Tungsten deposition

Tungsten deposits occur in association with metamorphic rocks and granitic igneous rocks throughout the world (Table 2). Deposits in China constitute over half of the world reserves and over five times the reserves of the second largest source, Canada. 

Figure 2.4. (a) Tungsten deposition in a tubular reactor, (b) boundary layer conditions. 

Figure 5.7. Cold-wall laboratory reactor for tungsten deposition.

Singer, P., The Multiple Challenges of Tungsten Deposition, Semiconcuctor International, pp. 36-39 (Aug. 1992)... 

Park, K.H. Park, H.l. 1980. On the genesis of Ulsan Iron-Tungsten deposits. Journal of Korean Institution of Mining Geology, 13, 104-16 (in Korean with English abstract). 

Petrologic, geochemical characteristics, and age of skarn-related granitoids at the Mactung Tungsten Deposit, Yukon, Canada... 

The northern Canadian Cordillera is one of the most well-endowed (richest) tungsten districts in the world (e.g., Dick Hodgson 1982). The highest grade tungsten deposit in this district is the Cantung mine, a world-class tungsten skarn with recent reserve estimates of 2.9 Mt at 1.21%W03 indicated and 0.73 Mt at 0.74%W03 inferred (Clow et al. 2006), and over 4.6 Mt at 1.6%W03 removed prior to temporary mine shut-down in 2003 (Rasmussen 2004). 

Keywords Quartzs-veins-type tungsten deposit banded structure ductile shear zone °Ar- Ar dating Hukeng, Jiangxi... 

Liu, J. et al. 2008. Re-Os dating of molybdenite from the Hukeng tungsten deposit in Wugongshan area,Jiangxi Province, and its geological implications[J]. Acta Geologica Sinica, 82(11), 1576-1583. 

This reaction is actually slightly endothermic (A// = 88 kJ/mol), but the large net increase in entropy and the nonequilibrium nature of most CVD processes lead to significant tungsten deposition. As with the Ge example, the deposition mechanism involves adsorption steps and surface reactions. At low pressures and under conditions of excess hydrogen gas, the deposition rate follows the general form ... 

Tungsten hexachloride has not been studied as extensively as the fluoride for tungsten deposition, since the chloride is a solid at room temperature and must be heated to 170°C to achieve a reasonable vapor pressure. Of course, all... 

Figure 15 Tungsten deposit thickness as a function of time for several temperatures.24 Reprinted by permission of the publisher, The Electrochemical Society, Inc.

Since the mechanism whereby silicon reduces WF6 involves the consumption of silicon (i.e., production of SiF4, SiF2, etc.), there is concern that there should not be too much encroachment of the tungsten into the silicon. Assuming the silicon is consumed uniformly, then two atoms of silicon will be released for each tungsten atom deposited. As tungsten is a denser material than Si, this translates into a thickness of Si consumed which is twice the thickness of tungsten deposited. 

The Si consumption can be beneficial in that a more intimate contact between W and Si is promoted.25 It can, however, lead to encroachment problems that will be discussed later. As in the blanket tungsten deposition case, film resistivities are higher than bulk. For selective deposition, thinner films are useful, so it is important to recognize that resistivity varies with film thickness, as shown in Figure 16.26... 

Figure 17 Photographs of two limiting tungsten films (I) Tungsten deposited with dilute HF preclean (II) Tungsten deposited with CF4/02 glow discharge clean (a) SEM (b) TEM.27...

Figure 18 Selective tungsten deposition in a contact hole.

Figure 15 Tungsten deposition rates versus substrate temperature for p = 200 mTorr, H2/WF6 = 3 and 30 watts.16...

Electrophoretic deposition (EPD) is a colloidal process in which the charged colloidal particles are driven by a dc electric field to deposit on a substrate, forming a condensed film. This process is a combination of electrophoresis and deposition (Sarkar and Nicholson 1996). It has a long history and the first application was in 1927 for Th02 and tungsten deposition on a platinum cathode. Recently, photocatalyst semiconductor nanoparticles/microparticles have also been assembled by this... 

Reduction reactions of halide precursors are very commonly used in CVD technologies. In many cases, the use of a hydrogen carrier gas provides the reducing agent in excess, as in the cases of tungsten deposition from the hexafluoride WF + 3 W(s) + 6 HF, or the... 

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