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Why 2 contacts cant be merged ....

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kiran_elec

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Hello all ,i have a small doubt..why there is drc between 2 contacts ...what happens if we merge 2 contacts to make a big contact ..Pls mention the exact reason why is that not possible ??
 

2 VIAs shorted together.. Tell me how DRC knows that they are supposed to be shorted or not and you'll know why they don't short them.
 
lostinxlation said:
2 VIAs shorted together.. Tell me how DRC knows that they are supposed to be shorted or not and you'll know why they don't short them.
Click to expand...

sorry i did not understand the point you are emphasizing..i feel that if we merge 2 contacts or vias it will show drc error that minimum distance between them is not followed..i feel we should not have such error ..because bigger the contact area better it is ...i wanted to know is there any problem from fabrication point of view...
 

kiran_elec said:
... is there any problem from fabrication point of view...
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That's the essential point:
  • contacts and vias are the most frequent and tinyest structures in a layout.
  • In sub-micron processes, the actual layout structure data (contacts and vias usually are squares) always are subject to a special treatment called "data prep" (preparation), which needs a lot of CPU calculation time. I.e. the original layout data set (the "GDSII tape") has to be extensively mathematically reworked before - from the result of this treatment - masks can be produced.
  • The mathematical "corrections" of these data structures depend on their shapes and dimensions, i.e. they are very much individually tailored - that's why data prep is so CPU-intensive.
  • As contacts and vias are the most frequent structures (s. above), it is highly desirable that all of them have the same shape and dimension ("unit shape") in order to run their data prep operation just once - instead of a million times.
 
Thanks for replies...

I have understood that shape formed by merging the Contacts and vias cannot be recognized by drc ... This is because the DRC checks by an operation similar to "geometrical and operation" ,this operation when performed between the shape formed by merging and unit shape wil not give a logic 1 value (i.e shape is not recognized )

Pls correct if i have understood something wrong...
 

After about 1um dimension foundries standardized on a
single contact dimension so they can optimize that, instead
of trying to print any crazy dimension people come up with.
There's a rule, they run to the rule, you get to follow it.
It's not like "why?" will help you, or change their mind about
how to run their fab.
 
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