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Why do need Dummies in layout

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hi all,
can any one tell why do we place dummies on left and right sides of layout mostly, why not on top and bottom. clear explanation please


thanks in advance.
 

Sorry. I'm not a backend expert. Just came across this paper...
 

We need dummies to avoid proximity effects, higher etching (sorry I forgot proper word for this ;-) ) of polysilicon on the edges, etc.

In some accurate circuits like DACs we used double ring of dummies, in diff pairs single ring from dummies is enough.
Good and short explanation You can find in the first sections of this chapter
 
Dominik Przyborowski said:
We need dummies to avoid proximity effects, higher etching (sorry I forgot proper word for this ;-) ) of polysilicon on the edges, etc.

In some accurate circuits like DACs we used double ring of dummies, in diff pairs single ring from dummies is enough.
Good and short explanation You can find in the first sections of this chapter
Click to expand...

hi dominik,
i got some idea about your answer, but one small doubt, u told that to avoid etching from sides we use dummies, but what about the etching effects from top and bottom
 

Usually from top/bottom sides of elements we have contacts to metalization, so for resistors, etching in this regions doesn't changes electrical parameters.
In mosfets, lack of dummies from one side could affected source/drain region implantation profile due to ions scattering so most often dummies around active tranistors are used.


//EDIT: I mistook chapters from book. In my previous post should be the link to this chapter
 

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