Dummy fill strategy

[Cascoded]

Hi everybody,

I am designing several area-consuming circuits. Symmetry is crucial for performance. Let us say I have a 128x8 array of unit cells and it is not possible to include any dummy filler on it. In fact, the whole block is bigger than the checking window, so I can not add the dummies outside the block.

I would like to ask you whether you use some "dummy fill strategy" in order to meet density rules.

In my opinion, the best option would be to increase the width of the unit so I can increase, for instance, the width of a ground line (using almost all metal layers) and fulfill the coverage requirements.

Regards.

 

[dick_freebird]

Do not neglect the waiver process; in fact you
should push any things like this at the foundry
early on, to see what slack you can get.

You might be able to place, perfectly symmetrically,
density-improving features that will make the
foundry willing to waive "close, but not meeting"
densities. That's certainly more likely to happen if
gave it an honest try. Like, make your supply lines
"sandwiches" of metal layers and full of vias; put
poly "resistors" that go from vss to vss, or make
"decoupling caps" out of stacked active, poly, metal
and as many contacts and vias as can fit, again
place them so as to not bother symmetry. Use
more vias then you need. That kind of thing. Run
some density checks to see what you're coming
up short, on and then deal.

 

[Cascoded]

Do not neglect the waiver process; in fact you
should push any things like this at the foundry
early on, to see what slack you can get.

You might be able to place, perfectly symmetrically,
density-improving features that will make the
foundry willing to waive "close, but not meeting"
densities. That's certainly more likely to happen if
gave it an honest try. Like, make your supply lines
"sandwiches" of metal layers and full of vias; put
poly "resistors" that go from vss to vss, or make
"decoupling caps" out of stacked active, poly, metal
and as many contacts and vias as can fit, again
place them so as to not bother symmetry. Use
more vias then you need. That kind of thing. Run
some density checks to see what you're coming
up short, on and then deal.

Thank you so much for your reply!

The foundry told me they do waive sometimes (in fact, it is a CIS process), so I will do what you said to increase density as much as possible.