Foundry requirement: metal density requirement when tape-out

时间：04-09 整理：3721RD 点击：

Chartered foundry require us that the minimum metal density is 30%, but we can't meet this requirement because of too much inductor and MIM cap. No matter what effort we do, the metal density is still below 20%. How could I resolve this problem? THks.
In addition, which foundry can automatically fill the metal dummy for customers? as far as I know, chartered doesn't do this job for customer.

I think you can just add metal layers not connected to anything at free areas where this metal is not available till you get metal density above 30%. You can also make a script to automatically do that for you.

Metal density is warning, not an error. Usually it is not fatal if you didn't meet the requirement. But if there are free areas, you'd better add more.

When you are doing the top level intergration, you will add many ESD, PADs and very wide metal to connect each other, the metal density may ok.

But in my circuits, there are too many inductors and MIM cap (palcing metal dummy in these device regions are not allowed), so, even I place metal dummy at all the idle area, the density is still below 30%.
PS: how to make the script as you mentioned? Thanks

Added after 4 minutes:

Metal density is warning, not an error. Usually it is not fatal if you didn't meet the requirement. But if there are free areas, you'd better add more.

When you are doing the top level intergration, you will add many ESD, PADs and very wide metal to connect each other, the metal density may ok.

The problem is that it is very difficult to define a DRC depending on metal density.

In the ideal case the line width is minimum if the density around the line/space is about 50%. If the density drops the line width or spacing should increase. For your inductors line/space is not minimum.

So you know the phycical background simply trick the rule. There must be a measurement area or square where the density rule is checked. So if the minimum density is 20% is this box you should add in some subbox area 50% density but not creating shorting inductor loops.

20%=0%(no metal)*(1-p)+50%*p

p=0.4

So 40% of the measurement box should be 50% metal density to create 20% overall density. If the box is 50umx50um the spacing of the metal fill to the critical inductor is

(1-p)*50um=30um

The next issue would be where the boxes start checking and how much stepping is set for check boxes.

To fill-up the metal density, you should use "tailing" utility of your technology ..
It will fill-up the spaces automatically ( of course by spacing and dimensions rules are considered )
Tailing is a special pattern that consists of metal,PO,PP and sometimes N-WELL layers.. ( or DTI pattern)