Gate Poly extends beyond the channel area by some amount

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iVenky

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If you see the vertical view of the MOS device you can see that the gate polysilicon is extended beyond the channel area by some amount. and contact windows are in this place unlike sources and drain. Do you know the reason behind this?

Thanks in advance.
 

iVenky said:
... contact windows are in this place unlike sources and drain.
Click to expand...

Sorry, I can't understand your statement (or question?). Could you clarify, possibly?
 

The region where the channel is located is the most sensitive area of the FET.
We really do not want any poly contacts in that area.
Better still, we do not want any metal/vias on top of it either.
 
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    iVenky

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iVenky said:
... the gate extends beyond the channel region. I need the reason behind this.
Click to expand...

Agree with checkmate. The reason for the poly extension is to provide a margin for misalignment, s. here:
 

erikl said:
Agree with checkmate. The reason for the poly extension is to provide a margin for misalignment, s. here:
Click to expand...
I just couldn't understand these terms -
poly overhang, poly extenstion, diffusion mask, poly mask

What do you mean by that highlighted sentence?

Seems to be too much jargons for me.

Thanks in advance.
 

iVenky said:
I just couldn't understand these terms -
poly overhang, poly extenstion, diffusion mask, poly mask

What do you mean by that highlighted sentence?

Seems to be too much jargons for me.
Click to expand...

Suggest that you should read some books about layout, lithography and IC technology, e.g. -- the above picture is from this book, and the highlighted sentence exactly means what it says -- you'll understand it when you study the book.
 

erikl said:
Suggest that you should read some books about layout, lithography and IC technology, e.g. -- the above picture is from this book, and the highlighted sentence exactly means what it says -- you'll understand it when you study the book.
Click to expand...

I understood what Checkmate was saying. Are they similar?
 

iVenky said:
I understood what Checkmate was saying. Are they similar?
Click to expand...
Not quite. Checkmate explained why (usually) no contacts over gate are allowed, whereas I tried to explain why the poly must extend over the gate, and both explanations together should explain why the gate contact should be outside of the real gate over a gate poly extension.
HTH!
 
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