What Does Metal Fill Pattern Typically Look Like?

[tasctasc]

Just wondering what the metal fill pattern typically looks like in industrial designs? Is there a certain pattern used? Are all the metal layers connected together? Are they all connected to ground?

 

[JoannesPaulus]

A metal fill pattern is generally made up by floating squares of various sizes. The distance between the squares and their size depends on the fill algorithm.

 

[tasctasc]

Thank you Joannes. So just to confirm the fill is not connected to any node in most cases? Is the fill algorithm capable of connecting the fill to a node (VDD or Vss) if desired?

 

[JoannesPaulus]

To my best knowledge, the fill pattern is always floating. You could modify the fill algorithm, usually a skill script in c@dence environment, to connect the metal fill to some net of your choice.

 

[complexplasma]

Basically it is not needed to connect the dummy fill to any metals because they are mainly needed to solve the ILD uniformity issue during CMP. They should be either floating or grounded and not abutted to other active metal structures. Pattern Density was the thing which matters in CMP, that is why you want to put dummy fills there.