Mimimum and Maximum density rule check ..!

Hi All,

I have couple of questions and need clarifications :

1. Why do we do minimum and maximum metal density check ? :-(

My understanding is that minimum density check should be done to avoid any sweep away of small metals in less denser areas during etching process. Maximum density check should be done to avoid the dishing ( i.e the plane surface dipping down due to heavy weight of the metal above it because oxide is porous). Am I right in both the cases ?

2. Why should we check the density rules for base layers? (like active area) :shock:

Please reply..

Yes, on point 1. On a basic level the density checks are to ensure an even spread of metal and to ensure all required metal is formed correctly.

On point 2, the need is also present for the base layers because these also have effect on device performance. Some effects can be
- Well proximity (distance to NWELL regions)
- Length of active diffusion (threshold voltage can be effected by length of active layer or diffusion layer)
- Active space effect, STI effect. This is a mechanical stress caused by differences in active layer space

So, there are density rules for these layers to ensure an even distribution of the layers so the spacing in your layout will correspond correctly to the actual spacing in the final silicon.

Hi DharmaSlice,

After reading your post I now quite have a better idea on how the STI might affect. Can you please explain a little more on how the WPE and LOD are affected by the dummy filling of base layers?

And also which all base layers are checked for their density ? I have not come across nwell dummy till now in my work...

starinspace said:

Hi DharmaSlice,

After reading your post I now quite have a better idea on how the STI might affect. Can you please explain a little more on how the WPE and LOD are affected by the dummy filling of base layers?

And also which all base layers are checked for their density ? I have not come across nwell dummy till now in my work...

Click to expand...

The only base layer dummy are diffusion and poly.

I was just pointing out effects with layers other than metal in my last comment. Didn't mean to imply the NWELL was also a dummy layer required.

DharmaSlice said:

The only base layer dummy are diffusion and poly.

I was just pointing out effects with layers other than metal in my last comment. Didn't mean to imply the NWELL was also a dummy layer required.

Click to expand...

Thank-you very much for your clarifications..