metal layer and base layer

[deba_fire]

Hi everyone,

I just started learning layout.And I came across these jargons like metal layer tapeout and base layer tape out.I understand about the metal layer where we do interconnections among different cells.But what does base layer mean?And when taping out a chip which layer is taped out first,is there a priority?

Please help me in knowing these terms.If there some sort of tutorial on this please guide me to that.

Thanks everyone

 

[erikl]

Metal layer tapeout and base layer tape out - never heard of such wording. Tape out includes all production layers, there's no layer priority re. tape out.

Layer numbers could stand for something like priority, but this concerns only the layer representation on a 2D-display: higher layer numbers cover lower layer numbers.

 

[dinesh hegde]

Base layers are the layers which are laid out on silicon substrate. Ex: active layer, NWELL layer, etc. In process base layers are taped out first and then metal layers.

 

[erikl]

Hi dinesh,

Tape out is the design base delivery to the foundry, so it includes all layers without any priority.
You are right, however, with the timely order of the layers during processing.

Rgds, erikl

 

[checkmate]

You should already have a rough understanding of what metal and base layers are. The key point is that base layers comprise the highest precision masks (read expensive). As such, designers often park redundant circuits that could be activated simply via a metal change.

 

[erikl]

Ok, understood: With the basic layers' tapeout you create your "personal master chip", with the metal layers' tapeout you may achieve different solutions - or repair the "challenges" from your first shuttle.
Thanks, checkmate!

BTW: The connection layer masks (contact, vias, lower metals) do not rank behind the basic layers concerning precision, and so may be equally expensive.

 

[deba_fire]

Hello everyone

Thanks for your replies.

So just to repeat.

Base layers are laid on the Si substrate and the first layer to be taped out to a foundry.I guess since they are the first and on the Si substrate,they must be the costliest.Please comment on this.

Metal layers are the ones on which it is preferred to do changes after the first shuttle tape out.

 

[erikl]

... since they are the first and on the Si substrate, they must be the costliest. Please comment on this.

Not because they "are on the Si substrate", but because with the first tapeout you have to pay for the shuttle order itself (setup cost).

Metal layers are the ones on which is preferred to do changes after the first shuttle tape out.

Yes. But of course already the first shuttle also needs a metal layers' tapeout.

 

[design_oriented]

Base layers are also called "frontend" layers. Metal layers are the "backend" layers.

 

[W_Heisenberg]

Why do we need many matel layers?

 

[Simranjeet Singh]

we need many metal layers because with a single layer it is not possible to route as the congestion will be very high.