Titanium silicides

Titanium Silicides. The titanium—silicon system includes Ti Si, Ti Si, TiSi, and TiSi (154). Physical properties are summarized in Table 18. Direct synthesis by heating the elements in vacuo or in a protective atmosphere is possible. In the latter case, it is convenient to use titanium hydride instead of titanium metal. Other preparative methods include high temperature electrolysis of molten salt baths containing titanium dioxide and alkalifluorosiUcate (155) reaction of TiCl, SiCl, and H2 at ca 1150°C, using appropriate reactant quantities for both TiSi and TiSi2 (156) and, for Ti Si, reaction between titanium dioxide and calcium siUcide at ca 1200°C, followed by dissolution of excess lime and calcium siUcate in acetic acid. 

Table 18. Structure and Physical Constants of Titanium Silicides ...

Figure 3.3 Chemical potential diagram for the transport of titanium silicides by chlorine, showing that only TaSi2 can provide the proper ratio of Ta and Si for stoichiometric transport...

The theoretical studies " have been focused on TiSi2. Some attempts, with use of high-symmetry crystal structures, have been made to understand some of the other titanium silicides. This paper deals vith Ti,5Si.3. Because of the crucial interplay between structure and bonding we have studied the proposed stable low-symmetry crystal structure. This will give a better picture of the electronic structure and the bonding properties in this system. An investigation of seven members in the Ti-Si system will be presented in a future publication. ... 

A typical semiconductor device (found in the back-end of the line or the interconnects) consists of a layer of glass followed by a sputtered layer of titanium, which is thermally treated to form a titanium silicide. Next, a layer of titanium nitride is deposited on top of the silicide and on the sidewall of the contacts by sputtering or by MOCVD (see Fig. 13.3 in Ch. 13).P ]P ] This layer of TiN acts as a diffusion barrier and an adhesion promoter. It is followed by the main interconnect, which is an aluminum-copper alloy, in turn followed by another layer of TiN, which acts as adhesion and antireflecting layer. 

Titanium pyrophosphate, 25 57 Titanium sesquioxide, 25 14 Titanium sesquisulfide, 25 58 Titanium silicates, 25 56, 102 Titanium silicides, 25 55—56 Titanium—silicon alloy, 22 520 Titanium silicon compounds, 25 55—56 Titanium slag, 19 388, 389 Titanium sponge... 

Rosier, R.S. and Engle, G.M., Plasma enhanced CVD of titanium silicide. 

Titanium silicides are used in the preparation of abrasion- and heat-resistant refractories. Compositions based on mixtures of T Si, TiC, and diamond have been claimed to make wear-resistant cutting-tool tips (157). Titanium silicide can be used as an electric—resistant material, in electrically conducting ceramics (158), and in pressure-sensitive elastic resistors, the electric resistance of which varies with pressure (159). 

Miura, Y. and Fujieda, S., Structural investigation of thermally nitrided amorphous titanium silicide. J. Appl. Phys. 81 (1997)6476-6478. 

Rogachev, A. S., Shugaev, V. A., Khomenko, I. A., Varma, A., and Kachelmyer, C., On the mechanism of structure formation during combustion synthesis of titanium silicides. Combust. Sci. Tech., 109,53(1995). 

Alloying titanium with silicon is influencing on final structure of as-cast alloy. Interval of silicon content 2-3-wt.% is critical. At the critical amount of silicon the Ti-Si-alloy solidifies with formation of polygonal structure with decreasing grain size at increase of silicon content. At higher silicon content structure of the Ti-Si-alloys is dendritic-eutectic one with the titanium-silicide eutectic between dendrites. 

The temperature dependence of the linear thermal expansion coefficients a(T) of the investigated titanium silicides are illustrated in fig. 6. The complex hexagonal Ti5Si3 compound exhibits a (T) values lower than those of the disilicide TiSi2 with the closer packed C54 structure. Another reason is that the anharmonicity of the lattice vibrations -phonons- and the asymmetry of the lattice potential curves of the Ti-Si and Si-Si bonds of the C54 structure are more pronounced compared to that of the D8S lattice. 

Ti5Si3 fibers was estimated to 2530 MPa. This value is higher than the fiber strength reported in the paper of Crossman et al. [24], The estimated stress is of the order of the strength of titanium silicide whiskers prepared by chemical vapor deposition. However, it should be noted that it is very difficult to determine the exact flow stress and tensile strength at room and somewhat higher temperatures because of the brittle behaviour of the Ti5Si3 fibers. 

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