What is TCD cell in ASIC Physical Design?

[Rashiba]

Hi everyone
I’m a beginner in Physical Design. While studying about Physical cells, I come accross TCD cell but have no glue about it. Could you explain what kind of that cell and its purpose?
Thank you

 

[FvM]

TCD (Test-key Critical Dimension) Cell

For technology nodes below 40nm, there are few important rules that must be considered while creating the floorplan...

vlsibasic.blogspot.com

 

[dick_freebird]

You mean like the old "CD Bars" we used to put on the
product die, along with the alignment marks and mask
level IDs, before smart people decided to put them in
the scribe lanes?

The ones in the link look a lot fancier and more of 'em.
Just what I would not want to sacrifice product die area,
for.

So I guess they're back on the product die, again. For
reasons. Somebody else's reasons.

 

[ThisIsNotSam]

You mean like the old "CD Bars" we used to put on the
product die, along with the alignment marks and mask
level IDs, before smart people decided to put them in
the scribe lanes?

The ones in the link look a lot fancier and more of 'em.
Just what I would not want to sacrifice product die area,
for.

So I guess they're back on the product die, again. For
reasons. Somebody else's reasons.

It is a good reason actually. If you have an MPW, with designs of all sizes and shapes, you could potentially generate reticles that violate wafer-level rules. For instance, one rule from a know foundry is to have one TCD cell every 5mmx5mm region. The foundry then pushed these rules to individual dies, so if your tiny 1mmx1mm die respects the rule, you can make a reticle in any way you want and it will still be respected. Something like this.

 

[Rashiba]

It is a good reason actually. If you have an MPW, with designs of all sizes and shapes, you could potentially generate reticles that violate wafer-level rules. For instance, one rule from a know foundry is to have one TCD cell every 5mmx5mm region. The foundry then pushed these rules to individual dies, so if your tiny 1mmx1mm die respects the rule, you can make a reticle in any way you want and it will still be respected. Something like this.

I know that TCD cells are put on the die to monitor the critical dimension linewidth of some components when manufacturing. But I don’t understand the way TCD cell monitor the linewidth ?

 

[ThisIsNotSam]

I know that TCD cells are put on the die to monitor the critical dimension linewidth of some components when manufacturing. But I don’t understand the way TCD cell monitor the linewidth ?

the cell itself does nothing, it is not connected to anything. it is just process monitoring for the foundry