Yes, generally (in new technologies) we place one via over other via, for e.g via1 over via2.
what r advantages n disadvantages by placing like that (stacked via).
Well, the obvious advantage is more compact routing: less chip area and less parasitics. Using stacked vias near gates can introduce a little bit more stress, but usually, if the process allows for stacked vias, there are mostly advantages
Advantages:
In the bond pad structures, stacked vias are used to provide support for the thicker copper metal lines running above. This is also known as CLVS (Copper line Via Support) structure and is a necessity in sub 90nm bond pad structures.
Disadvantages:
I cannot think of any except for the sole reason that it might affect mask making in some ways or the other.
I know that in case of larger number of vias it is recommended to stagger them due to stress on metals. So place M1 and M2 offsett and M3 again on M1 etc.
I know that in case of larger number of vias it is recommended to stagger them due to stress on metals. So place M1 and M2 offsett and M3 again on M1 etc.
Even I encountered a similar DFM guideline for a UMC project.
But could not understand that if the same stacked vias are used to support the metal stress in one process, how can they add stress in the other :?:
Even I encountered a similar DFM guideline for a UMC project.
But could not understand that if the same stacked vias are used to support the metal stress in one process, how can they add stress in the other :?:
Even I encountered a similar DFM guideline for a UMC project.
But could not understand that if the same stacked vias are used to support the metal stress in one process, how can they add stress in the other :?:
I was just referring to what Teddy had written. But I did encounter the DFM guideline while doing layouts wherein I was not supposed to stack more than three layers of vias.
Even I encountered a similar DFM guideline for a UMC project.
But could not understand that if the same stacked vias are used to support the metal stress in one process, how can they add stress in the other :?:
I was just referring to what Teddy had written. But I did encounter the DFM guideline while doing layouts wherein I was not supposed to stack more than three layers of vias.
Well, the obvious advantage is more compact routing: less chip area and less parasitics. Using stacked vias near gates can introduce a little bit more stress, but usually, if the process allows for stacked vias, there are mostly advantages
advantage is it reduces area of the metal and provides more free space for routing, as we can stack different vias one above the other.
disadvntage is if we are placing all the vias at the same place, one above the other each time during fabrication we will have to etch the same place and this can create aproblem if any one of the vias fail during fabrication time.
therefore every foundary doesnot give this feature.
i will suggest to use more than 1 via of 1 kind, i.e. 2 or via1 then 2 or more via2 over it and the same way for others.