Tungsten hexafluoride reduction

CVD processing can be used to provide selective deposition on certain areas of a surface. Selective tungsten CVD is used to fill vias or holes selectively through siUcon oxide layers in siUcon-device technology. In this case, the siUcon from the substrate catalyzes the reduction of tungsten hexafluoride, whereas the siUcon oxide does not. Selective CVD deposition can also be accompHshed using lasers or focused electron beams for local heating. 

Kara, T., Miyamato, T., Hagiwara, H., Bromley, E., and Harshbarger, W., Composition of Tungsten Silicide Films Deposited by Dichlorosilane Reduction of Tungsten Hexafluoride, /. Electrochem. Soc., 137(9) 2955-2959 (Sept. 1990)... 

The formation of CVD-W plug was studied by a nonselective or blanket CVD-W and a selective CVD-W. Blanket CVD-W is deposited by the hydrogen or monosilane reduction of tungsten hexafluoride as shown in Eqns. (27), (35) and (36). At present, monosilane is mainly used as a reducing agent because of its high rates even at a low temperature. 

Oxidative cleavage of hydrazones. Dimethylhydrazones and tosylhydrazones are reductively cleaved to carbonyl compounds by either M0OCI3 or MoFo. Yields are generally in the range of 70-90%. Cf. Tungsten hexafluoride, this volume. 

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Tungsten pentafluofide [19357-83-6] prepared by the reduction of the hexafluoride on a hot tungsten filament in almost quantitative yield... 

Tungsten tetrafluofide [13766-47-7] WF, is a nonvolatile, hygroscopic, reddish-brown soHd. It has been prepared in low yields by the reduction of the hexafluoride with phosphoms trifluofide in the presence of Hquid anhydrous hydrogen fluoride at room temperature (6). 

The hydrogen reduction of the hexafluoride process has also been developed in a hot wall process.21 Experiments were carried out in a traditional diffusion furnace tube with deposition rates approximately 100 A/min. Resistivities of 14 ju 2-cm were found for 2000 A thick pure tungsten films. Adhesion of these films on silicon was reported to be good, but not good on silicon dioxide. 

The reaction between molybdenum hexacarbonyl and elemental fluorine at —65° results in the formation of Mo2F9, which upon thermal degradation produces molybdenum pentafluoride as one of the products.1 Other syntheses of molybdenum pentafluoride include the reduction of molybdenum hexafluoride with phosphorus trifluoride,2 tungsten hexacarbonyl, or molybdenum metal at high temperatures3 and the oxidation of powdered molybdenum metal with elemental fluorine at 900°.3 The present method consists in the reaction of molybdenum hexafluoride with powdered molybdenum metal at 60° and results in the formation of pure molybdenum pentafluoride in yields of 80% and greater. 

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... 

Clean deposits of Co, Rh, Ir, Ni, or Pd have also been achieved from similar hydrocarbon metal precursors (77,12). However, it would be more desirable to deposit a good conducting metal such as tungsten under these mild conditions. Tungsten is now deposited by reduction of the volatile hexafluoride, WP6, in the presence of hydrogen. However, this is accompanied by production of the corrosive reaction product HF, whose presence cannot be tolerated by other components of delicate microelectronic circuits. Hie first attempts to deposit tungsten from the volatile hydrocarbon precursor... 

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