Tantalum silicide

To return to die problem of die vaporization of die tantalum silicides, which could be transported as the tetraiodide of each element, but not as the elementary species. From these data it can be concluded that whatever die starting point in the composition range, the composition of the surface phase will tend towards Tag Sis, which is die most nearly congruently vaporizing composition. 

Priceman, C. and Soma, L., Development of Fused Slurry Silicide Coatings for the Elevated Temperature Oxidation Protection of Niobium and Tantalum Alloys, Report AFML-TR-68-210, Sylvania Electric Products Inc., Dec. (1968)... 

Hallowell, J.B., Maykuth, D.J. and Ogden, H.R., Silicide Coatings for Tantalum and Tantalum-Base Alloys, in Refractory Metals and Alloys III Applied Aspects, 30, Part 2, American Institute of Mining, Metallurgical and Petroleum Engineers, Dec. (1963)... 

Silicides are useful compounds characterized by their refractoriness and high electrical conductivity. There are many silicides, since silicon reacts with most metals and often more than one silicide is formed. For instance, there are five known tantalum silicides. 

The silicides of major industrial importance are the disilicides of the refractory metals molybdenum, tantalum, titanium, tungsten, vanadium, and zirconium.pl] These compounds are of great interest par-... 

Another example is the silicidizing of tantalum, basically an oxidation— reduction reaction. The packing is sodium fluoride and silicon. After deposition, the coating diffuses continuously into the substrate, according to the following reactions ... 

Aluminide and silicide cementation coatings such as TaAl3 on tantalum and MoSy on molybdenum oxidize at slow rates and possess some inherent self-repair characteristics. Fine cracks that appear and are common to these coatings can be tolerated because stable, protective oxides form within the cracks and seal them. Thermal cycling, however, accelerates failure because of thermal expansion mismatch that ultimately disrupts the protective oxide coating. 

In this section, we will restrict our attention to the silicides of tungsten, molybdenum, tantalum and titanium. CVD WSi2 is currently being used commercially, and the other three have either been considered seriously or used to a limited extent. We will start with WSi2. 

Unfortunately, the tantalum silicide deposited was very metal rich, and close to Ta5Si3. Although attempts to vary the stoichiometry by changing the... 

Figure 11 Sheet resistance map of silicon wafer with 3000 A film of tantalum silicide.

Figure 3 shows a depth profile of tantalum silicide on silicon. The sputter rate Is approximately 200A/mln. In this example, the Interface can be easily Identified at a sputter time of ten minutes. Figures 4 is the Ta 4f photoelectron region prior to the start of sputtering (spectrum a) and after five minutes (spectrum b). 

Figure 3. Depth profile of tantalum silicide on silicon.

Tantalum captures carbon strongly and does not severely deteriorate the layer quality. Moreover, it appears to be possible to fabricate the crucible and the internal parts entirely from tantalum. This decreases the contamination by nitrogen and boron. It should be emphasised that the tantalum parts must be previously annealed in a graphite crucible in the presence of small amounts of SiC or of hydrogen traces until tantalum carbide is formed on the surface. Otherwise, liquid tantalum silicide may be formed which welds the parts to each other. 

Inorganic antireflection coatings are typically deposited by sputtering, and as opposed to organic antireflection coatings, may in some cases be left in the finished device. Typical inorganic antireflection coatings include silicon oxynitride, amorphous silicon, tantalum silicide, titanium nitride, etc. 

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