From this thread:
Contact is connection to source, drain or poly. While vias is used to
make connection between two metal layers. Both vias and contact are
formed using metals. Vias are generally made of tungsten while
contact is made using aluminum.
Why is that vias are generally made of tungsten while contact is made using aluminum? Is it because of conductivity, cost or something else?
EDIT: this question is about vias and contacts in VLSI.
According to this web page:
Deposition of pure W can be used to fill the holes that make contact to the transistor source and drain ("contact holes") and also to fill vias between successive layers of metal. This approach is known as a tungsten plug process. Tungsten is used because of the extraordinarily good conformality of CVD from WF6. It is necessary to provide an adhesion/barrier layer such as Ti/TiN, to protect the underlying Si from attack by fluorine and to ensure adhesion of W to the silicon dioxide
W = Tungsten (from Wolfram)
CVD = Chemical Vapour Deposition
WF6 = Tungsten(VI) fluoride, also known as tungsten hexafluoride
Ti/TiN = Titanium/Titanium Nitride
Si = Silcon
As the web page explains in some detail, the tungsten plug-aluminum conductor interface is prone to electromigration failure due to the aluminum, while copper interconnects are more resilient.
This is a novel case and not generally true. Vias are made of copper and often filled with solder.
The problem is in the question from missing assumptions.
Semiconductor vias or TSV's have several choices.
