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materials used for metallization in chips

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arava prakash

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greetings for the day.

1.which metals are used for metallization and contact between layers of a layout.
2. can we use normal metal for contacts instead of using tungstun which having high resistance ranges from (2 to 20 ohms)
because metals have less resistance normally .02
ohms
 

Usually Aluminum and copper (Cu) is used, s. this **broken link removed**. The 8th photo shows a 3-level Cu interconnect, with - I think - one level Al as lowest metal interconnect. One photo above shows a 6-level Cu interconnect metalization (both SEM photos from IBM, 1997).
 

I have worked in technologies that used molybdenum (makes
really nice MIM caps, low bottom-electrode roughness) and
tungsten (no good reason, but they did). MMICs in III-V
technologies still use gold because aluminum is a III dopant
if it is entrained to the substrate.

Tungsten plugs are de rigeur nowadays in CMP processes.
Tiny contacts with high aspect ratios are hard to get good
repeatable reliable fill by simple dep, even hot-metal only
goes so far and you get in-via electromigration or edge-
of-via electromigration. Tungsten fixes this (but puts the
problem onto the contacted layers because you cannot
migrate "make-up" metal along the current track from
layer to via to layer, the tungsten being a hard barrier).
 

Tungsten is used only in the vias between metal layers. So they are very small. They are cylinders where the vertical dimension >> their diameter. The tungsten deposition process (and the TiN/Ti barrier) allows efficient filling of such high aspect ratio holes. As also mentioned, the electro-migration properties are excellent. In most 130nm processes or better, the tungsten contact is only used at the first metal layer. All subsequent layers use dual damacene Cu process,where Cu is used for both the interconnect and the via in 1deposition step ( the inside if the via still has a barrier layer).
 

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