In our CMOS ckt. layouts we can use metal (1-6) or PolySilicon for interconnections. I normally blindly used metal for its lower resistivity and accompanied propagation delay as compared to PolySilicon. I looked for answers in books by Pucknell, Rabaey and Uyemura but did not get an answer as to which (metal or PolySilicon) to use when and why.
Can anyone please tell when to use which and why? Or if you know any source which gives this, please provide reference.
Thanks a lot in advance.