperatures (200 oC) [3, 4]. Moreover, Cu acts as deep-level contaminant in Si that has an adverse effect on device performance. Thus, in order to apply the Cu interconnections in manufacturing devices, a diffusion barrier to prevent the Cu penetration into the Si substrate must be developed. Various materials have been investigated as a diffusion barrier between Cu and Si such as transition metals [5, 6], intermetallic compounds [7], carbides [8], nitrides [9, 10] and ternary amorphous diffusion barriers [11, 12]. Wang [13] summarized in detail some of these barriers against Cu and their properties. Because of the excellent physical properties of TiB2 [14, 15] it has been considered as a candidate for barrier application. Although this possibility was sugges
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