Deposition process and film properties

In this section we will discuss the process in terms of reaction kinetics, film composition and film properties. Important to note is that the degree of utilization of WF6 under typical deposition conditions (ie. 50 nm/min and 2 seem WF6 per 6 wafer) is at least 50%. Thus the reactor is very likely to run in a depletion or feed controlled mode. As a result we expect the deposition rate to depend strongly on the WF6 total flow and be relatively insensitive to temperature variation. 

Grain size and dominant crystal phase at different anneal temp. 

The oxidation rate in dry oxygen was found to be very similar to that of 100 silicon (see figure 9.8). This indicates that during oxidation silicon from the underlying poly-Si diffuses to the surface of the WSix where it becomes available for oxidation. It has been found [Saraswat et al.225] that for practical purposes the dry oxidation rate of CVD-WSix atop of poly-Si can be described by  

A detailed process characterization was published by Clark226 in 1988. Using experimental design the deposition process and resultant film properties were studied. Some results obtained in this study are presented in the contour plots in figures 9.9 and 9.10. The centerpoints used in this study were temperature = 360°C, SiH4 flow = 1200 seem, WF6 flow = 12 seem and pressure = 230 mTorr. It was concluded from these contour plots that a fairly wide process window will give deposition rates of about 60 

The as-deposited thin film resistivity increases with increasing silicon content as is clear from figure 9.11. The post-annealed resistivity follows a similar trend as observed earlier by Brors et al.224. The tensile stress of both the as-deposited and annealed film decreases with increasing Si content. It is important to note that the stress after anneal is higher than before anneal. For more details about stress see section 9.8. 

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