CVD tungsten source material

At least three different tungsten sources have been reported to give CVD tungsten films WF6, WC16 and W(CO)6. Some properties of these sources are listed in table 6.1. 

From this we see that WF6 is the most convenient source in terms of vapor pressure and physical state. Generally, solid sources are much more difficult to deliver to the reactor in a reproducible way. The halides are very stable and decompose only at high temperatures whereas the carbonyl compound will decompose readily at temperatures above 200°C. In the following section we will discuss tungsten deposition results obtained with each source. 

W(CO)6 [Diem et al.169c, Kaplan et al.170, Vogt171]. This tungsten source has the clear advantage in that silicon erosion will not occur as will happen in the other two cases (see below). The tungsten is deposited at substrate temperatures of greater than 200°C according to the decomposition reaction  

The quality of the tungsten film is poor in terms of purity. The carbon and oxygen content are very high, typically about 20 at.% each. This can lead to a high resistivity 50-500 /iHcm. Also, the combination of H2 and W(CO)6 has been reported [Vogt171] but the presence of hydrogen had no positive effect on film properties. 

We see that these reactions will sustain themselves since the Si02 formed in reaction 6.3 can initiate reaction 6.2. The films deposited by the hydrogen reduction contained typically 0.05-0.1 at.% chlorine. 

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