Polysilicon Gate Contact Directly on top of Active Gate

[shuichi]

Really need some help with this issue....

There is a minimum distance design rule for the polysilicon gate contact to the gate area, such that the contact cut is on top of the thick FOX instead of directly above the thin gate oxide.

The reason for such a rule may be due to junction spiking of Aluminum diffusing into Silicon/polysilicon with in direct contact. This is valid for older technologies whereby W-plugs or barrier layers are not in use yet.

With the introduction of W-plugs and barrier layers as 'cushions' that prevent direct contact of aluminum with silicon. Are there any potential reliability issues if we violate this rule and have the contact cut DIRECTLY on top of the transistor gate with thin gate oxide below it???

 

[steer]

Fabs are often asked this question.
To my knowledge, no fab has completed a defect statistics and long term reliability study on this.
You might consider to do these tests by yourself, if your company has sufficient resourses.
Or try to persuade you far to do this, you've large enough influence on it.
From the first sight this should work, but the defects statistics and reliability is unknown to me.

 

[shuichi]

Appreciate yr reply steer!!

But I am from a startup company with limited resources....
Dun think my boss will not be that charitable to do reliability analysis on it...
He would prefer getting resources from books or net as cheap means....

 

[steer]

If you boss likes risks, he and you have a good chance for reward.
I know people who put contact on gate in their test chip and it worked. They did it in violation with foundry design rules. However, they did not test yeild statistics or long-term reliability.

 

[Teddy]

I would say that as you are in startup you guys should focus on making it work first then go to science.
Foundries would do it for you just in case you would run a big volumes what will probably not be the case.
Alsoi - how much would that save you? Would you (in case you do CMOS) place Nand Pmoses right nex to each other? I would not.
I beleive that though it would work you would be causing more troubles than anything else. No libraries available etc.
But if you would love risk and think that scrapping a lot time to time or having low yield is something you would be able to live with - go for it.