Charges accumulated during Antenna Effect

[dinesh hegde]

What type of charges (positive or negative) results in Antenna violations ?
I guess its both, but I need confirmation in actual process.

 

[yashiro]

It cannot be both in the same metal sheet, as it will compensate each other.
It all depends on the chemicals used in the process., so it can be both negative or positive. Still it does not matter, the effect will be the same.

 

[erikl]

What type of charges (positive or negative) results in Antenna violations ?

During ion etch positive charge accumulates. During CMP (or more exactly: after CMP, during wafer cleaning and drying) either pos. or neg. charge accumulation can occur, as yashiro noted above.

 

[dinesh hegde]

Thanks,

We usually add a Antenna diode to discharge the charges. If both type of charges gets accumulated then how the diode operation will be?

My assumptions, (diode is placed on p-substrate)
Case1 : Metal is charged with negative ions then,
diode is forward biased and it will discharge the accumulated charges.

Case2 : If metal is charged with positive ions then,
diode is reverse biased, will this current sufficient to discharge the accumulated charges?

 

[erikl]

Case2 : If metal is charged with positive ions then, diode is reverse biased, will this current sufficient to discharge the accumulated charges?

For a big antenna area I wouldn't rely on it. In such case I used to add a second p+ in n-well diode (n-well connected to VDD, of course).

 

[yashiro]

Thanks,

Case1 : Metal is charged with negative ions then,
diode is forward biased and it will discharge the accumulated charges.

Case2 : If metal is charged with positive ions then,
diode is reverse biased, will this current sufficient to discharge the accumulated charges?

The charges accumulated will create a potential of hundreds or maybe thousands of volts so the diode will operate in either forward or reversed biasing and at this voltage level it will be opened either way.

If it will be forward biased it will open at around 0,6V
If it will be reversed biased, it will have a opening voltage of around -60V (it depends on the technology and diode size)

 

[erikl]

... If it will be reversed biased, it will have a opening voltage of around -60V (it depends on the technology and diode size)

... and the connected gate will be destroyed :sad: :evil:

 

[dick_freebird]

The diode doesn't have a lot of current to deal with, and
most likely the UV / soft X-rays of the plasma generator
will make it conduct plenty in either direction. You only
need a non-insulating shunt path across any gate oxide
(though for tiny metal bits, tunneling current alone can
suffice, which is why there is a length below which you
aren't dinged).

 

[dinesh hegde]

Whether wafer is grounded during wafer processing steps?

 

[erikl]

Whether wafer is grounded during wafer processing steps?

During plasma etch in any case: it's the cathode of the etch system. HV ion acceleration is needed to get the necessary etch energy + perpendicular etching.