Feasibility of selective and blanket contact or via fill

In table 4.1 a comparison is made between selective and blanket tungsten for contact and via fill. In the following we will discuss each of these process requirements. 

Contact Diameter In principle, selective tungsten has almost no limitations as to the contact size. However, especially in the SiH4/WF6 case, the local growth rate can drop when the contact size is too large, when the contact density is very high, or when the scribe lines are open. Blanket tungsten has, as discussed in chapter II, an upper limit for the contact size. 

Process limitations for blanket and selective contact/via fill 

Degree of Planarization (DOP) Whereas the result of the blanket tungsten etch back will be very sensitive for the DOP, selective tungsten is virtually 

Compatibility with The Substrate and Dielectric The adhesion layer in the blanket-W case now proves to be an advantage. Most commonly this is sputtered TiW or TiN. The contact resistance and reliability issues of these materials have been well studied and are under control. Thus for blanket tungsten no additional problems are expected here. In the case of selective tungsten a completely new interface is created, namely that between silicon and the tungsten. Also, because of the wide variety of substrates and 

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