Re: Sheet resistance
Hi,
Probably I'll make the question more clear...
I am working on an analog project (single poly – 3 metal) & am involved in the top-level integration of the entire chip. Currently, I am laying out the power grid for the chip.
As seen in the image provided, MET1, MET2 & MET3 have the same thickness i.e. 0.6550um. The sheet resistance values are also the same, Minimum = 50, Nominal = 60, Maximum = 70 mohm/square.
Since the sheet resistance is the same for all 3 metals, does this mean that the resistance of all 3 metals is also the same per square (for the same L & W)? & hence all 3 metals are the same?
R = Rs (L/W)
Normally, when we do power planning for a particular technology (e.g. single poly – 6 metal), the sheet resistances for the metals are different i.e. Metal1 will be most resistive & Metal6 will be the least resistive. Hence we use Metal5 & Metal6 for power planning so that there is a uniform distribution of power/gnd throughout the chip i.e. IR drop is reduced. Therefore, the 6 metals are different & not the same.
In my case, if all 3 metals are the same then would it make a difference with what metal I use to create the power grid?