N-type and P-type antenna diodes roles

[omsi]

Hello all,
I have one clarification, can anyone help me in this?

Actually for antenna effects, we keep antenna diode to protect gate from charge formed on long metals connected to gate. Normally which type of diodes are preferable? N-type or P-type? else we should keep both N-type and p-type diodes at the gate?

Please clarify my doubt.

Regards,
Omsi.

 

[renwl]

tie down diode

i think there is no difference.

 

[electronXwork]

antenna diode

we use two kinds of diode for antenna effect one is tie-down diode which is located to the nearest gate and the other is the antenna diode usually located at the edge of the cell frame going to the pins. I think there is no difference wether you use P or N type diode. The basic construction of the diode we use is just diffusion and the well or substrate. Therefore, for P type devices(like P channel transistor) we use P type diode and N type diode for N type devices. For the other type of antenna diode I mentioned, usually we use N type diode for simplicity when we are already using P+ as the substrate. If you are going to use pdiode then it will require additional biasing for its nwell.

 

[omsi]

well antenna

Thanks for your earliest reply.

How can we know that the charge formed on metal is positive or negative?
if we place N-diode, then it will discharge negative charge and vice versa for p-diode.
Now which diode we keep at gate input.And also please tell me the prominance of Tie down diode.

Thanks,
Omsi

 

[ajaytronic]

antenna metal with protection diode

The diode used for antenna effect is either avalanche or tunel diode ( not sure pls smbody confirm )
So if high current or charge ( +ve or -ve, no matter ) occurs, it will be ibreakdown & all chargs will be grounded. normally it will be in reverse bise state, so won't effect any circuit function.

 

[protonixs]

what is antenna diode

NAC/tie down/vt-shift diodes are different from antenna diodes but the purpose is almost the same.
NAC/tiedown/vt-shift diodes are placed near the gate of the transistors and should be connected to the gate using 1st metal. gates that are connected to drains using 1st metal don't need this diode anymore. the type (p or n) of the diode is similar to the transistor it is connected to.
whereas antenna diodes are usually n-type and they are placed in the pins near the cell frame.

 

[electronXwork]

antenna protection using antenna diodes

How can we know that the charge formed on metal is positive or negative?

Omsi

Dry etching is known to deposit charges upon the surfaces of the wafer. Exposed conductors can collect an electrical charge that can damage the thin gate dielectrics. This failure mechanism is called process plasma-induced damage, or also known as antenna effect. The antenna effect generates stress-induced leakage currents that can lead to either immediate or delayed failure of the ovestressed dielectrics. The plasma itself contains an equal number of positive and negative particles.

Added after 3 hours 28 minutes:

NAC/tie down/vt-shift diodes are different from antenna diodes .

How can you say their are not antenna diodes when they are used to correct antenna violations? They maybe called in diffrent names but their purpose is to protect the gate from antenna effect.

 

[analayout]

antenna effect,plasma induced damage,layout

Hi,

I think we can put only n+ diode only.

if we put p+ then it is same as the gate is connected to substrate.

Regards,
Analayout.

 

[erikl]

antenna diode near gate

Hi,
if we put p+ then it is same as the gate is connected to substrate.
Regards,
Analayout.

Not, if it's a p+diode in n-well, and n-well is biased by vdd !
Cheers, erikl

 

[sridhar540]

nac diode

Place the antenna diiode , such that it is in reverse biased condition .So in a ptype substrate simply connect the net with Ndiff .Avoi d using forward biased diodes .It effects your circuitry.

 

[analayout]

how bise a transistor

hi,

erikil wrote

Not, if it's a p+diode in n-well, and n-well is biased by vdd !
Cheers, erikl

if its n+ diode in Nwell then its not allowed.

so my point is the diode should be reverse biased.

its better to put in substate than in nwell.

because this will cause well antenna error.


regards,

analayout.

 

[erikl]

nwell antenna

hi,
if its n+ diode in Nwell then its not allowed.

Doesn't create a good diode, anyway ;-)

so my point is the diode should be reverse biased.

Only so protection diodes make sense!

its better to put in substate than in nwell.
because this will cause well antenna error.

Why should it? At pMOS gates I've often used p+nwell diodes
against antenna charge. They're as good as n+p
substrate diodes for nMOS gates.
Cheers, erikl.

 

[holla1112]

Re: antenna protection using antenna diodes

The antenna effect generates stress-induced leakage currents that can lead to either immediate or delayed failure of the ovestressed dielectrics. The plasma itself contains an equal number of positive and negative particles.

can you plz explain a bit...???

- - - Updated - - -

If doide breaks down then the doide distroys and make path between gate singanl and grnd rite..??

 

[erikl]

Re: antenna protection using antenna diodes

The antenna effect generates stress-induced leakage currents that can lead to either immediate or delayed failure of the ovestressed dielectrics. The plasma itself contains an equal number of positive and negative particles.

can you plz explain a bit...???

This relates to all of several plasma etch processes during the chip fabrication, where the individual metal routing layers are defined by etching off unused metal. Even if the plasma itself contains an equal number of positive and negative particles, only one part of them (either positive or negative ones) are accelerated onto the silicon target in order to etch off the metal at the non-masked positions. Impinging ions on the remaining metal (the routing wires = "antenna") create the antenna charge.

If doide breaks down then the doide distroys and make path between gate singanl and grnd rite..??

Either the antenna diode is operated in forward direction (e.g. an n⁺p substrate diode discharging negatively charged plasma ions), or it is operated in reverse direction (e.g. an n⁺p substrate diode discharging positively charged plasma ions). In this latter case, such an antenna diode has a breakdown voltage of only a few volts, and the breakdown power is low enough to not destroy the diode.

So no path between gate and substrate is created even by a "breakdown protection".

 

[holla1112]

Re: antenna protection using antenna diodes

or it is operated in reverse direction (e.g. an n⁺p substrate diode discharging positively charged plasma ions)..

here i dint get that when the positive charge bulid up the voltage at n+ is positive voltage and the p sub is at 0 volt so how can it discharge the positive charge to ground(diode is revers biased) ??

 

[erikl]

Re: antenna protection using antenna diodes

... when the positive charge bulid up the voltage at n+ is positive voltage and the p sub is at 0 volt so how can it discharge the positive charge to ground(diode is revers biased) ??

As I told above (pls. read thoroughly):

... or it is operated in reverse direction (e.g. an n⁺p substrate diode discharging positively charged plasma ions). In this latter case, such an antenna diode has a breakdown voltage of only a few volts, and the breakdown power is low enough to not destroy the diode.

Of course the breakdown voltage of the antenna diode must be lower than the gate oxide breakdown voltage. This can be assured by using an n⁺p⁺ diode in substrate (or by using a p⁺n diode in n-well, which then is operated in forward direction).

 

[Prashanthanilm]

Erikl,
Thank you for the explanation. Few questions .
Diff between N diode in pwell vs Pdiode in nwell.
Antenna effect will be during fabrication of the device.
Since, psub is tied at VSS potential, NDiode is used in most cases.
But, If we want to use Pdiode then we need to tie NWELL to some potential.

This is the reason we use NDiode most of the cases.

Now, whether the above is correct ?.

 

[erikl]

n⁺p substrate diodes are used to protect NMOS gates, p⁺n well diodes to protect PMOS gates.

 

[Prashanthanilm]

n⁺p substrate diodes are used to protect NMOS gates, p⁺n well diodes to protect PMOS gates.

This is technology dependant right?.
Few Technology might have n+p for both pMOS and nMOS protection.

 

[erikl]

This is technology dependant right?.

Not at all.

Few Technology might have n+p for both pMOS and nMOS protection.

Possible, but IMHO impractical: it's much simpler to add one more (min. area) p⁺ diffusion (the antenna diode) next to the p⁺ source diffusion of the pMOS, and connect it to its gate. --> Shorter connection to the gate to be protected.

But in principle you are right: actually it doesn't matter where the antenna diode resides (if you don't get antenna error(s) for lower metal(s)) - and if it's n⁺p or p⁺n - or both (e.g. the output driver of an I/O pad).