Densty Rule in Lower tech

[Prashanthanilm]

Hi,

Why there are Density rule in lower technology?

What does it imply actually?

Thank you,
Prashanth

 

[dick_freebird]

Pattern density is a way of setting a minimum uniformity
of etch-loading, especially older wet etches suffered
from depletion of the active etchant in areas where
more material is being taken off, less where the load
is light, leading to local variations in W, L of whatever
layer is in question.

I'm not sure whether these rules have "gone away"
in advanced nodes, or if the device-device spacings
are now so small that density violations just don't
happen (much), or if the foundries have decided to
apply the density-fills after receiving the customer
database just to cut down on the whining and errors.

 

[Prashanthanilm]

especially older wet etches suffered
from depletion of the active etchant in areas where
more material is being taken off, less where the load
is light, leading to local variations in W, L of whatever
layer is in question.
rs.

So, Pattern density rules are for uniform etching purpose.

Still, the doubt is not fully clear. Can you elaborate more?.

What do you mean by older wet etches?